【摘要】 <正> 铜厂街蛇绿混杂岩位于晚古生代的昌宁—孟连蛇绿岩带的北部。杨嘉文最早报道了该区蛇绿岩,认为铜厂街蛇绿岩属于“陆间裂谷型”。根据我们对该区的初步调查,本文探讨了该区蛇绿岩的性质,成因及构造环境。铜厂街蛇绿岩经历了强烈的构造破坏,洋壳和上地幔成分与陆壳浅海灰岩混杂在一起,组成蛇绿混杂岩。蛇绿混杂岩中的火山岩可分为两类,更多还原

【Abstract】 Tongchangjie Ophiolite Melange is situated in the northern part of Changning-Menlian Ophiolite belt and composed of deep sea sediments, ophiolite and allochthonous limestone blocks which were undergone strongly tectonic deformation all together. The ophiolite includes harzburgite, cumulate websterite, gabbro and basalt which are accompanied by radiolarian siliceous rock and flyschlike sediments.Two groups of basalts are found in Tongchangjie area. The firstgroup has only undergone a low-grade metamorphism and contains some se- condary hydrous minerals such as actinolite,episode,chlorite,and muscovite etc. which are considered as greenschest facies.The chemical compositions are characterized by high-Fe, and low-Mg contents.usually it contains normative quartz and hence is commonly referred to as a more evolved rock. Some trace element ratios from metabasalts,such as K/Rb=439,Sr/Rb=54,and Ti/Y=407,are almost similar to that of E-type MORB （above-mentioned ratios of the E-type MORB are 492,46,and 400,respectively）.REE patterns show slight LREE-depleted with （La/Sm）_N=0.70 and（La/Yb）_N=0.93, however, （La/Ce）_N=1.0 indicates that the metabasalts from Tongchangjie area are similar to,but not necessarily diagnostic of, typical N-type MORB.According to some effective deferminative plots for basaltic rocks such as Zr vs.Ti,Ti vs.Cr,Ti/Cr vs.Ni,and TiO₂vs.Y the metabasalts from Tongchangjie area are also similar to the ocean ridge basalts.The second group is high-Ti basalts which are characterized by the presence of plagioclase phenocryst.All of them are almost fall into the field of plagioclase-tholeiite in the triangular diagram of normalized pl-px-ol. Some dots falling on plagioclase-pyroxene join indicate that plagioclase and pyroxene control the process of fractional crystallization of magma and can be considered as a more evolved rocks.The high-Ti basalts are similar in composition to the metabasalts as exemplified by their high-Fe and low Mg contents. They differ from the metabasalts by their high P,K,Na,Zr,Y,Ba,Rb,and their REE strongly fractional patterns. It is posible that the high-Ti basalts have undergone a low pressure fractionation in terms of their lower Mg’（average 0.43）which are also considered to be more evolved rocks during fractional process of magma.Some incompatible element ratios of the high-Ti basalts from Tongchangjie area, such as K/Rb=529,K/Ba=10,Sr/Rb=26,and Ti/V=68 are similar to oceanic island basalts within ocean basin（latter corresponding ratios are 436,25,36, and more than 50, respe ctively）. The patterns of LREE strongly enriched and HREE distinctly depleted also support the above concluction.Two groups of basalt show obvious differences in terms of major and trace elements which indicate that they could derive from different sources, respectively. The metabasalts with low REE contents and LREE-depleted patterns couldbe derived from a typical large ion lithophile element （LILE）-depleted mantlesource,while the high-Ti basalts with LILE-enriched and the REE strongly fractional patterns are derived from a LILE-enriched and relatively original source. Both metabasalts and high-Ti basalts occurring together indicate that they could represent an ocean ridge environment overlaped with mantle plume.It is likely that aseismic ridge environment may be a reasonable explanation.更多还原