Ultrahigh-temperature metamorphism followed by two-stage decompression of garnet-orthopyroxene-sillimanite granulites from Ganguvarpatti, Madurai block, southern India

K. Sajeev, Y. Osanai, M. Santosh

Research output: Contribution to journalArticle

97 Citations (Scopus)

Abstract

The Mg-Al granulites from Ganguvarpatti consist of orthopyroxene-sillimanite-garnet ± quartz as peak assemblage, with a few porphyroblasts of cordierite and sapphirine. These assemblages were strongly overprinted by late symplectites and coronas. Orthopyroxene inclusions in garnet and porphyroblast cores have the highest XMg (0.80) and A12O3 content (10.7 wt%). The estimated near-peak metamorphic conditions (1,000 ± 50°C and 11 kbar) using garnet-orthopyroxene geothermobarometry are consistent with those determined using a petrogenetic grid. The proposed multi-stage evolution process implies an initial decompression, deduced from multi-phase symplectites, followed by cooling during biotite formation. Further late decompression is explained from the orthopyroxene rims on biotite. This proposed P-T path thus suggests a unique and complex evolution history for the UHT granulites of southern India. Present results are comparable with similar adjacent terranes in the Gondwana supercontinent, but the lack of structural and geochronological data makes a link with any major metamorphic event uncertain.

Original languageEnglish
Pages (from-to)29-46
Number of pages18
JournalContributions to Mineralogy and Petrology
Volume148
Issue number1
DOIs
Publication statusPublished - Sep 1 2004

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

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