北山造山带南缘潘家井子二叠纪弧岩浆岩的识别及构造意义  

Identification of the Permian Arc-Related Magmatic Rocks and Its Significance in Panjiajingzi Area,Southern Margin of Beishan Orogenic Belt

作　　者：查显锋[1] 黄博涛 罗克勇[1] 孙吉明[1] 关冲 王欣[1] ZHA Xianfeng;HUANG Botao;LUO Keyong;SUN Jiming;GUAN Chong;WANG Xin(Xi’an Center of China Geological Survey,Center for Orogenic Belt Geology of China Geological Survey,Xi’an 710119,Shaanxi,China)

机构地区：[1]中国地质调查局西安地质调查中心,造山带地质研究中心,陕西西安710119

出　　处：《西北地质》2024年第6期58-77,共20页Northwestern Geology

基　　金：中国地质调查局项目“东天山–北山成矿带区域地质调查”(DD20240029);“东天山–北山造山带区域地质调查”(DD20221636-1);陕西省自然科学基金项目(2023-JC-YB-249)联合资助。

摘　　要：北山造山带位于中亚造山带南缘,对该带内原先划定的“前寒武系”的准确厘定或解体对理解造山带属性和构造演化过程认识具有重要意义。笔者对瓜州潘家井子一带原划定的敦煌岩群开展区域地质调查,表明其为变粒岩、浅粒岩、变质砾岩及少量斜长角闪岩和黑云石英片岩等组成的一套具有强变形、低级变质的变火山–碎屑岩。获得灰白色变粒岩、云母石英片岩和浅粒岩的锆石U-Pb年龄为294~285 Ma,同时还获得变质砾岩中花岗质砾石中锆石的最小U-Pb年龄为(272±6)Ma,未发现古老年代学信息,表明该套变质火山–碎屑岩形成时代不早于中二叠世。变质基性火山岩具有拉斑玄武岩地球化学特征,呈略微右倾的稀土元素配分模式,显示出高TiO_(2)、Na_(2)O含量,明显的Nb-Ta亏损特征,类似于弧玄武岩特征。结合本次研究成果和区域地质特征认为,潘家井子一带原划定的“敦煌岩群”应厘定为二叠纪变火山碎屑岩,形成于早—中二叠世俯冲作用相关的局部伸展构造环境。The Beishan Orogenic Belt,located at the southern margin of the Central Asian Orogenic Belt,is important for understanding the tectonic affinity and evolutionary history,in terms of the accurate determination or disintegration of the namely Precambrian basement rocks.The originally defined Dunhuang Group in Panjiajingzi area is composed mainly of leptynite,leptite,meta-conglomerate,minor amphibolite,and mica quartz schist,and is characterized by strong deformation and low-grade metamorphosed pyroclastic rocks,based on re gional geological investigation.Zircon U-Pb ages of 294~285 Ma for leptynite,mica quartz schist,and leptite samples,as well as the minimum age of(272±6)Ma for gravel sample from meta-conglomerate have been obtained with no ancient geochronological information.All these dating data indicate that these mata pyroclastic rocks were deposited later than Middle Permian.In addition,the meta basic volcanic samples have high TiO_(2) and Na_(2)O contents with obvious Nb-Ta trough,and display right-sloping chondrite-nomalized REE patterns,resembling that of the arc basalts.Combining our data and regional geology,it is reasonable to believe that these meta pyroclastic rocks were formed in a local extension setting during the subduction process during Early to Middle Permian,and thus these rocks should be disintegrated from the Dunhuang Group.

关 键 词：锆石年代学 二叠纪岩浆作用 石板山构造带 北山造山带 

分 类 号：P581[天文地球—岩石学]