Climate controlled erosion during the Late Triassic rapid exhumation of the ultrahigh pressure metamorphic rocks in the Dabie Mountains

Abstract

Climatic effects on erosion is usually covered up by tectonics and not well understood in active mountains. The Dabie Mountains in central China evolved from a collisional orogen between North China and South China with development of Triassic ultrahigh pressure metamorphic (UHPM) rocks. In the Late Triassic these UHPM rocks experienced a rapid cooling after peak metamorphism and has been linked to compressional uplift during the collisional orogenesis. During this period, the climate changed from arid-semi arid to humid in the northern South China. This climate change is clearly recorded in the Late Triassic successions of upper Puqi and Jigongshan formations in the Huangshi Basin to the south of the Dabie Mountains. Combining tuff zircon U-Pb dating and magneto-stratigraphy, the upper Puqi Formation with arid climate was constrained in the early Norian (~228−221 Ma) with the overlying Jigonghsan Formation with humid climate in the late Rhaetian according to youngest detrital zircon ages. Detrital zircon and rutile U-Pb ages were combined with paleocurrents and sandstone petrography to determine the sedimentary provenance. For the upper Puqi Formation the deposited sediments were likely recycled from the Paleozoic sedimentary rocks in the Dabie Mountains. However, the Jiligang Formation has sediment mainly derived from the middle Neoproterozoic and late Paleoproterozoic basement rocks in the northern South China and Dabie Mountains. This rapid shift in provenance is associated with and plausibly resulted from the Late Triassic climate change, which may force rapid erosion in the southern Dabie Mountains. The deposition of the upper Puqi Formation was temporally overlapping with the rapid cooling and tectonic uplift of the Dabie Mountains, but there were no large changes in sedimentary provenance. This observation suggests low erosion rates in active mountains under a under an arid-semi arid climate.