Vein-type graphite deposits in Sri Lanka: the ultimate fate of granulite fluids

Touret, Jacques L.R., Huizenga, Jan Marten, Kehelpannala, K.V. Wilbert, and Piccoli, Francesca (2018) Vein-type graphite deposits in Sri Lanka: the ultimate fate of granulite fluids. Chemical Geology. (In Press)

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Abstract

Hydrothermal graphite vein deposits hosted in granulite facies metamorphic rocks in Sri Lanka are unique because of their large size and high crystallinity. In this paper, we present a review of the structural-metamorphic setting of the graphite veins and of the graphite stable carbon isotope data, and we present fluid inclusion data from quartz in the graphite veins and in the host rocks from several graphite deposits in Sri Lanka. The studied host rocks show decompression rims of plagioclase and orthopyroxene after garnet. The quartz in these decompression rim textures comprise, in order of abundance, high-salinity brine, H2O-CO2, and low-salinity aqueous fluid inclusions. The brine fluid is responsible for metasomatic features observed in garnet decompression rims, including feldspar leaching and re-precipitation. Quartz cogenetic with vein graphite comprises, in order of abundance, low-salinity aqueous, CO2, high-salinity brine, and H2O-CO2 fluid inclusions. Published graphite carbon isotope data indicates a dominant mantle source, mixed with small amounts of carbon-bearing fluids of supracrustal origin. We propose that large quantities of mantle-derived CO2 fluid are temporarily stored in the lower crust during the final stage of Gondwana supercontinent amalgamation. The CO2 is subsequently released from the lower crustal rocks during decompression associated with fast uplift. The graphite veins in Sri Lanka were formed during this uplift stage and represent as such paleofluid channels. In this respect, they are comparable to the quartz‑carbonates mega-shear zones found in other granulite terranes. Depending on the redox conditions, mantle CO2 and brines may either result in the formation of graphite or quartz‑carbonate veins.

Item ID: 54139
Item Type: Article (Research - C1)
ISSN: 1872-6836
Keywords: Sri Lanka, hydrothermal vein graphite, granulite, CO 2 fluid, high salinity brine, lower crust
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This work was presented at the European Current Research on Fluid Inclusions (ECROFI) 2017 biennial meeting, 23-29 June 2017, Nancy, France. The abstract of this presentation is available through ResearchOnline at the related URL.

Date Deposited: 11 Jul 2018 04:05
FoR Codes: 04 EARTH SCIENCES > 0402 Geochemistry > 040299 Geochemistry not elsewhere classified @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 100%
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