东准噶尔卡拉麦里蛇绿混杂岩中斜长角闪岩的发现与洋中脊构造环境的确认

发布时间：2018-11-25 20:48

【摘要】：在新疆东准噶尔卡拉麦里蛇绿混杂带中新发现了斜长角闪岩,主要呈透镜状夹持于变质橄榄岩之中。采用LA-ICP-MS锆石U-Pb定年方法,获得斜长角闪岩锆石U-Pb年龄为(402.7±4.9)Ma,表明其原岩形成时代为早泥盆世。岩相学、岩石地球化学及Sr-Nd同位素分析表明,斜长角闪岩的原岩可能为变辉长岩,样品SiO_2含量为47.58%~50.57%,MgO含量为8.04%~9.12%及对应的Mg#值为63.89~67.64,Ni和Cr含量分别为68.9×10~(-6)~99.2×10~(-6)和306×10~(-6)~398×10~(-6),与洋中脊拉斑玄武岩一致。稀土元素配分曲线呈弱亏损型至平坦型,微量元素蛛网图总体与N-MORB相似,无明显的Nb、Ta Zr、Hf及Ti的亏损,各元素的丰度也与N-MORB接近。样品均具有较高εNd(t)值(8.7~9.2),表明其原始岩浆来源于亏损地幔。在TiO_2-FeOT/MgO和Th-Ta-Hf/3构造环境判别图解中,所有样品均落入洋中脊玄武岩区域内。结合区域地质构造背景,认为斜长角闪岩可能形成于洋中脊构造环境,代表了被肢解的古洋盆岩石圈残片,应为卡拉麦里蛇绿混杂岩的组成部分,揭示了该洋盆的开启时限至少可追溯至早泥盆世。
[Abstract]:A new amphibolite has been found in the Kalamaili ophiolite melange belt in East Junggar Xinjiang. The amphibolite is mainly caught in the metamorphic peridotite in the form of lens. Using the LA-ICP-MS zircon U-Pb dating method, the zircon U-Pb age of the amphibolite is (402.7 卤4. 9) Ma, which indicates that the origin age of the amphibolite is early Devonian. Petrography, petrogeochemistry and Sr-Nd isotopic analysis indicate that the original rocks of amphibolite may be metamorphic gabbro, and the SiO_2 content of the sample is 47.58 ~ 50.57. The MgO content is 8.049.12% and the corresponding Mg# value is 63.890.67.64 Ni and 68.9 脳 10 ~ (-6) ~ 99.2 脳 10 ~ (-6) and 306 脳 10 ~ (-6) ~ 398 脳 10 ~ (-6), respectively, which are consistent with the oceanic ridge tholeiite basalts, and the corresponding Mg# values are 63.89 脳 10 ~ (-6) ~ 99.2 脳 10 ~ (-6) and 306 脳 10 ~ (-6) ~ 398 脳 10 ~ (-6), respectively. The distribution curve of rare earth elements is weakly depleted to flat, and the trace element cobweb diagram is similar to that of N-MORB, and there is no obvious deficiency of Nb,Ta Zr,Hf and Ti, and the abundance of each element is close to that of N-MORB. The samples all have a higher 蔚 Nd (t) value (8.7 ~ 9.2), indicating that the original magma originated from the depleted mantle. In the TiO_2-FeOT/MgO and Th-Ta-Hf/3 tectonic environment discriminant diagrams, all samples fall into the mid-oceanic ridge basalt area. Combined with the regional geological tectonic setting, it is considered that the amphibolite may form the tectonic environment of the middle ridge of Yu Yang, which represents the fragments of the ancient oceanic basin lithosphere, and should be part of the Kalamari ophiophoric melange. It is revealed that the opening time of the basin can be traced back to the early Devonian at least.
【作者单位】：陕西区域地质矿产研究院;
【基金】：中国地质调查局项目(1212011120500) 中央返还两权价款资金项目(Y15-1-LQ02)联合资助~~
【分类号】：P542;P588.3

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