Exhumation and its Mechanisms: A Review of Exhumation Studies in the Himalaya

Abstract

Exhumation has been recognised as a key factor in understanding the dynamics of a mountain belt. Normal faulting, erosion and ductile thinning are the three basic mechanisms to exhume the deeper high grade metamorphic rocks to the surface. Convergent orogenic belts are characterised by over-thickening of the crust due to thrusting and folding. The interplay of uplift due to over-thickening of crust and climatic-erosion is the most plausible mechanism of exhumation as suggested by the numerical models and analogue experiments. The analysis of 534 thermo-chronological dates through 1D-thermal numerical model in the Himalaya suggest that the exhumation is dominantly due to erosion but the pattern of erosion is controlled by local tectonic activities in different sector of the Himalaya since Miocene, indicating that tectonic force as the prime mechanism of exhumation in Himalaya.

Erosion rates of the Bhutanese Himalaya determined using in situ-produced 10Be

“…Apatite fission track exhumation rates in western Bhutan (1.4 mm yr −1 since 2.5 Ma) are higher than those in eastern Bhutan (0.7 mm yr −1 since 5.1 Ma), and may reflect a difference resulting from the uplift of the Shillong Plateau in northern India ( Fig. 1A; Grujic et al, 2006;Biswas et al, 2007;Adlakha et al, 2013a;Coutand et al, 2014). The Shillong Plateau creates an orographic rain shadow along the front ranges in eastern Bhutan (Fig.…”

“…1B inset), which may (Grujic et al, 2006;Biswas et al, 2007) or may not (Adlakha et al, 2013b;Coutand et al, 2014) have caused decreased erosion rates and thus decreased erosion-driven exhumation rates. In contrast, greater precipitation along the western Bhutanese front ranges may facilitate higher exhumation rates and oversteepened slopes in the Puna Tsang Chhu region (Duncan et al, 2003;Grujic et al, 2006;Adlakha et al, 2013a). The far northern reaches of the Puna Tsang Chhu basin are glaciated and fed by the summer monsoonal precipitation with evidence for numerous glacial advanceretreat cycles since the Pleistocene (Iwata et al, 2002;Meyer et al, 2009).…”

Mio-Pliocene Tectonics and Exhumation Histories of the NW– and NE–Himalaya

“…Two most recent reviews by Adlakha et al (2013a) and Thiede and Ehlers (2013) have observed large spatial and temporal variations in the Himalayan exhumation. Adlakha et al (2013a) have correlated the surface structures with the thermochronological ages and suggested that local tectonics of the area is the main factor controlling the exhumation.…”

“…Two most recent reviews by Adlakha et al (2013a) and Thiede and Ehlers (2013) have observed large spatial and temporal variations in the Himalayan exhumation. Adlakha et al (2013a) have correlated the surface structures with the thermochronological ages and suggested that local tectonics of the area is the main factor controlling the exhumation. Thiede and Ehlers (2013) remained focus over the temporal variations in exhumations and differentiated the patterns of denudations along the frontal ranges and northern higher elevation ranges over different span of time.…”

First geomorphological and sedimentological evidence for the combined tectonic and climate control on Quaternary Yarlung river diversion in the eastern Himalaya

“…Considering the fact that the eastern Himalaya has experienced >5-10 km of crustal denudation since ca. 15 Ma (Grujic et al, 2006;Yin et al, 2010;Adlakha et al, 2013;McQuarrie and Ehlers, 2015;Adams et al, 2015), the morphologic and related sedimentological records of the inferred river (i.e., a linked longitudinal-transverse river flowing over the Himalayan crest) must have been erased. To resolve this issue we investigated the Quaternary geomorphologic and sedimentologic evolution of a Quaternary valley-fill sequence across a segment of the Yarlung-Subansiri divide in the eastern Himalaya (Fig.…”