西南三江永平卓潘碱性杂岩体源区与形成机制:全岩元素、锆石U-Pb年代学和Hf同位素联合约束  

Magma source and formation mechanism of the Zhuopan alkaline complex in Yongping,Southwest China: Constraints from geochemistry,zircon U-Pb geochronology and Hf isotopes

作　　者：杜斌[1] 王长明[1] 杨立飞[1] 石康兴 张端 陈奇 祝佳萱 张淑花[2] DU Bin;WANG ChangMing;YANG LiFei;SHI KangXing;ZHANG Duan;CHEN Qi;ZHU JiaXuan;ZHANG ShuHua(School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China;The 606 Team of Sichuan Metallurgy Geology Exploration Bureau, Chengdu 611730, China)

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]四川省冶金地质勘查局六零六大队,成都611730

出　　处：《岩石学报》2018年第5期1376-1396,共21页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划(2015CB452603;2009CB421008);高等学校学科创新引智计划(B07011);地质过程与矿产资源国家重点实验室科技部专项经费(37132018002);中央高校基本科研业务费(2652017223)联合资助

摘　　要：永平卓潘碱性杂岩体是三江特提斯新生代钾质岩浆带重要组成部分,位于兰坪盆地西缘。岩石类型主要为正长辉石岩、辉石正长岩、正长岩以及少量霞石正长岩。岩石化学性质显示高碱、高K_2O/Na_2O比值、低TiO_2和高Al_2O_3的特征。岩体微量元素显示富集大离子亲石元素(LILE),相对亏损高场强元素(HFSE)元素,特别是"Ta-Nb-Ti"负异常更明显,具有典型俯冲带岩浆的特征。稀土总含量都比较高,LREE富集,HLEE相对亏损,Eu负异常不明显或无Eu负异常,(La/Yb)_N值较大介于38.2～80.3之间。对卓潘岩体的正长岩和正长辉石岩2个样品进行了LA-ICP-MS锆石U-Pb定年,年龄分别为33.40±0.38Ma和34.22±0.33Ma。正长辉石岩εHf(t)值介于-10.6～-4.3之间,二阶段模式年龄在1356～1759Ma之间。卓潘碱性杂岩体不同岩性的稀土元素配分曲线和微量元素原始地幔标准化图解基本一致,表明卓潘碱性杂岩体不同类型的岩石是同源岩浆演化的产物。岩体的Nb/U均值为2.95介于俯冲带流体和全球俯冲沉积物之间以及岩体微量元素明显亏损高场强元素Ti、Nb、Ta,稀土元素表现为轻稀土富集、无或弱的负Ce和负Eu异常,暗示了岩浆源区存在俯冲的洋壳或陆壳沉积物的流体或熔融体与岩石圈地幔的交代富集作用。岩浆源区经历晚石炭世-晚二叠世(305～250Ma)古特提斯昌宁-孟连洋和古特提斯金沙江-哀牢山洋双向俯冲,岩石圈地幔发生富集作用并形成富钾的交代岩石圈地幔。在新生代,新特提斯洋岩石圈从印度大陆岩石圈断离,引发交代富集大陆岩石圈地幔拆沉,热的软流圈上涌,熔融交代的富钾岩石圈地幔,岩浆侵位分异形成卓潘岩体。The Zhuopan alkaline complex in the western margin of the Lanping Basin,is an important part of the Cenozoic potassic magmatic belt in Sanjiang Tethys. The Zhuopan alkaline complex mainly consists of syenite-pyroxenolite,gabbro-syenite,syenite and nepheline. Those rocks are characterized by high alkaline,high K2 O/Na2 O,low TiO2 and high Al2 O3. Primitive mantle-normalized incompatible trace element patterns exhibit strong enrichments in large ion lithophile elements,relatively high field strength elements and strong negative Ta,Nb,Ti anomalies content,which are typical characteristics of subduction-related magma. Chondrite-normalized rare earth element（ REE） patterns show enrichment in light rare earth elements（ LREE）,flat heavy rare earth elements（ HREE）patterns and no or weak negative Eu anomalies and high（ La/Yb）Nvalue ranging from 38. 2 to 80. 3. The LA-ICP-MS zircon U-Pb ages from the syenite and syenite-pyroxencterite are 33. 40 ± 0. 38 Ma and 34. 22 ± 0. 33 Ma. Zircon εHf（t） values range from-10. 6 to-4. 3,corresponding Hf crust model ages（ tDM^c） rang from 1. 36 Ga to 1. 76 Ga. All of the rocks in the Zhuopan alkaline complex have similar chondrite-normalized REE patterns and primitive mantle-normalized trace element patterns,suggesting that they were derived from similar parental magmas. Mean Nb/U values 2. 95 between the subduction zone fluid and the global subduction sediments,exhibits strong negative high field strength elements（ HFSE） such as Ta,Nb,Ti,and shows enrichment in LREE and no or weak negative Ce and Eu anomalies. Those characteristics suggest that the fluid of the subducted oceanic or continental crust deposits in the magmatism source area or shows the metasomatic enrichment in molten rock and lithosphere mantle. The double-sided subduction of Changning-Menglian Paleo-Tethyan oceanic and Jinshajing-Ailaoshan Paleo-Tethyan oceanic resulted in the formation of metasomatic enriched mantle magma during,Late Carboniferous-Late Permian（305 - 205 Ma） and K-rich

关 键 词：岩浆源区 形成机制 拆沉作用 卓潘岩体 兰坪盆地 

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