浙南牛头山岩体SHRIMP锆石U-Pb年龄及地质意义

Zircon Shrimp U-pb Age of Niutoushan Pluton in Southern Zhejiang and Its Geological Implications

牛头山岩体位于丽水-余姚断裂带南部,岩体为花岗岩,通过对其进行详细的野外的调查的基础上,对其进行了岩石地球化学和锆石SHRIMP成岩年龄分析,结果从结构序列上从边部到中心具有从细粒→中细粒→中粒的变化趋势,可划分为三个相带,从成分序列上可划分为中粗粒花岗岩和细粒斑状花岗岩两个期次,岩石地球化学显示岩体为高钾钙碱性系列花岗岩,轻重稀土元素分异不明显,铕负异常明显。岩石地球化学特征表明具A型花岗岩特征。SHRIMP锆石U-Pb加权平均年龄为126.8±5.3 Ma,代表岩体的成岩年龄;岩体主要受控于丽水-余姚断裂带,是沿着断裂带侵位;指示构造环境为活动陆缘弧。

The Niutoushan pluton, which is located in the south of the Lishui – Yuyao Fault, mainly consists of granites. Basing on the field investigation in detail, it could be divided into three facies in terms of the structure sequence, which has the change of particles from fine grained to medium grained from the edge to the center. Simultaneously, from the composition sequence ,the Niutoushan pluton experienced two of the times including the medium-coarse grained granite and the fine-grained porphyritic granite. Geochemical analysis of the rocks show that the pluton was high potassium calc-alkaline granite, and it characteristics with A-type granites.The results indicate that LREE and HREE f ractionation was obvious , while Eu negative anomaly was distinct. SHRIMP U-Pb zircon dating of samples yield ages of 126.8 ± 5.3 Ma , represented the era of conformation of the pluton. The Niutoushan pluton ,mainly controlled by the Lishui-Yuyao Fault, was emplacing along the fault. On the basis of researches of the rock-forming environment and the regional geology , it was confirmed that the pluton was formed in active continental marginal arc environment.