Provenance analysis of Jurassic basins alongChaling–Chenzhou–LinwuFault, South China: Implications for palaeogeographic reconstruction and Mesozoic tectonic transition

Abstract

Tectonic transition from the Tethys to Palaeo‐Pacific regimes occurred during the Mesozoic in the South China Block. But the switching time and palaeogeographic pattern are still controversial. The Late Triassic to Middle Jurassic Longhai and Sandu basins along the NNE‐striking Chaling–Chenzhou–Linwu Fault were selected for provenance analysis and palaeogeographic reconstruction. Detrital zircons of all six samples from the Lower and Middle Jurassic yield peak ages of 250 ~ 400 Ma, 407 ~ 497 Ma, 562 ~ 1,167, 1,603 ~ 2,170 Ma, and 2,270 ~ 2,800 Ma, revealing pre‐Triassic tectono‐thermal events occurred within or beyond the South China Block. Late Triassic (207 ~ 236 Ma) and Early Jurassic (186 ~ 198 Ma) detrital zircons are also preserved in the Lower and Middle Jurassic. Composition and content variations of zircon ages in the Longhai Basin imply Jurassic stratigraphic inversion, which was caused by Middle Jurassic top‐to‐the‐SE thrusting of the Chaling–Chenzhou–Linwu Fault. Cathodoluminescence images, Th/U ratios, and rare earth elements patterns show that almost all analyzed zircons are of magmatic origin. Y versus U/Yb and Nb/Yb versus U/Yb discrimination diagrams indicate that 250 ~ 400 Ma, 207 ~ 250 Ma, and 186 ~ 198 Ma detrital zircons are continental zircons derived from Late Palaeozoic, Triassic, and Early Jurassic continental arcs, respectively. Provenance analysis indicate that the Middle and Lower Jurassic in the Longhai Basin were derived from the Nanling tectonic belt to the south, whereas the Lower Jurassic in the Sandu Basin from the Wuyishan domain to the east. The source‐to‐sink systems indicate that an NNE‐striking watershed occurred during Early to Middle Jurassic and separated the Longhai and Sandu basins. Tectonic uplift of the NNE‐striking watershed resulted from by Late Triassic transpression along the Chaling–Chenzhou–Linwu Fault. Combining these with two‐stage tectonic deformation and granitoids in the South China Block, the Mesozoic tectonic transition from the Tethys regime to the Palaeo‐Pacific regime occurred during the Late Triassic.