Shift in erosion pattern of the Himalaya-Karakoram mountains during the mid-Pleistocene transition recorded by Indus Fan deposits

Abstract Understanding how erosion processes respond to climatic and tectonic variations is a key issue in geosciences. The Himalaya-Karakoram mountains, with their high elevations, relief, and significant water discharge that feeds deep-sea turbidite fans, offer a prime setting for deciphering the relative controls on erosion. However, the extent to which climate change has influenced the erosion patterns of this tectonically active region remains debated, partly due to the limited detailed record of its erosional history during periods of pronounced climate fluctuations, such as the Pleistocene. In this study, we present multiproxy provenance and thermochronological analyses of turbidite sediments from the Indus Fan to reconstruct the Pleistocene erosional history of the Himalaya-Karakoram mountains. Detrital zircon U-Pb age spectra and Nd-Sr isotopes from the Indus Fan detritus indicate an increase in erosional contribution from the Lesser Himalayan Sequence starting at ca. 1.2 Ma, peaking ca. 0.9 Ma, and declining to pre–1.2 Ma levels after ca. 0.8 Ma. Detrital apatite fission-track ages further suggest that the source region experienced accelerated erosion between ca. 1.2 Ma and 0.9 Ma. We propose that during the middle Pleistocene, erosion in the Himalaya-Karakoram mountains was concentrated in frontal parts of the Himalaya, where dominantly the Lesser Himalayan Sequence is exposed, which experienced rapid erosion and contributed more material to the Indus Fan compared to earlier and later periods. This shift in erosion patterns was likely linked to a southward shift in the orographic precipitation, driven by weakening of the South Asian monsoon during the mid-Pleistocene transition.