The Kalkarindji Large Igneous Province, Australia: Petrogenesis of the Oldest and Most Compositionally Homogenous Province of the Phanerozoic

The Kalkarindji Large Igneous Province, Australia: Petrogenesis of the Oldest and Most... Abstract The Kalkarindji Large Igneous Province (LIP) is a Middle Cambrian (511 Ma) continental flood basalt (CFB) province located in northern and central–west Australia that has been linked to an extinction event at the Early–Middle Cambrian boundary. The extent of this LIP has been estimated at about 2·1 x 106 km2, with exposures in Western Australia, Northern Territory, Queensland and South Australia. Major and trace element datasets reveal geochemical characteristics typical for continental flood basalts (CFBs) including: tholeiitic affinity; an enrichment in incompatible elements, in particular, large-ion lithophile elements (LILE); enrichment of light rare earth elements (LREE) compared to heavy rare earth elements (HREE) relative to N-MORB; negative Nb and Ta anomalies in normalized extended element patterns. Here we present the first comprehensive geochemical investigation of the Kalkarindji CFB province. The Kalkarindji CFBs are geochemically homogeneous, low-Ti basaltic andesites, with a nearly complete lack of basalts as defined using a total-alkalis vs silica diagram. All of the rocks analysed for Sr, Nd, Pb isotopic ratios display enriched initial (t = 511 Ma) isotopic compositions (143Nd/144Ni = 0·511928–0·511981; 87Sr/86Sri = 0·70917–0·71029; 206Pb/204Pbi = 18·105–18·843; 207Pb/204Pbi = 15·726–15·805; 208Pb/204Pbi = 38·374–39·208). Crustal assimilation models are interpreted to suggest that the geochemical characteristics, as well as the homogenous composition across the entire province, cannot be explained by continental crust contamination. Therefore, the enriched isotopic ratios (particularly the extremely high 207Pb/204Pbi and elevated 208Pb/204Pbi for moderate 206Pb/204Pbi), coupled with relative depletions in Nb and Ta concentrations, indicate the involvement of an ancient enriched lithospheric-like component in the genesis of the Kalkarindji CFB. We propose a model in which the source region was affected by an enrichment event at around 2·5 Ga (possibly through the addition of subducted sediments). Decompression melting and mantle warming (focused by edge driven convection) allowed melting of the fertile mantle to generate the Kalkarindji CFB province at c. 511 Ma. INTRODUCTION Large igneous provinces (LIPs) are voluminous accumulations of magma emplaced during relatively short periods of time (Hofmann et al., 1997; Courtillot & Renne, 2003; Bryan & Ernst, 2008; Ernst, 2014). These magmatic provinces typically cover areas greater than 106 km2, with igneous volumes greater than 106 km3, and they are mainly characterized by basaltic magmatism. The emplacement of these provinces takes place in short magmatic pulses (Courtillot & Renne, 2003; Pirajno & Hoatson, 2012; Ernst, 2014) with about 75–80% of the total volume emplaced in about 1 Myr or less (Courtillot & Renne, 2003; Bryan & Ernst, 2008; Ernst, 2014). The origin of LIPs is controversial, with many different models proposed to account for the rapid generation of these large volumes of igneous material. Some hypotheses involve dynamic processes dominated by the upwelling of a deep-seated mantle plume (Campbell & Griffiths, 1990; Hill, 1991). In these models, continental flood basalts (CFBs) originate from the melting of a mantle plume head as it travels towards the surface. Active models propose that tectonic shifts such as rifting and continental breakup are due to the upwelling of these mantle plumes (e.g. Bronner et al., 2011). However, the observation that many CFBs are located around plate boundaries has provided the basis for alternative models with more passive mechanisms being proposed for the formation of CFBs. These include: processes related to plate tectonics (Foulger, 2007) in extensional environments such as continental rifting (White & McKenzie, 1989); mantle upwelling due to lateral thermal gradients around the edges of cratons known as edge-driven convection (Anderson et al., 1992; Anderson, 1994; King & Anderson, 1995); and plate delamination or thermal incubation occurring below supercontinents, which allows for the generation of LIPs ultimately leading to breakup (Gurnis, 1988; Coltice et al., 2007, 2009). More recently a model involving slab-triggered upwelling of wet mantle from a hydrous mantle transition zone has been proposed to account for the lack of pre-magmatic tectonic bulging of the lithosphere, the absence of ocean island basalt (OIB) geochemical signatures and the geochemical diversity found in many CFBs (Wang et al., 2016). A number of tholeiitic CFB suites has been recognized in much of the north and west–central parts of Australia (Glass & Phillips, 2006; Evins et al., 2009; Pirajno & Hoatson, 2012). The Kalkarindji province is composed of a large number of lithostratigraphic units: the Antrim Plateau Volcanics, Milliwindi Dolerite, Nutwood Downs, Helen Springs, Peaker Piker and Colless Volcanics (Glass & Phillips, 2006; Evins et al., 2009; Pirajno & Hoatson, 2012) (Fig. 1a). These scattered suites are exposed over about 425, 000 km2 (Bultitude, 1976; Veevers, 2001; Glass & Phillips, 2006; Evins et al., 2009; Marshall et al., 2016), distributed across northern and central portions of Western Australia, much of the Northern Territory, western Queensland, and western South Australia. The original extent of the Kalkarindji CFB province has been estimated to be at least 2·1 x 106 km2 making it one of the largest LIPs in the Phanerozoic (Evins et al., 2009). Kalkarindji is recognized as the oldest Phanerozoic LIP, with an age of c. 511 Ma, and it has been linked to the first significant extinction event of the Phanerozoic (Jourdan et al., 2014). Fig. 1. View largeDownload slide (a) Sketch map showing the distribution and constituent suites of the Kalkarindji continental flood basalt (CFB) province. Blue colors represent samples or well locations from the Antrim Plateau Volcanics; red colors represent samples or well locations from the Table Hill Volcanics. (b) Sketch map of the Kalkarindji CFB province. Proterozoic basins and orogens locally associated with the Kalkarindji province are also indicated. Paleozoic basins are labeled in italics. Modified and created after Jourdan et al. (2014), Hoatson et al. (2008), and Glass & Phillips (2006) with outcrop locations provided as ArcGIS shapefiles from the Geological Survey of Western Australia. Australian crustal elements from Shaw et al. (1995) and Pirajno & Bagas (2008). Fig. 15 schematic cross section locations marked with line A–A’. Fig. 1. View largeDownload slide (a) Sketch map showing the distribution and constituent suites of the Kalkarindji continental flood basalt (CFB) province. Blue colors represent samples or well locations from the Antrim Plateau Volcanics; red colors represent samples or well locations from the Table Hill Volcanics. (b) Sketch map of the Kalkarindji CFB province. Proterozoic basins and orogens locally associated with the Kalkarindji province are also indicated. Paleozoic basins are labeled in italics. Modified and created after Jourdan et al. (2014), Hoatson et al. (2008), and Glass & Phillips (2006) with outcrop locations provided as ArcGIS shapefiles from the Geological Survey of Western Australia. Australian crustal elements from Shaw et al. (1995) and Pirajno & Bagas (2008). Fig. 15 schematic cross section locations marked with line A–A’. Despite the considerable size of this province, the study of the geochemistry and origin of Kalkarindji is limited with very little discussion of the possible sources of this LIP and only a handful of data presented in published papers and survey reports (Bultitude, 1976; Mory & Beere, 1988; Grey et al., 2005; Glass & Phillips, 2006; Evins et al., 2009; Marshall et al., 2016). This study provides the first in depth look at the geochemical characteristics of the Kalkarindji CFB province based on a large data set including 182 new major and trace element analyses and 10 Sr, Nd, and Pb isotopic analyses of the various constituents of the Kalkarindji. This comprehensive data set enables detailed comparison between the related basaltic suites and is used to understand the possible magma source(s) and origin of this province. GEOLOGIC SETTING The Antrim Plateau Volcanics (Fig. 1a) comprise the largest areal exposures of the Kalkarindji CFB province. With a maximum thickness of 1500 m west of Halls Creek, the Antrim Plateau Volcanics make up the thickest section and they provide an indication of a possible location for the primary vents from which the magmas were erupted (Bultitude, 1976; Mory & Beere, 1988; Grey et al., 2005; Glass & Phillips, 2006; Evins et al., 2009; Marshall et al., 2016). The Antrim Plateau Volcanics are exposed along the eastern edge of the Kimberley Block and form the boundary between the eastern edges of the Victoria River Basin and the western Wiso Basin (Fig. 1b). These volcanics are made up primarily of basaltic lava flows, although they also contain minor breccias and agglomerates. Discontinuous quartz sandstones, siltstones, cherts, sedimentary breccias, and limestones are intercalated with the lavas and volcanic breccias (Bultitude, 1976; Marshall et al., 2016). Exposures of the Peaker Piker Volcanics, Colless Volcanics, and Helen Springs Volcanics are found on the eastern and northern margins of the Georgina Basin (Fig. 1b). The Nutwood Downs Volcanics are exposed along the margins of the Daly River Basin (Fig. 1b). These areas of the Kalkarindji CFB are exposed as small outcrops interbedded with sedimentary layers and are separated from the Antrim Plateau Volcanics by younger basin fill sediments (Bultitude, 1976; Grey et al., 2005; Glass & Phillips, 2006; Evins et al., 2009; Marshall et al., 2016). The maximum thicknesses of these outcrops are significantly less than that found in the Antrim Plateau Volcanics; 122 m for the Nutwood Downs Volcanics, 37 m for the Helen Springs Volcanics and the Peaker Piker Volcanics, and 61 m for the Colless Volcanics (Bultitude, 1976 and references therein). Data from borehole samples indicate that the volcanics extend below the younger sediments of the Daly River, Georgina, and Wiso Basins giving a stratigraphic connection between many of the outcrops in the north, east, and west (Bultitude, 1976). Due to this stratigraphic connection, and for simplicity in the discussion, all of these various suites will be referred to as the Antrim Plateau Volcanics. The Table Hill Volcanics Suite (herein referred to as the Table Hill Volcanics) is a series of tholeiitic basalt outcrops exposed along the northern borders of the Officer Basin. Note however that, despite its effusive denotation, it includes several dykes and sills that extend underneath much of the basin (Bultitude, 1976; Stevens & Apak, 1999; Grey et al., 2005; Glass & Phillips, 2006; Evins et al., 2009). On the basis of similar geochemical composition and ages, the Table Hill Volcanics within the Officer Basin have been linked to the Antrim Plateau Volcanics as part of the Kalkarindji province (Evins et al., 2009). A map of drill-holes that intersected the Kalkarindji CFB province throughout northern Australia was presented by Bultitude (1976). The intersections indicate that the volcanics become more fragmented and thin to the east and south away from the thick outcrops of the Antrim Plateau Volcanics (Fig. 1a). Based on several exploration well completion reports, there is no evidence for the presence of any Kalkarindji CFB related rocks within the Ngalia and Amadeus Basins of central Australia. This could be the result of a lack of geochronological data for intersected volcanics or structural barriers that prevented the province from extending into this region. The distribution of the Table Hill Volcanics also appears to be highly influenced by structural domains surrounding the basin as Kalkarindji CFBs are commonly discontinuous in spatially close drill-holes. The highest concentration of sills and dykes occurs within the Savory Basin with the exposures and intersections lessening toward the eastern boundaries of the Officer Basin and no known drill-hole intersections in South Australia (Fig. 1). The Antrim Plateau Volcanics were emplaced entirely within the North Australian Craton, whereas the Table Hill Volcanics occur primarily within the West Australian Craton, with exposures extending into the Musgrave Province between the West Australian and South Australian Cratons. The geochemistry (including isotopic compositions) of lamproite and kimberlite pipes (and associated xenoliths) found all through the Kimberley Block and Halls Creek Orogen, S-wave tomography of the surrounding regional lithosphere/asthenosphere, and diamond occurrences, indicate that the upper crust below the Kalkarindji province is underlain by an old thick lithospheric root (Jaques et al., 1990; Shaw et al., 1995; Myers et al., 1996; Graham et al., 1999; Sheppard et al., 1999; Betts et al., 2002; Luguet et al., 2009); in particular diamondiferous Archean peridotite xenoliths have been found (Jaques et al., 1990; Graham et al., 1999; Luguet et al., 2009) within the Kimberley Block. It has been proposed that tectonic activity along the Halls Creek Orogen was associated with a plate boundary between the Kimberley Block and the rest of the North Australian Craton (Jaques et al., 1990; Shaw et al., 1995; Myers et al., 1996; Graham et al., 1999; Sheppard et al., 1999; Betts et al., 2002; Luguet et al., 2009) indicating that the final joining of the Kimberley Block and the North Australian Craton occurred at around 1·85 Ga. The last major tectonic activity to occur in the western portion of the Australian continent before the Kalkarindji CFB event was orogenic activity within the Musgrave province before 1·2 Ga (Wade et al., 2008; Aitken & Betts, 2009; Smithies et al., 2015). PREVIOUS GEOCHRONOLOGICAL RESULTS 40Ar/39Ar plateau ages range from 509·0 ± 2·6 Ma to 511·9 ± 1·9 Ma for the Helen Springs Volcanics, Antrim Plateau Volcanics and the Table Hill Volcanics (data from Glass & Phillips, 2006 and Evins et al., 2009; recalculated to the decay constant of Renne et al., 2011). An 40Ar/39Ar analysis on a plagioclase separate from a Kalkarindji CFB dolerite from the Officer Basin gave a plateau age of 510 ± 4 Ma, twenty-eight baddeleyite crystals from mafic enclaves found in the Munro well produced a statistically concordant upper intercept of 511 ± 5 Ma, and chemical abrasion thermal ionization mass spectrometry (CA-TIMS) analyses on zircons from the coarse-grained Milliwindi Dolerite dike provide a weighted 238U/206Pb age of 510·7 ± 0·6 Ma (Jourdan et al., 2014). Collectively, these data constrain the age of the main emplacement pulse for Kalkarindji to c. 511 Ma (Middle–Lower Cambrian boundary), although the duration of the emplacement is still not well constrained (Jourdan et al., 2014). SAMPLE SELECTION Nine samples from the Antrim Plateau Volcanics selected for analysis exhibit a range in textures from porphyritic basalts to fine grained massive basalts collected from outcrops throughout the Antrim Plateau Volcanics region, as well as a number of cores drilled within the main Antrim Plateau Volcanics found on the boarder of Western Australia and the Northern Territory (Table 1). Twenty-three dolerite samples from sills and dykes of the Table Hill Volcanics were selected from the Geological Survey of Western Australia (GSWA) core library (Table 1). These 32 samples were combined with geochemical analyses of another 150 rock-chip and drill core samples from northern Australia and the Officer Basin (with a high abundance of samples concentrated within the Savory Basin) region provided as an Excel database by AusQuest Limited. Table 1: Major and trace element analyses of representative samples from the Kalkarindji CFB province a) Major and trace element analyses from the Kalkarindji CFB province, samples analysed for Sr, Nd, and Pb isotopes Type: Antrim Plateau Volcanics Suite Type: Table Hill Volcanics Suite Sample 052 (28) 109 (29) 111 (30) 112 (31) P04 (32) 07THD-001B_3 THD-008_8 09THD-029_12 09THD-028_16 07THD-002_19 Rock Type Basalt Basalt Basalt Basalt Basalt Dolerite Dolerite Dolerite Dolerite Dolerite Locations Kirrikimbie Spring Creek Spring Creek Spring Creek Bungle Bungle MN1 MN1 MN5 MN5 Boondawarri Zone 52 52 52 52 52 51 51 51 51 51 Easting 543 159 480 282 481 086 481 266 427 461 340 154 340 828 366 034 367 563 342 847 Northing 8 069 121 8 143 676 8 142 640 8 142 424 8 080 318 7 367 674 7 367 809 7 332 952 733 542 7 392 547 Major Elements (wt %): SiO2 53·37 52·91 55·02 53·56 53·62 53·76 53·7 54·06 53·91 53·40 Al2O3 13·82 13·93 13·05 14·02 13·65 15·08 13·73 14·39 13·21 16·42 Fe2O3 12·77 12·63 14·37 12·77 12·20 10·92 11·62 11·46 13·09 9·88 MgO 4·65 4·81 3·62 4·91 5·47 5·44 6·78 5·73 5·55 4·68 CaO 6·65 6·38 5·59 7·15 7·01 8·97 9·18 8·66 7·66 9·49 Na2O 3·38 3·59 3·07 3·39 3·07 2·27 2·18 2·41 2·36 2·35 K2O 2·12 2·98 2·26 1·9 1·95 1·17 1·23 1·4 1·45 1·46 TiO2 1·23 1·18 1·54 1·21 1·21 0·94 0·92 1·03 1·24 0·85 P2O5 0·141 0·135 0·172 0·137 0·154 0·114 0·105 0·126 0·15 0·11 MnO 0·18 0·2 0·36 0·17 0·13 0·170 0·200 0·180 0·20 0·17 H2O+/LOI 1·34 1·08 0·72 0·66 1·31 1·12 0·81 0·6 0·63 0·82 H2O- Total 99·65 99·83 99·77 99·88 99·77 99·95 100·46 100·05 99·45 99·63 Trace Elements (ppm): La 21·3 20·4 29·6 21·1 19·2 19·7 18·5 21·8 21·20 19·40 Ce 45 42·4 60·9 42·9 39·8 40·4 37·5 44·4 44·10 38·90 Pr 5·26 4·94 7·01 4·91 4·83 4·68 4·3 5·22 5·10 4·50 Nd 21·9 20·4 28·7 20·8 20·2 19 18·1 21·3 20·80 18·40 Sm 4·99 4·54 6·29 4·58 4·36 3·98 3·86 4·38 4·41 4·00 Eu 1·33 1·23 1·56 1·27 1·3 1·1 1·08 1·19 1·24 1·06 Gd 5·24 5·03 6·45 5·2 4·6 4·46 4·2 4·85 4·87 4·28 Tb 0·85 0·82 1·08 0·85 0·83 0·75 0·72 0·8 0·79 0·72 Dy 5·67 5·13 6·59 5·4 5·24 4·64 4·51 5·03 5·21 4·38 Ho 1·16 1·09 1·34 1·09 1·09 0·93 0·9 1·04 1·04 0·90 Er 3·46 3·2 4·02 3·29 3·07 2·7 2·52 3·03 3·00 2·56 Yb 3·19 3·04 3·72 2·99 2·89 2·62 2·45 2·72 2·85 2·46 Lu 0·51 0·47 0·57 0·44 0·45 0·39 0·4 0·39 0·45 0·43 Rb 69·5 63·1 89·3 62·9 61·1 49·9 54·1 60·8 56·70 66·40 Ba 276 303·6 266 202·8 277·2 243·6 216·4 241·8 231·30 259·30 Th 9·28 8·22 13·32 8·51 7·05 8·25 7·37 8·9 8·55 8·00 U 1·55 1·33 2·28 1·4 1·17 1·67 1·42 1·7 1·66 1·61 Nb 8·1 7·3 10·1 7·4 6·8 6·9 6·2 7·3 7·30 6·40 K 18104·8 25320·6 19178·1 16077·2 16619·3 9916·8 10345·1 11799·3 12 317 12 348 a) Major and trace element analyses from the Kalkarindji CFB province, samples analysed for Sr, Nd, and Pb isotopes Type: Antrim Plateau Volcanics Suite Type: Table Hill Volcanics Suite Sample 052 (28) 109 (29) 111 (30) 112 (31) P04 (32) 07THD-001B_3 THD-008_8 09THD-029_12 09THD-028_16 07THD-002_19 Rock Type Basalt Basalt Basalt Basalt Basalt Dolerite Dolerite Dolerite Dolerite Dolerite Locations Kirrikimbie Spring Creek Spring Creek Spring Creek Bungle Bungle MN1 MN1 MN5 MN5 Boondawarri Zone 52 52 52 52 52 51 51 51 51 51 Easting 543 159 480 282 481 086 481 266 427 461 340 154 340 828 366 034 367 563 342 847 Northing 8 069 121 8 143 676 8 142 640 8 142 424 8 080 318 7 367 674 7 367 809 7 332 952 733 542 7 392 547 Major Elements (wt %): SiO2 53·37 52·91 55·02 53·56 53·62 53·76 53·7 54·06 53·91 53·40 Al2O3 13·82 13·93 13·05 14·02 13·65 15·08 13·73 14·39 13·21 16·42 Fe2O3 12·77 12·63 14·37 12·77 12·20 10·92 11·62 11·46 13·09 9·88 MgO 4·65 4·81 3·62 4·91 5·47 5·44 6·78 5·73 5·55 4·68 CaO 6·65 6·38 5·59 7·15 7·01 8·97 9·18 8·66 7·66 9·49 Na2O 3·38 3·59 3·07 3·39 3·07 2·27 2·18 2·41 2·36 2·35 K2O 2·12 2·98 2·26 1·9 1·95 1·17 1·23 1·4 1·45 1·46 TiO2 1·23 1·18 1·54 1·21 1·21 0·94 0·92 1·03 1·24 0·85 P2O5 0·141 0·135 0·172 0·137 0·154 0·114 0·105 0·126 0·15 0·11 MnO 0·18 0·2 0·36 0·17 0·13 0·170 0·200 0·180 0·20 0·17 H2O+/LOI 1·34 1·08 0·72 0·66 1·31 1·12 0·81 0·6 0·63 0·82 H2O- Total 99·65 99·83 99·77 99·88 99·77 99·95 100·46 100·05 99·45 99·63 Trace Elements (ppm): La 21·3 20·4 29·6 21·1 19·2 19·7 18·5 21·8 21·20 19·40 Ce 45 42·4 60·9 42·9 39·8 40·4 37·5 44·4 44·10 38·90 Pr 5·26 4·94 7·01 4·91 4·83 4·68 4·3 5·22 5·10 4·50 Nd 21·9 20·4 28·7 20·8 20·2 19 18·1 21·3 20·80 18·40 Sm 4·99 4·54 6·29 4·58 4·36 3·98 3·86 4·38 4·41 4·00 Eu 1·33 1·23 1·56 1·27 1·3 1·1 1·08 1·19 1·24 1·06 Gd 5·24 5·03 6·45 5·2 4·6 4·46 4·2 4·85 4·87 4·28 Tb 0·85 0·82 1·08 0·85 0·83 0·75 0·72 0·8 0·79 0·72 Dy 5·67 5·13 6·59 5·4 5·24 4·64 4·51 5·03 5·21 4·38 Ho 1·16 1·09 1·34 1·09 1·09 0·93 0·9 1·04 1·04 0·90 Er 3·46 3·2 4·02 3·29 3·07 2·7 2·52 3·03 3·00 2·56 Yb 3·19 3·04 3·72 2·99 2·89 2·62 2·45 2·72 2·85 2·46 Lu 0·51 0·47 0·57 0·44 0·45 0·39 0·4 0·39 0·45 0·43 Rb 69·5 63·1 89·3 62·9 61·1 49·9 54·1 60·8 56·70 66·40 Ba 276 303·6 266 202·8 277·2 243·6 216·4 241·8 231·30 259·30 Th 9·28 8·22 13·32 8·51 7·05 8·25 7·37 8·9 8·55 8·00 U 1·55 1·33 2·28 1·4 1·17 1·67 1·42 1·7 1·66 1·61 Nb 8·1 7·3 10·1 7·4 6·8 6·9 6·2 7·3 7·30 6·40 K 18104·8 25320·6 19178·1 16077·2 16619·3 9916·8 10345·1 11799·3 12 317 12 348 Type: Antrim Plateau Volcanics Suite Type: Table Hill Volcanics Suite Sample 052 (28) 109 (29) 111 (30) 112 (31) P04 (32) 07THD-001B_3 THD-008_8 09THD-029_12 09THD-028_16 07THD-002_19 Rock Type Basalt Basalt Basalt Basalt Basalt Dolerite Dolerite Dolerite Dolerite Dolerite Locations Kirrikimbie Spring Creek Spring Creek Spring Creek Bungle Bungle MN1 MN1 MN5 MN5 Boondawarri Zone 52 52 52 52 52 51 51 51 51 51 Easting 543 159 480 282 481 086 481 266 427 461 340 154 340 828 366 034 367 563 342 847 Northing 8 069 121 8 143 676 8 142 640 8 142 424 8 080 318 7 367 674 7 367 809 7 332 952 733 542 7 392 547 Trace Element (ppm): Continued Ta 0·6 0·6 0·8 0·6 0·5 0·5 0·5 0·6 0·60 0·50 Pb 9·9 8 13·5 7·4 9·7 7·3 12·2 11·5 11·00 10·80 Sr 123·5 337·1 126 174·7 170·2 147·2 138·4 150·3 133·10 163·60 P 633·0 603·0 767·2 609·4 689·9 507·9 464·2 558·2 665·33 489·03 Hf 3·7 3·2 4·6 3·4 3·3 2·9 2·8 3·1 3·10 2·80 Zr 148 140 182 141 138 125 112 129 135·00 112·00 Ti 7585·3 7240·1 9436·8 7393·5 7446·8 5753·4 5587·6 6268·6 7606 5191 Tb 0·85 0·82 1·08 0·85 0·83 0·75 0·72 0·8 0·79 0·72 Y 31·2 30·4 36·8 30·6 28·4 26·4 25 28·2 29·00 24·50 Co Cr Cu Ni V Zn Type: Antrim Plateau Volcanics Suite Type: Table Hill Volcanics Suite Sample 052 (28) 109 (29) 111 (30) 112 (31) P04 (32) 07THD-001B_3 THD-008_8 09THD-029_12 09THD-028_16 07THD-002_19 Rock Type Basalt Basalt Basalt Basalt Basalt Dolerite Dolerite Dolerite Dolerite Dolerite Locations Kirrikimbie Spring Creek Spring Creek Spring Creek Bungle Bungle MN1 MN1 MN5 MN5 Boondawarri Zone 52 52 52 52 52 51 51 51 51 51 Easting 543 159 480 282 481 086 481 266 427 461 340 154 340 828 366 034 367 563 342 847 Northing 8 069 121 8 143 676 8 142 640 8 142 424 8 080 318 7 367 674 7 367 809 7 332 952 733 542 7 392 547 Trace Element (ppm): Continued Ta 0·6 0·6 0·8 0·6 0·5 0·5 0·5 0·6 0·60 0·50 Pb 9·9 8 13·5 7·4 9·7 7·3 12·2 11·5 11·00 10·80 Sr 123·5 337·1 126 174·7 170·2 147·2 138·4 150·3 133·10 163·60 P 633·0 603·0 767·2 609·4 689·9 507·9 464·2 558·2 665·33 489·03 Hf 3·7 3·2 4·6 3·4 3·3 2·9 2·8 3·1 3·10 2·80 Zr 148 140 182 141 138 125 112 129 135·00 112·00 Ti 7585·3 7240·1 9436·8 7393·5 7446·8 5753·4 5587·6 6268·6 7606 5191 Tb 0·85 0·82 1·08 0·85 0·83 0·75 0·72 0·8 0·79 0·72 Y 31·2 30·4 36·8 30·6 28·4 26·4 25 28·2 29·00 24·50 Co Cr Cu Ni V Zn b) A selection of representative major and trace element analyses from the Kalkarindji CFB province Type: Antrim Plateau Volcanics Suite Type: Table Hill Volcanics Suite Sample A001-104·3 A001-432·7 A002-157·8 ANT024 ANT005 AOB06 TH1 122 601 AOB010 AOB09 389 057 TH9 Rock Type Basalt Basalt Basalt Basalt Basalt Basalt Gabbro Gabbro Basalt Baggro Basalt Gabbro Location ANTD001 ANTD001 ANTD002 Outcrop Outcrop Boodawarri 1 Nyianinya RH M. Jilyili Sill Empress 1A Boondawarri 1 MD-1A Trainor Hills Zone 52 52 52 52 52 51 51 51 51 51 51 51 Easting 7 978 167 7 978 167 7 995 173 8 031 315 8 222 530 7 398 348 7 406 548 7 265 369 7 005 943 7 398 348 7 404 962 7 312 085 Northing 572 022 572 022 564 818 487 875 509 015 349 097 287 374 262 834 714 042 349 097 319 217 419 452 Major Elements (wt %): SiO2 52·71 53·23 55·48 52·66 52·78 52·41 52·22 53·79 52·17 51·79 52·7 53·64 Al2O3 14·99 13·27 15·51 13·98 14·12 14·57 15·5 15·97 14·84 13·89 15 13·38 Fe2O3 10·42 13·68 9·26 12·33 12·44 9·83 9·47 12·41 9·56 9·14 9·36 11·17 MgO 5·1 4·04 4·35 5·82 5·22 6·88 6·82 2·88 7·13 8·73 6·96 6·06 CaO 7·88 6·76 7·61 6·87 7·59 10·06 10·61 7·45 9·71 11·33 9·51 8·22 Na2O 3·33 4·17 3·29 3·67 2·94 2·29 2·15 2·9 2·13 2·01 2·12 2·38 K2O 1·72 1·95 1·84 2·02 1·81 1·16 0·86 1·6 0·96 0·7 1·16 1·45 TiO2 1·28 1·59 1·07 1·32 1·27 0·92 0·9 1·49 0·82 0·72 0·95 1·16 P2O5 0·15 0·19 0·15 0·13 0·12 0·120 0·090 0·158 0·070 0·090 0·130 0·140 MnO 0·19 0·2 0·13 0·17 0·17 0·170 0·160 0·160 0·140 0·170 0·160 0·190 LOI 1·65 1·39 1·62 1·07 1·12 0·56 0·37 1·08 1·41 0·28 1·01 0·92 H2O- Total 99·42 100·47 100·31 100·04 99·58 98·97 99·15 99·89 98·94 98·85 99·06 98·71 Trace Elements (ppm): La 20·5 24·94 23·9 17·66 20·46 18·58 14·04 25·93 13·84 12·9 18·39 22·64 Ce 44·11 54·07 50·04 36·5 42·02 38·86 29·18 52·92 29·92 27·22 36·93 45·91 Pr 5·272 6·472 5·861 4·409 5·014 4·234 3·446 6·132 3·268 3·191 4·304 5·429 Nd 20·85 26·24 23·44 17·83 19·77 16·87 13·28 24·82 12·91 12·52 15·54 20·6 Sm 4·82 5·97 5·15 4·18 4·46 3·76 3·26 5·59 3·15 2·75 3·61 4·67 Eu 1·38 1·6 1·3 1·27 1·22 1·16 1·01 1·45 0·93 0·91 1·15 1·33 Gd 5·18 6·63 5·43 4·74 4·84 4·06 3·67 6 3·61 3·02 3·8 5·14 Tb 0·917 1·109 0·906 0·802 0·804 0·704 0·682 0·988 0·674 0·525 0·614 0·881 Dy 6·03 7·5 6·01 5·41 5·49 4·46 4·53 6·29 4·51 3·58 4·32 6·15 Ho 1·17 1·43 1·17 1·06 1·04 0·86 0·86 1·28 0·88 0·7 0·88 1·11 Er 3·33 4·29 3·34 3·12 3·01 2·37 2·49 3·71 2·42 1·92 2·42 3·24 Yb 3·18 3·88 3·24 2·83 2·88 2·31 2·34 3·38 2·47 1·93 2·35 3·05 Lu 0·452 0·569 0·469 0·421 0·412 0·342 0·371 0·511 0·363 0·283 0·4 0·477 Rb 65·45 84·98 82·04 59·01 70·84 56·24 37·03 77·03 37·57 29·89 34·33 68·45 Ba 311·4 262 322·2 260 243 236·6 167 343·8 174·8 185·2 246·1 261·8 Th 7·85 9·99 10·64 6·33 8·49 5·73 5·43 10·87 7·58 3·98 5·86 9·65 U 1·23 1·67 1·89 1·13 1·53 1·05 0·96 1·78 1·26 0·67 1·31 1·73 Nb 9·45 10·86 8·86 6·32 7·19 5·13 5·08 9·93 4·28 3·43 6·41 7·68 b) A selection of representative major and trace element analyses from the Kalkarindji CFB province Type: Antrim Plateau Volcanics Suite Type: Table Hill Volcanics Suite Sample A001-104·3 A001-432·7 A002-157·8 ANT024 ANT005 AOB06 TH1 122 601 AOB010 AOB09 389 057 TH9 Rock Type Basalt Basalt Basalt Basalt Basalt Basalt Gabbro Gabbro Basalt Baggro Basalt Gabbro Location ANTD001 ANTD001 ANTD002 Outcrop Outcrop Boodawarri 1 Nyianinya RH M. Jilyili Sill Empress 1A Boondawarri 1 MD-1A Trainor Hills Zone 52 52 52 52 52 51 51 51 51 51 51 51 Easting 7 978 167 7 978 167 7 995 173 8 031 315 8 222 530 7 398 348 7 406 548 7 265 369 7 005 943 7 398 348 7 404 962 7 312 085 Northing 572 022 572 022 564 818 487 875 509 015 349 097 287 374 262 834 714 042 349 097 319 217 419 452 Major Elements (wt %): SiO2 52·71 53·23 55·48 52·66 52·78 52·41 52·22 53·79 52·17 51·79 52·7 53·64 Al2O3 14·99 13·27 15·51 13·98 14·12 14·57 15·5 15·97 14·84 13·89 15 13·38 Fe2O3 10·42 13·68 9·26 12·33 12·44 9·83 9·47 12·41 9·56 9·14 9·36 11·17 MgO 5·1 4·04 4·35 5·82 5·22 6·88 6·82 2·88 7·13 8·73 6·96 6·06 CaO 7·88 6·76 7·61 6·87 7·59 10·06 10·61 7·45 9·71 11·33 9·51 8·22 Na2O 3·33 4·17 3·29 3·67 2·94 2·29 2·15 2·9 2·13 2·01 2·12 2·38 K2O 1·72 1·95 1·84 2·02 1·81 1·16 0·86 1·6 0·96 0·7 1·16 1·45 TiO2 1·28 1·59 1·07 1·32 1·27 0·92 0·9 1·49 0·82 0·72 0·95 1·16 P2O5 0·15 0·19 0·15 0·13 0·12 0·120 0·090 0·158 0·070 0·090 0·130 0·140 MnO 0·19 0·2 0·13 0·17 0·17 0·170 0·160 0·160 0·140 0·170 0·160 0·190 LOI 1·65 1·39 1·62 1·07 1·12 0·56 0·37 1·08 1·41 0·28 1·01 0·92 H2O- Total 99·42 100·47 100·31 100·04 99·58 98·97 99·15 99·89 98·94 98·85 99·06 98·71 Trace Elements (ppm): La 20·5 24·94 23·9 17·66 20·46 18·58 14·04 25·93 13·84 12·9 18·39 22·64 Ce 44·11 54·07 50·04 36·5 42·02 38·86 29·18 52·92 29·92 27·22 36·93 45·91 Pr 5·272 6·472 5·861 4·409 5·014 4·234 3·446 6·132 3·268 3·191 4·304 5·429 Nd 20·85 26·24 23·44 17·83 19·77 16·87 13·28 24·82 12·91 12·52 15·54 20·6 Sm 4·82 5·97 5·15 4·18 4·46 3·76 3·26 5·59 3·15 2·75 3·61 4·67 Eu 1·38 1·6 1·3 1·27 1·22 1·16 1·01 1·45 0·93 0·91 1·15 1·33 Gd 5·18 6·63 5·43 4·74 4·84 4·06 3·67 6 3·61 3·02 3·8 5·14 Tb 0·917 1·109 0·906 0·802 0·804 0·704 0·682 0·988 0·674 0·525 0·614 0·881 Dy 6·03 7·5 6·01 5·41 5·49 4·46 4·53 6·29 4·51 3·58 4·32 6·15 Ho 1·17 1·43 1·17 1·06 1·04 0·86 0·86 1·28 0·88 0·7 0·88 1·11 Er 3·33 4·29 3·34 3·12 3·01 2·37 2·49 3·71 2·42 1·92 2·42 3·24 Yb 3·18 3·88 3·24 2·83 2·88 2·31 2·34 3·38 2·47 1·93 2·35 3·05 Lu 0·452 0·569 0·469 0·421 0·412 0·342 0·371 0·511 0·363 0·283 0·4 0·477 Rb 65·45 84·98 82·04 59·01 70·84 56·24 37·03 77·03 37·57 29·89 34·33 68·45 Ba 311·4 262 322·2 260 243 236·6 167 343·8 174·8 185·2 246·1 261·8 Th 7·85 9·99 10·64 6·33 8·49 5·73 5·43 10·87 7·58 3·98 5·86 9·65 U 1·23 1·67 1·89 1·13 1·53 1·05 0·96 1·78 1·26 0·67 1·31 1·73 Nb 9·45 10·86 8·86 6·32 7·19 5·13 5·08 9·93 4·28 3·43 6·41 7·68 Type: Antrim Plateau Volcanics Suite Type: Table Hill Volcanics Suite Sample A001-104·3 A001-432·7 A002-157·8 ANT024 ANT005 AOB06 TH1 122 601 AOB010 AOB017 389 057 TH9 Rock Type Basalt Basalt Basalt Basalt Basalt Basalt Gabbro Gabbro Basalt Basalt Basalt Gabbro Location ANTD001 ANTD001 ANTD002 Outcrop Outcrop Boodawarri 1 Nyianinya RH M. Jilyili Sill Empress 1A Yowalga 2 MD-1A Trainor Hills Zone 52 52 52 52 52 51 51 51 51 51 51 51 Easting 7 978 167 7 978 167 7 995 173 8 031 315 8 222 530 7 398 348 7 406 548 7 265 369 7 005 943 7 102 250 7 404 962 7 312 085 Northing 572 022 572 022 564 818 487 875 509 015 349 097 287 374 262 834 714 042 796 690 319 217 419 452 Trace Element (ppm): Continued K 14 762 16 568 15 625 17 158 15 456 9785 7222 13 614 8171 5895 9822 12 310 Ta 0·92 0·75 0·71 0·51 0·54 0·41 0·5 0·43 0·27 0·49 0·64 Pb Sr 160 101 162 156 148 210 144 203·93 101 179 208 145 P 676·7 848·6 669·6 580·5 538·7 532·1 397·6 707·1 313·2 398·4 578·6 624·8 Hf 4·45 5·05 4·55 3·57 3·51 2·95 2·55 2·54 1·45 3·03 3·59 Zr 160·9 177·8 165 123 119 98·7 97·3 148 85·2 56·2 107·2 137 Ti 7933 9755 6561 8096 7831 5604 5462 9155 5040 4378 5808 7111 Tb 0·917 1·109 0·906 0·802 0·804 0·704 0·682 0·988 0·674 0·525 0·614 0·881 Y 29·1 36·76 29·69 29·98 27·25 22·53 22·63 34·77 23·22 18·15 23·24 29·57 Co 37 41 28 45·3 47·5 41 39 54 42 41 39 44 Cr 85 20 85 150 111 77 142 7 93 184 63 37 Cu 49 57 22 29 16 98 68 53 67 91 106 46 Ni 50 20 42 44 33 62 68 26 52 91 68 36 V 262 316 180 333 359 248 235 395 242 216 255 276 Zn 87 128 72 99 96 73 66 148 73 69 72 89 Type: Antrim Plateau Volcanics Suite Type: Table Hill Volcanics Suite Sample A001-104·3 A001-432·7 A002-157·8 ANT024 ANT005 AOB06 TH1 122 601 AOB010 AOB017 389 057 TH9 Rock Type Basalt Basalt Basalt Basalt Basalt Basalt Gabbro Gabbro Basalt Basalt Basalt Gabbro Location ANTD001 ANTD001 ANTD002 Outcrop Outcrop Boodawarri 1 Nyianinya RH M. Jilyili Sill Empress 1A Yowalga 2 MD-1A Trainor Hills Zone 52 52 52 52 52 51 51 51 51 51 51 51 Easting 7 978 167 7 978 167 7 995 173 8 031 315 8 222 530 7 398 348 7 406 548 7 265 369 7 005 943 7 102 250 7 404 962 7 312 085 Northing 572 022 572 022 564 818 487 875 509 015 349 097 287 374 262 834 714 042 796 690 319 217 419 452 Trace Element (ppm): Continued K 14 762 16 568 15 625 17 158 15 456 9785 7222 13 614 8171 5895 9822 12 310 Ta 0·92 0·75 0·71 0·51 0·54 0·41 0·5 0·43 0·27 0·49 0·64 Pb Sr 160 101 162 156 148 210 144 203·93 101 179 208 145 P 676·7 848·6 669·6 580·5 538·7 532·1 397·6 707·1 313·2 398·4 578·6 624·8 Hf 4·45 5·05 4·55 3·57 3·51 2·95 2·55 2·54 1·45 3·03 3·59 Zr 160·9 177·8 165 123 119 98·7 97·3 148 85·2 56·2 107·2 137 Ti 7933 9755 6561 8096 7831 5604 5462 9155 5040 4378 5808 7111 Tb 0·917 1·109 0·906 0·802 0·804 0·704 0·682 0·988 0·674 0·525 0·614 0·881 Y 29·1 36·76 29·69 29·98 27·25 22·53 22·63 34·77 23·22 18·15 23·24 29·57 Co 37 41 28 45·3 47·5 41 39 54 42 41 39 44 Cr 85 20 85 150 111 77 142 7 93 184 63 37 Cu 49 57 22 29 16 98 68 53 67 91 106 46 Ni 50 20 42 44 33 62 68 26 52 91 68 36 V 262 316 180 333 359 248 235 395 242 216 255 276 Zn 87 128 72 99 96 73 66 148 73 69 72 89 A complete list of major and trace element results can be found in Major and Trace Element Supplementary Data Table S1. Analysis details can be obtained in Analytical Supplementary Data Table S2. Samples with trace element data left blank were not analysed for those particular trace elements. LOI, loss on ignition. GPS Datum: AGD84 unless otherwise noted. Table 1: Major and trace element analyses of representative samples from the Kalkarindji CFB province a) Major and trace element analyses from the Kalkarindji CFB province, samples analysed for Sr, Nd, and Pb isotopes Type: Antrim Plateau Volcanics Suite Type: Table Hill Volcanics Suite Sample 052 (28) 109 (29) 111 (30) 112 (31) P04 (32) 07THD-001B_3 THD-008_8 09THD-029_12 09THD-028_16 07THD-002_19 Rock Type Basalt Basalt Basalt Basalt Basalt Dolerite Dolerite Dolerite Dolerite Dolerite Locations Kirrikimbie Spring Creek Spring Creek Spring Creek Bungle Bungle MN1 MN1 MN5 MN5 Boondawarri Zone 52 52 52 52 52 51 51 51 51 51 Easting 543 159 480 282 481 086 481 266 427 461 340 154 340 828 366 034 367 563 342 847 Northing 8 069 121 8 143 676 8 142 640 8 142 424 8 080 318 7 367 674 7 367 809 7 332 952 733 542 7 392 547 Major Elements (wt %): SiO2 53·37 52·91 55·02 53·56 53·62 53·76 53·7 54·06 53·91 53·40 Al2O3 13·82 13·93 13·05 14·02 13·65 15·08 13·73 14·39 13·21 16·42 Fe2O3 12·77 12·63 14·37 12·77 12·20 10·92 11·62 11·46 13·09 9·88 MgO 4·65 4·81 3·62 4·91 5·47 5·44 6·78 5·73 5·55 4·68 CaO 6·65 6·38 5·59 7·15 7·01 8·97 9·18 8·66 7·66 9·49 Na2O 3·38 3·59 3·07 3·39 3·07 2·27 2·18 2·41 2·36 2·35 K2O 2·12 2·98 2·26 1·9 1·95 1·17 1·23 1·4 1·45 1·46 TiO2 1·23 1·18 1·54 1·21 1·21 0·94 0·92 1·03 1·24 0·85 P2O5 0·141 0·135 0·172 0·137 0·154 0·114 0·105 0·126 0·15 0·11 MnO 0·18 0·2 0·36 0·17 0·13 0·170 0·200 0·180 0·20 0·17 H2O+/LOI 1·34 1·08 0·72 0·66 1·31 1·12 0·81 0·6 0·63 0·82 H2O- Total 99·65 99·83 99·77 99·88 99·77 99·95 100·46 100·05 99·45 99·63 Trace Elements (ppm): La 21·3 20·4 29·6 21·1 19·2 19·7 18·5 21·8 21·20 19·40 Ce 45 42·4 60·9 42·9 39·8 40·4 37·5 44·4 44·10 38·90 Pr 5·26 4·94 7·01 4·91 4·83 4·68 4·3 5·22 5·10 4·50 Nd 21·9 20·4 28·7 20·8 20·2 19 18·1 21·3 20·80 18·40 Sm 4·99 4·54 6·29 4·58 4·36 3·98 3·86 4·38 4·41 4·00 Eu 1·33 1·23 1·56 1·27 1·3 1·1 1·08 1·19 1·24 1·06 Gd 5·24 5·03 6·45 5·2 4·6 4·46 4·2 4·85 4·87 4·28 Tb 0·85 0·82 1·08 0·85 0·83 0·75 0·72 0·8 0·79 0·72 Dy 5·67 5·13 6·59 5·4 5·24 4·64 4·51 5·03 5·21 4·38 Ho 1·16 1·09 1·34 1·09 1·09 0·93 0·9 1·04 1·04 0·90 Er 3·46 3·2 4·02 3·29 3·07 2·7 2·52 3·03 3·00 2·56 Yb 3·19 3·04 3·72 2·99 2·89 2·62 2·45 2·72 2·85 2·46 Lu 0·51 0·47 0·57 0·44 0·45 0·39 0·4 0·39 0·45 0·43 Rb 69·5 63·1 89·3 62·9 61·1 49·9 54·1 60·8 56·70 66·40 Ba 276 303·6 266 202·8 277·2 243·6 216·4 241·8 231·30 259·30 Th 9·28 8·22 13·32 8·51 7·05 8·25 7·37 8·9 8·55 8·00 U 1·55 1·33 2·28 1·4 1·17 1·67 1·42 1·7 1·66 1·61 Nb 8·1 7·3 10·1 7·4 6·8 6·9 6·2 7·3 7·30 6·40 K 18104·8 25320·6 19178·1 16077·2 16619·3 9916·8 10345·1 11799·3 12 317 12 348 a) Major and trace element analyses from the Kalkarindji CFB province, samples analysed for Sr, Nd, and Pb isotopes Type: Antrim Plateau Volcanics Suite Type: Table Hill Volcanics Suite Sample 052 (28) 109 (29) 111 (30) 112 (31) P04 (32) 07THD-001B_3 THD-008_8 09THD-029_12 09THD-028_16 07THD-002_19 Rock Type Basalt Basalt Basalt Basalt Basalt Dolerite Dolerite Dolerite Dolerite Dolerite Locations Kirrikimbie Spring Creek Spring Creek Spring Creek Bungle Bungle MN1 MN1 MN5 MN5 Boondawarri Zone 52 52 52 52 52 51 51 51 51 51 Easting 543 159 480 282 481 086 481 266 427 461 340 154 340 828 366 034 367 563 342 847 Northing 8 069 121 8 143 676 8 142 640 8 142 424 8 080 318 7 367 674 7 367 809 7 332 952 733 542 7 392 547 Major Elements (wt %): SiO2 53·37 52·91 55·02 53·56 53·62 53·76 53·7 54·06 53·91 53·40 Al2O3 13·82 13·93 13·05 14·02 13·65 15·08 13·73 14·39 13·21 16·42 Fe2O3 12·77 12·63 14·37 12·77 12·20 10·92 11·62 11·46 13·09 9·88 MgO 4·65 4·81 3·62 4·91 5·47 5·44 6·78 5·73 5·55 4·68 CaO 6·65 6·38 5·59 7·15 7·01 8·97 9·18 8·66 7·66 9·49 Na2O 3·38 3·59 3·07 3·39 3·07 2·27 2·18 2·41 2·36 2·35 K2O 2·12 2·98 2·26 1·9 1·95 1·17 1·23 1·4 1·45 1·46 TiO2 1·23 1·18 1·54 1·21 1·21 0·94 0·92 1·03 1·24 0·85 P2O5 0·141 0·135 0·172 0·137 0·154 0·114 0·105 0·126 0·15 0·11 MnO 0·18 0·2 0·36 0·17 0·13 0·170 0·200 0·180 0·20 0·17 H2O+/LOI 1·34 1·08 0·72 0·66 1·31 1·12 0·81 0·6 0·63 0·82 H2O- Total 99·65 99·83 99·77 99·88 99·77 99·95 100·46 100·05 99·45 99·63 Trace Elements (ppm): La 21·3 20·4 29·6 21·1 19·2 19·7 18·5 21·8 21·20 19·40 Ce 45 42·4 60·9 42·9 39·8 40·4 37·5 44·4 44·10 38·90 Pr 5·26 4·94 7·01 4·91 4·83 4·68 4·3 5·22 5·10 4·50 Nd 21·9 20·4 28·7 20·8 20·2 19 18·1 21·3 20·80 18·40 Sm 4·99 4·54 6·29 4·58 4·36 3·98 3·86 4·38 4·41 4·00 Eu 1·33 1·23 1·56 1·27 1·3 1·1 1·08 1·19 1·24 1·06 Gd 5·24 5·03 6·45 5·2 4·6 4·46 4·2 4·85 4·87 4·28 Tb 0·85 0·82 1·08 0·85 0·83 0·75 0·72 0·8 0·79 0·72 Dy 5·67 5·13 6·59 5·4 5·24 4·64 4·51 5·03 5·21 4·38 Ho 1·16 1·09 1·34 1·09 1·09 0·93 0·9 1·04 1·04 0·90 Er 3·46 3·2 4·02 3·29 3·07 2·7 2·52 3·03 3·00 2·56 Yb 3·19 3·04 3·72 2·99 2·89 2·62 2·45 2·72 2·85 2·46 Lu 0·51 0·47 0·57 0·44 0·45 0·39 0·4 0·39 0·45 0·43 Rb 69·5 63·1 89·3 62·9 61·1 49·9 54·1 60·8 56·70 66·40 Ba 276 303·6 266 202·8 277·2 243·6 216·4 241·8 231·30 259·30 Th 9·28 8·22 13·32 8·51 7·05 8·25 7·37 8·9 8·55 8·00 U 1·55 1·33 2·28 1·4 1·17 1·67 1·42 1·7 1·66 1·61 Nb 8·1 7·3 10·1 7·4 6·8 6·9 6·2 7·3 7·30 6·40 K 18104·8 25320·6 19178·1 16077·2 16619·3 9916·8 10345·1 11799·3 12 317 12 348 Type: Antrim Plateau Volcanics Suite Type: Table Hill Volcanics Suite Sample 052 (28) 109 (29) 111 (30) 112 (31) P04 (32) 07THD-001B_3 THD-008_8 09THD-029_12 09THD-028_16 07THD-002_19 Rock Type Basalt Basalt Basalt Basalt Basalt Dolerite Dolerite Dolerite Dolerite Dolerite Locations Kirrikimbie Spring Creek Spring Creek Spring Creek Bungle Bungle MN1 MN1 MN5 MN5 Boondawarri Zone 52 52 52 52 52 51 51 51 51 51 Easting 543 159 480 282 481 086 481 266 427 461 340 154 340 828 366 034 367 563 342 847 Northing 8 069 121 8 143 676 8 142 640 8 142 424 8 080 318 7 367 674 7 367 809 7 332 952 733 542 7 392 547 Trace Element (ppm): Continued Ta 0·6 0·6 0·8 0·6 0·5 0·5 0·5 0·6 0·60 0·50 Pb 9·9 8 13·5 7·4 9·7 7·3 12·2 11·5 11·00 10·80 Sr 123·5 337·1 126 174·7 170·2 147·2 138·4 150·3 133·10 163·60 P 633·0 603·0 767·2 609·4 689·9 507·9 464·2 558·2 665·33 489·03 Hf 3·7 3·2 4·6 3·4 3·3 2·9 2·8 3·1 3·10 2·80 Zr 148 140 182 141 138 125 112 129 135·00 112·00 Ti 7585·3 7240·1 9436·8 7393·5 7446·8 5753·4 5587·6 6268·6 7606 5191 Tb 0·85 0·82 1·08 0·85 0·83 0·75 0·72 0·8 0·79 0·72 Y 31·2 30·4 36·8 30·6 28·4 26·4 25 28·2 29·00 24·50 Co Cr Cu Ni V Zn Type: Antrim Plateau Volcanics Suite Type: Table Hill Volcanics Suite Sample 052 (28) 109 (29) 111 (30) 112 (31) P04 (32) 07THD-001B_3 THD-008_8 09THD-029_12 09THD-028_16 07THD-002_19 Rock Type Basalt Basalt Basalt Basalt Basalt Dolerite Dolerite Dolerite Dolerite Dolerite Locations Kirrikimbie Spring Creek Spring Creek Spring Creek Bungle Bungle MN1 MN1 MN5 MN5 Boondawarri Zone 52 52 52 52 52 51 51 51 51 51 Easting 543 159 480 282 481 086 481 266 427 461 340 154 340 828 366 034 367 563 342 847 Northing 8 069 121 8 143 676 8 142 640 8 142 424 8 080 318 7 367 674 7 367 809 7 332 952 733 542 7 392 547 Trace Element (ppm): Continued Ta 0·6 0·6 0·8 0·6 0·5 0·5 0·5 0·6 0·60 0·50 Pb 9·9 8 13·5 7·4 9·7 7·3 12·2 11·5 11·00 10·80 Sr 123·5 337·1 126 174·7 170·2 147·2 138·4 150·3 133·10 163·60 P 633·0 603·0 767·2 609·4 689·9 507·9 464·2 558·2 665·33 489·03 Hf 3·7 3·2 4·6 3·4 3·3 2·9 2·8 3·1 3·10 2·80 Zr 148 140 182 141 138 125 112 129 135·00 112·00 Ti 7585·3 7240·1 9436·8 7393·5 7446·8 5753·4 5587·6 6268·6 7606 5191 Tb 0·85 0·82 1·08 0·85 0·83 0·75 0·72 0·8 0·79 0·72 Y 31·2 30·4 36·8 30·6 28·4 26·4 25 28·2 29·00 24·50 Co Cr Cu Ni V Zn b) A selection of representative major and trace element analyses from the Kalkarindji CFB province Type: Antrim Plateau Volcanics Suite Type: Table Hill Volcanics Suite Sample A001-104·3 A001-432·7 A002-157·8 ANT024 ANT005 AOB06 TH1 122 601 AOB010 AOB09 389 057 TH9 Rock Type Basalt Basalt Basalt Basalt Basalt Basalt Gabbro Gabbro Basalt Baggro Basalt Gabbro Location ANTD001 ANTD001 ANTD002 Outcrop Outcrop Boodawarri 1 Nyianinya RH M. Jilyili Sill Empress 1A Boondawarri 1 MD-1A Trainor Hills Zone 52 52 52 52 52 51 51 51 51 51 51 51 Easting 7 978 167 7 978 167 7 995 173 8 031 315 8 222 530 7 398 348 7 406 548 7 265 369 7 005 943 7 398 348 7 404 962 7 312 085 Northing 572 022 572 022 564 818 487 875 509 015 349 097 287 374 262 834 714 042 349 097 319 217 419 452 Major Elements (wt %): SiO2 52·71 53·23 55·48 52·66 52·78 52·41 52·22 53·79 52·17 51·79 52·7 53·64 Al2O3 14·99 13·27 15·51 13·98 14·12 14·57 15·5 15·97 14·84 13·89 15 13·38 Fe2O3 10·42 13·68 9·26 12·33 12·44 9·83 9·47 12·41 9·56 9·14 9·36 11·17 MgO 5·1 4·04 4·35 5·82 5·22 6·88 6·82 2·88 7·13 8·73 6·96 6·06 CaO 7·88 6·76 7·61 6·87 7·59 10·06 10·61 7·45 9·71 11·33 9·51 8·22 Na2O 3·33 4·17 3·29 3·67 2·94 2·29 2·15 2·9 2·13 2·01 2·12 2·38 K2O 1·72 1·95 1·84 2·02 1·81 1·16 0·86 1·6 0·96 0·7 1·16 1·45 TiO2 1·28 1·59 1·07 1·32 1·27 0·92 0·9 1·49 0·82 0·72 0·95 1·16 P2O5 0·15 0·19 0·15 0·13 0·12 0·120 0·090 0·158 0·070 0·090 0·130 0·140 MnO 0·19 0·2 0·13 0·17 0·17 0·170 0·160 0·160 0·140 0·170 0·160 0·190 LOI 1·65 1·39 1·62 1·07 1·12 0·56 0·37 1·08 1·41 0·28 1·01 0·92 H2O- Total 99·42 100·47 100·31 100·04 99·58 98·97 99·15 99·89 98·94 98·85 99·06 98·71 Trace Elements (ppm): La 20·5 24·94 23·9 17·66 20·46 18·58 14·04 25·93 13·84 12·9 18·39 22·64 Ce 44·11 54·07 50·04 36·5 42·02 38·86 29·18 52·92 29·92 27·22 36·93 45·91 Pr 5·272 6·472 5·861 4·409 5·014 4·234 3·446 6·132 3·268 3·191 4·304 5·429 Nd 20·85 26·24 23·44 17·83 19·77 16·87 13·28 24·82 12·91 12·52 15·54 20·6 Sm 4·82 5·97 5·15 4·18 4·46 3·76 3·26 5·59 3·15 2·75 3·61 4·67 Eu 1·38 1·6 1·3 1·27 1·22 1·16 1·01 1·45 0·93 0·91 1·15 1·33 Gd 5·18 6·63 5·43 4·74 4·84 4·06 3·67 6 3·61 3·02 3·8 5·14 Tb 0·917 1·109 0·906 0·802 0·804 0·704 0·682 0·988 0·674 0·525 0·614 0·881 Dy 6·03 7·5 6·01 5·41 5·49 4·46 4·53 6·29 4·51 3·58 4·32 6·15 Ho 1·17 1·43 1·17 1·06 1·04 0·86 0·86 1·28 0·88 0·7 0·88 1·11 Er 3·33 4·29 3·34 3·12 3·01 2·37 2·49 3·71 2·42 1·92 2·42 3·24 Yb 3·18 3·88 3·24 2·83 2·88 2·31 2·34 3·38 2·47 1·93 2·35 3·05 Lu 0·452 0·569 0·469 0·421 0·412 0·342 0·371 0·511 0·363 0·283 0·4 0·477 Rb 65·45 84·98 82·04 59·01 70·84 56·24 37·03 77·03 37·57 29·89 34·33 68·45 Ba 311·4 262 322·2 260 243 236·6 167 343·8 174·8 185·2 246·1 261·8 Th 7·85 9·99 10·64 6·33 8·49 5·73 5·43 10·87 7·58 3·98 5·86 9·65 U 1·23 1·67 1·89 1·13 1·53 1·05 0·96 1·78 1·26 0·67 1·31 1·73 Nb 9·45 10·86 8·86 6·32 7·19 5·13 5·08 9·93 4·28 3·43 6·41 7·68 b) A selection of representative major and trace element analyses from the Kalkarindji CFB province Type: Antrim Plateau Volcanics Suite Type: Table Hill Volcanics Suite Sample A001-104·3 A001-432·7 A002-157·8 ANT024 ANT005 AOB06 TH1 122 601 AOB010 AOB09 389 057 TH9 Rock Type Basalt Basalt Basalt Basalt Basalt Basalt Gabbro Gabbro Basalt Baggro Basalt Gabbro Location ANTD001 ANTD001 ANTD002 Outcrop Outcrop Boodawarri 1 Nyianinya RH M. Jilyili Sill Empress 1A Boondawarri 1 MD-1A Trainor Hills Zone 52 52 52 52 52 51 51 51 51 51 51 51 Easting 7 978 167 7 978 167 7 995 173 8 031 315 8 222 530 7 398 348 7 406 548 7 265 369 7 005 943 7 398 348 7 404 962 7 312 085 Northing 572 022 572 022 564 818 487 875 509 015 349 097 287 374 262 834 714 042 349 097 319 217 419 452 Major Elements (wt %): SiO2 52·71 53·23 55·48 52·66 52·78 52·41 52·22 53·79 52·17 51·79 52·7 53·64 Al2O3 14·99 13·27 15·51 13·98 14·12 14·57 15·5 15·97 14·84 13·89 15 13·38 Fe2O3 10·42 13·68 9·26 12·33 12·44 9·83 9·47 12·41 9·56 9·14 9·36 11·17 MgO 5·1 4·04 4·35 5·82 5·22 6·88 6·82 2·88 7·13 8·73 6·96 6·06 CaO 7·88 6·76 7·61 6·87 7·59 10·06 10·61 7·45 9·71 11·33 9·51 8·22 Na2O 3·33 4·17 3·29 3·67 2·94 2·29 2·15 2·9 2·13 2·01 2·12 2·38 K2O 1·72 1·95 1·84 2·02 1·81 1·16 0·86 1·6 0·96 0·7 1·16 1·45 TiO2 1·28 1·59 1·07 1·32 1·27 0·92 0·9 1·49 0·82 0·72 0·95 1·16 P2O5 0·15 0·19 0·15 0·13 0·12 0·120 0·090 0·158 0·070 0·090 0·130 0·140 MnO 0·19 0·2 0·13 0·17 0·17 0·170 0·160 0·160 0·140 0·170 0·160 0·190 LOI 1·65 1·39 1·62 1·07 1·12 0·56 0·37 1·08 1·41 0·28 1·01 0·92 H2O- Total 99·42 100·47 100·31 100·04 99·58 98·97 99·15 99·89 98·94 98·85 99·06 98·71 Trace Elements (ppm): La 20·5 24·94 23·9 17·66 20·46 18·58 14·04 25·93 13·84 12·9 18·39 22·64 Ce 44·11 54·07 50·04 36·5 42·02 38·86 29·18 52·92 29·92 27·22 36·93 45·91 Pr 5·272 6·472 5·861 4·409 5·014 4·234 3·446 6·132 3·268 3·191 4·304 5·429 Nd 20·85 26·24 23·44 17·83 19·77 16·87 13·28 24·82 12·91 12·52 15·54 20·6 Sm 4·82 5·97 5·15 4·18 4·46 3·76 3·26 5·59 3·15 2·75 3·61 4·67 Eu 1·38 1·6 1·3 1·27 1·22 1·16 1·01 1·45 0·93 0·91 1·15 1·33 Gd 5·18 6·63 5·43 4·74 4·84 4·06 3·67 6 3·61 3·02 3·8 5·14 Tb 0·917 1·109 0·906 0·802 0·804 0·704 0·682 0·988 0·674 0·525 0·614 0·881 Dy 6·03 7·5 6·01 5·41 5·49 4·46 4·53 6·29 4·51 3·58 4·32 6·15 Ho 1·17 1·43 1·17 1·06 1·04 0·86 0·86 1·28 0·88 0·7 0·88 1·11 Er 3·33 4·29 3·34 3·12 3·01 2·37 2·49 3·71 2·42 1·92 2·42 3·24 Yb 3·18 3·88 3·24 2·83 2·88 2·31 2·34 3·38 2·47 1·93 2·35 3·05 Lu 0·452 0·569 0·469 0·421 0·412 0·342 0·371 0·511 0·363 0·283 0·4 0·477 Rb 65·45 84·98 82·04 59·01 70·84 56·24 37·03 77·03 37·57 29·89 34·33 68·45 Ba 311·4 262 322·2 260 243 236·6 167 343·8 174·8 185·2 246·1 261·8 Th 7·85 9·99 10·64 6·33 8·49 5·73 5·43 10·87 7·58 3·98 5·86 9·65 U 1·23 1·67 1·89 1·13 1·53 1·05 0·96 1·78 1·26 0·67 1·31 1·73 Nb 9·45 10·86 8·86 6·32 7·19 5·13 5·08 9·93 4·28 3·43 6·41 7·68 Type: Antrim Plateau Volcanics Suite Type: Table Hill Volcanics Suite Sample A001-104·3 A001-432·7 A002-157·8 ANT024 ANT005 AOB06 TH1 122 601 AOB010 AOB017 389 057 TH9 Rock Type Basalt Basalt Basalt Basalt Basalt Basalt Gabbro Gabbro Basalt Basalt Basalt Gabbro Location ANTD001 ANTD001 ANTD002 Outcrop Outcrop Boodawarri 1 Nyianinya RH M. Jilyili Sill Empress 1A Yowalga 2 MD-1A Trainor Hills Zone 52 52 52 52 52 51 51 51 51 51 51 51 Easting 7 978 167 7 978 167 7 995 173 8 031 315 8 222 530 7 398 348 7 406 548 7 265 369 7 005 943 7 102 250 7 404 962 7 312 085 Northing 572 022 572 022 564 818 487 875 509 015 349 097 287 374 262 834 714 042 796 690 319 217 419 452 Trace Element (ppm): Continued K 14 762 16 568 15 625 17 158 15 456 9785 7222 13 614 8171 5895 9822 12 310 Ta 0·92 0·75 0·71 0·51 0·54 0·41 0·5 0·43 0·27 0·49 0·64 Pb Sr 160 101 162 156 148 210 144 203·93 101 179 208 145 P 676·7 848·6 669·6 580·5 538·7 532·1 397·6 707·1 313·2 398·4 578·6 624·8 Hf 4·45 5·05 4·55 3·57 3·51 2·95 2·55 2·54 1·45 3·03 3·59 Zr 160·9 177·8 165 123 119 98·7 97·3 148 85·2 56·2 107·2 137 Ti 7933 9755 6561 8096 7831 5604 5462 9155 5040 4378 5808 7111 Tb 0·917 1·109 0·906 0·802 0·804 0·704 0·682 0·988 0·674 0·525 0·614 0·881 Y 29·1 36·76 29·69 29·98 27·25 22·53 22·63 34·77 23·22 18·15 23·24 29·57 Co 37 41 28 45·3 47·5 41 39 54 42 41 39 44 Cr 85 20 85 150 111 77 142 7 93 184 63 37 Cu 49 57 22 29 16 98 68 53 67 91 106 46 Ni 50 20 42 44 33 62 68 26 52 91 68 36 V 262 316 180 333 359 248 235 395 242 216 255 276 Zn 87 128 72 99 96 73 66 148 73 69 72 89 Type: Antrim Plateau Volcanics Suite Type: Table Hill Volcanics Suite Sample A001-104·3 A001-432·7 A002-157·8 ANT024 ANT005 AOB06 TH1 122 601 AOB010 AOB017 389 057 TH9 Rock Type Basalt Basalt Basalt Basalt Basalt Basalt Gabbro Gabbro Basalt Basalt Basalt Gabbro Location ANTD001 ANTD001 ANTD002 Outcrop Outcrop Boodawarri 1 Nyianinya RH M. Jilyili Sill Empress 1A Yowalga 2 MD-1A Trainor Hills Zone 52 52 52 52 52 51 51 51 51 51 51 51 Easting 7 978 167 7 978 167 7 995 173 8 031 315 8 222 530 7 398 348 7 406 548 7 265 369 7 005 943 7 102 250 7 404 962 7 312 085 Northing 572 022 572 022 564 818 487 875 509 015 349 097 287 374 262 834 714 042 796 690 319 217 419 452 Trace Element (ppm): Continued K 14 762 16 568 15 625 17 158 15 456 9785 7222 13 614 8171 5895 9822 12 310 Ta 0·92 0·75 0·71 0·51 0·54 0·41 0·5 0·43 0·27 0·49 0·64 Pb Sr 160 101 162 156 148 210 144 203·93 101 179 208 145 P 676·7 848·6 669·6 580·5 538·7 532·1 397·6 707·1 313·2 398·4 578·6 624·8 Hf 4·45 5·05 4·55 3·57 3·51 2·95 2·55 2·54 1·45 3·03 3·59 Zr 160·9 177·8 165 123 119 98·7 97·3 148 85·2 56·2 107·2 137 Ti 7933 9755 6561 8096 7831 5604 5462 9155 5040 4378 5808 7111 Tb 0·917 1·109 0·906 0·802 0·804 0·704 0·682 0·988 0·674 0·525 0·614 0·881 Y 29·1 36·76 29·69 29·98 27·25 22·53 22·63 34·77 23·22 18·15 23·24 29·57 Co 37 41 28 45·3 47·5 41 39 54 42 41 39 44 Cr 85 20 85 150 111 77 142 7 93 184 63 37 Cu 49 57 22 29 16 98 68 53 67 91 106 46 Ni 50 20 42 44 33 62 68 26 52 91 68 36 V 262 316 180 333 359 248 235 395 242 216 255 276 Zn 87 128 72 99 96 73 66 148 73 69 72 89 A complete list of major and trace element results can be found in Major and Trace Element Supplementary Data Table S1. Analysis details can be obtained in Analytical Supplementary Data Table S2. Samples with trace element data left blank were not analysed for those particular trace elements. LOI, loss on ignition. GPS Datum: AGD84 unless otherwise noted. Thin sections of the 32 samples and cores collected from the Antrim Plateau Volcanics and Table Hill Volcanics were examined for any evidence of alteration as well as to identify magmatic phases. A sub-set of ten of the freshest samples was selected for Sr, Nd, and Pb isotope analysis. In order to obtain a representative rock selection from the whole province, five samples from the Antrim Plateau Volcanics and five samples from the Table Hill Volcanics were selected for isotopic analysis. The five samples selected from the Antrim Plateau Volcanics are all outcrop samples of fine-grained basalt flows. The five samples selected from the Table Hill Volcanics are dolerite sills inferred to be part of the feeding system of the province. A complete list of samples, locations, and rock types is given in Supplementary Data Table S1; supplementary data are available for downloading at http://www.petrology.oxfordjournals.org. ANALYTICAL PROCEDURES The 32 samples collected for this study were analysed for major and trace elements at Genalysis Laboratory Services Pty Ltd in Perth (Australia). Major and trace element geochemistry from the 150 rock-chip and drill core samples from northern Australia and the Officer Basin region have been previously analysed following the same procedure within the same laboratory and instruments, thus avoiding any inter-laboratory bias. These data were provided as an Excel database by AusQuest Limited. Major element geochemical analysis was conducted using X-ray fluorescence (XRF) on fused discs produced using a lithium borate fusion technique in platinum crucibles (Genalysis Laboratory Services Pty Ltd method code FB1/XRF20). Trace element analyses were conducted using the inductively coupled plasma mass spectrometry (ICP-MS) method on samples dissolved using a lithium metaborate/tetraborate fusion (Genalysis Laboratory Services Pty Ltd method code FB6/MS). Utilizing the same lithium borate fusion, Sc and V were analysed by inductively coupled plasma optical (atomic) emission spectrometry (ICP-OES). A four-acid digestion (hydrofluoric, nitric, perchloric and hydrochloric acids in Teflon Tubes) was used to prepare samples for ICP-MS (for elements Ag, As, Be, Bi, Cd, Co, Ge, In, Li, Mo, Pb, Re, Sb, Se, Te, Tl: method code 4A/MS) and ICP-OES (for elements Cu, Ni, Zn: method code 4A/OE) analyses. To ensure reproducibility, analyses of samples THD001B and THD002 were duplicated. Overall the 67 elements analysed show extremely good reproducibility; only elements for which concentrations were close to the detection limits displayed significant inconsistencies. Three procedural blank analyses were also performed: one control blank for every major and trace element analysis and two other control blanks for trace element analyses. Acid blanks analyses were also performed for the trace element measurements. Internal standards (SARM1, SARM4, and SY-4 for the major element analyses and SY-4, WPR-1, OREAS45a, OREAS45b, 40100, GenFe-3, GenFe-5, MA-1b, CD-1, WGB-1 and AMIS0076 for the trace element analyses) were used to monitor the accuracy of the analyses (analytical results for the 32 samples and standards analysed can be found in Supplementary Data Table S2). Table 2: Sr–Nd–Pb isotope data for the Kalkarindji CFB province Sample Sr (ppm) Rb (ppm) 87Rb/ 86Sr 87Sr/ 86Srmeas ± 1σ (87Sr/ 86Sr)i. Nd (ppm) Sm (ppm) 147Sm/ 144Nd 143Nd/ 144Ndmeas ± 1σ (143Nd/ 144Nd)i. εNd(0) εNd(511 Ma) Table Hill volcanics 07THD-001B_3(A) 49·9 147·2 0·98074 0·71648 0·0000035 0·70934 19·0 4·0 0·111226 0·512249 0·0000019 0·511959 −7·60 −13·2 THD-008_8 54·1 138·4 1·13109 0·71825 0·0000024 0·71001 18·1 3·9 0·113236 0·512257 0·0000017 0·511950 −7·42 −13·4 09THD-029_12(A) 60·8 150·3 1·17053 0·71835 0·0000017 0·70983 21·3 4·4 0·109187 0·512253 0·0000014 0·511981 −7·50 −12·8 09THD-028_16(B) 56·7 133·1 1·23269 0·71861 0·0000081 0·70964 20·8 4·4 0·112577 0·512259 0·0000015 0·511933 −7·40 −13·8 07THD-002_19 66·4 163·6 1·17447 0·71878 0·0000056 0·71023 18·4 4·0 0·115430 0·512234 0·0000021 0·511928 −7·87 −13·8 Antrim Plateau Volcanics 052 (28) 69·5 123·5 1·62899 0·72216 0·0000020 0·71029 21·9 5·0 0·120985 0·512248 0·0000026 0·511918 −7·60 −14·0 109 (29) 63·1 337·1 0·54136 0·71311 0·0000033 0·70917 20·4 4·5 0·118168 0·512251 0·0000013 0·511938 −7·55 −13·7 111 (30) 89·3 126·0 2·05216 0·72520 0·0000030 0·71026 28·7 6·3 0·116371 0·512210 0·0000030 0·511936 −8·35 −13·7 112 (31) 62·9 174·7 1·04167 0·71678 0·0000041 0·70920 20·8 4·6 0·116917 0·512251 0·0000010 0·511935 −7·55 −13·7 P04 (32) 61·1 170·2 1·03862 0·71684 0·0000090 0·70928 20·2 4·4 0·114607 0·512308 0·0000017 0·511937 −6·44 −13·7 Sample Sr (ppm) Rb (ppm) 87Rb/ 86Sr 87Sr/ 86Srmeas ± 1σ (87Sr/ 86Sr)i. Nd (ppm) Sm (ppm) 147Sm/ 144Nd 143Nd/ 144Ndmeas ± 1σ (143Nd/ 144Nd)i. εNd(0) εNd(511 Ma) Table Hill volcanics 07THD-001B_3(A) 49·9 147·2 0·98074 0·71648 0·0000035 0·70934 19·0 4·0 0·111226 0·512249 0·0000019 0·511959 −7·60 −13·2 THD-008_8 54·1 138·4 1·13109 0·71825 0·0000024 0·71001 18·1 3·9 0·113236 0·512257 0·0000017 0·511950 −7·42 −13·4 09THD-029_12(A) 60·8 150·3 1·17053 0·71835 0·0000017 0·70983 21·3 4·4 0·109187 0·512253 0·0000014 0·511981 −7·50 −12·8 09THD-028_16(B) 56·7 133·1 1·23269 0·71861 0·0000081 0·70964 20·8 4·4 0·112577 0·512259 0·0000015 0·511933 −7·40 −13·8 07THD-002_19 66·4 163·6 1·17447 0·71878 0·0000056 0·71023 18·4 4·0 0·115430 0·512234 0·0000021 0·511928 −7·87 −13·8 Antrim Plateau Volcanics 052 (28) 69·5 123·5 1·62899 0·72216 0·0000020 0·71029 21·9 5·0 0·120985 0·512248 0·0000026 0·511918 −7·60 −14·0 109 (29) 63·1 337·1 0·54136 0·71311 0·0000033 0·70917 20·4 4·5 0·118168 0·512251 0·0000013 0·511938 −7·55 −13·7 111 (30) 89·3 126·0 2·05216 0·72520 0·0000030 0·71026 28·7 6·3 0·116371 0·512210 0·0000030 0·511936 −8·35 −13·7 112 (31) 62·9 174·7 1·04167 0·71678 0·0000041 0·70920 20·8 4·6 0·116917 0·512251 0·0000010 0·511935 −7·55 −13·7 P04 (32) 61·1 170·2 1·03862 0·71684 0·0000090 0·70928 20·2 4·4 0·114607 0·512308 0·0000017 0·511937 −6·44 −13·7 Sample Pb (ppm) U (ppm) Th (ppm) 206Pb/ 204Pbmeas ± 1σ 206Pb/ 204Pbi 207Pb/ 204Pbmeas ± 1σ 207Pb/ 204Pbi 208Pb/ 204Pbmeas ± 1σ 208Pb/ 204Pbi Table Hill Volcanics 07THD-001B_3(A) 7·3 1·7 8·3 19·334 0·000866 18·105 15·798 0·000730 15·726 40·392 0·001903 38·445 THD-008_8 12·2 1·4 7·4 19·221 0·000291 18·598 15·797 0·000291 15·761 40·244 0·000917 39·208 09THD-029_12(A) 11·5 1·7 8·9 19·044 0·000261 18·258 15·800 0·000288 15·755 39·922 0·000950 38·602 09THD-028_16(B) 11·0 1·7 8·6 19·108 0·000222 18·304 15·793 0·000202 15·747 40·038 0·000508 38·710 07THD-002_19 10·8 1·6 8·0 18·987 0·000310 18·196 15·792 0·000303 15·746 39·786 0·000904 38·526 Antrim Plateau Volcanics 052 (28) 9·9 1·6 9·3 19·693 0·000398 18·843 15·854 0·000351 15·805 40·777 0·001088 39·146 109 (29) 8·0 1·3 8·2 19·241 0·000280 18·349 15·792 0·000299 15·740 40·481 0·000873 38·711 111 (30) 13·5 2·3 13·3 19·323 0·000342 18·416 15·808 0·000406 15·755 40·413 0·001377 38·713 112 (31) 7·4 1·4 8·5 19·509 0·000423 18·482 15·811 0·000384 15·752 41·017 0·001102 39·015 P04 (32) 9·7 1·2 7·1 18·875 0·000685 18·238 15·736 0·000619 15·699 39·604 0·001605 38·374 Sample Pb (ppm) U (ppm) Th (ppm) 206Pb/ 204Pbmeas ± 1σ 206Pb/ 204Pbi 207Pb/ 204Pbmeas ± 1σ 207Pb/ 204Pbi 208Pb/ 204Pbmeas ± 1σ 208Pb/ 204Pbi Table Hill Volcanics 07THD-001B_3(A) 7·3 1·7 8·3 19·334 0·000866 18·105 15·798 0·000730 15·726 40·392 0·001903 38·445 THD-008_8 12·2 1·4 7·4 19·221 0·000291 18·598 15·797 0·000291 15·761 40·244 0·000917 39·208 09THD-029_12(A) 11·5 1·7 8·9 19·044 0·000261 18·258 15·800 0·000288 15·755 39·922 0·000950 38·602 09THD-028_16(B) 11·0 1·7 8·6 19·108 0·000222 18·304 15·793 0·000202 15·747 40·038 0·000508 38·710 07THD-002_19 10·8 1·6 8·0 18·987 0·000310 18·196 15·792 0·000303 15·746 39·786 0·000904 38·526 Antrim Plateau Volcanics 052 (28) 9·9 1·6 9·3 19·693 0·000398 18·843 15·854 0·000351 15·805 40·777 0·001088 39·146 109 (29) 8·0 1·3 8·2 19·241 0·000280 18·349 15·792 0·000299 15·740 40·481 0·000873 38·711 111 (30) 13·5 2·3 13·3 19·323 0·000342 18·416 15·808 0·000406 15·755 40·413 0·001377 38·713 112 (31) 7·4 1·4 8·5 19·509 0·000423 18·482 15·811 0·000384 15·752 41·017 0·001102 39·015 P04 (32) 9·7 1·2 7·1 18·875 0·000685 18·238 15·736 0·000619 15·699 39·604 0·001605 38·374 Initial calculations are age-calculated to 511 Ma. Uncertainties on initial ratios include in-run errors and uncertainties on blank corrections. Sample locations can be found in Table 1. εNd calculated for a present-day CHUR value of 143Nd/144Nd = 0·512638 (Jacobsen & Wasserburg, 1980). Table 2: Sr–Nd–Pb isotope data for the Kalkarindji CFB province Sample Sr (ppm) Rb (ppm) 87Rb/ 86Sr 87Sr/ 86Srmeas ± 1σ (87Sr/ 86Sr)i. Nd (ppm) Sm (ppm) 147Sm/ 144Nd 143Nd/ 144Ndmeas ± 1σ (143Nd/ 144Nd)i. εNd(0) εNd(511 Ma) Table Hill volcanics 07THD-001B_3(A) 49·9 147·2 0·98074 0·71648 0·0000035 0·70934 19·0 4·0 0·111226 0·512249 0·0000019 0·511959 −7·60 −13·2 THD-008_8 54·1 138·4 1·13109 0·71825 0·0000024 0·71001 18·1 3·9 0·113236 0·512257 0·0000017 0·511950 −7·42 −13·4 09THD-029_12(A) 60·8 150·3 1·17053 0·71835 0·0000017 0·70983 21·3 4·4 0·109187 0·512253 0·0000014 0·511981 −7·50 −12·8 09THD-028_16(B) 56·7 133·1 1·23269 0·71861 0·0000081 0·70964 20·8 4·4 0·112577 0·512259 0·0000015 0·511933 −7·40 −13·8 07THD-002_19 66·4 163·6 1·17447 0·71878 0·0000056 0·71023 18·4 4·0 0·115430 0·512234 0·0000021 0·511928 −7·87 −13·8 Antrim Plateau Volcanics 052 (28) 69·5 123·5 1·62899 0·72216 0·0000020 0·71029 21·9 5·0 0·120985 0·512248 0·0000026 0·511918 −7·60 −14·0 109 (29) 63·1 337·1 0·54136 0·71311 0·0000033 0·70917 20·4 4·5 0·118168 0·512251 0·0000013 0·511938 −7·55 −13·7 111 (30) 89·3 126·0 2·05216 0·72520 0·0000030 0·71026 28·7 6·3 0·116371 0·512210 0·0000030 0·511936 −8·35 −13·7 112 (31) 62·9 174·7 1·04167 0·71678 0·0000041 0·70920 20·8 4·6 0·116917 0·512251 0·0000010 0·511935 −7·55 −13·7 P04 (32) 61·1 170·2 1·03862 0·71684 0·0000090 0·70928 20·2 4·4 0·114607 0·512308 0·0000017 0·511937 −6·44 −13·7 Sample Sr (ppm) Rb (ppm) 87Rb/ 86Sr 87Sr/ 86Srmeas ± 1σ (87Sr/ 86Sr)i. Nd (ppm) Sm (ppm) 147Sm/ 144Nd 143Nd/ 144Ndmeas ± 1σ (143Nd/ 144Nd)i. εNd(0) εNd(511 Ma) Table Hill volcanics 07THD-001B_3(A) 49·9 147·2 0·98074 0·71648 0·0000035 0·70934 19·0 4·0 0·111226 0·512249 0·0000019 0·511959 −7·60 −13·2 THD-008_8 54·1 138·4 1·13109 0·71825 0·0000024 0·71001 18·1 3·9 0·113236 0·512257 0·0000017 0·511950 −7·42 −13·4 09THD-029_12(A) 60·8 150·3 1·17053 0·71835 0·0000017 0·70983 21·3 4·4 0·109187 0·512253 0·0000014 0·511981 −7·50 −12·8 09THD-028_16(B) 56·7 133·1 1·23269 0·71861 0·0000081 0·70964 20·8 4·4 0·112577 0·512259 0·0000015 0·511933 −7·40 −13·8 07THD-002_19 66·4 163·6 1·17447 0·71878 0·0000056 0·71023 18·4 4·0 0·115430 0·512234 0·0000021 0·511928 −7·87 −13·8 Antrim Plateau Volcanics 052 (28) 69·5 123·5 1·62899 0·72216 0·0000020 0·71029 21·9 5·0 0·120985 0·512248 0·0000026 0·511918 −7·60 −14·0 109 (29) 63·1 337·1 0·54136 0·71311 0·0000033 0·70917 20·4 4·5 0·118168 0·512251 0·0000013 0·511938 −7·55 −13·7 111 (30) 89·3 126·0 2·05216 0·72520 0·0000030 0·71026 28·7 6·3 0·116371 0·512210 0·0000030 0·511936 −8·35 −13·7 112 (31) 62·9 174·7 1·04167 0·71678 0·0000041 0·70920 20·8 4·6 0·116917 0·512251 0·0000010 0·511935 −7·55 −13·7 P04 (32) 61·1 170·2 1·03862 0·71684 0·0000090 0·70928 20·2 4·4 0·114607 0·512308 0·0000017 0·511937 −6·44 −13·7 Sample Pb (ppm) U (ppm) Th (ppm) 206Pb/ 204Pbmeas ± 1σ 206Pb/ 204Pbi 207Pb/ 204Pbmeas ± 1σ 207Pb/ 204Pbi 208Pb/ 204Pbmeas ± 1σ 208Pb/ 204Pbi Table Hill Volcanics 07THD-001B_3(A) 7·3 1·7 8·3 19·334 0·000866 18·105 15·798 0·000730 15·726 40·392 0·001903 38·445 THD-008_8 12·2 1·4 7·4 19·221 0·000291 18·598 15·797 0·000291 15·761 40·244 0·000917 39·208 09THD-029_12(A) 11·5 1·7 8·9 19·044 0·000261 18·258 15·800 0·000288 15·755 39·922 0·000950 38·602 09THD-028_16(B) 11·0 1·7 8·6 19·108 0·000222 18·304 15·793 0·000202 15·747 40·038 0·000508 38·710 07THD-002_19 10·8 1·6 8·0 18·987 0·000310 18·196 15·792 0·000303 15·746 39·786 0·000904 38·526 Antrim Plateau Volcanics 052 (28) 9·9 1·6 9·3 19·693 0·000398 18·843 15·854 0·000351 15·805 40·777 0·001088 39·146 109 (29) 8·0 1·3 8·2 19·241 0·000280 18·349 15·792 0·000299 15·740 40·481 0·000873 38·711 111 (30) 13·5 2·3 13·3 19·323 0·000342 18·416 15·808 0·000406 15·755 40·413 0·001377 38·713 112 (31) 7·4 1·4 8·5 19·509 0·000423 18·482 15·811 0·000384 15·752 41·017 0·001102 39·015 P04 (32) 9·7 1·2 7·1 18·875 0·000685 18·238 15·736 0·000619 15·699 39·604 0·001605 38·374 Sample Pb (ppm) U (ppm) Th (ppm) 206Pb/ 204Pbmeas ± 1σ 206Pb/ 204Pbi 207Pb/ 204Pbmeas ± 1σ 207Pb/ 204Pbi 208Pb/ 204Pbmeas ± 1σ 208Pb/ 204Pbi Table Hill Volcanics 07THD-001B_3(A) 7·3 1·7 8·3 19·334 0·000866 18·105 15·798 0·000730 15·726 40·392 0·001903 38·445 THD-008_8 12·2 1·4 7·4 19·221 0·000291 18·598 15·797 0·000291 15·761 40·244 0·000917 39·208 09THD-029_12(A) 11·5 1·7 8·9 19·044 0·000261 18·258 15·800 0·000288 15·755 39·922 0·000950 38·602 09THD-028_16(B) 11·0 1·7 8·6 19·108 0·000222 18·304 15·793 0·000202 15·747 40·038 0·000508 38·710 07THD-002_19 10·8 1·6 8·0 18·987 0·000310 18·196 15·792 0·000303 15·746 39·786 0·000904 38·526 Antrim Plateau Volcanics 052 (28) 9·9 1·6 9·3 19·693 0·000398 18·843 15·854 0·000351 15·805 40·777 0·001088 39·146 109 (29) 8·0 1·3 8·2 19·241 0·000280 18·349 15·792 0·000299 15·740 40·481 0·000873 38·711 111 (30) 13·5 2·3 13·3 19·323 0·000342 18·416 15·808 0·000406 15·755 40·413 0·001377 38·713 112 (31) 7·4 1·4 8·5 19·509 0·000423 18·482 15·811 0·000384 15·752 41·017 0·001102 39·015 P04 (32) 9·7 1·2 7·1 18·875 0·000685 18·238 15·736 0·000619 15·699 39·604 0·001605 38·374 Initial calculations are age-calculated to 511 Ma. Uncertainties on initial ratios include in-run errors and uncertainties on blank corrections. Sample locations can be found in Table 1. εNd calculated for a present-day CHUR value of 143Nd/144Nd = 0·512638 (Jacobsen & Wasserburg, 1980). The ten samples selected for Sr, Nd, and Pb isotope analyses were crushed into small chips using a cleaned hydraulic press. Once rinsed with distilled H2O the chips were carefully selected under a microscope to avoid any saw marks or weathered surfaces. The clean chips were then powdered by hand using an agate mortar and pestle. Approximately 150 mg of powder were dissolved for 7 days in Savillex® Teflon vials using 4 ml of concentrated HF and 1 ml of HNO3 15 M, at 140°C. The vials were placed in ultrasonic bath for 30 min twice a day (Chiaradia et al., 2011). Subsequently, samples were dried down and re-dissolved for 3 days (also with 30 min ultrasonication twice a day) in 3 ml of HNO3 15 M and dried down again. Strontium, Nd and Pb were purified from the sample matrix by cascade column chromatography with Sr-Spec, TRU-Spec and Ln-Spec ion exchange resins according to a protocol modified after Pin et al. (1994). Lead was further purified with an AG-MP1-M anion exchange resin in a hydrobromic medium. Lead, Sr and Nd isotope ratios were measured on a Thermo TRITON TIMS using Faraday cups in static mode, at the Department of Earth Sciences, University of Geneva (Switzerland). Lead and Sr were loaded on Re single filaments using silica gel (Gerstenberger & Haase, 1997) and Ta oxide solution respectively. Neodymium was loaded on double Re filaments using1M HNO3. Strontium and Nd were analysed using the virtual amplifier design to cancel out biases in gain calibration among amplifiers. All samples and standards were measured at a pyrometer-controlled temperature. Lead isotope ratios were corrected for instrumental fractionation by a factor of 0·07% per a.m.u. based on more than 90 measurements of the SRM981 standard and using the values of Todt et al. (1996). External reproducibility of the standard ratios is 0·08% for 206Pb/204Pb, 0·12% for 207Pb/204Pb and 0·16% for 208Pb/204Pb. 87Sr/86Sr values were internally corrected for instrumental fractionation using an 88Sr/86Sr value of 8·375209. Raw values were further corrected for external fractionation by a value of + 0·03‰, determined by repeated measurements of the SRM987 standard; 87Sr/86Sr = 0·710248 (McArthur et al., 2001). The long-term external reproducibility of the 87Sr/86Sr ratio for the SRM987 standard is 7 ppm (1σ). 143Nd/144Nd values were internally corrected for instrumental fractionation using a 146Nd/144Nd value of 0·7219 and the 144Sm interference on 144Nd was monitored on the mass 147Sm and corrected by using a 144Sm/147Sm value of 0·206700. These values were further corrected for external fractionation by a value of + 0·03‰, determined by repeated measurements of the JNdi-1 standard; 143Nd/144Nd 1/4 0·512115 (Tanaka et al., 2000). Long-term external reproducibility of the JNdi-1 standard is < 5 ppm. Total procedural blanks were < 500 pg for Pb and < 100 pg for Sr and Nd which are insignificant compared to the amounts of these elements purified from the whole rock samples investigated. RESULTS Mineralogy The mineralogy of the Kalkarindji CFBs displays little variation across the province. The minerals found within the rocks of the Antrim Plateau Volcanics include plagioclase, augite, pigeonite, ilmenite, titano-magnetite and minor amounts of orthopyroxene (enstatite) (Sweet et al., 1974; Bultitude, 1976). Plagioclase is the most prominent phenocryst, ranging in average size from 1–4 mm, throughout the Antrim Plateau Volcanics. However, occasional clinopyroxene and titano-magnetite grains are present as larger, subhedral to euhedral phenocrysts. The fine-grained groundmass is composed of glass, cryptocrystalline plagioclase, clinopyroxene and titano-magnetite. A small proportion of the plagioclase phenocrysts exhibit characteristic polysynthetic twinning, but twinning is more common in the groundmass crystals. The Antrim Plateau Volcanics exhibit an aphanitic to porphyritic and on occasion glomeroporphyritic texture. In some samples amygdaloidal and brecciated textures are apparent. Analyses of samples showing these textures were not included in the data set because of the possibility of hydrothermal alteration. Most of the rock suites display pervasive alteration affecting both the groundmass and phenocrysts. Much of the alteration is apparent as chlorite and sericite crystallization. However, the intensity of this alteration varies considerably across the province from sample to sample. Although basalt flows also occur within the Officer Basin as small isolated outcrops, the Table Hill Volcanics data from this study focuses exclusively on samples from the intrusive sills and dykes found throughout the Officer Basin. Therefore, the studied Table Hill Volcanics have coarser textures than the majority of the Antrim Plateau Volcanics, with medium to coarse-grained doleritic textures (sub-ophitic texture) and occasionally, very coarse-grained textures. A slight mineralogical difference between the intrusive rocks of the Table Hill Volcanics and Antrim Plateau Volcanics is apparent, with the former being dominated by plagioclase (labradorite), clinopyroxene (augite), occasional hornblende and minor ilmenite, and titano-magnetite (Grey et al., 2005). Secondary (alteration) minerals have also been observed within the rocks of the Table Hill Volcanics. These include sericite, which is apparent in cloudy plagioclase grains and pervasive chlorite alteration that gives a slight green tinge to the appearance of many of the sills. As with the Antrim Plateau Volcanics, the degree of alteration is variable from sample to sample. Some of the sills are more differentiated toward the cores, which are characterized by coarser textures compared to the surrounding doleritic and gabbroic textures. Some, of the hand specimen samples of sill cores display a strong pink color (Jourdan et al., 2014) due the presence of quartz-feldspar intergrowths (Grey et al., 2005). Hornblende, chlorite and acicular apatite have also been petrographically recognized as secondary phases (Grey et al., 2005; Jourdan et al., 2014). Major and trace elements To discard samples that may have been affected by alteration, geochemical analyses were filtered rigorously using several geochemical criteria. Loss on ignition (LOI) was the primary means used to evaluate the freshness of the samples; all samples with more than 2 wt % LOI were considered as altered. Out of all 182 samples, 137 displayed low LOI values of less than 2 wt %. A plot of (Na2O + K2O)/MgO vs CaO/MgO was also used as an indication of feldspar alteration; altered samples contain sericite and have low CaO values and high alkalis (Simpson, 1954). Samples showing this characteristic were also discarded. Furthermore, a few altered samples were identified by anomalously high concentrations of MnO (e.g. ≥ 6 wt %). Bulk-rock compositions of the remaining samples are sub-alkalic (tholeiitic) with the majority of the samples plotting in the basaltic andesite field on the total alkalis-silica diagram (Le Bas et al., 1986) (Fig. 2). A few samples plot in the fields of basaltic trachyandesite. Some samples, in particular from the Table Hill Volcanics have more evolved compositions plotting along the trachyandesite/andesite boundary and reaching the boundary between the trachyte/dacite fields (Fig. 2). The majority of these samples are relatively evolved with MgO contents less than 8 wt % and Mg # [100 * mol. MgO/(MgO + FeO)] ranging from 69 to 19. Mg # shows clear negative and positive covariations when plotted against most major oxide contents (Fig. 3a, c, d, and f). All samples can be classified as low-Ti, with TiO2 contents < 2 wt %. A notable difference between the Antrim Plateau Volcanics and the Table Hill Volcanics is that they define slightly different trends on major element vs Mg # variation diagrams (Fig. 3). No Antrim Plateau Volcanics sample has MgO less than 3·5 wt % (Mg # = 37). In contrast, the samples from the Table Hill Volcanics display broader variations in SiO2 contents and Mg # values (19–69), with an inflection point occurring in the trends between 30 and 35 Mg #. This inflection is not apparent on major element variation diagrams for samples from the Antrim Plateau Volcanics. Fig. 2. View largeDownload slide Total alkalis–silica (TAS) diagram (Le Bas et al., 1986) for the basalts of the Kalkarindji province. Alkalic–subalkalic boundary line from Irvine & Baragar (1971). Fig. 2. View largeDownload slide Total alkalis–silica (TAS) diagram (Le Bas et al., 1986) for the basalts of the Kalkarindji province. Alkalic–subalkalic boundary line from Irvine & Baragar (1971). Fig. 3. View largeDownload slide Major element (wt %) vs Mg-number [100 x atomic ratio of Mg/ (Mg +  Fe2+) with Fe2O3/FeO normalized to 0·15] diagrams for basalts of the Kalkarindji province. Fig. 3. View largeDownload slide Major element (wt %) vs Mg-number [100 x atomic ratio of Mg/ (Mg +  Fe2+) with Fe2O3/FeO normalized to 0·15] diagrams for basalts of the Kalkarindji province. All the samples have compatible trace element abundances below the contents expected of primitive liquids in equilibrium with a peridotite source. The Ni content varies from 0 ppm to 91 ppm and the Cr content from 0 ppm to 228 ppm. One coarse grained sample from the Boondawari Dolerite (AOB09) (Fig. 1, Table 1), correlated with the Table Hill Volcanics, has an MgO content higher than 8 wt % (Mg # of 69, Fig. 3). This sample was identified as a gabbro in the sample description received from AusQuest Limited. Due to the lack of hand sample and thus thin section availability, we used the geochemistry to assess whether this sample is a cumulate. The Ni content (91 ppm) of this sample is higher than those of the rest of the sample suite (0–75 ppm); however, it is still well below typical values expected of mantle-derived primitive melts (Allègre et al., 1977) (Fig. 4a). The Cr content of this higher MgO sample (184 ppm) is also well below values typical of primitive compositions (500–800 ppm, Allègre et al., 1977) and it is not the highest value found in the province (Fig. 4b). Therefore, Ni and Cr values for AOB09 are not high enough to be consistent with a primitive liquid in equilibrium with mantle compositions and thus, we have concluded that this sample formed as a cumulate. Fig. 4. View largeDownload slide (a) Ni (ppm) vs MgO (wt %), (b) Co (ppm) vs MgO (wt %) and (c) Cr (ppm) vs MgO (wt %) for the Kalkarindji basalts. Gray band represents the typical range of primitive basalts. Nickel content range expected for magmas in equilibrium with their mantle source is 200–500 ppm (Allègre et al.,1977). Fig. 4. View largeDownload slide (a) Ni (ppm) vs MgO (wt %), (b) Co (ppm) vs MgO (wt %) and (c) Cr (ppm) vs MgO (wt %) for the Kalkarindji basalts. Gray band represents the typical range of primitive basalts. Nickel content range expected for magmas in equilibrium with their mantle source is 200–500 ppm (Allègre et al.,1977). Hand specimens were not available for the samples analysed by AusQuest Limited and consequently a mafic vs felsic index diagram (McDougall, 1962) was used to determine the nature of a high SiO2–low Mg # subset of data. This most differentiated subset of data is exclusive to samples collected within the Savory Basin (Fig. 1b). The Savory Basin samples display trends observed in other thick differentiated dykes and dolerites from other CFBs, for instance, the Red Hill dolerite dyke (Tasmania) from the Ferrar CFB. Collectively, these observations indicate that this highly evolved subset is likely to have formed by the differentiation of thick sills, represented by the coarse-grained regions found in some sill and dyke cores and recognized petrographically in previous studies of some of the dykes found within the Savory Basin (Grey et al., 2005; Jourdan et al., 2014). The chondrite-normalized rare earth element (REE) patterns of the studied Kalkarindji samples are characterized by a modest enrichment of light over middle REE, with (La/Sm)cn varying between 1·83 and 3·64 (Fig. 5). In some cases, a small negative Eu anomaly is observed. However, the Kalkarindji basalts display a large range of light over heavy REE enrichment, with (La/Yb)cn ratios varying between 2·98 and 8·06 (Fig. 5). The primitive mantle normalized incompatible trace element patterns of the Kalkarindji province basalts display pronounced negative Nb and Ta anomalies and a positive Pb anomaly (Fig. 5a–c). Fig. 5. View largeDownload slide (a)–(c) Primitive mantle normalized incompatible trace elements patterns for the Kalkarindji basalts. (d)–(f) Chondrite–normalized REE patterns for the Kalkarindji CFB Province. (c) and (f) show the Table Hill Volcanics and the Antrim Plateau Volcanics plotted together. Normalization parameters from Sun & McDonough (1989). Average Indian MORB compositions from PetDB (www.earthchem.org/petdb). Fig. 5. View largeDownload slide (a)–(c) Primitive mantle normalized incompatible trace elements patterns for the Kalkarindji basalts. (d)–(f) Chondrite–normalized REE patterns for the Kalkarindji CFB Province. (c) and (f) show the Table Hill Volcanics and the Antrim Plateau Volcanics plotted together. Normalization parameters from Sun & McDonough (1989). Average Indian MORB compositions from PetDB (www.earthchem.org/petdb). Sr, Nd, Pb isotopes A subset of samples was selected for isotope analysis. These samples are the freshest rocks based on their low LOI and microscopic observation of thin sections and rock chips. This study provides the first isotopic data to be published on the Kalkarindji LIP. The measured isotopic ratios were corrected for the in situ decay of the parental radiogenic isotopes using an age of 511 Ma (40Ar/39Ar plagioclase age and U–Pb zircon ages determined by Jourdan et al., 2014) and parent/daughter ratios derived from the elemental concentrations measured by ICP-MS (Table 1). Only a slight variation of isotopic values is observed for the analysed Kalkarindji sample suite (143Nd/144Ni = 0·51193–0·51198; 87Sr/86Sri = 0·7092–0·7103; 206Pb/204Pbi = 18·11–18·84; 207Pb/204Pbi = 15·73–15·81; 208Pb/204Pbi = 38. 37–39·21) (Table 2; Fig. 6), spanning the entire area of the province (Fig. 1). Fig. 6. View largeDownload slide Plots of isotopic data for basalts of the Kalkarindji province. (a) 87Sr/86Sr initial isotopic composition vs SiO2 wt %; (b) 206Pb/204Pb initial isotopic composition vs SiO2 wt %; (c) 87Sr/86Sr initial isotopic composition vs Mg-number; (d) 143Nd/144Nd initial isotopic composition vs Mg-number. All isotopic data have been age-corrected to 511 Ma. Fig. 6. View largeDownload slide Plots of isotopic data for basalts of the Kalkarindji province. (a) 87Sr/86Sr initial isotopic composition vs SiO2 wt %; (b) 206Pb/204Pb initial isotopic composition vs SiO2 wt %; (c) 87Sr/86Sr initial isotopic composition vs Mg-number; (d) 143Nd/144Nd initial isotopic composition vs Mg-number. All isotopic data have been age-corrected to 511 Ma. It should be noted that the Nd isotopic compositions display a narrower range of values than those of the Sr and Pb isotope compositions (Fig. 7). As the Sm–Nd system is known to be more resilient than the U–Pb and Rb–Sr systems to post-emplacement disturbance, particularly in hydrothermal conditions, larger variations of Sr and Pb isotopic compositions could be related to alteration or metasomatic processes. Although such disturbance cannot be completely ruled out, our rigorous selection yielded the most unaltered samples of the rock suite for isotope work. Therefore, we attribute the variations of the isotopic ratios to magmatic processes. Fig. 7. View largeDownload slide Initial (511 Ma) Sr, Nd, and Pb isotopic compositions of the Kalkarindji continental flood basalt (CFB) province. In the two Pb vs Pb isotope diagrams, the Northern Hemisphere Reference Line (NHRL) of Hart (1984) is shown. Approximate locations of mantle end-members age-corrected to 511 Ma (elemental compositions and isotopic ratios used in age-correction of mantle end-members from Zindler & Hart, 1986) are indicated for reference. Also shown are the fields of selected CFBs; Karoo, Central Atlantic Magmatic Province (CAMP), Deccan, and Ferrar. All data for these CFBs are from the GEOROC database, Pb isotopic data for Ferrar are from Hergt et al. (1989). The ellipsoids represent where roughly 90% of the data clusters. Data for referenced CFBs are age-corrected to the respective time of emplacement using elemental averages of the GEOROC isotopic data for each respective province: Karoo (183 Ma); CAMP (201 Ma); Deccan (66·5 Ma); and Ferrar (183 Ma). Fig. 7. View largeDownload slide Initial (511 Ma) Sr, Nd, and Pb isotopic compositions of the Kalkarindji continental flood basalt (CFB) province. In the two Pb vs Pb isotope diagrams, the Northern Hemisphere Reference Line (NHRL) of Hart (1984) is shown. Approximate locations of mantle end-members age-corrected to 511 Ma (elemental compositions and isotopic ratios used in age-correction of mantle end-members from Zindler & Hart, 1986) are indicated for reference. Also shown are the fields of selected CFBs; Karoo, Central Atlantic Magmatic Province (CAMP), Deccan, and Ferrar. All data for these CFBs are from the GEOROC database, Pb isotopic data for Ferrar are from Hergt et al. (1989). The ellipsoids represent where roughly 90% of the data clusters. Data for referenced CFBs are age-corrected to the respective time of emplacement using elemental averages of the GEOROC isotopic data for each respective province: Karoo (183 Ma); CAMP (201 Ma); Deccan (66·5 Ma); and Ferrar (183 Ma). The 87Sr/86Sri and 143Nd/144Ndi ratios do not display any correlation with Mg # (Fig. 6d). As the 143Nd/144Ndi isotopic ratios have a more restricted range of values than those of87Sr/86Sri and 206Pb/204Pbi, the covariations of these ratios in the 143Nd/144Ndi vs 87Sr/86Sri and 143Nd/144Ndi vs 206Pb/204Pbi plots are near horizontal. (Fig. 7c and e). This is in stark contrast to many other CFB provinces that show a negative correlation between the 143Nd/144Ndi and 87Sr/86Sri (Fig. 7c). However, it should be noted that the Ferrar CFB province has signatures very similar to the Kalkarindji CFBs (Fig. 7). There are no discernable differences in Pb isotope composition between the Antrim Plateau Volcanics and Table Hill Volcanics. All the data plot above the Northern Hemisphere Reference Line (NHRL) (Fig. 7a and d). The 207Pb/204Pbi compositions for the Antrim Plateau Volcanics exhibit a wider range in values compared to the Sr and Nd isotopic data. The Kalkarindji data display a positive correlation on a 206Pb/204Pbi vs 208Pb/204Pbi plot. In contrast, 87Sr/86Sri vs 206Pb/204Pbi and 207Pb/204Pbi vs 206Pb/204Pbi plots for the Kalkarindji CFB data show a cluster of data with no discernable trend. The 87Sr/86Sri isotope compositions for the Kalkarindji suite also appear to be very radiogenic for a given 206Pb/204Pbi (Fig. 7b), especially when considering other CFBs. For all isotopic systems except 207Pb/204Pb, the Kalkarindji CFBs plot in close proximity to the field of the enriched mantle II (EMII) mantle end-member. DISCUSSION Petrogenesis Fractional crystallization The major element contents of the Kalkarindji basalts indicate relatively evolved compositions, as all samples except one have less than 8 wt % MgO and all samples have Mg # lower than 69. The petrographic observations, coupled with the major element compositions, are consistent with patterns and trends for typical gabbroic suites that are commonly interpreted in terms of fractional crystallization involving clinopyroxene and feldspar with a minor amount of oxide minerals (primarily ilmenite). The MELTS program and code of Ghiorso & Sack (1995) was used to calculate and test the fractionation trend observed in the Kalkarindji CFB rocks as well as to provide an estimate for the composition of the residual liquid (Fig. 8). Isenthalpic calculations were made using several different initial parameters to model the possible fractionation trends of the Kalkarindji CFB magmas [P = 1–3 kbar, H2O = 0–1%, ƒO2 = QFM +1 (quartz–fayalite–magnetite)]. For the starting composition, sample AOB07 from the Table Hill Volcanics was chosen, because this sample has the highest MgO and the lowest SiO2 content. Fig. 8. View largeDownload slide Rhyolite-MELTS fractional crystallization modeling curves for selected major element trends for the Kalkarindji continental flood basalts. Low pressure (1 kbar) anhydrous, moderate pressure (3 kbar) anhydrous, low pressure (1 kbar) hydrous (1% H2O), and moderate pressure (3 kbar) hydrous (1% H2O) calculations are displayed. The QFM + 1 (Quartz–Fayalite–Magnetite) buffer was used for ƒO2 (Ghiorso & Sack, 1995). [Circles represent % of fractionation at 15% intervals]. Model completion percentages: Dry–1 kbar = 86%, Dry–3 kbar = 81%, Wet 1%–1 kbar = 65%, Wet 1%– 3 kbar = 61%. Fig. 8. View largeDownload slide Rhyolite-MELTS fractional crystallization modeling curves for selected major element trends for the Kalkarindji continental flood basalts. Low pressure (1 kbar) anhydrous, moderate pressure (3 kbar) anhydrous, low pressure (1 kbar) hydrous (1% H2O), and moderate pressure (3 kbar) hydrous (1% H2O) calculations are displayed. The QFM + 1 (Quartz–Fayalite–Magnetite) buffer was used for ƒO2 (Ghiorso & Sack, 1995). [Circles represent % of fractionation at 15% intervals]. Model completion percentages: Dry–1 kbar = 86%, Dry–3 kbar = 81%, Wet 1%–1 kbar = 65%, Wet 1%– 3 kbar = 61%. Fig. 9. View largeDownload slide Diagram of mafic vs felsic index for basalts and dolerites of the Kalkarindji continental flood basalt (CFB) province and comparisons with the Ferrar CFB province (Red Hill Dolerite). Mafic index calculation: [(FeO + Fe2O3) x 100 / (FeO + Fe2O3 + MgO)]; felsic index calculation: [(Na2O + K2O) x 100 / (Na2O + K2O + CaO)], after Simpson (1954). Data for the Red Hill Dolerite (part of the Tasmanian dolerite) from McDougall (1962). Fig. 9. View largeDownload slide Diagram of mafic vs felsic index for basalts and dolerites of the Kalkarindji continental flood basalt (CFB) province and comparisons with the Ferrar CFB province (Red Hill Dolerite). Mafic index calculation: [(FeO + Fe2O3) x 100 / (FeO + Fe2O3 + MgO)]; felsic index calculation: [(Na2O + K2O) x 100 / (Na2O + K2O + CaO)], after Simpson (1954). Data for the Red Hill Dolerite (part of the Tasmanian dolerite) from McDougall (1962). The MELTS calculations indicate that the Kalkarindji CFB rocks can be represented by up to 81% anhydrous fractional crystallization at moderate pressure (3 kbar) (Fig. 8) with the solid extract comprising plagioclase (47 wt %), augite (30 wt %), pigeonite (17 wt %) and magnetite (5 wt %). MELTS modeling predicts a crystallization sequence of augite + plagioclase → augite + pigeonite + plagioclase → augite + pigeonite + plagioclase + titano-magnetite. The MELTS models and mineral assemblages are consistent with petrographic observations and the geochemical data indicating a realistic possibility for the petrogenesis of the magmas represented by the samples from Kalkarindji. The MELTS models also properly reproduce the shift in the trend visible in the TiO2 vs Mg # plot (which is due to the crystallization of Ti-magnetite) in the more evolved sub-set found in the dykes of the Officer Basin. The MELTS models also properly reproduce the shift in the trend visible in the TiO2 vs Mg # plots (which is due to the crystallization of Ti-magnetite) in the more evolved sub-set found in the dykes of the Officer Basin (Fig. 9). The estimated 81% of fractionation, coupled with the acceptable fit of this model for nearly all major oxide vs Mg # plots (a trend to be expected by the covariance observed in all plots) is interpreted to indicate that fractional crystallization was the dominant process controlling the evolution of the Kalkarindji suite. Although this model provides the best fit for these chemical trends, the starting composition used is not a primary magma. Thus, these calculations give minimum values for the extent to which fractional crystallization has occurred; they do not take into account any evolution or fractionation that may have occurred earlier or at a deeper level. Open system assimilation In the 87Sr/86Sri vs 143Nd/144Ndi diagram (Fig. 7c) the Kalkarindji CFB samples plot near, but off, the mantle array displaying highly radiogenic 87Sr/86Sri ratios (0·7092–0·7104) and low, less-radiogenic, 143Nd/144Ndi ratios (0·51193–0·51198) typical of enriched CFB-type magmas. It should be noted that the Kalkarindji CFBs have more radiogenic isotopic compositions than other CFBs (Fig. 7). The enriched signature of CFBs has been interpreted by some authors to reflect shallow contamination by the continental crust of mantle-derived magmas (Arndt & Christensen, 1992). Therefore, before discussing the nature of the mantle source of the Kalkarindji basalts, an assessment will be made of the involvement of shallow crustal contamination. Along with the absence of covariation in 87Sr/86Sri or 143Nd/144Ndi vs Mg # plots (Fig. 6), the Kalkarindji CFB sample suite does not display an obvious negative correlation between higher Sr and lower Nd isotope ratios that is typical of other CFBs (Fig. 7c), features that are generally attributed to crustal contamination. A lack of covariance is also apparent when isotopic compositions are plotted against SiO2 content; the variation of isotopic composition is not commensurate with changes in SiO2 content (Fig. 6a). This suggests that crustal contamination has had no, or very limited, influence on the chemical characteristics of these rocks. Furthermore, if assimilation had an important role in the petrogenesis of the Kalkarindji basalts, the Sr and Nd isotopic compositions should display a large range of values, as is commonly observed for other CFBs. For example, the 87Sr/86Sri of crustally-contaminated low-Ti magmas in the Karoo CFB province range from 0·7053 to more than 0·718 (Jourdan et al., 2007 and references therein). To further test if crustal contamination has affected the composition of the Kalkarindji CFB magmas, the energy-constrained assimilation and fractional crystallization (EC-AFC) model (Bohrson & Spera, 2001) was applied to the isotopic data for the Kalkarindji suite. The thermal parameters used were those of Spera & Bohrson (2001) for a standard upper crust. For the contaminant, the isotopic data were those of the granodioritic Shaw Batholith in the Pilbara Craton. This was chosen because Sr, Nd, and Pb isotopic data are available for this old cratonic crustal material. The Kalkarindji CFB was not directly emplaced through the Shaw Batholith, but it is still geographically close to the western occurrences of the Table Hill Volcanics and is, therefore, considered to be a valid proxy for at least one of many potential contaminants for the Kalkarindji CFB magmas. Two different assimilation models were considered (compositions and model parameters given in Table 3). Table 3: EC-AFC parameters for the Kalkarindji CFB and potential contaminants Sample T (°C) NAFC NAFC Magma liquidus temperature 1280 Equilibration temperature 949 Magma initial temperature 1280 Crystallization enthalpy (J/kg) 396 000 Assimilant liquidus temperature 950 Isobaric specific heat of magma (J/kg per K) 1484 Assimilant initial temperature 300 Fusion enthalpy (J/kg) 270 000 Solidus temperature 900 Isobaric specific heat of assimilant (J/kg per K) 1370 Composition parameters Sr Nd 206Pb/204Pb 207Pb/204Pb 208Pb/204Pb Kalkarindji CFB Sample - THD-008_8  Magma initial concentration (ppm) 138·4 18·1 12·2 12·2 12·2  Magma isotope ratio 0·71001 0·511825 18·598 15·761 39·208  Magma trace element distribution coefficient 1·5 0·25 0·17 0·17 0·17 Kalkarindji CFB Sample - 031  Magma initial concentration (ppm) 174·7 20·8 7·40 7·40 7·40  Magma isotope ratio 0·70919 0·511805 18·482 15·752 39·015  Magma trace element distribution coefficient 1·5 0·25 0·17 0·17 0·17 Indian MORB  Magma initial concentration (ppm) 206 9·3 0·60 0·60 0·60  Magma isotope ratio 0·70563 0·512289 18·1577 15·4950 38·0321  Magma trace element distribution coefficient 1·5 0·25 0·17 0·17 0·17 Australian Crust Assimilant  Assimilant initial concentration (ppm) 574·8 31·8 8·95 8·95 8·95  Assimilant isotope ratio 0·72868 0·510185 22·2909 16·9377 41·6347  Assimilant trace element distribution coefficient 1·5 0·25 0·56 0·56 0·56 Sample T (°C) NAFC NAFC Magma liquidus temperature 1280 Equilibration temperature 949 Magma initial temperature 1280 Crystallization enthalpy (J/kg) 396 000 Assimilant liquidus temperature 950 Isobaric specific heat of magma (J/kg per K) 1484 Assimilant initial temperature 300 Fusion enthalpy (J/kg) 270 000 Solidus temperature 900 Isobaric specific heat of assimilant (J/kg per K) 1370 Composition parameters Sr Nd 206Pb/204Pb 207Pb/204Pb 208Pb/204Pb Kalkarindji CFB Sample - THD-008_8  Magma initial concentration (ppm) 138·4 18·1 12·2 12·2 12·2  Magma isotope ratio 0·71001 0·511825 18·598 15·761 39·208  Magma trace element distribution coefficient 1·5 0·25 0·17 0·17 0·17 Kalkarindji CFB Sample - 031  Magma initial concentration (ppm) 174·7 20·8 7·40 7·40 7·40  Magma isotope ratio 0·70919 0·511805 18·482 15·752 39·015  Magma trace element distribution coefficient 1·5 0·25 0·17 0·17 0·17 Indian MORB  Magma initial concentration (ppm) 206 9·3 0·60 0·60 0·60  Magma isotope ratio 0·70563 0·512289 18·1577 15·4950 38·0321  Magma trace element distribution coefficient 1·5 0·25 0·17 0·17 0·17 Australian Crust Assimilant  Assimilant initial concentration (ppm) 574·8 31·8 8·95 8·95 8·95  Assimilant isotope ratio 0·72868 0·510185 22·2909 16·9377 41·6347  Assimilant trace element distribution coefficient 1·5 0·25 0·56 0·56 0·56 EC-AFC parameters for the Kalkarindji CFB and potential contaminants. Thermodynamic parameters and Sr and Nd distribution coefficients from Bohrson & Spera (2001). Pb distribution coefficients from Jourdan et al. (2007) calculated using values reported in the GERM database (http://earthref.org/GERM/). For in-suite composition comparisons initial compositional parameters from samples THD-008_8 (Table Hill Volcanics) and sample 031 (Antrim Plateau Volcanics). Sr and Nd isotopic and element concentrations for assimilant are from a 15% trimmed mean of north Australia felsic crust (NAFC) from the GEOROC database. Pb isotopic and element concentrations for the assimilant are from the Shaw Batholith located in the Pilbara Craton from the GEOROC database. Average Indian MORB compositions from PetDB(www.earthchem.org/petdb). Table 3: EC-AFC parameters for the Kalkarindji CFB and potential contaminants Sample T (°C) NAFC NAFC Magma liquidus temperature 1280 Equilibration temperature 949 Magma initial temperature 1280 Crystallization enthalpy (J/kg) 396 000 Assimilant liquidus temperature 950 Isobaric specific heat of magma (J/kg per K) 1484 Assimilant initial temperature 300 Fusion enthalpy (J/kg) 270 000 Solidus temperature 900 Isobaric specific heat of assimilant (J/kg per K) 1370 Composition parameters Sr Nd 206Pb/204Pb 207Pb/204Pb 208Pb/204Pb Kalkarindji CFB Sample - THD-008_8  Magma initial concentration (ppm) 138·4 18·1 12·2 12·2 12·2  Magma isotope ratio 0·71001 0·511825 18·598 15·761 39·208  Magma trace element distribution coefficient 1·5 0·25 0·17 0·17 0·17 Kalkarindji CFB Sample - 031  Magma initial concentration (ppm) 174·7 20·8 7·40 7·40 7·40  Magma isotope ratio 0·70919 0·511805 18·482 15·752 39·015  Magma trace element distribution coefficient 1·5 0·25 0·17 0·17 0·17 Indian MORB  Magma initial concentration (ppm) 206 9·3 0·60 0·60 0·60  Magma isotope ratio 0·70563 0·512289 18·1577 15·4950 38·0321  Magma trace element distribution coefficient 1·5 0·25 0·17 0·17 0·17 Australian Crust Assimilant  Assimilant initial concentration (ppm) 574·8 31·8 8·95 8·95 8·95  Assimilant isotope ratio 0·72868 0·510185 22·2909 16·9377 41·6347  Assimilant trace element distribution coefficient 1·5 0·25 0·56 0·56 0·56 Sample T (°C) NAFC NAFC Magma liquidus temperature 1280 Equilibration temperature 949 Magma initial temperature 1280 Crystallization enthalpy (J/kg) 396 000 Assimilant liquidus temperature 950 Isobaric specific heat of magma (J/kg per K) 1484 Assimilant initial temperature 300 Fusion enthalpy (J/kg) 270 000 Solidus temperature 900 Isobaric specific heat of assimilant (J/kg per K) 1370 Composition parameters Sr Nd 206Pb/204Pb 207Pb/204Pb 208Pb/204Pb Kalkarindji CFB Sample - THD-008_8  Magma initial concentration (ppm) 138·4 18·1 12·2 12·2 12·2  Magma isotope ratio 0·71001 0·511825 18·598 15·761 39·208  Magma trace element distribution coefficient 1·5 0·25 0·17 0·17 0·17 Kalkarindji CFB Sample - 031  Magma initial concentration (ppm) 174·7 20·8 7·40 7·40 7·40  Magma isotope ratio 0·70919 0·511805 18·482 15·752 39·015  Magma trace element distribution coefficient 1·5 0·25 0·17 0·17 0·17 Indian MORB  Magma initial concentration (ppm) 206 9·3 0·60 0·60 0·60  Magma isotope ratio 0·70563 0·512289 18·1577 15·4950 38·0321  Magma trace element distribution coefficient 1·5 0·25 0·17 0·17 0·17 Australian Crust Assimilant  Assimilant initial concentration (ppm) 574·8 31·8 8·95 8·95 8·95  Assimilant isotope ratio 0·72868 0·510185 22·2909 16·9377 41·6347  Assimilant trace element distribution coefficient 1·5 0·25 0·56 0·56 0·56 EC-AFC parameters for the Kalkarindji CFB and potential contaminants. Thermodynamic parameters and Sr and Nd distribution coefficients from Bohrson & Spera (2001). Pb distribution coefficients from Jourdan et al. (2007) calculated using values reported in the GERM database (http://earthref.org/GERM/). For in-suite composition comparisons initial compositional parameters from samples THD-008_8 (Table Hill Volcanics) and sample 031 (Antrim Plateau Volcanics). Sr and Nd isotopic and element concentrations for assimilant are from a 15% trimmed mean of north Australia felsic crust (NAFC) from the GEOROC database. Pb isotopic and element concentrations for the assimilant are from the Shaw Batholith located in the Pilbara Craton from the GEOROC database. Average Indian MORB compositions from PetDB(www.earthchem.org/petdb). Kalkarindji parental magmas assimilation models The first model involves the introduction of a crustal contaminant into a more MORB-like melt (Fig. 10). In this scenario, the EC-AFC curves intercept the Sr isotopic compositions of the Kalkarindji CFB samples with the lowest concentration of Sr (ppm). However, the overlap occurs at a minute percentage of assimilation close to 0. The Kalkarindji CFB data display a wide range in Sr concentrations for nearly no change in 87Sr/86Sri, which is in stark contrast to the trend predicted by the EC-AFC model curve (Fig. 10a, MORB initial). More depleted MORB initial compositions were modeled as well, but the models were unable to reproduce the trends observed for the Kalkarindji province in all isotopic systems. Kalkarindji CFB Nd and Pb data form clusters rather than trends on isotope diagrams and the chemical trends predicted in the models are not matched once assimilation of the crustal material begins. Even when considering the vectors calculated with a MORB parent, the geochemical trends in the Kalkarindji data do not follow the modeled trends, indicating that no continental crust input is feasible if a MORB parent is used. Fig. 10. View largeDownload slide Model isotopic ratios and trace element data for the Kalkarindji basalts (a) Initial 87Sr/86Sr vs Sr (ppm); (b) initial 143Nd/144Nd vs Nd (ppm); (c) initial 206Pb/204Pb vs Pb (ppm); (d) initial 208Pb/204Pb vs Pb (ppm); (e) initial 207Pb/204Pb vs Pb (ppm) showing energy constrained assimilation and fractional crystallization (EC-AFC) model curves for three possible initial conditions (compositions given in Table 3) calculated using the code of Spera & Bohrson (2001). Small circles on curves indicate the percentage of assimilated contaminant. All isotopic data have been age-corrected to 511 Ma. Fig. 10. View largeDownload slide Model isotopic ratios and trace element data for the Kalkarindji basalts (a) Initial 87Sr/86Sr vs Sr (ppm); (b) initial 143Nd/144Nd vs Nd (ppm); (c) initial 206Pb/204Pb vs Pb (ppm); (d) initial 208Pb/204Pb vs Pb (ppm); (e) initial 207Pb/204Pb vs Pb (ppm) showing energy constrained assimilation and fractional crystallization (EC-AFC) model curves for three possible initial conditions (compositions given in Table 3) calculated using the code of Spera & Bohrson (2001). Small circles on curves indicate the percentage of assimilated contaminant. All isotopic data have been age-corrected to 511 Ma. Within suite isotopic variability assimilation models A second model was used to test if the variability within each suite can be explained by distinct local crustal components. For this model, the samples chosen for the parent magmas of the Kalkarindji suite were THD-008_8 (the sample from the Table Hill Volcanic suite with the most ‘primitive’ isotopic composition) and APV-31 (most ‘primitive’ sample from the Antrim Plateau Volcanic). The EC-AFC models predict an initial increase in Pb and Nd (ppm) concentrations and a decrease in Sr (ppm) concentrations with no change in the isotopic compositions for any of the systems (Fig. 10b–e). This flat trajectory in the models is caused by the lack of any production of anatectic melt due to the time taken for the country-rock to reach the solidus temperature. Therefore, this portion of the model corresponds to the effect of the fractional crystallization process only (Bohrson & Spera, 2001). These results agree with the MELTS models that indicate a dominant role for fractional crystallization in explaining the variation of major elements. Once assimilation begins, there is a dramatic increase in the 206Pb/204Pbi, 207Pb/204Pbi, 208Pb/204Pbi and 87Sr/86Sri and a decrease in 143Nd/144Ndi for all modeled assimilation paths (Fig. 10). Such sharp isotopic variations, even for a small variation in the amount of assimilant, contrasts with the limited amount of isotopic variation observed in the Kalkarindji suite. These models indicate that contamination by the continental crust during the ascent of the magma to the surface is unlikely to have been a major influence controlling chemical variation in the Kalkarindji suite. Furthermore, the Antrim Plateau Volcanics and the Table Hill Volcanics are separated by more than 1000 km, implying that these two suites were emplaced through chemically different units of continental crust. Nevertheless, the major and trace element contents as well as the Sr, Nd, Pb isotopic compositions directly overlap for each suite. This homogeneity is at odds with the variation expected; assimilation of crustal components should have influenced the geochemical compositions of the magmas. As the isotopic dataset provided by this study represents a comprehensive areal coverage of the Kalkarindji province, the available data indicate that large-scale crustal contamination is unlikely to account for the enriched nature of the magmas. Partial melting As with the major element abundance patterns and isotopic compositions of the Kalkarindji suite, the REE and other incompatible trace element patterns of both the Antrim Plateau Volcanic and the Table Hill Volcanic suites are very similar. Variation between the abundances of the light rare earth elements (LREE), middle rare earth elements (MREE), and heavy rare earth elements (HREE) have been controlled by crystal fractionation for the evolved samples in particular but they are also an indication of genetic and evolutionary processes and source characteristics controlling the compositions of the original primary melts. These could include: (i) the degree of partial melting, which controls LREE/MREE vs MREE/HREE variations at source; (ii) source composition in terms of enrichment of LREE relative to HREE; and (iii) variation in source mineralogy (MREE/LREE variations), with residual garnet or spinel. At constant degrees of melting, the elevated La/Yb ratios of the most primitive rocks could indicate source enrichment prior to melting. However, melting is the only process able to increase dramatically the LREE/MREE without significant effects on the MREE/HREE ratio. In addition, MREE/HREE ratios close to or > 1 are evidence of residual garnet in the source. For the Kalkarindji basalts, the (La/Sm)cn values are in the range of 1·83–3·64 and the Dy/Yb ratios vary from 1·03–1·82. These ratios, coupled with the relatively low La/Yb ratios (4·16–11·23) represent modest relative enrichments in incompatible trace element abundances compared with those of average Indian MORB and they are indications that: (1) source enrichment can account for the observed variations of the REE ratios; (2) a specific degree of partial melting can be inferred; and (3) garnet was not a residual phase during mantle melting, with melting occurring in the shallow spinel field. To test the melting conditions for the Kalkarindji CFBs and match the observations made from the LREE/HREE ratios (e.g. La/Smcn 1·83–3·64; Dy/Yb 1·03–1·82), the equations from Shaw (1970) were used to model the REE distribution during partial melting. Mantle xenoliths have not been found in the Kalkarindji CFBs so non-modal batch melting calculations were made assuming two theoretical, slightly LREE-enriched peridotites: a spinel-bearing lherzolite; and a garnet-bearing lherzolite. These two mineral assemblages are appropriate for the mantle source of CFBs (e.g. Jourdan et al., 2007) (Fig. 11). The partition coefficients used in the calculations are from McKenzie & O'Nions (1983). The spinel–lherzolite source used in the calculations was assumed to have a modal composition of 55 wt % olivine, 15 wt % orthopyroxene, 28 wt % clinopyroxene, and 2 wt % spinel, with a melting mode of 20 wt % olivine, 20 wt % orthopyroxene, 55 wt % clinopyroxene, and 5 wt % spinel. The modal composition assumed for the garnet–lherzolite source was 52 wt % olivine, 33 wt % orthopyroxene, 10 wt % clinopyroxene, and 5 wt % garnet, with a melting mode of 16 wt % olivine, -12 wt % orthopyroxene, 81 wt % clinopyroxene, and 15 wt % garnet (Jourdan et al., 2007 and references therein). Due to the compositional homogeneity of the province, the same LREE composition was utilized for calculating melting of both spinel and garnet-lherzolites. The samples that display less than 5% fractional crystallization (as calculated using the MELTS models) were first considered as representative compositions because these should have compositions closest to those of primitive melts. However, it must also be noted that the degree of fractional crystallization should not noticeably affect the light versus heavy REE ratios for these most primitive rocks (Fig. 11). Only the spinel–lherzolite melting curve intersects with the data from both the Table Hill Volcanics and Antrim Plateau Volcanics and this is interpreted to indicate that the primary melts were generated by 3–5% melting, in the field of spinel (Robinson & Wood, 1998) (Fig. 11a and b). These modeled results are comparable with the low range of those found for some other provinces, such as the Central Atlantic magmatic province (CAMP) (Deckart et al., 2005; Verati et al., 2005). For CAMP, during the initial stages the degree of melting is around 4% rising to 7–15% in the later stages and the low-Ti units (Deckart et al., 2005; Verati et al., 2005). Nevertheless, models for tholeiites more typically give melt fractions in the range of 15–20% melting (Green & Ringwood, 1967). Regardless, we have shown previously that the mantle source of the Kalkarindji melts is enriched beyond the level of a ‘standard’ lherzolite; therefore, we modeled the melting of an enriched lherzolite with an initial La/Sm ratio of 3·64. The latter model indicates that the mantle source underwent a higher degree of partial melting (∼ 9–30%), compared to that predicted for a standard lherzolite composition. At this stage, and without xenolithic samples from the mantle source itself, it is not clear which of the two models is most appropriate and we can only bracket mantle melting values between 5 and 30%. Fig. 11. View largeDownload slide Partial melting models for basalts of the Kalkarindji continental flood basalt province. (a) (Sm/Yb)cn vs (La/Sm)cn and (b) (La/Yb)cn vs (Eu/Yb)cn are non-modal partial melting model results using a garnet lherzolite (grey curve) and a spinel lherzolite (black curve) mantle source. Inset graphs are zoomed-in plots of the spinel model curves. Calculations made using the equations of Shaw (1970). Compositions are chondrite-normalized after Sun & McDonough (1989). Partition coefficients used in the calculations are from McKenzie & O'Nions (1983). Modal compositions of the spinel lherzolite source: 55 wt % olivine, 15 wt % orthopyroxene, 28 wt % clinopyroxene and 2 wt % spinel. Melting mode: 20 wt % olivine, 20 wt % orthopyroxene, 55 wt % clinopyroxene, and 5 wt % spinel. Modal compositions of the garnet lherzolite source: 52 wt % olivine, 33 wt % orthopyroxene, 10 wt % clinopyroxene, and 5 wt % garnet. Melting mode: 16 wt % olivine, -12 wt % orthopyroxene, 81 wt % clinopyroxene and 15 wt % garnet after Jourdan et al. (2007). Fig. 11. View largeDownload slide Partial melting models for basalts of the Kalkarindji continental flood basalt province. (a) (Sm/Yb)cn vs (La/Sm)cn and (b) (La/Yb)cn vs (Eu/Yb)cn are non-modal partial melting model results using a garnet lherzolite (grey curve) and a spinel lherzolite (black curve) mantle source. Inset graphs are zoomed-in plots of the spinel model curves. Calculations made using the equations of Shaw (1970). Compositions are chondrite-normalized after Sun & McDonough (1989). Partition coefficients used in the calculations are from McKenzie & O'Nions (1983). Modal compositions of the spinel lherzolite source: 55 wt % olivine, 15 wt % orthopyroxene, 28 wt % clinopyroxene and 2 wt % spinel. Melting mode: 20 wt % olivine, 20 wt % orthopyroxene, 55 wt % clinopyroxene, and 5 wt % spinel. Modal compositions of the garnet lherzolite source: 52 wt % olivine, 33 wt % orthopyroxene, 10 wt % clinopyroxene, and 5 wt % garnet. Melting mode: 16 wt % olivine, -12 wt % orthopyroxene, 81 wt % clinopyroxene and 15 wt % garnet after Jourdan et al. (2007). The mantle sources of Kalkarindji CFBs Evidence for an enriched component in the mantle source The absence of correlation between SiO2 or MgO abundances and Sr and Nd initial isotopic ratios, the EC-AFC results, and the lack of isotopic variation across the province, are indications that the enriched signatures measured in the Kalkarindji samples are not the result of the contamination of mantle-derived melts by the assimilation of crustal material. They are more consistent with a model whereby the peridotitic mantle source was enriched prior to the Kalkarindji melting event. In a study of two different dyke swarms within the 1070 Ma Warakurna LIP in Western Australia (Wingate et al., 2004; Zhao and McCulloch, 1993) it has been shown that, although the two swarms were emplaced into two different crustal elements, they had similar isotopic compositions. This suggested the involvement of an enriched sub-continental lithospheric mantle source (SCLM). The covariance observed in major element plots (Fig. 3) and the similar trace elements patterns (Fig. 5) for both the Antrim Plateau Volcanics and the Table Hill Volcanics are indications that there was not a drastic change of source composition during the eruption of all the basalts of the Kalkarindji province and, therefore, a large-scale (>1000 km wide) mantle source has to be considered. The LILE enrichment relative to the HFSE and the negative Nb anomaly in normalized incompatible trace element plots are typical chemical characteristics of CFBs (Arndt et al., 1993; Molzahn et al., 1996; Puffer, 2001; Ewart et al., 2004; Jourdan et al., 2007; Merle et al., 2013) and they are generally attributed to an enriched, continental crust-like component in the mantle source. The 143Nd/144Ndi isotopic compositions are much lower than would be expected in the asthenospheric (depleted) mantle and are consistent with a continental crustal input at source (Fig. 7). Similarly, whereas 206Pb/204Pbi is consistent with MORB values, the 207Pb/204Pbi ratio is significantly higher than typical MORB values. Indeed, the Kalkarindji basalts show high 207Pb/204Pbi for a given 206Pb/204Pbi ratio, plotting well above the NHRL (Fig. 7a). As shown by the REE patterns, the Kalkarindji basalts display MREE to HREE patterns similar to those of Indian MORB (Fig. 5). This observation can be explained if an asthenospheric-like mantle was enriched by addition of continental crust-like material. Such an hypothesis has been put forward to explain the enriched signature of the CAMP and the Karoo basalts; in both cases, extensive shallow crustal contamination can be ruled out (Jourdan et al., 2007; Merle et al., 2011, 2013). In addition, two possible processes have been suggested to account for the enriched, continental crust-like, trace element and isotopic signatures of CFBs: (i) shallow metasomatism of the mantle by percolation of silicate or hydrous fluids during an ancient subduction event (Duncan et al., 1984; Puffer, 2001; Ewart et al., 2004); or (ii) the introduction of a small amount of enriched material (e.g. sediment from a subduction event) directly into the source region (Hergt et al., 1989). The melting models are consistent with a shallow mantle source with residual spinel (asthenospheric mantle or SCLM) and enrichment by ancient subduction. Therefore, such a hypothesis is realistic for the mantle source of the Kalkarindji basalts. A sub-continental lithospheric mantle (SCLM) component SCLM metasomatized by the percolation of fluids Metasomatic processes have been shown to be effective in creating heterogeneous mantle, geochemically and mineralogically (Menzies et al., 1987). Percolation of fluids and melts through the lithospheric mantle can lead to refertilized domains due to fluid–rock interactions (Müntener et al., 2010). Such refertilized domains can contain clinopyroxenite veins (from the introduction of fluids) that are more fusible than the average peridotite. The occurrence of large clinopyroxene-rich domains can lead to large-scale melting of the SCLM, which is required to produce the large volumes of magmas within the Kalkarindji province. Furthermore, diamonds found within peridotites can provide evidence of metasomatism (O’Reilly & Griffin, 2013). Small-scale melting of enriched domains in the SCLM has been suggested from the presence of diamonds in the lamproites, lamprophyres, and kimberlites of the Kimberley Block; e.g. Ellendale and Argyle (Gibson et al., 2006) (Fig. 1b). However, the presence of diamonds has yet to be recognized outside the Kimberley Block. SCLM enrichment by subducted sediments Another possibility is the introduction of a small percentage of continental material into the shallow mantle through the process of subduction. Deep recycling of continental sediments has been proposed as a mechanism for generating the EMII mantle component (Zindler & Hart, 1986). The similarity of the isotopic composition of the Kalkarindji basalts to the EMII mantle end-member, could indicate the introduction of sediment into the source region. Hergt et al. (1989) argue that sediment input at source is a plausible process for explaining the geochemistry of the Tasmanian dolerites (Ferrar CFB province), which have signatures very similar to the Kalkarindji basalts (Fig. 7). Hergt et al. (1989) and Merle et al. (2013) found that only a small amount of sediment (< 3 wt %) is needed to produce the enriched ‘crustal’ like characteristics of the Tasmanian dolerites and Eastern North America CAMP. Ben Othman et al. (1989) postulated that ancient sediment has high 232Th/238U, which would lead to high present day 208Pb/204Pb ratios. Due to the systematics of the decay of 238U and 235U, coupled with the high 232Th/238U ratios, ancient recycled sediments should be characterized by high 207Pb/204Pb and 208Pb/204Pb at low 206Pb/204Pb ratios, compared to asthenospheric mantle values. The Kalkarindji basalts display similar isotopic characteristics as described above, as well as high Th/Yb ratios (1·08–4·82) (Fig. 12b) that are characteristic of sediments. Therefore, the involvement of ancient sediment in the source of these basalts is a possibility. The contrast of incompatible trace element concentrations between the depleted MORB mantle-like peridotites and continental-crust derived sediments is likely to produce incompatible trace element signatures in the magmas dominated by the sediment signature, whereas the major elements would retain basaltic characteristics. In addition, the subducted sediment input could also explain: (1) the negative Nb and Ta anomalies in normalized extended element plots, (a prominent geochemical feature of subduction-related magmas; e.g. Pearce, 1982; Briqueu et al., 1984; Baier et al., 2008); and (2) the enriched isotopic compositions of the magmas. The high 207Pb/204Pb and high 87Sr/86Sr for the given low Nd values of the Kalkarindji basalts when compared to MORB are consistent with enrichment of the SCLM by ancient subduction. Fig. 12. View largeDownload slide Selected trace element ratio vs ratio graphs for the Kalkarindji basalts. CAMP is the Central Atlantic Magmatic Province. The Deccan, CAMP, Karoo, and Ferrar compositions are from the GEOROC database. Fig. 12. View largeDownload slide Selected trace element ratio vs ratio graphs for the Kalkarindji basalts. CAMP is the Central Atlantic Magmatic Province. The Deccan, CAMP, Karoo, and Ferrar compositions are from the GEOROC database. Age of the enrichment The elevated 207Pb/204Pb isotopic values with moderate 206Pb/204Pb values can only be explained if source enrichment occurred a long time before the Kalkarindji CFB event (when 235U was still abundant) and the enriched source must have been relatively stable for a long enough period of time for the decay of these two systems to decouple. This has been suggested for several CFBs (e.g. Jourdan et al., 2007; Merle et al., 2013). Lead isotopic compositions of mantle end-member analogues (EMI, EMII, DMM, or HIMU), age-corrected to 511 Ma, are not able to reproduce the observed Pb isotopic signatures of the Kalkarindji basalts, thus necessitating an ancient U enrichment of the SCLM. In order to calculate the age of the lithospheric enrichment, the growth curve calculations of Stacey & Kramers (1975) were used. This approach is taken due to the absence of evidence from the major and trace element data that the Pb system has been disturbed by alteration. The Pb isotope ratios were calculated for different ages of enrichment in attempts to determine the most probable minimum age of enrichment that can reproduce the measured isotopic ratios of the Kalkarindji basalts. The Stacey & Kramers (1975) lead growth curve evolves initially from 4·57 Ga with a 238U/204Pb ratio of 7·19 and a 232Th/238U of 4·62 (Table 4; Fig. 13), from which Stacey & Kramers (1975) postulate a second stage curve with a higher µ (238U/204Pb = 9·74 and 232Th/238U = 3·78) beginning at 3·7 Ga. The isotopic Pb starting composition for the Kalkarindji CFB source area falls on the second stage curve of the Stacey & Kramers (1975) lead model. The enrichment event is assumed to have involved a 238U/204Pb value typical of upper continental crust (UCC) of 12·72 (Zartman & Haines, 1988). The UCC 232Th/238U ratio (3·78) of Zartman & Haines (1988), however, is identical to that of the postulated second stage of Stacey & Kramers (1975). The high 208Pb/204Pb isotopic ratios of the Kalkarindji province basalts require a higher 232Th/238U ratio during the enrichment event than would be derived from the curve of Stacey & Kramers (1975). Therefore, a slight modification of the Th content from 14·8 to 16 ppm was introduced to the model to provide a 232Th/238U ratio greater than four (232Th/238U = 4·06). This is in agreement with Ben Othman et al. (1989) who suggested that the 232Th/238U is difficult to constrain but, from mass balance considerations, they inferred that the value is likely to be greater than four. These UCC 238U/204Pb and 232Th/238U ratios were affected by various enrichment events at different times prior to the emplacement of the Kalkarindji CFBs. As a consequence of these enrichments, the isotopic composition of the SCLM source area evolved away from the Stacey & Kramers (1975) Pb evolution curve to the present day values. These calculations were repeated until a particular enrichment time successfully reproduced the measured Pb isotopic values of the Kalkarindji basalts. The models are consistent with an enrichment event at around 2·5 Ga. This model produces the observed Pb isotopic ratios of the Kalkarindji basalts (Fig. 14). Table 4: Enrichment model parameters for the Kalkarindji CFB province Sample Time (b.y.) 206Pb/204Pb 207Pb/204Pb 208Pb/204Pb 238U/204Pb 232Th/204Pb 232Th/238U 147Sm/144Nd Start of 1st Stage 4·57 9·307 10·294 29·487 7·19 33·21 4·62 – Start of 2nd Stage 3·70 11·152 12·998 31·230 9·74 36·84 3·78 – Enrichment Event 2·50 14·089 14·871 33·780 13·37 54·30 4·06 0·1818 Sample Time (b.y.) 206Pb/204Pb 207Pb/204Pb 208Pb/204Pb 238U/204Pb 232Th/204Pb 232Th/238U 147Sm/144Nd Start of 1st Stage 4·57 9·307 10·294 29·487 7·19 33·21 4·62 – Start of 2nd Stage 3·70 11·152 12·998 31·230 9·74 36·84 3·78 – Enrichment Event 2·50 14·089 14·871 33·780 13·37 54·30 4·06 0·1818 Calculations from Stacey & Kramers (1975). The elemental compositions used in calculations modified from Zartman & Haines (1988). Table 4: Enrichment model parameters for the Kalkarindji CFB province Sample Time (b.y.) 206Pb/204Pb 207Pb/204Pb 208Pb/204Pb 238U/204Pb 232Th/204Pb 232Th/238U 147Sm/144Nd Start of 1st Stage 4·57 9·307 10·294 29·487 7·19 33·21 4·62 – Start of 2nd Stage 3·70 11·152 12·998 31·230 9·74 36·84 3·78 – Enrichment Event 2·50 14·089 14·871 33·780 13·37 54·30 4·06 0·1818 Sample Time (b.y.) 206Pb/204Pb 207Pb/204Pb 208Pb/204Pb 238U/204Pb 232Th/204Pb 232Th/238U 147Sm/144Nd Start of 1st Stage 4·57 9·307 10·294 29·487 7·19 33·21 4·62 – Start of 2nd Stage 3·70 11·152 12·998 31·230 9·74 36·84 3·78 – Enrichment Event 2·50 14·089 14·871 33·780 13·37 54·30 4·06 0·1818 Calculations from Stacey & Kramers (1975). The elemental compositions used in calculations modified from Zartman & Haines (1988). Fig. 13. View largeDownload slide Kalkarindji continental flood basalt (CFB) province initial lead isotope calculation model. Calculations after Stacey & Kramers (1975): O = troilite Pb, 4·57 Ga; n(ti): new zero cord, age t1 (3·7 Ga), t2 (2·5 Ga); P(t1): intercept of n(t1) and the meteoric isochron; g(tl): Stacey & Kramers (1975) single-stage growth curve; Q(t1): composition of terrestrial Pb at the enrichment event, tl (3·7 Ga. ago); Q(t2): composition of Kalkarindji source Pb at the enrichment event t2 (2·5 Ga ago); K(t1): growth curve for the second stage for average modern Pb. K(t2): growth curve of the source for the Kalkarindji CFB province after the enrichment event. Fig. 13. View largeDownload slide Kalkarindji continental flood basalt (CFB) province initial lead isotope calculation model. Calculations after Stacey & Kramers (1975): O = troilite Pb, 4·57 Ga; n(ti): new zero cord, age t1 (3·7 Ga), t2 (2·5 Ga); P(t1): intercept of n(t1) and the meteoric isochron; g(tl): Stacey & Kramers (1975) single-stage growth curve; Q(t1): composition of terrestrial Pb at the enrichment event, tl (3·7 Ga. ago); Q(t2): composition of Kalkarindji source Pb at the enrichment event t2 (2·5 Ga ago); K(t1): growth curve for the second stage for average modern Pb. K(t2): growth curve of the source for the Kalkarindji CFB province after the enrichment event. Fig. 14. View largeDownload slide Three component-mixing models for the Kalkarindji basalts showing Indian MORB melts swamped by SCLM that was contaminated by an ancient, subducted, enriched component. Average Indian MORB compositions from PetDB (www.earthchem.org/petdb), SCLM composition is the BSE estimated average, isotopes from Rollinson (1993) and trace element information from the mantle estimates of Zartman & Haines (1988), enriched component isotopic data are calculated assuming an enrichment event at 2·5 Ga with elemental compositions taken from the upper continental crust estimates of Zartman & Haines (1988). All isotope data age-corrected to 511 Ma. Fig. 14. View largeDownload slide Three component-mixing models for the Kalkarindji basalts showing Indian MORB melts swamped by SCLM that was contaminated by an ancient, subducted, enriched component. Average Indian MORB compositions from PetDB (www.earthchem.org/petdb), SCLM composition is the BSE estimated average, isotopes from Rollinson (1993) and trace element information from the mantle estimates of Zartman & Haines (1988), enriched component isotopic data are calculated assuming an enrichment event at 2·5 Ga with elemental compositions taken from the upper continental crust estimates of Zartman & Haines (1988). All isotope data age-corrected to 511 Ma. To test whether the sediment composition used to estimate the separation age of the Kalkarindji CFB enriched reservoir is appropriate, model isotopic compositions were also calculated using alternative crustal compositions including: an upper continental crust composition (Taylor & McLennan, 1985); the bulk continental crust composition of Rudnick & Fountain (1995); and the GLOSS values of Plank & Langmuir (1998). None of these alternative crustal compositions has a µ value that can produce viable results for Kalkarindji basalts at any time of enrichment. They all have 238U/204Pb and 232Th/238U ratios that are too low to match the expected isotopic compositions. If slight changes in the 238U/204Pb and 232Th/238U ratios can affect the estimated enrichment age, these ratios can be constrained by comparing the results from all three Pb isotopic systems as well as the tectonic history of the area. The calculated age of enrichment of 2·5 Ga is consistent with estimates for the amalgamation of the North Australian Craton, which occurred around this time (Cawood & Korsch, 2008; Drüppel et al., 2009). Involvement of a MORB-like component: a tri-component source? The geochemical characteristics of the Kalkarindji basalts are compatible with the involvement of SCLM enriched by an ancient sediment input. However, the least incompatible trace elements and HREE patterns of the Kalkarindji basalts show similarities with Indian MORB (Fig. 5d–f). In addition, some isotopic compositions are close to the mantle array in a 143Nd/144Nd vs 87Sr/86Sr diagram. These observations are compatible with the involvement of an asthenospheric component. Alternative models of wholesale melting of the SCLM suggest contamination of melts from the sub-lithospheric convective mantle (asthenosphere) by fluids or melts originating from the SCLM (Arndt & Christensen, 1992; Gibson et al., 2006; Heinonen et al., 2010). Therefore, the source for the Kalkarindji basalts could be derived by mixing liquids from the SCLM, an enriched, continental-like component, and MORB melts. Such a tri-component mixture has been suggested for other CFBs sources; e.g. Paraná/Etendeka (Ewart et al., 2004) and CAMP (Merle et al., 2013). A tri-component mixing model was tested for the Kalkarindji basalts using realistic geochemical parameters to assess the contribution of each component to the isotopic characteristics of the source of the basalts. The three component mixing models were calculated using: (i) an average Indian MORB melt composition to represent the primitive component in the system and a SCLM consisting of a mixture between: (ii) a pre-enriched SCLM component with estimated isotopic composition close to the average of bulk silicate earth (BSE) from Rollinson (1993), with trace element compositions from the mantle reservoir estimates of Zartman & Haines (1988); and (iii) a 2·5 Ga sediment enriched component calculated from the isotopic ratios utilizing trace element ratios of the average upper crustal composition of Zartman & Haines (1988). Note that the SCLM component is assumed to have had the trace element contents of a peridotite. Therefore, this approach models the isotopic composition of the source through a process involving asthenospheric MORB-like melt swamping an enriched peridotite created by the solid mixing of components (ii) and (iii) described above. Prior to the proposed enrichment event, the composition of the SCLM would not have produced a low enough 143Nd/144Nd isotopic ratio to account for the extremely low radiogenic values of the Kalkarindji basalts. To encompass the Nd isotopic results for the Kalkarindji basalts requires a slightly higher 147Sm/144Nd ratio than the BSE mantle values of Zartman & Haines (1988). Therefore, the pre-enriched SCLM component for the model was calculated using a 147Sm/144Nd of 0·259 rather than a value of 0·222. The adjustment is minor considering that a worldwide average value is unlikely to represent a particular mantle end-member and as such, it is considered appropriate for the modeling of the Kalkarindji CFB province isotopic compositions. Uncertainties to consider when interpreting these results are slight variations of the sediment composition in incompatible elements and/or preferential leaching of elements by fluids or melts that would result in changes to the shape of the mixing curves. The mixing field defined by the three components adequately encompasses the observed Kalkarindji CFB values (Fig. 14). The isotopic composition of the Kalkarindji CFB can be best modeled by an SCLM enriched with no more than 10% of sediment melt mixing with less than 10% Indian MORB melt for the Pb isotopic ratios and between 10 and 20% Indian MORB melt for the Sr–Nd isotopic ratios (Fig. 14). This model shows that the chemical signature of the enriched part of the SCLM (SCLM plus the ancient enrichment) dominated the isotopic composition of the Kalkarindji magmas. This is consistent with the proposal that the source of Kalkarindji basalts is a sediment-enriched SCLM which interacted with MORB-like melts before the CFB melting event. The array defined by the Pb isotope data for the Kalkarindji basalts parallels the modeled mixing curves between the SCLM and the ancient sediment end-member components. This apparent smearing of the Pb isotope data could be due to: (i) slight variations of U/Pb and Th/U values from the enriched material introduced into the source area that are related to variations of either these ratios in the sediments or the degree of sediment melting; or (ii) a continuous input over time, possibly hundreds of millions of years, into the SCLM source(s) causing a variation in the isotopic ratios within the source (Merle et al., 2013). In addition, the slight difference in the 147Sm/144Nd ratio from the BSE elemental composition of Zartman & Haines (1988) needed to model the Kalkarindji basalts could be due to the level of variation possible when using an average, as discussed above, or alternatively it could indicate that the system was affected by a second enrichment event, which introduced a slightly higher 147Sm/144Nd ratio. Such an event would, however, have to be characterized by U/Pb and Th/U values similar to those prevailing during the initial enrichment event. This later scenario is unlikely, however, as it is not sustained by any geological evidence (Fig. 14). Geodynamics Cause for the Kalkarindji CFB magmatism Mantle plume involvement In terms of chemical characteristics, the data and model results do not require a major contribution of a mantle plume in the genesis of the Kalkarindji magmas. Furthermore, the Kalkarindji province does not display convincing evidence for any dyke swarm and even less for radiating dyke swarms, which have been used to indicate the impingement of a plume head on the lithosphere during the generation of other LIPs. We note that, in any case, the link between dyke swarms and plume head impingement on the lithosphere has been questioned in recent studies due to the role of pre-existing lithospheric structures (e.g. Karoo; Jourdan et al., 2006). Therefore, if present, a mantle plume could only be indirectly involved in the genesis of the Kalkarindji CFBs by providing additional heating and subsequent melting of the enriched Archean SCLM. Heat flux differences in the SCLM at craton boundaries King & Anderson (1995) suggested that at least the initial control of CFB volcanism could be attributed to the physical differences in the craton and non-craton lithosphere observed near boundary areas. Small-scale convection (or edge driven convection) develops at cratonic-non cratonic discontinuities that are usually associated with orogenic sutures. The Kalkarindji CFB province is located along the margin of the Kimberley Block and North Australian Craton, as well as near the margin of the West Australian Craton and the orogenic material between the North and West Australian Cratons (Fig. 1b). This particular location between thick crustal blocks could facilitate the development of edge driven convection in several locations within the province. A key requirement of the numerical models of King & Anderson (1995) is the asymmetry between the craton and non-craton boundary which they recognize requires extensional tectonics to focus the flow at these suture zones. Although many of the orogenic events amalgamating these areas occurred on the order of 1·5 to 2·0 Gyr ago, tectonic activity and reorganization continued in these zones throughout the construction of Gondwana and into the Phanerozoic, i.e. the Cambrian rotation of Gondwana suggested by Veevers (2001). The rotation that occurred on the Australian continent throughout the Cambrian caused significant changes in the stress regime of the continent, leading to regional extension; there is evidence for this in the formation of the Ord, Bonaparte, Arafura, Daly River, and Wiso Basins (Fig. 1b). The Antrim Plateau Volcanics floor many of these basins and the Table Hill Volcanics intrude into and floor the lower sediments of the Officer Basin indicating that magmas were emplaced during the formation of these basins. Decompression melting of the SCLM Decompression melting can occur in three conceivable ways for this province: (i) delamination of the lithosphere, possibly by a catastrophic lithosphere failure or collapse of basaltic crust transformed into dense eclogite at the crust-mantle boundary (Ringwood & Green, 1966; Houseman & Molnar, 2001); (ii) thinning of the lithosphere due to continental rifting (Bond et al., 1984; Li et al., 1996; Olierook et al., 2016); or (iii) thinning of the lithosphere over areas of global mantle warming during periods of supercontinent formation (Coltice et al., 2007). Torsional stress from roughly 540–470 Ma caused a ∼ 90° rotation of Gondwana (Veevers, 2001), destabilizing dense lithospheric mantle beneath northern Australia. This could have resulted in a catastrophic delamination of the SCLM, which would allow for a large melting event such as the Kalkarindji magmatic event. However, if the hot rising asthenosphere was the main source of the basalts, it would be inconsistent with the enrichment event around 2·5 Ga; this period of isolation is required before the Kalkarindji magmatism. Furthermore, the evidence provided by young diamond pipes sourced in the lower SCLM indicates that the asthenosphere did not replace the SCLM. Decompression melting due to the thinning of the continental lithosphere below Kalkarindji by the initiation of rifting has also been proposed to explain aspects of the tectonic history of the breakup of the China and Australia continents (Bond et al., 1984; Li et al., 1996). Studies by Bond et al. (1984) and Li et al. (1996) have suggested that the Kimberley Block of Australia and the Tarim Block of southern China were connected in the past. These studies propose that the Antrim Plateau Volcanics are evidence of a failed arm of a triple junction that resulted from the separation of the Tarim Block and the Australian continent. However, this interpretation was made before the Table Hill Volcanics of the Officer Basin were confirmed as being related and included in the Kalkarindji province. Therefore, with the inclusion of Kalkarindji CFB as far south as the Officer Basin, and the lack of any current evidence of a dyke swarm, this is unlikely to be the geologic process that formed the Kalkarindji CFB province. Evidence for thinning of the continental lithosphere is provided by large-scale coeval basin formation across the western portion of the Australian continent around the time of emplacement of the Kalkarindji CFB, further supporting the suggestion that decompression melting was involved in the genesis of the province. The extensional stresses that were required to form these basins, and the resultant crustal thinning, may have induced decompression melting of the enriched SCLM (± a minor amount of asthenosphere along the lower SCLM). Olierook et al. (2016) argue that the melting of a shallow enriched patch of mantle located within a larger, subducted, enriched SCLM could have produced the enriched geochemical signatures observed for the Bunbury Basalts, on the margin of Western Australia, without the need for involvement of the Kerguelen mantle plume. This model could very well apply to the genesis of the Kalkarindji CFB, but at a much larger scale. Preferred model for Kalkarindji magmatism In a long and relatively stable continental environment, decompression melting following tectonic extension is likely to operate in conjunction with the global mantle warming scenario that has been suggested to occur underneath large continents (Coltice et al., 2007). Coltice et al. (2007) propose that an increase in sub-continental lithosphere temperature of up to 100°C can be obtained on a timescale of about 300 Myr after continental assembly. The tectonic history of the western portion of Australia provides a stable period for the Australian continent in the order of nearly 700 Myr; the last major tectonic activity to occur in the western portion of the Australian continent before the Kalkarindji CFB event was the orogenic activity of the Musgrave province, which occurred at 1·2 Ga (Wade et al., 2008; Aitken & Betts, 2009; Smithies et al., 2015). The calculated ∼ 100°C per 300 Myr of Coltice et al. (2007) may not apply to this stable connection of Australia and Antarctica, due to the smaller size than a conventional super-continent but the 700 Myr period of stability before the Kalkarindji CFB magmatic event, provides more than enough time for the mantle below this portion of Gondwana to accumulate the heat needed to form the Kalkarindji CFB province. The presence of Kalkarindji basalts within and flooring basins throughout Australia indicates that thinning of the lithosphere was occurring contemporaneously with the emplacement of Kalkarindji CFB. Therefore, our preferred model for the formation of the Kalkarindji province involves decompression melting of an enriched source region through thinning of the lithosphere (Fig. 15). The source region was warmed below the Gondwana continent starting from at least 1·2 Ga, but most likely initiating in the north at ∼ 1·85 Ga. Extensional basin formation facilitated edge driven convection around the many cratonic keels that formed between the basins. Thinning of warm SCLM resulted in large-scale decompression melting. In this scenario, melts associated with the genesis of the Kalkarindji CFB province would be produced mostly within the SCLM, with perhaps a small contribution of melts derived from the depleted MORB-like asthenosphere (less than 10%; Fig. 14) which may have impregnated the SCLM immediately below the enriched part (Fig. 15). Such a scenario would account for the size, volume, and production timescale of the Kalkarindji province, and the province-wide homogeneity. Fig. 15. View largeDownload slide Schematic presentation of the internal mantle heating geodynamic model for the generation of the Kalkarindji continental flood basalt province. Fig. 15. View largeDownload slide Schematic presentation of the internal mantle heating geodynamic model for the generation of the Kalkarindji continental flood basalt province. Comparison with the Ferrar province The Ferrar and the Kalkarindji provinces are most chemically similar compared to other LIPs (Fig. 7). These two provinces share many similar geochemical signatures such as the absence of a high-Ti suite, as well as high SiO2 and low MgO contents in igneous rocks. These similar geochemical signatures suggest these two provinces might have a similar origin or at least formed by the same process. With this study, both provinces have now been linked to an old lithospheric enrichment process. Only slight differences in some of the trace element ratios are apparent between the Ferrar and Kalkarindji provinces such as the Nb/La ratios of Kalkarindji (0·2–0·4), which lie at the lower range of the Ferrar Nb/La ratios (0·2–0·7) (Fig. 12c). The Kalkarindji CFB samples have noticeably higher 87Sr/86Sri and 143Nd/144Ndi than most other continental flood basalts (Fig. 7c), but the 87Sr/86Sri of the Kalkarindji basalts overlap completely with those measured for the Ferrar LIP (Fig. 7b and c). The 143Nd/144Ndi isotopic compositions are, however, significantly lower. The Kalkarindji basalts have isotopic compositions similar to those of other CFBs (Fig. 7d) with moderate 208Pb/204Pbi and 206Pb/204Pbi ratios. However, a marked difference is apparent in the 207Pb/204Pb ratios, (Fig. 7a) which are significantly higher, plotting well above the NHRL (207Pb/204Pb = 15·7–15·8); these values are also significantly higher than the average 207Pb/204Pbi isotopic ratios of the Ferrar CFB. The age calculated for the enrichment event that affected the mantle source of the Kalkarindji basalts is much older than the ages proposed for Ferrar enrichment (490 to 300 Ma; Hergt et al., 1989), which fits well with the differences in the 207Pb/204Pb values of the two provinces. Hergt et al. (1989) found that simple contamination through the processes of bulk assimilation or partial melts of contaminants or even assimilation and fractional crystallization mixing models could not account for both the trace element and isotopic signatures observed for the Ferrar. In addition, Molzahn et al. (1996) showed that the 187Os/188Os and 87Sr/86Sr ratios are within mantle ranges, thereby excluding assimilation of upper and/or lower crust as the cause of the enriched signature of the Ferrar CFB province. Brauns et al. (2000) suggested that the observed geochemical trends are better explained by the introduction of an enriched component into the SCLM source region prior to melting (Hergt et al., 1989, 1991; Molzahn et al., 1996; Brauns et al., 2000). The geochemical parallels between the Kalkarindji and Ferrar CFB provinces reinforce our proposed model for the genesis of the Kalkarindji CFB province. The model of a SCLM enriched by subducted crustal material model proposed here for the Kalkarindji basalts is similar to that proposed for Ferrar (Hergt et al., 1989; Molzahn et al., 1996). The older enrichment event recorded by Kalkarindji could indicate that the Antarctic and Australian cratons were not connected at 2·5 Ga, during the timing of enrichment suggested here for the Kalkarindji CFB province. CONCLUSIONS New geochemical and Sr, Nd, Pb isotopic data for the Kalkarindji CFB province provides novel insights into the petrogenesis of the oldest large igneous province of the Phanerozoic. The continental-like geochemical characteristics of the Kalkarindji basalts are unlikely to be the product of crustal assimilation, but rather they are the signature of an enriched mantle source. The decoupling of the 238U and 235U decay systems indicates that an ancient enriched component must be involved in the genesis of the Kalkarindji CFB. The model proposed here involves enrichment by an ancient subducted sediment component, which was introduced into the mantle source around 2·5 Ga. Such a scenario accounts for the lithospheric incompatible trace element signatures as well as the enriched Sr, Nd, and Pb initial isotopic compositions of the province. Numerical modeling provides the basis for an interpretive model source comprising a mix of < 10% of a MORB like component and a dominant SCLM component that was enriched at 2·5 Ga. The mantle source of the Kalkarindji magmas then experienced warming below the stable Australian continent (as part of Gondwana) from c. 1·2 Ga to 511 Ma. The warming was boosted and focused by edge driven convection around the old cratonic structures of the West Australian and North Australian Cratons. Magmatism occurred by the decompression melting of the warm upper mantle and fertilized SCLM during extensional tectonism and basin formation at c. 500 Ma, possibly the result of a large-scale rotation of the continent. ACKNOWLEDGMENTS Arto Luttinen, Richard Ernst and an anonymous reviewer provided much appreciated constructive reviews, and Richard Price and Marjorie Wilson are thanked for editorial handling. The support of the John de Laeter Centre and the School of Earth and Planetary Sciences at Curtin University of Technology is gratefully acknowledged. FUNDING This research was funded by Australian Research Council Discovery grant DP130100517. SUPPLEMENTARY DATA Supplementary data are available at Journal of Petrology online. REFERENCES Aitken A. R. A. , Betts P. G. ( 2009 ). Constraints on the Proterozoic supercontinent cycle from the structural evolution of the south-central Musgrave Province, central Australia . Precambrian Research 168 , 284 – 300 . Google Scholar CrossRef Search ADS Allègre C. J. , Treuil M. , Minster J.-F. , Minster B. , Albarède F. ( 1977 ). Systematic use of trace element in igneous process . Contributions to Mineralogy and Petrology 60 , 57 – 75 . 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The Kalkarindji Large Igneous Province, Australia: Petrogenesis of the Oldest and Most Compositionally Homogenous Province of the Phanerozoic