浙东早白垩世岩浆混合作用:新昌小将岩体U-Pb年代学及地球化学证据  

Late Mesozoic magma mixing in eastern Zhejiang Province: Evidence from U-Pb geochronology and geochemistry of Xiaojiang pluton in Xinchang

作　　者：王对兴[1,2] 李春麟[3] 高万里[3] 王宗秀[3] 赵志丹[1] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,中国地质大学地球科学与资源学院,北京100083 [2]石家庄经济学院资源学院,石家庄050031 [3]中国地质科学院地质力学研究所,中国地质科学院页岩油气调查评价重点实验室,北京100081

出　　处：《岩石学报》2013年第11期3993-4003,共11页Acta Petrologica Sinica

基　　金：中国地调局项目(1212011121068);深部探测技术与实验研究专项课题(Sinoprobe-04-02);111计划(B07011)联合资助

摘　　要：在中国东南沿海地区广泛发育的中生代中酸性岩浆岩中多处发现了暗色包体，被认为是大规模壳幔相互作用和岩浆混合作用的产物。本文获得了浙东新昌地区小将岩体的花岗岩及暗色闪长质包体的锆石U-Pb年代学和和地球化学新结果。锆石U-Pb定年表明寄主花岗岩（121．1±0．9Ma）与暗色闪长质包体（117．6±1．0Ma）近于同期形成于早白垩纪。寄主花岗岩为高硅、富碱、富钾、准铝质或弱过铝质的钙碱性花岗岩，具有较强的铕负异常（8Eu=0．23～0．30）和Sr、Ba、P和Ti等元素的亏损，属于高分异的I型花岗岩；暗色闪长质包体具有重稀土亏损的特征，与寄主花岗岩在主量和微量元素上呈现混合作用趋势。小将岩体的上述特征与浙东晚中生代和福建沿海同期的岩浆岩特征一致，它们可能都是在早白垩纪伸展构造背景下，起源于俯冲交代的岩石圈地幔部分熔融产生的基性岩浆或者演化为闪长质成分，并与壳源花岗质岩浆发生混合作用的结果。本文研究为浙东及浙闽沿海地区晚中生代壳-幔作用和岩浆混合作用提供了新的证据。The mafic enclaves have been found in the widely distributed Mesozoic intrusives in southeast coast of China, which explained to be produced by crust-mantle reaction and magma mixing. This paper present new result of zircon U-Pb dating and geochemistry on the Xiaojiang pluton in Xinchang area, eastern Zhejiang Province. The zircon U-Pb ages of host granite （121.1 ± 0.9Ma） and dioritic enclave （117.6 ± 1.0Ma） were both intruding in Early Cretaceous simultaneously. The host rocks are peraluminous cal-alkaline granite, with enriched SiO2, total alkalis, and potassium. They also exhibit significant Eu negative anomaly （SEu =0. 23 -0. 30）, and depletion of Sr, Ba, P, and Ti. The host granites show the feature of highly-fractionated I-type granite. The dioritic enclaves are depleted in heavy rare earth elements （ REEs）, and forming a mixing trend with the host granites in both major and trace element compositions. The above geochemical features are agreed well with the Late Mesozoic intrusives from the coastal areas of eastern Zhejiang and Fujian provinces. The rocks possibly derived from the magma mixing between the basaltic magma （ or evolved dioritic magma） originally from metasomatic mantle wedge partial melting, with the felsic magma from middle-lower crustal melting. This study provides a new evidence for the crust-mantle reaction and magma mingling in the southeastern coast of China.

关 键 词：锆石U-PB年代学 地球化学 岩浆混合作用 早白垩世 浙东小将岩体 

分 类 号：P588.121[天文地球—岩石学] P588.122[天文地球—地质学]