Rift Structure along the Eastern Continental Margin of India - new constraints on style of breakup of the Indian landmass from the eastern Gondwanaland

Abstract:

The Eastern Continental Margin of India (ECMI), a classical passive margin has evolved after breakup of the Indian landmass from the East Antarctica during the Early Cretaceous. Anomalous thick sediments and lack of cohesive magnetic signatures in the Bay of Bengal hampered delineation of rift-structure and age assignment for the continental breakup between India and East Antarctica. Further, absence of lithological and geochronological information and a few seismic profiles from the margin led to put forward several competing models for the rift initiation and evolution of the ECMI. Here, we analyze long streamer seismic reflection data and deep-water drill well information from the western Bay of Bengal to infer the buried rift structure, crustal architecture and stratigraphy along the ECMI. Following the structural pattern of the margin, the region is divided into four domains as decoupled, coupled, exhumed and oceanic, which in turn helped us to demarcate the variations in rift structure from south to north along the margin. The southern segment in the vicinity of Cauvery Basin consists of steep continental shelf associated with few major normal faults, which indicates that the segment was evolved as mix shear-rifted margin. The central segment off southern part of the Krishna-Godavari Basin is controlled by a series of fault-bounded half-graben structures and presence of thinned continental crust over the exhumed mantle body, revealing that the segment was formed under hyper-rifting process. While the northern segment extends up to Mahanadi Basin shows relatively less gradient continental slope with a few major faults, suggesting that the segment was evolved by hypo-extended process. Variable crustal architecture lying along the ECMI supports each segment of the margin formed in a specific rift process. A breakup unconformity considered as important geological constraint for completion of rift process between India and East Antarctica is clearly mapped on hyper- and hypo-extended margin segments. On correlation of rift structures to Indian Shield's geology, it is found that rheology of stable cratonic blocks and bordered Gondwana grabens/ mobile belts may have played a role in controlling the rift process between the continental masses, India and East Antarctica.