西秦岭西段西功卡和卡力岗岩体岩石地球化学、年代学及构造意义

发布时间：2018-04-14 19:32

  本文选题：锆石U-Pb年代学 + 元素地球化学　； 参考：《中国地质大学(北京)》2015年硕士论文

【摘要】：西秦岭造山带出露较多的花岗质岩石,其形成和侵位过程是大陆造山带形成演化中极为重要的问题,记录着西秦岭地区与原特提斯洋和古特提斯洋密切相关的洋壳俯冲、陆陆(弧)碰撞和碰撞后等构造事件,也是长期以来地质学家们研究的重点。本文对西秦岭西段侵位于中下三叠统隆务河组的西功卡花岗闪长岩和卡力岗闪长玢岩两个岩体进行了详细的岩石学、元素地球化学、锆石U-Pb同位素年代学分析研究,以期揭示其岩石成因及构造属性,对恢复重建西秦岭造山带西段印支期构造格架及地球动力学过程均具有重要的理论意义。元素地球化学特征显示,两个岩体具高钾钙碱性I型花岗岩特征。西功卡岩体Na2O和K2O的含量分别为1.98~3.4%和3.12~4%,A/CNK值主体小于1.1(0.97~1.2),平均为1.08。稀土总量∑REE=106.69~136.47×10-6,轻稀土LREE=97.84~131.03×10-6,重稀土HREE=5.44~10.07×10-6,LREE/HREE比值介于11~24.1。卡力岗岩体Na2O和K2O的含量分别为2.57%~3.66%和2.3%~3.95%,A/CNK值全部小于1.1(0.85~1),平均为0.92。稀土总量∑REE=117.08~146.42×10-6,轻稀土LREE=104.89~133.27×10-6,重稀土HREE=12.18~13.42×10-6,LREE/HREE比值介于8.5~10.1。两者在球粒陨石标准化稀土元素配分曲线图解上也表现出具弱的负Eu异常、轻稀土富集、重稀土显著亏损的曲线平滑的右倾特征,在原始地幔标准化微量元素蛛网图表现出大离子亲石元素(Cs、Rb、Ba、Th、U)明显富集,高场强元素(Nb、Ta、P)明显亏损的特征。分析认为两者具有同源演化的特征。LA-ICP-MS锆石U-Pb同位素定年显示,西功卡花岗闪长岩体的岩浆结晶年龄为227.2±7.3Ma,形成于晚三叠世卡尼期;卡力岗闪长玢岩体岩浆结晶年龄为238.7±7Ma,形成于中三叠世拉丁期。由于岩体均侵位于隆务河组,结合隆务河组沉积岩碎屑锆石测年资料,综合限定了隆务河组形成时代为奥伦尼阶-拉丁阶。通过微量元素组合判别并结合前人研究资料,认为两个岩体都是在碰撞后环境下,由于岩石圈拆沉后幔源基性岩浆底侵导致下地壳变基性岩石部分熔融形成的,并可能发生了一定程度的壳幔岩浆混合作用。
[Abstract]:The formation and emplacement of granitic rocks in the West Qinling orogenic belt are very important problems in the formation and evolution of continental orogenic belts, and record the oceanic crust subduction in the West Qinling region, which is closely related to the original Tethys Ocean and the PaleoTethys Ocean.Continental (arc) collision and post-collision tectonic events have long been the focus of geologists.In this paper, detailed petrology, element geochemistry and zircon U-Pb isotopic chronology of the Xigongka granodiorite and Kaligang diorite porphyrite in the western part of the western Qinling Mountains, located in the middle and lower Triassic Longwuhe formation, have been studied in detail.In order to reveal its petrogenesis and tectonic properties, it is of great theoretical significance to reconstruct the Indosinian tectonic framework and geodynamic process in the western part of the Western Qinling orogenic belt.The geochemical characteristics of elements show that the two rock bodies are characterized by high potassium calc-alkaline I type granite.The contents of Na2O and K _ 2O in Xigongka rock mass are 1.98 ~ 3.4% and 3.12 ~ 4% respectively.The total amount of rare earth 鈭，

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