辽东刘家河地区古元古代花岗闪长岩年代学、地球化学及地质意义

    Geochronology and geochemistry of Paleoproterozoic granodiorite in Liujiahe area, eastern Liaoning Province: Geological implication

    • 摘要: 大量出露于辽东地区的花岗质岩体是探讨胶-辽-吉古元古代造山带构造演化历史的重要载体. 通过对辽东刘家河地区古元古代花岗闪长岩岩石学、年代学和地球化学进行研究,确定其成因,并进一步探讨胶-辽-吉古元古代造山带构造属性. 研究表明,花岗闪长岩锆石U-Pb LA-ICP-MS测试207Pb/206Pb加权平均年龄为2 180.7±9.0 Ma,形成时代为古元古代. SiO2含量为66.39%~71.65%,平均值69.11%; Al2O3为11.35%~15.58%,平均值12.67%; K2O+Na2O为7.22%~9.05%,平均值7.89%; K2O/Na2O为0.53~0.59,平均值0.55; CaO为0.65%~4.12%,平均值2.44%,含量较高; MgO为0.16%~0.86%,平均值0.51%. 样品为钙碱性-高钾(钙碱性)系列,其A/CNK和A/NK分别为0.63~1.10和1.06~1.20,属于偏铝质-过铝质. 样品REE含量较低,相对亏损Nb、Ta、Ti、Ba等高场强元素,显示I型花岗岩的特征. 地球化学特征表明花岗闪长岩是源于低压条件下长英质地壳部分熔融的I型花岗岩,具有明显的岛弧岩浆特征. 在构造判别图解中所有样品落入火山弧花岗岩区域,代表了辽吉造山带在古元古代早期(2.2~2.1 Ga)存在俯冲作用导致的弧岩浆活动.

       

      Abstract: A large number of granitic rock mass exposed in eastern Liaoning Province serves as a critical medium for investigating the tectonic evolution history of Paleoproterozoic Jiao-Liao-Ji orogenic belt. Through the study of petrology, chronology, and geochemistry of the Paleoproterozoic granodiorites in Liujiahe area of eastern Liaoning Province, this paper determines the genesis and further explore the tectonic attributes of Paleoproterozoic Jiao-Liao-Ji orogenic belt. The study shows that the zircon U-Pb dating of granodiorite yields a weighted mean age of 2 180.7 ± 9.0 Ma, indicating its Paleoproterozoic formation. The SiO2 content is 66.39%-71.65%(averagely 69.11%), Al2O3 11.35%-15.58% (averagely 12.67%), K2O+Na2O 7.22%-9.05%(averagely 7.89%), K2O/Na2O 0.53-0.59(averagely 0.55), with high content of CaO (0.65%-4.12%, averagely 2.44%) and MgO (0.16%-0.86%, averagely 0.51%). The sample is of calc-alkaline to high-K (calc-alkaline) series, with A/CNK of 0.63-1.10 and A/NK of 1.06-1.20, belonging to metaluminous-peraluminous rocks, characterized by low REE content, and relatively depletion of HFSEs(Nb, Ta, Ti, Ba), showing the characteristics of I-type granites. The geochemical characteristics indicate that the granodiorite is originated from the partial melting of partial melting of felsic crust under low-pressure conditions, with distinct island arc magmatic features. In the tectonic discrimination diagram, all samples plot within the volcanic arc granite field, indicating the subduction-induced arc magmatism in Liao-Ti orogeny during early Paleoproterozoic(2.2-2.1 Ga).

       

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