T96 Approaches for Extracting Shear Zone History from the Ductile Rock Record: Probing Their Initiation, Evolution, and Reactivation II

Tuesday, 27 October 2020
5:30 PM - 8:00 PM
Meeting Rooms

STRAIN PARTITIONING WITHIN THRUST SHEETS: INSIGHTS FROM FAR-EASTERN SIANG WINDOW, ARUNACHAL HIMALAYAN FOLD THRUST BELT

Paper number: T96-10
Program: Technical Sessions
Time: 6:55 PM – 7:05 PM

Authors

  • Jyoti Prasad Das Presenting Author
    Indian Institute of Science Education Research Kolkata (IISERK), Mohanpur
  • Kathakali Bhattacharyya
    Indian Institute of Science Education Research (IISER) Kolkata, Mohanpur, West Bengal

Abstract

In a fold thrust belt (FTB), penetrative strain within thrust sheets vary in its magnitude, orientation and type. Addressing variation in magnitude and orientation of strain from major thrust sheets in an FTB, both along the transport direction and along-strike, enable us to understand the complexity of strain partitioning during orogeny. Tectonic windows provide an opportunity to understand the impact of footwall structures on finite strain geometry and orientations. In this study, we investigate how penetrative strain is partitioned from the internal to the external major thrust sheets in the Siang window in far-eastern Arunachal Himalayan FTB.

We conduct finite strain analysis on quartz grains using Rf-Φ, normalized Fry and Shape Matrix Eigenvector methods. The studied lithologies are gneiss for the internal Pelling-Munsiari thrust (PT) sheet, while quartzite and sandstone dominantly comprise the external Main Boundary thrust (MBT) and the Main Frontal thrust (MFT) sheets. The northernmost Main Central thrust (MCT) of the Himalayan FTB lies farther north of the study area and is not accessible. Results from this study indicate that all the studied rocks record an overall flattening strain. Magnitude of the finite penetrative strain decreases from the internal PT sheet to the external MBT, MFT sheets in the Siang window. The long axes of the finite strain ellipsoids (X) generally have a low plunge and a dominant bearing of N-S, irrespective of the structural positions of the different thrust sheets. Finite strain ellipses are folded along with the thrust sheets indicating that the penetrative strain developed prior to folding of the thrust sheets. The results also indicate that the footwall structures affect the strain geometry in the interior part of the Himalayan wedge. Preliminary results indicate modification of early layer parallel shortening strain in both internal and external thrust sheets in the Siang window.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-357064

© Copyright 2020 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.