Petrological evolution of sapphirine-bearing granulites and charnockites of the Kodaikanal Massif, Southern Granulite Terrane

Sumedha, D. (2022) Petrological evolution of sapphirine-bearing granulites and charnockites of the Kodaikanal Massif, Southern Granulite Terrane. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS disertation of Sumedha D (17MS182)) 17MS182_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (6MB)

Abstract

The Southern Granulite Terrane occupies a central position in reconstructions of the Neoproterozoic eastern Gondwana supercontinent, and the Kodaikanal massif is a vital part of it. Application of feldspar thermometry to sapphirine-bearing granulites and conventional Fe-Mg exchange thermometry to garnet-bearing charnockites from the study area resulted in peak temperatures (900-1000°C) that can be ascribed to ultrahigh-temperature metamorphism. The sapphirine-bearing granulites contain sapphirine-cordierite symplectites, while the garnet-bearing charnockites contain double coronal textures of orthopyroxene and plagioclase around garnet grains. Both features are indicative of a decompressive P-T path. The two rock types also show retrograde rehydration-associated biotite overgrowth on most phases, possibly indicating a near-isobaric cooling path. Geobarometry on the charnockites hinted at an ultrahigh-temperature isothermal decompression retrograde evolution from ~9-6kbar. A fuller picture showing a clockwise P-T evolution passing through a peak of at least 910°C, 12kbar along a retrograde isothermal decompression to about 6kbar, followed by near isobaric cooling was recovered by constructing pseudosections for both the rock types. The results from both rock types were important to get a fuller picture of the clockwise P-T evolution of the study area. This is in keeping with a continental collisional tectonic setting during the late Neoproterozoic as part of Gondwana amalgamation and a large-hot orogen model for the attainment of extreme thermal conditions.

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