赣南—湘东湖南洞岩体的锆石U-Pb年代学研究及其对加里东构造背景的意义

Zircon U-Pb Dating of the Hunandong-granite and Its Caledonian Tectonic Significance,South Jiangxi-East Hunan Province

湖南洞岩体位于湘赣交界处,侵位于淋洋岩体中。在野外系统地质调查的基础上,对湖南洞岩体进行了详细的激光剥蚀-多接收器电感耦合等离子体质谱(LA-MC-ICPMS)锆石U-Pb同位素年龄测定。这些锆石的阴极发光图像发育环带结构,Th/U比值较高(大于0.1),具有岩浆成因锆石的特征。研究结果表明,湖南洞岩体锆石的206Pb/238U加权平均年龄为(447.2±1.8)Ma,为晚奥陶世,反映了华南加里东期岩浆活动的一个重要阶段。结合本次锆石U-Pb同位素定年结果及前人研究资料,认为湖南洞岩体的形成可能与扬子地块和华夏地块之间的碰撞拼贴作用有关,从而为进一步理解华南加里东期花岗质岩浆活动及其动力学背景等提供了有力的证据。

Hunandong granite located on the border of Hunan and Jiangxi, intruded into the Linyang granite. Based on the investigation of field geology, detailed zircon U-Pb age measurements were done on the Hunandong granite. These zircons have high Th/U ratio with zonal structure, which indicate magmatie zircons. The zircon U-Pb age is （447.2± 1.8） Ma, which shows that the Hunandong granite was formed in the late Ordovician period, reflecting the important stage of Caledonian magmatism. According to the result together with other information published, the authors think that the formation of Hunandong granite may be related to the amalgamation and collision between Cathaysian block and Yantze block, providing strong evidence for further understanding the Caledonian magmatism and its geodynamic process in South China.