Research Article Implication of Dynamic Recrystallization Mechanism for the Exhumation of Lower Crustal Rocks: A Case Study in the Shear Zones of the Ambaji Granulite, NW India Sudheer Kumar Tiwari , 1 Anouk Beniest, 2 Priti Rai, 3 Sohini Chatterjee, 4 Ruturaj Vilas Daphale, 5 Tapas Kumar Biswal, 3 Anand Kumar Yadav, 1 and Subha Kundu 1 1 Department of Earth Sciences, Indian Institute of Technology Roorkee, 247667, India 2 Department of Earth Sciences, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, Netherlands 3 Department of Earth Sciences, Indian Institute of Technology Bombay, 400076, India 4 Department of Geological Sciences, Jadavpur University, Kolkata 700032, India 5 School of Earth Ocean and Atmospheric sciences, Goa University, Taleigao Plateau 403206, India Correspondence should be addressed to Sudheer Kumar Tiwari; sudheer030192@gmail.com Received 1 June 2021; Accepted 23 February 2022; Published 21 March 2022 Academic Editor: Koushik Sen Copyright © 2022 Sudheer Kumar Tiwari et al. Exclusive Licensee GeoScienceWorld. Distributed under a Creative Commons Attribution License (CC BY 4.0). Shear zones are important channels for the exhumation of lower crustal rocks. The Ambaji granulite of the Aravalli-Delhi mobile belt (ADMB) has been exhumed along several shear zones, and earlier studies have shown a two-stage exhumation process during a continuous compressional tectonic event, consisting of an initial phase of vertical flow that brought the granulites to the brittle- ductile transition zone and a successive phase during which the granulite underwent a lateral flow. In this contribution, we studied the microtectonics of granulites by analyzing the dynamic recrystallization behaviour of quartz, while the granulite was passing through the vertical flow regime to the horizontal flow regime. We show that the dynamic recrystallization process assists the flow pattern at different levels of exhumation. The vertical flow is dominated by grain boundary migration (GBM), registering high temperatures for recrystallization between 490 and 600 ° C and low flow stresses of 12-15 MPa. The horizontal flow at the brittle-ductile transition (BDT) is characterized by bulging (BLG) and subgrain rotation (SGR), which occurred at low temperatures of 390-490 ° C and high flow stresses of 18-26 MPa. Strain rates are between 1:20 × 10 -12 and 7:26 × 10 -14 /s. For the ductile exhumation of the granulite, we suggest that at depths of ~22 km, the granulite exhumed in a vertical direction facilitated by GBM. Once the granulite reached the BDT, at ~16 km depth, the material flowed laterally assisted by BLG and SGR. Once an exhuming body reaches the BDT, the deformation mechanism changes to BLG-SGR, and the only direction in which the material can move further is in the horizontal plane. 1. Introduction Exhumation of granulites from middle to lower crustal depths to the surface involves different exhumation mecha- nisms (for example, see reviews by [1, 2] and references therein). One of the most important mechanisms is exhuma- tion along shear zones. Shear zones experience simple shear deformation with various proportions of pure shear ([3], which vary with different mineral assemblages that depend on PT condition and fluid composition. Quartz-rich shear zones are specifically characteristic for their variations in dynamic recrystallization processes that include bulging (BLG, [4, 5]), subgrain rotation (SGR), and grain boundary migration (GBM, [6]) depending on temperature flow stress and strain rate. Hence, studies of shear zones lead to our understanding of how flow stress and strain rate variations account for the exhumation of the granulite at different levels of the crust. The low- to medium-grade Aravalli-Delhi mobile belt of NW India exposes several isolated exhumed mid to lower crustal rocks. The Ambaji granulite (Figure 1) is one of such exhumed crustal bodies, and it belongs to the South Delhi GeoScienceWorld Lithosphere Volume 2022, Article ID 6593243, 15 pages https://doi.org/10.2113/2022/6593243 Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/doi/10.2113/2022/6593243/5577055/6593243.pdf by guest on 27 March 2022