Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

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Structure and Metamorphic Characteristics of Cordierite-Bearing Gneiss of South Kerala


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1 Centre for Earth Science Studies, Trivandrum, India
     

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Cordierite-bearing gneiss of the Quilon district, Kerala, occurs in a 8-10km wide zone within quartzo-feldspathic gneiss, being bordered on the north by a charnockite massif. These gneisses are deformed and are polymetamorphic in character. The cordierite-forming metamorphism is the second in metamorphic chronology. The reaction producing the bulk of cordierite was: biotite + sillimanite + quartz ⇌ cordierite + garnet + K-fetdspar + H2O. The KD (Mg-Fe) values of coexisting garnet-cordierite and garnet-biotite pairs indicate that the PT conditions of metamorphism (∼ 7 kb, ∼ 720°C) were those of granulite facies. Under these conditions cordierite was produced from Fe-Mg enriched melt restite, being trapped at the fringe of the charnockite massif.
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  • Structure and Metamorphic Characteristics of Cordierite-Bearing Gneiss of South Kerala

Abstract Views: 181  |  PDF Views: 4

Authors

S. Sinha-Roy
Centre for Earth Science Studies, Trivandrum, India
John Mathai
Centre for Earth Science Studies, Trivandrum, India
Narayanaswamy
Centre for Earth Science Studies, Trivandrum, India

Abstract


Cordierite-bearing gneiss of the Quilon district, Kerala, occurs in a 8-10km wide zone within quartzo-feldspathic gneiss, being bordered on the north by a charnockite massif. These gneisses are deformed and are polymetamorphic in character. The cordierite-forming metamorphism is the second in metamorphic chronology. The reaction producing the bulk of cordierite was: biotite + sillimanite + quartz ⇌ cordierite + garnet + K-fetdspar + H2O. The KD (Mg-Fe) values of coexisting garnet-cordierite and garnet-biotite pairs indicate that the PT conditions of metamorphism (∼ 7 kb, ∼ 720°C) were those of granulite facies. Under these conditions cordierite was produced from Fe-Mg enriched melt restite, being trapped at the fringe of the charnockite massif.