Tectonothermal evolution of the Lohit Valley, Eastern Himalaya: New low‐temperature thermochronological constraints

Abstract

The present contribution provides the first low-temperature thermochronological record from the Lohit Valley, Eastern Himalaya, presenting eight ZHe and two AHe cooling ages across the major tectonic boundaries. The ZHe cooling ages range from 6.94 ± 1.17 Ma to 12.51 ± 2.84 Ma, whereas AHe ages vary between 1.73 ± 0.15 Ma and 3.56 ± 0.42 Ma. The ZHe cooling ages suggest that the Mishmi Crystallines exposed at the southwestern mountain front are the slowest exhuming domain since ~12 Ma. The ZHe ages are youngest in the Demwe Thrust (DT) zone, and the contact between the frontal low-grade metamorphic rocks of Mishmi Crystalline and high-grade gneissic rocks of the Mayodia Group. The rapid exhumation in the DT zone as obtained from the ZHe cooling ages suggests an out-of-sequence thrusting at ~7 Ma. The QTQt thermal history modelling of the co-genetic pairs of ZHe and AHe cooling ages of the northeasternmost Lohit Plutonic Complex suggests that the exhumation rates in this region were as high as ~3.7 mm/year during the Pliocene-Quaternary. These high exhumation rates are in good correlation with the local topographic relief, hill slopes, and channel steepness, which suggests the establishment of the present-day topography of the Lohit valley region at the latest by Pliocene-Quaternary. Variation in exhumation rates does not correlate with the present-day precipitation pattern. Tectonics appears to be the prime driver for exhumation rates of the Lohit valley region of the easternmost Himalaya.

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

“…This Special Issue‐ Part 2 is a continuation of earlier Special Issue‐ Part 1 published in vol. 57 (2), of Geological Journal , which contained 26 research articles (Ao & Satyanarayanan, 2022; Baral et al, 2022; Bhowmik et al, 2022; Bora, Borah, et al, 2022; Bora, Mukherjee, et al, 2022; Deb & Ray, 2022; Devi & Singh, 2022; Devrani et al, 2022; Doley et al, 2022; Gogoi et al, 2022; Gupta et al, 2022; Hazarika & Kayal, 2021; Imtisunep et al, 2022; Liu et al, 2022; Luirei et al, 2022; Lukram & Tandon, 2022; Bidyananda et al, 2022; Majumdar, Gogoi, & Ghatak, 2022; Majumdar, Gogoi, Ghatak, Saikia, et al, 2022; Mukherjee et al, 2022; Pebam et al, 2021; Rashid et al, 2022; Saikia et al, 2022; Singh and Kshetrimayum, 2021; Singh, Guruaribam, Singh et al, 2022; Singh, Singh, Singh, et al, 2022; Srivastava, 2021; Srivastava & Kichu, 2021). Figure 2 displays the area of study of 29 papers included in this Special Issue 2.…”

“…This Special Issue-Part 2 is a continuation of earlier Special Issue-Part 1 published in vol. 57 (2), of Geological Journal, which contained 26 research articles (Ao & Satyanarayanan, 2022;Baral et al, 2022;Bhowmik et al, 2022;Bora, Mukherjee, et al, 2022;Deb & Ray, 2022;Devrani et al, 2022;Doley et al, 2022;Gogoi et al, 2022;Gupta et al, 2022;Hazarika & Kayal, 2021;Imtisunep et al, 2022;Liu et al, 2022;Luirei et al, 2022;Lukram & Tandon, 2022;Bidyananda et al, 2022;Majumdar, Gogoi, Ghatak, Saikia, et al, 2022;Mukherjee et al, 2022;Pebam et al, 2021;Rashid et al, 2022;Saikia et al, 2022;Singh and Kshetrimayum, 2021; F I G U R E 1 (a) Tectonic map of the peri-Indian region, showing the current plate boundaries and plate distributions, major continental blocks, suture zones, and salient fault systems. (b) Simplified regional geologic map of the Himalayan Orogen, Indo-Myanmar orogenic belt and adjoining areas (modified after Mitchell et al, 2007;Singh, 2013;Yin, 2006) Singh Srivastava, 2021;Srivastava & Kichu, 2021).…”