河北都山杂岩体地球化学特征及其地质意义  

Geochemical characteristics of the Dushan complex and their geological significance

作　　者：吴鸣谦[1] 赵国春[1] 高建伟[2] 王海涛[1] 

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]国土资源实物地质资料中心,北京101149

出　　处：《中国地质》2014年第1期108-121,共14页Geology in China

基　　金：中国地质调查局地质调查工作项目(1212011121072)资助

摘　　要：都山杂岩体由不同岩性的花岗类岩石组成,主要包括细粒石英二长岩,中细粒黑云母二长花岗岩（中心相）和粗中粒黑云母正长花岗岩.前人的年龄数据表明该杂岩体中不同岩性的岩体是近乎同时就位的.本文通过野外观察岩体接触关系,结合室内研究,认为该杂岩体具有同源岩浆演化的特点,具有高SiO2（平均值为69.90％）,高A12O3（平均值为14.82％）,MgO小于3％（平均值为1.09％）,高Sr（平均值为917.18μg/g）低Y（平均值为5.44μug/g）,低Yb（平均值为0.50 μug/g）,（La/Yb）N＞1（平均值为50.95）,以及Nb/Ta比值负异常等特点,在埃达克岩Sr/Y-Y和Sr/Yb-Yb判别图中显示为埃达克质岩石.岩石中出现的强烈的Nb-Ta解耦现象很可能是继承源区组分的特点,推测其源区主要成分为华北克拉通内广泛发育的TTG岩套（英云闪长岩-奥长花岗岩-花岗闪长岩）,源区中也存在少量变质玄武岩和变沉积岩.通过对都山杂岩体的地球化学分析,认为强烈的Nb/Ta负异常,高（La/Yb）N,高Sr以及无明显的负Eu异常说明残留矿物组合应该为角闪石＋石榴石±少量斜长石,残留相为角闪榴辉岩相,残留矿物中无金红石,推测其形成时的地壳厚度为50～70 km.按照地壳均衡原理,其反映出的古山脉高度为3000～5000m.结合区内部分其他岩体的资料,认为西伯利亚板块与中朝古板块碰撞造山作用在中—晚三叠世时期仍在持续,此时的华北克拉通北东缘出现了高耸的山脉.The Dushan complex consists of granitic rocks with different lithologic types, which are fine-grained quartz monzonite, medium-fine-grained biotite monzogranite and coarse-medium-grained biotite syenogranite. Previous chronological data indicate that the emplacements of these rocks were almost synchronous. Through field work and indoor research, the authors have concluded that this complex was a product of comagmatic evolution. Geochemically, the Dushan complex shows high-silica （69.90% on average）, high-aluminum （14.82% on average）, low-magnesia （1.09% on average）, high-strontium （917.18/lg/g on average）, low- yttrium （5.44 ~g/g on average）, low-ytterbium （0.50 btg/g on average）, （La/Yb）N higher than 1 （50.95 on average） and negatively abnormal Nb/Ta. Features of plots on the Sr/Y-Y and Sr/Yb-Yb discrimination diagrams show that they are adakitic rocks. Strong Nb-Ta negative anomaly in samples implies that the Dushan complex may inherit the characteristics of protoliths which are possibly TTGs in this region. Although some metabasaltic and metasedimentary components were involved in protoliths, the TTGs might be the most important. Through geochemical analysis, the strong Nb/Ta anomaly, high （La/Yb）N and high Sr as well as inconspicuous Eu anomaly indicate that the residual mineral assemblages were amphibole ＋ garnet ~ plagioclase, and the residual phase was amphibole eclogite facies without rutile. The estimated thickness of the crust was 50-70 km, which in turn reflected the height of the paleomountains of 3000~5000 m. In the light of data of other batholiths in the region, the authors have concluded that the orogenesis between Siberia plate and Sino-Korean paleoplate was occurring during mid-late Triassic. At that time, towering mountain chains appeared in the northeast margin of North China Craton.

关 键 词：都山杂岩体 同源岩浆 埃达克质 华北克拉通北东缘 山脉 

分 类 号：P588.121[天文地球—岩石学]