Inverse Analysis of Pearl River Source-to-Sink System, South China: Implications for SE Tibetan Uplift and Asian Monsoon Intensities
Résumé
The uplift history of the SE Tibetan Plateau has been a highly debated topic for decades, yet this problem remains of great importance to our understanding of how the crust deforms in response to continental collision, as well as how the solid Earth and climate systems interact. In particular, two contrasting models of crustal deformation have been proposed for SE Tibetan uplift, namely the "rigid-block uplift" (Tapponnier et al., 1981; 2001), and the "crustal-flow uplift" (Royden et al., 1997; Clark and Royden, 2000). This uplift has resulted in the formation of the large Pearl River catchment running from SE Tibet to the South China Sea. Asian monsoonal rain feeds this catchment, modulates sediment transport to the marginal sea, and affects the modern topography of SE Tibet. The sedimentary sequences preserved in the Pearl River Mouth Basin (PRMB) on the northern margin of the South China Sea represent an ideal natural laboratory to understand how tectonic deformation, river erosion and climate interact in this source-to-sink system. Here, we use a new efficient landscape evolution model to undertake an inverse analysis of the Pearl River source-to-sink system since the Middle Eocene (~45 Ma), in an attempt to unravel the history of river erosion (drainage evolution), climate (monsoon intensity), and tectonics (SE Tibetan uplift) that is compatible with the observed geometries of the drainage basin and the PRMB. For this, we use a Bayesian inversion scheme in which the misfit function is constructed by comparing the observed river profile, marine sediment thickness, shelf length and surface slope to those predicted by the model. Our simulations show that the crustal-flow uplift model cannot capture the geomorphic features of the SE Tibetan Plateau, and in particular the present-day profile of the Pearl River. The rigid-block uplift model can reproduce the observed geological and geomorphic features. The best-fitting values indicate that (i) the SE Tibetan Plateau started to uplift at ~15 Ma, and (ii) the monsoon intensity, simulated here by the precipitation rate, must have decreased by a factor of ~1.9 since 10 Ma. Our simulations, consistent with previous interpretations based on provenance data (Gao et al., 2018), show that the Pearl River catchment expanded towards its near-modern configuration in the Early Miocene.