华北克拉通新太古代地壳增生:来自山西云中山地区TTG片麻岩和二长花岗片麻岩的证据

发布时间：2018-06-23 23:14

  本文选题：TTG + 岩石成因　； 参考：《岩石学报》2017年09期

【摘要】：通过详细的野外地质工作,本文在山西云中山地区识别出一套岩石组合完整的TTG片麻岩岩系,与TTG片麻岩共生的还有后期发育的二长花岗片麻岩。LA-ICP-MS锆石U-Pb定年结果表明,花岗闪长质片麻岩的形成时间为2486±9Ma,二长花岗片麻岩的形成时间为2448±11Ma。地球化学特征显示研究区TTG片麻岩为高铝TTG。奥长花岗质片麻岩总体表现为高SiO_2(69.82%~73.54%)、富Na_2O(4.19%~5.16%)、高CaO(1.45%~3.03%)的特征,Al_2O_3含量为14.31%~15.74%,铝饱和指数(A/CNK)为1.00~1.03,属富钠过铝质系列岩石;英云闪长质片麻岩的特征与奥长花岗片麻岩基本相似,但K_2O含量更低,CaO含量更高;花岗闪长质片麻岩SiO_2(61.23%~61.97%)含量相对偏低,Na_2O/K_2O为1.00~1.32,Al2O3含量为15.03%~15.73%,铝饱和指数(A/CNK)为0.96~1.05,为准铝质或过铝质系列岩石。与上述TTG片麻岩不同的是,本区出露的二长花岗片麻岩表现为富钾(K_2O/Na_2O=1.22~1.44)、贫Al_2O_3(12.81%~14.27%)的特征。岩石稀土总量较低(∑REE=52.71×10~(-6)~262.0×10~(-6)),轻稀土富集,重稀土亏损,轻、重稀土强烈分馏。微量元素具有富集K、Rb、Th等大离子亲石元素,亏损Nb、Ta、Sr、P、Ti等元素的特点,Cr、Ni等相容元素含量也较低,表现出岛弧岩浆的特征。花岗闪长片麻岩和二长花岗片麻岩εHf(t)值均为正值,前者成岩年龄与二阶段模式年龄较为接近,暗示其来源为2.5~2.6Ga的新生地壳,而后者成岩年龄与二阶段模式年龄则相差较多,其测点大都落在2.7~2.8Ga地壳演化线的区域内,表明二长花岗片麻岩来自于2.7~2.8Ga的古老地壳。根据上述地球化学特征,并结合区域地质特征,推测研究区高Al的TTG片麻岩是"平俯冲"状态下洋壳部分熔融的产物,而二长花岗片麻岩为底侵古老地壳部分熔融的产物,形成于大陆边缘弧的构造环境,代表云中山地区一次重要的以水平增生为主的地壳生长事件,同时也表明在新太古代末期,云中山地区已完成克拉通化,进入陆内演化阶段。
[Abstract]:Through detailed field geological work, a set of integrated TTG gneiss series has been identified in Yunshan area, Shanxi Province. The zircon U-Pb dating results show that TTG gneiss is associated with TTG gneiss, and later developed Erchang granitic gneiss. LA-ICP-MS zircon U-Pb dating results show that TTG gneiss is associated with TTG gneiss. The formation time of granodiorite gneiss is 2486 卤9 Ma, and that of Erchang granitic gneiss is 2448 卤11 Ma. The geochemical characteristics indicate that the TTG gneiss in the study area is high alumina TTG. The Al2O3 content is 14.31% and 1.001.03%, respectively. The Al2O3 content is 14.31% and 1.001.03%, respectively. The Al2O3 content is 1.001.03% and 1.001.03%, respectively, and the characteristics of the amphiolite gneiss are basically similar to those of the amphiolite gneiss, which is characterized by high SiO2 (69.822%), Na2O rich (4.1920%), high Cao (1.45% 3.03%), and aluminum saturation index (Ar / CNK) 1.001.03%, respectively, and is similar to that of the amphiolite gneiss. The content of SiO2 (61.23%) of granodiorogenic gneiss is relatively low. The content of K _ 2O / K _ 2O is 1.001.32%. The content of Al _ 2O _ 3 is 15.03 ~ 15.73, and the saturation index of aluminum is 0.96 ~ 1.05, quasi-aluminous or peraluminous series rocks. Different from the TTG gneiss mentioned above, the gneiss of Erchang granitic in this area is characterized by K _ 2O / Na _ 2O _ (1.221.44) and Al2O3 (12.81 ~ 14.27%). The total amount of REE in rock is low (鈭，

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