Shifts in the Intertropical Convergence Zone, Himalayan exhumation, and late Cenozoic climate

The Early Miocene (ca. 23-16 Ma) was the time of peak Himalayan exhumation and postulated mid-crustal channel flow in the High Himalayas, a tectonic configuration not recognized before or after in the range. Previous models have correlated this rapid exhumation with the onset of the Asian monsoon, and/or suggested that it contributed ultimately to mid-Miocene global cooling via silicate weathering and/or organic carbon burial, and consequent atmospheric CO2 drawdown. Based on published Pacific Ocean sedimentation records and India-Eurasia plate reconstructions, we compare the position of the Intertropical Convergence Zone (ITCZ) with the paleolatitude of the Himalayas, and show that these converged in the Early Miocene. Because the ITCZ is a zone of high precipitation, we suggest that this convergence was an important driver of Early Miocene High Himalayan exhumation and erosion. Continued northward motion of the Indian plate took the Himalayas north of the ITCZ, which migrated south through the remainder of the Miocene. High Himalayan exhumation and ductile shearing correspondingly decreased after the Early Miocene. This mechanism for increased Himalayan erosion is independent of the timing of the onset or enhancement of the Asian monsoon, which is debated.