蚌埠隆起区煌斑岩锆石U-Pb测年及其地质意义

蚌埠地区中生代岩浆作用十分发育, 以酸性岩浆活动为主, 部分地区伴随基性岩脉侵入。本文利用LA-ICP-MS技术, 对蚌埠五河地区煌斑岩中的锆石进行U-Pb同位素定年。研究表明, 该煌斑岩中锆石多成半自形到浑圆状, 多为捕获锆石。锆石U-Pb年龄多集中在3 100 Ma、2 500 Ma和2 000 Ma附近, 少量新生锆石年龄约为156 Ma, 捕获锆石年龄与华北基底的五河杂岩相当吻合, 可能不具有扬子板块俯冲陆壳年代学信息。本次测得煌斑岩的形成年龄为156.1±8.2 Ma, 为晚侏罗世。蚌埠地区普遍存在一期构造变形事件, 表现为由南向北的逆冲推覆。由于煌斑岩脉遭受到逆冲推覆构造的改造, 因此煌斑岩的形成年龄也限定了蚌埠地区推覆构造变形事件的下限。

Zircon U-Pb dating of the lamprophyre in the Bengbu uplift and its geological implications

The magmatic activity was very fierce and frequent in the Bengbu area during Mesozoic, which is mainly acidic magma activity and mafic dikes only intruded in few areas. U-Pb chronology analyses LA-ICP-MS U-Pb isotopic dating has been conducted on zircon grains collected from the lamprophyre dyke from Bengbu-Wuhe area. The zircon grains are usually subhedral or rounded and probably captured from the wall rocks during magma ascending. Three peak ages of captured zircons are 3 100 Ma, 2 500 Ma and 2 000 Ma, respectively, which coincide well with the ages of the Wuhe complex that is the basement of the North China Craton in Bengbu area. Because of the lack ages of Neoproterozoic and Triassic period probably indicate that there is no subduction of continental crust material beneath the Bengbu-Wuhe area. However, two new zircon grains yield weighted mean age of 156±8 Ma, which indicated the intrusion of the lamprophyre occurred during Late Jurassic. There is a widespread northward thrust-nappe structure in Bengbu area which reworked the lamprophyre veins and caused the foliation formed. Therefore the age of the lamprophyre veins also constrains the lower age limit of this deformation event.