辽东岫岩地区两类古元古代花岗岩年代学、地球化学及地质意义  

Geochronology and Geochemistry of Two Types of Paleoproterozoic Granites and Their Geological Implications in the Xiuyan Area,Liaodong Peninsula

作　　者：赵岩[1,2] 张朋[1,2] 毕中伟[1,2] 杨中柱 寇林林[1,2] 顾玉超[1,2] 杨凤超[1,2] Zhao Yan;Zhang Peng;Bi Zhongwei;Yang Zhongzhu;Kou Linlin;Gu Yuchao;Yang Fengchao(Shenyang Center of Geological Survey,China Geological Survey,Shenyang 110034,China;Northeast Science&Technology Innovation Center,China Geological Survey,Shenyang 110034,China)

机构地区：[1]中国地质调查局沈阳地质调查中心,辽宁沈阳110034 [2]中国地质调查局东北地质科技创新中心,辽宁沈阳110034

出　　处：《地球科学》2020年第11期4072-4090,共19页Earth Science

基　　金：国家重点研发计划项目(Nos.2018YFC0603804,2016YFC0600108);中国地质调查局地质调查项目(No.DD20190156)。

摘　　要：辽东半岛岫岩一带出露大面积的辽河岩群变质地层与花岗岩类,是研究胶-辽-吉造山带早期演化的良好场所.通过系统采集岫岩地区大房身钾长花岗岩岩体与牧牛、松树沟二长花岗岩岩体和四门子花岗闪长岩岩体样品,进行了岩相学、地球化学与锆石U-Pb年代学研究.结果显示大房身与牧牛、松树沟岩体具有相近的高钾钙碱性A型花岗岩特征,SiO2含量介于70.56%~74.52%,Al2O3含量在11.85%~14.03%,K2O/Na2O高;岩石富集Ga、Zr、REE等元素,Sr、P、Ti等含量低;四门子岩体样品则具有较高的CaO含量(0.50%~3.76%),K2O/Na2O比值和A/CNK值均较低,相对更为亏损Nb、Ta、Hf等高场强元素,显示出I型花岗岩特征.锆石LA-ICP-MS测试显示钾长花岗岩样品U-Pb年龄为2198±11 Ma,二长花岗岩U-Pb年龄在~2171~2167 Ma,花岗闪长岩U-Pb测试结果为2166±11 Ma,几类花岗岩结晶年龄基本在误差范围内一致.I型花岗岩可能来自古元古代中期(~2.2~2.1 Ga)俯冲作用导致的弧岩浆活动,而A型花岗岩可能来自中下地壳物质的部分熔融的低压高温环境.结合辽吉地区报道的古元古代花岗岩类年龄资料,认为在岫岩地区及周边采集的两类古元古代花岗岩均产出在弧后拉张的构造背景下,胶辽吉造山带在古元古代中期演化接近"弧陆碰撞"模式,洋壳俯冲可能由西向东(现今方向)发生,并持续了较长时间.The Xiuyan region in Liaodong Peninsula is an ideal place for studying early evolution process of the Jiao-Liao-Ji orogenic belt,due to quantities of outcropped meta-sidimentary rocks and granitoids.A study of petrography,geochemistry and chronology is carried out on one K-feldspar granite,two mozogranite and one granodiorite samples collected from the Dafangshen,Muniu,Songshugou and Simenzi intrusions respectively.Although the K-feldspar granite and mozogranite samples show different features by petrography observation,they display similar geochemical natures of A-type granite.The samples have high contents of SiO2,ranging from 70.56%to 74.52%,relatively low Al2 O3 contents of 11.85%to 14.03%,and high ratio of K2 O/Na2 O,with enrichment of Ga,Zr and REE elements and depletion of Sr,P and Ti.The granodiorite sample from the Simenzi intrusion,on the other hand,shows characteristics of I-type granite.They have high content of CaO(0.50%-3.76%),but low ratio of K2 O/Na2 O and A/CNK,with relative depletion of some high field strength elements like Nb,Ta and Hf.Zircon LA-ICP-MS testing also reveals these granitoids intruded nearly simultaneously,with the K-feldspar granite sample yielding an U-Pb age of 2198±11 Ma,mozogranite samples yielding U-Pb ages between 2171-2167 Ma and granodiorite sample giving an U-Pb age of2166±11 Ma.The I-type granite may have derived from an arc magmatism in middle Paleoproterozoic(about 2.2-2.1 Ga),while the A-type granitoids intrusions may have sourced from a low pressure and high temperature environment of middle to lower crust partial melting.Taking previous studies on Paleoproterozoic granitoids into consideration,the K-feldspar granite and mozogranite intrusions are believed to be formed under a back-arc geodynamic setting.An arc-continent collison model is confirmed in middle stage of the Paleoproterozoic Jiao-Liao-Ji belt evolution,and the subduction of early ocean crust may have started by then from west to east and have lasted a relatively long time.

关 键 词：胶辽吉造山带 花岗岩类 锆石U-PB年龄 弧陆碰撞 华北克拉通 岫岩地区 地球化学 

分 类 号：P59[天文地球—地球化学]