【作者】 张媛媛；

【导师】 闫峻； 王爱国；

【作者基本信息】 合肥工业大学 ， 地质工程（专业学位）， 2017， 硕士

【摘要】 大别造山带分布有大量NNE走向的岩脉,其岩石类型多样,包括石英正长斑岩、花岗斑岩、石英闪长岩以及辉绿岩等。区内广泛发育中生代岩浆岩,以中酸性为主,伴有少量的基性岩。岩脉切穿区内广泛发育的岩浆岩,为燕山期岩浆活动最晚的产物。通过锆石LA-ICPMS定年方法得到石英正长斑岩、石英闪长岩和花岗斑岩3种类型的四件岩脉样品的年龄分别为127.1±4.5 Ma、127.5±1.9 Ma、127.4±2.5 Ma和127.9±2.1 Ma,这些岩脉的形成时代较为集中,其形成时代为早白垩世,代表了大别造山带中生代岩浆活动幕的结束。岩脉群是郯庐断裂带左行走滑动力学体制下,岩浆沿剪张裂隙侵入形成,岩脉的形成时代指示郯庐断裂带南段中生代第三次左行走滑可能发生在127 Ma左右。大别造山带中生代石英二长岩和二长岩体中暗色包体广泛发育。这些暗色包体具有典型的岩浆结构,与寄主岩有着相似的矿物组合,但矿物粒度更细,暗色矿物含量更高,岩性主要为闪长岩质。部分包体中发育钾长石斑晶和眼球状的石英,以及针状磷灰石。三个包体和一个寄主岩的锆石U-Pb定年表明,暗色包体的形成年龄主要为133~129 Ma,石英二长岩为130 Ma左右,表明包体与寄主岩的形成时代在误差范围内一致,都为早白垩世。单矿物的电子探针分析得到,二者矿物化学组分相似,形成的温压条件相仿,且包体中存在地幔物质的加入。在地球化学方面,包体和寄主岩的主量元素组成在Hacker图解中呈现出明显的线性关系。二者都较富集轻稀土元素和大离子亲石元素,亏损高场强元素,稀土元素配分图和微量元素蛛网图的配分模式表现出相似的特点,说明包体和寄主岩之间存在成因联系。综合包体和寄主岩的岩石学矿物学特点、锆石U-Pb年龄和相关地球化学特征,本文认为大别地区发育的暗色包体是岩浆混合作用的结果。早白垩世幔源岩浆底侵,诱发下地壳物质的部分熔融,进而发生铁镁质岩浆和长英质岩浆的混合作用。更多还原

【Abstract】 NNE-striking dike swarm,which are widespread in the Dabie orogen,are consisted by different rock types with familiar quartz-syenite porphyry,granite porphyry,quartz-diorite and diabase.These dikes cut through the Yanshanian intrusive bodies,indicating the dikes were the latest stage Yanshanian magmatic activity.LA-ICPMS zircon U-Pb dating yield weighted mean ages of 127.1±4.5 Ma,127.5 ±1.9 Ma,127.4±2.5 Ma and 127.9±2.1 Ma for the quartz-syenite porphyry,quartz-diorite and granite porphyry,respectively.The results reveal that the dikes are generated during a short time span and formed in the early Cretaceous,representing the termination of Mesozoic magmatism in this region.Owing to the sinistral strike-slip movement of the Tan-Lu fault zone,the dike swarm intruded along the shear-tensile cracks.The ages of these dikes indicate that the third sinistral strike-slip movement of the TLFZ might take place around 127 Ma.There are a large number of mafic enclaves occurring in Mesozoic quartz monzonite and monzonite in the Dabie orogen.Mafic dioritic enclaves,with a finer mineral size and more melanocratic mineral,have the typical magma structures and similar mineral assemblages to host rocks.K-feldspar porphyroblasts and augen quartz occur in some enclaves,and acicular apatite is common.The zircon U-Pb dating of enclaves and host rocks are about 133~129 Ma and 130 Ma respectively,suggest that the formation age of enclaves and host rocks were coeval in the error range and they were formed in the early Cretaceous.The results of electron microprobe analysis show that the minerals’ chemical compositions between enclaves and host rocks are similar,the temperature and pressure conditions are similar too.And there are additions of mantle material in the mafic enclaves.Geochemical data show that enclaves and host rocks have a clear linear relationship in the Hacker diagrams constructed by major elements.Meanwhile,the host and enclaves are all enriched in LILEs and LREEs and depleted in HFSEs and show.show similar REE and trace elements distributed patterns,suggest that they have genetic relation.Through the system analysis of petrograhic,mineralogical,zircon U-Pb dating and geochemical for mafic enclaves and host rocks,it is suggested that mafic enclaves are formed by magma mixing.In the early Cretaceous,the mantle derived magma underplated to the lower crust,and leads to partial melting of crust and mixing of mafic magma and felsic magma.更多还原