Abstract

Whether variations in the spatial distribution of erosion influence the location, style, and magnitude of deformation within the Himalayan orogen is a matter of debate. We report new 40Ar/39Ar white mica and apatite fission-track (AFT) ages that measure the vertical component of exhumation rates along an ∼120-km-wide NE-SW transect spanning the greater Sutlej region of northwest India. The 40Ar/39Ar data indicate that first the High Himalayan Crystalline units cooled below their closing temperature during the early to middle Miocene. Subsequently, Lesser Himalayan Crystalline nappes cooled rapidly, indicating southward propagation of the orogen during late Miocene to Pliocene time. The AFT data, in contrast, imply synchronous exhumation of a NE-SW–oriented ∼80 × 40 km region spanning both crystalline nappes during the Pliocene–Quaternary. The locus of pronounced exhumation defined by the AFT data correlates with a region of high precipitation, discharge, and sediment flux rates during the Holocene. This correlation suggests that although tectonic processes exerted the dominant control on the denudation pattern before and until the middle Miocene; erosion may have been the most important factor since the Pliocene.

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