Tectonothermal History of the Central Indian Tectonic Zone and Reactivation of Major FauIts/Shear Zones

Central Indian Tectonic Zone (CITZ), which divides the Indian subcontinent into Bundelkhand Block in the north and the Deccan Block in the south, is represented by a collage of different lithotectonic terranes ranging in age from Archaean to Recent. It comprises two parallel structural domains, namely the Son-Narmada (SONA) subzone in the north and the Sausar mobile belt (SMB) in the south. The ancestry of the SONA subzone is indicated by the Neoarchaean - Palaeoproterozoic ages yielded by the rocks of Mahakoshal fold belt; the Sausar belt, on the other hand, has yielded Meso- to Neo-proterozoic ages. The present response of CITZ to accumulation of stress and attendant seismicity is governed by the structures generated due to early tectonic history of rocks within it, particularly the development of number of E-W to ENE-WSW striking, brittle and ductile shear zones. While the Sausar belt has remained more or less stable since the late Precambrian, the SONA and Tapti lineament zones have been reactivated several times. Two prominent ENE-WSW trending deep fautts, termed the Son-Narmada North Fault (SNNF) and Son-Narmada South Fault (SNSF) have been episodically active from Neoarchaean onwards. The SNSF in particular has witnessed protracted reactivation well into the Phanerozoic. Intraplate seismicity in continents is commonly concentrated along ancient fault zones. Reactivation of faults or shear zones is favoured over new fault generation, since the SNSF is in a high shear stress orientation. Although the Sausar mobile belt is marked by a number of E-W trending parallel ductile shears, mass transfer processes such as silicification, recrystallization and grain growth during Precambrian appear to have healed them.