Determination of the P,T paths of natural eclogites during metamorphism—record of subduction

This contribution reports the metamorphic evolution of the high-pressure metamorphic rocks from the Bantimala Complex, South Sulawesi, Indonesia. Barroisite-bearing and barroisite-free eclogites were examined to assess their metamorphic evolutions, which have implications regarding the tectonic conditions in this region. The eclogites mainly consist of garnet, omphacite, phengite, rutile, and epidote, with or without barroisite. The variations in mineral assemblages are interpreted to depend upon local changes in the bulk chemical composition. The barroisite-bearing eclogites contain two types of euhedral garnet: coarse-(1-1.5 mm) and finegrained (<0.5 mm). Mineral inclusions in the coarse-grained garnet core and mantle show epidote + titanite and glaucophane + epidote assemblages, that stabilized at 0.9-1.5 GPa and 350-550°C within epidote blueschist-facies conditions. Mineral chemistry and chemical-mapping analyses indicate that both fine-grained garnet and the rim of coarse-grained garnet formed at peak P-T conditions, which were estimated as 2.3-2.7 GPa at 615-680°C based on the garnet-omphacite-phengite-quartz equilibrium. Peak P-T conditions for barroisitefree eclogite were similar (2.5-2.7 GPa at 650-690°C) to those for barroisite-bearing eclogite. Actinolite rims overgrowing matrix sodic-calcic amphiboles attest to retrogression at P < 0.5 GPa and T < 350°C in a clockwise P-T path. The very low geothermal gradient experienced during the prograde path (~5°C/km) likely suggests the subduction of an old and cold oceanic crust. The low geothermal gradient on the retrograde path suggests decompressional cooling during exhumation, possibly favored by a serpentinite-dominated matrix within a subduction channel environment.

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“…Fe 2+ /Fe 3+ ratios were determined from stoichiometry using the method of Ryburn et al (1976) as Fe…”

Section: Clinopyroxenementioning

confidence: 99%

Prograde and retrograde evolution of eclogites from the Bantimala Complex in South Sulawesi, Indonesia

Setiawan

Osanai

Nakano

et al. 2016

Journal of Mineralogical and Petrological Sciences

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“…In common eclogites the Fe 3+ /Fe tot ratio in garnet is expected to be low, but extreme caution must be used when applying the calculated Fe 3+ /Fe tot ratio for omphacite, and especially for Fe-poor systems (Krogh Ravna and Paquin, 2005). In this paper, the Fe 3+ /Fe tot ratio was calculated in accordance with Ryburn et al (1976) for both garnet and omphacite.…”

Section: Stage IIImentioning

confidence: 99%

“…2), contain quartz-white mica-plagioclasegarnet-biotite with possible kyanite relics. Ryburn et al (1976).…”

Section: Petrography and Mineral Chemistry Of Tasmanian Eclogitesmentioning

confidence: 99%

“…Structural formulae were calculated on the basis of 12 oxygens for garnet, 6 for pyroxene, 22 for micas, 8 for plagioclase, 12.5 for epidote, 29 for tourmaline, and 23 for amphiboles. Ferrous and ferric iron contents were calculated after Ryburn et al (1976) for garnet and pyroxene and according to Holland and Blundy (1994) and the THERMOCALC AX-program (Holland and Powell, 1998) for amphiboles and epidotes, respectively. B cations in tourmaline were calculated on the basis of stoichiometry.…”

Section: Mafic Rocksmentioning

confidence: 99%

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Petrology of the eclogites from western Tasmania: Insights into the Cambro-Ordovician evolution of the paleo-Pacific margin of Gondwana

Palmeri

Chmielowski

Sandroni

et al. 2009

Lithos

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Eclogite facies rocks along the Paleozoic active margin of Gondwana are rare. They are limited to isolated segments of Northern Victoria Land (Antarctica), western Tasmania, and southeastern Australia. New petrological data for mafic rocks and their host garnet-kyanite schists from the Franklin Metamorphic Complex (western Tasmania) permit reconstruction of six main stages of mineral growth for the eclogite. Stages I and II occurred at greenschist/ amphibolite-facies conditions (ca. 500-600°C; 0.55-0.7 GPa for stage II) before attaining high-pressure conditions (at ≈600-650°C; N 1.5 GPa for stage III). The following stages, IV and V, record the decompression from high-pressure conditions to amphibolite-facies (ca. 500-600°C; 0.4-1.0 GPa). Finally, stage VI represents the late greenschist-facies retrogression. However, the pelitic schist surrounding the eclogite records only the mediumpressure amphibolite-facies stage. The P-T evolution over time outlines a clockwise path that is quite steep in both the prograde and retrograde segments. The latter shows a nearly isothermal decompression between the eclogite and the high-pressure amphibolite-facies stage IV, which was achieved at deep crustal levels (≈30 km), and a final decrease in both pressure and temperature from deep/intermediate to shallow crustal levels, with a typical cooling-unloading path. The lack of a complete re-equilibration during the different stages and the high dP/dT for both the prograde and retrograde paths are indicative of a rapid burial and initially rapid exhumation. The similarity of the mafic whole-rock chemical composition, including N, T to E-MORB and of the peak metamorphic age (≈500 Ma) between the Tasmanian eclogites and the UHP rocks from Northern Victoria Land, supports the idea that they formed in the context of the same contractional event. However, the different P-T conditions and dP/dT point to different tectono-metamorphic settings for the two sectors of the paleo-Pacific margin of Gondwana during the Ross/Tyennan orogeny.

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“…Raw counts were corrected using on-line PAP routine. Fe 3+ in clinopyroxenes was calculated according to the charge balance proposed by Ryburn et al (1976). Fe 3+ in amphiboles was calculated assuming an ideal stoichiometry according to Schumacher (1997).…”

Section: Mineral Chemistrymentioning

confidence: 99%

Eclogites overprinted in the granulite facies from the Ďumbier Crystalline Complex (Low Tatra Mountains, Western Carpathians)

Janák¹,

Mikuš²,

Pitoňák³

et al. 2009

Geologica Carpathica

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Abstract:Metabasites with evidence for breakdown of former eclogites and recrystallization under granulite facies conditions occur in the Ďumbier Crystalline Complex of the Low Tatra Mountains, Central Western Carpathains. Textural relationships, phase equilibrium modelling and thermobarometry have been used to determine the P-T evolution of these rocks. Omphacite diagnostic for the eclogites facies stage is absent but its former presence is inferred from the symplectitic intergrowths of clinopyroxene +plagioclase. The re-equilibration in high-pressure granulite facies conditions is demonstrated by the assemblage garnet + clinopyroxene (< 10 % Jd) + plagioclase + quartz. The phase equilibrium modelling using THERIAK-DOMINO program and conventional geothermobarometry suggest the P-T conditions of 750-760 °C and 1.1-1.5 GPa for the high-pressure granulite stage. Orthopyroxene formed in the clinopyroxene + plagioclase symplectites and kelyphites and coronas around garnet at P-T conditions of ca. 0.7-1.0 GPa and 650-700 °C. P-T evolution of granulitized eclogites is interpreted as the result of two metamorphic events; early Variscan eclogite facies metamorphism was followed by granulite facies thermal overprint in the Carboniferous time. The second metamorphic event was crucial for breakdown of eclogites, these are only seldom preserved in the pre-Alpine basement of the Western Carpathians.

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Determination of the P,T paths of natural eclogites during metamorphism—record of subduction

Cited by 85 publications

References 4 publications

Prograde and retrograde evolution of eclogites from the Bantimala Complex in South Sulawesi, Indonesia

Prograde and retrograde evolution of eclogites from the Bantimala Complex in South Sulawesi, Indonesia

Petrology of the eclogites from western Tasmania: Insights into the Cambro-Ordovician evolution of the paleo-Pacific margin of Gondwana

Eclogites overprinted in the granulite facies from the Ďumbier Crystalline Complex (Low Tatra Mountains, Western Carpathians)

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