Brittle tectonics in the western Arunachal Himalayan frontal fold belt, northeast India: Change in stress regime from pre‐collisional extension to collisional compression

Abstract

The study of brittle deformation of the collisional mountains can explain its shallow crustal tectonic evolution and the palaeostress regime. The Main Boundary Thrust (MBT) zone in the western Arunachal Himalaya displays imbrication in the Permian Gondwana sequence between the MBT‐1 (/Bome Thrust/MBT‐Upper) in the north and MBT‐2 (/MBT‐Lower) in the south with consistent northerly dip. The Lower Gondwana rocks occur in the footwall of the MBT‐1 with the Proterozoic Bomdila Group in the hangingwall. The upper Gondwana rocks constitute the hangingwall sequence for the MBT‐2 with Neogene Siwalik rocks in the footwall. This article analyses palaeostress using brittle fractures in the Gondwana rocks that crop out for ~120 km2 in the study area. The fault‐bounded imbricate zone depicts eight brittle shear indicators and four sets of joints (J1 and J2: inclined and J3 and J4: subvertical). The signatures of the inherited pre‐Himalayan extensional deformation are preserved in the Lower Gondwana Miri Formation. The Bichom and Bhareli rocks exhibit brittle deformation features of the Himalayan Orogeny under strong ~N‐S compression. The palaeostress analysis of all joint sets indicates three phases of brittle deformation in the Gondwana and Siwalik rocks of the area. The subvertical joint sets and normal faults in the Miri Formation indicate a north‐northwest (NNW)‐directed extensional phase of the pre‐Himalayan origin. The inclined joint sets of the Bichom and Bhareli formations of the Gondwana sequence depict Himalayan orogeny with ~N‐S compressional phases. The third phase of brittle deformation in the Siwalik sequence depicts an east‐west (~E‐W) extension. The arc‐parallel extension in the frontal fold belt of the Arunachal Himalaya may be due to oblique India‐Asia collisional tectonics.

Introduction, Part 2—Geodynamic evolution of Eastern Himalaya and Indo‐Myanmar orogenic belts: Advances through interdisciplinary studies

“…Goswami, Gogoi, et al (2022) have documented outcrop mapping, and study of brittle structures and palaeostress regime from the Pinjoli‐Sessa‐Nichiphu‐Kimi‐Bhalukpong area of western Arunachal Himalaya based on joints and faults. They considered that the MBT zone in the western Arunachal Himalaya displays imbrication in the Permian Gondwana sequence between the MBT‐1 (/Bome Thrust/MBT‐Upper) in the north and MBT‐2 (/MBT‐Lower) in the south with consistent northerly dip.…”

“…Geological map of Eastern Himalaya, Indo‐Myanmar orogenic belt, northern, Central Myanmar, and adjacent areas (modified after Mitchell et al, 2007; Searle et al, 2007; Y. R. Singh, Singh, Singh, et al, 2022). Locations of study area presented in the issue include 1/S2: Kundu and Hazarika (2022); 2/S2: Y. R. Singh, Singh, Singh, et al (2022); 3/S2: Rawat and Luirei (2022); 4/S2: Kayal et al (2022); 5/S2: Choudhury et al (2022); 6/S2: N. M. Sharma et al (2022); 7/S2: Goswami, Gogoi, et al (2022); 8/S2: Bikramaditya et al (2022); 9/S2: Goswami, Kalita, et al (2022); 10/S2: Joshi (2022); 11/S2: Jha and Sharma (2022); 12/S2: Shukla et al (2022); 13/S2: Khonglah et al (2022); 14/S2: Ali and Duarah (2022); 15/S2: Mohanty et al (2022); 16/S2: Chanu et al (2022); 17/S2: Majumdar, Gogoi, and Ghatak (2022); Majumdar, Gogoi, Ghatak, Saikia, et al (2022); 18/S2: Ding et al (2022); 19/S2: Ghose et al (2022); 20/S2: Hussain and Dey (2022); 21/S2: Ozukum et al (2022); 22/S2: Jamir et al (2022); 23/S2: Chaubey et al (2022); 24/S2: Bora, Borah, et al (2022); Bora, Mukherjee, et al (2022); 25/S2: Khuman and Ibotombi (2022); 26/S2: Y. R. Singh, Singh, Singh, et al (2022); 27/S2: Thokchom and Kshetrimayum (2021); 28/S2: Barman et al (2022); 29/S2: V. Sharma and Biswas (2022)…”

Geochemistry and U–Pb zircon geochronology of the Jutogh Thrust sheet, Himachal Pradesh, NW‐Himalaya: Implications to the petrogenesis and regional tectonic setting

“…The Lesser Himalayan crystallines (LHC) either occur as a synformal klippe over the LHS zone or as a roughly continuous thrust sheet in the footwall of the Vaikrita Thrust (VT) (Mukherjee, 2013; Singh, 2014; Singh et al, 2012). These LHC may be broadly extended along the entire length of the Himalaya, in the footwall of the Main Central Thrust/Vaikrita Thrust (MCT/VT) known as Salkhala in Kashmir, Chamba‐Pandoh‐Kullu‐Jutogh in Himachal Pradesh, Lansdown‐Almora‐Baijnath in Kumaun‐Garhwal region, Dudalhera‐Kathmandu allochthon in Nepal, Daling in Sikkim, Shumar in Bhutan, and Bomdila in Arunachal Himalaya (Bhargava et al, 1991, 2016, 2021; Bhargava & Bassi, 1994; Bhargava & Srikantia, 2014; Bhattacharyya et al, 2015; Bikramaditya Singh et al, 2017; Goswami et al, 2022; Patel et al, 2015; Singh & Patel, 2017, 2022; Srikantia & Bhargava, 1988; Warren et al, 2014 and references therein).…”