New insights into the crustal magnetization of the eastern Indian shield inferred from the aeromagnetic data-based depth to the bottom of the magnetic sources (DBMS)

Evaluation of the crustal magnetisation through depth to the bottom of the magnetic sources (DBMS; Curie depth) offers an interesting possibility for examining the geodynamics and thermo-tectonic evolution of a region. In the present study, aeromagnetic data is used to unravel the DBMS using the modified centroid method for scaling the distribution of sources. The derived DBMS varies between 14 and 35 km, being shallow (14-20) in the nucleus of the Singhbhum Craton and the southeast of the Chhotanagpur Gneissic Complex. The western part of the Singhbhum Craton is found to have moderate DBMS (20-26 km), whereas deeper depths (26-32) are observed in the south-west Chhotanagpur Gneissic Complex and Eastern Ghats Mobile Belt. The proxy surface heat flow derived from DBMS broadly varies in the range of 40-125 mW/m(2) being high (90-125 mW/m(2)) in the northern part of the Singhbhum nucleus and south-eastern part of the Chhotanagpur Gneissic Complex, moderate (similar to 70 mW/m(2)) in the western part of the Singhbhum Craton and Singhbhum Mobile Belt and the south-western part of the Chhotanagpur Gneissic Complex, and low (40-70 mW/m(2)) in the Eastern Ghats Mobile Belt and Bengal basin. The DBMS-Moho depth difference varies between-5 to-25 km, suggesting that the lowermost part of the crust beneath the eastern Indian shield is paramagnetic. The DBMS lying much above the Moho indicates a crustal extension event that accommodates the exhumation of metamorphic massifs that were buried deep. Else the recurring tectono-magmatic processes have profusely changed the thermal state of the crust. Thermally active sub-continental mantle, substantial mafic-ultramafic crustal-scale intrusions, association with mineralization, migmatization, faulting and extensive folding, and heat-producing radioactive sources (granit-oids) in the upper crust are the possible reasons for anomalous crustal thermal structure beneath the eastern Indian shield.