吉林白城岭下地区花岗质糜棱岩锆石U-Pb年代学与地球化学特征对松辽盆地西缘晚古生代以来的俯冲背景的制约  

Geochronologic and geochemistric evidence of granitic mylonites from Lingxia area of Baicheng City,Jinlin,constraints on subduction in the western of the Songliao basin since the Late Paleozoic

作　　者：汪岩[1] 钱程[1] 马永非[1] 庞雪娇[1] 付俊彧[1] 秦涛[1] 杨晓平[1] 杨雅军[1] 钟辉[1] 刘桂香[1] WANG Yan;QIAN Cheng;MANG Yongfei;PANG Xuejiao;FU Junyu;QIN Tao;YANG Xiaoping;YANG Yajun;ZHONG Hui;LIU Guixiang(Shenyang Center of Geological Survey,China Geological Survey,Shenyang ,110034)

机构地区：[1]中国地质调查局沈阳地质调查中心,沈阳110034

出　　处：《地质学报》2019年第1期117-137,共21页Acta Geologica Sinica

基　　金：中国地质调查局项目(DD20160048-01;DD20160048-16;DD20160048-03;DD20160345-17;121201207000171401)联合资助的成果

摘　　要：东北地区古生代经历了古亚洲构造域演化,中生代经历了蒙古-鄂霍茨克构造域向西太平洋构造域的转换,这期间形成了不同期次的岩浆活动。本文对松辽盆地西缘吉林省白城市岭下地区的花岗质糜棱岩首次进行了锆石LA-ICP-MS U-Pb年代学和岩石地球化学研究,确定其侵位时代、岩石成因,从而揭示区域构造背景及转换机制。岭下地区花岗质糜棱岩中的锆石多呈半自形-自形,振荡生长环带明显,暗示其岩浆成因。测年结果显示,花岗质糜棱岩原岩形成于281.9±7.4Ma和296.2±2.7Ma,为早二叠世岩浆事件的产物。岩石具有高硅(SiO2=64.10%~75.98%)、富铝(Al2O3=11.22%~16.00%)、贫铁(Fe2O3多介于0.23%~0.85%)等特征,在地球化学上属于准铝质-过铝质(A/CNK=0.97~1.19)系列。岭下地区花岗质糜棱岩相对富集轻稀土元素(LREE)和大离子亲石元素(LILE),亏损重稀土元素(HREE)和高场强元素(HFSE)。上述特征表明,岭下地区花岗质糜棱岩的岩浆起源于高温高压下加厚陆壳物质脱水的部分熔融。结合区域地质特征,岭下地区早二叠世花岗质糜棱岩的侵位应与古亚洲洋闭合过程中的弧后拉张体制有关;花岗质糜棱岩的变质岩浆热事件年龄(157~153Ma)与蒙古-鄂霍茨克洋的挤压闭合事件有关;而花岗质糜棱岩的主变形时代(137~117Ma)为早垩世早中期,其限定了西太平洋伊泽奈崎板块向欧亚大陆的斜向俯冲的起始时间。The Paleozoic era experienced the evolution of Paleo-Asian tectonic regime in the Northeast China,the Mesozoic experienced the transition from Mongol-Okhotsk to Western Pacific tectonic regime,in this period forming different temporal magmatic activities.Zircon U-Pb dating and whole-rock geochemical analyses are undertaken for the granitic mylonites in Lingxia area,Baicheng city of Jilin province,the western of the Songliao Basin,with the aim of constraining its emplacement time,petrogenesis and the regional tectonic setting.Zircons from the granitic mylonites in Lingxia area are euhedral-subhedral in shape,and display fine-scale oscillatory growth zoning,indicating a magmatic origin.LA-ICP-MS zircon U-Pb dating indicates that the country rock of granitic mylonites formed in the Early Permain(281.9±7.4 Ma and 296.2±2.7 Ma).The granitic mylonites have SiO2=64.10%~75.98%,Al2 O3=11.22%~16.00%,Fe2 O3=0.23%~0.85%,and belong chemically to metaluminous-peraluminous series(A/CNK=0.97~1.19).In addition,these granitic mylonites are enriched in light rare earth elements(LREE)and large ion lithophile elements(LILE),and depleted in heavy rare earth elements(HREE)and high field strength elements(HFSE).The above features indicate that the primary magma was derived from partial melting of dehydrated thickened crust under high temperature and high pressure.Combined with the regional geological features,we conclude that the granitic mylonites in the Lingxia area emplaced in a extensionism setting of back-arc,which is related to the closure of the Paleo-Asia ocean;the age(157~153 Ma)of metamorphic magma thermal events in the granitic mylonites is related to the closure of the Mongol-Okhotsk ocean;the main deformation time(137~117 Ma)of the granitic mylonites is the Midstage of early Cretaceous,its limits on the starting time of the Western Pacific Izanagi plate obliquely subducting under the Eurasia plate.

关 键 词：古亚洲构造域 蒙古-鄂霍茨克构造域 西太平洋构造域 花岗质糜棱岩 锆石U-PB年代学 地球化学 岭下 松辽盆地西缘 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]