额尔古纳地块北东部二十一站岩体花岗岩类岩石成因与构造环境  

Petrogenesis and tectonic setting of granitoids in the Ershiyizhan intrusion,northeastern Erguna block

作　　者：程贤达 赵元艺[2] 张龙 孙建伟 CHENG Xianda;ZHAO Yuanyi;ZHANG Long;SUN Jianwei(Xi’an Center of Mineral Resources Survey,China Geological Survey,Xi’an 710100,Shaanxi,China;Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]中国地质调查局西安矿产资源调查中心,陕西西安710100 [2]中国地质科学院矿产资源研究所,北京100037

出　　处：《地球化学》2023年第3期360-382,共23页Geochimica

基　　金：中国地质调查项目(DD20208079);国家重点研发计划(2017YFC0601303)联合资助

摘　　要：二十一站岩体位于中亚造山带东段额尔古纳地块北东部上黑龙江盆地Cu-Au成矿带内,经过多年勘查研究,岩体中已发现斑岩型铜金矿化,但由于未进行系统工作,在物质来源和岩浆演化方面尚未取得重大突破。本研究对二十一站岩体系统采样,进行锆石U-Pb年代学、岩石地球化学、Sr-Nd-Pb同位素研究。结果显示,二十一站岩体岩浆活动大致分2个阶段,花岗岩、石英正长岩和二长花岗岩形成于186.5~206.9 Ma,属于晚三叠世-早侏罗世;石英二长斑岩和石英二长岩形成于127.6~133.2 Ma,属于早白垩世。岩体2个阶段花岗岩类岩浆岩主要为高钾钙碱性系列-钾玄岩系列,为Ⅰ型花岗岩。微量元素方面,样品富集大离子亲石元素(Rb、Th、K、Pb等),Pb具有明显正异常,亏损高场强元素(Nb、Ta、Ti、P等),表现出弧岩浆或主动大陆边缘岩浆的特征。稀土元素方面,样品表现为轻稀土元素富集,重稀土元素亏损的平滑右倾型分配模式,具有轻微的Eu负异常(0.62~0.90),LREE/HREE值为9.48~14.81,(La/Yb)N值为11.57~23.22,轻、重稀土元素分馏明显,表明岩浆经历了强烈的分离结晶作用。锆石Hf同位素和岩石Sr-Nd-Pb同位素表明,二十一站岩体岩浆源区具有壳源性质,并有部分地幔物质参与。结合区域构造演化历史,本研究认为二十一站岩体晚三叠世-早侏罗世岩浆岩形成于蒙古-鄂霍茨克洋向额尔古纳地块俯冲环境下,早白垩世岩浆岩形成于鄂霍茨克洋闭合后,陆陆碰撞造成增厚下地壳的拆沉引起的局部伸展环境。The Ershiyizhan intrusion in the Upper Heilongjiang Basin Cu-Au Metallogenic belt is located in the northeast of the Erguna Block of the Eastern Part of the Central Asian Orogenic Belt(CAOB).Although previous studies have shown that porphyry Cu-Au deposits are present in the intrusion,the magmatic source and evolution are poorly constrained.Here,we report the zircon U-Pb dating,Hf isotopic,whole-rock major,trace elements,and Sr-Nd-Pb isotopic characteristics of the rocks in the Ershiyizhan intrusion.The results showed that there was a two-stage magmatism in the Ershiyizhan intrusion:granite,quartz syenite,and monzogranite(185.7 Ma to 206.9 Ma)of the Late Triassic-Early Jurassic,and masanophyre and quartz monzonite(127.6 Ma to 133.2 Ma)of the Early Cretaceous.These Mesozoic magmatic rocks in the Ershiyizhan intrusion are typical type I granitoids,belonging to the high-K calcalkaline-shoshonite series.In addition,they are enriched in large ion lithophile elements(Rb,Th,K,and Pb)and depleted in high field strength elements(Nb,Ta,Ti,and P),suggesting an island-arc environment or active continental marginal environment.The rare earth element contents in these granitoids showed a trend of systematic enrichment of LREE and depletion of HREE,with a slightly negative Eu anomaly of 0.62 to 0.90,LREE/HREE of 9.48 to 14.81,and(La/Yb)N of 11.57 to 23.22,indicating a strong fractionation and crystallization process during the magmatic evolution.The characteristics of the zircon Hf isotope and whole-rock Sr-Nd-Pb isotopes suggest that the primary magmas were generated by partial melting of the lower crust materials,with a minor contribution of mantle materials.This study,combined with the regional tectonic evolution history,indicates that the Late Triassic-Early Jurassic magmatism of the Ershiyizhan intrusion occurred under the tectonic setting of the Mongolian-Okhotsk Ocean southward subduction beneath the Erguna block.In addition,the Early Cretaceous magmatism occurred in an extensional environment related to the delamination

关 键 词：二十一站 花岗岩类 岩浆演化 岩石成因 构造环境 

分 类 号：P597[天文地球—地球化学]