Constraining the exhumation history of the Greater Himalayan Sequence, Kali Gandaki, Central Nepal

Abstract

To understand the evolution of the Himalayan orogen, we first need to understand how the South Tibetan Detachment System (STDS) evolved through time and space. We present new (and previously published) thermochronological results from a transect in the footwall and ductile shear zone of the basal structure of the STDS in the Kali Gandaki region: the Annapurna detachment. The exhumation history is interpreted from observations using 1D thermal–kinematic models that invert to give the exhumation rate of samples. Recently published data have suggested that high-temperature slip on the detachment persisted until at least c. 12 Ma, more recently than is commonly assumed for STDS deformation. Our new data and modelling support these findings and suggest that the cessation of slip coincided with a dramatic (>50%) decrease in the exhumation rate of the shear zone and its footwall at c. 12–10 Ma. Exhumation rates remained low until c. 3 Ma, after which they increased to levels comparable with those that characterized STDS activity. Plausible causes of this late pulse of exhumation include an intensification of the Asian winter monsoon and the establishment of today's Indian summer monsoon, glaciation and/or an internal structural reorganization of the Himalayan orogenic wedge driving localized rock uplift in the hinterland. Supplementary Material, including method descriptions, full datasets and supplemental figures, is available at https://doi.org/10.6084/m9.figshare.c.6949467