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

Abstract

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.

“Geochronology and geochemistry of pelitic granulite from the South Delhi Terrane of the Aravalli Delhi Mobile Belt, NW India: implications for petrogenesis and geodynamic model”

“…For this purpose, we have compared our present findings with some recent geochronological histories provided by previous workers (Bhowmik et al . 2010; Singh et al 2010, 2020; Tiwari & Biswal, 2019; Prakash et al 2021; Biswal et al 2022; Kumar et al 2022; Tiwari et al 2022). We have inferred, on the basis of our findings and geochronological interpretations that the collisional orogeny took place in the ADMB during the Grenvillian epoch (≈ca.…”

“…The Kui-Chitraseni shear zone is the extension of the Phulad Dislocation Zone (PDZ), and it stands out as an enormous fault striking NNE-SSW. It runs roughly parallel to the Banas river, and it is considered to preserve evidence of reactivation of the fault (Biswal et al 2004; Sarkar & Biswal, 2005; Anbazhagan et al 2006; Bhowmik et al 2010; Singh et al 2010, 2020; Tiwari & Biswal, 2019; Tiwari et al 2022; Biswal et al 2022). Exhumation of the granulites terrene was caused by thrusting and obduction that occurred between the terrane borders of the Surpagla and Kui-Chitraseni faults.…”

“…Kishangarh nepheline syenite intruded at 1490 ± 150 Ma, while South Delhi Terrane (SDT) granites were also intruded at 1012 ± 78 Ma (Crawford, 1970). Additionally, due to deformations that occurred millions of years ago in the Aravalli-Delhi mountain ranges, the Sandmata rocks that are found along the terrane boundary have been bent (Naha & Halyburton, 1974; Sen, 1980; Srivastava, 2001; Bhowmik et al 2010; Singh et al 2010, 2020; Roy et al 2012, 2016; Tiwari & Biswal, 2019; Biswal et al 2022; Tiwari et al 2022). Therefore, the older ages of the Mangalwar and Sandmata complexes are reset to younger ages, particularly in the northern part of the Banas shear zone (Bhowmik & Dasgupta, 2012; Ahmad & Mondal, 2016; Kumar et al 2019; D’Souza et al 2021).…”

“…Therefore, the older ages of the Mangalwar and Sandmata complexes are reset to younger ages, particularly in the northern part of the Banas shear zone (Bhowmik & Dasgupta, 2012; Ahmad & Mondal, 2016; Kumar et al 2019; D’Souza et al 2021). It is generally agreed that the collision between the Bundelkhand craton and the Marwar craton was the primary driving force behind the orogeny that resulted in the development of the ADMB (Bhowmik et al 2010; Singh et al 2010, 2020; Tiwari & Biswal, 2019; Biswal et al 2022; Tiwari et al 2022).…”

“…Pelitic granulite found in the region have a structure similar to gneiss and are composed of minerals that are organized into coarse bands of varying shades of light and dark colours having characteristic minerals such as spinel, cordierite, garnet, sillimanite, hypersthene, feldspar, quartz, biotite and plagioclase. The lighter bands are composed of quartzo-feldspathic material, while the darker bands are predominantly composed of cordierite and contain reddish brown garnets scattered/dispersed throughout (Bhowmik et al 2010; Singh et al 2010, 2020; Tiwari & Biswal 2019; Prakash et al 2021; Biswal et al 2022; Tiwari et al 2022).…”