Depositional Characteristics and Tectonic Response in the Lunan and Mile Basins: U–Pb Zircon Dating and Magnetic Fabric Analysis

Abstract The synchronous impact of tectonic strain from the early stage India–Asia collision on the far‐field margin of the Tibetan Plateau is essential for comprehending plateau deformation and growth processes. Nevertheless, early phase sedimentary records related to the India–Asia collision are lacking in the southeastern margin of the Tibetan Plateau (SEMTP). We aimed to comprehend how the sediments of basins in the SEMTP document the far‐field tectonic response to the India–Asia collision. To achieve this, we analyzed the sedimentary sequence of the Lunan and Mile Basins on the SEMTP, delineating the deposition timing and regional stress direction at initial deposition. This was achieved by combining depositional characteristics with U–Pb detrital zircon dating and magnetic fabric analysis. Our results reveal that the initial sedimentary age of the basins is estimated to be 50–47 Ma, with the provenance of the basin identified as originating from west of the Xiaojiang Fault (XJF). Magnetic anisotropy analyses reveal that the study area experienced NWW–SEE‐oriented compressional stress during the early Eocene (approximately 53–47 Ma). This stress regime suggests the XJF primarily acted as a reverse fault during this period, challenging the prevailing strike‐slip fault interpretation. The presence of conglomerate rocks at the base of the basin may suggest that a tectonic event took place on the SEMTP during the early Cenozoic and was documented by basin deposition. The tectonic event recorded in the sedimentary basin, specifically the activity of the XJF, exhibits quasi‐synchronism with the initial stage of the India–Asia collision.