北淮阳东缘新元古代花岗质侵入体岩石学、地球化学及锆石U-Pb年代学特征

The petrology,geochemistry and zircon U-Pbgeochronologyof the Neoproterozoic granites in the eastern Beihuaiyang belt

北淮阳构造带东缘广泛出露新元古代变形花岗质岩体,其岩石成因对于认识北淮阳构造带的岩浆演化具有十分重要的意义。本文对出露于万佛湖北侧的变形花岗质岩体进行了详细的野外地质调查、LA-ICP-MS锆石U-Pb同位素测年和岩石地球化学分析,旨在查明其成岩时代和成因类型。结果表明,岩体的组成矿物主要为石英、钾长石、斜长石和黑云母等矿物。LA-ICP-MS锆石U-Pb同位素定年结果显示其成岩年龄为778 Ma,为新元古代岩浆活动的产物。岩体具有较高的SiO2含量,富集大离子亲石元素,亏损高场强元素和重稀土元素,A/CNK=0.98～1.21,地球化学特征显示其为钙碱性过铝质S型花岗岩,C/MF-A/MF图解显示源岩为泥岩及砂岩。根据岩石成因、构造环境判别以及区域构造演化过程,岩体应为新元古代扬子板块与大别地块碰撞产物。

There are a large number of Neoproterozoic deformed-granites exposed in the eastern part of the Beihuaiyang belt. It is a great significance to know the magmatic evolution of the Beihuaiyang belt through the petrogenesis. In this paper,the petrogenic age and genetic type of deformed-granites in the north of Wanfo Lake were investigated through field geological survey,LA-ICP-MS zircon U-Pb isotopic dating and geochemical analysis. The results show that deformed-granites are mainly composed of quartz,potassium feldspar,plagioclase andbiotite. LA-ICP-MS zircon U-Pb dating results showpetrogenic age was 778 Ma,should be the product ofNeoproterozoicPeriod magmatic activity.The deformed-granites has high content of SiO2,the trace elements are enriched in large ion lithophile elements,but strongly depleted in high field strength elements and heavy rare earth elements,A/CNK=0.98~1.21. All these geochemical characteristics point to calc-alkaline series,peraluminousS-type granite. The C/MF-A/MF diagram indicates that deformed-granites came from mudstones and sandstones. According to petrogenesis and discrimination of structural environment in combination with regional tectonic evolutional setting,the deformed-granites should be the collision product of the Yangtze plate and the Dabie block in late Neoproterozoic Period.