西秦岭德乌鲁岩体成因及地质意义——来自岩石地球化学的证据  

The origin and geological significance of the Dewulu pluton in West Qinling:Evidence from petrogeochemistry

作　　者：冯小明[1] 李注苍[1] 齐建宏[1] FENG Xiao-ming;LI Zhu-cang;QI Jian-hong(The Third Institute of Geology and Minerals Exploration,Gansu Provincial Bureau of Geology and Mineral Exploration and Development,Lanzhou 730000,China)

机构地区：[1]甘肃省地矿局第三地质矿产勘查院,甘肃兰州730000

出　　处：《岩石矿物学杂志》2021年第2期347-362,共16页Acta Petrologica et Mineralogica

基　　金：甘肃省省财政调查评价项目(甘财建[2010-254])。

摘　　要：西秦岭德乌鲁岩体位于夏河-合作断裂和力士山-围当山断裂之间,寄主岩石以花岗闪长岩为主,石英闪长岩和石英二长闪长岩次之,并含有大量暗色微粒包体(MMEs)。对德乌鲁岩体开展了年代学研究,获得的花岗闪长岩的LA-ICP-MS锆石U-Pb年龄为225.9±1.3 Ma,表明该岩体形成于晚三叠世早期,可能与扬子板块与华北板块陆陆碰撞有关。岩石地球化学研究表明,寄主岩石具有高K_(2)O,低Y、MgO的特点,而暗色微细粒包体(MMEs)具低K_(2)O,高Y、MgO的特点,在微量元素蛛网图解和稀土元素配分模式上它们具有类似的曲线,在Al_(2)O_(3)/MgOSiO_(2)/MgO图上呈现明显的线性关系,表明这些岩石之间发生了明显的物质交换,说明德乌鲁岩体中的石英闪长岩、石英二长闪长岩和花岗闪长岩是由镁铁质岩浆和长英质岩浆混合产生的,可能与扬子板块和华北板块陆陆碰撞后伸展环境下发生的强烈壳-幔相互作用有关。MMEs可能是镁铁质岩浆的残余物,地球化学特征显示可能有幔源物质的加入,并带来了Au、Cu等成矿元素,在岩体形成演化过程中生成富含Cu和Au的含矿热液,从而在德乌鲁岩体中形成了热液型铜金矿床。The Dewulu pluton is located between Xiahe-Hezuo fault and Lishishan-Weidangshan fault.The hose rock is predominantly composed of granodiorite with subordinate quartz diorite and quartz monzodiorite,and contains a large number of microgranular mafic enclaves(MMEs).Some Cu-Au deposits occur within the pluton and have been studied by many researchers;nevertheless,there are few researches on the pluton.LA-ICP-MS zircon UPb dating on the granodiorite of the Dewulu pluton yielded an age of 225.9±1.3 Ma,suggesting that the pluton was formed in the early period of late Triassic,and might have been related to the continental collision between the Yangtze and North China plates.Petrogeochemical studies show that host rocks are characterized by high K_(2) O and low Y and MgO,while the MMEs by low K_(2) O and high Y and MgO.Both host rocks and MMEs have similar features in trace element spider diagram and REE distribution pattern and obvious linear relationship on Al2 O3/MgO-SiO_(2)/MgO diagram.These phenomena indicate that material exchange took place in these rocks,and quartz diorite,quartz monzodiorite and granodiorite were generated by the mixing of mafic and felsic magmas resulting from the strong crust-mantle interaction occurring in the extensional environment after the collision of the Yangtze and North China plates.MMEs may be the remnant of the parental mafic magma,and their geochemical characteristics show that they might have been derived from the mantle which was enriched in Au,Cu and other ore-forming elements.The Cu and Au enriched fluid was produced during the evolution of the mixed magma,and precipitated in the Dewulu pluton to form the hydrothermal Cu-Au deposits.

关 键 词：年代学 地球化学 岩浆混合 德乌鲁岩体 西秦岭 

分 类 号：P597.3[天文地球—地球化学] P588.122[天文地球—地质学]