西秦岭与赛什塘铜矿床有关的花岗质岩石岩浆源区特征及大地构造背景探讨  

Magma source and tectonic setting of the granitoids associated with Saishitang Cu deposit in the West Qinling terrane

作　　者：付长垒[1] 闫臻[1] 郭现轻[2] 牛漫兰[3] 陈雷[2] 夏文静[4] 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]中国地质科学院矿产资源研究所,北京100037 [3]合肥工业大学资源与环境工程学院,合肥230009 [4]中国科学院大学地球科学学院,北京100049

出　　处：《岩石学报》2016年第7期1997-2014,共18页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41372207);中国地质调查局地质调查项目(1212011120159;12120114080001;12120115069401;12120115027001;121201102000150020)联合资助

摘　　要：西秦岭赛什塘铜矿区内出露的三叠纪花岗质岩石有闪长玢岩、石英闪长岩、石英闪长玢岩、花岗斑岩和石英斑岩,其岩浆源区与形成构造环境可为古特提斯洋演化和区域成矿作用研究提供证据。岩石地球化学特征共同表明,这些花岗质岩石属于准铝质钙碱性-高钾钙碱性系列,为I型花岗岩;Mg#值变化较大(39~68),LREE富集,HREE亏损,(La/Yb)N比值介于8.50~22.9,具有Eu负异常,δEu介于0.28~0.78,同时富集大离子亲石元素Cs、Rb、K、Pb,亏损高场强元素Nb、Ta、Ti,呈现出与典型俯冲作用密切相关岛弧花岗岩相一致地球化学特征。石英闪长玢岩和石英斑岩SHRIMP锆石U-Pb年龄分别为219.0±2.3Ma和220.0±2.0Ma,锆石εHf(t)分别为-4.5^-2.1和-2.5^+1.0,对应二阶段模式年龄分别为1392~1544Ma和1190~1415Ma。结合前人对西秦岭三叠纪花岗岩以及其南侧阿尼玛卿蛇绿混杂带研究成果,本文认为赛什塘铜矿区花岗质岩石与西秦岭同时期花岗岩形成于与古特提斯洋向北俯冲密切相关的大陆边缘弧环境,其岩浆源区为中元古代下地壳变基性岩,且岩浆可能受到地幔物质混染。The granitoids in Saishitang Cu deposit of the West Qiling terrane consist of diorite porphyrite,quartz diorite,quartz diorite porphyrite,granite porphyry and quartz porphyry. Their magma sources and tectonic setting can provide vital constrains on the evolution of the Paleotethyan Ocean and regional metallogenesis. Geochemical analyses indicate that these granitoids belong to metaluminous calc-alkaline to high-K calc-alkaline rock series with similar geochemical charcacteristics of I-type granite. They have variable Mg#values of 39 - 68,high（ La/Yb）Nratios of 8. 50 - 22. 9 with LREE enrichment,HREE depletion and negative Eu anomalies（ δEu = 0. 28 - 0. 78）. They are enriched in LILE（ Cs,Rb,K and Pb）,depleted in HFSE（ Nb,Ta and Ti）,showing typical features of subduction-related arc granitoids. Zircon SHRIMP U-Pb dating of quartz diorite porphyrite and quartz porphyry yields concordant ages of 219. 0 ± 2. 3Ma and 220. 0 ± 2. 0Ma,repectively. Their εHf（ t） values of magmatic zircons are- 4. 5 -- 2. 1 and- 2. 5 - ＋ 1. 0,with conresponding tDM2 ages of 1392 - 1544 Ma and 1190 - 1415 Ma,respectively. In combination with previous results on Triassic granitoids in the West Qinling terrane and A＇nymaqen ophiolitic mélange,we suggest that the coeval granitoids in the Saishitang Cu deposit and West Qinling terrane should be formed in continental margin arc environment by northward subduction of the Paleotethyan Ocean. They should mainly originate from the partial melting of Mesoproterozoic lower-crustal metabasic rocks and were contaminated by mantle-derived magmas.

关 键 词：花岗岩 岩浆源区 构造背景 赛什塘铜矿床 西秦岭 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]