上海南部齐贤桥辉石闪长岩体的锆石U-Pb定年及其地质意义

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

齐贤桥辉石闪长岩体为一小型岩株,侵位于上侏罗统和寒武系之中。本文采用LA-ICP-MS方法开展了岩体锆石U-Pb定年,并讨论了其地质意义。定年结果表明,岩体形成于早晚白垩世之交,侵位年龄在99.5±1.2Ma^100.56±0.57Ma。结合区域地质资料和已有年龄,将区内燕山晚期的岩浆侵入作用划分为三次,分别约119.6~120.1Ma、98.3~112.7Ma和81~88.1Ma左右,以后两者为主。认为岩体为燕山晚期伸展拉伸构造体制下,主要受张堰—南汇断裂带控制被动侵位形成。燕山晚期以来,上海地区的岩浆作用年代与江山—绍兴断裂、温州—镇海断裂带带间的浙东南地区具有很大相似性,可能指示该阶段浙东南和上海地区构造体制的一致性。

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 bythe Zhangyan-Nanhui fault belts, dunng 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.