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

D. Prakash ¹, M. Arima ², A. Mohan ¹

Affiliations
1 Departmeont of Geology, Banaras Hindu University, Varanasi-221005, IN
2 Geological Institute Yokohama National university, 79-7 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, JP

Abstract

Orthopyroxene-plagioclase symplecti tes have been observed in garnet-bearing mafic granulites from Panrirnalai, South India. Symplectites are arrested textures from which one can study diffusional processes. We have used colour-coded compositional mapping for reaction textures from mafic granulites to understand the element mobility pattern. The variable.composition of anorthite in plagioclase supports the interpretation that the orthopyroxene-plagioclase symplectites adjoining embayed garnet blast were formed by open-system diffusion - controlled reaction in the NCFMAS model system.

Keywords

Mafic granulites, Symplectites, Diffusion, South India.

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D. Prakash ¹

Affiliations
1 Center of Advanced Study in Geology, Banaras Hindu University, Varanasi - 221 005, IN

Abstract

Zircon cathodoluminescent imaging and SHRIMP U-Pb dating were carried out for metapelitic rocks (sapphirine-bearing granulites and garnet-cordierite gneisses) from the NW of Madurai, Southern India. The cathodoluminescence images reveal the complex, inhomogeneous internal structure having irregular-shaped core and overgrowths. Zircon grains have obliterated oscillatory zoning. SHRIMP U-Pb chronological results yield ages of 550±15 Ma and 530±50 Ma as a time of metamorphic overprint, and the age of 2509±12 Ma and 2509±30 Ma corresponding to a timing of protolith formation for sapphirine-bearing granulites and garnet-cordierite gneisses respectively. Zircon ages reflect that continental crust in the NW of Madurai region resulted from the recycling of Archaean protolith of an igneous origin similar to the preserved crust in the southern part of Dharwar craton. The present SHRIMP U-Pb zircon ages are in close agreement with earlier published Nd isotopic data which suggest an extended precrustal history of their protoliths. The abraded zircon grains indicate multiple recycling and repeated metamorphism that has ultimately resulted in present day continental crust exposed in Madurai region. These SHRIMP U-Pb zircon ages from metapelitic UHT granulites are also significant to understanding the architecture of the SGT during the amalgamation of Gondwana in Neoproterozoic time.

Keywords

Geochronology, SHRIMP, Zircon, Metapelitic Granulites, South India.

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B. P. Singh ¹, U. K. Shukla ¹, R. Bhatla ², D. Prakash ¹, A. S. Naik ¹, Kuldeep Prakash ¹, C. K. Singh ¹

Affiliations
1 Centre of Advanced Study in Geology and Banaras Hindu University, Varanasi - 221 005, IN
2 Department of Geophysics, Banaras Hindu University, Varanasi- 221 005, IN

Abstract

A National Seminar on “Geology and Geo-resources of the Himalaya and the cratonic regions of India” was organised by the Department of Geology, (Centre of Advanced Study), Kumaun University, Nainital during 10-12^th March, 2012. The Seminar was co-sponsored under the CAS Programme by the University Grants Commission, New Delhi; Department of Science and Technology, New Delhi; Uttarakhand State Council for Science and Technology, Dehradun; Kumaun University, Nainital; Censico International (P) Ltd., Agra. In all, 125 delegates from all over India actively participated in this national seminar.

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