TY - JOUR
AU - Kyle, Philip, R
AB - Abstract The magmatic evolution of The Pleiades, a Quaternary alkalic volcanic complex in Northern Victoria Land (NVL), Antarctica, is investigated using major and trace element, and Sr, Nd and Pb isotopic data. The volcanic rocks can be subdivided into two distinct magmatic lineages based on petrography and whole-rock compositions: (1) a sodic silica-undersaturated lineage with abundant kaersutite phenocrysts and (2) a potassic and mildly-alkalic, silica-saturated to slightly under-saturated lineage containing olivine phenocrysts but no kaersutite. The pressure–temperature paths estimated by clinopyroxene–liquid thermobarometry are similar in each lineage. Mass-balance calculations using whole-rock and mineral compositions show that kaersutite fractionation without olivine has played a major role in magmatic differentiation of the sodic lineage, whereas the compositional variations of the potassic lineage can be ascribed to fractionation of an assemblage of plagioclase, clinopyroxene, olivine, titanomagnetite and apatite, combined with about 10% lower crustal assimilation. The higher 87Sr/86Sr (> 0·7035), lower 143Nd/144Nd (< 0·51285), and 206Pb/204Pb (< 19·3) ratios of the evolved potassic lavas compared to the mafic lavas support crustal assimilation. The mafic lavas from both lineages are characterized by elevated 206Pb/204Pb (>19·5) ratios and narrow ranges of 87Sr/86Sr (0·70313–0·70327) and 143Nd/144Nd (0·51289–0·51290) ratios, which is consistent with a high µ-like (HIMU, where µ=(238U/204Pb)t=0) component typical of Cenozoic volcanic rocks in Antarctica and Zealandia. This HIMU-like isotopic signature of The Pleiades volcanic rocks, together with elevated Nb concentrations and negative K anomalies in primitive mantle-normalized diagrams, suggests an amphibole-bearing metasomatized lithospheric mantle source. We suggest that the primary magmas of the two lineages were formed by partial melting of metasomatic hydrous veins in the lithospheric mantle with varying degrees of reaction with the surrounding, anhydrous peridotite. The drier potassic magma experienced greater peridotite assimilation relative to the more hydrous sodic magmas. This hypothesis is supported by lower contents of Al2O3, TiO2, K2O, Rb, and Nb in the mafic potassic lavas compared to the sodic ones. This initial difference was intensified by crustal assimilation in the potassic magma suite, resulting in a silica-saturated alkalic trend which is distinct from the trend of the sodic silica-undersaturated alkalic magmas. INTRODUCTION Alkalic volcanic rocks occur in a variety of intraplate tectonic settings and they show a number of evolutionary differentiation trends. The settings include: oceanic islands (e.g. St. Helena, Baker, 1969; Iceland, Jakobsson et al., 1973; Tristan da Cunha, Le Roex et al., 1990; Freundt & Schmincke, 1995); continental rifts (e.g. West Antarctic Rift System, Kyle, 1990a; East African Rift System, Jung & Hoernes, 2000; Rogers, 2006; Lucassen et al., 2013; Rhine Graben rift system, Jung et al., 2012); extensional back-arc basins (e.g. Deception Island, Weaver et al., 1979; Ukinrek Maars, Kienle et al., 1980; Ulleung Island, Brenna et al., 2014), and other intraplate environments (Coombs & Wilkinson, 1969; Ayuso et al., 1998; Kuritani et al., 2009; Correale et al., 2014). The magmatic differentiation of alkalic volcanic suites can be subdivided into fractionation lineages (Coombs & Wilkinson, 1969). The silica-saturated to mildly-undersaturated lineage ranges from alkali basalt and hawaiite to mugearite, benmoreite and trachyte, and occasionally to alkalic rhyolite. The alkali-enriched, strongly silica-undersaturated lineage evolves from basanite, tephrite and rarely hawaiite through phonotephrite, tephriphonolite to phonolite. Volcanic suites can further be subdivided into sodic (K2O/Na2O < 2) and potassic trends (K2O/Na2O > 2). Although compositional variations in many volcanoes can be explained by a single trend, there are volcanoes in which two spatially and temporally related evolutionary trends coexist (Cantal volcano, Wilson et al., 1995; Mount Sidley, Panter et al., 1997; Pribilof Islands, Chang et al., 2009; Mount Morning, Martin et al., 2010; Siebengebirge, Kolb et al., 2012). The causes of such diversity in alkalic magmatism, especially in a single volcanic system, are a matter of debate. Green (1973a) attributed it partly to the nature of the parental basaltic magmas which form by varying degrees of partial melting of mantle peridotite. However, decades of studies have shown that the different physiochemical conditions, such as pressure and volatile contents, and consequently different fractionating mineral assemblages (e.g. Coombs & Wilkinson, 1969; Wilson et al., 1995; Nekvasil et al., 2004; Whitaker et al., 2006) or crustal assimilation (e.g. Foland et al., 1993; Schneider et al., 2016), can also affect the degree of silica-undersaturation during the evolution of alkalic magmas. Moreover, various melting processes of distinct mantle lithologies have been proposed to explain alkalic magma genesis: asthenospheric garnet peridotite (Green, 1973b; Baasner et al., 2016); pyroxenite (Sobolev et al., 2005); amphibole- or phlogopite-bearing lithospheric mantle (Class & Goldstein, 1997; Pilet et al., 2008), with or without addition of hydrous or carbonate fluids. Experimental studies have shown the importance of carbonate-rich volatiles in the mantle source during partial melting processes (Hirose, 1997; Dasgupta et al., 2007; Gerbode & Dasgupta, 2010). Those sources are closely linked to regional tectonic history and structures as well as the initial physiochemical conditions for partial melting. The Pleiades are a young volcanic complex in NVL, Antarctica (Fig. 1). They are part of the extensive Cenozoic McMurdo Volcanic Group (Kyle, 1990b; Wilson et al., 2002) in the western Ross Sea. Magmas with diverse composition ranging from alkali basalt and basanite to trachyte and phonolite have erupted through the thick crust of the Transantarctic Mountains (TAM) for ∼ 1 Ma at The Pleiades (Esser & Kyle, 2002). Two magmatic differentiation lineages (sodic vs potassic) have been identified at The Pleiades based on their marked chemical differences in the intermediate lava suites (Kyle, 1982). The sodic lineage lavas are basanite, tephrite, phonotephrite and tephriphonolite, whereas the potassic lineage consists of hawaiite, mugearite, trachyte, and phonolite. Kyle & Rankin (1976) also noted that the phenocryst assemblages within the two lineages are different. The sodic lineage resembles the kaersutite (Ti-rich calcic amphibole)-bearing basanite–phonolite lineage seen in the Dry Valley Drilling Project (DVDP) core drilled at Hut Point Peninsula on Ross Island (Kyle, 1981). Kaersutite is however rare in the potassic lineage. At The Pleiades, the eruptive ages, localities and compositional variations in the mafic suites of the two lineages overlap (Kyle, 1982; Esser & Kyle, 2002). The Pleiades lavas, therefore, provide an opportunity to examine processes that produced the two contrasting fractionation trends. In this study, we report a new set of mineralogical data, major and trace element data, and isotopic data for The Pleiades volcanic rocks of both lineages, and selected basement rocks. We examine partial melting and differentiation processes and provide petrogenetic models for the two contrasting lineages in The Pleiades. Fig. 1 View largeDownload slide (a) Distribution and location of the West Antarctic Rift System (WARS), Marie Byrd Land (MBL), and Transantarctic Mountains (TAM) in Antarctica. Grey and blue areas denote continent and ice shelf, respectively. (b) Satellite view of part of Northern Victoria Land (NVL) from Google Earth showing the location of The Pleiades (red box) on the crest of the Transantarctic Mountains. The sample locations of migmatite and Granite Harbour Intrusive Complex (GHIC), are shown. The Lanterman and Leap Year Faults mark the boundaries between the Wilson, Bowers, and Robertson Bay terranes. (c) Satellite view of The Pleiades volcanic complex (World-View image) showing the volcanic rock and xenolith sample locations. The numbered (1–12) and named (Alcyone and Taygete) cones and the two Peaks (Atlas and Pleiones) are marked (Kyle, 1982). Fig. 1 View largeDownload slide (a) Distribution and location of the West Antarctic Rift System (WARS), Marie Byrd Land (MBL), and Transantarctic Mountains (TAM) in Antarctica. Grey and blue areas denote continent and ice shelf, respectively. (b) Satellite view of part of Northern Victoria Land (NVL) from Google Earth showing the location of The Pleiades (red box) on the crest of the Transantarctic Mountains. The sample locations of migmatite and Granite Harbour Intrusive Complex (GHIC), are shown. The Lanterman and Leap Year Faults mark the boundaries between the Wilson, Bowers, and Robertson Bay terranes. (c) Satellite view of The Pleiades volcanic complex (World-View image) showing the volcanic rock and xenolith sample locations. The numbered (1–12) and named (Alcyone and Taygete) cones and the two Peaks (Atlas and Pleiones) are marked (Kyle, 1982). TECTONIC FRAMEWORK NVL consists of three major terranes accreted during the Cambro–Ordovician Ross Orogeny (Federico et al., 2006): the Wilson, Bowers and Robertson Bay terranes (Fig. 1b). The terranes are bounded by the northwest–southeast striking Lanterman and Leap Year Faults and mainly consists of pelitic metamorphic rocks and sedimentary rocks (Cooper et al., 1983; Palmeri, 1997; Henjes-Kunst & Schüssler, 2003). The Cambrian to early Ordovician Granite Harbour Intrusive Complex (GHIC) and the Devonian to early Carboniferous Admiralty Intrusives (AI) are widely distributed in NVL (Borg et al., 1987). The syn- and post-tectonic intrusions of the GHIC, which were formed during the Ross Orogeny, occur throughout the TAM, including the Wilson and Bowers terranes (Armienti et al., 1990). The AI occur only in the Robertson Bay and Bowers terranes as Devonian ‘stitching granitoids’ (Weaver et al., 1984). The West Antarctic Rift System (WARS; Behrendt, 1999; Fig. 1a) developed major basins in the Ross Sea from late Cretaceous to early Tertiary times (Decesari et al., 2007; Elliot, 2013). A sharp topographical contrast exists between the thin (∼20 km) Ross Sea and the thick (∼40 km) TAM crust (Chaput et al., 2014; Hansen et al., 2016) which has been attributed to the uplift of the TAM as a rift shoulder of the WARS (Behrendt, 1999). Recent geophysical studies around Victoria Land suggest that the TAM is supported by thermally buoyant, low-velocity mantle zones in which rift-related partial melting has occurred (Graw et al. 2016; Hansen et al. 2016; Brenn et al., 2017). Multiple suites of Cenozoic alkalic plutons, dykes and volcanic rocks have been emplaced in and adjacent to the WARS since 48 Ma in NVL and 34 Ma in Marie Byrd Land (MBL) (Rocchi et al., 2002, 2006). Studies of terrestrial volcanic rocks, marine sediments and ice-core tephra layers have confirmed that the volcanism in the Melbourne volcanic province was active from Miocene to Holocene times (Kyle, 1990a; Armienti & Baroni, 1999; Narcisi et al., 2012; Del Carlo et al., 2015). A mantle plume beneath the WARS has been suggested as the source of the young alkalic magmatism, based on its ocean island basalt (OIB)-like geochemical characteristics, the volume of volcanic rocks, the dome-shaped elevation of the MBL, seismic data, and high heat flow (Hole & LeMasurier, 1994; Behrendt, 1999; Storey et al., 1999; Sieminski et al., 2003; Winberry & Anandakrishnan, 2004; Schroeder et al., 2014). However, non-plume models have also been introduced to explain NVL volcanism. Rocchi et al. (2005) suggested that transtensional, oblique rifting has promoted Cenozoic NVL magmatism. This oblique rifting was controlled by reactivation of preexisting north to northwest-striking fault systems in conjunction with the movement of fracture zones in the Southern Ocean (Rocchi et al., 2002, 2005; Storti et al., 2006, 2007, 2008; Vignaroli et al., 2015). The non-plume model attributes the geochemical characteristics of the alkalic volcanic rocks around NVL to partial melting of metasomatized lithospheric mantle which has been heated by lateral asthenospheric mantle flow (Nardini et al., 2009; Panter et al., 2018). Hansen et al. (2014) reported a slow velocity anomaly beneath the TAM without a deep root (< 300 km), which supports a passive rift model for NVL. Recently, Shen et al. (2018) proposed that the slow velocity zone beneath the southern TAM was derived by lithospheric foundering and lateral flow of asthenosphere. VOLCANIC GEOLOGY Cenozoic alkalic volcanic rocks in the western Ross Sea area are termed the McMurdo Volcanic Group (Kyle, 1990b). The McMurdo Volcanic Group is divided into three provinces: Hallett, Melbourne, and Erebus. The Pleiades are part of the Melbourne volcanic province (Kyle, 1990a) which stretches from Mt. Melbourne on the coast, inland to The Pleiades (Fig. 1b) and beyond. The Pleiades are bounded to the northwest by the Evans Névé (Fig. 1b) and surrounded by a variety of basement rocks, including the sedimentary rocks of the Bowers Terrane, Paleozoic granitoid rocks of both the Granite Harbour Intrusive Complex (GHIC) and Admiralty Intrusives, Mesozoic Ferrar Group tholeiitic volcanic and intrusive rocks, and metamorphic rocks of the Wilson Terrane. The Pleiades itself consists of a stratovolcano and numerous volcanic cones and domes (Kyle, 1986). Those cones are aligned in a roughly northeast–southwest direction, perpendicular to the major strike-slip fault patterns of NVL. There are four named features and twelve unnamed cones which are numbered C1 to C12 (Kyle, 1982; Fig. 1c). The southern peaks of Mt. Pleiones and Mt. Atlas are parts of a single stratovolcano, which is the largest feature of The Pleiades. The Pleiones/Atlas stratovolcano rises ∼ 500 m above Evans Névé at the southern end of The Pleiades complex, surrounded by several smaller cinder cones, lava flows and moraines. The Pleiades has long been thought to be one of the youngest volcanic centers in the McMurdo Volcanic Group based on the undissected nature of the volcanic bodies (Nathan & Schulte, 1968; Riddolls & Hancox, 1968) and geochronology data (Armstrong, 1978; Esser & Kyle, 2002). For example, Taygete Cone is suggested to be a very young endogenous dome based on well-preserved slickensides, rock textures and morphology (Kyle, 1982), and has an 40Ar/39Ar age of 6 ± 6 (2σ) ka (Esser & Kyle, 2002). Narcisi et al. (2001) suspected the composition of a 1254 ± 2 CE trachytic tephra layer found in the Talos Dome ice core could have been erupted from Mt. Rittmann or The Pleiades. The Pleiades have also been suspected to be one possible source of other young tephra layers found around Talos Dome and in marine sediments (Del Carlo et al., 2015; Narcisi et al., 2016). Indeed, the 40Ar/39Ar age determinations of volcanic rocks from The Pleiades are all less than 1 Ma (Esser & Kyle, 2002). Kyle & Rankin (1976) proposed two differentiation trends at The Pleiades and subdivided them into potassic (Na2O/K2O< 2) and sodic (Na2O/K2O> 2) lineages. The potassic lineage is composed of mildly alkalic hawaiite, mugearite, benmoreite and trachyte suite rocks and constitutes the majority of the eruptive volume. The volumetrically minor sodic lineage comprises strongly silica-undersaturated basanite, phonotephrite, and terphriphonolite lavas. SAMPLE COLLECTION AND ANALYTICAL METHODS Samples of The Pleiades volcanic complex were collected during two field campaigns, one in December 2014 and one in January 2016. We sampled various lithologies from exposed cones and moraines (Fig. 1c) and these were taken to be representative of The Pleiades volcanic complex. Mineralogy and petrologic features were examined in thin sections and samples were selected for microprobe analysis. Relative abundances of phenocrysts were measured in representative thin sections by measuring the area of each phenocryst in digitized thin section images. Any samples showing alteration or magma mingling textures were excluded from this study. Selected samples were crushed into chips and ground in a tungsten carbide mill for analysis. We analysed 67 volcanic rocks, two granodiorite AI xenoliths from The Pleiades (see Supplementary Data S1 for age determination; supplementary data are available for downloading at http://www.petrology.oxfordjournals.org) and two basement rocks (GHIC and migmatite) from near Terra Nova Bay. Major elements were determined by X-ray fluorescence (XRF) at the Korean Polar Research Institute (KOPRI), on a PANalytical Axios Max wavelength dispersive XRF spectrometer equipped with a 4 kW Rh anode Super Sharp X-ray Tube (PW2592). Dried sample powders were mixed with lithium tetraborate (Li2B4O7) and lithium bromide (LiBr) and fused into glass discs (Fitton & Godard, 2004; Mori, 2005). Loss on ignition (LOI) was determined from the weight change when an aliquot of the sample was heated to 1000°C. Trace element contents were measured using an inductively coupled plasma mass spectrometer (Perkin-Elmer SCIEX Elan 6100 and iCAP Q) at KOPRI. Powdered samples (20 mg) were dissolved in an HF-HNO3 mixture for 2 days and diluted to ∼2% HNO3. The analytical accuracy and precision were monitored by multiple measurements of reference material BCR-2. The standard results for most of the elements are in agreement (<12%), except for Y and Pb (<17%), with the recommended values provided by Jochum et al. (2005) (Supplementary Data). The Sr, Nd and Pb isotopic compositions were measured using the laboratory and analytical procedures reported in Lee et al. (2015). Fresh rock chips, 1–2 mm in size, were leached in 2 N HCl at 70°C for 10 minutes and repeatedly rinsed with Milli-Q® water to remove possible remaining contaminants. The leached material was powdered in an agate mortar. The powdered samples were dissolved in concentrated HF and HClO4 at 120°C for about 3 days. The sample size was 50 mg for most samples, but 30 mg for some highly-evolved samples, i.e. phonolite, trachyte and granitic rocks, because of their high concentration of Pb (>15 µg/g or part per million, ppm) than other mafic to intermediate rocks (<10 ppm). An anion exchange column (0·5 mL column volume, Ag1 x8, 100–200 mesh resin) with an HBr medium was used to separate Pb which was collected with 6 N HCl. Strontium was then separated from rare earth element (REE) solutions through columns with Biorad AG50W-X8 (4 mL column volume, 100–200 mesh) resin. The columns with Biorad AG50W-X8 (0·7 column volume, 200–400 mesh) were used with 0·22 M alpha hydroxyisobuteric acid (α-HIBA) to collect Nd from the REE solution (Shibata & Yoshikawa, 2004). Analyses for Sr, Nd, and Pb isotopes were made at KOPRI on a thermal ionization mass spectrometer (TIMS, Thermo Finnigan, TRITON) equipped with 7 Faraday cups. Fractionations of Sr and Nd isotopes were corrected for by normalizing to 86Sr/88Sr = 0·1194 and 146Nd/144Nd = 0·7219. Replicate measurements of NBS 987 and JNdi-1 standards gave 87Sr/86Sr =  0·7102711 ± 6 (N = 15, 2σ) and 143Nd/144Nd = 0·512105 ± 2 (N = 15, 2σ). A lead double-spike technique with Southampton-Brest-Lead 207–204 (SBL74) solution was used to determine Pb isotopic ratios. Replicate analyses of the NBS 981 standard gave mean values of 206Pb/204Pb = 16·941 ± 0·002, 207Pb/204Pb = 15·497 ± 0·002, and 208Pb/204Pb = 36·724 ± 0·006 (N = 17; 2σ). The blanks for Sr, Nd, and Pb were all less than 100 pg, negligible compared to the analysed samples. The mineralogical compositions of representative samples of each lineage were analysed using a JEOL JXA-8530F field-emission electron probe microanalyser (FE-EPMA) equipped with five wavelength-dispersive spectrometers at KOPRI. Quantitative analyses were performed on carbon-coated thin sections with a focused beam of 3 μm diameter, an accelerating voltage of 15 kV, and a beam current of 15 nA. Peak position and background counting times were 20 and 10 seconds, respectively. Sodium was analysed first to mitigate any loss due to volatilization. Natural minerals and synthetic oxides were used for calibration standards. A suite of Smithsonian microbeam standards was analysed together with unknown samples daily to monitor data quality. All microprobe data were processed using the PRZ-A matrix correction method. RESULTS Petrography and field relationships Most lavas from The Pleiades have seriate or porphyritic textures, with phenocrysts set in a fine-grained, melanocratic groundmass. Vesicularity is variable. Felsic, trachytic lavas can be distinguished from mafic and intermediate lavas in the field by their typical leucocratic colors and almost aphyric nature. The cones and domes of The Pleiades are generally well preserved, but multiple generations of overlapping lava flows obscure the stratigraphic order. The locations of the samples have no recognizable spatial relationship between mafic and felsic rocks or sodic and potassic lineages. Centimetre to decimetre sized xenoliths of cognate essexite and syenite are common. Sodic lineage The mafic lavas of the sodic lineage are seriate-textured, with basanite and hawaiite compositions. Olivine, clinopyroxene, kaersutite, plagioclase and Fe–Ti oxide phenocrysts are surrounded by a melanocratic groundmass composed of clinopyroxene, oxides, and plagioclase (Fig. 2a). Euhedral to subhedral clinopyroxene is the most abundant phenocryst (e.g. ∼60% of the phenocrysts in the sample K16012708-4). Clinopyroxene often shows sector or discontinuous zonation and contains oxide, sulfide or melt inclusions, particularly in the center of the crystal. In plane-polarized light, some phenocrysts exhibit a pink clinopyroxene rim overgrown on either an olivine core or a green clinopyroxene core. Olivine phenocrysts are mostly euhedral to subhedral, with occasional occurrence as strongly-sieved microphenocrysts. Kaersutite phenocrysts show angular and prismatic shapes and are always mantled by 20–150 µm thick oxide rims. Some kaersutite phenocrysts contain clinopyroxene and oxide inclusions, suggesting that their onset of crystallization is preceded by the latter two phases. Two Si-poor basanite samples (K16012411-1 and K16012412-2) with abundant clinopyroxene (1–5 mm in size) and Fe–Ti oxide phenocrysts are also included in the sodic lineage, although they lack kaersutite. They are distinct from the mafic rocks of the potassic lineage by the absence of olivine phenocrysts. Plagioclase is a minor phenocryst phase and is mostly present in the groundmass or as microphenocrysts (<1 mm). Fig. 2 View largeDownload slide Representative thin section photographs of the sodic and potassic differentiation series in plane polarized light. (a) Sodic basanite (K16012708-4) containing kaersutite and clinopyroxene with minor olivine, plagioclase, and Fe–Ti oxides. (b) Olivine- and clinopyroxene-phyric potassic hawaiite (K16012424). (c) Sodic phonotephrite (K16012713-2) containing kaersutite and clinopyroxene with less abundant plagioclase and Fe–Ti oxides. (d) Potassic mugearite (K16012708-2) with abundant plagioclase and clinopyroxene, olivine, and oxide (micro)phenocrysts. (e) Sodic tephriphonolite (K16012713-1) with plagioclase, kaersutite, and kaersutite pseudomorphs, and (f) Trachyte (K16012407-1) containing fayalite (Ol), aegirine–augite (cpx), and sanidine (Sa) microphenocrysts. Note the more abundant plagioclase phenocrysts in mugearite (d) compared to the phonotephrite (c). Ol, Olivine; Cpx, clinopyroxene; Mt, (titano)magnetite; Krs, kaersutite; Pl, plagioclase; Sa, sanidine. Fig. 2 View largeDownload slide Representative thin section photographs of the sodic and potassic differentiation series in plane polarized light. (a) Sodic basanite (K16012708-4) containing kaersutite and clinopyroxene with minor olivine, plagioclase, and Fe–Ti oxides. (b) Olivine- and clinopyroxene-phyric potassic hawaiite (K16012424). (c) Sodic phonotephrite (K16012713-2) containing kaersutite and clinopyroxene with less abundant plagioclase and Fe–Ti oxides. (d) Potassic mugearite (K16012708-2) with abundant plagioclase and clinopyroxene, olivine, and oxide (micro)phenocrysts. (e) Sodic tephriphonolite (K16012713-1) with plagioclase, kaersutite, and kaersutite pseudomorphs, and (f) Trachyte (K16012407-1) containing fayalite (Ol), aegirine–augite (cpx), and sanidine (Sa) microphenocrysts. Note the more abundant plagioclase phenocrysts in mugearite (d) compared to the phonotephrite (c). Ol, Olivine; Cpx, clinopyroxene; Mt, (titano)magnetite; Krs, kaersutite; Pl, plagioclase; Sa, sanidine. Lavas of intermediate composition have clinopyroxene, kaersutite and plagioclase phenocrysts set in a leucocratic groundmass (Fig. 2c and e). The abundance of kaersutite phenocrysts increases at the expense of clinopyroxene phenocrysts as the magma evolves from phonotephrite to tephriphonolite. Kaersutite overgrowths on clinopyroxene are commonly observed. Most kaersutite phenocrysts are partially or entirely replaced by oxide rims. The modal abundance of plagioclase phenocrysts increases as the whole-rock composition evolves until they become the dominant phenocryst phase in the most evolved samples. For example, their abundance is <1% among phenocrysts in basanite sample K16012708-4 whereas it is ∼75% in the tephriphonolite sample K16012713-1. Nepheline is rare and only occurs as microphenocrysts (0·2–0·3 mm in size) rimmed by plagioclase laths in the most evolved whole-rock compositions. Potassic lineage The alkali basalt and hawaiite lavas have seriate to porphyritic textures (Fig. 2b). The most primitive lavas are olivine–phyric, and the modal abundance of clinopyroxene, Fe–Ti oxides and plagioclase phenocrysts gradually increases as the composition evolves. The petrology of the intermediate lavas (Fig. 2d) is characterized by a leucocratic groundmass surrounding abundant plagioclase phenocrysts (>50% throughout the intermediate suite). Euhedral clinopyroxene, olivine and oxide phenocrysts are ubiquitous in all potassic lava samples. Trachyte and phonolite lavas (Fig. 2f) are volumetrically minor at The Pleiades and occur as endogenous domes, such as Taygete Cone. They are classified as potassic by the absence of kaersutite, the presence of olivine microphenocrysts (0·1–0·3 mm) and their overall geochemical similarity to the intermediate lava compositions from the potassic lineage. Dominant phenocrysts are tabular sanidine with simple-twinning. Microphenocrysts (<0·7 mm) of green clinopyroxene and rounded olivine occur. The trachytic-textured groundmass is filled with feldspar-laths and interstitial clinopyroxene and oxides. Two trachyte samples (M16012710 and M16012714-2) contain kaersutite pseudomorphs, but they differ from the evolved lavas of the sodic lineage in the presence of fayalitic olivine microphenocrysts. Xenoliths and country rocks The granodiorite xenoliths are clinopyroxene-bearing, hornblende–biotite granodiorite. They occasionally carry some cm- to mm-sized enclaves comprising hornblende and biotite. They show varying degrees of alteration, particularly of feldspar. Relatively fresh granodiorite xenolith samples (K16012407-2 and K16012422-3) were chosen for this study. The two basement rocks collected around Terra Nova Bay are a migmatite and a deformed granite. The migmatite sample 141215-5B is a garnet–cordierite pelitic gneiss and its lithology is consistent with the description in Palmeri (1997). The granite sample 141123–1 A is representative of the GHIC group. Mineral compositions Olivine Olivine shows a large compositional variation from Fo87 to Fo01. In mafic lavas, euhedral olivine phenocrysts have a small variation in Fo content (Fo81 and Fo84–87 in K16012424 and K16012708-4, respectively), whereas outermost rims or resorbed grains have a wider compositional range (Fo68–86). Fayalite contents of olivine phenocrysts generally increase as the whole-rock wt % SiO2 contents of their host lavas increase. Trachyte, the most evolved rock type in The Pleiades, contains nearly pure fayalite (Fa98–99) microphenocrysts. Clinopyroxene Clinopyroxene is a ubiquitous phenocryst phase and shows variable compositions from diopside (or augite) to nearly pure hedenbergite. Because most of the clinopyroxene phenocrysts have sector, oscillatory and/or patchy zoning, their compositions vary widely, even within a single sample. However, the outer rims without disequilibrium textures show much narrower compositional variation. The rim compositions of clinopyroxene phenocrysts in basaltic rocks are moderately high in TiO2 (1·2–4·3 wt %) and Al2O3 (4·2–9·2 wt %). Most of the clinopyroxenes have less than 0·1 atoms of Ti per 6 oxygens and are not titanian (Morimoto, 1988). The clinopyroxene rim compositions in the mafic rocks are Wo45–52En34–44Fs09–14 and become increasingly enriched in Fe (Wo43–51En29–41Fs14–23) as the whole-rock composition evolves (Table 1). Clinopyroxene grains in trachyte and phonolite are strongly enriched in Fe (Wo42–45En02–24Fs33–55) and do not overlap with other clinopyroxene compositional ranges in this study. Calculated Fe3+/Fe2+ ratios (Fe3+=Na+IVAl–VIAl –2Ti–Cr; Lindsley, 1983) of the trachytic clinopyroxene are restricted to a very low range (<0·1). Table 1 Representative major element compositions of phenocrysts in The Pleiades volcanic rock samples Sample K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 D1601 D1601 D1601 D1601 D1601 K1601 K1601 K1601 K1601 2424 2424 2424 2708-2 2708-2 2708-2 2708-2 2708-2 2403 2403 2403 2403 2403 2407-1 2407-1 2407-1 2407-1 Lineage Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Rock type H H H Mu Mu Mu Mu Mu Bn Bn Bn Bn Bn Tr Tr Tr Tr Mineral Ol Cpx Mt Ol Cpx Pl Mt† Ilm† Ol Cpx Pl Mt Ilm Ol Cpx Sa Mt SiO2 39·37 48·69 0·15 36·93 50·06 55·51 0·14 0·02 35·15 49·52 56·38 0·08 0·17 29·44 49·43 67·15 0·18 TiO2 b.d.l. 1·69 16·69 0·06 1·49 0·08 2·84 48·68 0·09 1·30 0·08 21·48 46·55 0·03 0·30 0·03 14·49 Al2O3 0·02 5·57 5·07 b.d.l.· 4·50 28·05 2·47 0·14 0·02 3·95 26·74 4·34 3·20 b·d·l· 0·44 19·14 0·07 Cr2O3 0·03 0·33 4·77 b.d.l. b.d.l. b.d.l. 0·06 b.d.l. 0·02 0·04 0·00 0·01 0·14 b·d·l· 25·03 0·01 b·d·l· FeO 16·95 5·92 66·82 29·45 9·01 0·46 88·52 44·04 40·19 10·57 0·37 68·30 44·80 65·71 1·49 0·19 82·32 MnO 0·26 0·17 0·76 0·63 0·17 0·02 0·07 1·21 1·12 0·38 0·05 0·76 1·07 3·86 3·20 b·d·l· 1·08 MgO 43·07 14·15 5·09 32·65 13·32 0·02 1·07 3·88 23·59 12·42 0·05 2·88 2·44 0·78 18·97 b·d·l· 0·03 CaO 0·31 22·69 0·15 0·20 21·43 10·56 b.d.l. b.d.l.· 0·27 20·92 9·42 b.d.l. 0·02 0·34 0·81 0·32 b·d·l· Na2O 0·02 0·41 0·01 b.d.l. 0·55 4·93 0·03 b.d.l. 0·07 0·67 5·87 0·04 0·02 b·d·l· 0·04 7·46 0·02 K2O b.d.l. b.d.l. 0·04 b.d.l. b.d.l. 0·47 0·01 0·01 0·01 0·02 0·56 0·01 0·01 b·d·l· 0·01 6·18 b·d·l· NiO 0·12 b.d.l. 0·08 0·01 b.d.l. b.d.l. 0·04 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0·08 b·d·l· b·d·l· b·d·l· b·d·l· Total 100·1 99·6 99·6 99·9 100·5 100·1 95·2 98·0 100·5 99·8 99·5 97·89 98·50 100·2 99·7 100·5 98·19 Mg#/An* 81·3 81·0 65·7 72·5 52·7 50·2 67·7 45·5 1·9 18·6 Sample K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 2708-4 2708-4 2708-4 2708-4 2708-4 2708-4 2713-2 2713-2 2713-2 2713-2 2713-2 2422-2 2422-2 2422-2 2422-2 2422-2 Lineage Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Rock Bas Bas Bas Bas Bas Bas PhT PhT PhT PhT PhT TPh TPh TPh TPh TPh Mineral Ol Cpx Krs Pl Mt Ilm Cpx Krs Pl Mt Mt Cpx Krs Pl Ne Mt SiO2 40·38 47·56 39·02 51·61 0·10 0·05 47·42 38·56 55·55 0·09 0·08 44·94 38·25 59·41 45·04 0·02 TiO2 0·01 2·28 6·47 0·12 17·97 48·07 1·88 6·64 0·09 19·64 0·58 2·50 5·63 0·04 b·d·l· 18·72 Al2O3 0·05 6·53 13·18 30·01 7·30 0·84 5·92 13·43 27·82 4·83 0·01 7·72 13·12 25·11 32·84 5·50 Cr2O3 0·06 0·16 0·04 b·d·l· 0·78 b·d·l· 0·01 b.d.l. b.d.l. 0·04 b.d.l. b.d.l. 0·02 b·d·l· b·d·l· b·d·l· FeO 13·16 6·91 11·17 0·56 64·47 43·52 9·28 11·57 0·32 70·50 83·65 11·78 13·65 0·31 0·30 71·96 MnO 0·19 0·07 0·18 b.d.l. 0·45 0·48 0·22 0·11 0·03 0·70 0·01 0·33 0·10 b·d·l· 0·03 0·93 MgO 45·91 13·45 12·13 0·10 6·21 6·97 12·26 11·88 0·05 3·41 0·04 9·31 10·54 0·01 b·d·l· 2·18 CaO 0·29 21·63 11·73 13·14 b.d.l. 0·01 21·34 11·66 10·22 b.d.l. b.d.l. 21·66 11·68 6·86 0·22 b·d·l· Na2O b.d.l. 0·52 1·16 3·57 b.d.l. b.d.l. 0·67 0·91 5·53 0·04 0·02 0·91 1·32 6·93 17·19 0·02 K2O b.d.l. b.d.l. 2·49 0·31 b.d.l. 0·01 0·01 2·61 0·44 b.d.l. 0·02 0·03 2·48 0·82 3·96 b·d·l· NiO 0·22 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0·01 0·60 b.d.l. b.d.l. b·d·l· b·d·l· 0·06 Total 100·3 99·1 97·6 99·4 97·3 99·9 99·0 97·4 100·0 99·3 85·0 99·2 96·8 99·5 99·6 99·4 Mg#/An* 85·6 77·6 65·8 70·2 49·2 58·5 33·7 Sample K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 D1601 D1601 D1601 D1601 D1601 K1601 K1601 K1601 K1601 2424 2424 2424 2708-2 2708-2 2708-2 2708-2 2708-2 2403 2403 2403 2403 2403 2407-1 2407-1 2407-1 2407-1 Lineage Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Rock type H H H Mu Mu Mu Mu Mu Bn Bn Bn Bn Bn Tr Tr Tr Tr Mineral Ol Cpx Mt Ol Cpx Pl Mt† Ilm† Ol Cpx Pl Mt Ilm Ol Cpx Sa Mt SiO2 39·37 48·69 0·15 36·93 50·06 55·51 0·14 0·02 35·15 49·52 56·38 0·08 0·17 29·44 49·43 67·15 0·18 TiO2 b.d.l. 1·69 16·69 0·06 1·49 0·08 2·84 48·68 0·09 1·30 0·08 21·48 46·55 0·03 0·30 0·03 14·49 Al2O3 0·02 5·57 5·07 b.d.l.· 4·50 28·05 2·47 0·14 0·02 3·95 26·74 4·34 3·20 b·d·l· 0·44 19·14 0·07 Cr2O3 0·03 0·33 4·77 b.d.l. b.d.l. b.d.l. 0·06 b.d.l. 0·02 0·04 0·00 0·01 0·14 b·d·l· 25·03 0·01 b·d·l· FeO 16·95 5·92 66·82 29·45 9·01 0·46 88·52 44·04 40·19 10·57 0·37 68·30 44·80 65·71 1·49 0·19 82·32 MnO 0·26 0·17 0·76 0·63 0·17 0·02 0·07 1·21 1·12 0·38 0·05 0·76 1·07 3·86 3·20 b·d·l· 1·08 MgO 43·07 14·15 5·09 32·65 13·32 0·02 1·07 3·88 23·59 12·42 0·05 2·88 2·44 0·78 18·97 b·d·l· 0·03 CaO 0·31 22·69 0·15 0·20 21·43 10·56 b.d.l. b.d.l.· 0·27 20·92 9·42 b.d.l. 0·02 0·34 0·81 0·32 b·d·l· Na2O 0·02 0·41 0·01 b.d.l. 0·55 4·93 0·03 b.d.l. 0·07 0·67 5·87 0·04 0·02 b·d·l· 0·04 7·46 0·02 K2O b.d.l. b.d.l. 0·04 b.d.l. b.d.l. 0·47 0·01 0·01 0·01 0·02 0·56 0·01 0·01 b·d·l· 0·01 6·18 b·d·l· NiO 0·12 b.d.l. 0·08 0·01 b.d.l. b.d.l. 0·04 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0·08 b·d·l· b·d·l· b·d·l· b·d·l· Total 100·1 99·6 99·6 99·9 100·5 100·1 95·2 98·0 100·5 99·8 99·5 97·89 98·50 100·2 99·7 100·5 98·19 Mg#/An* 81·3 81·0 65·7 72·5 52·7 50·2 67·7 45·5 1·9 18·6 Sample K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 2708-4 2708-4 2708-4 2708-4 2708-4 2708-4 2713-2 2713-2 2713-2 2713-2 2713-2 2422-2 2422-2 2422-2 2422-2 2422-2 Lineage Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Rock Bas Bas Bas Bas Bas Bas PhT PhT PhT PhT PhT TPh TPh TPh TPh TPh Mineral Ol Cpx Krs Pl Mt Ilm Cpx Krs Pl Mt Mt Cpx Krs Pl Ne Mt SiO2 40·38 47·56 39·02 51·61 0·10 0·05 47·42 38·56 55·55 0·09 0·08 44·94 38·25 59·41 45·04 0·02 TiO2 0·01 2·28 6·47 0·12 17·97 48·07 1·88 6·64 0·09 19·64 0·58 2·50 5·63 0·04 b·d·l· 18·72 Al2O3 0·05 6·53 13·18 30·01 7·30 0·84 5·92 13·43 27·82 4·83 0·01 7·72 13·12 25·11 32·84 5·50 Cr2O3 0·06 0·16 0·04 b·d·l· 0·78 b·d·l· 0·01 b.d.l. b.d.l. 0·04 b.d.l. b.d.l. 0·02 b·d·l· b·d·l· b·d·l· FeO 13·16 6·91 11·17 0·56 64·47 43·52 9·28 11·57 0·32 70·50 83·65 11·78 13·65 0·31 0·30 71·96 MnO 0·19 0·07 0·18 b.d.l. 0·45 0·48 0·22 0·11 0·03 0·70 0·01 0·33 0·10 b·d·l· 0·03 0·93 MgO 45·91 13·45 12·13 0·10 6·21 6·97 12·26 11·88 0·05 3·41 0·04 9·31 10·54 0·01 b·d·l· 2·18 CaO 0·29 21·63 11·73 13·14 b.d.l. 0·01 21·34 11·66 10·22 b.d.l. b.d.l. 21·66 11·68 6·86 0·22 b·d·l· Na2O b.d.l. 0·52 1·16 3·57 b.d.l. b.d.l. 0·67 0·91 5·53 0·04 0·02 0·91 1·32 6·93 17·19 0·02 K2O b.d.l. b.d.l. 2·49 0·31 b.d.l. 0·01 0·01 2·61 0·44 b.d.l. 0·02 0·03 2·48 0·82 3·96 b·d·l· NiO 0·22 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0·01 0·60 b.d.l. b.d.l. b·d·l· b·d·l· 0·06 Total 100·3 99·1 97·6 99·4 97·3 99·9 99·0 97·4 100·0 99·3 85·0 99·2 96·8 99·5 99·6 99·4 Mg#/An* 85·6 77·6 65·8 70·2 49·2 58·5 33·7 H, hawaiite; Mu, mugearite; Bn, benmoreite; Tr, trachyte; Bas, basanite; PhT, phonotephrite; TPh, tephriphonolite; Ilm, ilmenite; Ne, nepheline; b.d.l., below detection limit. * Forsterite number, 100 ×Mg/[Mg+Fe+Mn+Ca], for olivine; Mg number, 100 ×Mg/[Mg+Fe] for clinopyroxene; anorthite number, 100 ×Ca/[Ca+Na+K] for plagioclase. † A pair of exsolved and host phases of a single grain. Table 1 Representative major element compositions of phenocrysts in The Pleiades volcanic rock samples Sample K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 D1601 D1601 D1601 D1601 D1601 K1601 K1601 K1601 K1601 2424 2424 2424 2708-2 2708-2 2708-2 2708-2 2708-2 2403 2403 2403 2403 2403 2407-1 2407-1 2407-1 2407-1 Lineage Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Rock type H H H Mu Mu Mu Mu Mu Bn Bn Bn Bn Bn Tr Tr Tr Tr Mineral Ol Cpx Mt Ol Cpx Pl Mt† Ilm† Ol Cpx Pl Mt Ilm Ol Cpx Sa Mt SiO2 39·37 48·69 0·15 36·93 50·06 55·51 0·14 0·02 35·15 49·52 56·38 0·08 0·17 29·44 49·43 67·15 0·18 TiO2 b.d.l. 1·69 16·69 0·06 1·49 0·08 2·84 48·68 0·09 1·30 0·08 21·48 46·55 0·03 0·30 0·03 14·49 Al2O3 0·02 5·57 5·07 b.d.l.· 4·50 28·05 2·47 0·14 0·02 3·95 26·74 4·34 3·20 b·d·l· 0·44 19·14 0·07 Cr2O3 0·03 0·33 4·77 b.d.l. b.d.l. b.d.l. 0·06 b.d.l. 0·02 0·04 0·00 0·01 0·14 b·d·l· 25·03 0·01 b·d·l· FeO 16·95 5·92 66·82 29·45 9·01 0·46 88·52 44·04 40·19 10·57 0·37 68·30 44·80 65·71 1·49 0·19 82·32 MnO 0·26 0·17 0·76 0·63 0·17 0·02 0·07 1·21 1·12 0·38 0·05 0·76 1·07 3·86 3·20 b·d·l· 1·08 MgO 43·07 14·15 5·09 32·65 13·32 0·02 1·07 3·88 23·59 12·42 0·05 2·88 2·44 0·78 18·97 b·d·l· 0·03 CaO 0·31 22·69 0·15 0·20 21·43 10·56 b.d.l. b.d.l.· 0·27 20·92 9·42 b.d.l. 0·02 0·34 0·81 0·32 b·d·l· Na2O 0·02 0·41 0·01 b.d.l. 0·55 4·93 0·03 b.d.l. 0·07 0·67 5·87 0·04 0·02 b·d·l· 0·04 7·46 0·02 K2O b.d.l. b.d.l. 0·04 b.d.l. b.d.l. 0·47 0·01 0·01 0·01 0·02 0·56 0·01 0·01 b·d·l· 0·01 6·18 b·d·l· NiO 0·12 b.d.l. 0·08 0·01 b.d.l. b.d.l. 0·04 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0·08 b·d·l· b·d·l· b·d·l· b·d·l· Total 100·1 99·6 99·6 99·9 100·5 100·1 95·2 98·0 100·5 99·8 99·5 97·89 98·50 100·2 99·7 100·5 98·19 Mg#/An* 81·3 81·0 65·7 72·5 52·7 50·2 67·7 45·5 1·9 18·6 Sample K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 2708-4 2708-4 2708-4 2708-4 2708-4 2708-4 2713-2 2713-2 2713-2 2713-2 2713-2 2422-2 2422-2 2422-2 2422-2 2422-2 Lineage Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Rock Bas Bas Bas Bas Bas Bas PhT PhT PhT PhT PhT TPh TPh TPh TPh TPh Mineral Ol Cpx Krs Pl Mt Ilm Cpx Krs Pl Mt Mt Cpx Krs Pl Ne Mt SiO2 40·38 47·56 39·02 51·61 0·10 0·05 47·42 38·56 55·55 0·09 0·08 44·94 38·25 59·41 45·04 0·02 TiO2 0·01 2·28 6·47 0·12 17·97 48·07 1·88 6·64 0·09 19·64 0·58 2·50 5·63 0·04 b·d·l· 18·72 Al2O3 0·05 6·53 13·18 30·01 7·30 0·84 5·92 13·43 27·82 4·83 0·01 7·72 13·12 25·11 32·84 5·50 Cr2O3 0·06 0·16 0·04 b·d·l· 0·78 b·d·l· 0·01 b.d.l. b.d.l. 0·04 b.d.l. b.d.l. 0·02 b·d·l· b·d·l· b·d·l· FeO 13·16 6·91 11·17 0·56 64·47 43·52 9·28 11·57 0·32 70·50 83·65 11·78 13·65 0·31 0·30 71·96 MnO 0·19 0·07 0·18 b.d.l. 0·45 0·48 0·22 0·11 0·03 0·70 0·01 0·33 0·10 b·d·l· 0·03 0·93 MgO 45·91 13·45 12·13 0·10 6·21 6·97 12·26 11·88 0·05 3·41 0·04 9·31 10·54 0·01 b·d·l· 2·18 CaO 0·29 21·63 11·73 13·14 b.d.l. 0·01 21·34 11·66 10·22 b.d.l. b.d.l. 21·66 11·68 6·86 0·22 b·d·l· Na2O b.d.l. 0·52 1·16 3·57 b.d.l. b.d.l. 0·67 0·91 5·53 0·04 0·02 0·91 1·32 6·93 17·19 0·02 K2O b.d.l. b.d.l. 2·49 0·31 b.d.l. 0·01 0·01 2·61 0·44 b.d.l. 0·02 0·03 2·48 0·82 3·96 b·d·l· NiO 0·22 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0·01 0·60 b.d.l. b.d.l. b·d·l· b·d·l· 0·06 Total 100·3 99·1 97·6 99·4 97·3 99·9 99·0 97·4 100·0 99·3 85·0 99·2 96·8 99·5 99·6 99·4 Mg#/An* 85·6 77·6 65·8 70·2 49·2 58·5 33·7 Sample K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 D1601 D1601 D1601 D1601 D1601 K1601 K1601 K1601 K1601 2424 2424 2424 2708-2 2708-2 2708-2 2708-2 2708-2 2403 2403 2403 2403 2403 2407-1 2407-1 2407-1 2407-1 Lineage Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Potassic Rock type H H H Mu Mu Mu Mu Mu Bn Bn Bn Bn Bn Tr Tr Tr Tr Mineral Ol Cpx Mt Ol Cpx Pl Mt† Ilm† Ol Cpx Pl Mt Ilm Ol Cpx Sa Mt SiO2 39·37 48·69 0·15 36·93 50·06 55·51 0·14 0·02 35·15 49·52 56·38 0·08 0·17 29·44 49·43 67·15 0·18 TiO2 b.d.l. 1·69 16·69 0·06 1·49 0·08 2·84 48·68 0·09 1·30 0·08 21·48 46·55 0·03 0·30 0·03 14·49 Al2O3 0·02 5·57 5·07 b.d.l.· 4·50 28·05 2·47 0·14 0·02 3·95 26·74 4·34 3·20 b·d·l· 0·44 19·14 0·07 Cr2O3 0·03 0·33 4·77 b.d.l. b.d.l. b.d.l. 0·06 b.d.l. 0·02 0·04 0·00 0·01 0·14 b·d·l· 25·03 0·01 b·d·l· FeO 16·95 5·92 66·82 29·45 9·01 0·46 88·52 44·04 40·19 10·57 0·37 68·30 44·80 65·71 1·49 0·19 82·32 MnO 0·26 0·17 0·76 0·63 0·17 0·02 0·07 1·21 1·12 0·38 0·05 0·76 1·07 3·86 3·20 b·d·l· 1·08 MgO 43·07 14·15 5·09 32·65 13·32 0·02 1·07 3·88 23·59 12·42 0·05 2·88 2·44 0·78 18·97 b·d·l· 0·03 CaO 0·31 22·69 0·15 0·20 21·43 10·56 b.d.l. b.d.l.· 0·27 20·92 9·42 b.d.l. 0·02 0·34 0·81 0·32 b·d·l· Na2O 0·02 0·41 0·01 b.d.l. 0·55 4·93 0·03 b.d.l. 0·07 0·67 5·87 0·04 0·02 b·d·l· 0·04 7·46 0·02 K2O b.d.l. b.d.l. 0·04 b.d.l. b.d.l. 0·47 0·01 0·01 0·01 0·02 0·56 0·01 0·01 b·d·l· 0·01 6·18 b·d·l· NiO 0·12 b.d.l. 0·08 0·01 b.d.l. b.d.l. 0·04 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0·08 b·d·l· b·d·l· b·d·l· b·d·l· Total 100·1 99·6 99·6 99·9 100·5 100·1 95·2 98·0 100·5 99·8 99·5 97·89 98·50 100·2 99·7 100·5 98·19 Mg#/An* 81·3 81·0 65·7 72·5 52·7 50·2 67·7 45·5 1·9 18·6 Sample K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 K1601 2708-4 2708-4 2708-4 2708-4 2708-4 2708-4 2713-2 2713-2 2713-2 2713-2 2713-2 2422-2 2422-2 2422-2 2422-2 2422-2 Lineage Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Sodic Rock Bas Bas Bas Bas Bas Bas PhT PhT PhT PhT PhT TPh TPh TPh TPh TPh Mineral Ol Cpx Krs Pl Mt Ilm Cpx Krs Pl Mt Mt Cpx Krs Pl Ne Mt SiO2 40·38 47·56 39·02 51·61 0·10 0·05 47·42 38·56 55·55 0·09 0·08 44·94 38·25 59·41 45·04 0·02 TiO2 0·01 2·28 6·47 0·12 17·97 48·07 1·88 6·64 0·09 19·64 0·58 2·50 5·63 0·04 b·d·l· 18·72 Al2O3 0·05 6·53 13·18 30·01 7·30 0·84 5·92 13·43 27·82 4·83 0·01 7·72 13·12 25·11 32·84 5·50 Cr2O3 0·06 0·16 0·04 b·d·l· 0·78 b·d·l· 0·01 b.d.l. b.d.l. 0·04 b.d.l. b.d.l. 0·02 b·d·l· b·d·l· b·d·l· FeO 13·16 6·91 11·17 0·56 64·47 43·52 9·28 11·57 0·32 70·50 83·65 11·78 13·65 0·31 0·30 71·96 MnO 0·19 0·07 0·18 b.d.l. 0·45 0·48 0·22 0·11 0·03 0·70 0·01 0·33 0·10 b·d·l· 0·03 0·93 MgO 45·91 13·45 12·13 0·10 6·21 6·97 12·26 11·88 0·05 3·41 0·04 9·31 10·54 0·01 b·d·l· 2·18 CaO 0·29 21·63 11·73 13·14 b.d.l. 0·01 21·34 11·66 10·22 b.d.l. b.d.l. 21·66 11·68 6·86 0·22 b·d·l· Na2O b.d.l. 0·52 1·16 3·57 b.d.l. b.d.l. 0·67 0·91 5·53 0·04 0·02 0·91 1·32 6·93 17·19 0·02 K2O b.d.l. b.d.l. 2·49 0·31 b.d.l. 0·01 0·01 2·61 0·44 b.d.l. 0·02 0·03 2·48 0·82 3·96 b·d·l· NiO 0·22 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0·01 0·60 b.d.l. b.d.l. b·d·l· b·d·l· 0·06 Total 100·3 99·1 97·6 99·4 97·3 99·9 99·0 97·4 100·0 99·3 85·0 99·2 96·8 99·5 99·6 99·4 Mg#/An* 85·6 77·6 65·8 70·2 49·2 58·5 33·7 H, hawaiite; Mu, mugearite; Bn, benmoreite; Tr, trachyte; Bas, basanite; PhT, phonotephrite; TPh, tephriphonolite; Ilm, ilmenite; Ne, nepheline; b.d.l., below detection limit. * Forsterite number, 100 ×Mg/[Mg+Fe+Mn+Ca], for olivine; Mg number, 100 ×Mg/[Mg+Fe] for clinopyroxene; anorthite number, 100 ×Ca/[Ca+Na+K] for plagioclase. † A pair of exsolved and host phases of a single grain. Amphibole Amphibole phenocrysts are calcic, have high Ti contents (5·2–6·7 wt % TiO2, 0·59–0·78 atom per formula unit, apfu; based on 24 oxygen per unit amphibole formula) and are pleochroic reddish brown in color. The high Ti content (Ti > 0·5 apfu) confirms the amphibole is kaersutite, a Ti- and Ca-rich oxy-amphibole (Hawthorne et al., 2012). The Mg-numbers of the kaersutite phenocrysts do not vary significantly (Mg/[Mg+Fe+Mn]=0·5–0·7) among the lavas. However, iron-rich (Mg/[Mg+Fe+Mn]<0·5) kaersutite phenocrysts can be found as rounded cores or outermost rims. Feldspar The feldspar phenocrysts in the mafic to intermediate volcanic rocks are mainly plagioclase. The most mafic lavas do not contain plagioclase phenocrysts. The earliest plagioclase phenocrysts are ‘labradorite’ (An66–60), although calcic (An80) cores have been found. Throughout the mafic to intermediate lava compositions, the composition of plagioclase phenocrysts and microphenocrysts ranges from An80 to An30. Alkali-feldspar phenocrysts occur in the trachyte lavas. Some compositions cluster near the borderline between anorthoclase and sodian sanidine (Deer et al., 2013). However, in this study, alkali-feldspars in trachyte and phonolite are simply called sanidine in accordance with the absence of albite and pericline twinning and the moderately potassium-rich (Or>35) nature of most of the analysed alkali-feldspars. Fe–Ti oxides and spinels Fe–Ti oxides are ubiquitous except in the most mafic potassic lavas. Most of the oxide microphenocrysts are titanomagnetite. Their Fe2+–Fe3+–Ti compositions fall approximately in the middle of the ulvöspinel–magnetite solid solution line. Pure magnetite was found only as a sub-solidus exsolved phase in the titanomagnetite grains. Ilmenite is scarce and rarely coexists with titanomagnetite. Xenocrystic chrome-rich spinel, overgrown by titanomagnetite, can be found in some of the most mafic lavas. Whole-rock compositions Major elements The volcanic rocks from The Pleiades exhibit a wide range of variation in alkali contents and in their degree of magmatic evolution (Table 2). The variation and classification are shown in the total alkalis vs silica (TAS) classification diagram (Fig. 3a) (Le Bas et al., 1986). The sodic lineage lavas are basanite, tephrite, phonotephrite and tephriphonolite, whereas the potassic lineage consists of hawaiite, mugearite, benmoreite, trachyte and phonolite. The two lineages are identifiable on a K2O vs Na2O diagram (Fig. 3b). The sodic lineage has a slightly higher K2O concentration than the potassic one in the mafic lavas and evolves to intermediate lavas with a constant Na2O/K2O ratio (∼0·5). The potassic lineage diverges from the sodic lineage with increasing K2O/Na2O ratio (0·5–0·81). These two lithological groups fit the sodic and mildly-potassic lineages reported by Kyle (1982), implying a close relationship between geochemical divergences and fractionating phases. Table 2 Whole-rock major (wt %) and trace element (ppm) compositions of representative samples and the calculated CIPW normative mineral abundances Group P-M P-M P-M P-M P-M P-I P-I P-I P-I P-I P-I P-I P-I P-I P-I P-F P-F P-F P-F Sample K1601 K1601 J1412 K1601 M1601 J1412 K1601 J1412 D1601 J1412 J1412 K1601 K1601 J1412 K1601 M1601 K1601 K1601 K1601 2408-1 2424 0503-2 2408-2 2705-1 0504-4 2708-2 0106-1 2403 0105-1 0103 2708-1 2707-1 0504-1 2709-1 2701 2425 2415 2422-1 Rock type AB H H H Bas Mu Mu Mu Bn Bn Bn Tr Tr Tr Ta Ph Ph Ph Tr SiO2 44·66 45·74 46·13 47·04 47·65 50·02 51·71 52·24 55·24 57·71 57·96 58·66 59·42 59·52 55·52 59·33 60·44 60·63 64·66 TiO2 2·90 2·44 2·46 3·09 2·48 2·51 2·24 2·28 1·35 1·07 1·31 0·91 0·88 0·77 1·32 0·27 0·19 0·19 0·33 Al2O3 14·06 14·20 14·61 16·19 16·91 16·00 17·04 16·92 17·45 17·56 17·69 17·59 17·79 17·49 17·47 17·93 18·51 18·59 17·14 FeOT 11·66 11·23 11·04 11·60 10·73 10·20 9·70 9·69 8·75 7·71 7·83 6·99 6·96 6·36 8·70 5·48 5·19 5·15 4·94 MnO 0·18 0·20 0·20 0·19 0·21 0·18 0·19 0·19 0·22 0·21 0·19 0·19 0·19 0·18 0·22 0·20 0·20 0·20 0·17 MgO 9·38 9·05 8·25 5·50 4·65 4·75 3·52 3·38 1·66 1·22 1·77 1·09 1·05 0·90 1·63 0·19 0·13 0·11 0·20 CaO 11·39 10·30 10·16 9·11 8·24 7·46 6·09 5·86 4·14 3·31 3·80 3·00 2·90 2·65 4·04 1·48 1·41 1·26 1·32 Na2O 2·91 3·47 3·52 3·87 4·97 4·26 4·91 4·93 6·02 6·25 5·71 6·12 6·17 6·21 6·20 7·50 7·94 8·01 6·62 K2O 1·32 1·42 1·48 1·73 2·07 2·35 2·77 2·78 3·53 3·90 3·81 4·29 4·37 4·45 3·52 5·43 5·48 5·50 5·30 P2O5 0·55 0·51 0·54 0·74 0·68 0·64 0·70 0·70 0·53 0·39 0·43 0·30 0·29 0·25 0·51 0·08 0·05 0·05 0·06 LOI −0·12 0·05 0·00 −0·37 −0·47 0·00 0·14 0·00 −0·21 0·00 0·00 −0·25 −0·25 0·00 −0·20 0·00 0·13 0·03 −0·05 Total 98·89 98·61 98·37 98·69 98·12 98·37 99·00 98·96 98·67 99·35 100·5 98·89 99·78 98·78 98·94 97·89 99·67 99·73 100·7 ne 7·32 7·90 6·98 4·71 10·4 1·57 1·96 0·83 3·24 1·59 0·69 0·28 3·85 10·2 11·6 11·5 di 25·7 23·6 22·4 15·5 15·6 12·6 7·82 7·21 5·85 4·71 3·83 4·36 3·87 4·11 6·16 6·14 5·94 5·24 4·14 ol 15·8 16·2 15·0 12·1 10·5 9·11 8·44 8·34 6·22 5·33 3·36 4·85 4·93 4·21 6·00 2·47 2·43 2·68 hy 4·03 0·10 3·06 q 1·76 Sc 35·6 25·7 n.d. 21·2 13·2 n.d. 11·2 n.d. 10·5 n.d. n.d. 4·24 3·23 n.d. 7·33 1·07 0·65 0·87 2·51 V 303 227 n.d. 224 157 n.d. 124 n.d. 20·6 n.d. n.d. 9·36 8·15 n.d. 18·1 1·98 0·91 1·85 0·60 Co 71·2 57·9 n.d. 47·6 37·3 n.d. 34·5 n.d. 23·9 n.d. n.d. 13·7 12·4 n.d. 17·0 12·0 8·37 6·82 12·6 Cu 59·8 60·5 n.d. 47·2 35·5 n.d. 25·2 n.d. 29·0 n.d. n.d. 9·09 9·01 n.d. 13·7 7·57 7·60 6·93 5·61 Rb 33·9 36·7 29·2 45·2 57·5 62·6 76·8 65·6 98·5 82·9 101 131 135 120 86·0 178 217 186 190 Sr 645 772 623 889 977 577 778 624 728 427·5 496 497 477 364 636 75·1 55·6 35·6 60·5 Y 27·5 27·0 21·7 27·6 30·5 23·7 30·8 25·5 41·7 30·6 28·1 32·2 33·1 26·9 37·1 33·0 38·9 32·7 41·8 Nb 70·7 82·2 58·9 82·4 121 77·0 118 84·5 164 116 109 158 159 117 150 120 219 163 192 Cs 0·41 0·52 0·61 0·75 0·84 1·56 1·13 1·29 1·57 1·55 1·94 2·34 2·55 2·35 1·55 3·60 3·82 3·76 5·08 Ba 391 608 547 565 876 524 791 689 1212 1130 907 1113 1126 1006 1171 752 340 282 610 Hf 5·39 5·36 5·21 5·47 6·91 7·34 8·32 8·06 10·8 11·1 11·7 12·3 12·9 12·5 10·1 14·9 18·3 15·3 15·6 Zr 220 224 184 235 343 281 386 334 572 465 483 605 643 553 484 807 936 809 748 Pb 2·24 2·64 2·51 3·23 4·11 7·22 7·80 6·73 8·47 9·26 10·3 13·3 11·9 12·3 7·41 9·45 16·2 12·4 13·7 Th 4·87 5·98 5·84 6·06 9·89 13·0 11·8 11·3 13·1 14·3 16·5 18·7 19·8 19·2 12·8 25·8 31·3 25·2 27·6 U 1·37 1·59 1·62 1·61 2·65 3·30 2·96 2·83 3·33 3·59 3·88 4·70 4·73 4·90 3·31 6·95 8·41 6·14 7·11 La 42·5 50·3 45·4 51·2 73·8 60·4 76·7 68·2 101 87·4 84·7 99·2 103 88·9 95·3 119 137 111 128 Ce 81·1 95·7 85·8 97·7 136 116 141 132 181 165 155 172 178 159 175 196 214 175 211 Pr 9·64 11·2 10·6 11·4 15·2 12·6 15·8 14·2 19·8 17·0 16·2 18·0 18·3 15·8 19·4 19·0 20·8 17·1 21·9 Nd 39·0 43·8 40·8 45·1 56·3 46·6 57·9 52·4 70·4 61·4 56·7 60·8 62·2 53·5 69·3 59·5 64·2 52·2 71·6 Sm 7·60 8·49 7·58 8·26 9·62 8·31 9·90 8·97 11·7 9·99 9·57 9·67 9·45 8·79 11·8 8·55 9·53 7·52 11·6 Eu 2·45 2·87 2·65 2·73 3·23 2·52 2·90 2·67 3·59 3·11 2·52 2·62 2·49 2·21 3·56 1·60 1·38 1·10 1·54 Gd 7·36 7·77 6·70 7·61 8·72 6·92 8·65 7·17 9·90 7·78 7·34 7·99 7·97 6·56 9·92 7·21 7·97 6·43 9·81 Tb 0·95 0·99 1·08 0·96 1·08 1·11 1·10 1·13 1·25 1·26 1·05 1·06 1·06 0·95 1·29 0·97 1·06 0·87 1·31 Dy 5·40 5·67 5·29 5·35 6·12 5·57 6·17 5·81 7·35 6·72 6·30 6·07 6·14 5·83 7·36 5·80 6·80 5·51 7·92 Ho 1·00 1·05 1·13 1·01 1·13 1·18 1·18 1·22 1·37 1·42 1·18 1·22 1·20 1·11 1·41 1·16 1·38 1·11 1·55 Er 2·61 2·77 2·70 2·68 3·08 2·93 3·33 3·06 3·86 3·66 3·35 3·56 3·58 3·23 4·02 3·52 4·30 3·43 4·64 Tm 0·35 0·36 0·38 0·35 0·40 0·43 0·44 0·45 0·54 0·55 0·51 0·52 0·51 0·51 0·54 0·54 0·66 0·55 0·68 Yb 2·12 2·29 2·20 2·19 2·63 2·57 2·89 2·74 3·53 3·45 3·28 3·45 3·53 3·31 3·60 3·69 4·69 3·79 4·77 Lu 0·31 0·31 0·37 0·32 0·37 0·43 0·43 0·45 0·52 0·57 0·52 0·52 0·53 0·53 0·52 0·57 0·69 0·58 0·69 Group P-M P-M P-M P-M P-M P-I P-I P-I P-I P-I P-I P-I P-I P-I P-I P-F P-F P-F P-F Sample K1601 K1601 J1412 K1601 M1601 J1412 K1601 J1412 D1601 J1412 J1412 K1601 K1601 J1412 K1601 M1601 K1601 K1601 K1601 2408-1 2424 0503-2 2408-2 2705-1 0504-4 2708-2 0106-1 2403 0105-1 0103 2708-1 2707-1 0504-1 2709-1 2701 2425 2415 2422-1 Rock type AB H H H Bas Mu Mu Mu Bn Bn Bn Tr Tr Tr Ta Ph Ph Ph Tr SiO2 44·66 45·74 46·13 47·04 47·65 50·02 51·71 52·24 55·24 57·71 57·96 58·66 59·42 59·52 55·52 59·33 60·44 60·63 64·66 TiO2 2·90 2·44 2·46 3·09 2·48 2·51 2·24 2·28 1·35 1·07 1·31 0·91 0·88 0·77 1·32 0·27 0·19 0·19 0·33 Al2O3 14·06 14·20 14·61 16·19 16·91 16·00 17·04 16·92 17·45 17·56 17·69 17·59 17·79 17·49 17·47 17·93 18·51 18·59 17·14 FeOT 11·66 11·23 11·04 11·60 10·73 10·20 9·70 9·69 8·75 7·71 7·83 6·99 6·96 6·36 8·70 5·48 5·19 5·15 4·94 MnO 0·18 0·20 0·20 0·19 0·21 0·18 0·19 0·19 0·22 0·21 0·19 0·19 0·19 0·18 0·22 0·20 0·20 0·20 0·17 MgO 9·38 9·05 8·25 5·50 4·65 4·75 3·52 3·38 1·66 1·22 1·77 1·09 1·05 0·90 1·63 0·19 0·13 0·11 0·20 CaO 11·39 10·30 10·16 9·11 8·24 7·46 6·09 5·86 4·14 3·31 3·80 3·00 2·90 2·65 4·04 1·48 1·41 1·26 1·32 Na2O 2·91 3·47 3·52 3·87 4·97 4·26 4·91 4·93 6·02 6·25 5·71 6·12 6·17 6·21 6·20 7·50 7·94 8·01 6·62 K2O 1·32 1·42 1·48 1·73 2·07 2·35 2·77 2·78 3·53 3·90 3·81 4·29 4·37 4·45 3·52 5·43 5·48 5·50 5·30 P2O5 0·55 0·51 0·54 0·74 0·68 0·64 0·70 0·70 0·53 0·39 0·43 0·30 0·29 0·25 0·51 0·08 0·05 0·05 0·06 LOI −0·12 0·05 0·00 −0·37 −0·47 0·00 0·14 0·00 −0·21 0·00 0·00 −0·25 −0·25 0·00 −0·20 0·00 0·13 0·03 −0·05 Total 98·89 98·61 98·37 98·69 98·12 98·37 99·00 98·96 98·67 99·35 100·5 98·89 99·78 98·78 98·94 97·89 99·67 99·73 100·7 ne 7·32 7·90 6·98 4·71 10·4 1·57 1·96 0·83 3·24 1·59 0·69 0·28 3·85 10·2 11·6 11·5 di 25·7 23·6 22·4 15·5 15·6 12·6 7·82 7·21 5·85 4·71 3·83 4·36 3·87 4·11 6·16 6·14 5·94 5·24 4·14 ol 15·8 16·2 15·0 12·1 10·5 9·11 8·44 8·34 6·22 5·33 3·36 4·85 4·93 4·21 6·00 2·47 2·43 2·68 hy 4·03 0·10 3·06 q 1·76 Sc 35·6 25·7 n.d. 21·2 13·2 n.d. 11·2 n.d. 10·5 n.d. n.d. 4·24 3·23 n.d. 7·33 1·07 0·65 0·87 2·51 V 303 227 n.d. 224 157 n.d. 124 n.d. 20·6 n.d. n.d. 9·36 8·15 n.d. 18·1 1·98 0·91 1·85 0·60 Co 71·2 57·9 n.d. 47·6 37·3 n.d. 34·5 n.d. 23·9 n.d. n.d. 13·7 12·4 n.d. 17·0 12·0 8·37 6·82 12·6 Cu 59·8 60·5 n.d. 47·2 35·5 n.d. 25·2 n.d. 29·0 n.d. n.d. 9·09 9·01 n.d. 13·7 7·57 7·60 6·93 5·61 Rb 33·9 36·7 29·2 45·2 57·5 62·6 76·8 65·6 98·5 82·9 101 131 135 120 86·0 178 217 186 190 Sr 645 772 623 889 977 577 778 624 728 427·5 496 497 477 364 636 75·1 55·6 35·6 60·5 Y 27·5 27·0 21·7 27·6 30·5 23·7 30·8 25·5 41·7 30·6 28·1 32·2 33·1 26·9 37·1 33·0 38·9 32·7 41·8 Nb 70·7 82·2 58·9 82·4 121 77·0 118 84·5 164 116 109 158 159 117 150 120 219 163 192 Cs 0·41 0·52 0·61 0·75 0·84 1·56 1·13 1·29 1·57 1·55 1·94 2·34 2·55 2·35 1·55 3·60 3·82 3·76 5·08 Ba 391 608 547 565 876 524 791 689 1212 1130 907 1113 1126 1006 1171 752 340 282 610 Hf 5·39 5·36 5·21 5·47 6·91 7·34 8·32 8·06 10·8 11·1 11·7 12·3 12·9 12·5 10·1 14·9 18·3 15·3 15·6 Zr 220 224 184 235 343 281 386 334 572 465 483 605 643 553 484 807 936 809 748 Pb 2·24 2·64 2·51 3·23 4·11 7·22 7·80 6·73 8·47 9·26 10·3 13·3 11·9 12·3 7·41 9·45 16·2 12·4 13·7 Th 4·87 5·98 5·84 6·06 9·89 13·0 11·8 11·3 13·1 14·3 16·5 18·7 19·8 19·2 12·8 25·8 31·3 25·2 27·6 U 1·37 1·59 1·62 1·61 2·65 3·30 2·96 2·83 3·33 3·59 3·88 4·70 4·73 4·90 3·31 6·95 8·41 6·14 7·11 La 42·5 50·3 45·4 51·2 73·8 60·4 76·7 68·2 101 87·4 84·7 99·2 103 88·9 95·3 119 137 111 128 Ce 81·1 95·7 85·8 97·7 136 116 141 132 181 165 155 172 178 159 175 196 214 175 211 Pr 9·64 11·2 10·6 11·4 15·2 12·6 15·8 14·2 19·8 17·0 16·2 18·0 18·3 15·8 19·4 19·0 20·8 17·1 21·9 Nd 39·0 43·8 40·8 45·1 56·3 46·6 57·9 52·4 70·4 61·4 56·7 60·8 62·2 53·5 69·3 59·5 64·2 52·2 71·6 Sm 7·60 8·49 7·58 8·26 9·62 8·31 9·90 8·97 11·7 9·99 9·57 9·67 9·45 8·79 11·8 8·55 9·53 7·52 11·6 Eu 2·45 2·87 2·65 2·73 3·23 2·52 2·90 2·67 3·59 3·11 2·52 2·62 2·49 2·21 3·56 1·60 1·38 1·10 1·54 Gd 7·36 7·77 6·70 7·61 8·72 6·92 8·65 7·17 9·90 7·78 7·34 7·99 7·97 6·56 9·92 7·21 7·97 6·43 9·81 Tb 0·95 0·99 1·08 0·96 1·08 1·11 1·10 1·13 1·25 1·26 1·05 1·06 1·06 0·95 1·29 0·97 1·06 0·87 1·31 Dy 5·40 5·67 5·29 5·35 6·12 5·57 6·17 5·81 7·35 6·72 6·30 6·07 6·14 5·83 7·36 5·80 6·80 5·51 7·92 Ho 1·00 1·05 1·13 1·01 1·13 1·18 1·18 1·22 1·37 1·42 1·18 1·22 1·20 1·11 1·41 1·16 1·38 1·11 1·55 Er 2·61 2·77 2·70 2·68 3·08 2·93 3·33 3·06 3·86 3·66 3·35 3·56 3·58 3·23 4·02 3·52 4·30 3·43 4·64 Tm 0·35 0·36 0·38 0·35 0·40 0·43 0·44 0·45 0·54 0·55 0·51 0·52 0·51 0·51 0·54 0·54 0·66 0·55 0·68 Yb 2·12 2·29 2·20 2·19 2·63 2·57 2·89 2·74 3·53 3·45 3·28 3·45 3·53 3·31 3·60 3·69 4·69 3·79 4·77 Lu 0·31 0·31 0·37 0·32 0·37 0·43 0·43 0·45 0·52 0·57 0·52 0·52 0·53 0·53 0·52 0·57 0·69 0·58 0·69 Group P-F P-F P-F P-F P-F S-M S-M S-M S-M S-M S-I S-I S-I S-I S-I X X B B Sample K1601 J1412 K1601 M1601 M1601 K1601 K1601 J1412 K1601 K1601 M1601 M1601 K1601 K1601 K1601 K1601 K1601 1412 1411 2407-1 0504-2 2412-1 2710 2714-2 2412-2 2411-1 0107-1 2708-4 2414 2707-1 2713-1 2713-2 2422-2 2713-1 2407-2 2422-3 15-5B 23-1A Rock type Tr Tr Tr Tr (A) Tr (A) Bas Bas Tp Bas Bas PhT PhT PhT TPh TPh Gr· Gr· Mg GHIC SiO2 64·73 64·93 66·01 60·27 61·04 43·97 43·98 44·84 45·62 47·12 48·23 48·46 50·41 53·03 54·89 67·44 68·85 59·24 69·17 TiO2 0·28 0·47 0·25 0·62 0·63 3·56 3·65 2·99 3·29 2·60 2·55 2·29 2·04 1·23 1·08 0·61 0·58 1·04 0·45 Al2O3 16·40 17·78 16·45 18·33 18·54 14·53 14·82 15·56 14·81 16·30 17·32 17·52 17·45 19·11 18·65 14·64 14·81 16·46 16·30 FeOT 4·92 4·85 4·72 5·18 5·26 11·88 11·87 11·20 11·04 11·29 10·54 9·86 9·97 8·10 8·26 3·56 3·25 8·93 3·10 MnO 0·18 0·16 0·16 0·19 0·19 0·19 0·19 0·21 0·18 0·21 0·23 0·22 0·21 0·24 0·22 0·07 0·06 0·31 0·06 MgO 0·13 0·51 0·06 0·57 0·60 7·14 6·45 5·07 7·29 5·84 3·44 3·00 2·97 1·26 1·46 2·15 1·95 4·77 1·14 CaO 1·15 1·74 1·08 2·12 2·11 10·90 10·76 9·68 9·60 8·91 7·66 7·06 6·19 4·59 4·17 3·20 3·32 0·99 4·20 Na2O 6·63 6·19 6·72 6·77 6·70 3·42 3·58 4·64 3·68 4·80 5·80 6·24 5·85 7·47 6·80 3·87 3·92 1·28 4·02 K2O 5·18 5·02 5·24 5·18 5·22 1·71 1·82 2·42 1·93 1·83 2·66 2·78 2·78 3·90 3·56 2·82 2·86 4·95 1·27 P2O5 0·05 0·15 0·03 0·14 0·15 0·68 0·72 0·82 0·56 0·63 0·62 0·55 0·68 0·36 0·50 0·05 0·05 0·05 0·07 LOI −0·14 0·00 0·13 0·26 0·14 −0·62 −0·68 0·00 0·80 −0·27 −0·38 −0·24 −0·34 −0·20 −0·25 0·70 0·74 1·02 0·15 Total 99·52 101·8 100·8 99·62 100·6 97·37 97·16 97·43 98·80 99·26 98·68 97·74 98·21 99·09 99·33 99·11 100·4 99·02 99·93 ne 4·70 3·56 9·85 10·5 15·6 8·28 11·2 14·7 16·5 9·63 18·0 9·14 di 4·79 1·48 4·54 4·52 3·75 25·1 24·7 23·7 21·3 18·5 17·1 16·7 11·0 11·4 6·47 ol 2·79 3·15 11·5 10·3 8·34 12·7 11·8 5·26 4·48 6·79 3·01 5·51 hy 2·82 4·82 2·72 q 2·81 3·96 3·70 Sc 3·97 n·d· 2·90 0·96 1·03 27·0 21·2 15·1 23·8 15·6 11·0 9·52 10·1 2·61 4·47 V 1·45 n·d· 1·35 12·5 12·0 307 252 213 259 165 140 120 95·0 29·4 22·2 Co 12·1 n·d· 9·46 12·1 12·1 58·1 48·8 44·2 51·5 46·2 33·4 28·6 30·5 14·1 21·8 Cu 3·11 n·d· 7·09 7·00 6·04 57·3 43·4 40·5 46·4 42·6 29·5 24·1 23·2 9·52 12·3 Rb 281 151 224 220 205 44·2 38·5 55·0 41·9 49·3 85·4 84·1 72·8 117 99·4 Sr 39·6 199 7·47 419 382 842 729 822 828 883 1087 1020 1014 930 902 Y 64·4 21·4 63·5 35·0 31·8 30·7 26·4 26·2 27·1 29·1 36·3 34·8 32·6 33·3 30·3 Nb 291 116 184 140 147 89·1 77·8 105 86·9 106 152 135 137 197 166 Cs 8·60 3·69 6·65 6·35 5·84 0·91 0·76 0·65 0·81 0·67 1·08 1·12 0·53 1·25 0·98 Ba 377 705 70·3 1004 932 570 503 731 663 638 872 856 855 923 1032 Hf 22·9 14·4 20·7 14·4 13·3 5·57 4·94 7·07 5·32 6·14 9·45 9·33 8·81 10·7 10·4 Zr 1124 633 1016 785 724 232 204 285 222 280 490 509 455 565 559 Pb 22·2 15·8 19·1 16·8 15·2 2·70 2·83 3·81 3·50 2·47 6·47 5·81 4·33 6·69 5·90 Th 43·2 29·2 32·3 35·7 32·1 6·00 5·30 10·1 6·09 6·95 14·1 15·0 10·0 17·7 13·7 U 10·7 7·36 8·01 10·5 8·66 1·63 1·43 2·61 1·63 1·91 3·80 4·12 2·59 4·77 3·19 La 197 87·2 150 130 119 52·1 45·5 73·2 50·7 62·5 95·2 94·6 85·7 116 102 Ce 328 148 265 212 193 101 88·6 141 98·5 117 173 167 153 199 174 Pr 32·5 14·0 28·0 20·3 18·5 12·2 10·7 15·3 11·8 13·4 18·8 17·8 16·7 20·3 18·1 Nd 104 44·0 95·2 64·3 58·0 49·4 43·4 58·4 46·9 50·7 68·4 64·2 60·5 67·8 60·7 Sm 15·8 6·98 16·0 9·08 8·31 9·63 8·42 10·0 9·05 9·08 11·3 10·4 10·1 11·0 9·39 Eu 1·25 1·37 0·95 2·03 1·88 3·05 2·66 3·18 2·89 2·87 3·56 3·29 3·20 3·13 2·95 Gd 13·6 5·04 13·8 7·72 7·15 8·86 7·86 8·12 8·27 8·11 10·2 9·26 8·71 9·08 7·80 Tb 1·84 0·75 1·89 1·01 0·92 1·11 0·98 1·27 1·03 1·04 1·27 1·16 1·08 1·12 0·95 Dy 11·1 4·70 11·7 6·01 5·47 6·40 5·55 6·28 5·75 5·84 7·11 6·61 6·08 6·59 5·58 Ho 2·23 0·89 2·30 1·19 1·09 1·16 1·00 1·29 1·07 1·08 1·34 1·25 1·14 1·22 1·05 Er 6·55 2·67 6·79 3·64 3·31 3·03 2·62 3·16 2·84 2·94 3·73 3·45 3·11 3·53 2·97 Tm 0·98 0·45 1·00 0·53 0·49 0·39 0·34 0·44 0·36 0·39 0·50 0·47 0·42 0·49 0·42 Yb 6·57 2·99 6·84 3·75 3·40 2·43 2·10 2·64 2·24 2·48 3·25 3·14 2·68 3·34 2·80 Lu 0·97 0·49 1·01 0·56 0·50 0·34 0·29 0·43 0·31 0·35 0·47 0·45 0·40 0·48 0·42 Group P-F P-F P-F P-F P-F S-M S-M S-M S-M S-M S-I S-I S-I S-I S-I X X B B Sample K1601 J1412 K1601 M1601 M1601 K1601 K1601 J1412 K1601 K1601 M1601 M1601 K1601 K1601 K1601 K1601 K1601 1412 1411 2407-1 0504-2 2412-1 2710 2714-2 2412-2 2411-1 0107-1 2708-4 2414 2707-1 2713-1 2713-2 2422-2 2713-1 2407-2 2422-3 15-5B 23-1A Rock type Tr Tr Tr Tr (A) Tr (A) Bas Bas Tp Bas Bas PhT PhT PhT TPh TPh Gr· Gr· Mg GHIC SiO2 64·73 64·93 66·01 60·27 61·04 43·97 43·98 44·84 45·62 47·12 48·23 48·46 50·41 53·03 54·89 67·44 68·85 59·24 69·17 TiO2 0·28 0·47 0·25 0·62 0·63 3·56 3·65 2·99 3·29 2·60 2·55 2·29 2·04 1·23 1·08 0·61 0·58 1·04 0·45 Al2O3 16·40 17·78 16·45 18·33 18·54 14·53 14·82 15·56 14·81 16·30 17·32 17·52 17·45 19·11 18·65 14·64 14·81 16·46 16·30 FeOT 4·92 4·85 4·72 5·18 5·26 11·88 11·87 11·20 11·04 11·29 10·54 9·86 9·97 8·10 8·26 3·56 3·25 8·93 3·10 MnO 0·18 0·16 0·16 0·19 0·19 0·19 0·19 0·21 0·18 0·21 0·23 0·22 0·21 0·24 0·22 0·07 0·06 0·31 0·06 MgO 0·13 0·51 0·06 0·57 0·60 7·14 6·45 5·07 7·29 5·84 3·44 3·00 2·97 1·26 1·46 2·15 1·95 4·77 1·14 CaO 1·15 1·74 1·08 2·12 2·11 10·90 10·76 9·68 9·60 8·91 7·66 7·06 6·19 4·59 4·17 3·20 3·32 0·99 4·20 Na2O 6·63 6·19 6·72 6·77 6·70 3·42 3·58 4·64 3·68 4·80 5·80 6·24 5·85 7·47 6·80 3·87 3·92 1·28 4·02 K2O 5·18 5·02 5·24 5·18 5·22 1·71 1·82 2·42 1·93 1·83 2·66 2·78 2·78 3·90 3·56 2·82 2·86 4·95 1·27 P2O5 0·05 0·15 0·03 0·14 0·15 0·68 0·72 0·82 0·56 0·63 0·62 0·55 0·68 0·36 0·50 0·05 0·05 0·05 0·07 LOI −0·14 0·00 0·13 0·26 0·14 −0·62 −0·68 0·00 0·80 −0·27 −0·38 −0·24 −0·34 −0·20 −0·25 0·70 0·74 1·02 0·15 Total 99·52 101·8 100·8 99·62 100·6 97·37 97·16 97·43 98·80 99·26 98·68 97·74 98·21 99·09 99·33 99·11 100·4 99·02 99·93 ne 4·70 3·56 9·85 10·5 15·6 8·28 11·2 14·7 16·5 9·63 18·0 9·14 di 4·79 1·48 4·54 4·52 3·75 25·1 24·7 23·7 21·3 18·5 17·1 16·7 11·0 11·4 6·47 ol 2·79 3·15 11·5 10·3 8·34 12·7 11·8 5·26 4·48 6·79 3·01 5·51 hy 2·82 4·82 2·72 q 2·81 3·96 3·70 Sc 3·97 n·d· 2·90 0·96 1·03 27·0 21·2 15·1 23·8 15·6 11·0 9·52 10·1 2·61 4·47 V 1·45 n·d· 1·35 12·5 12·0 307 252 213 259 165 140 120 95·0 29·4 22·2 Co 12·1 n·d· 9·46 12·1 12·1 58·1 48·8 44·2 51·5 46·2 33·4 28·6 30·5 14·1 21·8 Cu 3·11 n·d· 7·09 7·00 6·04 57·3 43·4 40·5 46·4 42·6 29·5 24·1 23·2 9·52 12·3 Rb 281 151 224 220 205 44·2 38·5 55·0 41·9 49·3 85·4 84·1 72·8 117 99·4 Sr 39·6 199 7·47 419 382 842 729 822 828 883 1087 1020 1014 930 902 Y 64·4 21·4 63·5 35·0 31·8 30·7 26·4 26·2 27·1 29·1 36·3 34·8 32·6 33·3 30·3 Nb 291 116 184 140 147 89·1 77·8 105 86·9 106 152 135 137 197 166 Cs 8·60 3·69 6·65 6·35 5·84 0·91 0·76 0·65 0·81 0·67 1·08 1·12 0·53 1·25 0·98 Ba 377 705 70·3 1004 932 570 503 731 663 638 872 856 855 923 1032 Hf 22·9 14·4 20·7 14·4 13·3 5·57 4·94 7·07 5·32 6·14 9·45 9·33 8·81 10·7 10·4 Zr 1124 633 1016 785 724 232 204 285 222 280 490 509 455 565 559 Pb 22·2 15·8 19·1 16·8 15·2 2·70 2·83 3·81 3·50 2·47 6·47 5·81 4·33 6·69 5·90 Th 43·2 29·2 32·3 35·7 32·1 6·00 5·30 10·1 6·09 6·95 14·1 15·0 10·0 17·7 13·7 U 10·7 7·36 8·01 10·5 8·66 1·63 1·43 2·61 1·63 1·91 3·80 4·12 2·59 4·77 3·19 La 197 87·2 150 130 119 52·1 45·5 73·2 50·7 62·5 95·2 94·6 85·7 116 102 Ce 328 148 265 212 193 101 88·6 141 98·5 117 173 167 153 199 174 Pr 32·5 14·0 28·0 20·3 18·5 12·2 10·7 15·3 11·8 13·4 18·8 17·8 16·7 20·3 18·1 Nd 104 44·0 95·2 64·3 58·0 49·4 43·4 58·4 46·9 50·7 68·4 64·2 60·5 67·8 60·7 Sm 15·8 6·98 16·0 9·08 8·31 9·63 8·42 10·0 9·05 9·08 11·3 10·4 10·1 11·0 9·39 Eu 1·25 1·37 0·95 2·03 1·88 3·05 2·66 3·18 2·89 2·87 3·56 3·29 3·20 3·13 2·95 Gd 13·6 5·04 13·8 7·72 7·15 8·86 7·86 8·12 8·27 8·11 10·2 9·26 8·71 9·08 7·80 Tb 1·84 0·75 1·89 1·01 0·92 1·11 0·98 1·27 1·03 1·04 1·27 1·16 1·08 1·12 0·95 Dy 11·1 4·70 11·7 6·01 5·47 6·40 5·55 6·28 5·75 5·84 7·11 6·61 6·08 6·59 5·58 Ho 2·23 0·89 2·30 1·19 1·09 1·16 1·00 1·29 1·07 1·08 1·34 1·25 1·14 1·22 1·05 Er 6·55 2·67 6·79 3·64 3·31 3·03 2·62 3·16 2·84 2·94 3·73 3·45 3·11 3·53 2·97 Tm 0·98 0·45 1·00 0·53 0·49 0·39 0·34 0·44 0·36 0·39 0·50 0·47 0·42 0·49 0·42 Yb 6·57 2·99 6·84 3·75 3·40 2·43 2·10 2·64 2·24 2·48 3·25 3·14 2·68 3·34 2·80 Lu 0·97 0·49 1·01 0·56 0·50 0·34 0·29 0·43 0·31 0·35 0·47 0·45 0·40 0·48 0·42 P, Potassic; S, sodic; -M, mafic; -I, intermediate; -F, felsic; X, xenolith; B, basement rock; Gr., granodiorite; Mg, migmatite; Tr (A), amphibole-bearing trachyte; AB, alkali-basalt; Tp, tephrite; Ph, phonolite; n.d., not determined. Table 2 Whole-rock major (wt %) and trace element (ppm) compositions of representative samples and the calculated CIPW normative mineral abundances Group P-M P-M P-M P-M P-M P-I P-I P-I P-I P-I P-I P-I P-I P-I P-I P-F P-F P-F P-F Sample K1601 K1601 J1412 K1601 M1601 J1412 K1601 J1412 D1601 J1412 J1412 K1601 K1601 J1412 K1601 M1601 K1601 K1601 K1601 2408-1 2424 0503-2 2408-2 2705-1 0504-4 2708-2 0106-1 2403 0105-1 0103 2708-1 2707-1 0504-1 2709-1 2701 2425 2415 2422-1 Rock type AB H H H Bas Mu Mu Mu Bn Bn Bn Tr Tr Tr Ta Ph Ph Ph Tr SiO2 44·66 45·74 46·13 47·04 47·65 50·02 51·71 52·24 55·24 57·71 57·96 58·66 59·42 59·52 55·52 59·33 60·44 60·63 64·66 TiO2 2·90 2·44 2·46 3·09 2·48 2·51 2·24 2·28 1·35 1·07 1·31 0·91 0·88 0·77 1·32 0·27 0·19 0·19 0·33 Al2O3 14·06 14·20 14·61 16·19 16·91 16·00 17·04 16·92 17·45 17·56 17·69 17·59 17·79 17·49 17·47 17·93 18·51 18·59 17·14 FeOT 11·66 11·23 11·04 11·60 10·73 10·20 9·70 9·69 8·75 7·71 7·83 6·99 6·96 6·36 8·70 5·48 5·19 5·15 4·94 MnO 0·18 0·20 0·20 0·19 0·21 0·18 0·19 0·19 0·22 0·21 0·19 0·19 0·19 0·18 0·22 0·20 0·20 0·20 0·17 MgO 9·38 9·05 8·25 5·50 4·65 4·75 3·52 3·38 1·66 1·22 1·77 1·09 1·05 0·90 1·63 0·19 0·13 0·11 0·20 CaO 11·39 10·30 10·16 9·11 8·24 7·46 6·09 5·86 4·14 3·31 3·80 3·00 2·90 2·65 4·04 1·48 1·41 1·26 1·32 Na2O 2·91 3·47 3·52 3·87 4·97 4·26 4·91 4·93 6·02 6·25 5·71 6·12 6·17 6·21 6·20 7·50 7·94 8·01 6·62 K2O 1·32 1·42 1·48 1·73 2·07 2·35 2·77 2·78 3·53 3·90 3·81 4·29 4·37 4·45 3·52 5·43 5·48 5·50 5·30 P2O5 0·55 0·51 0·54 0·74 0·68 0·64 0·70 0·70 0·53 0·39 0·43 0·30 0·29 0·25 0·51 0·08 0·05 0·05 0·06 LOI −0·12 0·05 0·00 −0·37 −0·47 0·00 0·14 0·00 −0·21 0·00 0·00 −0·25 −0·25 0·00 −0·20 0·00 0·13 0·03 −0·05 Total 98·89 98·61 98·37 98·69 98·12 98·37 99·00 98·96 98·67 99·35 100·5 98·89 99·78 98·78 98·94 97·89 99·67 99·73 100·7 ne 7·32 7·90 6·98 4·71 10·4 1·57 1·96 0·83 3·24 1·59 0·69 0·28 3·85 10·2 11·6 11·5 di 25·7 23·6 22·4 15·5 15·6 12·6 7·82 7·21 5·85 4·71 3·83 4·36 3·87 4·11 6·16 6·14 5·94 5·24 4·14 ol 15·8 16·2 15·0 12·1 10·5 9·11 8·44 8·34 6·22 5·33 3·36 4·85 4·93 4·21 6·00 2·47 2·43 2·68 hy 4·03 0·10 3·06 q 1·76 Sc 35·6 25·7 n.d. 21·2 13·2 n.d. 11·2 n.d. 10·5 n.d. n.d. 4·24 3·23 n.d. 7·33 1·07 0·65 0·87 2·51 V 303 227 n.d. 224 157 n.d. 124 n.d. 20·6 n.d. n.d. 9·36 8·15 n.d. 18·1 1·98 0·91 1·85 0·60 Co 71·2 57·9 n.d. 47·6 37·3 n.d. 34·5 n.d. 23·9 n.d. n.d. 13·7 12·4 n.d. 17·0 12·0 8·37 6·82 12·6 Cu 59·8 60·5 n.d. 47·2 35·5 n.d. 25·2 n.d. 29·0 n.d. n.d. 9·09 9·01 n.d. 13·7 7·57 7·60 6·93 5·61 Rb 33·9 36·7 29·2 45·2 57·5 62·6 76·8 65·6 98·5 82·9 101 131 135 120 86·0 178 217 186 190 Sr 645 772 623 889 977 577 778 624 728 427·5 496 497 477 364 636 75·1 55·6 35·6 60·5 Y 27·5 27·0 21·7 27·6 30·5 23·7 30·8 25·5 41·7 30·6 28·1 32·2 33·1 26·9 37·1 33·0 38·9 32·7 41·8 Nb 70·7 82·2 58·9 82·4 121 77·0 118 84·5 164 116 109 158 159 117 150 120 219 163 192 Cs 0·41 0·52 0·61 0·75 0·84 1·56 1·13 1·29 1·57 1·55 1·94 2·34 2·55 2·35 1·55 3·60 3·82 3·76 5·08 Ba 391 608 547 565 876 524 791 689 1212 1130 907 1113 1126 1006 1171 752 340 282 610 Hf 5·39 5·36 5·21 5·47 6·91 7·34 8·32 8·06 10·8 11·1 11·7 12·3 12·9 12·5 10·1 14·9 18·3 15·3 15·6 Zr 220 224 184 235 343 281 386 334 572 465 483 605 643 553 484 807 936 809 748 Pb 2·24 2·64 2·51 3·23 4·11 7·22 7·80 6·73 8·47 9·26 10·3 13·3 11·9 12·3 7·41 9·45 16·2 12·4 13·7 Th 4·87 5·98 5·84 6·06 9·89 13·0 11·8 11·3 13·1 14·3 16·5 18·7 19·8 19·2 12·8 25·8 31·3 25·2 27·6 U 1·37 1·59 1·62 1·61 2·65 3·30 2·96 2·83 3·33 3·59 3·88 4·70 4·73 4·90 3·31 6·95 8·41 6·14 7·11 La 42·5 50·3 45·4 51·2 73·8 60·4 76·7 68·2 101 87·4 84·7 99·2 103 88·9 95·3 119 137 111 128 Ce 81·1 95·7 85·8 97·7 136 116 141 132 181 165 155 172 178 159 175 196 214 175 211 Pr 9·64 11·2 10·6 11·4 15·2 12·6 15·8 14·2 19·8 17·0 16·2 18·0 18·3 15·8 19·4 19·0 20·8 17·1 21·9 Nd 39·0 43·8 40·8 45·1 56·3 46·6 57·9 52·4 70·4 61·4 56·7 60·8 62·2 53·5 69·3 59·5 64·2 52·2 71·6 Sm 7·60 8·49 7·58 8·26 9·62 8·31 9·90 8·97 11·7 9·99 9·57 9·67 9·45 8·79 11·8 8·55 9·53 7·52 11·6 Eu 2·45 2·87 2·65 2·73 3·23 2·52 2·90 2·67 3·59 3·11 2·52 2·62 2·49 2·21 3·56 1·60 1·38 1·10 1·54 Gd 7·36 7·77 6·70 7·61 8·72 6·92 8·65 7·17 9·90 7·78 7·34 7·99 7·97 6·56 9·92 7·21 7·97 6·43 9·81 Tb 0·95 0·99 1·08 0·96 1·08 1·11 1·10 1·13 1·25 1·26 1·05 1·06 1·06 0·95 1·29 0·97 1·06 0·87 1·31 Dy 5·40 5·67 5·29 5·35 6·12 5·57 6·17 5·81 7·35 6·72 6·30 6·07 6·14 5·83 7·36 5·80 6·80 5·51 7·92 Ho 1·00 1·05 1·13 1·01 1·13 1·18 1·18 1·22 1·37 1·42 1·18 1·22 1·20 1·11 1·41 1·16 1·38 1·11 1·55 Er 2·61 2·77 2·70 2·68 3·08 2·93 3·33 3·06 3·86 3·66 3·35 3·56 3·58 3·23 4·02 3·52 4·30 3·43 4·64 Tm 0·35 0·36 0·38 0·35 0·40 0·43 0·44 0·45 0·54 0·55 0·51 0·52 0·51 0·51 0·54 0·54 0·66 0·55 0·68 Yb 2·12 2·29 2·20 2·19 2·63 2·57 2·89 2·74 3·53 3·45 3·28 3·45 3·53 3·31 3·60 3·69 4·69 3·79 4·77 Lu 0·31 0·31 0·37 0·32 0·37 0·43 0·43 0·45 0·52 0·57 0·52 0·52 0·53 0·53 0·52 0·57 0·69 0·58 0·69 Group P-M P-M P-M P-M P-M P-I P-I P-I P-I P-I P-I P-I P-I P-I P-I P-F P-F P-F P-F Sample K1601 K1601 J1412 K1601 M1601 J1412 K1601 J1412 D1601 J1412 J1412 K1601 K1601 J1412 K1601 M1601 K1601 K1601 K1601 2408-1 2424 0503-2 2408-2 2705-1 0504-4 2708-2 0106-1 2403 0105-1 0103 2708-1 2707-1 0504-1 2709-1 2701 2425 2415 2422-1 Rock type AB H H H Bas Mu Mu Mu Bn Bn Bn Tr Tr Tr Ta Ph Ph Ph Tr SiO2 44·66 45·74 46·13 47·04 47·65 50·02 51·71 52·24 55·24 57·71 57·96 58·66 59·42 59·52 55·52 59·33 60·44 60·63 64·66 TiO2 2·90 2·44 2·46 3·09 2·48 2·51 2·24 2·28 1·35 1·07 1·31 0·91 0·88 0·77 1·32 0·27 0·19 0·19 0·33 Al2O3 14·06 14·20 14·61 16·19 16·91 16·00 17·04 16·92 17·45 17·56 17·69 17·59 17·79 17·49 17·47 17·93 18·51 18·59 17·14 FeOT 11·66 11·23 11·04 11·60 10·73 10·20 9·70 9·69 8·75 7·71 7·83 6·99 6·96 6·36 8·70 5·48 5·19 5·15 4·94 MnO 0·18 0·20 0·20 0·19 0·21 0·18 0·19 0·19 0·22 0·21 0·19 0·19 0·19 0·18 0·22 0·20 0·20 0·20 0·17 MgO 9·38 9·05 8·25 5·50 4·65 4·75 3·52 3·38 1·66 1·22 1·77 1·09 1·05 0·90 1·63 0·19 0·13 0·11 0·20 CaO 11·39 10·30 10·16 9·11 8·24 7·46 6·09 5·86 4·14 3·31 3·80 3·00 2·90 2·65 4·04 1·48 1·41 1·26 1·32 Na2O 2·91 3·47 3·52 3·87 4·97 4·26 4·91 4·93 6·02 6·25 5·71 6·12 6·17 6·21 6·20 7·50 7·94 8·01 6·62 K2O 1·32 1·42 1·48 1·73 2·07 2·35 2·77 2·78 3·53 3·90 3·81 4·29 4·37 4·45 3·52 5·43 5·48 5·50 5·30 P2O5 0·55 0·51 0·54 0·74 0·68 0·64 0·70 0·70 0·53 0·39 0·43 0·30 0·29 0·25 0·51 0·08 0·05 0·05 0·06 LOI −0·12 0·05 0·00 −0·37 −0·47 0·00 0·14 0·00 −0·21 0·00 0·00 −0·25 −0·25 0·00 −0·20 0·00 0·13 0·03 −0·05 Total 98·89 98·61 98·37 98·69 98·12 98·37 99·00 98·96 98·67 99·35 100·5 98·89 99·78 98·78 98·94 97·89 99·67 99·73 100·7 ne 7·32 7·90 6·98 4·71 10·4 1·57 1·96 0·83 3·24 1·59 0·69 0·28 3·85 10·2 11·6 11·5 di 25·7 23·6 22·4 15·5 15·6 12·6 7·82 7·21 5·85 4·71 3·83 4·36 3·87 4·11 6·16 6·14 5·94 5·24 4·14 ol 15·8 16·2 15·0 12·1 10·5 9·11 8·44 8·34 6·22 5·33 3·36 4·85 4·93 4·21 6·00 2·47 2·43 2·68 hy 4·03 0·10 3·06 q 1·76 Sc 35·6 25·7 n.d. 21·2 13·2 n.d. 11·2 n.d. 10·5 n.d. n.d. 4·24 3·23 n.d. 7·33 1·07 0·65 0·87 2·51 V 303 227 n.d. 224 157 n.d. 124 n.d. 20·6 n.d. n.d. 9·36 8·15 n.d. 18·1 1·98 0·91 1·85 0·60 Co 71·2 57·9 n.d. 47·6 37·3 n.d. 34·5 n.d. 23·9 n.d. n.d. 13·7 12·4 n.d. 17·0 12·0 8·37 6·82 12·6 Cu 59·8 60·5 n.d. 47·2 35·5 n.d. 25·2 n.d. 29·0 n.d. n.d. 9·09 9·01 n.d. 13·7 7·57 7·60 6·93 5·61 Rb 33·9 36·7 29·2 45·2 57·5 62·6 76·8 65·6 98·5 82·9 101 131 135 120 86·0 178 217 186 190 Sr 645 772 623 889 977 577 778 624 728 427·5 496 497 477 364 636 75·1 55·6 35·6 60·5 Y 27·5 27·0 21·7 27·6 30·5 23·7 30·8 25·5 41·7 30·6 28·1 32·2 33·1 26·9 37·1 33·0 38·9 32·7 41·8 Nb 70·7 82·2 58·9 82·4 121 77·0 118 84·5 164 116 109 158 159 117 150 120 219 163 192 Cs 0·41 0·52 0·61 0·75 0·84 1·56 1·13 1·29 1·57 1·55 1·94 2·34 2·55 2·35 1·55 3·60 3·82 3·76 5·08 Ba 391 608 547 565 876 524 791 689 1212 1130 907 1113 1126 1006 1171 752 340 282 610 Hf 5·39 5·36 5·21 5·47 6·91 7·34 8·32 8·06 10·8 11·1 11·7 12·3 12·9 12·5 10·1 14·9 18·3 15·3 15·6 Zr 220 224 184 235 343 281 386 334 572 465 483 605 643 553 484 807 936 809 748 Pb 2·24 2·64 2·51 3·23 4·11 7·22 7·80 6·73 8·47 9·26 10·3 13·3 11·9 12·3 7·41 9·45 16·2 12·4 13·7 Th 4·87 5·98 5·84 6·06 9·89 13·0 11·8 11·3 13·1 14·3 16·5 18·7 19·8 19·2 12·8 25·8 31·3 25·2 27·6 U 1·37 1·59 1·62 1·61 2·65 3·30 2·96 2·83 3·33 3·59 3·88 4·70 4·73 4·90 3·31 6·95 8·41 6·14 7·11 La 42·5 50·3 45·4 51·2 73·8 60·4 76·7 68·2 101 87·4 84·7 99·2 103 88·9 95·3 119 137 111 128 Ce 81·1 95·7 85·8 97·7 136 116 141 132 181 165 155 172 178 159 175 196 214 175 211 Pr 9·64 11·2 10·6 11·4 15·2 12·6 15·8 14·2 19·8 17·0 16·2 18·0 18·3 15·8 19·4 19·0 20·8 17·1 21·9 Nd 39·0 43·8 40·8 45·1 56·3 46·6 57·9 52·4 70·4 61·4 56·7 60·8 62·2 53·5 69·3 59·5 64·2 52·2 71·6 Sm 7·60 8·49 7·58 8·26 9·62 8·31 9·90 8·97 11·7 9·99 9·57 9·67 9·45 8·79 11·8 8·55 9·53 7·52 11·6 Eu 2·45 2·87 2·65 2·73 3·23 2·52 2·90 2·67 3·59 3·11 2·52 2·62 2·49 2·21 3·56 1·60 1·38 1·10 1·54 Gd 7·36 7·77 6·70 7·61 8·72 6·92 8·65 7·17 9·90 7·78 7·34 7·99 7·97 6·56 9·92 7·21 7·97 6·43 9·81 Tb 0·95 0·99 1·08 0·96 1·08 1·11 1·10 1·13 1·25 1·26 1·05 1·06 1·06 0·95 1·29 0·97 1·06 0·87 1·31 Dy 5·40 5·67 5·29 5·35 6·12 5·57 6·17 5·81 7·35 6·72 6·30 6·07 6·14 5·83 7·36 5·80 6·80 5·51 7·92 Ho 1·00 1·05 1·13 1·01 1·13 1·18 1·18 1·22 1·37 1·42 1·18 1·22 1·20 1·11 1·41 1·16 1·38 1·11 1·55 Er 2·61 2·77 2·70 2·68 3·08 2·93 3·33 3·06 3·86 3·66 3·35 3·56 3·58 3·23 4·02 3·52 4·30 3·43 4·64 Tm 0·35 0·36 0·38 0·35 0·40 0·43 0·44 0·45 0·54 0·55 0·51 0·52 0·51 0·51 0·54 0·54 0·66 0·55 0·68 Yb 2·12 2·29 2·20 2·19 2·63 2·57 2·89 2·74 3·53 3·45 3·28 3·45 3·53 3·31 3·60 3·69 4·69 3·79 4·77 Lu 0·31 0·31 0·37 0·32 0·37 0·43 0·43 0·45 0·52 0·57 0·52 0·52 0·53 0·53 0·52 0·57 0·69 0·58 0·69 Group P-F P-F P-F P-F P-F S-M S-M S-M S-M S-M S-I S-I S-I S-I S-I X X B B Sample K1601 J1412 K1601 M1601 M1601 K1601 K1601 J1412 K1601 K1601 M1601 M1601 K1601 K1601 K1601 K1601 K1601 1412 1411 2407-1 0504-2 2412-1 2710 2714-2 2412-2 2411-1 0107-1 2708-4 2414 2707-1 2713-1 2713-2 2422-2 2713-1 2407-2 2422-3 15-5B 23-1A Rock type Tr Tr Tr Tr (A) Tr (A) Bas Bas Tp Bas Bas PhT PhT PhT TPh TPh Gr· Gr· Mg GHIC SiO2 64·73 64·93 66·01 60·27 61·04 43·97 43·98 44·84 45·62 47·12 48·23 48·46 50·41 53·03 54·89 67·44 68·85 59·24 69·17 TiO2 0·28 0·47 0·25 0·62 0·63 3·56 3·65 2·99 3·29 2·60 2·55 2·29 2·04 1·23 1·08 0·61 0·58 1·04 0·45 Al2O3 16·40 17·78 16·45 18·33 18·54 14·53 14·82 15·56 14·81 16·30 17·32 17·52 17·45 19·11 18·65 14·64 14·81 16·46 16·30 FeOT 4·92 4·85 4·72 5·18 5·26 11·88 11·87 11·20 11·04 11·29 10·54 9·86 9·97 8·10 8·26 3·56 3·25 8·93 3·10 MnO 0·18 0·16 0·16 0·19 0·19 0·19 0·19 0·21 0·18 0·21 0·23 0·22 0·21 0·24 0·22 0·07 0·06 0·31 0·06 MgO 0·13 0·51 0·06 0·57 0·60 7·14 6·45 5·07 7·29 5·84 3·44 3·00 2·97 1·26 1·46 2·15 1·95 4·77 1·14 CaO 1·15 1·74 1·08 2·12 2·11 10·90 10·76 9·68 9·60 8·91 7·66 7·06 6·19 4·59 4·17 3·20 3·32 0·99 4·20 Na2O 6·63 6·19 6·72 6·77 6·70 3·42 3·58 4·64 3·68 4·80 5·80 6·24 5·85 7·47 6·80 3·87 3·92 1·28 4·02 K2O 5·18 5·02 5·24 5·18 5·22 1·71 1·82 2·42 1·93 1·83 2·66 2·78 2·78 3·90 3·56 2·82 2·86 4·95 1·27 P2O5 0·05 0·15 0·03 0·14 0·15 0·68 0·72 0·82 0·56 0·63 0·62 0·55 0·68 0·36 0·50 0·05 0·05 0·05 0·07 LOI −0·14 0·00 0·13 0·26 0·14 −0·62 −0·68 0·00 0·80 −0·27 −0·38 −0·24 −0·34 −0·20 −0·25 0·70 0·74 1·02 0·15 Total 99·52 101·8 100·8 99·62 100·6 97·37 97·16 97·43 98·80 99·26 98·68 97·74 98·21 99·09 99·33 99·11 100·4 99·02 99·93 ne 4·70 3·56 9·85 10·5 15·6 8·28 11·2 14·7 16·5 9·63 18·0 9·14 di 4·79 1·48 4·54 4·52 3·75 25·1 24·7 23·7 21·3 18·5 17·1 16·7 11·0 11·4 6·47 ol 2·79 3·15 11·5 10·3 8·34 12·7 11·8 5·26 4·48 6·79 3·01 5·51 hy 2·82 4·82 2·72 q 2·81 3·96 3·70 Sc 3·97 n·d· 2·90 0·96 1·03 27·0 21·2 15·1 23·8 15·6 11·0 9·52 10·1 2·61 4·47 V 1·45 n·d· 1·35 12·5 12·0 307 252 213 259 165 140 120 95·0 29·4 22·2 Co 12·1 n·d· 9·46 12·1 12·1 58·1 48·8 44·2 51·5 46·2 33·4 28·6 30·5 14·1 21·8 Cu 3·11 n·d· 7·09 7·00 6·04 57·3 43·4 40·5 46·4 42·6 29·5 24·1 23·2 9·52 12·3 Rb 281 151 224 220 205 44·2 38·5 55·0 41·9 49·3 85·4 84·1 72·8 117 99·4 Sr 39·6 199 7·47 419 382 842 729 822 828 883 1087 1020 1014 930 902 Y 64·4 21·4 63·5 35·0 31·8 30·7 26·4 26·2 27·1 29·1 36·3 34·8 32·6 33·3 30·3 Nb 291 116 184 140 147 89·1 77·8 105 86·9 106 152 135 137 197 166 Cs 8·60 3·69 6·65 6·35 5·84 0·91 0·76 0·65 0·81 0·67 1·08 1·12 0·53 1·25 0·98 Ba 377 705 70·3 1004 932 570 503 731 663 638 872 856 855 923 1032 Hf 22·9 14·4 20·7 14·4 13·3 5·57 4·94 7·07 5·32 6·14 9·45 9·33 8·81 10·7 10·4 Zr 1124 633 1016 785 724 232 204 285 222 280 490 509 455 565 559 Pb 22·2 15·8 19·1 16·8 15·2 2·70 2·83 3·81 3·50 2·47 6·47 5·81 4·33 6·69 5·90 Th 43·2 29·2 32·3 35·7 32·1 6·00 5·30 10·1 6·09 6·95 14·1 15·0 10·0 17·7 13·7 U 10·7 7·36 8·01 10·5 8·66 1·63 1·43 2·61 1·63 1·91 3·80 4·12 2·59 4·77 3·19 La 197 87·2 150 130 119 52·1 45·5 73·2 50·7 62·5 95·2 94·6 85·7 116 102 Ce 328 148 265 212 193 101 88·6 141 98·5 117 173 167 153 199 174 Pr 32·5 14·0 28·0 20·3 18·5 12·2 10·7 15·3 11·8 13·4 18·8 17·8 16·7 20·3 18·1 Nd 104 44·0 95·2 64·3 58·0 49·4 43·4 58·4 46·9 50·7 68·4 64·2 60·5 67·8 60·7 Sm 15·8 6·98 16·0 9·08 8·31 9·63 8·42 10·0 9·05 9·08 11·3 10·4 10·1 11·0 9·39 Eu 1·25 1·37 0·95 2·03 1·88 3·05 2·66 3·18 2·89 2·87 3·56 3·29 3·20 3·13 2·95 Gd 13·6 5·04 13·8 7·72 7·15 8·86 7·86 8·12 8·27 8·11 10·2 9·26 8·71 9·08 7·80 Tb 1·84 0·75 1·89 1·01 0·92 1·11 0·98 1·27 1·03 1·04 1·27 1·16 1·08 1·12 0·95 Dy 11·1 4·70 11·7 6·01 5·47 6·40 5·55 6·28 5·75 5·84 7·11 6·61 6·08 6·59 5·58 Ho 2·23 0·89 2·30 1·19 1·09 1·16 1·00 1·29 1·07 1·08 1·34 1·25 1·14 1·22 1·05 Er 6·55 2·67 6·79 3·64 3·31 3·03 2·62 3·16 2·84 2·94 3·73 3·45 3·11 3·53 2·97 Tm 0·98 0·45 1·00 0·53 0·49 0·39 0·34 0·44 0·36 0·39 0·50 0·47 0·42 0·49 0·42 Yb 6·57 2·99 6·84 3·75 3·40 2·43 2·10 2·64 2·24 2·48 3·25 3·14 2·68 3·34 2·80 Lu 0·97 0·49 1·01 0·56 0·50 0·34 0·29 0·43 0·31 0·35 0·47 0·45 0·40 0·48 0·42 Group P-F P-F P-F P-F P-F S-M S-M S-M S-M S-M S-I S-I S-I S-I S-I X X B B Sample K1601 J1412 K1601 M1601 M1601 K1601 K1601 J1412 K1601 K1601 M1601 M1601 K1601 K1601 K1601 K1601 K1601 1412 1411 2407-1 0504-2 2412-1 2710 2714-2 2412-2 2411-1 0107-1 2708-4 2414 2707-1 2713-1 2713-2 2422-2 2713-1 2407-2 2422-3 15-5B 23-1A Rock type Tr Tr Tr Tr (A) Tr (A) Bas Bas Tp Bas Bas PhT PhT PhT TPh TPh Gr· Gr· Mg GHIC SiO2 64·73 64·93 66·01 60·27 61·04 43·97 43·98 44·84 45·62 47·12 48·23 48·46 50·41 53·03 54·89 67·44 68·85 59·24 69·17 TiO2 0·28 0·47 0·25 0·62 0·63 3·56 3·65 2·99 3·29 2·60 2·55 2·29 2·04 1·23 1·08 0·61 0·58 1·04 0·45 Al2O3 16·40 17·78 16·45 18·33 18·54 14·53 14·82 15·56 14·81 16·30 17·32 17·52 17·45 19·11 18·65 14·64 14·81 16·46 16·30 FeOT 4·92 4·85 4·72 5·18 5·26 11·88 11·87 11·20 11·04 11·29 10·54 9·86 9·97 8·10 8·26 3·56 3·25 8·93 3·10 MnO 0·18 0·16 0·16 0·19 0·19 0·19 0·19 0·21 0·18 0·21 0·23 0·22 0·21 0·24 0·22 0·07 0·06 0·31 0·06 MgO 0·13 0·51 0·06 0·57 0·60 7·14 6·45 5·07 7·29 5·84 3·44 3·00 2·97 1·26 1·46 2·15 1·95 4·77 1·14 CaO 1·15 1·74 1·08 2·12 2·11 10·90 10·76 9·68 9·60 8·91 7·66 7·06 6·19 4·59 4·17 3·20 3·32 0·99 4·20 Na2O 6·63 6·19 6·72 6·77 6·70 3·42 3·58 4·64 3·68 4·80 5·80 6·24 5·85 7·47 6·80 3·87 3·92 1·28 4·02 K2O 5·18 5·02 5·24 5·18 5·22 1·71 1·82 2·42 1·93 1·83 2·66 2·78 2·78 3·90 3·56 2·82 2·86 4·95 1·27 P2O5 0·05 0·15 0·03 0·14 0·15 0·68 0·72 0·82 0·56 0·63 0·62 0·55 0·68 0·36 0·50 0·05 0·05 0·05 0·07 LOI −0·14 0·00 0·13 0·26 0·14 −0·62 −0·68 0·00 0·80 −0·27 −0·38 −0·24 −0·34 −0·20 −0·25 0·70 0·74 1·02 0·15 Total 99·52 101·8 100·8 99·62 100·6 97·37 97·16 97·43 98·80 99·26 98·68 97·74 98·21 99·09 99·33 99·11 100·4 99·02 99·93 ne 4·70 3·56 9·85 10·5 15·6 8·28 11·2 14·7 16·5 9·63 18·0 9·14 di 4·79 1·48 4·54 4·52 3·75 25·1 24·7 23·7 21·3 18·5 17·1 16·7 11·0 11·4 6·47 ol 2·79 3·15 11·5 10·3 8·34 12·7 11·8 5·26 4·48 6·79 3·01 5·51 hy 2·82 4·82 2·72 q 2·81 3·96 3·70 Sc 3·97 n·d· 2·90 0·96 1·03 27·0 21·2 15·1 23·8 15·6 11·0 9·52 10·1 2·61 4·47 V 1·45 n·d· 1·35 12·5 12·0 307 252 213 259 165 140 120 95·0 29·4 22·2 Co 12·1 n·d· 9·46 12·1 12·1 58·1 48·8 44·2 51·5 46·2 33·4 28·6 30·5 14·1 21·8 Cu 3·11 n·d· 7·09 7·00 6·04 57·3 43·4 40·5 46·4 42·6 29·5 24·1 23·2 9·52 12·3 Rb 281 151 224 220 205 44·2 38·5 55·0 41·9 49·3 85·4 84·1 72·8 117 99·4 Sr 39·6 199 7·47 419 382 842 729 822 828 883 1087 1020 1014 930 902 Y 64·4 21·4 63·5 35·0 31·8 30·7 26·4 26·2 27·1 29·1 36·3 34·8 32·6 33·3 30·3 Nb 291 116 184 140 147 89·1 77·8 105 86·9 106 152 135 137 197 166 Cs 8·60 3·69 6·65 6·35 5·84 0·91 0·76 0·65 0·81 0·67 1·08 1·12 0·53 1·25 0·98 Ba 377 705 70·3 1004 932 570 503 731 663 638 872 856 855 923 1032 Hf 22·9 14·4 20·7 14·4 13·3 5·57 4·94 7·07 5·32 6·14 9·45 9·33 8·81 10·7 10·4 Zr 1124 633 1016 785 724 232 204 285 222 280 490 509 455 565 559 Pb 22·2 15·8 19·1 16·8 15·2 2·70 2·83 3·81 3·50 2·47 6·47 5·81 4·33 6·69 5·90 Th 43·2 29·2 32·3 35·7 32·1 6·00 5·30 10·1 6·09 6·95 14·1 15·0 10·0 17·7 13·7 U 10·7 7·36 8·01 10·5 8·66 1·63 1·43 2·61 1·63 1·91 3·80 4·12 2·59 4·77 3·19 La 197 87·2 150 130 119 52·1 45·5 73·2 50·7 62·5 95·2 94·6 85·7 116 102 Ce 328 148 265 212 193 101 88·6 141 98·5 117 173 167 153 199 174 Pr 32·5 14·0 28·0 20·3 18·5 12·2 10·7 15·3 11·8 13·4 18·8 17·8 16·7 20·3 18·1 Nd 104 44·0 95·2 64·3 58·0 49·4 43·4 58·4 46·9 50·7 68·4 64·2 60·5 67·8 60·7 Sm 15·8 6·98 16·0 9·08 8·31 9·63 8·42 10·0 9·05 9·08 11·3 10·4 10·1 11·0 9·39 Eu 1·25 1·37 0·95 2·03 1·88 3·05 2·66 3·18 2·89 2·87 3·56 3·29 3·20 3·13 2·95 Gd 13·6 5·04 13·8 7·72 7·15 8·86 7·86 8·12 8·27 8·11 10·2 9·26 8·71 9·08 7·80 Tb 1·84 0·75 1·89 1·01 0·92 1·11 0·98 1·27 1·03 1·04 1·27 1·16 1·08 1·12 0·95 Dy 11·1 4·70 11·7 6·01 5·47 6·40 5·55 6·28 5·75 5·84 7·11 6·61 6·08 6·59 5·58 Ho 2·23 0·89 2·30 1·19 1·09 1·16 1·00 1·29 1·07 1·08 1·34 1·25 1·14 1·22 1·05 Er 6·55 2·67 6·79 3·64 3·31 3·03 2·62 3·16 2·84 2·94 3·73 3·45 3·11 3·53 2·97 Tm 0·98 0·45 1·00 0·53 0·49 0·39 0·34 0·44 0·36 0·39 0·50 0·47 0·42 0·49 0·42 Yb 6·57 2·99 6·84 3·75 3·40 2·43 2·10 2·64 2·24 2·48 3·25 3·14 2·68 3·34 2·80 Lu 0·97 0·49 1·01 0·56 0·50 0·34 0·29 0·43 0·31 0·35 0·47 0·45 0·40 0·48 0·42 P, Potassic; S, sodic; -M, mafic; -I, intermediate; -F, felsic; X, xenolith; B, basement rock; Gr., granodiorite; Mg, migmatite; Tr (A), amphibole-bearing trachyte; AB, alkali-basalt; Tp, tephrite; Ph, phonolite; n.d., not determined. Fig. 3 View largeDownload slide Whole-rock chemical data for samples from this study. (a) Total alkalis vs silica (TAS) classification diagram for volcanic rocks from The Pleiades (Le Bas, 1986). Major element compositions are normalized to 100% anhydrous. The analysed AI xenoliths, pelitic migmatite and GHIC samples analysed in this study, together with previous Pleiades volcanic rock data (Kyle, 1982) and reported NVL relict granulite compositions (Talarico, 1995) are plotted for comparison. (b) A weight percent K2O vs Na2O diagram. The solid black line denotes K2O/Na2O = 0·5. Fig. 3 View largeDownload slide Whole-rock chemical data for samples from this study. (a) Total alkalis vs silica (TAS) classification diagram for volcanic rocks from The Pleiades (Le Bas, 1986). Major element compositions are normalized to 100% anhydrous. The analysed AI xenoliths, pelitic migmatite and GHIC samples analysed in this study, together with previous Pleiades volcanic rock data (Kyle, 1982) and reported NVL relict granulite compositions (Talarico, 1995) are plotted for comparison. (b) A weight percent K2O vs Na2O diagram. The solid black line denotes K2O/Na2O = 0·5. The variations of the major element lava compositions are plotted in Fig. 4. Although both lineages follow similar trends of sharp decreases in MgO, FeOt, CaO and TiO2 and increases of Al2O3, Na2O and K2O in the mafic suites with increasing SiO2, the basanites of the sodic lineage tends to have slightly more TiO2, Al2O3, Na2O, K2O and P2O5 and less MgO and CaO than hawaiite in the potassic lineage. Among the intermediate lavas, the sodic lineage is characterized by stronger depletion of TiO2, FeOt, MgO and P2O5 and by higher contents of Al2O3, Na2O and K2O than the potassic lineage. It is also notable that there is a sharp shift in the trend from the mafic to intermediate lava compositions in the potassic lineage for Al2O3 and Na2O, whose increasing trends flatten or even decrease with increasing SiO2. Fig. 4 View largeDownload slide Whole-rock Harker diagrams for The Pleiades lava samples (this study and Kyle, 1982; in wt %). See Fig. 3 for symbol definitions. Fig. 4 View largeDownload slide Whole-rock Harker diagrams for The Pleiades lava samples (this study and Kyle, 1982; in wt %). See Fig. 3 for symbol definitions. As mentioned above, all felsic rocks are grouped as the potassic lineage based on the absence of kaersutite and presence of olivine. Indeed, the plateau of high K2O concentrations (4·8–5·5 wt %) with respect to Na2O supports the idea that the felsic lavas, even in the case of phonolite, are linked to the potassic lineage rather than the sodic one. The trachyte samples are characterized by their highly depleted TiO2 (<0·6 wt %), CaO (<2·1 wt %), MgO (<0·6 wt %), FeOt (<5·5 wt %) and P2O5 (<0·15 wt %) contents and by high K2O (>4·3 wt %) contents. A gap in SiO2 contents (61·0–64·2 wt %), accompanied by a slight drop in Al2O3 from the benmoreite to the trachyte samples, is also notable. The phonolite, on the other hand, becomes more enriched in Al2O3 and slightly more alkali enriched than the trachyte samples, without a significant SiO2 increase. The two granodiorite xenoliths plot in the andesite field in the TAS diagram, and their compositions are slightly alkali-rich compared to those of the GHIC sample (141123-1A; Fig. 3). The cordierite garnet migmatite sample (141215-5B) is less silica-rich, deficient in Na2O (1·3 wt %), and enriched in K2O (5 wt %). Trace elements Selected trace element variations in The Pleiades volcanic rocks are plotted in Fig. 5. Mafic to intermediate rocks from both lineages share common trends of positive correlations between SiO2 content and REE abundances, high field strength elements (HFSE), alkali elements (Cs and Rb), Ba, and Pb. Transition metals Sc, V, and Cu, sharply decrease before SiO2 contents reach 50 wt % and then gently decrease in more evolved rocks. However, it should be noted that the mafic sodic lineage is characterized by slightly higher contents of large ion lithophile elements (LILE), Nb, light-REE (LREE), and middle-REE (MREE) and lower contents of transition metals (except V) than the mafic potassic lineage. The discrepancy becomes larger in the intermediate rocks. The decreasing trends of the MREE, Eu, and Gd, are distinct from the gently increasing trends of the potassic lineage. The intermediate sodic lavas are also marked by their high Sr concentrations (>800 ppm) relative to the other samples studied, whereas the Sr content in the potassic lineage decreases from ∼ 1000 ppm to below 800 ppm as their SiO2 exceeds 50 wt %. Fig. 5 View largeDownload slide Silica variation diagrams showing selected trace elements (in ppm) for The Pleiades lava samples. See Fig. 3 for symbol definitions. Fig. 5 View largeDownload slide Silica variation diagrams showing selected trace elements (in ppm) for The Pleiades lava samples. See Fig. 3 for symbol definitions. The trace element variations in trachyte and phonolite are marked by extreme enrichments or depletions. Concentrations of transition metals and the feldspar-hosted elements Sr, Ba and Eu decrease to almost zero, whereas the concentrations of other incompatible trace elements such as Zr increase. Barium concentration increases in both lineages up to 1270 ppm in the intermediate rocks, but then decreases in the trachyte samples. Primitive mantle normalized trace element patterns are plotted in Fig. 6. The mafic rocks from the two lineages share the same OIB-like intraplate volcanic patterns with enrichment in highly to moderately incompatible trace elements. All samples show highly fractionated patterns with negative K and Pb anomalies, mild Th, U, Zr, Hf troughs and positive Nb anomalies. Fig. 6 View largeDownload slide Whole-rock primitive mantle normalized (McDonough & Sun, 1995) trace element patterns for The Pleiades volcanic rocks. (a–d) The averaged values and the average compositions from their counterpart lineage are shown together. In (a) and (b), mafic rocks with MgO less than 5 wt % are excluded. (e) Trachyte and phonolite compositions are plotted together with the average mafic lava compositions from (a) and (b) for comparison. Fig. 6 View largeDownload slide Whole-rock primitive mantle normalized (McDonough & Sun, 1995) trace element patterns for The Pleiades volcanic rocks. (a–d) The averaged values and the average compositions from their counterpart lineage are shown together. In (a) and (b), mafic rocks with MgO less than 5 wt % are excluded. (e) Trachyte and phonolite compositions are plotted together with the average mafic lava compositions from (a) and (b) for comparison. Different behavior of Sr between the intermediate sodic and potassic lineages is evident in Fig. 6c and d. The evolved lavas of both lineages share concave upward patterns in the middle- to heavy-REE. Extreme enrichment of most elements compared to mafic lavas and strong depletion of Ba, Sr and Eu in trachyte and phonolite lavas are prominent in Fig. 6e. Sr–Nd–Pb isotopes Volcanic rocks Whole-rock Sr, Nd, and Pb isotopic compositions have been measured on six sodic lineage and twelve potassic lineage samples (Table 3; Fig. 7). The sodic lineage lavas have a narrow range in 87Sr/86Sr and 143Nd/144Nd from 0·703143 to 0·703442 and 0·512859 to 0·512897 (εNd = 4·3–5·1), respectively. Lead isotopes also have narrow ranges of 206Pb/204Pb (19·7–19·9), 208Pb/204Pb (39·5–39·6) and 207Pb/204Pb (15·6), except for an outliner, K16012708-4, whose Pb isotopic ratios are 206Pb/204Pb (19·4), 208Pb/204Pb (39·3) and 207Pb/204Pb (15·6) (Fig. 7c and d). None of those isotopic ratios from the sodic lineage correlates with differentiation indices such as SiO2, MgO or Th. Table 3 Whole-rock Sr, Nd and Pb isotopic compositions of The Pleiades samples Sample Group Rock type 87Sr/86Sr ±2σ (·10-6) 143Nd/144Nd ±2σ (·10-6) 206Pb/204Pb ±2σ (·10-4) 207Pb/204Pb ±2σ (·10-4) 208Pb/204Pb ±2σ (·10-4) K16012408-1 P-M AB 0·704003 5 0·512797 6 19·051 17 15·639 16 39·094 49 K16012424 P-M H 0·703232 5 0·512876 4 19·641 9 15·624 8 39·484 26 J14120503-2 P-M H 0·703272 5 0·512831 10 19·598 9 15·628 8 39·476 25 J14120504-4 P-I Mu 0·703717 5 0·512813 6 19·159 6 15·638 5 39·143 16 J14120106-1 P-I Mu 0·704027 5 0·512781 7 19·072 6 15·636 6 39·095 18 J14120107-2 P-I Bn 0·703477 5 0·512847 5 n.d. n.d.· n.d. J14120105-1 P-I Bn 0·703884 5 0·512805 6 19·195 10 15·640 9 39·198 28 J14120103 P-I Bn 0·703998 5 0·512791 6 19·056 8 15·638 7 39·093 22 J14120504-1 P-I Tr 0·703999 5 0·512797 5 19·052 8 15·640 7 39·094 23 K16012709-1 P-I Bn 0·703852 5 0·512823 7 19·205 8 15·635 8 39·188 24 K16012425 P-F Ph 0·703973 5 0·512813 6 19·510 14 15·636 12 39·425 38 M16012710 P-F Tr 0·703747 5 0·512811 5 19·229 7 15·641 6 39·245 19 J14120107-1 S-M Tp 0·703143 6 0·512872 7 19·721 9 15·625 8 39·524 26 K16012708-4 S-M Bas 0·703442 6 0·512870 5 19·371 7 15·642 7 39·300 21 M16012713-1 S-I PhT 0·703182 5 0·512880 6 19·993 8 15·656 7 39·781 23 K16012713-2 S-I PhT 0·703169 5 0·512859 9 19·849 9 15·629 8 39·630 24 K16012422-2 S-I TPh 0·703190 6 0·512897 8 19·772 8 15·631 7 39·568 21 K16012713-1 S-I TPh 0·703152 5 0·512891 4 19·856 8 15·627 7 39·632 24 K16012407-2 X Gr· 0·715561 5 0·512387 6 18·966 10 15·660 9 39·139 28 K16012422-3 X Gr· 0·715740 5 0·512356 4 18·552 6 15·632 5 39·013 17 141215-5B B Mg 0·761940 5 0·511751 4 18·203 6 15·687 5 39·040 17 141123-1A B GHIC 0·714313 4 0·511908 6 18·197 4 15·647 4 38·482 11 Sample Group Rock type 87Sr/86Sr ±2σ (·10-6) 143Nd/144Nd ±2σ (·10-6) 206Pb/204Pb ±2σ (·10-4) 207Pb/204Pb ±2σ (·10-4) 208Pb/204Pb ±2σ (·10-4) K16012408-1 P-M AB 0·704003 5 0·512797 6 19·051 17 15·639 16 39·094 49 K16012424 P-M H 0·703232 5 0·512876 4 19·641 9 15·624 8 39·484 26 J14120503-2 P-M H 0·703272 5 0·512831 10 19·598 9 15·628 8 39·476 25 J14120504-4 P-I Mu 0·703717 5 0·512813 6 19·159 6 15·638 5 39·143 16 J14120106-1 P-I Mu 0·704027 5 0·512781 7 19·072 6 15·636 6 39·095 18 J14120107-2 P-I Bn 0·703477 5 0·512847 5 n.d. n.d.· n.d. J14120105-1 P-I Bn 0·703884 5 0·512805 6 19·195 10 15·640 9 39·198 28 J14120103 P-I Bn 0·703998 5 0·512791 6 19·056 8 15·638 7 39·093 22 J14120504-1 P-I Tr 0·703999 5 0·512797 5 19·052 8 15·640 7 39·094 23 K16012709-1 P-I Bn 0·703852 5 0·512823 7 19·205 8 15·635 8 39·188 24 K16012425 P-F Ph 0·703973 5 0·512813 6 19·510 14 15·636 12 39·425 38 M16012710 P-F Tr 0·703747 5 0·512811 5 19·229 7 15·641 6 39·245 19 J14120107-1 S-M Tp 0·703143 6 0·512872 7 19·721 9 15·625 8 39·524 26 K16012708-4 S-M Bas 0·703442 6 0·512870 5 19·371 7 15·642 7 39·300 21 M16012713-1 S-I PhT 0·703182 5 0·512880 6 19·993 8 15·656 7 39·781 23 K16012713-2 S-I PhT 0·703169 5 0·512859 9 19·849 9 15·629 8 39·630 24 K16012422-2 S-I TPh 0·703190 6 0·512897 8 19·772 8 15·631 7 39·568 21 K16012713-1 S-I TPh 0·703152 5 0·512891 4 19·856 8 15·627 7 39·632 24 K16012407-2 X Gr· 0·715561 5 0·512387 6 18·966 10 15·660 9 39·139 28 K16012422-3 X Gr· 0·715740 5 0·512356 4 18·552 6 15·632 5 39·013 17 141215-5B B Mg 0·761940 5 0·511751 4 18·203 6 15·687 5 39·040 17 141123-1A B GHIC 0·714313 4 0·511908 6 18·197 4 15·647 4 38·482 11 P, potassic lineage; S, sodic lineage; -M, mafic; -I, intermediate; -F, felsic; X, xenolith; B, basement rock; AB, alkali-basalt; H, hawaiite; Mu, mugearite, Bn, benmoreite; Tr, trachyte; Ph, phonolite; Tp, tephrite; Bas, basanite; PhT, phonotephrite; TPh, tephriphonolite; Gr·, AI granodiorite; Mg, migmatite; GHIC, Granite Harbour Intrusive Complex; n.d., not determined. Table 3 Whole-rock Sr, Nd and Pb isotopic compositions of The Pleiades samples Sample Group Rock type 87Sr/86Sr ±2σ (·10-6) 143Nd/144Nd ±2σ (·10-6) 206Pb/204Pb ±2σ (·10-4) 207Pb/204Pb ±2σ (·10-4) 208Pb/204Pb ±2σ (·10-4) K16012408-1 P-M AB 0·704003 5 0·512797 6 19·051 17 15·639 16 39·094 49 K16012424 P-M H 0·703232 5 0·512876 4 19·641 9 15·624 8 39·484 26 J14120503-2 P-M H 0·703272 5 0·512831 10 19·598 9 15·628 8 39·476 25 J14120504-4 P-I Mu 0·703717 5 0·512813 6 19·159 6 15·638 5 39·143 16 J14120106-1 P-I Mu 0·704027 5 0·512781 7 19·072 6 15·636 6 39·095 18 J14120107-2 P-I Bn 0·703477 5 0·512847 5 n.d. n.d.· n.d. J14120105-1 P-I Bn 0·703884 5 0·512805 6 19·195 10 15·640 9 39·198 28 J14120103 P-I Bn 0·703998 5 0·512791 6 19·056 8 15·638 7 39·093 22 J14120504-1 P-I Tr 0·703999 5 0·512797 5 19·052 8 15·640 7 39·094 23 K16012709-1 P-I Bn 0·703852 5 0·512823 7 19·205 8 15·635 8 39·188 24 K16012425 P-F Ph 0·703973 5 0·512813 6 19·510 14 15·636 12 39·425 38 M16012710 P-F Tr 0·703747 5 0·512811 5 19·229 7 15·641 6 39·245 19 J14120107-1 S-M Tp 0·703143 6 0·512872 7 19·721 9 15·625 8 39·524 26 K16012708-4 S-M Bas 0·703442 6 0·512870 5 19·371 7 15·642 7 39·300 21 M16012713-1 S-I PhT 0·703182 5 0·512880 6 19·993 8 15·656 7 39·781 23 K16012713-2 S-I PhT 0·703169 5 0·512859 9 19·849 9 15·629 8 39·630 24 K16012422-2 S-I TPh 0·703190 6 0·512897 8 19·772 8 15·631 7 39·568 21 K16012713-1 S-I TPh 0·703152 5 0·512891 4 19·856 8 15·627 7 39·632 24 K16012407-2 X Gr· 0·715561 5 0·512387 6 18·966 10 15·660 9 39·139 28 K16012422-3 X Gr· 0·715740 5 0·512356 4 18·552 6 15·632 5 39·013 17 141215-5B B Mg 0·761940 5 0·511751 4 18·203 6 15·687 5 39·040 17 141123-1A B GHIC 0·714313 4 0·511908 6 18·197 4 15·647 4 38·482 11 Sample Group Rock type 87Sr/86Sr ±2σ (·10-6) 143Nd/144Nd ±2σ (·10-6) 206Pb/204Pb ±2σ (·10-4) 207Pb/204Pb ±2σ (·10-4) 208Pb/204Pb ±2σ (·10-4) K16012408-1 P-M AB 0·704003 5 0·512797 6 19·051 17 15·639 16 39·094 49 K16012424 P-M H 0·703232 5 0·512876 4 19·641 9 15·624 8 39·484 26 J14120503-2 P-M H 0·703272 5 0·512831 10 19·598 9 15·628 8 39·476 25 J14120504-4 P-I Mu 0·703717 5 0·512813 6 19·159 6 15·638 5 39·143 16 J14120106-1 P-I Mu 0·704027 5 0·512781 7 19·072 6 15·636 6 39·095 18 J14120107-2 P-I Bn 0·703477 5 0·512847 5 n.d. n.d.· n.d. J14120105-1 P-I Bn 0·703884 5 0·512805 6 19·195 10 15·640 9 39·198 28 J14120103 P-I Bn 0·703998 5 0·512791 6 19·056 8 15·638 7 39·093 22 J14120504-1 P-I Tr 0·703999 5 0·512797 5 19·052 8 15·640 7 39·094 23 K16012709-1 P-I Bn 0·703852 5 0·512823 7 19·205 8 15·635 8 39·188 24 K16012425 P-F Ph 0·703973 5 0·512813 6 19·510 14 15·636 12 39·425 38 M16012710 P-F Tr 0·703747 5 0·512811 5 19·229 7 15·641 6 39·245 19 J14120107-1 S-M Tp 0·703143 6 0·512872 7 19·721 9 15·625 8 39·524 26 K16012708-4 S-M Bas 0·703442 6 0·512870 5 19·371 7 15·642 7 39·300 21 M16012713-1 S-I PhT 0·703182 5 0·512880 6 19·993 8 15·656 7 39·781 23 K16012713-2 S-I PhT 0·703169 5 0·512859 9 19·849 9 15·629 8 39·630 24 K16012422-2 S-I TPh 0·703190 6 0·512897 8 19·772 8 15·631 7 39·568 21 K16012713-1 S-I TPh 0·703152 5 0·512891 4 19·856 8 15·627 7 39·632 24 K16012407-2 X Gr· 0·715561 5 0·512387 6 18·966 10 15·660 9 39·139 28 K16012422-3 X Gr· 0·715740 5 0·512356 4 18·552 6 15·632 5 39·013 17 141215-5B B Mg 0·761940 5 0·511751 4 18·203 6 15·687 5 39·040 17 141123-1A B GHIC 0·714313 4 0·511908 6 18·197 4 15·647 4 38·482 11 P, potassic lineage; S, sodic lineage; -M, mafic; -I, intermediate; -F, felsic; X, xenolith; B, basement rock; AB, alkali-basalt; H, hawaiite; Mu, mugearite, Bn, benmoreite; Tr, trachyte; Ph, phonolite; Tp, tephrite; Bas, basanite; PhT, phonotephrite; TPh, tephriphonolite; Gr·, AI granodiorite; Mg, migmatite; GHIC, Granite Harbour Intrusive Complex; n.d., not determined. Fig. 7 View largeDownload slide (a), (b) 143Nd/144Nd vs 87Sr/86Sr and (c) 207Pb/204Pb and (d) 208Pb/204Pb vs 206Pb/204Pb for The Pleiades volcanic rocks and analysed basement rocks. Basement rock data include: Northern Victoria Land (NVL) granulite (Talarico, 1995), GHIC granitoids (Armienti et al., 1990; Di Vincenzo & Rocchi, 1999; Dallai et al., 2003); the pelitic migmatite (Di Vincenzo et al., 1999). Also plotted are young alkali-rich basalts from the northwest Ross Sea (Panter et al., 2018), Zealandia (Panter et al., 2006) and the Ross seafloor (Lee et al., 2015). Mixing lines are shown between the mafic potassic lava sample (J14120503-2) and potential contaminants (GHIC, granodiorite AI xenoliths, granulite, and migmatite). End-member mantle components in (d) are from Zindler & Hart (1986). Fig. 7 View largeDownload slide (a), (b) 143Nd/144Nd vs 87Sr/86Sr and (c) 207Pb/204Pb and (d) 208Pb/204Pb vs 206Pb/204Pb for The Pleiades volcanic rocks and analysed basement rocks. Basement rock data include: Northern Victoria Land (NVL) granulite (Talarico, 1995), GHIC granitoids (Armienti et al., 1990; Di Vincenzo & Rocchi, 1999; Dallai et al., 2003); the pelitic migmatite (Di Vincenzo et al., 1999). Also plotted are young alkali-rich basalts from the northwest Ross Sea (Panter et al., 2018), Zealandia (Panter et al., 2006) and the Ross seafloor (Lee et al., 2015). Mixing lines are shown between the mafic potassic lava sample (J14120503-2) and potential contaminants (GHIC, granodiorite AI xenoliths, granulite, and migmatite). End-member mantle components in (d) are from Zindler & Hart (1986). The potassic lineage shows wider variation in Sr, Nd, and Pb isotopic ratios than the sodic lineage. The mafic potassic samples are similar in isotopic composition to those of the sodic lineage, whereas the evolved (SiO2>50 wt %) samples have more elevated 87Sr/86Sr (>0.70370) and lower 143Nd/144Nd (<0·51280), 206Pb/204Pb (<19·5) and 208Pb/204Pb (<39·4). Unlike other mafic potassic samples, one sample (K16012408-1) has high 87Sr/86Sr (0·704003) and low 143Nd/144Nd (0·512797). The isotopic compositions of the mafic rocks from The Pleiades generally overlap with primitive lavas from Mt. Melbourne (Lee et al., 2015), Mt. Erebus, and Mt. Morning (Sims et al., 2008; Martin et al., 2013). In Fig. 7, the Sr–Nd–Pb isotope data for the Ross seafloor basanite (Lee et al., 2015), the northwest Ross Sea basalts (mostly the Adare Trough and the Hallett Volcanic Province lavas; Panter et al., 2018), and the New Zealand HIMU-like basalts (Panter et al., 2006) are plotted together to illustrate that the isotopic ratios of the most mafic suites in The Pleiades are comparable with the isotopic range of those basaltic rocks. Basement rocks The granodiorite xenoliths from The Pleiades have elevated 143Nd/144Nd (0·512356 and 0·512387) compared to the migmatite and the GHIC samples (0·511751 and 0·511908, respectively; Fig. 7a). The 87Sr/86Sr of the migmatite sample (0·761940) is much higher than that of the xenoliths (0·715561 and 0·715740) and the GHIC (0·714313). The 206Pb/204Pb ratios of the GHIC and migmatite (both are 18·20) are much less than the granodiorite xenoliths (18·55 and 18·97). Although 143Nd/144Nd is slightly high, the isotopic ratios of the GHIC sample are broadly similar to reported data on the GHIC (Armienti et al., 1990). The isotopic ratios of the granodiorite xenoliths are distinct from both GHIC (Armienti et al., 1990; Di Vincenzo & Rocchi, 1999; Dallai et al., 2003) and AI (Borg et al., 1987; Armienti et al., 1990). DISCUSSION Pressure and temperature Phenocryst compositions and crystallization in magmas are controlled by pressure (depth) and temperature conditions during their ascent through the crust (e.g. Ablay et al., 1998; Genske et al., 2012; Grant et al., 2013; Putirka, 2017). Clinopyroxene–melt thermobarometry (Putirka et al., 2003; Putirka, 2008) is used here to estimate liquidus temperatures and pressures. Clinopyroxene is ubiquitous in all the lavas. The core textures and compositions of clinopyroxene in The Pleiades volcanic rocks are variable, but the cores are mostly enveloped by euhedral outer rims with a more restricted range of composition, implying there was equilibrium with the surrounding melt composition during the last stage of magma evolution before the eruption. Rim compositions of clinopyroxene phenocrysts without disequilibrium textures were used for the calculations. Phenocrysts with fine oscillatory zoning and sector zoning were excluded. The whole-rock compositions of samples containing < 5% total phenocryst area in thin section were used for liquid compositions, because neither co-existing melt inclusions nor glassy lavas were available. The whole-rock composition, however, does not necessarily equilibrate with the clinopyroxene rim compositions (e.g. Giacomoni et al., 2016). Putirka (2008) suggested that the equilibrated pairs of liquid and clinopyroxene produce a specific range of KD(Fe–Mg)Cpx-liquid = 0·28 ± 0·08 which is slightly temperature dependent. We used the clinopyroxene–whole-rock pairs whose KD(Fe–Mg)Cpx-liquid values fall within the 20% of equilibrium values using equation 35 from Putirka (2008). If clinopyroxene rim compositions were out of equilibrium with their host, then the paired whole-rock compositions were replaced by another of The Pleiades lava compositions which produced the appropriate equilibrium KD value (e.g. Giacomoni et al., 2016). The clinopyroxene compositions which fail to be equilibrated after this correction were considered to be xenocrysts and excluded from the data and discussion. Temperatures and pressures were calculated for the selected clinopyroxene–liquid pairs using the clinopyroxene–liquid thermobarometer from Putirka (2008). Equations 31 and 33 were used and give values with standard errors of ± 2·9 kbar and ± 45°C. The amounts of H2O in the potassic and sodic lavas in The Pleiades were assumed to be 0·5 wt % and 1·5 wt %, respectively, based on melt inclusion data from Ross Island whose two representative fractionation trends (DVDP and Erebus lineages) resemble those of The Pleiades (Rasmussen et al., 2017). It should be noted that a change of ± 1 wt % H2O produces only about ±0·4 kbar difference, which is within the error of the calculated values. The results of the thermobarometry are shown in Table 4 and Fig. 8. The mafic samples (K16012424, K16012408-2, M16012705-1, K16012708-4, and K16012414) record higher temperatures (1152–1216°C) than the intermediate ones (K16012708-2, M16012707-1, and K16012713-2; 1082–1130°C). Although the calculated pressure ranges for the mafic and intermediate lavas broadly overlap, mafic lavas record higher pressure (10·1–12·5 kbar) than the intermediate lavas (9·1–11·7 kbar). The ‘re-equilibrated’ clinopyroxene–liquid pairs from the mafic lavas also produce a similar temperature range (1156–1196°C), but show slightly lower pressure conditions (9·3–10·9 kbar) similar to the range of the intermediate lavas. Table 4 Liquidus pressure and temperature estimated using the thermobarometers described in Putirka et al. (2003), Putirka (2008) and Masotta et al. (2013) Sample Group n Putirka et al. (2003) Putirka (2008) Masotta et al. (2013) T (°C) ±1σ P (kbar) ±1σ T (°C) ±1σ P (kbar) ±1σ T (°C) ±1σ P (kbar) ±1σ K16012424 P-M 10 1227 5·9 11·1 0·5 1202 8·4 11·4 0·6 K16012424 (R)* P-M 4 1195 3·3 9·4 0·3 1192 2·4 10·1 0·5 K16012408-2 P-M 5 1173 3·3 9·5 0·3 1185 6·1 12·0 0·3 M16012705-1 P-M 2 1133 8·3 1158 10·7 K16012708-2 P-I 5 1081 2·5 6·9 0·4 1090 4·7 9·9 0·5 K16012708-2 (R) P-I 1 1131 7·5 1131 10·2 K16012412-1 P-F 6 853 7·4 1·0 0·3 K16012407-1 P-F 2 859 1·5 K16012708-4 S-M 2 1195 10·1 1174 11·5 K16012708-4 (R) S-M 6 1150 4·0 8·2 0·3 1163 3·5 10·0 0·6 K16012414 S-M 2 1167 9·9 1174 11·8 M16012707-1 S-I 7 1094 3·4 7·9 0·3 1121 5·6 11·3 0·3 K16012713-2 S-I 2 1064 7·1 1086 10·2 Sample Group n Putirka et al. (2003) Putirka (2008) Masotta et al. (2013) T (°C) ±1σ P (kbar) ±1σ T (°C) ±1σ P (kbar) ±1σ T (°C) ±1σ P (kbar) ±1σ K16012424 P-M 10 1227 5·9 11·1 0·5 1202 8·4 11·4 0·6 K16012424 (R)* P-M 4 1195 3·3 9·4 0·3 1192 2·4 10·1 0·5 K16012408-2 P-M 5 1173 3·3 9·5 0·3 1185 6·1 12·0 0·3 M16012705-1 P-M 2 1133 8·3 1158 10·7 K16012708-2 P-I 5 1081 2·5 6·9 0·4 1090 4·7 9·9 0·5 K16012708-2 (R) P-I 1 1131 7·5 1131 10·2 K16012412-1 P-F 6 853 7·4 1·0 0·3 K16012407-1 P-F 2 859 1·5 K16012708-4 S-M 2 1195 10·1 1174 11·5 K16012708-4 (R) S-M 6 1150 4·0 8·2 0·3 1163 3·5 10·0 0·6 K16012414 S-M 2 1167 9·9 1174 11·8 M16012707-1 S-I 7 1094 3·4 7·9 0·3 1121 5·6 11·3 0·3 K16012713-2 S-I 2 1064 7·1 1086 10·2 * (R) denotes the re-equilibrated calculation. The re-equilibrated whole-rock compositions of K16012424, K16012708–2 and K16012708–4 are those of K16012412-2, J14120504–4 and J14120107–1, respectively. Refer to Supplementary Data for the result of each clinopyroxene-liquid pair. Table 4 Liquidus pressure and temperature estimated using the thermobarometers described in Putirka et al. (2003), Putirka (2008) and Masotta et al. (2013) Sample Group n Putirka et al. (2003) Putirka (2008) Masotta et al. (2013) T (°C) ±1σ P (kbar) ±1σ T (°C) ±1σ P (kbar) ±1σ T (°C) ±1σ P (kbar) ±1σ K16012424 P-M 10 1227 5·9 11·1 0·5 1202 8·4 11·4 0·6 K16012424 (R)* P-M 4 1195 3·3 9·4 0·3 1192 2·4 10·1 0·5 K16012408-2 P-M 5 1173 3·3 9·5 0·3 1185 6·1 12·0 0·3 M16012705-1 P-M 2 1133 8·3 1158 10·7 K16012708-2 P-I 5 1081 2·5 6·9 0·4 1090 4·7 9·9 0·5 K16012708-2 (R) P-I 1 1131 7·5 1131 10·2 K16012412-1 P-F 6 853 7·4 1·0 0·3 K16012407-1 P-F 2 859 1·5 K16012708-4 S-M 2 1195 10·1 1174 11·5 K16012708-4 (R) S-M 6 1150 4·0 8·2 0·3 1163 3·5 10·0 0·6 K16012414 S-M 2 1167 9·9 1174 11·8 M16012707-1 S-I 7 1094 3·4 7·9 0·3 1121 5·6 11·3 0·3 K16012713-2 S-I 2 1064 7·1 1086 10·2 Sample Group n Putirka et al. (2003) Putirka (2008) Masotta et al. (2013) T (°C) ±1σ P (kbar) ±1σ T (°C) ±1σ P (kbar) ±1σ T (°C) ±1σ P (kbar) ±1σ K16012424 P-M 10 1227 5·9 11·1 0·5 1202 8·4 11·4 0·6 K16012424 (R)* P-M 4 1195 3·3 9·4 0·3 1192 2·4 10·1 0·5 K16012408-2 P-M 5 1173 3·3 9·5 0·3 1185 6·1 12·0 0·3 M16012705-1 P-M 2 1133 8·3 1158 10·7 K16012708-2 P-I 5 1081 2·5 6·9 0·4 1090 4·7 9·9 0·5 K16012708-2 (R) P-I 1 1131 7·5 1131 10·2 K16012412-1 P-F 6 853 7·4 1·0 0·3 K16012407-1 P-F 2 859 1·5 K16012708-4 S-M 2 1195 10·1 1174 11·5 K16012708-4 (R) S-M 6 1150 4·0 8·2 0·3 1163 3·5 10·0 0·6 K16012414 S-M 2 1167 9·9 1174 11·8 M16012707-1 S-I 7 1094 3·4 7·9 0·3 1121 5·6 11·3 0·3 K16012713-2 S-I 2 1064 7·1 1086 10·2 * (R) denotes the re-equilibrated calculation. The re-equilibrated whole-rock compositions of K16012424, K16012708–2 and K16012708–4 are those of K16012412-2, J14120504–4 and J14120107–1, respectively. Refer to Supplementary Data for the result of each clinopyroxene-liquid pair. Fig. 8 View largeDownload slide Calculated pressure and temperature conditions of The Pleiades volcanic rocks based on the clinopyroxene-liquid thermobarometry. The equations from Putirka et al. (2003) and Equations 31 and 33 from Putirka (2008) were used for the mafic to intermediate lavas. Open circles are the estimated values from the re-equilibrated clinopyroxene–liquid pairs; open squares are the clinopyroxene–liquid pairs which are within the equilibrium range based on the Equation 35 in Putirka (2008); the filled square is the estimated pressure and temperature based on the methods described in Masotta et al. (2013). The grey bar is the equivalent pressure range of the reported Moho depths (Hansen et al., 2016) assuming the mean crustal density is 3·0 g/cm3. The error bars denote standard error of estimates (SEE) of 45°C and 2·9 kbar (number 1) for Putirka (2008), 33°C and 1·7 kbar (number 2) for Putirka et al. (2003), and 18·2°C and 1·15 kbar (number 3) for Masotta (2013) methods. Fig. 8 View largeDownload slide Calculated pressure and temperature conditions of The Pleiades volcanic rocks based on the clinopyroxene-liquid thermobarometry. The equations from Putirka et al. (2003) and Equations 31 and 33 from Putirka (2008) were used for the mafic to intermediate lavas. Open circles are the estimated values from the re-equilibrated clinopyroxene–liquid pairs; open squares are the clinopyroxene–liquid pairs which are within the equilibrium range based on the Equation 35 in Putirka (2008); the filled square is the estimated pressure and temperature based on the methods described in Masotta et al. (2013). The grey bar is the equivalent pressure range of the reported Moho depths (Hansen et al., 2016) assuming the mean crustal density is 3·0 g/cm3. The error bars denote standard error of estimates (SEE) of 45°C and 2·9 kbar (number 1) for Putirka (2008), 33°C and 1·7 kbar (number 2) for Putirka et al. (2003), and 18·2°C and 1·15 kbar (number 3) for Masotta (2013) methods. The KD values between the trachyte whole-rock and clinopyroxene phenocrysts (excluding aegirine-augite) vary widely from 0·14 to 0·29. Among them, seven grains are within the expected equilibrium range based on the Putirka (2008) equation 35. The calculated pressure and temperature conditions are much lower (841–864°C, 0·8–1·7 kbar), broadly consistent with previous plagioclase thermometry estimates (776–891°C; Kyle, 1986). Masotta et al. (2013) provided a modified KD equation (Equation 35alk) specifically for the trachyte–phonolite system. According to this modified equation, one clinopyroxene–whole-rock pair is at equilibrium and produces similar crystallization conditions (858°C, 0·9 kbar). Therefore, crystallization of clinopyroxene in the trachyte lavas occurred at a very shallow depth (<2 kbar) and low temperature (∼ 850°C). The Moho depth below the TAM in NVL has been estimated to be about 40 km (Block et al., 2009; Hansen et al., 2016), which is similar to Southern Victoria Land (e.g. Bannister et al., 2003; Lawrence et al., 2006; Watson et al., 2006; Chaput et al., 2014). The 40 km depth is equivalent to a pressure of 11–12 kbar, assuming a crustal density of 2·8–3·1 g/cm3. The crystallization pressures of 10·1–12·5 kbar, estimated from the mafic lavas of The Pleiades, indicate the mafic magmas crystallizing at the Moho. Crystallization pressures for the intermediate composition lavas (6·4–11·7 kbar) fall in the range of lower crustal pressures (Fig. 8). The above calculation suggests that the mafic to intermediate lavas of The Pleiades have mainly pooled at the Moho and in the lower crust. The calculations from the trachyte samples record much shallower depths (<2 kbar). The shallow emplacement of felsic magmas is consistent with other trachyte and phonolite studies (Peccerillo et al., 2007; Martel et al., 2013; Moussallam et al., 2013; Brenna et al., 2015). The low pressure conditions may indicate a shallow magma chamber (Brenna et al., 2015) or conduit-fill, endogenous dome or cryptodome emplacement (Hoblitt & Harmon, 1993; Hammer et al., 1999). Endogenous dome emplacement is recorded at Taygete Cone. In whichever case, the vesicle-poor and crystal-rich features of trachyte are consistent with shallow-depth degassing processes. It is notable that the mafic and intermediate magmas of the two lineages share similar liquidus pressure and temperature ranges. Some lavas exhibit mingling textures of kaersutite-bearing and plagioclase-rich melts. This suggests that the mixing of the two lineages may have occurred in the lower crust. Therefore, the evolution of the two lineages should be attributed to factors other than pressure and temperature conditions, because the two lineages have similar crystallization conditions at lower crustal depths. Effect of fractional crystallization The sodic and potassic fractionation trends The systematic difference in chemical composition between the two lithological groups can be explained by fractional crystallization processes. Least-squares mass-balance models (OPTIMASBA software; Cabero et al., 2012) were calculated using the measured whole-rock and crystal compositions (Fig. 9). Representative whole-rock compositions used for the parent and daughter magma compositions and the measured phenocryst compositions of the parent stage used for fractionating crystal compositions are reported in Table 5. In order to investigate the potential effect of crustal contamination processes, the whole-rock compositions of the migmatite sample, the GHIC and the granodiorite AI xenolith samples, and granulite data from Talarico et al. (1995) were included in the model. All calculations produced good regression fits (R2>99·99%; SEE ≤ 0·10). Table 5 Calculated fractionated mineral assemblages of The Pleiades lineages using least-squares fractional crystallization and assimilation modeling Sodic lineage Potassic lineage Stage basanite – Phonotephrite phonotephrite – Tephriphonolite tephriphonolite – phonolite hawaiite – mugearite mugearite – trachyte trachyte – trachyte trachyte – phonolite Parent K16012708-4 K16012713-2 K16012713-1 J14120503-2 J14120106-1 K16012707-1 K16012707-1 Daughter K16012713-2 K16012713-1 K16012415 J14120106-1 K16012708-1 K16012422-1 M16012701 Ol (%) 8·1 – 6·8 19·3 14·2 5·9 6·9 Pl 14·8 20·6 – 33·7 55·1 29·6 – Sa/Ano† – – 0/60·6 – – 52·5/0 44·6/36·2 Aug/Aeg* 33·2 21 3 59·7 14·5 1/4·8 3·2 Krs 35·8 36·2 17·7 – – – 8·3 Mt/Ilm‡ 6·2/1 10·4 3·1 11/0·4 5/8·2 5·3 <0·1/0·8 Ap† 0·9 2·3 1·6 0·8 3·1 0·9 – Ne – 9·6 7·1 – – – – Contaminant – – – −24·9 – – – F.C. (%) 45·5 27·7 64·3 38·6 39·8 64·9 89·7 SSE 0·002 0·102 0·048 0·101 0·035 0·048 0·000 R2 1·000 1·000 1·000 1·000 1·000 1·000 1·000 Sodic lineage Potassic lineage Stage basanite – Phonotephrite phonotephrite – Tephriphonolite tephriphonolite – phonolite hawaiite – mugearite mugearite – trachyte trachyte – trachyte trachyte – phonolite Parent K16012708-4 K16012713-2 K16012713-1 J14120503-2 J14120106-1 K16012707-1 K16012707-1 Daughter K16012713-2 K16012713-1 K16012415 J14120106-1 K16012708-1 K16012422-1 M16012701 Ol (%) 8·1 – 6·8 19·3 14·2 5·9 6·9 Pl 14·8 20·6 – 33·7 55·1 29·6 – Sa/Ano† – – 0/60·6 – – 52·5/0 44·6/36·2 Aug/Aeg* 33·2 21 3 59·7 14·5 1/4·8 3·2 Krs 35·8 36·2 17·7 – – – 8·3 Mt/Ilm‡ 6·2/1 10·4 3·1 11/0·4 5/8·2 5·3 <0·1/0·8 Ap† 0·9 2·3 1·6 0·8 3·1 0·9 – Ne – 9·6 7·1 – – – – Contaminant – – – −24·9 – – – F.C. (%) 45·5 27·7 64·3 38·6 39·8 64·9 89·7 SSE 0·002 0·102 0·048 0·101 0·035 0·048 0·000 R2 1·000 1·000 1·000 1·000 1·000 1·000 1·000 F.C., amount of crystallization from the parent melt; SEE, sum of squared errors; Ano, anorthoclase; Aug, augite; Aeg, aegirine–augite; Ap, apatite. Details on the calculation are presented in Supplementary Data C. * Aegirine–augite and apatite compositions adopted from previous mineral data in Kyle (1986). † Anorthoclase composition adopted from Kelly et al. (2008) where anorthoclase phenocryst compositions in Erebus volcanic bombs are reported. ‡ Numbers without slash (/) denotes 0% involvement of aegirine-augite or ilmenite. Table 5 Calculated fractionated mineral assemblages of The Pleiades lineages using least-squares fractional crystallization and assimilation modeling Sodic lineage Potassic lineage Stage basanite – Phonotephrite phonotephrite – Tephriphonolite tephriphonolite – phonolite hawaiite – mugearite mugearite – trachyte trachyte – trachyte trachyte – phonolite Parent K16012708-4 K16012713-2 K16012713-1 J14120503-2 J14120106-1 K16012707-1 K16012707-1 Daughter K16012713-2 K16012713-1 K16012415 J14120106-1 K16012708-1 K16012422-1 M16012701 Ol (%) 8·1 – 6·8 19·3 14·2 5·9 6·9 Pl 14·8 20·6 – 33·7 55·1 29·6 – Sa/Ano† – – 0/60·6 – – 52·5/0 44·6/36·2 Aug/Aeg* 33·2 21 3 59·7 14·5 1/4·8 3·2 Krs 35·8 36·2 17·7 – – – 8·3 Mt/Ilm‡ 6·2/1 10·4 3·1 11/0·4 5/8·2 5·3 <0·1/0·8 Ap† 0·9 2·3 1·6 0·8 3·1 0·9 – Ne – 9·6 7·1 – – – – Contaminant – – – −24·9 – – – F.C. (%) 45·5 27·7 64·3 38·6 39·8 64·9 89·7 SSE 0·002 0·102 0·048 0·101 0·035 0·048 0·000 R2 1·000 1·000 1·000 1·000 1·000 1·000 1·000 Sodic lineage Potassic lineage Stage basanite – Phonotephrite phonotephrite – Tephriphonolite tephriphonolite – phonolite hawaiite – mugearite mugearite – trachyte trachyte – trachyte trachyte – phonolite Parent K16012708-4 K16012713-2 K16012713-1 J14120503-2 J14120106-1 K16012707-1 K16012707-1 Daughter K16012713-2 K16012713-1 K16012415 J14120106-1 K16012708-1 K16012422-1 M16012701 Ol (%) 8·1 – 6·8 19·3 14·2 5·9 6·9 Pl 14·8 20·6 – 33·7 55·1 29·6 – Sa/Ano† – – 0/60·6 – – 52·5/0 44·6/36·2 Aug/Aeg* 33·2 21 3 59·7 14·5 1/4·8 3·2 Krs 35·8 36·2 17·7 – – – 8·3 Mt/Ilm‡ 6·2/1 10·4 3·1 11/0·4 5/8·2 5·3 <0·1/0·8 Ap† 0·9 2·3 1·6 0·8 3·1 0·9 – Ne – 9·6 7·1 – – – – Contaminant – – – −24·9 – – – F.C. (%) 45·5 27·7 64·3 38·6 39·8 64·9 89·7 SSE 0·002 0·102 0·048 0·101 0·035 0·048 0·000 R2 1·000 1·000 1·000 1·000 1·000 1·000 1·000 F.C., amount of crystallization from the parent melt; SEE, sum of squared errors; Ano, anorthoclase; Aug, augite; Aeg, aegirine–augite; Ap, apatite. Details on the calculation are presented in Supplementary Data C. * Aegirine–augite and apatite compositions adopted from previous mineral data in Kyle (1986). † Anorthoclase composition adopted from Kelly et al. (2008) where anorthoclase phenocryst compositions in Erebus volcanic bombs are reported. ‡ Numbers without slash (/) denotes 0% involvement of aegirine-augite or ilmenite. Fig. 9 View largeDownload slide Magmatic differentiation trends for the potassic (blue symbols) and sodic (yellow symbols) lineages. Calculated model trends (see the key in (d)) are based on assimilation and fractional crystallization mass-balance calculations using the OPTIMASBA Microsoft Excel workbook (Cabero et al., 2012). Modelled sodic trends of S1 and S2, potassic trends P1, P2, and P3, and trachyte–phonolite trend P4 are annotated in (a). Refer to text for details of each trend. Fig. 9 View largeDownload slide Magmatic differentiation trends for the potassic (blue symbols) and sodic (yellow symbols) lineages. Calculated model trends (see the key in (d)) are based on assimilation and fractional crystallization mass-balance calculations using the OPTIMASBA Microsoft Excel workbook (Cabero et al., 2012). Modelled sodic trends of S1 and S2, potassic trends P1, P2, and P3, and trachyte–phonolite trend P4 are annotated in (a). Refer to text for details of each trend. The results of the mass balance model are consistent with petrography, showing that the compositional variation of the sodic lineage is mainly controlled by clinopyroxene and kaersutite fractionation. The removal of about 45 wt % of crystalline solid with the assemblage olivine (8, i.e. 8% of the crystalline solid), clinopyroxene (33), kaersutite (36), plagioclase (15), Fe–Ti oxides (7), and apatite (1) can explain the trend from hawaiite (K16012708-4, MgO = 7·3 wt %) to phonotephrite (K16012713-2, MgO = 3·0 wt %) (trend S1 in Fig. 9). Although kaersutite is one of two alkali-rich phases together with plagioclase, fractionation of kaersutite suppresses the fractionation of olivine and plagioclase, which results in the alkali-rich nature of the sodic lineage. The compositional variation from phonotephrite (K16012713-2, SiO2=51·2 wt %) to tephriphonolite (K16012713-1, SiO2=55·1 wt %) in the sodic lineage (trend S2, Fig. 9) can be produced by 28 wt % fractionation of kaersutite (36), clinopyroxene (21), plagioclase (21), Fe–Ti oxides (10), nepheline (10), and apatite (2). The result agrees with the petrography, which confirms that kaersutite is the dominant fractionating phase in the intermediate sodic lineage. On the other hand, the petrography suggests that fractionation of the potassic lineage is dominated by olivine and clinopyroxene in the early stage and plagioclase in the later stage. The mass balance model suggests that the evolution from a parental hawaiite (J14120503-2, MgO = 8·3 wt %) to a mugearite (J14120106-1, MgO = 3·4 wt %) is best explained by 48 wt % fractionation with the mineral assemblage (wt %) of olivine (15), clinopyroxene (48), plagioclase (27), Fe–Ti oxides (9), and apatite (1), combined with crustal assimilation to varying degrees from 9 to 17 wt %, depending on the contaminant used for the model (trend P1, Fig. 9). The extensive fractionation of clinopyroxene is consistent with its high abundance in hawaiite and mugearite. Although MgO-rich (>5 wt %) lava samples lack Fe–Ti oxide microphenocrysts, later involvement of significant oxide fractionation is supported by abundant oxide phenocrysts in the mugearite. The crustal contamination effectively lowers the Na, K, and Al contents in the magma, resulting in the potassic nature of these rocks (i.e. mugearite). Details on the effect of crustal assimilation are discussed below. Fractional crystallization from mugearite (J14120106-1, SiO2=52·8 wt %) to trachyte (K16012708-1, SiO2= 59·2 wt %) can be modelled by ∼40 wt % fractionation of olivine (14), clinopyroxene (14), plagioclase (55), Fe–Ti oxides (13), and apatite (3), without assimilation of crustal material (trend P2, Fig. 9). The abundant (>50%) plagioclase and increased amounts of Fe–Ti oxide phenocrysts in the mugearite and benmoreite samples are consistent with this model. The differentiation from trachyte sample K16012707-1 (SiO2=60 wt %) to a highly-evolved trachytic sample (K16012422-1, SiO2=64 wt %) is also calculated (Table 5; Fig. 9). Aegirine was included in the model following Kyle (1986). The result suggests that the differentiation can be attributed to 57 wt % fractionation of sanidine (52), plagioclase (30), hedenbergite and aegirine (6), olivine (6), magnetite (5), and apatite (1) (trend P3, Fig. 9). Because most feldspar in the trachyte is sanidine, which is absent in the less evolved lava suites, the gradual change of fractionating feldspar from sodic plagioclase into sanidine during the formation of the trachytic melt is expected. The strong fractionation of feldspar causes the decrease in Al2O3, and the negative anomalies of Ba, Sr, and Eu in the primitive mantle-normalized trace element patterns of the highly-evolved trachyte samples (Fig. 6e). In summary, the mass balance models show kaersutite and clinopyroxene are strongly fractionated in the sodic lineage with relatively minor plagioclase fractionation, whereas strong plagioclase and prolonged olivine fractionation without any kaersutite drove the evolution of the potassic lineage. This difference caused the sharp increase of the K2O/Na2O ratio in the potassic lineage due to the low K2O/Na2O ratio of plagioclase (Fig. 3b). Additionally, slight elevation of MgO, TiO2, and FeOt in the intermediate potassic lavas compared to the sodic ones can be ascribed to their incompatible nature in plagioclase. These are consistent with the variation of trace element abundances. The Sr contents in the potassic lineage sharply decrease during magma differentiation, whereas the sodic lineage retains high Sr concentrations (>800 ppm) (Fig. 5d). The fast depletion of Sc, V, and Co in the sodic lineage can be accounted for by strong fractionation of kaersutite and clinopyroxene, and suppression of plagioclase fractionation, because these transitional metals are compatible in kaersutite and clinopyroxene (Villemant et al., 1981; Tiepolo et al., 2007). Experimental studies have shown that high H2O concentration is one of the major factors controlling kaersutite fractionation, and suppressing plagioclase crystallization in mafic to intermediate suites (e.g. Nekvasil et al., 2004; Caricchi et al., 2006; Iacovino et al., 2016). Also, calculations based on the mineral modal proportions in the Chaîne des Puys (French Massif Central) trachyte suggests that at least 1·5 wt % of water is required for parental alkalic basaltic magma to fractionate kaersutite (Martel et al., 2013). At Mt. Erebus, about 1 wt % difference in H2O contents is enough to result in contrasting fractionation trends with and without kaersutite (Oppenheimer et al., 2011; Rasmussen et al., 2017). Phonolite lavas Three phonolite samples (M16012701, K16012425, and K16012415) have elevated Al2O3 contents (≥18 wt %) and are distinct from the decreasing Al2O3 trend from benmoreite to trachyte compositions (Fig. 4b). It has been suggested that phonolite can be formed by fractional crystallization of strongly alkalic melts (Kyle et al., 1992; Panter et al., 1997; Thompson et al., 2001; Bryan et al., 2002; Martin et al., 2010; Jung et al., 2013) or by fractionation from trachyte (White et al., 2012; AckermAn et al., 2015). Because of the similar petrology of the sodic lineage and the basanite–phonolite DVDP trend in Ross Island, it would seem that the phonolite is derived from the sodic lineage. However, a compositional gap between tephriphonolite samples, elevated K2O contents, and isotopic compositions similar to the evolved potassic samples, imply that the phonolite lavas are derived from the potassic lineage. According to our mass-balance calculation, the phonolite composition can be produced by fractional crystallization from both tephriphonolite and trachyte. If the starting composition was tephriphonolite (K16012713-1, SiO2=56 wt %), ∼ 64 wt % fractionation of anorthoclase (61), kaersutite (18), clinopyroxene (3), nepheline (7), magnetite (3), and apatite (2) can produce a composition similar to phonolite sample (M16012701). On the other hand, 90 wt % fractionation of anorthoclase (36), sanidine (45), clinopyroxene (3), kaersutite (8), olivine (7), and oxides (1) from the trachytic melt (K16012707-1, SiO2=60 wt %), can explain the composition of phonolite sample K16012415 (P4 trend in Fig. 9). In both cases, the compositions of plagioclase in the tephriphonolite and benmoreite lavas are too calcic and thus the anorthoclase composition was adopted from Kelly et al. (2008). If the calculation from tephriphonolite to phonolite is correct, the basanite–phonolite trend does not require any crustal contamination. However, the phonolite is isotopically enriched (K16012425, 87Sr/86Sr = 0·70397, 143Nd/144Nd = 0·512813), and addition of a crustal composition as a contaminant in the calculation produces an erroneous result. Also, the calculation is not compatible with sanidine fractionation, which is one of the major phases in the phonolite samples. On the other hand, we found two trachyte samples (M16012710 and M16012714-2) which contain kaersutite pseudomorphs, and these samples show transitional whole-rock compositions between benmoreite and phonolite. The degree of silica-undersaturation in the potassic lineage continuously falls from 5–10 wt % normative nepheline (ne) in hawaiites to zero in trachyte, but these two trachyte samples (ne = 3·6–4·7 wt %) show increasing trends toward highly silica-undersaturated (ne > 10 wt %) phonolite samples. The compositions of these ‘transitional’ samples match the trachyte–phonolite fractionation modeling trend (Fig. 9). Thus, the phonolite lavas are derivatives of the potassic lineage, aided by late fractionation of kaersutite. Ackerman et al. (2015) and White et al. (2012) also suggested large amounts, 70–80% and >90% respectively, of amphibole-included fractionating mineral assemblages from trachyte to phonolite, which is broadly similar to our values. CRUSTAL ASSIMILATION The fractionation mass-balance model and isotopic data show that the potassic basaltic magmas need crustal assimilation to produce intermediate magmas. Considering that the main fractionating phases lack Na and K, even in the case of plagioclase (An80–60, Na2O+K2O <5 wt %), the addition of crustal material in the potassic lineage is needed to balance the relatively high alkali contents resulting from differentiation. Conversely, without crustal assimilation, the potassic lineage would follow a trend similar to the sodic lineage, which is the case in other volcanic systems such as Mt. Erebus (Kyle et al., 1992) and Tenerife (Ablay et al., 1998). Wilson et al. (1995) suggested that the assimilation process can help exaggerate the compositional variations in basaltic to intermediate magmas, and Schneider et al. (2016) also stressed that the assimilation could significantly elevate the degree of silica-saturation in alkalic magmas. The trace element ratios and Sr–Nd–Pb isotope data from The Pleiades support the addition of crustal materials to the potassic magmas. The Sr concentrations in the potassic lavas decrease below 800 ppm once the SiO2 content exceeds 50 wt %; similar discontinuities can be found in the trends of Ba, Nb, Eu, and other REE (Fig. 5). The Ce/Pb (9·4–29·5) and Nb/U (13·3–49·9) ratios of the evolved potassic lavas also become much lower than those of the mafic lavas (Ce/Pb = 30–41; Nb/U = 36·3–54·8; Fig. 10), converging toward the average ratios in the crustal materials (Ce/Pb = 3–5·1; Nb/U = 4·4–25; Hacker et al., 2015). Fig. 10 View largeDownload slide Ce/Pb vs Nb/U for The Pleiades volcanic rocks and the analysed basement rocks. The light green bars denote the ratios of oceanic basalts (Hofmann, 1986). The grey square denotes the recommended lower continental crust from Rudnick & Gao (2003). Fig. 10 View largeDownload slide Ce/Pb vs Nb/U for The Pleiades volcanic rocks and the analysed basement rocks. The light green bars denote the ratios of oceanic basalts (Hofmann, 1986). The grey square denotes the recommended lower continental crust from Rudnick & Gao (2003). The addition of crustal materials into the potassic magmas is shown in the Sr–Nd–Pb isotope data. The radiogenic signature of 87Sr/86Sr (>0·70375) and decreased 143Nd/144Nd (<0·51282) in the potassic intermediate lavas are significantly different from the most mafic lavas (Fig. 7a and b;87Sr/86Sr <0·70344 and 143Nd/144Nd >0·51287). The Pb isotopic ratios of the evolved potassic lavas (206Pb/204Pb ≤19·5; 208Pb/204Pb ≤39·4) are also shifted toward the lower ratios from the basement. The isotopic ratios of trachyte and phonolite overlap with those of the intermediate lavas, implying that little additional assimilation is required for the felsic suites. This trend is consistent with the mass balance calculation above. To constrain the crustal contaminants and the degree of assimilation, several possible candidates were examined. Although the xenoliths in The Pleiades are of granodiorite, the majority of the 143Nd/144Nd ratios of the evolved potassic lavas are below the mixing trend between the mafic lavas and the granodiorite xenoliths (Fig. 7b). The mixing of the GHIC sample is also inconsistent, because its high Sr content (353 ppm) compared to Rb (55 ppm) produces a concave-up mixing line (Fig. 7a and b). On the other hand, the mixing lines with granulite or migmatite overlap with most of the isotopic ratios of the evolved lavas. There are some samples whose isotopic ratios are close to the upper crust mixing lines (K16012708-4, K16012425), implying contamination with upper crust material to some extent. Nevertheless, given that the estimated equilibration pressure (5–12 kbar) indicates lower to middle-crustal depths (> 20 km), assimilation of granulite or migmatite is more plausible than of typical upper crustal granitoids. The amount of crustal material required depends on the bulk-rock composition and isotopic ratios of the candidate crustal rock. The mass balance calculation suggests the composition of intermediate lavas are compatible with the assimilation of 10 wt % migmatite or 9–14 wt % of granulite. The mafic granulite (12B22, SiO2=49 wt %; Talarico et al., 1995) can be ruled out because an unrealistic amount (∼ 24 wt %) of assimilation is required. The predicted amount of crustal materials from the isotope data (5–10%) is slightly lower than that from the mass-balance calculation using major element data (9·6–13·8 wt %). The estimation using the retrogressed felsic granulite (13B29) show the best consistency between the mass balance calculation based on major elements (9·6 wt %) and isotopic ratios (∼10 wt %). The migmatite in the Wilson Terrane can also explain the isotopic ratios and major element variations, but the depth at which the migmatite is stable (<6 kbar) is much shallower (Palmeri, 1997) than the lower crust; and thus the ‘deep-sited migmatite’ would be granulitic after all. Accordingly, roughly 10 wt % assimilation of pelitic granulite best explains the radiogenic isotopic compositions of the evolved lavas of The Pleiades. The lithology of the lower crust beneath The Pleiades is unknown. Although it can include a variety of rock types, its composition is usually considered to be mafic to intermediate (Hacker et al., 2015). The accretion models for the Ross Orogeny (e.g. Flöttmann & Kleinschmidt, 1991; Federico et al., 2006; Rocchi et al., 2011) depict a (south) westward-dipping paleo-subduction zone and accordingly southwestward-dipping or sub-vertical terrane boundaries. Therefore, the assimilated lower crust beneath The Pleiades could be the underlying pelitic to psammitic fragments of the Bowers Terrane. The inconsistency in the required amount of assimilants between the mass-balance calculation using major element data and isotopic ratios, together with the uncertain nature of the lower crust lithology, suggests that another more suitable endmember may exist beneath The Pleiades. SOURCES OF THE PRIMITIVE MAGMAS The petrography and geochemistry data have shown that the volcanic suites in The Pleiades can be divided into two lineages. The two magma evolution trends can be ascribed to distinctive fractionation and crustal assimilation processes between the two lineages. However, the systematic differences in petrology between basanite and hawaiite suggest that the difference of the two lineages, especially of the hydrous and anhydrous characteristics of the sodic and potassic lineages, respectively, may have been inherited from their mantle sources. The input of dry lower crust material may have enhanced dehydration of the potassic lineage, but the difference in the crystallizing mineral assemblages between the two lineages precedes the assimilation process in the differentiation trends. The similar temporal and spatial distribution and the pressure–temperature path between two lineages suggest that a selective increase in the partial pressure of H2O in the sodic magmas during ascent is also unlikely. In this section, we discuss possible mantle sources and partial melting processes beneath The Pleiades based on the compositions of basanite and hawaiite. The composition of an intraplate primitive magma is a function of its source composition, pressure and degree of partial melting (Wilson et al., 1995; Panter et al., 1997; Beier et al., 2008; Kolb et al., 2012; McGee et al., 2013, 2015; Pilet, 2015; Baasner et al., 2016). In various volcanic systems, several trace element ratios least affected by fractional crystallization have been used to trace source compositions from melt compositions (Hofmann, 2003). For instance, Hofmann et al. (1986) suggested constant ratios of Nb/U (∼47) and Ce/Pb (∼25) in OIB and mid-ocean ridge basalts (MORB). The mafic lavas from both lineages in The Pleiades share similar ranges of Nb/U (36·3–55·7), Ce/Pb (21·5–47·4), and Nd/Pb (9·5–20·5) (Fig. 10). Also, only a minor difference can be found between the primitive mantle normalized trace element patterns of the two lineages (Fig. 6). This compositional similarity between the mafic lavas from each lineage implies that they share a similar source. The differentiation of The Pleiades volcanic lineages begins at the silica-poor (SiO2 <45%) basanite and hawaiite. Because the phenocrysts in the most SiO2 deficient sample (SiO2=44·9 wt %) of the sodic lineage are mainly clinopyroxene and kaersutite, the parental magma of the sodic lineage should have more MgO and less SiO2 than the most mafic sodic samples. Partial melting experiments on dry garnet lherzolite suggest that the major and trace element compositions of silica-poor OIB magmas requires either a non-peridotitic source lithology or addition of volatiles, or both (Davis et al., 2011; Davis & Hirschmann, 2013). It has been suggested that subducted eclogite and pyroxenite could reside in the asthenosphere based on the mineral compositions of various volcanic suites (Hauri, 1996; Sobolev et al., 2005; Prytulak & Elliott, 2007; Herzberg, 2011), experiments (Irving, 1974; Ito & Kennedy, 1974; Hirschmann et al., 2003; Kogiso, 2004) and isotopic data (Chase, 1981; Hofmann & White, 1982; Kokfelt, 2006). Recent studies of mantle xenoliths have suggested that eclogite in the lithospheric mantle is one of the source components of the Cenozoic magmatism around Victoria Land (Di Vincenzo et al., 1997; Melchiorre et al., 2011; Martin et al., 2015). Alternatively, the occurrence of amphibole- and/or mica-bearing metasomatized mantle rocks has also been recognized (O’Reilly & Griffin, 1988; Haggerty, 1995) and has led to the idea that presence of those minerals in the lithosphere may result in the alkali-enriched nature of the alkalic magmatism (Kushiro et al., 1967; Varne, 1968; Lloyd & Bailey, 1975; Sun & Hanson, 1975; Pilet et al., 2008, 2011; Davis & Hirschmann, 2013). It is also notable that not all basanite–phonolite alkali-rich trends are hydrous, as in the case of the dry lineages from Mt. Morning and Mt. Erebus (Kyle et al., 1992; Martin et al. 2010). For instance, Martin et al. (2013) showed that the amphibole-free Riviera Ridge Lineage at Mt. Morning was derived from a nominally anhydrous mantle domain. Conversely, the amphibole-bearing basanite suites from volcanic fields in Madagascar and Germany were inferred to originate from lithospheric mantle containing hydrous minerals (Melluso et al., 2007; Kolb et al., 2012; Jung et al., 2013; Melluso et al., 2018). These observations imply that the mantle source beneath The Pleiades contains hydrous minerals. The mafic lavas of both lineages of The Pleiades show negative K and positive Nb anomalies in primitive mantle-normalized trace element patterns (Fig. 6). The negative K anomaly suggests the presence of a K-rich residual phase in the melting region. The effect of K-rich mineral fractionation should be negligible because of their mafic nature (MgO >8 wt %) and lack of K-rich phenocrysts in the potassic lavas. Phlogopite and amphibole can be stable at upper mantle conditions (Kushiro et al., 1967; Sato et al., 1997; Sudo & Tatsumi, 1990; Greenough, 1988). The positive Nb and the negative Pb anomalies in the trace element patterns of the mafic lavas are also consistent with the expected melt composition derived from an amphibole-bearing source (Pilet et al., 2011). It has been suggested that absence of Ba fractionation from La in the mafic lavas indicates that amphibole, rather than phlogopite, is the dominant phase in the source (e.g. Jung & Hoernes, 2000; Schubert et al., 2015). Amphibole- or phlogopite-bearing metasomatized mantle xenoliths has been reported from around Victoria Land (Hornig & Wörner, 1991; Zipfel & Wörner, 1992; Perinelli et al., 2006, 2011; Martin et al. 2014, 2015). The stability of amphibole in the upper mantle depends on temperature, pressure, and volatile content. Pargasitic amphibole can be stable at ∼3 GPa or less at a maximum temperature of ∼1100°C (Dai et al., 2014; Mandler & Grove, 2016). This pressure range broadly matches with the upper level of the low-velocity anomaly beneath the TAM (roughly 60–160 km; Graw et al., 2016) which is interpreted as the partial melting zone (Lawrence et al., 2006; Brenn et al., 2017). The thickness of the lithosphere beneath the TAM is not well constrained, but ten Brink et al. (1997) suggested that the elastic thickness of the plate around the TAM is ∼ 85 ± 15 km. An et al. (2015) suggested 1300–1400°C for the basal (∼80 km) temperature of the lithosphere beneath the TAM and that an abnormally high temperature (>1150°C) reaches up to near the Moho boundary. This temperature range for the lithospheric mantle beneath the TAM matches with experiments and Monte Carlo simulated conditions for partial melting of amphibole metasomes (1150–1400°C) ( Pilet et al., 2008, 2011). These observations then support the presence of an amphibole- and/or phlogopite-bearing metasomatized lithospheric mantle source beneath The Pleiades. The elevated 206Pb/204Pb (>19·5) and low 143Nd/144Nd (<0·51290), together with the negative Pb and positive Nb anomalies and the enrichment of incompatible elements, suggest that the isotopic signature of The Pleiades mantle source can be described as a HIMU component mixed with enriched and depleted sources or, alternatively, as a near-FOZO source ( Finn et al., 2005; Sims et al., 2008; Aviado et al., 2015; Fig. 7d). The Pleiades isotopic data overlap with data for Cenozoic volcanic rocks around the Ross Sea, which extend from the HIMU-like Zealandia basalts to the less radiogenic Ross seafloor basalts (Panter et al., 2006, 2018; Timm et al., 2010; Scott et al., 2013; van der Meer et al., 2017). This isotopic signature with a HIMU-affinity is widespread throughout the WARS, Zealandia, and eastern part of the Indo-Australian plate, referred to the as a diffuse alkalic magma province (DAMP; Finn et al., 2005). Because the underlying continental blocks of the DAMP were contiguous before 100 Ma as a part of the margin of Gondwana, their unique compositional variations have been considered to be, at least partly, derived from the common metasomatism of the lithospheric mantle (Coombs et al., 1986; Panter et al., 2000, 2006; Finn et al., 2005; Hoernle et al., 2006; McCoy-West et al., 2010; Timm et al., 2010; Martin et al., 2013; Aviado et al., 2015; Scott et al., 2016; van der Meer et al., 2017). The details of the causes of this metasomatism and the source of the isotopic signatures are still controversial. Various hypotheses include a fossil mantle plume (Lanyon et al., 1993; Weaver et al., 1994; Rocholl et al., 1995; Hart et al., 1997), subduction-related fluids and melts (Panter et al., 2006; Sprung et al., 2007), mantle upwelling due to the detachment of a subducted slab (Finn et al., 2005) and foundering of the lithospheric mantle (Timm et al., 2010; Shen et al., 2018). Because carbonate can have a high [U+Th]/Pb ratio and high Nb concentrations, recycled carbonate and CO2-rich melt/carbonatite metasomatized mantle have recently been suggested to be potential intraplate HIMU-like source (Pfänder et al., 2012; Castillo, 2015; McCoy-West et al., 2016). Considering that a carbonatite metasomatic signature in the lithospheric mantle has also been found in the WARS (Martin et al., 2013) and Zealandia (Scott et al., 2014; McCoy-West et al., 2015) and that The Pleiades also show the positive Nb anomaly and the HIMU-like Pb isotopic ratios, The Pleiades magmas may have similar source characteristics and partial melting processes to the DAMP. PARTIAL MELTING OF THE SOURCE The formation of and partial melting processes in metasomatized lithospheric mantle have been proposed by a number of authors (e.g. Pilet et al., 2008; Rooney et al., 2014; Pilet, 2015). These authors suggested that previous or contemporary melt percolation and differentiation in the lithospheric mantle forms pyroxene- to amphibole/phlogopite-rich metasomatic veins. Partial melting of these metasomes, with and without interaction with the surrounding peridotite, can produce variably SiO2-poor alkalic magmas. Also, Pilet et al. (2008) showed that the variable degrees of interaction between silica-deficient melts and their surrounding peridotite can explain the compositional variations among nephelinite to alkali–basalt melts. If the petrogenesis of the parental basaltic magmas at The Pleiades follows this scenario of partial melting of metasomatized lithospheric mantle, the potassic lineage might have resulted from more interaction with the surrounding dry peridotite than the sodic lineage. The lower contents of Al2O3, TiO2, K2O, and Rb and higher ratios of Zr/Nb (>2·6) in the mafic potassic magmas compared to the sodic ones (Figs 4, 5 and 11b) are consistent with a higher degree of assimilation of the surrounding peridotite (Pilet et al., 2008). Additionally, Panter et al. (2018) recently suggested that the systematic variation of the Nb/Y ratio and decrease of the normative nepheline and leucite in the basaltic lavas from the Adare Trough and the Hallett Volcanic Province can be attributed to differences in the degree of involvement of the amphibole-rich metasomes during partial melting in the lithospheric mantle. Indeed, the mafic lavas of the sodic lineage have more normative nepheline and leucite and higher Nb/Y ratios than those of the potassic lineage (Fig. 11a). Considering that the potassic lavas comprise most of The Pleiades lavas, we suggest the more extensive melting of the metasomatized lithosphere has reacted with the surrounding peridotite and produced the potassic magmas, whereas the sodic lineage has been derived from smaller degrees of partial melting of the metasomes. Fig. 11 View largeDownload slide (a) CIPW normative nepheline+leucite vs Nb/Y and (b) Ce/Yb vs Zr/Nb for The Pleiades volcanic rocks. The basalt compositions from the northwest Ross Sea (Panter et al., 2018) and the melting experiments (Pilet et al., 2008) are also potted. The normative nepheline and leucite contents of The Pleiades volcanic rocks and comparative data were calculated based on the assumption that Fe3+/Fetot. is 0·2. Fig. 11 View largeDownload slide (a) CIPW normative nepheline+leucite vs Nb/Y and (b) Ce/Yb vs Zr/Nb for The Pleiades volcanic rocks. The basalt compositions from the northwest Ross Sea (Panter et al., 2018) and the melting experiments (Pilet et al., 2008) are also potted. The normative nepheline and leucite contents of The Pleiades volcanic rocks and comparative data were calculated based on the assumption that Fe3+/Fetot. is 0·2. Heat flux provided by lateral mantle flow, possibly due to mantle upwelling associated with the WARS or lithospheric foundering beneath the TAM, was suggested to trigger the partial melting of metasomes beneath Victoria Land (Nardini et al., 2009; Panter et al., 2018; Shen et al., 2018). The elevated temperature under the lithosphere has produced minor volcanic cones around NVL, which are mostly basanite in composition (Kyle, 1990b). Transtensional re-activation of preexisting faults may have enhanced the local thermal anomaly beneath NVL, and produced more voluminous, less silica-undersaturated magmas (Vignaroli et al., 2015). The Pleiades may represent both cases, the former corresponds to the sodic lineage and the latter to the potassic lineage. Similar trends are also observed in other major volcanic fields around NVL. The Melbourne Volcanic Field is mainly composed of hawaiite–trachyte lavas with peripherally occurring minor amphibole-bearing basanite and tephrite (Kyle, 1990b; Giordano et al., 2012). Two lineages similar to The Pleiades have also been reported from Mt. Overlord (Kyle, 1990b). Our partial melting model for The Pleiades thus emphasizes the significance of mantle source control on the primitive magma compositions of the NVL volcanoes, or possibly of the intra-continental alkalic magmatism in general. CONCLUSIONS The petrological, geochemical and Sr–Nd–Pb isotope dataset from this study provides new insights for the sodic and potassic differentiation lineages at The Pleiades volcanic complex of NVL. The two lineages overlap spatially and temporally. The petrography, geochemistry and the mass-balance calculations show that the potassic lineage can be modelled by the fractionation of anhydrous mineral phases: olivine, clinopyroxene, plagioclase, Fe–Ti oxides with minor apatite. The Sr–Nd–Pb isotopic ratios suggest that the intermediate potassic magma assimilated lower crustal granulite and migmatite. The phonolite and trachyte lavas are the final products of the strong fractional crystallization of the potassic lineage. The crystallizing mineral assemblage of mainly plagioclase and olivine in the potassic lineage points to the anhydrous nature of this lineage. On the other hand, the sodic magma is hydrous, supported by the constant fractionation of kaersutite and the absence of olivine in the intermediate lavas. The pressure and temperature estimations using pyroxene thermobarometry suggest that the mafic to intermediate magmas of both lineages shared similar mama ascent paths, and mostly resided in the lower crust. The HIMU-like signatures and the positive Nb and negative K anomalies in the mafic lavas argue for an amphibole-rich, metasomatized lithospheric mantle source beneath The Pleiades, which is consistent with the young HIMU-like alkalic volcanism in Zealandia and Antarctica. The compositions of the mafic lavas from the sodic lineage have more affinity towards previously reported hornblendite melt compositions than the potassic lavas. This compositional difference implies that the melts derived from the melting of the metasomes in NVL lithosphere experienced a higher degree of interaction with the surrounding dry peridotite compared to the relatively minor sodic melts. The stronger involvements of the dry peridotite in partial melting also led to the drier nature of the potassic magmas compared to the sodic ones. This study shows that diverse magma differentiation lineages can be produced even if the lineages are spatially (kilometre-scale) and temporally (<1 Ma) indistinguishable within a single intracontinental volcanic complex. The initial difference in the water content of the source which resulted in the two lineages can be enhanced by assimilation of crustal materials. Our data suggest that the HIMU-like magmas in The Pleiades have been sourced from metasomatized lithospheric mantle beneath NVL. Acknowledgements We thank the KOPRI and USAP G081 team members for the assistance during field work. We are grateful to Jin Hong Kim, David Parmelee, Anne Foster, and Young-Min Kim for help with sample collection and field safety, and to Seunghee Han, Seung-Ah Ha, and Jongmin Baek, who run the ICP-MS and TIMS facilities in KOPRI. Changkun Park, Jeongjin Moon, and Sun Young Park are thanked for supporting EPMA analyses. Yun Seok Yang is thanked for XRF analyses. 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TI - Evolution of Alkalic Magma Systems: Insight from Coeval Evolution of Sodic and Potassic Fractionation Lineages at The Pleiades Volcanic Complex, Antarctica
JO - Journal of Petrology
DO - 10.1093/petrology/egy108
DA - 2019-01-01
UR - https://www.deepdyve.com/lp/oxford-university-press/evolution-of-alkalic-magma-systems-insight-from-coeval-evolution-of-dMFNCO4s4a
SP - 117
VL - 60
IS - 1
DP - DeepDyve
ER -