Granulite-facies Overprint in Garnet Peridotites and Kyanite Eclogites of Monte Duria (Central Alps, Italy): Clues from Srilankite- and Sapphirine-Bearing Symplectites

Granulite-facies Overprint in Garnet Peridotites and Kyanite Eclogites of Monte Duria (Central... Abstract Peridotites and different types of eclogites occurring in the Monte Duria area (Adula–Cima Lunga unit, Central Alps, Italy) share a common eclogite-facies peak at P = 2·6–3·0 GPa and T = 710–750°C, constrained by conventional thermobarometry and thermodynamic modelling. High-pressure minerals are replaced both in peridotites and in eclogites by lower-P and high-T assemblages. In peridotites, the zirconium titanate srilankite occurs as micrometre-sized crystals in textural equilibrium with spinel, clinopyroxene and orthopyroxene in kelyphites developed between garnet and olivine. By using a new ZrO2–TiO2 solid-solution model, we provide evidence that srilankite is stable in peridotites relative to zircon + rutile for T > 810°C at an assumed P ≈ 0·9 GPa, consistent with estimates of T ≈ 850°C (at assumed P = 0·9 GPa) determined for symplectites made of sapphirine + spinel + Al-rich orthopyroxene + amphibole found in fractures within garnet. In eclogites, kyanite is replaced by symplectites made of anorthite-rich plagioclase + spinel ± sapphirine ± corundum, formed at T ≈ 850°C and P = 0·8–1·0 GPa, conditions that are coincident with the high-T overprint observed in the peridotites. Thermodynamic modelling coupled with a material-transfer study provides constraints for these sapphirine-bearing symplectites. In these micro-domains, the ‘inert’ components could not fully equilibrate with the surrounding rock, and the locally high Al content promoted the stability of the Al-rich phases (i.e. mosaic equilibrium). This is the first report from the Alps of eclogite-facies rocks of supposed Alpine age showing a granulite-facies metamorphic overprint, which is, in contrast, well documented in the Variscan belt. On these grounds, although the age of the high-pressure and high-temperature stages in the Monte Duria rocks is still not constrained, the possibility that they reached eclogitic and granulitic conditions in pre-Alpine times should be taken into account. INTRODUCTION Outcrops of eclogite-facies rocks showing a granulite-facies overprint are restricted to only a few localities worldwide. These rocks often show spectacular examples of metamorphic reactions, where relicts of high-pressure (HP) minerals are partially replaced by high-temperature (HT) symplectitic assemblages (e.g. Nakamura & Hirajima, 2000; Morishita et al., 2001; Scott et al., 2013). The study of these symplectites is not always straightforward (e.g. Nicollet & Goncalves, 2005), owing to the small dimension of the phases and the possible differences in bulk composition between the symplectite micro-domain and the surrounding rock caused by variable element mobility and the opening of the system (e.g. Keller et al., 2006, 2007). Nevertheless, their understanding can provide unrivalled records of the transition between eclogite and granulite facies. Spinel + orthopyroxene + clinopyroxene symplectites (kelyphites) surrounding HP garnet in deep mantle peridotites are relatively common and similar, resulting from the retrograde reaction between garnet and olivine (e.g. Godard & Martin, 2000). In the Alps, examples can be found in garnet peridotites from the Central Alps (Adula–Cima Lunga unit) and the Eastern Alps (Ulten zone; see review by Morten & Trommsdorff, 2003). HT overprinting in eclogites can lead to complex assemblages, varying as a function of the bulk chemistry and the availability of fluids. In kyanite-bearing eclogites, spinel ± sapphirine ± corundum symplectites have been described in different granulite terranes from the Precambrian to the Caledonides and the Variscides (Johansson & Möller, 1986; Carswell et al., 1989; Liati & Seidel, 1996; O’Brien, 1997; Godard & Mabit, 1998; Möller, 1999; Baldwin et al., 2007). Here we present an integrated approach to study the HT overprint on garnet peridotites and different types of eclogites cropping out in the Duria area in the southern part of the Adula nappe in the Central Alps. In particular, we focused on the following: (1) Zr-bearing kelyphites containing the zirconium titanate srilankite (ZrTi2O6); (2) sapphirine-bearing symplectites replacing garnet in peridotite; (3) sapphirine ± corundum-bearing symplectites replacing kyanite in eclogites. Thermodynamic modelling of Zr-bearing symplectites in peridotites has been accomplished by developing a new binary solution model between ZrO2 (baddeleyite) and TiO2 (rutile) with the intermediate compound srilankite, calibrated against published experimental data at HP conditions. A material-transfer study has been performed by calculating P–T–X phase diagrams to assess the stability of sapphirine in symplectites replacing garnet (in peridotite) and kyanite (in eclogite). The integration of conventional thermobarometry, thermodynamic modelling and material-transfer study allowed us to retrieve the petrological processes that occurred in these rocks from the eclogite- to the granulite-facies transition, and to provide new P–T estimates of the eclogite-facies peak and the granulite-facies metamorphic overprint, which are discussed in the framework of the pre-Alpine and Alpine metamorphism of this polycyclic basement. GEOLOGICAL SETTING The Adula–Cima Lunga nappe complex is located on the eastern flank of the Lepontine Dome (Fig. 1) and represents the highest portion of the Sub-Penninic units of the Central Alps (e.g. Milnes, 1974; Schmid et al., 1996). Its position in the Central Alps is located between the nappe stack formed by the Leventina–Lucomagno and Simano units at the bottom and the Middle Penninic units (Maggia, Tambo, Suretta; Fig. 1) at the top. The contact with the Middle Penninic nappes occurs along the Misox Zone, a thin unit composed of metasediments, mid-ocean ridge basalt (MORB)-derived amphibolites and slivers of continental basement (Steinmann & Stille, 1999; Stucki et al., 2003). The lower contact of the Adula nappe is somewhat less well defined owing to lithological similarities to the Simano gneiss and the Tertiary high-grade metamorphism of the Lepontine Dome that overprinted existing tectonic structures (Nagel, 2008). To the south, a lithologically heterogeneous east–west-trending zone, the Southern Steep Belt or Bellinzona–Dascio Zone (Schmid et al., 1996), is interposed between the Adula nappe and the western end of the Bergell pluton (Fig. 1). To the east, the Gruf Complex, considered part of the Adula nappe (Berger et al., 2005), is separated from the main units of the nappe complex by the Forcola normal fault (Ciancaleoni & Marquer, 2006). It is worth noting here that the interpretation of the Gruf Complex as pertaining to the Adula nappe has been recently challenged by Galli et al. (2013), who suggested a pre-Alpine history for this complex. Fig. 1. View largeDownload slide (a) Tectonic scheme of the Lepontine Dome in the Central Alps. Isotherms for the post nappe-stacking Barrovian metamorphic event and the extent of the migmatite belt are from Todd & Engi (1997) and Burri et al. (2005), respectively. (b) Detailed geological scheme of the Duria area with the locations of Monte Duria and Borgo outcrops. Main geological features are modified from Berger et al. (2005). At, Antigorio; Gt, Gotthard massif; Mg, Maggia; Sm, Simano; L-L, Leventina–Lucomagno; Tb, Tambo; Su, Suretta; SSB, Southern Steep Belt. Fig. 1. View largeDownload slide (a) Tectonic scheme of the Lepontine Dome in the Central Alps. Isotherms for the post nappe-stacking Barrovian metamorphic event and the extent of the migmatite belt are from Todd & Engi (1997) and Burri et al. (2005), respectively. (b) Detailed geological scheme of the Duria area with the locations of Monte Duria and Borgo outcrops. Main geological features are modified from Berger et al. (2005). At, Antigorio; Gt, Gotthard massif; Mg, Maggia; Sm, Simano; L-L, Leventina–Lucomagno; Tb, Tambo; Su, Suretta; SSB, Southern Steep Belt. The Adula nappe largely consists of orthogneiss and paragneiss of pre-Mesozoic origin (Frey & Ferreiro-Mählmann, 1999; Liati et al., 2009; Rubatto et al., 2009), variably retrogressed eclogites preserved as boudins within paragneiss, minor ultramafic bodies and metasedimentary rocks of presumed Mesozoic age (Galster et al., 2012), the last chiefly preserved in the middle and northern domains of the nappe. Paleogeographical reconstructions locate the Adula nappe in the former distal European margin (Schmid et al., 1990), to the north of the North Penninic Ocean, which opened at the end of the Jurassic and later closed during the Late Cretaceous–Eocene phase of convergence between Europe and Africa–Adria (Dewey et al., 1989). During the Tertiary Alpine orogenic cycle, the Adula nappe and the crustal slivers that now constitute the Southern Steep Belt were subducted to mantle depths (Evans & Trommsdorff, 1978; Heinrich, 1986; Becker, 1993; Gebauer, 1996). Metamorphic conditions at peak pressure are found to increase southward, from ≈1·7 GPa and ≈650°C in the north to 2·5–3·0 GPa and ≈750°C in the south (Dale & Holland, 2003; Brouwer et al., 2005). Even more extreme conditions have been estimated for the peridotite and meta-peridotite lenses that occur at the southern, western and eastern margins of the nappe (Fumasoli, 1974; Pfiffner & Trommsdorff, 1998). Garnet lherzolite bodies crop out at three localities; these are, from west to east, Cima di Gagnone, Alpe Arami and Monte Duria (Fig. 1). Such mantle-derived rocks equilibrated at P ≈ 3 GPa and T = 800–850°C (e.g. Nimis & Trommsdorff, 2001; Hermann et al., 2006). An older HP event of Variscan age (Liati et al., 2009; Herwartz et al., 2011) is rarely preserved within eclogitic boudins of the central and northern sector of the Adula nappe. After the partial subduction of the European distal margin beneath the Adria margin, the HP rocks of the Adula nappe and the Southern Steep Belt were overprinted by upper amphibolite-facies metamorphism (Wenk, 1970; Todd & Engi, 1997), which postdates the main phase of nappe-stacking. In the southern sector of the Lepontine Dome, adjacent to the Insubric Fault (Fig. 1), metamorphic conditions promoted extensive migmatization of both metasedimentary and metagranitoid rocks (‘Migmatite belt’; Burri et al., 2005). Partial melting occurred between 32 and 22 Ma (Rubatto et al., 2009) and was promoted essentially by fluid-present processes (Berger et al., 2008), whereas fluid-absent melting of white mica was restricted to a narrow zone between Bellinzona and Lake Como (Fig. 1) in the Adula nappe and the Southern Steep Belt (Burri et al., 2005). Field aspects of peridotites and hosting crustal rocks Two sites of the Monte Duria area have been investigated in detail: (1) the outcrop of Borgo and (2) outcrops within sight of Monte Duria (Figs 1 and 2; coordinates are given in Supplementary Data Table S4; supplementary data are available for downloading at http://www.petrology.oxfordjournals.org). Fig. 2. View largeDownload slide Map of the Borgo outcrop along the Ledù stream. AG, amphibole-bearing migmatitic gneiss; E, kyanite eclogites; HAE, high-Al2O3 rim between kyanite eclogites and the hosting amphibole-bearing migmatitic gneiss; ME, mafic eclogites; MG, migmatitic gneiss; OGN, orthogneiss; PDT, retrogressed garnet peridotite. (See text for details) Fig. 2. View largeDownload slide Map of the Borgo outcrop along the Ledù stream. AG, amphibole-bearing migmatitic gneiss; E, kyanite eclogites; HAE, high-Al2O3 rim between kyanite eclogites and the hosting amphibole-bearing migmatitic gneiss; ME, mafic eclogites; MG, migmatitic gneiss; OGN, orthogneiss; PDT, retrogressed garnet peridotite. (See text for details) At Borgo (Fig. 2), a kilometre-sized peridotite body is in contact with amphibole-bearing migmatites with preserved boudins of mafic eclogite. The peridotite body and its mafic rim are hosted within migmatitic gneisses, like those hosting peridotites at Monte Duria (Fig. 2). In the peridotite body, garnet was not observed, but rounded chlorite-rich pseudomorphs that probably formed after garnet porphyroclasts are abundant; millimetre- to centimetre-sized garnet (up to 3 cm), often partially replaced by chlorite and/or kelyphite, has been found in nearby loose blocks downstream in the Rio Ledù stream bed (Fig. 3a). In the Borgo body, compositional layering marked by chlorite-rich and chlorite-poor layers represents the main fabric element at the mesoscale (Fig. 3b). Such layering is locally transposed by a second foliation marked by chlorite. The contact between the peridotite and hosting crustal rocks is characterized by the occurrence of a decimetre-thick metasomatic rim rich in amphibole and phlogopite. Lenses rich in amphibole and phlogopite have been also found as centimetre-sized boudins embedded in the surrounding mafic rocks (Fig. 2). A phlogopite-rich pegmatite intruded the peridotite–mafic rocks contact and is folded together with chlorite-defined foliation in the peridotite and the main foliation of the hosting mafic gneiss. The heterogeneous rock association constituting the rim of the peridotite body consists chiefly of amphibole-bearing migmatitic gneiss (AG in Fig. 2) with boudins of eclogite (Figs 2 and 3c, d) that show differences in terms of their mineralogy and deformation intensity. Fine-grained, partially retrogressed, dark green eclogites (ME in Fig. 2) occur as boudins (decimetres to metres in size, Fig. 3c) included in AG gneisses. A second type of eclogite occurs in larger, light green-coloured boudins (Figs 2 and 3d). The contact between the second type of eclogite (E in Fig. 2) and the surrounding AG gneisses is locally marked by millimetre-sized layers (Fig. 3e; HAE in Fig. 2) in which centimetre-sized crystals of emerald-green zoisite surrounded by reddish coronae have been found (Fig. 3f). Fig. 3. View largeDownload slide Field aspect of peridotite lenses at Borgo (a–f) and Monte Duria (g, h). (a) Loose block of partially retrogressed garnet peridotite downstream of the Borgo outcrop; (b) compositional layering comprising garnet-rich and garnet-poor layers in the Borgo peridotite; a pervasive chlorite-defined foliation overprinting the layering occurs within 4–5 m from the contact with hosting crustal rocks; (c) a boudin of mafic eclogite (ME) within amphibole-bearing migmatitic gneiss (AG); (d) a large (c. 7 m × 5 m) boudin of kyanite eclogite (E); (e) detail of the contact between kyanite eclogite and hosting gneiss with a red- to pink-coloured Al2O3-rich rim (HAE); (f) emerald green zoisite crystal within the HAE rim; (g) peridotite lens on the SE ridge of Monte Duria (L. Pellegrino for scale); garnet porphyroclasts are preserved only at cores, whereas a chlorite foliation, associated with retrogression in the spinel stability field, occurs on the outer rim; (h) detail of anhedral to sub-euhedral garnet porphyroclasts with dark-coloured thin kelyphitic rims. Fig. 3. View largeDownload slide Field aspect of peridotite lenses at Borgo (a–f) and Monte Duria (g, h). (a) Loose block of partially retrogressed garnet peridotite downstream of the Borgo outcrop; (b) compositional layering comprising garnet-rich and garnet-poor layers in the Borgo peridotite; a pervasive chlorite-defined foliation overprinting the layering occurs within 4–5 m from the contact with hosting crustal rocks; (c) a boudin of mafic eclogite (ME) within amphibole-bearing migmatitic gneiss (AG); (d) a large (c. 7 m × 5 m) boudin of kyanite eclogite (E); (e) detail of the contact between kyanite eclogite and hosting gneiss with a red- to pink-coloured Al2O3-rich rim (HAE); (f) emerald green zoisite crystal within the HAE rim; (g) peridotite lens on the SE ridge of Monte Duria (L. Pellegrino for scale); garnet porphyroclasts are preserved only at cores, whereas a chlorite foliation, associated with retrogression in the spinel stability field, occurs on the outer rim; (h) detail of anhedral to sub-euhedral garnet porphyroclasts with dark-coloured thin kelyphitic rims. On the southernmost ridge of Monte Duria, about 250 m from the summit (Fig. 1), several scattered peridotite bodies (Fig. 3g) occur within migmatitic gneisses (Fumasoli, 1974). Peridotites are often garnet bearing, although garnet (millimetre- to centimetre-sized) is invariably surrounded by kelyphites (Fig. 3h) and often fully replaced by pseudomorphic assemblages (Fig. 3a). Orthopyroxene (opx) and emerald-green clinopyroxene (cpx) occur often as millimetre- to centimetre-sized porphyroclasts in an oriented dark fine-grained olivine matrix. Garnet-bearing clinopyroxenite veins locally cut these peridotite bodies. The peridotite lenses commonly display a strongly foliated rim (Fig. 3b and g), with a chlorite foliation parallel to the main foliation of hosting gneisses and a core where compositional layering with garnet-rich and garnet-poor horizons occurs. MATERIALS AND METHODS Major element whole-rock analyses were performed by inductively coupled plasma mass spectrometry (ICP-MS) and LECO combustion analysis (total C, S) (Bureau Veritas ACME Mineral Laboratories, Canada). Bulk-rock chemistry (Table 1) has been evaluated by using bivariate plots (Supplementary Data Fig. S1) and principal component analysis (Supplementary Data Fig. S2). Quantitative analyses of minerals were performed using a JEOL 8200 wavelength-dispersive (WDS) electron microprobe (EMP), at 15 kV accelerating potential, 5 nA sample current and 1 μm beam diameter. Standards used were omphacite (Na), grossular (Ca, Al and Si), fayalite (Fe), olivine (Mg), orthoclase (K), rhodonite (Mn), ilmenite (Ti), niccolite (Ni), pure Cr (Cr) and zircon (Zr, Hf). A counting time of 30 s was used for all elements. Zr in rutile was measured using a 15 kV accelerating potential and a 100 nA sample current, with a counting time of 300 s (150 s for background). Hf in micrometre-sized zircon, srilankite and baddeleyite in peridotite was measured at 15 kV accelerating potential and a 5 nA sample current (15 nA for larger zircon crystals in eclogite), with a counting time of 300 s (150 s for background). The Fe3+/FeTOT ratio in minerals reported in Tables 2 and 3 was calculated by stoichiometry and charge balance. Cathodoluminescence images of quartz were collected at 15 kV accelerating potential and a 100 nA sample current. Table 2: Representative WDS microprobe analyses of olivine (Ol), clinopyroxene (Cpx), orthopyroxene (Opx) and garnet (Gt) in selected samples Lithology: Grt-peridotite Sample: A2C2 B1 Phase: Ol Ol Fine Cpx C Cpx R Cpx InGt Cpx Sym Opx C Opx R Opx InCpx Opx Sym Gt C Gt R Ol Cpx Cpx Sym Opx Opx Sym Gt C Gt R SiO2 39·55 39·74 54·14 54·39 53·40 55·19 56·85 56·92 57·18 56·32 40·29 41·72 40·04 54·00 52·90 56·97 55·47 42·01 40·66 TiO2 0·03 0·01 b.d.l. b.d.l. 0·12 0·24 b.d.l. 0·10 0·02 0·06 0·17 0·17 b.d.l. 0·07 0·02 0·06 0·01 0·07 0·07 Al2O3 0·02 0·00 0·88 0·98 2·05 1·40 0·77 0·80 1·00 1·91 20·15 22·55 b.d.l. 1·47 1·33 0·85 2·54 22·89 22·37 Cr2O3 b.d.l. b.d.l. 0·24 0·36 1·27 0·03 0·20 0·21 0·17 0·01 1·98 1·49 b.d.l. 0·75 0·18 0·17 0·10 2·49 2·45 FeO* 9·84 9·72 1·87 1·91 2·38 1·84 6·41 6·52 6·64 8·43 10·62 11·47 9·46 2·18 1·95 6·13 7·11 8·78 12·64 MnO 0·10 0·14 0·05 0·05 0·04 0·10 0·10 0·09 0·13 0·32 0·55 0·52 0·11 0·08 0·08 0·11 0·18 0·40 0·96 NiO 0·37 0·43 0·13 0·13 0·05 b.d.l. 0·14 0·04 0·08 0·05 0·09 0·05 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. MgO 49·68 49·88 17·19 17·22 16·25 17·91 35·30 34·95 34·90 33·22 18·25 18·62 48·93 16·34 17·23 34·45 33·31 19·28 16·89 CaO 0·00 0·01 24·11 23·50 22·53 24·29 0·21 0·22 0·23 0·19 4·94 4·86 0·02 22·60 24·55 0·21 0·25 5·24 5·18 Na2O b.d.l. b.d.l. 0·41 0·51 0·99 0·06 b.d.l. 0·01 0·02 0·03 b.d.l. b.d.l. b.d.l. 0·84 0·06 b.d.l. b.d.l. 0·03 0·04 K2O b.d.l. 0·01 b.d.l. b.d.l. 0·00 0·01 0·01 b.d.l. b.d.l. 0·01 0·01 b.d.l. b.d.l. 0·01 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. Total 99·59 99·93 99·09 99·09 99·17 101·07 100·22 99·98 100·49 100·66 97·24 101·62 98·56 98·34 98·43 98·95 99·04 101·22 101·46 Si 0·97 0·97 1·98 1·99 1·96 1·98 1·95 1·96 1·96 1·95 2·99 2·96 0·99 1·99 1·95 1·98 1·94 2·97 2·93 Ti 0·00 0·00 — — 0·00 0·01 — 0·00 0·00 0·00 0·01 0·01 — 0·00 0·00 0·00 0·00 0·00 0·00 Al 0·00 0·00 0·04 0·04 0·09 0·06 0·03 0·03 0·04 0·08 1·76 1·89 — 0·06 0·06 0·03 0·10 1·91 1·90 Cr — — 0·01 0·01 0·04 0·00 0·01 0·01 0·00 0·00 0·12 0·08 — 0·02 0·01 0·00 0·00 0·14 0·14 Fe3+ 0·00 0·00 0·02 0·01 0·03 0·00 0·05 0·03 0·03 0·03 0·11 0·08 0·00 0·00 0·04 0·00 0·02 0·01 0·11 Fe2+ 0·20 0·20 0·04 0·05 0·05 0·06 0·13 0·16 0·16 0·21 0·55 0·60 0·20 0·07 0·02 0·18 0·19 0·51 0·65 Mn 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·01 0·03 0·03 0·00 0·00 0·00 0·00 0·01 0·02 0·06 Ni 0·01 0·01 0·00 0·00 0·00 — 0·00 0·00 0·00 0·00 0·01 0·00 — — — — — — — Mg 1·82 1·82 0·94 0·94 0·89 0·96 1·81 1·80 1·79 1·71 2·02 1·97 1·81 0·90 0·95 1·79 1·73 2·03 1·81 Ca 0·00 0·00 0·95 0·92 0·88 0·93 0·01 0·01 0·01 0·01 0·39 0·37 0·00 0·89 0·97 0·01 0·01 0·40 0·40 Na — — 0·03 0·04 0·07 0·00 — 0·00 0·00 0·00 — — — 0·06 0·00 — — 0·00 0·01 K — 0·00 — — 0·00 0·00 0·00 — — 0·00 0·00 — — 0·00 — — — — — Total 3·00 3·00 4·00 4·00 4·00 4·00 4·00 4·00 4·00 4·00 8·00 8·00 3·00 4·00 4·00 4·00 4·00 8·00 8·00 XMg (Fe tot) 0·90 0·90 0·94 0·94 0·92 0·95 0·91 0·91 0·90 0·88 0·75 0·74 0·90 0·93 0·94 0·91 0·89 0·80 0·70 XMg (Fe2+) 0·90 0·90 0·96 0·95 0·95 0·95 0·93 0·92 0·92 0·89 0·79 0·77 0·90 0·93 0·98 0·91 0·90 0·80 0·74 Lithology: Grt-peridotite Sample: A2C2 B1 Phase: Ol Ol Fine Cpx C Cpx R Cpx InGt Cpx Sym Opx C Opx R Opx InCpx Opx Sym Gt C Gt R Ol Cpx Cpx Sym Opx Opx Sym Gt C Gt R SiO2 39·55 39·74 54·14 54·39 53·40 55·19 56·85 56·92 57·18 56·32 40·29 41·72 40·04 54·00 52·90 56·97 55·47 42·01 40·66 TiO2 0·03 0·01 b.d.l. b.d.l. 0·12 0·24 b.d.l. 0·10 0·02 0·06 0·17 0·17 b.d.l. 0·07 0·02 0·06 0·01 0·07 0·07 Al2O3 0·02 0·00 0·88 0·98 2·05 1·40 0·77 0·80 1·00 1·91 20·15 22·55 b.d.l. 1·47 1·33 0·85 2·54 22·89 22·37 Cr2O3 b.d.l. b.d.l. 0·24 0·36 1·27 0·03 0·20 0·21 0·17 0·01 1·98 1·49 b.d.l. 0·75 0·18 0·17 0·10 2·49 2·45 FeO* 9·84 9·72 1·87 1·91 2·38 1·84 6·41 6·52 6·64 8·43 10·62 11·47 9·46 2·18 1·95 6·13 7·11 8·78 12·64 MnO 0·10 0·14 0·05 0·05 0·04 0·10 0·10 0·09 0·13 0·32 0·55 0·52 0·11 0·08 0·08 0·11 0·18 0·40 0·96 NiO 0·37 0·43 0·13 0·13 0·05 b.d.l. 0·14 0·04 0·08 0·05 0·09 0·05 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. MgO 49·68 49·88 17·19 17·22 16·25 17·91 35·30 34·95 34·90 33·22 18·25 18·62 48·93 16·34 17·23 34·45 33·31 19·28 16·89 CaO 0·00 0·01 24·11 23·50 22·53 24·29 0·21 0·22 0·23 0·19 4·94 4·86 0·02 22·60 24·55 0·21 0·25 5·24 5·18 Na2O b.d.l. b.d.l. 0·41 0·51 0·99 0·06 b.d.l. 0·01 0·02 0·03 b.d.l. b.d.l. b.d.l. 0·84 0·06 b.d.l. b.d.l. 0·03 0·04 K2O b.d.l. 0·01 b.d.l. b.d.l. 0·00 0·01 0·01 b.d.l. b.d.l. 0·01 0·01 b.d.l. b.d.l. 0·01 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. Total 99·59 99·93 99·09 99·09 99·17 101·07 100·22 99·98 100·49 100·66 97·24 101·62 98·56 98·34 98·43 98·95 99·04 101·22 101·46 Si 0·97 0·97 1·98 1·99 1·96 1·98 1·95 1·96 1·96 1·95 2·99 2·96 0·99 1·99 1·95 1·98 1·94 2·97 2·93 Ti 0·00 0·00 — — 0·00 0·01 — 0·00 0·00 0·00 0·01 0·01 — 0·00 0·00 0·00 0·00 0·00 0·00 Al 0·00 0·00 0·04 0·04 0·09 0·06 0·03 0·03 0·04 0·08 1·76 1·89 — 0·06 0·06 0·03 0·10 1·91 1·90 Cr — — 0·01 0·01 0·04 0·00 0·01 0·01 0·00 0·00 0·12 0·08 — 0·02 0·01 0·00 0·00 0·14 0·14 Fe3+ 0·00 0·00 0·02 0·01 0·03 0·00 0·05 0·03 0·03 0·03 0·11 0·08 0·00 0·00 0·04 0·00 0·02 0·01 0·11 Fe2+ 0·20 0·20 0·04 0·05 0·05 0·06 0·13 0·16 0·16 0·21 0·55 0·60 0·20 0·07 0·02 0·18 0·19 0·51 0·65 Mn 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·01 0·03 0·03 0·00 0·00 0·00 0·00 0·01 0·02 0·06 Ni 0·01 0·01 0·00 0·00 0·00 — 0·00 0·00 0·00 0·00 0·01 0·00 — — — — — — — Mg 1·82 1·82 0·94 0·94 0·89 0·96 1·81 1·80 1·79 1·71 2·02 1·97 1·81 0·90 0·95 1·79 1·73 2·03 1·81 Ca 0·00 0·00 0·95 0·92 0·88 0·93 0·01 0·01 0·01 0·01 0·39 0·37 0·00 0·89 0·97 0·01 0·01 0·40 0·40 Na — — 0·03 0·04 0·07 0·00 — 0·00 0·00 0·00 — — — 0·06 0·00 — — 0·00 0·01 K — 0·00 — — 0·00 0·00 0·00 — — 0·00 0·00 — — 0·00 — — — — — Total 3·00 3·00 4·00 4·00 4·00 4·00 4·00 4·00 4·00 4·00 8·00 8·00 3·00 4·00 4·00 4·00 4·00 8·00 8·00 XMg (Fe tot) 0·90 0·90 0·94 0·94 0·92 0·95 0·91 0·91 0·90 0·88 0·75 0·74 0·90 0·93 0·94 0·91 0·89 0·80 0·70 XMg (Fe2+) 0·90 0·90 0·96 0·95 0·95 0·95 0·93 0·92 0·92 0·89 0·79 0·77 0·90 0·93 0·98 0·91 0·90 0·80 0·74 Lithology: Grt-peridotite Sample: B3A MD20 Phase: Ol Cpx Cpx Sym Opx Opx Sym Gt C Gt R Ol Cpx C Cpx R Cpx Sym1 Opx C Opx R Opx Sym1 Opx Sym2 Gt SiO2 39·82 54·91 54·23 56·75 57·02 42·11 41·50 41·76 41·27 54·73 54·33 54·81 58·39 56·98 57·01 55·41 41·09 TiO2 0·05 0·04 0·17 0·06 b.d.l. 0·11 0·12 0·02 0·03 0·13 0·14 0·14 0·01 0·04 0·04 0·05 0·06 Al2O3 0·01 1·68 1·23 0·83 1·25 22·78 22·53 0·01 b.d.l. 1·61 1·38 1·30 0·63 0·80 1·52 3·93 22·60 Cr2O3 0·01 1·05 0·05 0·14 0·09 2·30 2·39 0·03 b.d.l. 0·88 0·79 0·08 0·04 0·15 0·04 0·29 2·08 FeO* 8·96 2·28 1·85 5·94 7·73 8·22 9·74 8·33 9·53 2·17 1·92 1·98 6·19 5·97 7·33 6·80 9·90 MnO 0·13 0·06 0·07 0·14 0·30 0·43 0·51 0·13 0·19 0·09 0·02 0·05 0·19 0·09 0·29 0·12 0·49 NiO b.d.l. b.d.l. n.a. b.d.l. n.a. b.d.l. b.d.l. 0·35 0·46 0·08 b.d.l. n.a. 0·07 0·07 b.d.l. n.a. 0·05 MgO 49·14 16·18 17·69 34·90 33·91 20·27 18·99 50·29 50·14 16·83 16·82 17·36 35·41 34·94 34·24 33·38 19·10 CaO 0·03 21·84 25·13 0·18 0·20 5·08 5·08 b.d.l. 0·01 23·07 23·53 24·97 0·16 0·21 0·21 0·17 5·38 Na2O 0·02 1·25 b.d.l. 0·02 0·01 0·04 0·01 b.d.l. b.d.l. 0·93 0·74 0·06 b.d.l. b.d.l. b.d.l. 0·03 0·03 K2O b.d.l. b.d.l. 0·01 0·01 0·01 b.d.l. b.d.l. b.d.l. b.d.l. 0·01 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. Total 98·16 99·30 100·51 99·05 100·58 101·46 100·98 100·91 101·64 100·59 99·82 100·76 101·10 99·31 100·76 99·49 101·04 Si 0·99 2·00 1·96 1·97 1·97 2·96 2·95 1·01 0·99 1·97 1·97 1·98 1·99 1·97 1·96 1·92 2·92 Ti 0·00 0·00 0·00 0·00 — 0·01 0·01 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 Al 0·00 0·07 0·05 0·03 0·05 1·89 1·89 0·00 — 0·07 0·06 0·06 0·03 0·03 0·06 0·16 1·90 Cr 0·00 0·03 0·00 0·00 0·00 0·13 0·13 0·00 — 0·03 0·02 0·00 0·00 0·00 0·00 0·01 0·12 Fe3+ 0·00 0·00 0·02 0·02 0·02 0·06 0·06 0·00 0·00 0·02 0·02 0·00 0·00 0·01 0·02 0·01 0·14 Fe2+ 0·19 0·07 0·03 0·15 0·15 0·42 0·52 0·17 0·19 0·05 0·05 0·06 0·18 0·16 0·19 0·18 0·45 Mn 0·00 0·00 0·00 0·00 0·01 0·03 0·03 0·00 0·00 0·00 0·00 0·00 0·01 0·00 0·01 0·00 0·03 Ni — — — — — — — 0·01 0·01 0·00 — — 0·00 0·00 — — 0·00 Mg 1·82 0·88 0·95 1·81 1·74 2·12 2·01 1·81 1·80 0·90 0·91 0·93 1·80 1·80 1·75 1·72 2·03 Ca 0·00 0·85 0·97 0·01 0·01 0·38 0·39 — 0·00 0·89 0·92 0·96 0·01 0·01 0·01 0·01 0·41 Na 0·00 0·09 — 0·00 0·00 0·01 0·00 — — 0·06 0·05 0·00 — — — 0·00 0·00 K — — 0·00 0·00 0·00 — — — — 0·00 — — — — — — — Total 3·00 4·00 4·00 4·00 4·00 8·01 8·00 3·00 3·00 4·00 4·00 4·00 4·00 4·00 4·00 4·00 8·00 XMg (Fetot) 0·91 0·93 0·95 0·91 0·89 0·82 0·78 0·91 0·90 0·93 0·94 0·94 0·91 0·91 0·89 0·91 0·78 XMg (Fe2+) 0·91 0·93 0·96 0·92 0·92 0·83 0·79 0·91 0·90 0·95 0·95 0·94 0·91 0·92 0·90 0·90 0·82 Lithology: Grt-peridotite Sample: B3A MD20 Phase: Ol Cpx Cpx Sym Opx Opx Sym Gt C Gt R Ol Cpx C Cpx R Cpx Sym1 Opx C Opx R Opx Sym1 Opx Sym2 Gt SiO2 39·82 54·91 54·23 56·75 57·02 42·11 41·50 41·76 41·27 54·73 54·33 54·81 58·39 56·98 57·01 55·41 41·09 TiO2 0·05 0·04 0·17 0·06 b.d.l. 0·11 0·12 0·02 0·03 0·13 0·14 0·14 0·01 0·04 0·04 0·05 0·06 Al2O3 0·01 1·68 1·23 0·83 1·25 22·78 22·53 0·01 b.d.l. 1·61 1·38 1·30 0·63 0·80 1·52 3·93 22·60 Cr2O3 0·01 1·05 0·05 0·14 0·09 2·30 2·39 0·03 b.d.l. 0·88 0·79 0·08 0·04 0·15 0·04 0·29 2·08 FeO* 8·96 2·28 1·85 5·94 7·73 8·22 9·74 8·33 9·53 2·17 1·92 1·98 6·19 5·97 7·33 6·80 9·90 MnO 0·13 0·06 0·07 0·14 0·30 0·43 0·51 0·13 0·19 0·09 0·02 0·05 0·19 0·09 0·29 0·12 0·49 NiO b.d.l. b.d.l. n.a. b.d.l. n.a. b.d.l. b.d.l. 0·35 0·46 0·08 b.d.l. n.a. 0·07 0·07 b.d.l. n.a. 0·05 MgO 49·14 16·18 17·69 34·90 33·91 20·27 18·99 50·29 50·14 16·83 16·82 17·36 35·41 34·94 34·24 33·38 19·10 CaO 0·03 21·84 25·13 0·18 0·20 5·08 5·08 b.d.l. 0·01 23·07 23·53 24·97 0·16 0·21 0·21 0·17 5·38 Na2O 0·02 1·25 b.d.l. 0·02 0·01 0·04 0·01 b.d.l. b.d.l. 0·93 0·74 0·06 b.d.l. b.d.l. b.d.l. 0·03 0·03 K2O b.d.l. b.d.l. 0·01 0·01 0·01 b.d.l. b.d.l. b.d.l. b.d.l. 0·01 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. Total 98·16 99·30 100·51 99·05 100·58 101·46 100·98 100·91 101·64 100·59 99·82 100·76 101·10 99·31 100·76 99·49 101·04 Si 0·99 2·00 1·96 1·97 1·97 2·96 2·95 1·01 0·99 1·97 1·97 1·98 1·99 1·97 1·96 1·92 2·92 Ti 0·00 0·00 0·00 0·00 — 0·01 0·01 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 0·00 Al 0·00 0·07 0·05 0·03 0·05 1·89 1·89 0·00 — 0·07 0·06 0·06 0·03 0·03 0·06 0·16 1·90 Cr 0·00 0·03 0·00 0·00 0·00 0·13 0·13 0·00 — 0·03 0·02 0·00 0·00 0·00 0·00 0·01 0·12 Fe3+ 0·00 0·00 0·02 0·02 0·02 0·06 0·06 0·00 0·00 0·02 0·02 0·00 0·00 0·01 0·02 0·01 0·14 Fe2+ 0·19 0·07 0·03 0·15 0·15 0·42 0·52 0·17 0·19 0·05 0·05 0·06 0·18 0·16 0·19 0·18 0·45 Mn 0·00 0·00 0·00 0·00 0·01 0·03 0·03 0·00 0·00 0·00 0·00 0·00 0·01 0·00 0·01 0·00 0·03 Ni — — — — — — — 0·01 0·01 0·00 — — 0·00 0·00 — — 0·00 Mg 1·82 0·88 0·95 1·81 1·74 2·12 2·01 1·81 1·80 0·90 0·91 0·93 1·80 1·80 1·75 1·72 2·03 Ca 0·00 0·85 0·97 0·01 0·01 0·38 0·39 — 0·00 0·89 0·92 0·96 0·01 0·01 0·01 0·01 0·41 Na 0·00 0·09 — 0·00 0·00 0·01 0·00 — — 0·06 0·05 0·00 — — — 0·00 0·00 K — — 0·00 0·00 0·00 — — — — 0·00 — — — — — — — Total 3·00 4·00 4·00 4·00 4·00 8·01 8·00 3·00 3·00 4·00 4·00 4·00 4·00 4·00 4·00 4·00 8·00 XMg (Fetot) 0·91 0·93 0·95 0·91 0·89 0·82 0·78 0·91 0·90 0·93 0·94 0·94 0·91 0·91 0·89 0·91 0·78 XMg (Fe2+) 0·91 0·93 0·96 0·92 0·92 0·83 0·79 0·91 0·90 0·95 0·95 0·94 0·91 0·92 0·90 0·90 0·82 Lithology: Grt-peridotite Mafic eclogite Eclogite Sample: MD25 D6 D3 Phase: Ol C Ol R Cpx C Cpx R Cpx Sym1 Opx C Opx R Opx Sym1 Opx Sym2 Gt C Gt R Cpx Gt C Gt R Cpx Sym1 Gt C Gt R SiO2 41·16 40·80 55·39 55·75 53·62 58·02 57·96 56·67 55·50 41·40 42·97 54·41 40·14 39·34 54·54 40·58 40·46 TiO2 0·05 0·02 0·11 0·08 0·14 b.d.l. 0·09 b.d.l. 0·06 0·12 0·20 0·06 0·07 0·08 0·05 0·06 0·01 Al2O3 0·01 0·02 1·02 1·01 1·83 0·82 1·21 1·51 4·94 20·81 23·22 1·92 22·73 22·33 1·02 22·44 22·74 Cr2O3 b.d.l. 0·02 0·43 0·32 0·40 0·17 0·19 0·05 0·48 1·05 1·44 0·02 0·01 0·17 0·01 0·63 0·06 FeO* 9·73 9·90 1·79 2·02 1·84 6·46 6·87 6·33 5·35 10·18 8·16 5·07 19·10 24·61 5·79 18·37 21·92 MnO 0·13 0·19 0·08 0·02 0·11 0·18 0·10 0·21 0·05 0·53 0·30 0·08 0·45 1·80 0·13 0·44 0·88 NiO 0·36 0·45 0·05 0·07 n.a. 0·07 0·06 n.a. 0·01 b.d.l. b.d.l. b.d.l. n.a. n.a. b.d.l. b.d.l. b.d.l. MgO 49·45 47·68 17·56 17·18 17·30 35·00 34·66 34·22 34·48 18·66 20·72 15·26 9·49 5·88 14·55 9·95 8·89 CaO 0·01 0·07 24·65 23·79 24·97 0·21 0·18 0·18 0·16 4·99 4·92 22·26 9·28 7·16 23·27 9·39 7·23 Na2O 0·02 b.d.l. 0·26 0·65 0·06 b.d.l. 0·03 b.d.l. 0·01 0·03 0·03 0·82 b.d.l. 0·04 0·58 b.d.l. b.d.l. K2O 0·01 0·01 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0·01 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. Total 100·94 99·16 101·35 100·88 100·36 100·93 101·36 100·11 101·12 97·88 102·00 99·91 101·30 101·41 99·94 101·87 102·19 Si 1·00 1·01 1·98 2·00 1·94 1·98 1·97 1·96 1·88 3·04 2·99 1·99 2·99 3·01 2·01 3·00 3·01 Ti 0·00 0·00 0·00 0·00 0·00 — 0·00 — 0·00 0·01 0·01 0·00 0·00 0·00 0·00 0·00 0·00 Al 0·00 0·00 0·04 0·04 0·08 0·03 0·05 0·06 0·20 1·80 1·91 0·08 1·99 2·02 0·04 1·96 2·00 Cr — 0·00 0·01 0·01 0·01 0·00 0·01 0·00 0·01 0·06 0·08 0·00 0·00 0·01 0·00 0·04 0·00 Fe3+ 0·00 0·00 0·00 0·00 0·02 0·00 0·00 0·02 0·02 0·06 0·02 0·00 0·02 0·00 0·00 0·00 0·00 Fe2+ 0·20 0·21 0·05 0·06 0·03 0·18 0·20 0·18 0·13 0·57 0·46 0·16 1·17 1·58 0·18 1·14 1·37 Mn 0·00 0·00 0·00 0·00 0·00 0·01 0·00 0·01 0·00 0·03 0·02 0·00 0·03 0·12 0·00 0·03 0·06 Ni 0·01 0·01 0·00 0·00 — 0·00 0·00 — 0·00 — — — — — — — — Mg 1·79 1·76 0·94 0·92 0·93 1·78 1·76 1·76 1·74 2·04 2·15 0·83 1·05 0·67 0·80 1·10 0·99 Ca 0·00 0·00 0·95 0·92 0·97 0·01 0·01 0·01 0·01 0·39 0·37 0·87 0·74 0·59 0·92 0·74 0·58 Na 0·00 — 0·02 0·04 0·00 — 0·00 — 0·00 0·00 0·00 0·06 — 0·01 0·04 — — K 0·00 0·00 — — — — — — — 0·00 — — — — — — — Total 3·00 3·00 4·00 4·00 4·00 4·00 4·00 4·00 4·00 8·00 8·00 4·00 8·00 8·00 4·00 8·00 8·00 XMg (Fetot) 0·90 0·89 0·95 0·94 0·94 0·91 0·90 0·90 0·92 0·77 0·82 0·84 0·47 0·30 0·82 0·49 0·42 XMg (Fe2+) 0·90 0·90 0·95 0·94 0·97 0·91 0·90 0·91 0·93 0·78 0·82 0·84 0·47 0·30 0·82 0·49 0·42 Lithology: Grt-peridotite Mafic eclogite Eclogite Sample: MD25 D6 D3 Phase: Ol C Ol R Cpx C Cpx R Cpx Sym1 Opx C Opx R Opx Sym1 Opx Sym2 Gt C Gt R Cpx Gt C Gt R Cpx Sym1 Gt C Gt R SiO2 41·16 40·80 55·39 55·75 53·62 58·02 57·96 56·67 55·50 41·40 42·97 54·41 40·14 39·34 54·54 40·58 40·46 TiO2 0·05 0·02 0·11 0·08 0·14 b.d.l. 0·09 b.d.l. 0·06 0·12 0·20 0·06 0·07 0·08 0·05 0·06 0·01 Al2O3 0·01 0·02 1·02 1·01 1·83 0·82 1·21 1·51 4·94 20·81 23·22 1·92 22·73 22·33 1·02 22·44 22·74 Cr2O3 b.d.l. 0·02 0·43 0·32 0·40 0·17 0·19 0·05 0·48 1·05 1·44 0·02 0·01 0·17 0·01 0·63 0·06 FeO* 9·73 9·90 1·79 2·02 1·84 6·46 6·87 6·33 5·35 10·18 8·16 5·07 19·10 24·61 5·79 18·37 21·92 MnO 0·13 0·19 0·08 0·02 0·11 0·18 0·10 0·21 0·05 0·53 0·30 0·08 0·45 1·80 0·13 0·44 0·88 NiO 0·36 0·45 0·05 0·07 n.a. 0·07 0·06 n.a. 0·01 b.d.l. b.d.l. b.d.l. n.a. n.a. b.d.l. b.d.l. b.d.l. MgO 49·45 47·68 17·56 17·18 17·30 35·00 34·66 34·22 34·48 18·66 20·72 15·26 9·49 5·88 14·55 9·95 8·89 CaO 0·01 0·07 24·65 23·79 24·97 0·21 0·18 0·18 0·16 4·99 4·92 22·26 9·28 7·16 23·27 9·39 7·23 Na2O 0·02 b.d.l. 0·26 0·65 0·06 b.d.l. 0·03 b.d.l. 0·01 0·03 0·03 0·82 b.d.l. 0·04 0·58 b.d.l. b.d.l. K2O 0·01 0·01 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0·01 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. Total 100·94 99·16 101·35 100·88 100·36 100·93 101·36 100·11 101·12 97·88 102·00 99·91 101·30 101·41 99·94 101·87 102·19 Si 1·00 1·01 1·98 2·00 1·94 1·98 1·97 1·96 1·88 3·04 2·99 1·99 2·99 3·01 2·01 3·00 3·01 Ti 0·00 0·00 0·00 0·00 0·00 — 0·00 — 0·00 0·01 0·01 0·00 0·00 0·00 0·00 0·00 0·00 Al 0·00 0·00 0·04 0·04 0·08 0·03 0·05 0·06 0·20 1·80 1·91 0·08 1·99 2·02 0·04 1·96 2·00 Cr — 0·00 0·01 0·01 0·01 0·00 0·01 0·00 0·01 0·06 0·08 0·00 0·00 0·01 0·00 0·04 0·00 Fe3+ 0·00 0·00 0·00 0·00 0·02 0·00 0·00 0·02 0·02 0·06 0·02 0·00 0·02 0·00 0·00 0·00 0·00 Fe2+ 0·20 0·21 0·05 0·06 0·03 0·18 0·20 0·18 0·13 0·57 0·46 0·16 1·17 1·58 0·18 1·14 1·37 Mn 0·00 0·00 0·00 0·00 0·00 0·01 0·00 0·01 0·00 0·03 0·02 0·00 0·03 0·12 0·00 0·03 0·06 Ni 0·01 0·01 0·00 0·00 — 0·00 0·00 — 0·00 — — — — — — — — Mg 1·79 1·76 0·94 0·92 0·93 1·78 1·76 1·76 1·74 2·04 2·15 0·83 1·05 0·67 0·80 1&middo