Abstract
AbstractThe Himalayan syntaxes, characterized by extreme rates of rock exhumation co-located with major trans-orogenic rivers, figure prominently in the debate on tectonic versus erosional forcing of exhumation. Both the mechanism and timing of rapid exhumation of the Namche Barwa massif in the eastern syntaxis remain controversial. It has been argued that coupling between crustal rock advection and surface erosion initiated in the late Miocene (8–10 Ma). Recent studies, in contrast, suggest a Quaternary onset of rapid exhumation linked to a purely tectonic mechanism. We report new multisystem detrital thermochronology data from the most proximal Neogene clastic sediments downstream of Namche Barwa and use a thermo-kinematic model constrained by new and published data to explore its exhumation history. Modeling results show that exhumation accelerated to ∼4 km/m.y. at ca. 8 Ma and to ∼9 km/m.y. after ca. 2 Ma. This three-stage history reconciles apparently contradictory evidence for early and late onset of rapid exhumation and suggests efficient coupling between tectonics and erosion since the late Miocene. Quaternary acceleration of exhumation is consistent with river-profile evolution and may be linked to a Quaternary river-capture event.
Highlights
The Nanga Parbat and Namche Barwa massifs, at the respective western and eastern syntaxial terminations of the Himalaya (Fig. 1), share characteristics that have focused research into the coupling between tectonics and surface processes (Zeitler et al, 2001b; Finnegan et al, 2008; Korup et al, 2010; Koons et al, 2013; Wang et al, 2014)
We report new multisystem detrital thermochronology data from the most proximal Neogene clastic sediments downstream of Namche Barwa and use a thermo-kinematic model constrained by new and published data to explore its exhumation history
Tectonic mechanisms include range-parallel buckling in the indenterplate corner (Burg et al, 1998), uplift driven by a geometrically stiffened bend in the subducting plate (Bendick and Ehlers, 2014), and orogenparallel crustal transport arising from velocity and/or strain partitioning (Whipp et al, 2014)
Summary
The Nanga Parbat and Namche Barwa massifs, at the respective western and eastern syntaxial terminations of the Himalaya (Fig. 1), share characteristics that have focused research into the coupling between tectonics and surface processes (Zeitler et al, 2001b; Finnegan et al, 2008; Korup et al, 2010; Koons et al, 2013; Wang et al, 2014). Our best-fit inversion uses the internally consistent data set and implies a three-stage exhumation history for the Namche Barwa massif, with an early (8.2 ± 1.8 Ma) onset of rapid exhumation and a late (1.3 ± 0.8 Ma) acceleration (Fig. 3).
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