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柴北缘冷湖盐场北山镍铜矿区发育辉长岩和角闪辉长岩,属亚碱性岩石系列。球粒陨石、原始地幔标准化曲线呈两组特征,但配分型式基本一致,反映其来自同一源区。稀土标准化曲线表现为弱右倾型,Eu基本无异常,说明斜长石分离结晶作用不明显。Rb、Nb、Zr、Cr等微量元素丰度及比值具有近似平行部分熔融的演化趋势。结合岩体Mg~#值和岩体固结指数(SI)高等特点,揭示原始岩浆具有幔源原生玄武岩浆特征,认为其成因与俯冲板片流体交代地幔楔源区的部分熔融有关,而且,Nb、Zr、Y元素丰度表明辉长岩源区为过渡型地幔。另外,两类岩体强烈亏损Nb、Ta、Zr、Hf、Ti等高场强元素(HFSE),富集Ba、Th、U、Pb等大离子亲石元素,反映明显的消减带和岛弧环境岩浆岩典型特征。LA-ICPMS锆石U-Pb测年结果表明辉长岩形成于254±3 Ma,结合该时期区域地质构造背景,认为柴北缘晚二叠世处于俯冲作用之下的岛弧构造环境,具有活动大陆边缘性质。
The North Lake in the northern margin of cold lake salt field Beishan nickel-copper mining gabbro and hornblende gabbro, is a series of sub-alkaline rocks. The chondrite and primitive mantle normalization curve are two groups of characteristics, but the distribution patterns are basically the same, reflecting that they come from the same source area. Rare earth normalized curve showed a weak right-sided type, Eu almost no exception, indicating that the separation of plagioclase crystallization is not obvious. The abundances and ratios of trace elements such as Rb, Nb, Zr and Cr have the similar trend of melting in parallel. Combined with the Mg ~ # value and the high consolidation index (SI) of the rock mass, it is revealed that the original magma has the features of mantle-derived primary basaltic magma. It is believed that the origin of the magma is related to the partial melting of the subducted slab fluid in the wedge source region. The elemental abundances of Nb, Zr and Y indicate that the gabbro source region is a transitional mantle. In addition, both types of rock mass strongly depleted HFSE, such as Nb, Ta, Zr, Hf and Ti, enriched in large ion lithophile elements such as Ba, Th, U and Pb, reflecting obvious depleted zone and island arc Environmental magmatic rocks typical characteristics. LA-ICPMS zircon U-Pb dating results show that the gabbro is formed at 254 ± 3 Ma. Combined with the regional geological tectonics during the period, the Late Permian in the northern margin of the Qaidam basin is characterized by island arc tectonics under subduction, Continent edge nature.