Late Neogene tectonically driven crustal exhumation of the Sikkim Himalaya: Insights from inversion of multithermochronologic data

Abstract

Apatite fission track and zircon (U‐Th)/He data are reported for 34 bedrock samples distributed between the foothills and the topographic crest of the Darjeeling‐Sikkim Himalaya. The pattern of observed cooling ages does not correlate with topography, rainfall distribution, and the deeply incised high‐relief Tista window, indicating that tectonic processes are mainly responsible for their spatial distribution. Inversion of this thermochronometric data set using 3‐D thermokinematic modeling constrained by independent geological and geophysical observations was performed to evaluate the contribution of slip partitioning, duplex development, and relief growth on the evolution of the thermal structure of the Himalaya during the last 12 Ma. Models involving significant relief growth do not show a substantial influence of topography evolution on the cooling age distribution, while models involving duplex growth demonstrate that tectonic processes exert a dominant influence on their distribution. In concert with equivalent studies in Bhutan, central Nepal, and NW India, our results attest that the lateral variation of the geometry and kinematics of the Himalayan basal décollement locally associated with duplex formation exert a leading influence on lateral variations of middle to upper crustal long‐term exhumation rates documented along the strike of the Himalaya.

The underthrusting Indian crust and its role in collision dynamics of the Eastern Himalaya in Bhutan: Insights from receiver function imaging

“…For western Bhutan, such a tectonic interpretation would be consistent with our results for the MHT beneath the Higher Himalaya and provides a comprehensive explanation in combination with long-term exhumation rates derived by Coutand et al [2014]. Nevertheless, to sustain the overall long-term growth of the Himalaya orogenic wedge for at least the last 11 Myr, including the Landry et al, 2016], imbrication of material from the underthrusting Indian crust is needed [Bollinger et al, 2006;Herman et al, 2010;Landry et al, 2016].…”

“…For western Bhutan, such a tectonic interpretation would be consistent with our results for the MHT beneath the Higher Himalaya and provides a comprehensive explanation in combination with long‐term exhumation rates derived by Coutand et al []. Nevertheless, to sustain the overall long‐term growth of the Himalaya orogenic wedge for at least the last 11 Myr, including the development of duplex structures in the Lesser Himalaya and formation of tectonic windows, like the Tista‐Rangit window in Sikkim, Paro window in western, and Kuru Chu half‐window in eastern Bhutan [ Coutand et al , ; Landry et al , ], imbrication of material from the underthrusting Indian crust is needed [ Bollinger et al , ; Herman et al , ; Landry et al , ].…”

The Influence of Foreland Structures on Hinterland Cooling: Evaluating the Drivers of Exhumation in the Eastern Bhutan Himalaya

“…This link between foreland structures and hinterland ramps can be exploited to create a series of testable cross-section geometries ( Figure 6) that all match the geology at the surface but provide different subsurface geometries and thus different uplift histories. In particular, active uplift in the hinterland of the Himalayan fold-thrust belt has been proposed to be a function of an active duplex (Adams et al, 2013(Adams et al, , 2016Landry et al, 2016;Webb et al, 2011Webb et al, , 2013, out-of-sequence thrusting (Adlakha et al, 2013;Wobus et al, 2003Wobus et al, , 2006, and an active ramp in the décollement (Bollinger et al, 2006;Gilmore et al, 2018;Herman et al, 2010;Long et al, 2012;Robert et al, 2011). These different driving mechanisms predict different uplift, exhumation, and topographic evolutions, which can be directly compared to measured thermochronometers and modern topography.…”

“…These tectonic and climatic factors also control the record of rock exhumation in an orogen (e.g., Ehlers & Farley, 2003;Huerta & Rodgers, 2006;Rahn & Grasemann, 1999;Shi & Wang, 1987;Willett & Brandon, 2002). Attempts to understand how climate and tectonics interact to propel exhumation, as well as differing opinions as to which is the dominant driver of exhumation, have spurred multiple debates, particularly in the eastern Himalaya (Adams et al, 2015;Adlakha et al, 2013;Coutand et al, 2014;Duncan et al, 2003;Gilmore et al, 2018;Grujic et al, 2006;Landry et al, 2016;Long et al, 2012;McQuarrie et al, 2014;McQuarrie & Ehlers, 2015). The range of different hypotheses presented to explain the exhumation history of the eastern Himalaya, as well as the diverse methods of quantifying this history, has led to a suite of related questions.…”

Along‐strike variations in the Himalayan orogenic wedge structure in Bhutan from ambient seismic noise tomography

“…The expression of these variations is clearly seen in the surface relief [ Bookhagen and Burbank , ], gravity anomalies [ Berthet et al ., ; Hammer et al ., ; Hetényi et al ., ], foreland basin depth [ Burbank et al ., ], and sampled by several seismological experiments [e.g., Rai et al ., ; Monsalve et al ., ; Guo et al ., ; Huang et al ., ; Nabelek et al ., ; Caldwell et al ., ]. Deviations from cylindrical structure are also indicated in the upper crust by tectonic klippen and windows, like the pronounced Tista‐Rangit double‐window in Sikkim [e.g., Landry et al ., ] or the crystalline Kathmandu klippe in Central Nepal [ Stöcklin , ].…”