Feedbacks Between Erosion, Climate and Uplift in the Gongga Granite on the Eastern Margin of the Tibetan Plateau

Abstract:

In regions such as the Himalayan syntaxes, feedbacks between high erosion rates, rapid exhumation, and the rise of hot weak crust have been proposed, where high erosion rates lead to thermal weakening of the crust, leading to focused deformation and uplift, high topography, focusing of precipitation, and further rapid erosion. To help elucidate these interactions and their inception, we turn to a system with pronounced spatial variations in climate, topography, and exhumation. Gongga Shan, a 7500 m peak on the eastern margin of the Tibetan Plateau, caps an area of localized anomalous topography and sits at the southern end of the Gonnga Shan granite, a Cenozoic intrusive body about 120 km long that parallels the NNW-SSE strike-slip Xianshuihe Fault. U-Pb zircon ages indicate that granite emplacement spanned most of the Cenozoic, with melting at depth possibly continuing to the present. While the southern end of the granite contains extremely high relief, the rest of the granite has subdued topography, with gentle slopes and low relief. Cosmogenic ¹⁰Be basin wide erosion rates are extremely high (> 5 mm/yr) in the Gongga region with rates decreasing in all directions to as low as 0.1 mm/yr over a distance of ~30 km. Thus, Gongga Shan is a region of extremely high topography in hot crust experiencing localized rapid exhumation, while the granite to the north is also a region of hot crust, but without high topography or rapid erosion. This contrast coincides with differences in precipitation and preexisting relief, as the granite stretches from the plateau margin with orographically enhanced precipitation in the south to the dry plateau interior in the north. Gongga Shan is also adjacent to the deeply incised Dadu River; which created substantial local relief even prior to the development of anomalous topography. We propose that the combination of focused precipitation, preexisting relief, and hot crust in the southern part of the granite set into motion a series of feedbacks between erosion, uplift, and orographic precipitation that has resulted in the extremely high topography and rapid erosion rates seen today. Only where all three of the driving factors are present do we observe the topographic and erosional extremes, and each of these driving factors was likely present prior to the initiation of extremely rapid uplift of Gongga Shan.