西天山高压脉及主岩的氧同位素研究——古俯冲带深部流体及俯冲特征的启示  

Study on oxygen isotope of high-pressure veins and host-rocks from western Tianshan in China:implications for deep fluids flow and the characteristic of subduction.

作　　者：黄德志[1] 高俊[2] 张进富[1] 张德贤[1] 戴塔根[1] Reiner KLEMD 

机构地区：[1]中南大学地学与环境工程学院 [2]中国科学院地质与地球物理研究所 [3]Mineralogisches Institut,Universitt Würzburg,Am Hubland 97074,Würzburg,Germany

出　　处：《岩石学报》2006年第1期74-82,共9页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划项目(2001CB409803)研究成果。

摘　　要：位于中国南天山的西天山高压变质带代表了伊犁-中天山与塔里木两个板块间古生代南天山洋的古俯冲混杂岩带。高压变质带内广泛发育高压脉。为探讨古俯冲深部流体来源及运移特点及板块俯冲特征，对高压脉和主岩的全岩及主要的高压变质矿物的氧同位素进行了分析。高压脉的δ^18O值变化于＋8．28‰与＋10．70‰之间，多数在＋9．50‰±1范围内。基性变质岩的主岩与高压脉具相似的氧同位素组成，变化于＋9．25‰～＋10．10‰之间。高压脉和主岩的全岩δ^18O值变化不大。高压脉与相邻主岩间、同一高压脉中间与边部间氧同位素组成的变化没有明显的规律，一般变化不大，对于大多数脉-主岩对，变化小于1‰。与全岩完全不同的是，单矿物氧同位素组成显示出很大的变化范围，石英、石榴石、绿辉石的δ^18O值分别为＋11．40‰～＋15．20‰，＋3．59‰-＋11．60‰和＋8．30‰～＋13．05‰，多硅白云母和蓝闪石δ^18O的变化较小，分别为＋10．00‰～＋11．10‰和＋9．26‰-＋9．94‰。榴辉质岩石中高压变质矿物间氧同位素分馏广泛不平衡。全岩氧同位素组成特征表明，俯冲带深部流体主体来自邻近主岩，外来流体对氧同位素贡献有限。单矿物氧同位素广泛不平衡特征可能指示古俯冲带俯冲板片的快速俯冲和折返以及部分外来流体的参与。The western Tianshan high-pressure （HP） metamorphic belt, which is probably to represent paleosubduction mrlange of Paleozoic south Tianshan ocean between the Yili-central Tianshan and Tarim plates, is situated in the south Tianshan Mountains in China. High-pressure veins are extensively developed in this HP belt. Analyses of oxygen isotope of main HP-metamorphic mineral separates and whole rocks are conducted for HP veins and host rocks in order to get inquiring into the sources and flows of deep fluids in the paleo-subduction zone and the characteristic of the subduction of the slab. The δ^18O values of high-pressure vein are from 8.28‰ to ＋ 10.70‰, most of which are at the range of ＋ 9.50‰± 1. The metabasic host rocks have the similar range of δ^18O values （ ＋9.25‰- ＋ 10.10‰） to the high-pressure veins. Both of veins and host rocks don＇t show large variations in δ^18O values. The variations in oxygen isotope ratios between a vein and its host rocks or between the center and the rim of a single vein are irregular. Generally, these variations are not significant. For most pairs, the variations in δ^18O values are less than 1‰. Contrary to whole rocks, mineral separates show a very large range of oxygen isotopic composition. The δ^18O values of quartz, garnet and omphacite separates are ＋ 11.40‰ - ＋ 15.20‰, ＋ 3.59‰ - ＋ 11.60‰ and ＋ 8.30‰ - ＋ 13.05‰ separately. Phengites and glaucophanes show narrow ranges of δ^18O value, which are ＋ 10.00‰ - ＋ 11. 10‰ and ＋ 9.26‰ - ＋ 9. 94‰ respectively. The oxygen isotope fractionations between various HP metamorphic minerals in eclogitic rocks from western Tianshan are extensively disequilibria at peak metamorphic temperature. The data of oxygen isotope of whole rocks indicates that the deep fluids in the paleosubduction zones mainly originated from adjacent host-rocks. The extensively disequilibria of oxygen isotope fractionations between minerals probably shows that the subduction and exhumation of t

关 键 词：高压脉 主岩 氧同位素 俯冲带深部流体 西天山 

分 类 号：P597.2[天文地球—地球化学]