洞错盆地蛇绿岩地球化学特征及大地构造意义

本文以改则的洞错盆地蛇绿岩为研究对象，开展了洞错盆地蛇绿岩的岩石学、岩相学及地球化学方面的研究工作。结果表明：地幔橄榄岩以方辉橄榄岩为主，为烟斗型稀土元素配分型式；形成于熔融程度较高的地幔残余物质，具有Nb、Ta负异常。辉绿岩稀土元素配分型式与N-MORB类似，其稀土元素来自亏损的软流圈地幔；Ta、Ti、Y等高场强元素分布特征与N-MORB相似；辉绿岩既有MORB特征又有IAT特征，在洋内弧后盆地扩张环境中形成。辉长岩稀土配分曲线与N-MORB的类似；微量元素中K、Rb、Ba等富集，Nb、Ta亏损，有岛弧火山岩的特征，与典型的N-MORB特征有区别；既有MORB特征，也显示了俯冲带物质的参与，为消减带上弧后盆地次级扩张产生的新洋壳。因此，洞错蛇绿岩为SSZ型蛇绿岩。

Geochemical characteristics of ophiolite in Dongcuo basin and the geotectonic signoficance

This paper deals with petrology, petrography and geochemistry of ophiolite in Dongcuo basin. The mantle Peridotite is mainly harzburgite with tobacco pipe-like REE pattern and negative Nb, Ta anomaly. The harzburgite is derived from highly melted residual mantle materials. REE of the diabase come from depleted astheno-sphere mantle and the distribution pattern as well as the distribution pattern of high field strength elements of Ta, Ti, Y etc. is similar to that of N-MORB. The diabase shares characteristics of MORB and IAT suggesting that it is formed in the spreading environment of intra-ocean back basin. REE pattern of the gabbro is similar to that of N-MORB with K, Rb and Ba enrichment and Nb, Ta depletion sharing characteristics of island arc volcanic rock. The pattern differs from typical N-MORB and suggests not only characteristics of MORB but also incorperation of the subduction materials. The gabbro should be new ocean crust generated by sub-spreading of back arc basin on the subduction zone. The ophiolite in Dongcuo basin belongs to SSZ type ophiolite.