柴达木盆地北缘果可山石英闪长岩LA-ICP-MS锆石U-Pb定年及其成因

发布时间：2018-05-27 09:22

本文选题：果可山 + 石英闪长岩　；参考：《地质学报》2017年01期

【摘要】：柴达木盆地北缘果可山地区石英闪长岩LA-ICP-MS锆石U-Pb定年获得的206 Pb/238 U加权平均年龄为247±3 Ma。石英闪长岩由斜长石(55%~60%)、石英(15%~20%)、角闪石(10%~15%)和黑云母(5%~10%)组成,属准铝质-弱过铝质系列(A/CNK=0.95~1.02),具有I型花岗岩特征。样品富集轻稀土元素和大离子亲石元素(K、Rb、Cs、Ba、Th等),相对亏损重稀土元素和高场强元素(Nb、Ta、P、Ti等),类似弧岩浆岩。样品中MgO含量(2.04%~2.44%)和Mg#值(48.9~51.9)均高于变玄武岩/变泥岩在1~4GPa压力下部分熔融形成的熔体,且包含大量暗色包体,这暗示它们可能是由角闪岩相下地壳部分熔融产生的岩浆和富集地幔来源的岩浆发生混合而成。低的锆石Ti温度和高Ce~(4+)/Ce~(3+)比值,表明其结晶自低温、高氧逸度岩浆,岩浆形成过程中可能有富水熔体/流体的加入。在花岗岩构造环境判别图解上,样品均落在火山弧环境;同时,样品La/Nb比值(2.27~2.64)与活动大陆边缘区高La/Nb比值(2.0)特征相吻合。结合区域地质背景分析,我们认为果可山石英闪长岩形成于古特提斯洋向北俯冲的活动大陆边缘弧环境。
[Abstract]:The weighted mean age of 206 Pb/238 U obtained from LA-ICP-MS zircon dating of quartz diorite in Guokeshan area, northern margin of Qaidam Basin, is 247 卤3 Ma. Quartz diorite is composed of plagioclase (55) and plagioclase (55), quartz (15), hornblende (10) and biotite (10). It is a quasialuminum-weakly peraluminous series (A / CNK _ (0.95N) 1.02) and is characterized by I-type granite. The samples are enriched with light rare earth elements and large ion lithophile elements, such as K ~ (2 +) Rb ~ (2 +) C ~ (1) ~ (1) ~ (1) ~ (1) ~ (2) ~ (2 +), etc., and are similar to arc-magmatic rocks. The contents of MgO and Mg# in the samples are higher than that of melts formed by partial melting of metamorphic rocks / metamorphic rocks under the pressure of 1~4GPa, and contain a large number of dark inclusions, the content of which is 2.04 ~ 2.44) and the value of Mg# is 48.9% ~ 51.9%, which is higher than that of melts formed by partial melting of metamorphic rocks under 1~4GPa pressure. This suggests that they may be a mixture of magma derived from the partial melting of the lower crust of amphibolite facies and magma enriched from the mantle. The low zircon Ti temperature and the high Ce~(4 / ce ~ (3) ratio indicate that the crystallization of the zircon is derived from low temperature, high oxygen fugacity magma and the addition of water-rich melts / fluids during magma formation. In the judging diagram of granite tectonic environment, the samples all fall in volcanic arc environment, and the La/Nb ratio of the samples is 2.272.64) which is consistent with the high La/Nb ratio 2.0 in the active continental margin. Based on the analysis of regional geological background, we think that the quartz diorite of Guokeshan was formed in the active continental margin arc environment of the PaleoTethys ocean subducting northward.
【作者单位】：合肥工业大学资源与环境工程学院;
【基金】：国家自然科学基金项目(编号:41272221,41372207) 中国地质调查局地质调查项目(编号:12120115069401,1212011120159)资助的成果
【分类号】：P597.3;P588.122

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