东昆仑造山带海德乌拉铝质A型流纹岩成因及其意义  

Genesis and implications of peraluminous A-type rhyolite in the Haidewula area,East Kunlun Orogen

作　　者：雷勇亮 戴佳文 白强 王凯兴[1,2] 孙立强 刘晓东 余驰达[1] 何世伟 LEI YongLiang;DAI JiaWen;BAI Qiang;WANG KaiXing;SUN LiQiang;LIU XiaoDong;YU ChiDa;HE ShiWei(State Key Laboratory of Nuclear Resources and Environment,East China University of Technology,Nanchang 330013,China;School of Earth Sciences,East China University of Technology,Nanchang 330013,China;Qinghai Nuclear Industry Geological Bureau,Xining 810001,China)

机构地区：[1]核资源与环境国家重点实验室,东华理工大学,南昌330013 [2]东华理工大学地球科学学院,南昌330013 [3]青海省核工业地质局,西宁810001

出　　处：《岩石学报》2021年第7期1964-1982,共19页Acta Petrologica Sinica

基　　金：国家自然科学青年基金项目(42072095);中国核工业集团高校科研攻关项目(201619);青海省地勘基金项目(2019048108kc050、2020021041kc008)联合资助。

摘　　要：东昆仑造山带古生代后碰撞岩浆岩的成因及后碰撞伸展环境的形成机制一直备受争议。本文选择东昆仑造山带古生代海德乌拉流纹岩开展锆石U-Pb-Hf同位素地质学及全岩地球化学研究,分析其成因并探讨后碰撞伸展环境的起始时间和形成机制。锆石LA-ICP-MS U-Pb同位素定年结果显示,海德乌拉流纹岩形成于426Ma,属于志留纪罗德洛世岩浆活动产物。样品显示高钾钙碱性-钾玄岩系列岩石特征;其A/CNK值为1.04-1.18,属于过铝质-强过铝质岩石。在原始地幔标准化微量元素图解上,样品显示Th、U和Pb等元素相对富集,Nb、Ta、Ti、Ba和Sr等元素相对亏损的特征;在球粒陨石标准化稀土元素图解上,海德乌拉样品显示轻稀土相对富集且具有明显Eu负异常(δEu=0.03-0.06)。海德乌拉流纹岩显示出高FeOT/MgO和10^(4)×Ga/Al比值以及高场强元素总量(Zr+Nb+Ce+Y),属于A型岩浆岩范畴。样品的锆石εHf(t)为+0.60-+2.39,对应的二阶段模式年龄介于1285-1370Ma之间。元素和同位素地球化学特征显示海德乌拉A型流纹岩可能是在高温和中地壳压力下长英质火成岩熔融而成。结合东昆仑造山带古生代岩浆岩和变质岩的年代学和地球化学特征,笔者认为在志留纪罗德洛世东昆仑造山带处于典型的后碰撞伸展环境,该伸展环境可能是受到冈瓦纳大陆东北缘碰撞后加厚岩石圈拆沉作用的影响。The initiation time and formation mechanism of the post-collisional extension in the East Kunlun Orogenic Belt(EKOB)have been controversial.A combined study of zircon U-Pb chronology,geochemistry,and Hf isotope composition has been carried out for the Silurian rhyolite in the Haidewula region of the EKOB,to further reveal their genesis and formation mechanism.Zircon LA-ICP-MS U-Pb isotope dating reveals that the Haidewula rhyolite formed at 426Ma,representing Silurian Radero magmatic activity.The samples belong to the high-K calc-alkaline to shoshonite series,and display peraluminous to strong peraluminous affinity with A/CNK ratio ranging from 1.04 to 1.31.In the primitive-mantle normalization trace element diagrams,the samples show Th,U,and Pb enrichment,and Nb,Ta,Ti,Ba,and Sr depletion.They are also rich in LREE with strongly negative Eu anomalies(δEu=0.03-0.06).The Haidewula rhyolite belongs to A-type magmatic rock with high FeOT/MgO and 10^(4)×Ga/Al ratios,and high contents of high-field strength element(Zr+Nb+Ce+Y).The samples have zirconεHf(t)values of 0.60-2.39 with corresponding Hf isotope two-stage model age ranging from 1285Ma to 1370Ma.Elemental and isotopic geochemical characteristics reveal that the Haidewula A-type rhyolite was formed by high-temperature,middle-crust pressure melting of Ordovician felsic igneous rocks.Combined with the chronologic and geochemical characteristics of Paleozoic magmatic rocks and metamorphic rocks,it is suggested that the EKOB was in a typical post-collisional extension during the Silurian Roderlo epoch,which may have been influenced by the post-collisional lithospheric delamination of the northeastern margin of Gondwana.

关 键 词：东昆仑造山带 A型流纹岩 志留纪 后碰撞伸展 锆石U-PB年龄 

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