东昆仑中段灶火沟花岗岩锆石U-Pb年代学、地球化学特征及其构造意义  

Zircon U-Pb Dating and Geochemical Characteristics of Zaohuogou Granitoids in the Middle Part of East Kunlun,China and Their Tectonic Significance

作　　者：菅坤坤 何元方 赵端昌 高峰 王星 袁璋 JIAN Kun-kun;HE Yuan-fang;ZHAO Duan-chang;GAO Feng;WANG Xing;YUAN Zhang(Shaanxi Institute of Geological Survey,Xi'an 710054,Shaanxi,China;Shaanxi Mineral Resources and Geological Survey,Xi'an 710068,Shaanxi,China)

机构地区：[1]陕西省地质调查院,陕西西安710054 [2]陕西省矿产地质调查中心,陕西西安710068

出　　处：《地球科学与环境学报》2020年第5期603-621,共19页Journal of Earth Sciences and Environment

基　　金：中国地质调查局地质调查项目(1212011086001);陕西省公益性地质项目(201918)。

摘　　要：东昆仑中段灶火沟花岗岩为一套石英闪长岩-英云闪长岩-花岗岩闪长岩-二长花岗岩的岩石组合。岩石具有连续的地球化学成分变化特征,SiO 2含量(质量分数,下同)为60.94%~74.14%,Al 2O 3含量为12.73%~16.22%,Na 2O+K 2O值为4.51%~7.61%,属中—高钾钙碱性的准铝质至弱过铝质I型花岗岩。岩石稀土元素总含量((106.62~182.76)×10^-6)较低,平均值为144.25×10^-6,总体表现出相对富集大离子亲石元素和轻稀土元素、亏损高场强元素的特征,同时具有Ta、Nb、Ti负异常。LA-ICP-MS锆石U-Pb年代学分析表明,该套花岗岩形成于262~260 Ma,属中二叠世晚期。岩石地球化学特征表明,灶火沟花岗岩形成于大陆弧环境。结合区域地质背景可知,中二叠世晚期古特提斯洋已开始向北俯冲。岩石成因研究表明,幔源岩浆的底侵作用导致下地壳部分熔融,随后壳源熔体与幔源熔体发生不同程度的混合作用形成母岩浆,而后经历了一定程度的结晶分异作用,最终固结成岩。Zaohuogou granitoids in the middle part of East Kunlun consist of quartz-diorite,tonalite,granodiorite and monzogranite.The rocks are characterized by variable SiO 2 contents(60.94%-74.14%),moderate to high Al 2O 3 and total alkaline(the contents of Al 2O 3 and Na 2O+K 2O are 12.73%-16.22%and 4.51%-7.61%),suggesting that Zaohuogou granitoids belong to I-type with middle-high potassium calc-alkaline and meta-aluminous to weak peraluminous.The total content of REE is low((106.62-182.76)×10^-6)with an average of 144.25×10^-6.They are characterized by relative enrichment in large ion lithophile elements(LILEs)and light rare earth elements(LREEs),but depletion in high field strength elements(HFSEs),in addition,they show Ti,Nb and Ta negative anomaly on the primitive mantle-normalized trace element spider diagram.LA-ICP-MS Zircon U-Pb dating shows that Zaohuogou granitoids are formed in 262-260 Ma,belong to the late Middle Permian.The geochemical characteristics indicate that the granitoids are formed in a continental margin arc environment.Combined with the regional geological background and previous data,it is suggested that the Paleotethys ocean begins to subduct northward beneath East Kunlun terrane in the late Middle Permian.During the subduction of Paleotethys ocean,the mantle-derived melts intrude into the lower crust and result in partial melting of lower crust leading to development of granitic magma.The magma is formed by magma mixing of the mantle-derived and crust-derived melts,then experiences some degree of crystallization differentiation,and finally consolidates into the granitoids.

关 键 词：I型花岗岩 地球化学 锆石U-Pb年龄 岩石成因 中二叠世 岩浆混合 大陆弧 东昆仑 

分 类 号：P595[天文地球—地球化学] P597[天文地球—地质学]