194 / 2019-06-13 15:25:38

Cretaceous detrital source-sink systems: implications for exhumation of UHP metamorphic rocks and paleogeographic evolution in Sulu Terrane and adjacent area

Cretaceous, Exhumation, paleogeographic evolution, Sulu orogenic belt, UHP

Abstract
Sulu orogenic belt is the collision relic of North China Block and South China Block in Triassic, and famous for being one of the biggest ultra-high pressure (UHP) metamorphic rock outcrop regions. It is important to reveal the processes of how the UHP metamorphic rocks exhumated from a depth over 120km to ground surface and constraining its precious time span. Even though, there are a lot of thermochronology data that indicate Late Mesozoic is an important period for Sulu UHP metamorphic rocks exhumating to surface. However, the exact time of exposure of UHP metamorphic rocks to the surface remains unclear. In this research, we focus on the relatively complete sedimentary records in east Shandong area, which was contemporarily deposited with exhumation process of Sulu UHP metamorphic rocks during Early Cretaceous. We carried out provenance analysis for Early Cretaceous sediments in Jiaolai and Lingshan Island Basins. Detrital Zircon U-Pb isotope dating and detrital white mica geochemistry composition analysis have been carried out. The results show that Si (p.f.u.) value of detrital moscovites in Laiyang profile ranges from 3.05 to 3.43, Zhuwu profile from 3.08 to 3.51 and Lingshan Island profile from 3.25 to 3.68. It is clear that the maximal Si (p.f.u.) value, which is a function of metamorphic pressure, is much higher in samples from Lingshan Island than others. Combining with previous published studies, we conclude that high pressure metamorphic rocks within Sulu orogenic belt had exposed to surface at the initial process of basin filling, while the UHP metamorphic rocks started to provide detrital material for sediments in the studied basins with its time confined to ~125Ma. Correspondingly, for Sulu Terrane and adjacent area, source-sink systems evolved with the exhumation processes of UHP-HP metamorphic rocks within the extensional tectonic setting during Early Cretaceous.