SHRIMP zircon dating of gabbro from the ophiolite melange in the northern Altyn Tagh and its geological implications.
SHRIMP zircon dating of gabbro from the ophiolite melange in the northern Altyn Tagh and its geological implications.
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发表时间：
2009
影响因子：
1.8
通讯作者：
Zhang Zhi;Guo Zhaojie
中科院分区：
文献类型：
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作者：
Zhang Zhi;Guo Zhaojie
阿克塞地区青崖子蛇绿杂岩位于阿尔金盆地北缘，是由蛇纹岩和辉长岩组成的块状断块岩。分析表明，蛇纹岩的主要特征是MgO含量高，Al_2O_3、CaO、TiO_2和∑REE含量低，与世界典型蛇绿岩的变质橄榄岩相似。辉长岩SiO_2含量为49.06%~50.70%，Fe_2O_3含量为6.36%~12.85%，MgO含量为7.16%~10.01%，TiO_2含量为0.31% ~1.02%，Na_2O和K_2O含量相等（平均分别为0.73%和0.75%）。与e型MORB和/（或）OIB相似，辉长岩∑REE含量较低，LREE/HREE分馏较低（(La/Yb)_N = 1.07 ~5.19），没有或有轻微的Eu异常。辉长岩的主要元素和微量元素特征表明，它不仅保留了MORB的起源特征，而且记录了SSZ环境转化的结果。上述结果表明，青崖子蛇绿岩可能起源于不同的构造环境，表明青崖子蛇绿岩是一个复杂的板块缝合线。青崖子蛇绿混杂岩辉长岩锆石SHRIMP U-Pb年龄为521±12Ma (MSWD = 2.1)，代表洋盆形成时期。锆石SHRIMP U-Pb年龄测定结果表明，辉长岩的变质年龄为472±10.0Ma(MSWD =0.20)，可能代表古生代洋盆闭合的最小年龄。
The Qingyazi ophiolitic melange in the Akesai area, located in the northern margin of the Altyn Tagh, is composed of massive fauited-block rocks of serpentinite and gabbro. Analysis shows that the serpentinites are mostly characterized by high MgO contents, low Al_2O_3, CaO, TiO_2 and ∑REE contents, which are similar to the metamorphic peridotite of the world's typical ophiolite. The gabbrao has 49.06%～50.70% SiO_2, high Fe_2O_3 (6.36%～12.85% ) and MgO (7.16%～10.01% ), and low to moderate TiO_2 (0.31% ～1.02% ) contents, with equal of Na_2O and K_2O (the average is 0.73 % and 0.75 % , respectively ). It is similar to the E-type MORB and /(or) OIB that the gabbro has lower contents of ∑REE with low fractionation of LREE/HREE ( (La/Yb)_N = 1.07 ～5.19) and no or slightly Eu anomaly. The major and trace elements characteristics of the gabrro indicate that it may not only retained the MORB origin signatures, but also records the results of the transformation of SSZ environment. All mentioned above show that some of the ophiolitic units in the melange may have originated in different tectonic settings, indicating that the Qingyazi ophiolitic m6lange represents a complex plate suture. The SHRIMP U-Pb age of zircons from gabbro of the Qingyazi ophiolitic melange is 521±12Ma (MSWD = 2.1) , which stands for the formation time of the ocean basin. The result of the zircons SHRIMP U-Pb age shows that the gabbro has a metamorphic age of 472±10.0Ma( MSWD =0.20) , possibly representing the minimum age of the closure of Paleozoic ocean basin.