Paleostress variation during the same regional deformation in the Eastern Dharwar Craton (southern India)

The objective of this study is to evaluate progressive variation in the state of stress at ca 2.5 Ga in Hutti region of Eastern Dharwar Craton (EDC, southern India). Paleostress analysis is performed using quartz vein orientations in metavolcanic and granitoid rocks (ca 2.5 Ga) of the region. It is established that veins in the metavolcanic rocks formed during regional D3 deformation under N-S compression that is related to N-S directed far-field stress, which is also responsible for D3 folds with E-W striking axial planes in parts of the EDC. Anisotropy of magnetic susceptibility data from the granitoids yields NNW-SSE striking fabric anisotropy that developed during regional D1/D2 deformation. Paleostress analysis using veins in the granitoids of the region yields NE-SW compression. However, the kinematics of formation of these veins is shown to be compatible with dextral simple shear along pre-existing NNW-SSE oriented fabric under N-S directed D3 compression. Therefore, it is established that veins in the metavolcanic and granitiod rocks of the study area formed under the same N-S directed D3 far-field stress, an interpretation that is further supported by the similar values of stress ratio obtained from 3D Mohr circle analysis of vein data from the two lithologies. Thus, the study demonstrates that there are pitfalls in direct evaluation of paleostress using only vein orientations and that understanding kinematics of vein emplacement is critical in paleostress analysis. Our data further reveal that the granitoids were subjected to faulting during the final stages of D3 due to which the veins are displaced. Paleostress analysis using fault-slip data from the granitoids yields NNE-SSW compression. This local variation of paleostress in granitoids is due to late-D3 brittle deformation during cratonization of the Dharwar Craton at ca 2.5 Ga.