中朝克拉通东部上地幔精细圈层结构:来自朝鲜核爆源深地震测深剖面的约束  

Fine-layer structure of the upper mantle in the eastern Sino-Korean Craton:constrained by deep seismic sounding profile with the Democratic People′s Republic of Korea nuclear explosion source

作　　者：张晓青 Hans Thybo Irina M.Artemieva 徐涛[1,8] 白志明[1,8] ZHANG XiaoQing;Hans Thybo;Irina M.Artemieva;XU Tao;BAI ZhiMing(State Key Laboratory of lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;University of Chinese Academy of Sciences,Beijing 100049,China;Chinese Academy of Geological Sciences,Beijing 100037,China;School of Earth Science,China University of Geosciences,Wuhan 430074,China;Eurasia Institute of Earth Science,Istanbul Technical University,Maslak,34469 Istanbul,Turkey;Department of Geophysics,Stanford University,Stanford,CA 94305,USA;Section of Marine Geodynamics,GEOMAR Helmholtz Center for Ocean Research,Kiel 24148,Germany;Innovation Academy for Earth Science,CAS,Beijing 100029,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]中国科学院大学,北京100049 [3]中国地质科学院,北京100037 [4]中国地质大学(武汉)地球科学学院,武汉430074 [5]Eurasia Institute of Earth Science,Istanbul Technical University,Maslak,34469 Istanbul,Turkey [6]Department of Geophysics,Stanford University,Stanford,CA 94305,USA [7]Section of Marine Geodynamics,GEOMAR Helmholtz Center for Ocean Research,Kiel 24148,Germany [8]中国科学院地球科学研究院,北京100029

出　　处：《地球物理学报》2023年第7期2843-2859,共17页Chinese Journal of Geophysics

基　　金：国家自然科学基金(92500210,42130807,41974048,42104042)资助。

摘　　要：晚中生代以来,中朝克拉通经历了一系列强烈构造和岩浆事件,岩石圈性质发生显著变化.为此,中朝克拉通“破坏”一词被提出,但破坏形态主要来自地表地质、地球化学、地壳结构和上地幔较大尺度的地震学成像等的约束.因较大能量的人工震源方法较难在人口密集的华北地区实施,基于深地震测深剖面对整个上地幔精细圈层结构的探究仍限于较少地区.为此,我们根据中国地震台网和部分流动台站记录的2017年9月3日朝鲜地下核试验地震数据,利用宽角反射/折射成像方法,揭示了中朝克拉通东部及邻区5个不同方位剖面的高垂向分辨率一维地壳和上地幔P波速度结构.结果显示,中朝克拉通东部及周边地区平均地壳厚度为29~30 km,全地壳平均速度在6.10~6.17 km·s^(-1)之间,远低于全球大陆地壳平均值,表明该区下地壳很薄甚至缺失,且在地壳底部可能存在因局部拆沉而形成的强水平各向异性.该区80 km左右深度可观测岩石圈正速度梯度内部间断面,推测其可能是由尖晶石到石榴石相变引起.在约220 km深度,我们探测到通常存在于稳定克拉通下方的Lehmann间断面,揭示中朝克拉通东部还部分保留类似稳定克拉通的圈层结构.介于80 km间断面和Lehmann间断面之间的上地幔P波速度较全球IASP91模型明显偏低,且上地幔震相(Pn、PL和P410)到时介于稳定克拉通区域和活动构造区域之间,表明中朝克拉通东部及邻区上地幔整体处于“冷”至“热”的过渡状态.Since the Late Mesozoic,the lithospheric properties of the Sino-Korean Craton have changed significantly.However,the specific form of craton"destruction"is mainly based on the investigation of surface geology,geochemistry,crustal structure imaging and the detection of low-velocity discontinuity in the upper mantle,lacking constraints on the fine structure and properties of the entire upper mantle.Therefore,based on the seismic observations from the nuclear explosion on September 3,2017 in North Korea recorded by the national seismic network of China and some temporary broadband seismic stations,we obtain high-vertical-resolution one-dimensional VP models of the upper mantle beneath the eastern Sino-Korean Craton and its adjacent areas by using deep seismic sounding imaging method.The results reveal that the regional average crustal thickness is about 29~30 km,and the average crustal velocity is about 6.10~6.17 km·s^(-1),which is significantly lower than the global continental average value,indicating the lower crust below these profiles is extremely thin or even missing.Thin and strong reflection coefficient across the Moho discontinuity may be caused by the existence of strong horizontal anisotropy at the base of the thin crust.An intra-lithospheric discontinuity(ILD)with small positive velocity gradient is detected at about 80 km depth.We speculate it may be caused by the phase transformation from spinel to garnet.the Lehmann discontinuity is observed at about 220 km,which usually exist below stable cratons.What′s more,the velocity of the upper mantle between the ILD and Lehmann discontinuity is significantly lower than that of the global IASP91 model.The arrival times of these upper mantle seismic phases(Pn,PL and P410)are between the stable craton region and the active tectonic region,indicating that the upper mantle in the eastern Sino-Korean Craton and its adjacent areas is in a"cold"to"hot"transition state as a whole.

关 键 词：朝鲜核爆 深地震测深剖面 薄下地壳 上地幔间断面 中朝克拉通东部 

分 类 号：P315[天文地球—地震学]