Dynamic recrystallization mechanism, Paleo piezometry, Strain rate, and Deformation temperature calculation of Purulia Shear Zone, Central Indian Tectonic Zone, India.

Abstract

The Central Indian Tectonic Zone (CITZ) is a prominent suture zone in Central India which formed due to the Proterozoic Collision of the North Indian and South Indian block and has a long evolutionary history spanning about 1000 Mys (2.1-0.9 Ga). The Chotanagpur Gneissic Complex (CGC) which is located in the Eastern part of CITZ , also suffered various phases of metamorphism and deformation leading to development of two prominent shear zones the South Purulia Shear Zone (SPSZ) and the North Purulia Shear Zone (NPSZ). However, these lower crustal metamorphic rocks are at surface in present day, In our study we tried to decipher how these lower crustal rocks are exhumed to the surface in present day, with the help of dynamic recrystallization mechanism, paleo piezometry and strain rate calculation along the two prominent shear zones the North Purulia Shear Zone (NPSZ) and the South Purulia Shear Zone (SPSZ).The thin section (XZ sections) were prepared subjected to microstructural analysis and Petrographical studies, further we calculated the paleo piezometry, strain rate and the deformation temperature. The Recrystallization mechanism in the SPSZ ranges from BLG-SGR transition to GBM, and the differential flow stresses for high temperature deformation varies from 8.229 to 12.078 MPa and for low temperature deformation it varies from 13.249 to 19.203 MPa. For NPSZ the Recrystallization mechanism ranges from SGR to GBM, and the differential flow stresses vary from 6.7 to 12.2Mpa for high-temperature deformation and from 13.3 to 16 MPa for low temperature deformation. The strain rate for the shear zones varies between 1.71 10E-12 and 9.46 E-14 /s, similar to the strain rates that are observed in natural shear zones. In this study we observed from our results that as we move sequentially from west to east in SPSZ the recrystallization mechanism changes from GBM in the westernmost parts, SGR-GBM transition, and SGR in the middle parts and BLG-SGR in the easternmost parts. A similar pattern is observable in the NPSZ also where the samples taken from the western part shows GBM recrystallization and the eastern parts show SGR-GBM transition and SGR recrystallization.