喀喇昆仑北羌塘地体加勒万河地区中——基性岩地球化学与年代学研究

Geochemistry and geochronology of intermediate–basic rocks in the Galwan Valley area of the North Qiangtang terrane,Karakoram

【研究目的】加勒万河谷位于北羌塘地体的喀喇昆仑山,紧邻火烧云超大型铅锌矿床。对加勒万河地区新发现的岩浆岩开展岩石地球化学及年代学研究有助于深入理解区域成矿动力学背景和岩浆演化历史,为区域岩浆-构造-成矿作用研究提供理论基础。【研究方法】本研究报道了加勒万河地区7件中—基性岩浆岩样品,岩性包括玄武岩、辉绿岩和闪长岩,并对这些样品进行了系统的矿物学、主量和微量元素、锆石U–Pb年龄和微量元素分析。【研究结果】锆石U–Pb定年结果表明冰洞闪长岩的侵位年龄为(98.9±1.2)Ma,其全岩成分具有低钾钙碱性的特点,而玄武岩中锆石U–Pb定年结果显示其喷发年龄为(232±9)Ma,全岩地球化学组成上具有钙碱性—过碱性的特点。锆石定年结果显示闪长岩与玄武岩中均发育大量约800 Ma的继承锆石,且二者继承锆石年龄频谱均出现6个不同时代的年龄峰。【结论】冰洞闪长岩是地壳增厚背景下壳-幔混合作用的产物,与新特提斯洋闭合后印度板块与欧亚板块碰撞造山的远程效应有关。闪长岩与玄武岩中大量800 Ma继承锆石的发育表明他们来源于新元古代基底物质的熔融。闪长岩与玄武岩中的6个不同的锆石年龄峰反映了中元古代结晶基底、Rodinia超大陆的裂解至新特提斯洋闭合碰撞造山等6个期次的构造岩浆活动。

This paper is the result of geological survey engineering.Objective The Galwan Valley,which adjacent to the Huoshaoyun super large lead−zinc deposit,located in the Karakoram Mountains of the Northern Qiangtang terrane.A systematically lithogeochemistry and chronological studies was conducted on the newly discovered magmatic rocks in the Galwan Valley area to helps us deeply understanding the regional metallogenic dynamics and magmatic evolution history,providing a theoretical foundation for the study of regional magmatic−tectonic−mineralization processes.Methods This study reports seven samples of intermediate−basic magmatic rocks in the Galwan Valley area,including basalt,diabase,and diorite.A systematic mineralogical,major and trace element,zircon U–Pb age,and trace element analyses were conducted on these samples.Results The zircon U–Pb dating results indicate that the Bingdong diorite is emplaced at(98.9±1.2)Ma,and its whole−rock composition is characterized by low−potassium calc−alkaline features.In contrast,the zircon U–Pb dating results for the basalt show an eruption age of(232±9)Ma,with its whole−rock geochemical composition displaying calcium alkali or peralkaline characteristics.The zircon dating results show that both the diorite and basalt samples contain a large number of~800 Ma inherited zircons,and both have age spectra featuring six distinct age peaks.Conclusions The Bingdong diorite is a product of crust−mantle mixing under a crustal thickening background,related to the remote effect of the India–Asia collision orogeny following the closure of the Neo–Tethys Ocean.The existence of numerous~800 Ma inherited zircons in the diorite and basalt indicates that they originated from the melting of Neoproterozoic basement material.The six distinct zircon age peaks in both the diorite and basalt reflect six periods of tectono–magmatic activity,ranging from the Mesoproterozoic crystalline basement and the breakup of the Rodinia supercontinent to the closure of the Neo–Tethys Ocean and subsequent collisional orogeny.