西昆仑奇台达坂岩体和暗色包体锆石U-Pb年代学、地球化学特征及其地质意义  

Zircon U-Pb age,geochemical and Sr-Nd isotopic compositions of granites and mafic magmatic enclaves from the Qitaidaban pluton,West Kunlun Orogen,and their geological significance

作　　者：张晓宇 魏小鹏 王核[1] 闫庆贺 周楷麟 ZHANG Xiaoyu;WEI Xiaopeng;WANG He;YAN Qinghe;ZHOU Kailin(Key Laboratory of Mineralogy and Metallogeny,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;University of Chinese Academy of Sciences,Beijing 100049,China;School of Resource Environment and Earth Sciences,Yunnan University,Kunming 650500,Yunnan,China)

机构地区：[1]中国科学院广州地球化学研究所矿物学与成矿学重点实验室,广东广州510640 [2]中国科学院大学,北京100049 [3]云南大学资源环境与地球科学学院,云南昆明650500

出　　处：《地球化学》2024年第6期849-869,共21页Geochimica

基　　金：第三次新疆综合科学考察项目(2022XJKK1302);国家自然科学基金项目(91962215、41972088、42002073)联合资助。

摘　　要：奇台达坂岩体位于西昆仑造山带东段甜水海地体中段,本研究对奇台达坂黑云母二长花岗岩及其镁铁质暗色包体开展了锆石U-Pb年代学、岩相学、矿物学、地球化学和Sr-Nd同位素综合研究,探讨西昆仑造山带中晚三叠世构造–岩浆活动和古特提斯洋构造演化。结果表明:奇台达坂黑云母二长花岗岩与暗色包体形成于约213 Ma。黑云母二长花岗岩属于高钾钙碱性Ⅰ型花岗岩,具有高Mg^(#)值(35~37),铝饱和指数(A/CNK)为1.01~1.05,为弱过铝质岩石。微量元素表现出富集大离子亲石元素(如U、Th、Pb)、亏损高场强元素(如Nb、Ta)特征,显示弱Eu负异常。相比于寄主岩体,奇台达坂暗色包体具有更高的MgO含量(2.89%~4.91%)和Mg^(#)值(39~43),更低的SiO_(2)含量(53.53%~59.73%)。Sr-Nd同位素组成表明,奇台达坂黑云母二长花岗岩及暗色包体可能是由前寒武纪变质火成岩和变质沉积岩部分熔融形成,暗色包体应为岩浆混合作用的产物。因此,本研究认为奇台达坂岩体属于碰撞后阶段的产物,由俯冲古特提斯洋壳拆离,随后上涌的软流圈诱发交代岩石圈地幔部分熔融,并进一步导致前寒武纪变质火成岩和变质沉积岩部分熔融形成。The Qitaidaban pluton is located in the middle of the Tianshuihai terrane in the eastern section of the West Kunlun orogenic belt.In this study,we carried out a comprehensive study of zircon U-Pb age,petrography,mineralogy,geochemistry,and Sr-Nd isotopes on biotite monzogranites and mafic magmatic enclaves(MMEs)in the Qitaidachan pluton to investigate the Middle and Late Triassic tectonics and magmatism and Paleo-Tethyan tectonic evolution of this orogenic belt.The results show that the Qitaidaban biotite monzogranites were coeval with the MMEs(about 213 Ma).The biotite monzogranites are high-K calc-alkaline Ⅰ-type granites with high Mg^(#)(35-37),showing weak-peraluminous affinities(A/CNK=1.01-1.05).They are also characterized by enrichment of LLIEs(e.g.,U,Th and Pb),depletion of HFSEs(e.g.,Nb and Ta),and weak negative Eu anomalies(Eu/Eu^(*)=0.49-0.88).In contrast,the MMEs had lower SiO2(53.53%-59.73%),higher MgO(2.89%-4.91%),and higher Mg^(#)values(39-43).The Sr-Nd isotope compositions of the Qitaidaban biotite monzogranites indicate an origin of partial melting of Precambrian metaigneous and metasedimentary rocks,and the mafic magmatic enclaves may have been the products of magma mixing.Therefore,this study suggests that the Qitaidaban pluton was emplaced in a post-collisional setting,which was caused by the break off of the subducted Paleotethys oceanic crust,followed by the partial melting of the lithospheric mantle induced by the upwelling of the asthenosphere,which further led to the partial melting of Precambrian metaigneous and metasedimentary rocks.

关 键 词：西昆仑造山带 地球化学 花岗岩 暗色包体 奇台达坂 岩石成因 

分 类 号：P595[天文地球—地球化学] P597[天文地球—地质学]