赣杭带早白垩世粗面岩锆石SHRIMP U-Pb年龄及其意义

Early Cretaceous Zircon SHRIMP U-Pb Age of the Trachyte and Its Significances of the Gan-Hang Belt

赣杭构造火山岩铀成矿带的石溪盆地,属中国东南大陆中生代火山岩带的一部分,盆地内出现的粗面岩具有橄榄玄粗岩系火山岩的主元素的特征。精确确定该粗面岩的地质年龄,无论对地球动力学研究还是对铀成矿的成因研究都有重要的意义。粗面岩所含锆石具有明显的振荡环带,Th/U比值高,属典型的岩浆成因锆石。锆石SHRIMP U-Pb测年结果表明,14个点的年龄变化范围较小,为132～144Ma,加权平均年龄为(137.00±0.94)Ma,代表了火山岩的成岩年龄。根据国际最新地质年代表,侏罗纪与白垩纪的界限划在(145.5±4.0)Ma。因此,石溪组粗面岩的地质时代属早白垩世。中国东南部大规模中酸性火山活动发生在早白垩世,赣杭构造火山岩铀成矿带与碱交代有关的早期铀矿化也发生在早白垩世(120～130Ma)。石溪盆地石溪组早白垩粗面岩的厘定,说明中酸性火山活动与幔源岩浆活动有关、早期铀矿化与碱性岩浆活动合拍。

The Shixi basin was located at Gan-Hang tectonic volcanic uranium deposit of rock-magma belt which belong to a part of the Mesozoic volcanic rocks in the northeastern of China. The appearance of the trachyte in Shixi basin have the majoy elements characteristic of the shoshonite series volcanic rocks. To determine the geological age of trachyte have very important significance on the geodynamics research and the study on the cause of uranium mineralization. The zircons of the trachyte have clear ring and high Th/U ratio which belong to the typical magmatic zircons. The zircon SHRIMP U-Pb dating resules show that 14points＇ age range is very smaller is 132 144 Ma and the weighted average age is （ 137.00 ±0.94） Ma which represents the diagenetic age of volcanic rocks. Accronding to the latest International Stratigraphic Chart the boundary of Jurassic and Cretaceous is （ 145.4± 4.0） Ma. So the trachyte of Shixi Group belong to early Cretaceous. The large-scale acidic volcanic activity occurred in the Early Cretaceous in Southeastern China, and the Volcanic uranium deposit of Gan-Hang tectonic belt relate to Alkali metasomatism Uranium mineralization also occurred in the Early Cretaceous（ 120- 130 Ma）. The determined of trachyte in Shixi Group in the Early Cretaceous show that the acidic volcanic activity have connection with magma activity and the early Uranium mineralization consistent with the Alkali magma activity.