大兴安岭火山群区的深部速度结构及火山成因  

The deep seismic velocity structures beneath volcanoes in Great Xing′an Range and volcanic mechanism

作　　者：张风雪[1,2] 吴庆举[1,2] 李永华[1,2] 张瑞青[1,2] ZHANG FengXue;WU QingJu;LI YongHua;ZHANG RuiQing(Institute of Geophysics,China Earthquake Administration,Beijing 100081,China;Key Laboratory of Earthquake Source Physics,China Earthquake Administration,Beijing 100081,China)

机构地区：[1]中国地震局地球物理研究所,北京100081 [2]中国地震局震源物理重点实验室,北京100081

出　　处：《地球物理学报》2022年第4期1271-1287,共17页Chinese Journal of Geophysics

基　　金：中国地震局地球物理研究所基本科研业务费专项(DQJB19B26);国家自然科学基金(41874112,U1839210,41874072,41674103)联合资助.

摘　　要：中国东北地区新生代板内火山群广泛发育,其中大兴安岭火山群区的上地幔结构研究匮乏,火山群的演化机理尚不明确.本文收集近年来大兴安岭地区流动台站和固定台站的观测波形数据,通过波形互相关从远震事件记录中挑选出64575个P波震相走时残差,13566个S波震相走时残差,开展远震体波走时层析成像研究,获得该区上地幔的V_(P)、V_(S)以及V_(P)/V_(S)异常结构.研究结果显示,火山群区的低速异常分布在上地幔的不同深度范围内,火山群下方的低速异常向下延深并交汇于软流圈内.结合本文和已有的研究结果推断,岩石圈拆沉导致的软流圈物质上涌是大兴安岭火山群的深部成因.火山群区的速度异常比值优势值为1.5左右,表明速度异常既有温度变化成因也有物质成份成因.总体而言,处在地幔不同深度范围内的低速异常极值区基本和高波速比值区域相对应,暗示火山群下方的岩浆流体处在不同的深度位置,这可能是阿尔山和诺敏河火山群火山岩性存在差异的原因.The Cenozoic intraplate volcano sites are widespread among Northeast China.The upper mantle structures beneath the Great Xing′an Range were poorly understood and the mechanism of volcanic activities remained unclear.The waveform data was assembled from temporary and permanent seismic stations deployed in Great Xing′an Range in recent years.64575 P-wave and 13566 S-wave traveltime residuals were measured from teleseismic waveform using waveform correlation and were inverted to image upper mantle V_(P),V_(S)and V_(P)/V_(S)variations through teleseismic traveltime tomography.Results show that low-velocity anomalies are situated at different depths in the upper mantle beneath volcanic sites.In addition,those anomalies extend downward and connect with each other at the depth range of asthenosphere.Related to with previous studies,a model of asthenospheric upwelling,which is attributed to delamination of continental lithosphere,accounts for volcanic activities in the Great Xing′an Range.In the region of volcanic sites,the optimal value of S to P heterogeneity ratios are~1.5,indicating that both thermal variation and chemical composition are the primary factors for velocity anomaly.Generally,those low-velocity zones,which are characterized by peak value,are temporally consistent with high V_(P)/V_(S)ratio volumes at different depths in the mantle.It implies that magma fluid was generated at those different positions,which could contribute to compositional variations in basaltic rock between Aershan and Nuomin River volcanic sites.

关 键 词：阿尔山 诺敏河 火山成因 地震成像 

分 类 号：P315[天文地球—地震学]