西秦岭德乌鲁含矿岩体及其包体的岩石学成因和构造意义  

Petrogenesis and tectonic implications of the Dewulu ore-bearing pluton and mafic enclaves in western Qinling

作　　者：贾儒雅[1,2,3] 王涛 李康宁[6] 程志中 薛建玲 林成贵[1,2] 陈辉 刘铮[7] JIA Ruya;WANG Tao;LI Kangning;CHENG Zhizhong;XUE Jianling;LIN Chenggui;CHEN Hui;LIU Zheng(Development and Research Center,China Geological Survey,Beijing 100037,China;Technical Guidance Center for Mineral Resources Exploration,Ministry of Natural Resources,Beijing 100083,China;School of Earth Resources,China University of Geosciences(Wuhan),Wuhan 430074,China;Chinese Academy of Geological Sciences,Beijing 100037,China;Geological Society of China,Beijing 100037,China;Third Institute of Geological and Mineral Exploration,Gansu Provincial Bureau of Geology and Mineral Resources,Lanzhou 730050,China;School of Resource Environment and Earth Science,Yunnan University,Kunming 650091,China)

机构地区：[1]中国地质调查局发展研究中心,北京100037 [2]自然资源部矿产勘查技术指导中心,北京100083 [3]中国地质大学(武汉)资源学院,湖北武汉430074 [4]中国地质科学院,北京100037 [5]中国地质学会,北京100037 [6]甘肃省地质矿产勘查开发局第三地质矿产勘查院,甘肃兰州730050 [7]云南大学资源环境与地球科学学院,云南昆明650091

出　　处：《地学前缘》2019年第5期290-303,共14页Earth Science Frontiers

基　　金：国家重点研发计划深地资源勘查开采专项“深部矿产资源三维找矿预测评价示范”课题（2017YFC0601506）;中国地质调查局“矿集区矿产调查及深部找矿预测”二级项目（DD20190570）

摘　　要：德乌鲁岩体位于西秦岭地区,其主体岩性为花岗闪长岩,在岩体内及其接触带发育有多处金、铜矿床。LA-ICP-MS锆石U-Pb定年表明该岩体侵位于印支早期,年龄为(250±1.8)Ma,该岩体为准铝质,其铝饱和指数ASI为0.9~1.0。所有样品具有高的K2O含量(2.95%~3.52%)、K2O/Na2O比值(0.97~1.10)、Mg^#(0.57~0.61)和相容元素含量(w(Cr)=(88~132)×10^-6)。因此,我们认为德乌鲁寄主岩形成于壳幔岩浆的混合作用。在该岩体中广泛分布有镁铁质岩浆包体,这些包体即是镁铁质岩浆注入中酸性岩浆中时迅速降温形成的。德乌鲁包体具有中性的成分,其SiO2含量为56.17%~60.95%,岩性主要为辉长闪长岩和闪长岩。相对于寄主岩,包体有着更高的Mg^#(0.65~0.67)和低的TiO2含量(0.57%~0.62%)。它们也有着高的钾含量(1.74%~2.43%),属于高钾钙碱性系列岩石。所有样品具有高的相容元素含量,如Cr((212~419)×10^-6)和Ni((46~111)×10^-6)。相对于重稀土元素,样品中轻稀土元素相对富集,并且具有中等的Eu负异常。在原始地幔标准化的微量元素蛛网图上,所有包体具有明显的Nb-Ta负异常。德乌鲁暗色包体可能形成于曾受俯冲作用改造过的富钾的岩石圈地幔源区部分熔融过程,并伴随有后期镁铁质矿物的分异。本区的印支早期岩浆作用及与其有关的矿床很可能形成于活动大陆边缘环境。The Dewulu granodiorite pluton in the West Qinling Orogen contains a series of Au and Cu ore deposits.LA-ICP-MS yielded zircon U-Pb age of 250±1.8 Ma,indicating pluton emplacement occurred in the Early Indosinian.The pluton was found to be weak peraluminous with ASI of 0.9 to 1.0.All samples had high K2O content(2.95%-3.52%)and high K2O/Na2O ratio(0.97-1.10).The granitoids showed high Mg^# and compatible elemental content(Cr:(88-132)×10^-6).Thus,we consider that the Dewulu pluton was formed by the mixing of crust-and mantle-derived magmas.Abundant mafic enclaves occur in the pluton.These gabbro diorite or diorite enclaves had intermediate SiO2 content of 56.17%-60.95%.Relative to the host rocks,the mafic enclaves had high Mg^#(0.65-0.67)and low TiO2 content(0.57%-0.62%).They were high-K calc-alkaline rocks and had high K2O(1.74%-2.43%)and compatible elemental contents(Cr:(212-419)×10^-6;Ni:(46-111)×10^-6).They were enriched in LREEs related to HREEs showing intermediate negative Eu anomalies.In the trace element spider diagram,all the enclaves exhibited notable Nb-Ta anomalies.We consider that the Dewulu mafic enclaves are likely derived by partial melting of a potassic lithospheric mantle source,modified by subduction process with subsequent removal of mafic minerals.The Early Indosinian magmatism and associated ore deposits were likely emplaced at an active continental margin in this area.

关 键 词：花岗闪长岩 镁铁质包体 印支期 西秦岭 成矿大地构造背景 

分 类 号：P588.12[天文地球—岩石学] P581[天文地球—地质学]