Near N-S paleo-extension in the western Deccan region, India: Does it link strike-slip tectonics with India-Seychelles rifting?

This is the first detailed report and analyses of deformation from the W part of the Deccan large igneous province (DLIP), Maharashtra, India. This deformation, related to the India-Seychelles rifting during Late Cretaceous-Early Paleocene, was studied, and the paleostress tensors were deduced. Near N-S trending shear zones, lineaments, and faults were already reported without significant detail. An E-W extension was envisaged by the previous workers to explain the India-Seychelles rift at similar to 64 Ma. The direction of extension, however, does not match with their N-S brittle shear zones and also those faults (sub-vertical, similar to NE-SW/similar to NW-SE, and few similar to N-S) we report and emphasize in this work. Slickenside-bearing fault planes, brittle shear zones, and extension fractures in meso-scale enabled us to estimate the paleostress tensors (directions and relative magnitudes). The field study was complemented by remote sensing lineament analyses to map dykes and shear zones. Dykes emplaced along pre-existing similar to N-S to similar to NE-SW/similar to NW-SE shears/fractures. This information was used to derive regional paleostress trends. A similar to NW-SE/NE-SW minimum compressive stress in the oldest Kalsubai Subgroup and a similar to N-S direction for the younger Lonavala, Wai, and Salsette Subgroups were deciphered. Thus, a similar to NW/NE to similar to N-S extension is put forward that refutes the popular view of E-W India-Seychelles extension. Paleostress analyses indicate that this is an oblique rifted margin. Field criteria suggest only similar to NE-SW and similar to NW-SE, with some similar to N-S strike-slip faults/brittle shear zones. We refer this deformation zone as the Western Deccan Strike-slip Zone (WDSZ). The observed deformation was matched with offshore tectonics deciphered mainly from faults interpreted on seismic profiles and from magnetic seafloor spreading anomalies. These geophysical findings too indicate oblique rifting in this part of the W Indian passive margin. We argue that the Seychelles microcontinent separated from India only after much of the DLIP erupted. Further studies of magma-rich passive margins with respect to timing and architecture of deformation and emplacement of volcanics are required.