Seismic Characteristics of the South Indian Granulite Crust

Abhishek Rai, Shyam S. Rai, Vinod K. Gaur, and Keith Priestley

Analysis of broadband seismograms from ten seismic stations located on granulite terranes that surround the Archaean Dharwar Craton of the south Indian shield, indicate that the seismic characteristics of the crust of these exhumed terranes share some characteristics of the western Dharwar Craton but are significantly different from those of the eastern Dharwar Craton. Joint inversion of receiver functions and surface wave dispersion data show that the crust of the western Dharwar and granulite terranes are generally thick (~44 km) and have complex internal structures, whereas the crust of the eastern Dharwar is thinner (~35 km) with insignificant internal structure. The crust beneath the granulites and the western Dharwar Craton has a layered structure and a gradational Moho. Also, the lower crust of these terranes is relatively more mafic (Vs ~3.85-4.15 km/s) compared with those of the eastern Dharwar where Vs is ~3.7 km/s.

In view of the overall gentle relief of the south Indian shield with seismic characteristics of a classical Archaean craton in the eastern Dharwar, the thicker and seismically less transparent crust of the western Dharwar and the granulites require major geochemical reordering of the underlying lithospheres brought about by subsequent magmatic activity. This study is aimed at providing some depth-differentiated seismic constraints to help formulate tenable models of crust formation in the southern granulites of Indian shield.