柴北缘都兰UHP地体中两期不同性质的岩浆活动:对碰撞造山作用的启示  

Two constrasting magmatic events in the Dulan UHP metamorphic terrane:Implication for collisional orogeny

作　　者：于胜尧[1,2] 张建新[1,2] 侯可军[3] 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]大陆构造与动力学国家重点实验室,北京100037 [3]中国地质科学院矿产资源研究所,北京100037

出　　处：《岩石学报》2011年第11期3335-3349,共15页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41072151;40921001);中国地质调查项目(1212011120157)联合资助

摘　　要：本文报道了对柴北缘都兰地区英云闪长岩、花岗岩的地球化学、锆石U-Pb定年和Hf同位素的研究结果。锆石U-Pb定年结果表明,英云闪长岩侵位时代为432～434Ma,并显示出类似于埃达克质岩石的地球化学特征:(1)高SiO2、富Na2O、贫K2O、过铝质;(2)高Sr、低Y和相应的高Sr/Y值;(3)高La/Yb和低Yb;(4)轻重稀土分馏程度高,亏损重稀土;(5)富集Ba、Sr等大离子亲石元素,而亏损Nb、Ta等高场强元素。结合英云闪长岩高的εHf(t)值(3.3～10.7)和年轻的地壳模式年龄(732～1207Ma),可以认为本区英云闪长岩源自于增厚下地壳的部分熔融作用。锆石U-Pb定年结果表明,晚期花岗岩的结晶时代为382～391Ma,并显示出类似于S型花岗岩的地球化学特征:(1)高SiO2,低MgO和高K2O的特征,K2O/Na2O>1;(2)A/CNK几乎全部大于1,显示过铝质的特征;(3)轻、重稀土分馏程度低,(La/Yb)N=2.22～9.62,但具明显的负Eu异常(δEu=0.27～0.81);(4)强烈亏损Nb、Ta、Sr和Ti等元素,轻微亏损Ba元素。在综合对比花岗岩形成年龄与区域高压-超高压变质时代的基础上,结合地球化学特征,推断都兰地区花岗岩体可能形成于后碰撞造山伸展作用阶段,并可能是由其围岩富铝质片麻岩部分熔融形成,并可能有少量地幔物质的添加。In this article,we report the geochemical,zircon U-Pb dating and Hf isotopic data for tonalite and granite from Dulan area,the North Qaidam Mountains.Zircon U-Pb dating result indicates that the tonalite was emplaced at 432～434Ma,which shows a geochemical resemblance to adakite：（1） high SiO2,enriched in Na2O and depleted in K2O,and peraluminous;（2） high Sr and low Y,and thus corresponding to high Sr/Y;（3） high La/Yb amd low Yb;（4） depleted in HREE,and thus strongly partition between HREE and LREE;（5） enriched in LILE including Ba and Sr,depleted in HFSE such as Nb and Ta.In combination with the high εHf（t） values（3.3～10.7） and young crustal model age of 732～1207Ma,the tonalite was suggested to derived from partial melting of thickened basaltic lower crust.Zircon U-Pb dating result indicates that the granite was emplaced at 382～391Ma,and the granite shows geochemical character similar to S-type granite as followings：（1） high SiO2 and K2O,and low MgO,with K2O/Na2O values greater than 1.0;（2） peraluminous with A/CNK greater than 1.0;（3） slightly partition between LREE and HREE（La/Yb）N=2.22～9.62）,with negative Eu anomalies ranging from 0.27 to 0.81;（4） strongly depleted in Nb,Ta,Sr and Ti,and slightly depleted in Ba.On the basis of the age interval between granite and HP/UHP metamorphic event,in combination with the geochemical characteristic,the granite was suggested to derive from the partial melting of its country rock Al-rich gneiss with input of minor mantle material in post-collisional extension stage.

关 键 词：构造热事件 锆石U-Pb定年 HF同位素 都兰 柴北缘 

分 类 号：P542[天文地球—构造地质学]