[S-MP25] Deformed rocks, Metamorphic rocks and Tectonics

[SMP25-P03] Kinematics of North Almora Thrust estimated from mylonite, India

*Hirotoshi Kotama¹, Jun-ichi Ando¹, Kaushik Das¹, Dyuti Prakash Sarkar¹ (1.Hiroshima University)

Keywords:c-axis fabric, phyllosilicate minerals, mylonite

The purpose of this study is to clarify the faulting process of the North Almora Thrust (NAT) which belongs to a fault system of the Main Central Thrust, based on the characteristics of rock deformation microstructures. The study area lies in the north of Almora, Uttarakhand, India. The results obtained from the field study demonstrate that the granite and sandstone are mylonitized within ca. 7 km south of NAT. The mylonitization tends to change from "proto-mylonite" to "mylonite" closer to NAT, eventually to "ultramylonite". The strikes of these mylonite foliations are almost parallel to that of the NAT. The microstructures of mylonites are studied using an optical microscope, SEM, and SEM-EBSD. These methods combined with image analysis using ImageJ are used to measure the aspect ratio and grain size of dynamically recrystallized quartz. Similar measurements are also conducted using the orientation maps revealed by the SEM-EBSD analyses. The above microstructural observations helped us to determine 1) temperature, shear sense, three-dimensional strain field, and flow stress under which mylonitization occurred, and 2) the effect of phyllosilicate minerals on NAT faulting. In this presentation we shall report the faulting process of the NAT based on the above results.