Abstract：Diabase dikes exposed on the northwestern margin of the Tarim basin contain 44.34%－49.3% SiO2 have higher values of Na2O+K2O (4.32%–6.04%) and Na2O/K2O (2.23－9.15), showing the features of intraplate basalt. The diabase is also characterized by a lower total REE content (∑REE=35.71－47.95 μg/g) and a higher ratio of (La/Yb)N (11.66－14.77) and no pronounced Eu anomaly. The geochemistry of the diabase suggests that it was derived from enriched mantle sources. 40Ar/39Ar dating of the diabase yields ages of 235.6 and 203.7 Ma. The above-mentioned geochemical characteristics combined with an integrated analysis of the Triassic-Jurassic sedimentary and tectonic settings of the western Tarim basin, especially the Tajikistan basin and Karakumy basin west of the Tarim basin suggest that：in the Triassic-Jurassic the western Tarim basin was in a prelude stage of Cretaceous-Paleogene intense subsidence and its main part was still in an uplift stage against the general extensional setting.