Structural and Petrological Studies of Granulite Formation

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Tectonics of granulite mobile belts in East Gondwana were studied first, reviewing various published studies. The ca 1100 Ma events are characterized by overfolds, thrust faults, and granulite metamorphism which are regarded to be the characteristics of convergent tectonics and thus are explained to reflect the amalgamation of East Gondwana. The ca 550 Ma events which are correlated with the Pan-African events in West Gondwana include various folds, faults and metamorphisms associated with extensive granitic activities and are explained to form the rejuvenation of already formed crust. The ca 550 Ma events are associated with the incipient charnockite formation. The conjugate fracture system associated with this charnockite in Sri Lanka shows maximum extenstional stress axis normal to the major fold axs and is regarded to be supportive to the tectonic setting of the incipient charnockite occurrence demonstrated by Yoshida and Santosh (1994). During the middle to later periods of the research project, various analysis of granulite samples from the above areas were conducted and the following results were obtained. Carbon isotope studies of graphite and fluid inclusion studies clarified the influx and removal behavour of CO_2 fluid during the granulite metamorphism. It was found that there is an intimate relationship of CO_2 fluid with the rare element pegmatites which are characteristic in the Pan-African terranes. Studies of Sm-Nd isotopic systematics clarified the major granulite metamorphism of South India, SriLanka and Antarctica to have formed at ca 550 Ma. Compiling these results, the Pan-African granuilte formation in East Gondwana is considered principally to be under the extensional tectonics, most possibly related with some riftogenic crustal conditions. All these tectonic situations of the Pan-African granulite events are again supportive to the tectonic model of the incipient charnockite formation proposed by Yoshida and Santosh (1994).