【摘要】 双沟蛇绿岩由基底岩石、辉长—辉绿岩和玄武岩三部分组成。岩相学和地球化学研究表明,双沟斜长二辉橄榄岩中存在地幔交代作用的证据,属于浸染橄榄岩(impregnated peridotite)。蛇绿岩岩石组合中缺少超镁铁质堆晶岩和席状岩墙群,而辉绿岩和玄武岩的化学成分与MORB相拟,表明双沟蛇绿岩的形成机制与大洋中脊环境类似,但岩浆房很小,扩张速度缓慢,推测相当于哀牢山古特提斯小洋盆扩张早期的裂谷阶段的产物。更多还原

【Abstract】 The Ailao shan Mountain Ophiolite Belt is situated between the Yangtze Block and the Lincang Block. Shuanggou Ophiolite is exposed to the south of The Ailao shan Mountain Ophiolite Zone and is typical of Palaeo-Tethyan ophiolites. Shuanggou Ophiolite is composed of ophiolite melange, in which large ophiolite sheets include three petrologic unites from bottom to top: plagioclase lherzolite and spinel harzburgite, gabbro and diabase, and basalt which are overlain by slightly metamorphosed detrital rocks （Pz?） intercalated with basaltic rocks and a few radiolarianbearing siliceous rocks.The basement rocks in Shuanggou Ophiolite are mainly composed of Plagioclaselherzolite and spinel-harzburgite. The remnant microstrectures of peridotites indicate the feature of plastic flow deformation under high temperature and low stress rate in an upper mantis condition. But the most typical microstrictures in pIagioclese-lherzolite is magmatic impregnation which shows three patterns: glomerocryst of clinopyroxenes, colourless and dark isotopic patches. The Cpx is commonly associated with the elongate, subparallel, irregular dark-brown isotopic patches with high Ca, Al, and Si contents that appear to be altered plagioclase. The better crystallized patches contain grains of hydrsgarnct and gressular. The colourless patches are mainly composed of chlorite which is usually acompanied by lobate and dropped spinel. The segregations of Cpx, P1, Ch1 and Sp have been interpreted as solidified Dockets of in situ partial melts er as liquids that infiltrated a harzburgite host. It is known that these sgregatiors and their host should be referred to as "impregnated peridotites" and represent evidence of initial partial melting or metasomatism of mantle.In chemical compositions, Plagioclase-lherzolites within Shuanggou Ophiolite are rich in Si, Al, Ti, Ca, K, Na, V and LIL elements（e. g. Sr and Ba）comparing with the typical harzburgites, such as in Troodos. So the metamorphic peridotite is characterized by richness of compatible elements and depletion of incompatible elements, but the impregnated peridotites are rich both in compatible and in incompatible elements.The ultramafic cumulates and sheet dyke swarms are less developed or of nearly lacked here. It indicates that magma reservoir is small beneath the ocean floor and the spreading velocity of ocean basin is very slow.The diabases are poor in Al and the plagioclase basalts are rich in Al and then they can be divided into low-Al and high-Al subtypes. Their content range of TiO₂, MgO are similar, but the trace element abundances and ratios clearly differ from each other. It is suggested that diabases and PIagioclase-basalts came from different source respectively, although they have relations in origin. The geochemistry shows that both diabases and Plagioclase-basalts are similar to MORB, and differ from IAT. It is suggested that the origin of Shuanggou Ophiolite was not related to plate subduction. According to Ti/V ratios of diabases and Plagioclasebasalts, the former resembles N-MORB and the latter is similar to E-MORB, which implies an addition of materials derived from enriched mantle source. It is possible that the Shuanggou Ophiolite is formed in a rift environment during early openning stage in a small ocean basin.更多还原