Tectonic evolution of the intra-uplift Vigodi-Gugriana-Khirasra-Netra Fault System in the seismically active Kachchh rift basin, India: Implications for the western continental margin of the Indian plate

The E-W striking Kachchh Rift Basin (KRB) at the western continental margin of Indian plate is located in the northern part of Gujarat state, India. KRB has undergone polyphase deformation owing to changing stress-field since Late Triassic. We establish the kinematic framework along the NW striking intra-uplift Vigodi-Gugriana-Khirasra-Netra Fault System (VGKNFS) located at the western part of the KRB. The VGKNFS consists of 0.25-50 km long, sub-parallel, striated, reactivated dip-slip faults. A total of 1150 fault-slip data consisting of fault planes and striations attitude were recorded from 66 sites (including a single site with systematic joints). Slip-sense of faults was determined by documenting kinematic indicators. Paleostress analysis was carried out using Win Tensor, T-Tecto, FaultKin and SG2PS to compare and validate the results. The chi-square statistical analysis was undertaken to evaluate how relevant are paleostress analysis results to the present-day compressional stress field. Geophysical investigations were conducted at selected sites using Ground Penetrating Radar (GPR) to understand the shallow subsurface geometry and trace the continuity of faults buried below patchy alluvial cover. 15-17 m long, 2D GPR cross-sections were recorded across faults using monostatic antenna of 200 MHz frequency. Two major deformation events - D1 and D2 are determined in the present study. The extension event D1 shows W and NW-NNW extension during Late Triassic to Late Cretaceous. It occurred during the rift phase of KRB in response of the break-up of Gondwanaland. The latest event D2 shows NNE-NE compression from Late Cretaceous up to the present. It is interpreted to have developed during post-rift inversion phase, induced by collision of the Indian plate with the Eurasian plate at similar to 55 Ma.