勉略缝合带三岔子辉绿岩墙锆石U-Pb年龄及Hf同位素组成——古特提斯洋壳俯冲的年代学证据  

Zircon U-Pb Dating and Hf Isotopic Composition of the Diabase Dike Swarm from Sanchazi Area,Mianlue Suture——Chronology Evidence for the Paleo-Tethys Oceanic Crust Subduction

作　　者：赖绍聪[1,2] 秦江锋[1,2] 

机构地区：[1]西北大学大陆动力学国家重点实验室,陕西西安710069 [2]西北大学地质学系,陕西西安710069

出　　处：《地球科学与环境学报》2010年第1期27-33,共7页Journal of Earth Sciences and Environment

基　　金：国家自然科学基金项目(40872060);陕西省教育厅省级重点实验室科研与建设计划项目(08JZ62);西北大学大陆动力学国家重点实验室科技部专项项目

摘　　要：为了弄清楚勉略构造带中三岔子岛弧火山岩的形成时代及源区特征,对南秦岭勉略缝合带三岔子岛弧蛇绿混杂岩中的辉绿岩墙样品进行了锆石U-Pb年代学、锆石Hf同位素组成及微量元素组成研究。结果表明,三岔子辉绿岩中的锆石主要包括2个年龄区间:有8颗锆石记录古生代年龄信息,其n(206Pb)/n(238U)年龄为264~487 Ma,w(Th)/w(U)为0.4~0.8,其中有6颗锆石的N(176Hf)/N(177Hf)初始值为0.281 934~0.282 292,对应的εHf(t)值为-9.4^-16.4,为典型的壳源岩浆锆石,另外2个测点(BQG-014,BQG-021)的N(176Hf)/N(177Hf)为0.282 722~0.282 798,对应的εHf(t)值为4.5~6.3,为典型的幔源岩浆锆石;有15颗锆石记录了元古代—太古代的年龄信息,N(207Pb)/N(206Pb)年龄主要为1 713~2 559 Ma,N(176Hf)/N(177Hf)初始值为0.281 288~0.282 263,对应的εHf(t)值为-1.3~8.7,绝大部分锆石的εHf(t)值大于2,显示出幔源岩浆锆石的特征。根据锆石Hf同位素组成,BQG-014和BQG-021样品为典型的幔源岩浆锆石,因此,其形成年龄(264~295 Ma)应代表了勉略洋消减过程中一次重要的大陆弧岩浆作用时间。In order to make it clear that the {ormation age and source region of Sanchazi island arc volcanic rocks from the Mianlue suture, Ziron U-Pb dating, Hf isotopic composition and trace element concentration on the Diabase dike swarm collected from island-arc ophiolitic mdlange in Mianlue suture, south Qinling are studied. The result indicates two time periods of the zircon UPb ages. There are eight zirons recording the Paleozoic U-Pb ages, six of them are typical crust originated magmatic, n（Pb）/n（238U）=264-487 Ma, w（Th）/w（U）=0. 4～0. 8, N（176 Hf）/N（177 Hf） =0. 281 934～0. 282 292,εHf（t）=-9.4～-16.4, the other two Zirons in two test points （BQG 014, BQG-021） are typical mantle originated magmatic, N（176Hf）/N（177Hf）=0.282 722～0.282 798, εHf（t）=4.5～6.3. There are fifteen zirons recording the Proterozoic Archean U Pb ages, Zircon shows distinct geo of mantle magmatic origination, N（207 Pb）/N（206 Pb） = 1 713～ 2 559 Ma, N（176 Hf）/N=0. 281 288 --0. 282 263, εHf（t） 1.3 ～ 8. 7, and most exhibit εHf（t）〉 2. According to the zircon Hf isotopic composition,Ziron in two test points （BQG-014, BQG-021） is typical mantle originated magmatic; therefore, their forming age （264～295 Ma） indicates an important active continental margin magmatism during the Mianlue ancient ocean crust subduction process.

关 键 词：锆石 U-Pb定年 HF同位素 勉略洋 岛弧 三岔子 

分 类 号：P588.1[天文地球—岩石学]