辽北开原地区新太古代变质深成岩LA-ICP-MS 锆石U-Pb 年龄及地球化学特征

辽北开原地区新太古代变质深成岩位于华北板块北缘陆缘活动带东段,主要岩性为二长花岗质片麻岩、花岗闪长质片麻岩和英云闪长质片麻岩,其中英云闪长质片麻岩LA-ICP-MS锆石207Pb/206Pb年龄加权平均值为2489.6±9.1 Ma,为新太古代。新太古代变质深成岩属高钾钙碱性-钾玄岩,准铝-过铝质岩石系列,轻稀土元素较富集,重稀土元素相对亏损,具有下地壳或太古宙沉积岩部分熔融形成的特征。通过岩石学、岩石地球化学和构造环境及就位机制分析,结合邻区构造演化研究,认为辽北开原地区变质深成岩岩浆来自较浅的基性古陆壳局部熔融。大地构造位置可能处在洋壳与陆壳的接触带,说明新太古代清河断裂附近可能出现陆壳碰撞增生活动。闪长质-石英闪长质-花岗闪长质-二长花岗质片麻岩体现了陆壳经历长时间的增生、造陆活动,已由早期的基性陆壳向现今的硅铝质陆壳转变。

LA-ICP-MS zircon U-Pb age and geochemical characteristics of Neoarchaean metamorphic plutonic rocks in Kaiyuan area of northern Liaoning Province

Located in the Kaiyuan area of northern Liaoning Province on the northern margin of North China,the Neoarchaean metamorphic plutonic rocks are mainly composed of monzonitic granitic gneiss,granodioritic gneiss and quartz dioritic gneiss.According to LA-ICP-MS zircon U-Pb dating,they were formed in Neoarchaean,with the 207Pb/206Pb age of 2489.6±9.1 Ma.Neoarchean metamorphic plutonic rocks belong to high-K calc-alkaline-potassium basalt,quasi-aluminium-peraluminous rock series,and are enriched in LREE and relatively depleted in HREE,characterized by partial melting of the lower crust or Archean sedimentary rocks.Based on an analysis of petrology,petrogeochemistry,tectonic environment and emplacement mechanism,and combined with the study of tectonic evolution in adjacent areas,it is considered that the metamorphic plutonic magma in Kaiyuan area of northern Liaoning came from relatively shallow local melting of basic paleocontinental crust.Geotectonic location was in the contact zone between oceanic crust and continental crust,which indicates that there might have been collision and accretion of continental crust near Qinghe fault in Neoarchean.The diorite-quartz diorite-granodioritemonzogranitic gneiss body shows that the continental crust has undergone a long period of accretion and continental activity,and has changed from the early basic continental crust to the present silica-alumina continental crust.