Research Article Understanding the Deformation Structures and Tectonics of the Active Orogenic Fold-Thrust Belt: Insights from the Outer Indo-Burman Ranges Md. Sakawat Hossain , 1,2,3 Songjian Ao , 2,3,4 Tridib Kumar Mondal , 5 Arnab Sain , 6 Md. Sharif Hossain Khan , 1 Wenjiao Xiao , 3,4,7 and Pengpeng Zhang 2,3 1 Department of Geological Sciences, Jahangirnagar University, Dhaka 1342, Bangladesh 2 State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China 3 Innovation Academy for Earth Science, CAS, China 4 China-Pakistan Joint Research Center on Earth Sciences, Chinese Academy of Sciences, Chengdu, China 5 Geological Studies Unit, Indian Statistical Institute, Kolkata 700108, India 6 Department of Geology, Presidency University, Kolkata 700073, India 7 Xinjiang Research Center for Mineral Resources, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China Correspondence should be addressed to Songjian Ao; asj@mail.iggcas.ac.cn Received 20 November 2021; Accepted 18 March 2022; Published 18 April 2022 Academic Editor: Feng Cheng Copyright © 2022 Md. Sakawat Hossain et al. Exclusive Licensee GeoScienceWorld. Distributed under a Creative Commons Attribution License (CC BY 4.0). The tectonic deformation of the outer Indo-Burman Ranges (i.e., Chittagong Tripura Fold Belt, CTFB) is associated with the oblique convergence of Indo-Burmese plates since the latest Miocene. This article presents detailed field evidence of deformation structures and their kinematics in the exposed Tertiary successions in the CTFB. We combine observations made in this study with the published structural, geodetic, and seismic data sets to present an overview of the active tectonic framework of the region and its strain partitioning. To determine the kinematic evolution, décollement depth, and amount of strain, we combined geologic field mapping, structural analysis of fifteen anticlines, fracture/lineament analysis, and paleostress analysis of faults that define the ∼100 km wide CTFB. Structural data and kinematic analyses suggest subhorizontal plane strain with approximately 10% east-west shortening (oriented ~65 ° ) that is perpendicular to the axial plane (oriented ~155 ° ) of the CTFB anticlines. No evidence of significant transpression or strike-slip faulting has been observed in the CTFB and, therefore, suggests that full slip-partitioning is normal to the outer belt and parallel to the inner belt of the IBR. Paleostress analysis results are in good agreement with the present-day stress regime, and this implies that past and present deformation is dynamically related with the normal component of India-Burma oblique vector velocity motion. 1. Introduction Understanding the structural evolution of the outer Indo- Burman Rages (IBR) is crucial to reconstructing the Ceno- zoic geodynamics of the Bengal Basin and the complex development of collisional events between the Indian and Burmese plates [1]. The plate boundary region between the India and Burma plates in the outer IBR region consists of fold belts, and regional scale thrust (Figure 1) is a prominent earthquake-prone area, where deformation and kinematics are governed by oblique subduction of the Indian Plate beneath the Burma plate [1–6]. This oblique convergence- related transpressional tectonics in orogenic belts is a com- mon phenomenon giving rise to complex deformation pat- terns (e.g., [7–11]). Transpressional deformation involves both strike-slip and dip-slip components. However, the strike-slip deformations can deviate from simple shear when shortening oblique to the deformation zone [10]. At the GeoScienceWorld Lithosphere Volume 2022, Article ID 6058346, 23 pages https://doi.org/10.2113/2022/6058346 Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/doi/10.2113/2022/6058346/5587560/6058346.pdf by guest on 18 June 2024