北淮阳东段张冲闪长玢岩地球化学特征、LA-ICP-MS锆石U-Pb年龄及其地质意义

张冲闪长玢岩呈不规则状侵入佛子岭岩群诸佛庵岩组和毛坦厂组中。岩体具较高的SiO_2和Al_2O_3含量,为偏碱性、准铝质、高钾钙碱性系列岩石。富集大离子亲石元素(LILE)和轻稀土元素(LREE),亏损高场强元素(HFSE)、重稀土(HREE)和Y,无明显Eu异常,Sr正异常。通过LA-ICP-MS锆石U-Pb法确定张冲闪长玢岩年龄为129±3 Ma,表明该岩体侵位于早白垩世。通过对岩石主、微量元素特征研究,认为岩浆可能来源于底侵玄武岩,并受到地壳物质的混染。岩体形成于中生代构造体制转换期,可能属于北淮阳东段中生代第一旋回侵入岩。

Geochemical Characteristics and Zircon U-Pb Age of Zhangchong Diorite Porphyrite in the East Part of North Huaiyang and Their Geological Significance

The Zhangchong diorite porphyrite intruded into the Zhufo'an Formation and Maotanchang Formation of the Foziling Group.The diorite porphyries have high SiO2 and Al2O3 contents,and belong to metaluminous,high K Calc-alkalic series.The rocks are enriched in large ion lithophile elements and depleted in high field strength elements,showing positive Sr anomalies and insignificant Eu anomalies.LA-ICP-MS U-Pb dating of zircon from the Zhangchong diorite porphyrite yields an age of 129±3 Ma.Regarding the major and trace element geochemistry of the rocks,we suggest that the magma was derived from underplated basalt with crustal contamination.The pluton belongs to the first phase of Mesozoic magmatism in the eastern North Huaiyang emplaced under a tectonic transition of compression to extension in Late Jurassic to Early Cretaceous.