Jurassic tectonic regime transition of the southwestern Yangtze Block, SW China: evidence from sedimentary provenance analysis

The Lufeng Basin (LFB) in central Yunnan is located on the southwestern margin of the Yangtze Block in the eastern segment of the Tethys tectonic domain, where the Paleo-Tethys and the Paleo-Pacific tectonic domains converge. Jurassic red beds in this basin record the closure of the Paleo-Tethys Ocean and key information of the tectonic transition driven by the spreading of the Paleo-Pacific plate. We present sedimentary provenance analysis on these Jurassic red beds based on heavy mineral assemblages and detrital zircon geochronology. The results indicate that the strata in this basin were deposited after 214 Ma, and the Early Jurassic Lufeng Formation (Lufeng Fm.) mainly sourced from the west of the LFB with minor contributions from the western Yunnan. In contrast, the sedimentary provenance of the Middle Jurassic Chuanjie Formation (Chuanjie Fm.) and Laoluocun Formation (Laoluocun Fm.) shifted to the proximal ancient basement surrounding the basin and the east of the LFB. The regional unconformity between the Early and the Middle Jurassic may have resulted from the subduction of the Paleo-Pacific plate, jointly influenced by two tectonic domains. The sedimentary provenance shift in the Middle Jurassic may be related to the local uplift of the southwestern Yangtze Block caused by the subduction of the Paleo-Pacific plate. The tectonic regime transition associated with this highest peak of local uplift occurred at ∼170 Ma.