贺根山洋闭合与后造山伸展——来自科右中旗构造混杂岩带内晚三叠世花岗岩的证据  

Hegenshan ocean basin closure and post-orogenic extension——Evidences from Late Triassic granite in Horqin Right Middle Banner tectonic melange belt

作　　者：王帅 赵东芳 李英杰[1] 金松 董培培[1] 张夏炜 孟都 WANG Shuai;ZHAO Dongfang;LI Yingjie;JIN Song;DONG Peipei;ZHANG Xiawei;MENG Du(Hebei Province Collaborative Innovation Center for Strategic Critical Mineral Research,Hebei GEO University,Shijiazhuang,050031;School of Earth Sciences and Resources,China University of Geosciences,Beijing,100083;Geological Institute of Bureau and Mining of China Chemical Industry,Zhuozhou,Hebei,072750;Geological Institute of China Chemical Geology and Mine Bureau,Beijing,100101)

机构地区：[1]河北地质大学河北省战略性关键矿产研究协同创新中心,石家庄050031 [2]中国地质大学(北京)地球科学与资源学院,北京100083 [3]中化地质矿山总局中心实验室,河北涿州072750 [4]中化地质矿山总局地质研究院,北京100101

出　　处：《地质论评》2024年第1期346-362,共17页Geological Review

基　　金：国家自然科学基金资助项目(编号:41972061);中国地质调查局项目(编号:DD20160048-14);河北地质大学科技创新团队项目(编号:KJCXTD-2021-07);学生科技基金项目(编号:DAY202206)的成果。

摘　　要：内蒙古科尔沁右翼中旗巨日合A2型二长花岗岩位于贺根山缝合带东段,侵位于早石炭世杜尔基构造混杂岩(带)中。笔者等通过对其进行系统的野外地质特征、岩石学、地球化学和锆石U-Pb年代学研究,旨在厘定岩体成因和构造背景,为古亚洲洋分支洋盆—贺根山洋闭合时限提供证据。巨日合二长花岗岩主要由细粒二长花岗岩和中粒二长花岗岩组成。LA-ICP-MS锆石U-Pb测年结果显示巨日合二长花岗岩侵位于晚三叠世(203.7±1.6 Ma)。地球化学研究显示,该岩体高硅(SiO_(2)=71.08%~76.62%)、富碱(Na_(2)O+K_(2)O=7.99%~9.28%),贫钙(CaO=0.25%~1.67%)和镁(MgO=0.05%~0.63%);负Eu异常显著(δEu=0.14~0.50),Rb、Th、U、K、Ga元素较富集,而Ba、Sr、P、Ti元素相对亏损,且10000Ga/Al(3.62~4.90)、TFeO/MgO(3.40~14.80)、(Na_(2)O+K_(2)O)/CaO(5.03~31.96)值较高,显示出A2型花岗岩特征,代表其形成于后造山伸展拉张环境。同时结合岩浆起源温压条件研究,认为岩体可能为壳源含斜长石的角闪石质岩石在脱水条件下部分熔融及其后的结晶分异作用成因。结合中亚造山带东段早石炭—晚三叠世蛇绿岩、洋内弧和后造山型岩浆岩的时空演化关系,揭示贺根山洋可能在二叠纪末期闭合,并在三叠纪进入后造山伸展拉张阶段。Objectives:Lying along the eastern Hegenshan suture zone in Horqin Right Middle Banner of Inner Mongolia,the Jurihe A2-type monzogranite intruded into Early Carboniferous Duerji tectonic melange belt.Based on systematic field geological characteristics,petrology,geochemistry,zircon U-Pb chronology of it,the purpose of study is to determine genetic type of pluton,tectonic setting,and provide evidence for the closure time of Hegenshan Ocean,a branch of the Paleo-Asian Ocean.The Jurihe monzogranite is mainly composed of fine-grained and medium-grained monzogranite.LA-ICP-MS zircon U-Pb dating shows that the age of granite is 203.7±1.6 Ma,indicating that formation age is Late Triassic.The granite is geochemically characterized by high SiO_(2)(71.08%~76.62%)and alkali(Na_(2)O+K_(2)O=7.99%~9.28%),but low CaO(0.25%~1.67%)and MgO(0.05%~0.63%).The obvious negative Eu anomaly(Eu=0.14~0.50),relative enrichment of Rb,Th,U,K and Ga,depletion of Ba,Sr,P and Ti,as well as high 10000Ga/Al(3.62~4.90),TFeO/MgO(3.40~14.80),(Na_(2)O+K_(2)O)/CaO(5.03~31.96)values show characteristics of A2-type granite,representing that it was formed in post-orogenic extensional environment.At the same time,combining with the temperature and pressure conditions of magma origin,it is believed that the pluton may be caused by partial melting of crustal hornblende rocks containing plagioclase under the condition of dehydration and subsequent crystallization differentiation in postorogenic stage.Combined with the spatio—temporal evolution of Early Carboniferous—Late Triassic ophiolites,intra oceanic arcs and post-collisional granitoids in the eastern part of Central Asia Orogenic Belt,suggesting that the Hegenshan Ocean was probably closed at the end-Permian and entered post-orogenic extension stage in Triassic.Methods:Based on field geological surveying,petrology,geochemistry and LA-ICP-MS zircon U-Pb geochronology of the Jurihe monzogranite,this paper discusses the petrogenesis and tectonic setting of the monzogranite,and the final closure time an

关 键 词：A2型花岗岩 LA-ICP-MS锆石U-PB定年 晚三叠世 后造山伸展 内蒙古科右中旗 

分 类 号：P534.51[天文地球—古生物学与地层学] P588.121[天文地球—地质学] P597.3