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 ∼ 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 ∼ 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° 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 ∼ 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.