峨眉山大火成岩省的岩石圈结构:对地幔柱-岩石圈相互作用的启示  

Lithospheric structure of the Emeishan Large Igneous Province:Implications for plume-lithosphere interaction

作　　者：陈赟[1,2] 赵与同[1,2,3] 刘佳乐 梁晓峰 李玮[4] 徐义刚 CHEN Yun;ZHAO YuTong;LIU JiaLe;LIANG XiaoFeng;LI Wei;XU YiGang(State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;Innovation Academy for Earth Science,Chinese Academy of Sciences,Beijing 100029,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;School of Geophysics and Geomatics,China University of Geosciences(Wuhan),Wuhan 430074,China;State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China;CAS Center for Excellence in Deep Earth Science,Guangzhou 510640,China)

机构地区：[1]中国科学院地质与地球物理研究所,岩石圈演化国家重点实验室,北京100029 [2]中国科学院地球科学研究院,北京100029 [3]中国科学院大学地球与行星科学学院,北京100049 [4]中国地质大学(武汉)地球物理与空间信息学院,武汉430074 [5]中国科学院广州地球化学研究所,同位素地球化学国家重点实验室,广州510640 [6]中国科学院深地卓越创新中心,广州510640

出　　处：《岩石学报》2023年第9期2541-2553,共13页Acta Petrologica Sinica

基　　金：国家重点研发计划(2022YFF0801003)资助.

摘　　要：峨眉山大火成岩省位于扬子克拉通西缘,是中-晚二叠世峨眉山古地幔柱头熔融的产物。因此,该区岩石圈结构特征对于揭示地幔柱-岩石圈相互作用方式与机制具有重要的指示意义。本文基于COMPASS-ELIP宽频带地震台阵资料,开展S波接收函数成像研究,并与同剖面远震S波有限频层析成像、区域面波层析成像结果进行对比分析,识别了沿剖面岩石圈内部主要间断面,从而获得了峨眉山大火成岩省岩石圈结构的横向变化特征。结果显示,相对中带和外带,内带具有地壳增厚(增厚15~20km)、岩石圈减薄(减薄~50km)现象,且岩石圈地幔具有高速、分层特征,但下层底界面转换波震相并不明显;中带岩石圈厚度大(~170km),局部地段岩石圈-软流圈边界(LAB)缺失,对应位置存在地幔低速异常;外带岩石圈厚度略小(~150km),中带和外带均发育岩石圈中部不连续面(MLD)。结合地球化学、岩石学、物理/数值模拟等研究成果,本文推测上述特征记录了古地幔柱作用引起的不同程度岩石圈变形:地幔柱在内带以纵向作用为主,通过热-动力冲击方式造成岩石圈大幅度快速减薄,地幔柱头高程度减压熔融,产生的大规模岩浆穿透岩石圈地幔,在地壳发生底侵和内侵,部分喷出地表形成溢流玄武岩;地幔柱在中带以横向作用为主,通过底部剪切引起岩石圈地幔横向伸展,甚至造成局部撕裂,在撕裂部位进一步引发热-化学侵蚀并导致岩石圈破坏;地幔柱在外带以垂向拖曳为主,造成岩石圈的局部拆沉而减薄。此外,内带下方地幔的高速、分层特征,可能指示经历地幔柱作用减薄后的岩石圈,减薄产生的岩石圈空区因捕获地幔柱头熔融残留物而得到一定程度愈合,而受地幔柱改造后的残存岩石圈,因经历大量熔体抽取更加亏损而得到强化。综上,本文揭示的峨眉山大火成岩省岩石圈结构,为进一步理解地幔柱-岩石圈相Emeishan Large Igneous Province(LIP)is located at the western margin of the Yangtze Craton and is generally believed as the melting product of the Emeishan mantle plume head at the middle-late Permian.To better understand plume-lithosphere interaction processes,we used the S-wave receiver function method to image the lithospheric discontinuities across the Emeishan LIP,based on the broadband seismic data from the COMPASS-ELIP experiment.Combined with the S-wave velocity structures constructed by the teleseismic S-wave finite-frequency tomography based on the data of the same experiment,and extracted from the surface wave tomography in East Asia,we obtained the lateral variations of the lithospheric structure beneath the Emeishan LIP.Our results reveal crustal thickening by 15~20km and lithospheric thinning of~50km beneath the inner zone(INZ)of the Emeishan LIP.The lithospheric mantle beneath the INZ is characterized by the layered high-velocity anomaly,but with non-obviously converted phase of S-wave receiver functions at the base of the lithosphere.The thickest lithosphere of~170km is imaged beneath the intermediate zone(IMZ)and that beneath the outer zone(OTZ)is~150km.Moreover,our results show that the mid-lithospheric discontinuity(MLD)is well-developed beneath the IMZ and OTZ,and the lithosphere-asthenosphere boundary(LAB)is locally undetectable where the low-velocity anomaly exists in the upper mantle of the IMZ.These,together with petrological and geochemical analyses and geodynamic modeling,allow us to propose a plume-lithosphere interaction model to account for variable lithospheric deformation across the Emeishan LIP.The INZ s lithosphere was once rapidly thinned due to the thermal-mechanical impact of the mantle plume head.Meanwhile,the high-degree decompression melting of the mantle plume head generated large-volume magma,some of which had penetrated the lithospheric mantle and the crust,while some erupted as the Emeishan basalts.The INZ s lithosphere thus mainly shows a vertical deformation pattern.In

关 键 词：峨眉山大火成岩省 地幔柱-岩石圈相互作用 S波接收函数 岩石圈-软流圈边界 岩石圈中部不连续面 

分 类 号：P31[天文地球—固体地球物理学] P542.5[天文地球—地球物理学]