赣东北珍珠山群同位素年代学研究

Isotopic Geochronology of the Zhenzhushan Group in NE Jiangxi Province

赣东北婺源—乐平地区浅变质地层珍珠山群的地质时代,以往普遍认为归属于中元古代,但由于缺乏高精度的同位素测年资料,时代归属尚存争议,目前主要有中元古代、古元古代和晚古生代3种认识。近期开展的1:5万区域地质调查工作,采用单颗粒锆石U-Pb法获得一批介于1113±118Ma～1379±65Ma间的同位素年龄数据,从而将珍珠山群时代合理地厘定为中元古代蓟县纪;此外,还获得了代表捕获晶体或残留的继承性浑圆状锆石表面年龄2497±19Ma和含量极少的结晶锆石年龄1827±76 Ma,推断珍珠山群之下还掩埋着古元古代地层或岩石,为区域深层构造研究提供了新的资料。

The epi-metamorphic Zhenzhushan Group in the Wuyuan-Leping region of northeastern Jiangxi Province was considered to belong to the Mesoproterozoic. Because of the lack of high-precision isotopic age determination, the age of the group is still in dispute. The assignments of the group to the Mesoproterozoic, Paleopro-terozoic and Late Paleozoic were put forward. A single-grain zircon U-Pb dating gave isotopic ages between 1113±118Ma and 1379±65 Ma during a 1:50000 regional geological surveying. Therefore, the Zhenzhushan Group should be of the Mesoproterozoic Jixian system. In addition, an age of 1827 ± 76 Ma of crystallized zircons and a surface age of 2497± 19 Ma of perfectly rounded, trapped or inherited zircons were also obtained. These data show that Paleoproterozoic strata or rocks may be concealed under the Zhenzhushan Group. This result provides new data for the research on the regional deep structure.