Crustal reworking at Nanga Parbat, Pakistan: Metamorphic consequences of thermal‐mechanical coupling facilitated by erosion

Abstract

Abstract. Within the syntaxial bends of the India-Asia collision the Himalaya terminate abruptly in a pair of metamorphic massifs. Nanga Parbat in the west and Namche Barwa in the east are actively deforming antiformal domes which expose Quaternary metamorphic rocks and granites. The massifs are transected by major Himalayan rivers (Indus and Tsangpo) and are loci of deep and rapid exhumation. On the basis of velocity and attenuation tomography and microseismic, magnetotelluric, geochronological, petrological, structural, and geomorphic data we have collected at Nanga Parbat we propose a model in which this intense metamorphic and structural reworking of crustal lithosphere is a consequence of strain focusing caused by significant erosion within deep gorges cut by the Indus and Tsangpo as these rivers turn sharply toward the foreland and exit their host syntaxes. The localization of this phenomenon at the terminations of the Himalayan arc owes its origin to both regional and local feedbacks between erosion and tectonics.

Intense localized rock uplift and erosion in the St Elias orogen of Alaska

“…Our data provide direct evidence that exhumation varies considerably along strike in the St Elias orogen, with locally greater degrees of exhumation occurring at rates comparable to those seen in the highly active Himalayan syntaxes 12 or along the Alpine fault in New Zealand 25 . The upper Seward Glacier region may represent a 'tectonic aneurysm' analogous to features described in the eastern and western Himalayan syntaxes 11,12 but heretofore not identified outside the terminations of the Himalayan chain (further discussed in Supplementary Information). In the aneurysm model, coupling occurs between localized crustal strain and focused erosion, with significant amounts of erosion leading to heat advection and weakening of the crust, localization and intensification of strain, and building of high relief, thus feeding back into continued rapid erosion.…”

“…10). Similar to other active orogenic belts with high erosion rates, the St Elias range seems to have developed localized feedback between erosion and crustal strain [11][12][13] . Thus, it is puzzling that no evidence has emerged for locally enhanced exhumation and erosion in the form of localized young, higher-temperature cooling ages.…”

Paleo-erosion rates in Central Asia since 9Ma: A transient increase at the onset of Quaternary glaciations?

“…The ensuing redistribution of mass influences isostatic compensation in a way that induces tectonic deformation (Dahlen and Suppe, 1988;Whipple and Meade, 2006;Willett and Brandon, 2002). The resulting vertical movement of mass affects the thermal structure of the crust and hence its rheology (Avouac and Burov, 1996;Zeitler et al, 2001). Second, erosion is considered as a first order driving mechanism of Earth climate at the geological time scales because of its potential impact on atmospheric CO 2 through the creation of new surface enabling silicate weathering (Berner et al, 1983) but also because of its influence on the mechanical burial of organic carbon (Galy et al, 2007).…”

Three‐dimensional numerical models with varied material properties and erosion rates: Implications for the mechanics and kinematics of compressive wedges

“…This has been demonstrated using numerical [Avouac and Burov, 1996;Willett, 1999;Koons et al, 2002Koons et al, , 2003] and analog [Hoth et al, 2006] modeling, as well as through a number of field studies, particularly those utilizing fission track and other geochronologic methods [Zeitler et al, 2001;Thiede et al, 2004Thiede et al, , 2005Grujic et al, 2006;Berger and Spotila, 2008;. Despite recognition of the importance of coupling between tectonic and surfical processes, surprisingly little direct data exists for assessing exactly how an orogen responds to transient changes in boundary conditions, such as a change in the erosion rate.…”