东昆仑造山带早古生代的大陆碰撞:来自榴辉岩原岩性质的证据  

Paleozoic continental collision of the East Kunlun orogen:Evidence from protoliths of the eclogites

作　　者：孟繁聪[1] 崔美慧[1] 贾丽辉[1] 任玉峰[1] 冯惠彬 

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

出　　处：《岩石学报》2015年第12期3581-3594,共14页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41272052);中国地质调查局项目(1212010918003;1212011120158;12120114080101;12120115027001)联合资助

摘　　要：东昆仑东段温泉榴辉岩呈透镜状分布在片麻岩中,榴辉岩的SiO_2含量为47%~59%,Mg#指数为0.45~0.51,表明其原岩为分异程度较高的中-基性岩石,稀土元素显示为轻稀土富集型((La/Sm)N比值为1.42~1.72)和轻稀土亏损型((La/Sm)N比值为0.82~0.88),Eu轻微负异常(δEu=0.85~0.95),榴辉岩的εNd(t)值为+0.51^+6.17(原岩年龄t=934Ma)。榴辉岩原岩锆石与陆壳辉长岩锆石的U-Yb-Hf值类似,且具有正的εHf(t)值(+8^+10),这些特征类似于大陆拉斑玄武质岩,岩浆来自亏损地幔,遭受了地壳物质的混染及较高程度的结晶分异,表明榴辉岩原岩形成于大陆边缘环境。因此,该榴辉岩代表了俯冲的陆壳,进一步证明了东昆仑早古生代发生过陆-陆碰撞造山作用。Eclogites as lenses occur in the Proterozoic paragneiss at eastern segment of the East Kunlun orogen,with SiO_2 contents varying from 47% to 59% and Mg#from 0. 45 to 0. 51,implying that protoliths of the eclogites were basic-intermediate and highly fractionated. Chondrite-normalized REE patterns show slight enrichment and depleted in LREE（（ La / Sm）N= 1. 42 ~ 1. 72 and 0. 8 ~0. 88,respectively）,with weakly negative anomaly of Eu（ δEu = 0. 85 ~ 0. 95）. The eclogites have positive whole-rock εNd（ t） values of ＋ 0. 51 ~ ＋ 6. 17（ t = 934 Ma,age of protolith）. The features that U-Yb-Hf concentrations as well as positive εHf（ t）（ ＋ 8 ~ ＋ 10）of the zircons from protolith of the eclogites are similar to those from continental gabbros and continental tholeiitic basalt,indicating that the basic parental magma were derived from depleted mantle,contaminated by crust and highly fractionated during ascending to continent. Later they subducted and metamorphosed into eclogite. Therefore,the protoliths of the eclogites formed in continental margin setting,and represented the relics of subduction continent crust. This demonstrates that the East Kunlun orogen underwent continentcontinent collision in the Early Paleozoic.

关 键 词：榴辉岩 地球化学 ND同位素 锆石 HF同位素 东昆仑 

分 类 号：P588.348[天文地球—岩石学]