【摘要】 榆树沟变质基性-超基性岩带出露于塔里木板块与哈萨克斯坦板块之间的南天山北缘,主要由变质橄榄岩和变质基性岩组成。变质橄榄岩富相容元素Cr、Co和Ni,贫不相容元素,大离子亲石元素Ba、Rb和Sr含量较低,与世界典型蛇绿岩相似,代表了地幔残留物特征。REE分布模式为LREE亏损型,REE含量小于或等于2.5倍球粒陨石,类似于阿尔卑斯型变质橄榄岩,显示榆树沟的变质橄榄岩是原始地幔岩部分熔融萃取出玄武岩后的残留物。变质基性岩绝大部分为LREE亏损型,类似于N-MORB。所有样品均以富集Nb和Ta、高场强元素不分异,以及微量元素含量低为特征,指示岩浆源区总体上类似于MORB,Nb、Ta富集可能与OIB型源区有关,Nd、Sr同位素特征也显示其具有OIB型源区特征。综合分析认为,榆树沟变质基性岩石的岩浆可能经历了两个阶段的演化过程,即上地幔底部或下地幔顶部的OIB型原始岩浆形成阶段和软流圈地幔亏损阶段。更多还原

【Abstract】 The Yushugou ophiolite is located in the north margin of the South Tianshan tectonic belt, which is the boundary between the Tarim block and the Kazakhstan block. The ophiolite consists of meta mafic rocks and meta peridotites. The meta peridotites are characterized by being enriched in compatible elements (Cr, Co and Ni) and depleted in incompatible elements. Their REE distribution patterns showing depletion in LREE and the REE abundances are similar to those of the Alps type meta peridotites. All above evidences indicate the meta peridotites from Yushugou region represent the leftover of the original mantle from which basalts were extracted. The meta mafic rocks characterized by being depleted in LREE and lower content of trace elements show similarities to the mid oceanic basalt. In addition, enrichment in Nb, Ta and Nd, Sr isotopic geochemistry of the basalts indicate that the magma source may be related to the source of the oceanic island basalts. A two stage model of magma evolution is proposed based on synthesized analysis on all above geochemical characteristics. The first stage is the formation of the OIB type magma in the bottom of the upper mantle or the top of the lower mantle, and the second stage is the depletion of the magma formed in the first stage.更多还原