Contrasting mineral parageneses in high-temperature calc-silicate granulites: examples from the Eastern Ghats, India

Dasgupta, S. (1993) Contrasting mineral parageneses in high-temperature calc-silicate granulites: examples from the Eastern Ghats, India Journal of Metamorphic Geology, 11 (2). pp. 193-202. ISSN 0263-4929

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Official URL: http://onlinelibrary.wiley.com/doi/10.1111/j.1525-...

Related URL: http://dx.doi.org/10.1111/j.1525-1314.1993.tb00142.x

Abstract

Three types of mineral associations are described from calc-silicate granulites from the Eastern Ghats, India, where geothermobarometry in associated rocks suggests extremely high P-T conditions of metamorphism (c. 9 ± 1 kbar, 950° C). These mineral associations are: (i) calcite + quartz + scapolite + plagioclase, (ii) calcite + scapolite + wollastonite + porphyroblastic garnet + coronal garnet and (iii) calcite + quartz + wollastonite + scapolite + porphyroblastic garnet + coronal garnet, all coexisting with K-feldspar, titanite and clinopyroxene. The first two associations evolved through nearly isobaric cooling retrograde paths, whereas the third evolved through a nearly isothermal decompression path followed by an isobaric cooling retrograde path. Textural and compositional characteristics suggest the following mineral reactions in the calc-silicate granulites: calcite + quartz = wollastonite + CO2, calcite + plagioclase = scapolite, calcite + scapolite + wollastonite = porphyroblastic garnet ± quartz + CO2, CaTs + wollastonite = coronal garnet (association ii) and wollastonite + scapolite = coronal garnet (association iii) + quartz + CO2. Andradite content in garnet was buffered by the redox equilibria wollastonite + hedenbergite + O2= andradite + quartz (association iii) and wollastonite + andradite + CaTs + scapolite = hedenbergite + calcite + grossular + O2 (association ii). The contrasting mineral parageneses have been ascribed to interplay of variables such as XCO2, fO2, fHCl in the fluid, bulk Na content and the nature of the retrograde P-T-XCO2 paths through which the rocks evolved.

Item Type:Article
Source:Copyright of this article belongs to John Wiley and Sons.
Keywords:Calc-silicate Rocks; Eastern Ghats; Fluid Composition; High-temperature Metamorphism; Retrograde Path
ID Code:64654
Deposited On:12 Oct 2011 11:35
Last Modified:12 Oct 2011 11:35

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