赣南兴国杨村岩体锆石U-Pb年龄测定及其地质意义

位于南岭东段北部赣南地区兴国县境内的杨村岩体,侵入于前寒武纪基底变质岩中,其西侧又与白垩系赣州组砂岩、砾岩断层接触,因而其地质年代难以根据接触关系准确判断,而岩体本身风化程度比较高,难以利用K-Ar法和Rb-Sr等时线等方法获得可靠年龄,以往将该岩体归属于加里东期。文章采用激光剥蚀-多接收器电感耦合等离子体质谱(LA-MC-ICPMS)锆石U-Pb定年方法,获得其锆石206Pb/238U加权平均年龄为(175.8±1.0)Ma,从而准确地查明该岩体侵位于燕山早期第一阶段与第二阶段的过渡时期。这一阶段在南岭是钨多金属发生大规模成矿作用的开始阶段,因而杨村岩体地质年代的确定为今后的地质找矿提供了新的线索。

Zircon U-Pb Age Dating for the Yangcun Granite Masses from South Jiangxi Province and Its Geological Significance

The Yangcun granite mass is located northeast of Nanling and Xingguo country of the South Jiangxi area. It intrudes into metamorphosed rocks of Precambrian basement, and is adjacent to Cretaceous Sandstone and conglomerate at its west side with a fault. The forming time of this granite masses is difficult to judge correctly by its contact relations, and it was previously assigned to the Caledonian period. In this paper, we give a U-Pb age of (175.8±1.0) Ma of zircon by Laser Ablation-Multicollector Inductively Coupled Plasma-Mass Spectrometry (LA-MC-ICPMS) dating technology, thus ascertaining this granite mass as an intrusion during the period between the first and second stage of the early Yanshanian, and this period is the onset period of extensive mineralization of tungsten and multi-metals in the Nanling area. Therefore, the determination of the geochronology of the Yangcun granite masses will provide new information for prospecting in the future.