罗布莎蛇绿岩地幔橄榄岩同位素特征及其成因  

Sr-Nd-Pb Isotopic Characteristics and Origin of the Mantle Peridotites from the Luobusha Ophiolite

作　　者：程学展[1] 夏斌[2,3] 李建峰[3] 于漫[4] 钟立峰[3] 黄强太[3] 施秋华[3] 

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]中山大学海洋学院,广东广州510275 [3]中国科学院广州地球化学研究所,广东广州510640 [4]兰州大学资源环境学院,甘肃兰州730000

出　　处：《大地构造与成矿学》2011年第1期85-94,共10页Geotectonica et Metallogenia

基　　金：国家自然科学基金项目(项目号:40534019)资助

摘　　要：罗布莎蛇绿岩岩石单元出露齐全,以地幔橄榄岩为主,构造变形强烈;在堆积杂岩中上部产出有仰冲型斜长花岗岩小岩块;辉绿岩以脉状形式产出于地幔橄榄岩的方辉橄榄岩中;壳层岩石相对很薄且比较复杂。Sr、Nd和Pb同位素组成研究表明:罗布莎地幔橄榄岩绝大多数样品具有高ISr值(0.705489～0.714625);低INd值(0.511796～0.512605),其Pb同位素组成具有高Δ7/4Pb、Δ8/4Pb值,大部分样品接近或大于典型Dupal端员的Pb同位素标准(Δ8/4Pb>60),结合罗布莎地幔橄榄岩具有高的ΔSr值(81.54～154.01),认为罗布莎地幔橄榄岩存在明显的Dupal异常。同时结合罗布莎地区的构造演化,认为罗布莎地区富集的、具有Dupal异常的地幔橄榄岩应当是在特提斯洋形成过程中的同化了俯冲板片携带的沉积物的深地幔柱交代影响下形成的。The Luobusha ophiolite consisting of a complete ophiolite sequences,is located in the eastern segment of the Yarlung Zangpo suture zone. It is characterized by the occurrence of the strongly deformed mantle peridotites,obduction type plagiogranites in the upper part of the cumulate sequence,diabasic dikes intruded the peridotites; and thin complicated crustal lavas. Isotopic study of the Luobusha peridotites reveals that the rocks are characterized by high initial 87Sr/86Sr （0.705489-0.714625）,low initial 143Nd/144Nd （0.511796-0.512605） ratios and variabale εNd（t） values,which are similar to those of EMI. The high Δ7/4Pb and Δ8/4Pb values exhibit a source with Dupal anomaly. Considering the known regional tectonic evolution,the Luobusha ophiolitic peridotites should have been formed under the influence of a mantle plume that assimilated sediments from subducted slab.

关 键 词：罗布莎 地幔橄榄岩 Sr、Nd、Pb同位素 DUPAL异常 

分 类 号：P597[天文地球—地球化学]