Provenance shift during Early‐Middle Triassic and its response to the palaeogeographic and tectonic evolution of the southwestern South China Block

Abstract

To constrain the relationship between the plate boundary dynamics and the basin sedimentation in the southwestern South China Block (SCB), we undertook detrital zircon U–Pb–Hf isotope compositions of the Lower‐Middle Triassic turbidite system in the Youjiang Basin and biotite 40Ar/39Ar thermochronology of the adjacent Lingshan granite. The detrital zircons from Lower Triassic clastic rocks are dominated by age peaks at ~450 Ma and ~1,000 Ma and minor peaks at ~250–260 Ma with negative εHf(t) values (−6.4 to −10.1). In contrast, the Middle Triassic group contains more volcanic fragments and displays a different age peak at ~240–287 Ma with εHf(t) between −11.9 and 13.2 in addition to the former two peaks. These results suggest a potential provenance associated with juvenile and volcanic components in the adjacent region during the Middle Triassic. A summary of the Triassic tectonothermal history suggests that the eastern Youjiang Basin and Yunkai Terrane were uplifted throughout the Triassic, while the northeastern Indochina Block on the west of the SCB was uplifted mainly during the Middle Triassic. Combined with the palaeocurrent reconstruction, we infer that the turbidite system was filled primarily from east to west during the Early Triassic, mainly controlled by the Palaeo‐Pacific plate subduction. Subsequently, the Middle Triassic turbidite system involved juvenile and volcanic components from the eastern SCB and northeastern Indochina Block in addition to the Early Triassic provenance, as a result of dual impact from the Palaeo‐Pacific plate subduction and Indochina Block collision.

Advances in metallogeny and tectonics of the Eastern Tethyan Realm: Introduction

“…The study of the palaeogeographical and tectonic evolution of the south‐western South China Block is crucial to understanding whether it is controlled by the evolution of the Tethyan oceanic plate or the Palaeo‐Pacific plate. In the paper by Chen, Wang, et al (2023), detrital zircon U–Pb‐Hf isotopes of the Lower–Middle Triassic turbidite system and biotite 40 Ar/ 39 Ar thermochronology of the adjacent Lingshan granite are discussed to understand a major provenance shift of the Lower–Middle Triassic clastic rocks in response to the palaeogeographical and tectonic evolution of the south‐western South China Block. The Middle Triassic sandstones contain more volcanic fragments than the Lower Triassic samples and their detrital zircon age features and provenances are partly different.…”