The Bashisuhong rare earth deposit is located at the northern margin of the Tarim Basin and the southern Tianshan region, at the junction between the Tarim Craton and the Central Asian Orogenic Belt. There has been ongoing debate regarding its formation age and tectonic attributes. To address these issues. this study focuses on the bimodal intrusive rocks discovered in the region and attempts to provide evidence to resolve the aforementioned problems. Through petrographic, zircon U-Pb geochronology, in situ Hf isotope analysis and geochemical studies of the rocks, the results show that the zircon U-Pb ages of the diabase and alkaline granite are 278.50±0.87 Ma and 275.89±0.94 Ma, respectively, indicating their formation in the Middle Permian. In terms of geochemical characteristics, both rocks have similar εHf(t) values (diabase average: 4.17, alkaline granite average: 3.42). The alkaline granite has high SiO₂, K₂O, Na₂O, and low MgO, CaO, with relatively high total rare earth element content, significant light/heavy rare earth element ractionation, and a distinct negative Eu anomaly, along with enrichment in high-field-strength- elements. The diabase has lower SiO₂, K₂O, higher MgO, CaO, relatively lower total rare earth element content, significant light/heavy rare earth element fractionation, a weak positive Eu anomaly, and elevated Ba content. In terms of rock genesis, the diabase originates from the asthenospheric mantle, undergoing low-degree partial melting; the alkaline granite magma originates from partial melting of lower-pressure, high-temperature crustal gabbro, displaying characteristics of A1-type granites. Combined with regional geological background analysis, it is concluded that the Bashisuhong alkaline intrusive complex formed in a non-orogenic intra-continental rift environment during the Middle Permian, driven by mantle plume activity, rather than in a post-collision orogenic extension tectonic background resulting from plate stress release. This provides new data for the study of the Late Paleozoic tectonic setting in the northern margin of Tarim.