Aeromagnetic signatures of the cratons and mobile belts over India

Abstract

An aeromagnetic image map of India up to 25° North latitude and between 74° to 84° East longitude is prepared. The three cratons: Dharwar, Bastar and Sighbhum are clearly demarcated and are separated by the NW-SE trending Godavari and Mahanadi grabens and are surrounded by the mobile belts of the Central Indian Tectonic Zone, the Eastern Ghats and the Southern Granulite Terrain. The analytic signal map of the aeromagnetic data depicts that the main magnetic sources within the cratons are related to iron ore belts, schist belts and dyke systems while the sources within the mobile belts are due to the exhumed crust reflecting the high-grade granulite belts. The Euler solutions bring out the block structure and fractured nature of the region. Spectral estimates are utilised to evaluate the Curie isotherm depth. Regions of exhumed crust and mobile belts show a thinner magnetic crust than the cratons. Utilising the 1D heat conduction, steady state thermal model for the continental crust, we calculate the geothermal heat flux from the Curie isotherm depths, incorporating available surface heat flow and thermal conductivity for the various tectonic blocks of India. The calculated heat flux, for several areas match the surface heat flow measurements.