New seismic images of the Central Indian Suture Zone and their tectonic implications

Abstract

The Central Indian Suture (CIS), a mega shear zone, located in the central part of the Indian shield exhibits a complex structure with compositional heterogeneity. Multifold deep seismic reflection data acquired across the shear zone have been previously processed using the conventional common midpoint (CMP) method. In this study, we show results from imaging this shear zone using the common reflection surface (CRS) stack method, an alternative to the CMP stack. Our new images reveal geological features that are either poorly resolved or entirely absent in the earlier CMP stack section. Our major findings include a well-imaged Moho throughout the study area, existence of different crustal blocks each with distinct dipping reflection fabrics on the northern and southern sides of the CIS, a well-defined 8 km of Moho offset beneath the CIS, and a high-amplitude reflective zone representing the CIS. The Moho located at a depth of 48 km in the Bastar craton, to the south of the CIS, is also clearly resolved in our CRS stack, as well as in the time-migrated section. A deeply penetrating crustal-scale imbricated structure imaged up to a depth of 16.0 s two-way time (TWT), to the south of the CIS, suggests that the Bastar craton is subducting toward north. An oppositely dipping reflection fabric, a Moho offset, a positive-negative gravity anomaly pair, and the geological data indicate that the CIS represents a collision zone developed due to the interaction of the Bastar and Bundelkhand cratons with the evolution of the Sausar orogeny at ~1000 Ma. This orogeny is contemporaneous with the Grenvillian orogeny and Rodinia assembly. Another thrust fault extending from 4 to 14 s TWT observed to the north of the CIS may represent the earlier, pre-Sausar orogenic activity at 1.6-1.5 Ga. The available seismic characteristics suggest that the CIS, the collisional suture, is also likely to represent a strike-slip fault. ©2013. American Geophysical Union. All Rights Reserved.