Post-Deccan Trap stress reorientation under transpression: Evidence from fault slip analyses from SW Saurashtra, Western India

We analyze paleostress from a region in SW Saurashtra (India) using three free software, T-Tecto, WinTensor and FaultKin based on attitudes of similar to E-W trending, sub-vertical, brittle fault planes and associated horizontal, inclined and subvertical slickensides, developed over them. We present a detailed fault slip analysis of a previously unmapped E trending fault (herein referred as the Katar Fault) that cuts across and offset the southeastward dipping Deccan lava flows with a dense NE-SW trending dyke swarm belonging to Deccan Trap near Rajula (Gujarat, India). Measured fault strikes do not match exactly with similar to NW/NNW trending basement structures, deduced by previous geophysical studies, nor with faults reported from the offshore Saurashtra region. However, a few geomorphic features around Katar indicate a similar strike slip offset. A stress ratio of up to 0.2, and a SE maximum principal stress axis were deduced using T-Tecto, while WinTensor and FaultKin gave plunging stress axes. Therefore, stress analyses by T-Tecto seem more plausible. The SHmax direction usually remains close to one of the stress axes, and shows up to 36 degrees rotation when compared with the offshore region. We attribute the formation of Katar Fault to post-Deccan Trap oblique slip reverse faulting with sinistral slip due to intraplate transpressional stresses induced by the anticlockwise rotation and collision of the Indian plate with the Eurasian plate at similar to 55 Ma. This transpressional faulting post-dates the eastward tilting of lava flows and anticlockwise rotation in the dyke swarm patterns caused by the emplacement of large Girnar intrusive body. Detailed structural geological field-work in Saurashtra would be much required to understand its onshore tectonics.