Zircon LA-ICP-MS U-Pb dating of the Qixianqiao pyroxene diorite pluton in southern Shanghai, and its geological implications

The Qixianqiao pyroxene diorite pluton is a small-scale stock, which was emplaced between the Cambrian and Upper Jurassic periods. In this study, the pluton was Zircon LA-ICP-MS U-Pb dated and its geological implications discussed. The dating results showed that the pluton was intruded during the transition between the Early and Late Cretaceous, at about 99.5±1.2 to 100.56±0.57 Ma. Combining this new dating evidence with the regional geological data, this paper concludes that the Late Yanshania magma was intruded during three phases, at approximately 119.6–120.1, 98.3–112.7, and 81–88.1 Ma, the later two phases being the main intrusive episodes. The pluton intruded passively and was controlled by the Zhangyan-Nanhui fault belts, during the late Yanshanian extension. From the Yanshanian, magmatism in the Shanghai area was similar to that in southeastern Zhejiang between the Jiangshan-Shaoxing and Wenzhou-Zhenhai fault belts, indicating that the tectonic systems in these areas may have been similar during this period.