Chetan. P. Hanji ^1,2*, A. Sreenivasa² and Anant. G. Pujar²

¹Department of Geology, Maharani’s Science College for Women, Mysore 570005(KN), India ²Department of Studies in Geology, Karnatak University, Dharwad-580003 (KN), India (*Corresponding Author, E-mail:chetanhpk@gmail.com)

Abstract

The study investigates the tectonothermal history of a WNW-ESE trending fold system within the Proterozoic southern Kaladgi basin, India, an area where such analysis has been previously limited. Through detailed microstructural analysis of ten oriented quartzite samples using petrographic microscopy, we correlate observed deformation features with established experimental data to constrain the paleo-deformation conditions. The analysis identified a suite of recovery and recrystallization microstructures in quartz and feldspar grains, including bulging grain boundaries (BLG), sub-grain rotation (SGR), grain boundary migration (GBM), and chessboard extinction. These features constrain the average deformation temperature to a low-to-medium range of 300°C to 580°C, corresponding to lower-middle greenschist to lower amphibolite facies conditions. Higher temperatures are consistently localized in zones of increased strain, such as vicinity of faults, shears, and fold limbs. Fabric analysis and shear-sense indicators reveal a multi-stage deformation history driven by compressional forces, oriented NE-SW and N-S, which was overprinted by a significant NW-SE transpressional shear regime. By linking micro-scale evidence to the regional stress field, this research provides a comprehensive model for the basin’s structural evolution, offering crucial insights for tectonic reconstructions and resource exploration.

Keywords: Microstructures; Deformation temperature; Quartz; Grain boundary migration; Sedimentary basin; Proterozoic