Deformation temperature, differential stress, and strain rate variation across the Bomdila Gneiss, western Arunachal Himalaya, India

Constraining deformation temperature, differential stress, and strain rate variation from deformed rocks is crucial in developing tectonic models. The outcrop to grain scale fabrics of the Bomdila Gneiss (BG) in the Lesser Himalayan Sequence (LHS) of the western Arunachal Himalaya is studied to understand the variation of the intensity of deformation across the mylonitic batholithic intrusive. The BG represents a Paleoproterozoic magmatic activity in the LHS and subsequently underwent Miocene Himalayan orogenesis. The upper and lower contacts of the BG with Dirang Formation and Miri Quartzite are demarcated by Dirang Thrust (DT) and Bome thrust (BT), respectively, while in the middle, it has another thrust contact with the Tenga Formation, known as the Tenga Thrust (TT). The intensity of deformation across the BG is constrained through microstructural analysis, piezometric study, and fractal dimension analysis. Manifestations of the dynamic recrystallization are evidenced through grain boundary migration, sub-grain rotation, and grain boundary bulging microstructures of quartz crystals. We have estimated the deformation temperatures from microstructural characterization such as grain boundary migration, sub-grain rotation, and grain boundary bulging. The differential flow stresses are calculated through piezometric study. While, the fractal dimension values calculated through area–perimeter method along with deformation temperatures reveal the rates of strain in the BG. The deformation temperatures, differential flow stresses, and rates of strain in the BG are elevated near the thrust zones with maximum near TT and within the BG increases from SE to NW direction towards DT. Both BT and TT are imbrications indicating southward propagation of the thrusts in sequence. The initially buried BG under the Greater Himalayan Crystalline has been considered to exhume through the TT along with BT. An inverted thermal profile within the BG is found along the traverse, which may be due to the thrust imbrications in the MCT footwall.