中文摘要：

蛇绿岩中的地幔橄榄岩是蛇绿岩的重要组成部分,不仅记录了其所经历的板块构造事件,还可以探讨地幔的物质组成和深部地幔作用。位于雅江缝合带西段的普兰蛇绿岩以出露面积约600 km2的特大型地幔橄榄岩体而引人注目。为了探讨普兰蛇绿岩地幔橄榄岩的成因,本文在普兰地幔橄榄岩体的东段完成了一条穿过岩体的长约10km的地质剖面,对地幔橄榄岩进行了系统采样,开展了详细矿物学、地球化学研究,取得以下主要进展和认识：（1）普兰地幔橄榄岩中的二辉橄榄岩经历了9%~15%的部分熔融作用,方辉橄榄岩最终经历了15%~25%的部分熔融作用;（2）基于橄榄石-尖晶石矿物化学平衡计算的普兰地幔橄榄岩氧逸度？log（fo2）FMQ值从-1.11到＋0.45,略高于用VY含量估算出的氧逸度（在FMQ到FMQ-1趋势）,指示其形成于还原环境;（3）普兰地幔橄榄岩不是简单的地幔残余,还经历了后期熔体交代作用。对普兰地幔橄榄岩交代产生类似＂U＂型稀土配分模式的熔体可能是洋中脊（MOR）环境产生的低融岩浆;（4）地幔橄榄岩地球化学特征及氧逸度计算结果表明,普兰地幔橄榄岩可能形成于洋中脊（MOR）环境,并没有俯冲带（SSZ）环境的印记。对于普兰地幔橄榄岩以及雅鲁藏布江缝合带其他岩体的成因,前人主要根据地幔橄榄岩一些元素的富集特征提出的MOR→SSZ两阶段演化模式需要重新审视。

英文摘要：

The ophiolitic peridotites constitute an important part of the ophiolite in that they not only record the experienced plate tectonic events but also offer help to discuss the composition of the mantle and the effect of the deep mantle. The Purang ophiolite located in the western part of Yarlung Zangbo suture zone is characterized by containing a large mantle peridotite massif ca.600km2 in area. In order to discuss the petrogenesis and tectonic significance of the Purang peridotite massif, the authors sampled a section of about 10 km across the massif in the eastern part of the Purang mantle peridotite massif. Based on a detailed field survey and mineralogical and geochemical analysis of systematically selected mantle peridotite samples, the authors have achieved some results：（1） The lithofacies distribution of the Purang ophiolite peridotites has been determined. The profile across the massif shows that harzburgites form the main part of the Purang peridotite massif, the harzburgites are mainly located within the peridotite massif,the banded lherzolites are mainly distributed at the edge of the peridotite massif, and the ratio of the exposed area of harzburgites to that of lherzolites is about 4：1;（2） Based on olivine- spinel associations and the formulae based on the reaction of 6Fe2 Si O4＋ O2=3Fe2Si2O6＋ 2Fe3O4, the oxygen fugacity values have been calculated（ ？ log（fo2）FMQ range from- 1.11 to ＋ 0.45）, which are significantly higher than the f O2 value obtained using the V content, indicating a reducing tectonic setting;（3） The Purang peridotites are not the simple residues of partial melting and might have experienced later melts metasomatism. According to the whole rock geochemistry and oxygen fugacity values, this paper argues that the later metasomatic melts were probably derived from the lower partial melting magma formed in a mid- ocean ridge setting;（4） The Purang ophiolite peridotites show similar bulk geochemical features and oxygen fugacity characteristics to the mod