http://localhost:8081/jspui/handle/123456789/6 Mon, 14 Sep 2026 14:39:35 GMT 2026-09-14T14:39:35Z http://localhost:8081/jspui/handle/123456789/21407 Title: Dynamic recrystallization mechanism, Paleo piezometry, Strain rate, and Deformation temperature calculation of Purulia Shear Zone, Central Indian Tectonic Zone, India. Authors: Singh, Sourav 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. Mon, 01 May 2023 00:00:00 GMT http://localhost:8081/jspui/handle/123456789/21407 2023-05-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/21406 Title: Paleoenvironmental reconstruction using ichnological analysis of the Barren Measures Formation from the uppermost section of Chutua Nala, West Bokaro Basin, Jharkhand, India Authors: Sarkar, Suvarpan Abstract: Middle Permian Barren Measures Formation exposed in Chutua Nala, Northern part of West Bokaro Basin hosts sparse to densely bioturbated lithounits. The study area comprises of diverse primary sedimentary structures such as flaser, lenticular bedding, mud draped forests, herringbone cross stratification, bidirectionality of ripples which indicate an overall tidal influence. 3 sedimentary facies namely Lenticular Red Sandstone(F2), Carbonaceous Shale(F1) and Heterolith(F3) was observed. Ichnodensity as well as diversity is high in the region and 14 different ichnotaxa were identified; namely Bergaueria, Conichnus, Cylindrichnus, Diplocraterion, Macaronichnus, Ophiomorpha, Paleophycus, Planolites, Rhizocorallium, Skolithos, Taeinidium, Teichichnus, Thalassinoides and Zoophycos along with some Bivalve Resting traces, Fugichnia. These trace fossils represent the dwelling and feeding burrows of deposit as well as suspension feeders. These ichnotaxa mostly represent marine habitat (Teichichnus, Zoophycos,Cylindrichnus,Rhizocorallium) and are seen to occur periodically in the muddy substrate, therefore indicating several episodic pulses of marine incursions in the tide dominated setting. Further ichnofabric analysis was done and the section was classified under 5 ichnofabrics namely Thalassinoides Rhizocorallium (IF-1), Ophiomorpha-Planolites (IF-2), Skolithos-Macaronichnus (IF 3), Teichichnus (IF-4) and Ophiomorpha-Paleophycus (IF-5). IF-1 ichnofabric indicates deposit feeder dominance and low rate of sedimentation. IF-3 ichnofabric indicates a high energy phase associated with high rate of sedimentation, as observed from vertical burrow of Macaronichnus cutting across the foreset of sand. IF-5 ichnofabric dominantly indicates suspension feeding activity in the topmost part of the succession in a stressed environment. IF-4 ichnofabric symbolises the calm and low energy environment suitable for deposit feeders to dwell in muddy substrates experiencing variation of salinity, oxygen etc. IF-2 ichnofabric indicates assemblage of both suspension and deposit feeder. The study of the ichnofabric revealed how the nature of the substrate and feeding habits of the organism changed throughout the succession giving an idea of the sediment-organism relationship, oxygenation patterns and hydrodynamic energy fluctuation. Combining the sedimentological and ichnological aspects, it can be justified that the study area is a fluvio-marine transitional environment with high signatures of tidal activity as evident from the ichnofabric, ichnotaxa and sedimentological studies. Mon, 01 May 2023 00:00:00 GMT http://localhost:8081/jspui/handle/123456789/21406 2023-05-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/21405 Title: Study of fold and thrust belt deformation of Almora nappe using field observations, microstructural studies and strain analysis Authors: M, Vaisakhi Abstract: The Almora Crystalline Zone (ACZ) is one of the Lesser Himalaya's largest thrust nappes. The ACZ has a unique boat-shaped synclinal structure, which is a concave-up fold shaped like a trough or a boat. The ACZ syncline is bounded on its northern side by the North Almora Thrust (NAT), and on its southern side by the South Almora Thrust (SAT). Despite being a repository of tectonic deformation spanning from the Precambrian to the present, the Almora Crystalline Zone (ACZ) has received little attention. Therefore, this study aims to fill this gap by conducting a thorough investigation of the fold and thrust induced structural deformation in ACZ. This is done through a combination of field observations, microstructural studies, and 2D strain analysis. The study seeks to provide a detailed description of the structural features of ACZ and improve the understanding of the tectonic evolution of the region. Four distinct types of folds and a faults having NE thrusting have been identified from field study along Patiya river section. F1 folds are gently plunging isoclinal folds with recumbent geometry and dipping towards east. The F1 fold and S1 foliations are refolded by F2 folds having similar geometry. The F1 folds are rotated in Sirar village and the axial plane here is dipping due north. The axial plane of the F3 folds is dipping in NNE direction and plunging towards NNE direction having sub-vertical axial planes. The F4 folds are open type and are dipping towards the south. Thin section analysis of samples of cataclastic rocks taken from Sirar and Sunderpur revels static recrystallization with BLG and SGR recrystallization. The deformation temperature is calculated to be within 390-490°C from both recrystallized grain size data as well as from microstructural analysis. The value of 2D strain analysis on cataclastic samples varies within the range of 1.41-1.56 at both sites. The stress experienced in the area acted in an NNE-SSW direction. This study provides valuable insights into the deformation history of the ACZ, which may have broader implications for understanding the tectonic evolution of the Lesser Himalayas as well as MCT in general. Mon, 01 May 2023 00:00:00 GMT http://localhost:8081/jspui/handle/123456789/21405 2023-05-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/21404 Title: Evolution of magnetic fabric across the Main Central Thrust Zone (MCTZ), Garhwal Himalayas Authors: Roy, Writabrata Abstract: he collisional tectonic setting between the Eurasian and the Indian plate has created the most discussed orogeny called the Himalaya. The Himalayan orogen is one of the most complex and crucial tectonic settings that has maintained to grab much attention for the last few decades. It consists of several thrust bounded tectonic litho-units which have been in collocation since the onset of collision ~ 54 Ma (Yin et al. 2006; Hu et al. 2016; Dutta and Mukherjee 2021) There are many studies that depicts the time of formation, duration, Pressure-Temperature-time (PTt) condition that delineates the movement of Main Central Thrust zone (MCTz) all along the Himalayan Front (Roberts et al.,2020) and also about the exhumation of the crystallines of Higher Himalayan. Here, we majorly focus on the major tectonic unit called “The Main Central Thrust”. The Main Central Thrust is a 2400 km long crustal shear zone which directs how the Himalayan-Tibetan orogeny develops (Heim and Gansser, 1939). High-grade Proterozoic Cambrian rocks of the Greater Himalayan Series are deposited in the form of deep crustal slice by the Main Central Thrust above low-grade Proterozoic rocks of the Lesser Himalayan Sequence (Hodges, 2000; Hunter et al., 2018 Yin and Harrison, 2000). In the Eastern Garhwal Himalaya's Alaknanda Valley, close to the towns of Helang, Joshimath, and Tapoban, the Main Central Thrust manifests itself. The Alaknanda and Dhauliganga River valleys, which typically cut the rocks perpendicular to their strike, provide good exposure of the stratigraphy in this area (Jain et al., 2014). Therefore, the Alaknanda-Dhauliganga valley is chosen to study deformation pattern across the MCT. This study aims to integrate field investigation, microstructural characterization, evaluation of deformation temperature, variation in the rate of stress and strain of basement rocks which will help in inter-relationship between the thrust tectonics, superposed deformation in the basement rocks and to comment on the rapid exhumation of the Himalayan Foreland. Mon, 01 May 2023 00:00:00 GMT http://localhost:8081/jspui/handle/123456789/21404 2023-05-01T00:00:00Z