Tectonics of the Himalayas

Abstract

The Himalayan range was formed and uplifted in association with the southward migration of plate boundary thrusts that separate the Himalaya into four belts. Initially, during -Ma, the Tibetan marginal mountain range was uplifted after slab break-off of the Tethyan oceanic plate, which was subducted under the Asian continent to depths of up to km. During the second stage at ~ -Ma, the Mesoproterozoic sediments deposited on the northern passive margin of the Greater India were subducted and underwent moderate-pressure metamorphism at depths of ~ km. Subsequent to metamorphism, metamorphosed continental crust was separated from the underlying mantle by delamination, and its rapid exhumation and associated amphibolite facies metamorphism occurred during -Ma. Partially melted metamorphic rocks generated granitic melt that intruded both metamorphic rocks and Tibetan Tethys sediments during the Miocene. Exhumation of the metamorphic belt continued after its exposure at ~ Ma, forming an extensive metamorphic nappe covering the Lesser Himalayan sediments. After ceasing movement at -Ma, the Indian plate started to subduct along the Main Boundary Thrust (MBT), which was newly formed in front of the southern margin of the metamorphic nappe. At the same time, the nappe and weakly metamorphosed underlying Lesser Himalayan sediments started to cool laterally from the southern front to the root zone at a rate of ~ km/Myr. At -. Ma, the plate boundary fault shifted to the Main Frontal Thrust (MFT) to the south of the MBT, causing rapid uplift of the marginal range of the Lesser Himalaya and the Siwalik Hills. Today, the Indian Plate is converging with the Asian Continent at the rate of mm/yr, and half of this convergence is consumed by uplift of the Siwalik Hills along the MFT.

Denudation Process of Crystalline Nappes in a Continental Collision Zone Constrained by Inversion of Fission‐Track Data and Thermokinematic Forward Modeling: An Example From Eastern Nepalese Himalaya

“…A total of 17 rock samples were collected from the HHC nappe and the LHS in eastern Nepal (Figures 5a and 5b, and Table 1) for FT dating of zircon and apatite. Three additional rock samples (EN02, EN03, EN08) collected by previous studies (Sakai, Iwano, Danhara, Takigami, et al., 2013; Sakai et al., 2017) and FT data from them were also used in this study (Table 5). For these samples, we incorporated new FT length data for thermochronological inverse analysis.…”

“…(2013), and Sakai et al. (2017). Sample localities of these dated samples are projected perpendicularly onto the N5°E line.…”

“…Figure 5c summarizes the across‐strike distribution of newly‐obtained and published ZFT, AFT, and 40 Ar/ 39 Ar mica ages (Imayama et al., 2012; Larson et al., 2017; Sakai, Iwano, Danhara, Hirata, et al., 2013; Sakai et al., 2017). Samples collected from the frontmost part of the HHC nappe and the LHS yielded the ZFT age of ca.…”

“…Sample locations are also projected on the cross-section. (c) The across-strike distribution of the zircon fission track and apatite fission track ages from this study, Larson et al (2017), and Sakai et al (2017. Sample localities of these dated samples are projected perpendicularly onto the N5°E line.…”

“…Sample locations for the FT age dating (circles) and thermochronological inverse analyses (EN01-08: pins) are shown in the map. Locations of samples reported by previous studies(Larson et al, 2017;Sakai et al, 2017; are also shown. The geologic map was modified after Sakai, Iwano,,Schelling andArita (1991), andMahato (2011).…”