渤海海域庙西北凸起中生代花岗岩LA-ICP-MS锆石U-Pb测年及其地质意义

为了解渤海海域首个未变质花岗岩潜山油藏的形成演化,对庙西北凸起潜山花岗岩进行年代学及地球化学研究,讨论其岩石成因、源区性质和构造背景。庙西北凸起潜山二长花岗岩及花岗闪长岩均为钙碱性系列岩石,其锆石呈双锥柱状晶形,自形程度较高,测年数据证实岩浆结晶锆石年龄为155.4±2.5Ma,分析样品都具有重稀土元素亏损、轻稀土元素富集的特征,Eu正异常,富集大离子亲石元素(如Pb、Sr),亏损高场强元素(如Th、Nb、Zr)。综合分析认为,在早—中侏罗世受扬子板块及佳蒙地块挤压,地壳快速缩短增厚,由于升温使其下地壳部分发生熔融,最终上涌侵入,形成庙西北凸起潜山过铝质S型花岗岩。

LA-ICP-MS zircon U-Pb dating of Mesozoic granite in Miaoxibei uplift, Bohai Sea area, and its geological significance

For the purpose of better understanding of the formation, evolution and tectonic environment of the first unmetamor-phosed granite oil pool in Bohai Sea area, the authors carried out a study of granite buried hill of Miaoxibei uplift. Based on petrogra-phy, LA-ICP-MS zircon U-Pb ages and whole-rock major and trace elements, the authors investigated the petrogenesis, magma source and tectonic setting. LA-ICP-MS zircon U-Pb data of the granite yielded weighted age of 155.4±2.5Ma, the granite is of cale-alkaline suite with positive Eu anomaly, both samples have the characteristics of depletion of heavy rare earth elements and en-richment of light rare earth elements, and the granite is strongly enriched in large ion lithophile elements (LILEs, e.g., Pb, Sr) but de-pleted in high field strength elements (HFSEs, e.g. Th, Nb, Zr). It is thus held that the crust experienced shortening and thickening rapidly because of the pressure of Yangtze plate and the Jiamusi Mongolia block during the early Middle Jurassic, and that, due to the rising temperature, the lower crust was subjected to partial melting, which eventually surged and invaded, resulting in the formation of peraluminous S-type granite in the Miaoxibei uplift buried hill.