西藏西南部拉昂错地幔橄榄岩的地球化学特征及其构造意义  

Geochemistry and tectonic significance of mantle peridotites from the Laangcuo ophiolite massif, southwest Tibet

作　　者：徐德明[1] 黄圭成[1] 雷义均[1] 

机构地区：[1]宜昌地质矿产研究所,湖北宜昌443003

出　　处：《岩石矿物学杂志》2008年第1期1-13,共13页Acta Petrologica et Mineralogica

基　　金：中国地质调查局资源评价项目"西藏雅鲁藏布江西段铬铁矿资源远景调查"(1212010530108)

摘　　要：拉昂错蛇绿岩位于西藏西南部雅鲁藏布缝合带（YZSZ）的西段，由地幔橄榄岩和侵入其中的基性岩墙组成。拉昂错地幔橄榄岩普遍发育碎斑结构及熔体注入和交代结构，尖晶石的Cr^#值具有较广泛的变化（0．32～0．70），大多数样品富集LREE并伴随HFSE的明显增加，少数亏损LREE，前者部分熔融程度为15％～23％，后者为10％左右，这表明它们并不是地幔单阶段部分熔融的残余物，而是MORB型亏损橄榄岩在俯冲过程中再度部分熔融后熔体与残余地幔相互作用的产物，由于熔体不同程度的混合与交代，形成了各种再饱满程度不同的橄榄岩。对拉昂错地幔橄榄岩岩石学和地球化学特征的研究，为探讨YZSZ蛇绿岩带所代表的特提斯洋盆的形成和演化提供了新的证据。The Laangcuo ophiolite massif situated in southwest Tibet and the western part of the Yalung Zangbo Suture Zone （YZSZ） consists of mantle peridotites and intruded basaltic dikes. The Laangcuo peridotites exhibit a typical porphyroclastic texture as well as melt impregnation and metasomatism textures. Cr^# values of spinel in peridotites vary broadly from 0.32 to 0.70. Most of samples are LREE-enriched ones associated with increasing HFSE, but a few samples are LREE-depleted. The former underwent a high degree of partial melting （15 %- 23 % ）, whereas the latter experienced a slight partial melting （ -10%）. These features show that the Laangcuo peridotites were formed by partial re-melting of MORB-type depleted peridotites during the subduction and reformed by interaction between the melt and the residual mantle, but they were not residues of pyrolite formed directly after the single-phase partial melting. As a result of different degrees of mixing and metasomatism between the melt and the residual mantle, peridotites of different degrees of maturity were formed. Petrographic and geochemical studies of the Laangcuo peridotites provide new evidence for the formation and evolution of the Tethys oceanic basin represented by the YZSZ ophiolite zone.

关 键 词：地幔橄榄岩 地球化学 地幔熔融 熔体/地幔相互作用 西藏西南部拉昂错 

分 类 号：P588.1[天文地球—岩石学] P618.51[天文地球—地质学]