内蒙古金厂沟梁地区晚三叠世脉岩地球化学特征及成岩动力学背景  

Petrogenesis and Geodynamic Setting of Late Triassic Dykes of Jinchanggouliang,Eastern Inner Mongolia

作　　者：付乐兵[1] 魏俊浩[1] 魏启荣[1] 谭俊[1] 李艳军[1] 李闫华[2] 王明志[1] 蒋永建[1] 

机构地区：[1]中国地质大学资源学院,湖北武汉430074 [2]宜昌地质矿产研究所,湖北宜昌443005

出　　处：《地球科学（中国地质大学学报）》2010年第6期933-946,共14页Earth Science-Journal of China University of Geosciences

基　　金：教育部创新团队发展计划(No.IRT0755);全国危机矿山接替资源找矿项目(No.200714010);中国地质大学(武汉)地质过程与矿产资源国家重点实验室基金;中国地质大学(武汉)研究生学术探索基金(No.CUGYJS0812)

摘　　要：金厂沟梁位于张家口-赤峰-朝阳金矿集区东端,区内发育大量规模不等的脉岩,岩性以闪长岩、闪长玢岩为主.对其进行了锆石U-Pb年龄、主微量元素及Sr-Nd同位素分析.脉岩锆石LA-ICP-MS U-Pb年龄值可分为三组:2458～2524Ma、253±6Ma(MSWD=3.0)及228±1Ma(MSWD=0.26).2.5Ga锆石反映成岩过程中有古老地壳物质参与,253 Ma锆石可能与古亚洲洋闭合时的岩浆事件有关,228 Ma则为脉岩的形成年龄.脉岩Si O2(51.22%～68.48%)、MgO(1.35%～8.13%)含量变化较大,且具有高Na2O+K2O、Al2O3及低的TiO2、P2O5含量等特征.岩石LREE及LILE富集,HFSE亏损.脉岩(87Sr/86Sr)i比值较为一致(0.70495～0.70592),而εNd(t)(-0.2～-9.5)及T2DM(1.02～1.77Ga)值变化范围较大.主微量元素及同位素研究结果表明:部分熔融的岩石圈地幔熔体底侵到壳幔边界,诱发古老地壳物质的部分熔融,随后发生的幔源熔体与壳源熔体的混合是脉岩最可能的源区过程.主微量元素构造判别图解指示岩石形成于陆弧向板内演化的构造环境;结合区域上同时代脉岩群、碱性岩带及A2型花岗岩的侵位,认为晚三叠世华北板块北缘已完成与蒙古弧地体的碰撞并进入造山后伸展阶段.Jinchanggouliang region,which consists of Jinchanggouliang,Erdaogou and Xiaoerdaogou gold deposits,is located in the north of North China Craton（NCC） and south of Inner Mongolia-Daxinganling orogenic belt.Numerous early Mesozoic diorites and diorite porphyries occurred and yielded LA-ICP-MS zircon U-Pb age of 228±1 Ma（MSWD=0.26） in the region.Both diorites and diorite porphyries are dominated by shoshonitic rocks,which contain SiO2 ranging from 51.22% to 68.48% and MgO from 1.35% to 8.13%,and are characterized by high contents of Na2O＋K2O and Al2O3 but low concentrations of P2O5.These rocks are enriched in LREE,LILE but depleted in HFSE.All samples possess uniform（87Sr/86Sr）i isotopic ratios（0.704 95-0.705 92） but relatively wider range of εNd（t）（-0.2 to-9.5） and T2DM ages（1.02-1.77 Ga）.These results indicate that the magma source derived from mixing of lithospheric mantle and lower crust melt.Diagrams of major and trace elements reveal that dykes formed in transitional environment between land arc and intra-plate.Combined with some new discoveries in the neighborhood,such as dyke swarms,alkaline intrusive complex and A2-type granite,this study proposes that NCB had completed the collision with Siberia plate in Late Triassic and the north of NCC went into a post-orogenic extension stage.

关 键 词：脉岩 三叠纪 造山后伸展 地球化学 地质年代 内蒙古. 

分 类 号：P597[天文地球—地球化学]