蒙古—鄂霍次克洋早侏罗世构造演化:来自大兴安岭北段新立屯地区花岗岩的证据  

Geochronology and Petrogeochemical Characteristics of I-type Granites in Xinlitun Area,Northern Greater Hinggan Mountains and Their Geological Significance

作　　者：张国宾[1] 孔金贵 吴子杰 冯玥 何云龙 陈兴凯 ZHANG Guobin;KONG Jingui;WU Zijie;FENG Yue;HE Yunlong;CHEN Xingkai(School of Mines,Liaoning Technical University,Fuxin,Liaoning 123000,China;Liaoning Province Geological Exploration Institute Co.,Ltd.,Dalian,Liaoning 116000,China)

机构地区：[1]辽宁工程技术大学矿业学院,辽宁阜新123000 [2]辽宁省地质勘查院有限责任公司,辽宁大连116000

出　　处：《现代地质》2023年第2期404-418,共15页Geoscience

基　　金：中国地质调查局项目(1212011120342);辽宁省科技厅面上基金项目(20170540428,201601370);辽宁省教育厅面上基金项目(LJ2019JL027)。

摘　　要：大兴安岭地区显生宙花岗岩极其发育,本文选择大兴安岭北段新立屯地区花岗岩进行了系统的锆石U-Pb同位素年代学和地球化学研究,对比了大兴安岭北段晚中生代花岗岩的地球化学特征,旨在查明其成岩时代和岩石成因,并探讨其构造意义。锆石LA-ICP-MS U-Pb同位素定年结果显示,中细粒二长花岗岩和中细粒花岗闪长岩的成岩年龄分别为(187.2±2.3)Ma和(192.4±1.6)Ma,成岩时代为早侏罗世。岩石地球化学结果显示,新立屯地区早侏罗世花岗岩具有富硅、高碱、富钾、贫镁、低磷、低钛和较低的TFeO/MgO比值等特征,富集轻稀土元素、亏损重稀土元素,富集Rb、Ba、Th、K等大离子亲石元素,亏损Ta、Nb、P、Ti元素,负铕异常不明显,P_(2)O_(5)和Al_(2)O_(3)含量随SiO_(2)的增加而降低,显示出中等分异I型花岗岩的特征。岩石学及地球化学特征表明,其岩浆来源于壳幔混合源区。结合区域构造演化及构造判别,认为研究区早侏罗花岗岩形成于同碰撞火山弧花岗岩构造背景,与蒙古—鄂霍次克洋向南的俯冲作用密切相关。There are voluminous Phanerozoic granites in the Greater Hinggan Mountains.In this paper,zircon U-Pb geochronology and geochemistry of the Xinlitun granites in the northern Greater Hinggan Mountains have been studied.We compared the geochemical characteristics of these Late Mesozoic granites,and discussed their formation age,genesis and geological significance.Zircon LA-ICP-MS U-Pb dating indicates that the medium-fine-grained monzogranite and medium-fine-grained granodiorite were both formed in the Early Jurassic,at(187.2±2.3)Ma and(192.4±1.6)Ma,respectively.Whole-rock geochemical results show that these granites are Si-rich,high in alkalis(K-rich),and contain low Mg,P,Ti,and TFeO/MgO.The rocks are enriched in light rare earth elements and large ion lithophile elements(e.g.,Rb,Ba,Th,K),but depleted in heavy rare earth elements and high-field strength elements(e.g.,Ta,Nb,P,Ti).No distinct negative Eu anomalies have been identified.The contents of P_(2)O_(5)and Al_(2)O_(3)decrease with increasing SiO_(2).Collectively,we suggested that these granites are moderately differentiated I-type.The petrological and geochemical features indicate that their primary magmas were originated from a mixed crust-mantle source.Considering the regional tectonic background,we suggested that these Early Jurassic granites were formed in a syn-collision volcanic arc setting,closely related to the southward subduction of Mongolia-Okhotsk Ocean.

关 键 词：大兴安岭北段 Ⅰ型花岗岩 早侏罗世 锆石U-PB年龄 岩石地球化学 蒙古—鄂霍次克洋 

分 类 号：P588.12[天文地球—岩石学]