Three types of dunite occur in the Luobusa ophiolite, a thick layer of transition zone dunite, thin envelopes of dunite around podiform chromitites and small hands and lenses of dunite in the harzburgites, respectively. The transition zone dunite is about 700 ~ 1000m thick, and consists chiefly of high magnesium olivine (Fo93.95) ,low alumina and high magnesia clinopyroxene (A12O3 = 0. 47% ~ 0. 85% ; Mg = 95 ~ 97) , and high chrome and low magnesia Cr-spinel (Cr = ~ 77; Mg = ~ 51). Cr spinels in layers of disseminated chromite hosted in these dunites are similar in composition to those of the host rock but are slightly more magnesian (Mg = ~59) The dunite envelopes around the podiform chromitites are similar in composition to the transition zone dunite (obvine Fo92-94; A12O3 in clinopyroxene <1% and Mg =95 -97; Cr in Cr-spinel = 71 and Mg =52). The massive chromitites associated with the dunite envelopes have Cr's averaging 79 and Mg's averaging 68. The dunite lenses in harzburgite have olivine with somewhat lower Fo (91 -92) and Cr-spinel with lower Cr s (about 60), but clinopyroxene with higher A12O3(1.41% ~ 1.71%). The mineral compositions in these lenses overlap those in the host harzburgite, with a gradual transition between them. The transition zone dunite in the Luobusa ophiolite is distinctly different from classic ultramafic cumulates, and most likely formed by reaction between tholeiitic basalt melt and mantle peridotite. Dunite lenses in the harzburgite may reflect either inhomogeneous partial melting of the host peridotites or in-situ melt-rock reaction. The dunite envelopes around the podiform chromitites are thought to have formed in the same way as the transition zone dunite, but the origin of the massive chromitites is not clear.%罗布莎蛇绿岩中的纯橄岩有三种产出情况,除了与豆荚状铬铁矿伴生的薄壳状纯橄岩外,还有产在方辉橄榄岩底部被认为是堆晶岩的厚层状纯橄岩和方辉橄榄岩中的透镜状纯橄岩.厚层状纯橄岩约700 ～ 1000m厚,以橄榄石富镁(Fo 93～95),单斜辉石低铝富镁(Al2O30.47％ ～0.85％,Mg# 95 ～ 97),铬尖晶石高铬低镁(Cr#值平均77,Mg#平均51)为特征.该纯橄岩中的浸染状铬铁矿也是高铬低镁型,但Mg#值(平均59)高于厚层状纯橄岩的副矿物铬尖晶石.薄壳状纯橄岩与厚层状纯橄岩成分相近,其橄榄石Fo 92 ～ 94,单斜辉石Al2O3 ＜1％和Mg# 95～ 97；铬尖晶石的Cr#值平均71,Mg#值平均52.与薄壳状纯橄岩伴生的块状铬铁矿为高镁高铬型,但Mg#值(平均68)相对更高些,Cr#值平均79.透镜状纯橄岩的特征是橄榄石Fo(91～92)和铬尖晶石Cr#(60左右)均低于前两类纯橄岩,但单斜辉石的Al2O3(1.41％ ～1.71％)则高于前两者.透镜状纯橄岩的矿物成分与方辉橄榄岩重叠,两者为渐变过渡关系.研究对比表明,罗布莎厚层状纯橄岩不同于经典的蛇绿岩的超镁铁质堆晶岩,认为将其成因解释为拉斑玄武质熔体与地幔橄榄岩的反应较为合理.透镜状纯橄岩与方辉橄榄岩存在成生联系,可能是地幔橄榄岩高度部分熔融的产物,或熔体和方辉橄榄岩在原位发生反应的产物；薄壳状纯橄岩成因与厚层状纯橄岩相同,但与其相伴的块状铬铁矿是否由拉斑玄武质熔体与方辉橄榄岩反应形成,值得商榷.
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