中国东北地壳结构的地震层析成像

中国东北地区自晚古生代晚期以来,受古亚洲洋、蒙古—鄂霍茨克洋、太平洋构造域的叠加作用,壳幔结构极为复杂。本文收集中国东北地区国家地震台网接收的100 980个P波和91 030个S波到时数据,采用地震走时层析成像方法获得了该地区地壳P波和S波速度结构,进而获得了泊松比结构,用以探讨复杂的地壳结构。成像结果显示：中国东北地区地壳地震波速度结构呈明显的横向不均匀性,不同构造单元和构造单元内部都存在不同程度的不均匀性。松辽盆地整体上浅层地壳以低速异常为主,尤其是S波速度,但部分区域分辨率较低,中下地壳存在较大范围高速异常,推测与太平洋俯冲、后撤导致的岩石圈拆沉和热物质上涌等动力学过程有关;北部的大兴安岭重力梯级带和长白山一线主要表现为低速异常,表明具有大范围的岩浆作用,广泛岩浆作用为固体矿产资源的形成提供热源或物源;长白山、五大连池等近代活动的火山下方部分地壳区域均表现了较强低地震波速度和高泊松比异常结构特征,表明仍存在活动的可能。     

中国西部地壳岩石密度及其组成

本研究采用前人归纳的中国西部主要构造单元的P波波速结构来研究中国西部的地壳密度及组分特征。对地壳岩性推测依据:(1)实测地壳V_p值与实验室测量的常见不同岩性V_p值的对比,(2)根据波速(V_p)-密度(ρ)转换方法,将下地壳的P波波速结构转化为密度结构,并采用Monte Carlo法对密度值的误差进行估算。结果显示:除川西地区以外,中国西部各构造单元的(结晶)地壳密度值大于全球大陆地壳平均值2830 kg/m~3。中国西部各构造单元上地壳P波波速和密度均与中酸性岩类相当,中地壳P波波速和密度均与中性岩相当,下地壳P波波速和密度均与基性岩类相当。因此,中国西部上地壳是中酸性的,中地壳是中性的,下地壳是基性的。     

广西若干重大基础地质特征

文章根据华南地区物探、化探、遥感偏图广西综合解译成果,研究广西若干重大基础地质特征,着重讨论地壳结构、深部构造、主要隐伏深断裂带、基底性质等,以板块观点划分大地构造单元,提出广西地壳属陆壳型性质和扬子板块在广西的边界划在三江－大桥一线的新认识。     

青藏高原地区地壳—上地幔结构与巨厚地壳的形成

基于在青藏高原地区所进行的地壳与上地幔的爆炸地震探测资料;雅鲁藏布江以南和以北两条近东西向纵剖面(长约1000km左右),近南北向纵剖面(长约1200km左右),通过计算与分析,给出了青藏高原地区地壳与上地幔结构、速度分布的综合立体剖面图,发现地壳中存在著两个低速层,雅鲁藏布江是一条近于陡立的略向南倾的深大断裂带。地壳结构不论在纵向与横向都是不均匀的,最后探讨了大陆板块碰撞与巨厚地壳的形成。     

中国大陆地壳和岩石圈化学成分模型可信吗? ——来自大地热流值的检验

大地热流值是大陆地壳和岩石圈U，Th,K丰度的直接约束；根据地球化学元素丰度值推算出的大地构造单元的区域地壳热流值，必定不能大于区域的平均热流值，根据700余个实测大地热流数据，对目前发表的中国大陆地壳和岩石圈的化学成分模型进行了检验，结果表明，多数模型不能满足大地热充约束，如黎彤等的关于中国大陆及其内部构造单元的地壳和岩石圈成分模型，倪守斌等提出的新疆北部地壳生热率模型，以及高山等提出的扬子地台北缘地壳成分模型，这些模型的U，Th,K丰度值不太可靠，其他强不相容元素的丰度值的可信程度亦值得怀疑，而迟清华，鄢明才提出的华北地台地壳成分模型和高山等建立的中国东部及华北地台和秦岭造山带的地壳成分模型通过了区域大地热流的检验。     

内蒙中部地壳结构浅论

内蒙古是中国地壳结构最复杂的地区之一,笔者试图先以内蒙中部为例,作一初步探索。一、地震模式和密度模式“内蒙古中部地幔介质分层结构”一文,给出了清水河、和林格尔、呼和浩特、四子王旗、达茂旗、集宁六个地震台站下的地壳分层速度值和厚     

中国地壳结构构造与形成过程:来自构造变形的约束

中国地壳结构构造与形成过程,一直是地质界关注的重大地质构造问题。然而已有研究主要侧重于构造单元划分和构造演化,而对各个构造单元构造变形以及相互之间的构造关系,没有给予足够重视。文章基于对已有资料的综合研究和笔者研究积累,分析和总结了华南、华北、东北、西北、青藏高原和苏鲁-大别-秦岭等地区的构造变形特征与地壳结构构造,根据构造变形特征,结合其他方面的资料,提出松辽盆地两侧构造单元可以对比连接,东准噶尔与西准噶尔以及东天山与西天山构造单元分别属于不同古陆的增生边缘不应该对比连接,牡丹江缝合带不存在,以及中国东部发育两个方向的隆起-坳陷构造等新认识。基于不同时代构造变形特征,对华北古陆基底结构和形成时代、塔里木和扬子古陆基底形成时代、古生代至三叠纪中国大陆主体聚合过程以及侏罗纪以来中国东部构造变形对已有构造的叠加改造和现今中国地壳结构构造最终形成,进行了初步讨论。      

浙江省地壳构造综合研究

浙江地区基岩为大面积的中生代火山岩覆盖，对了解地壳深部的组成结构造成困难。本文通过对布格重力异常和航磁异常数据进行小波多尺度分解，深入地了解浙江省不同深度的地壳结构，结合地震和大地电磁资料，取得地壳构造的三维信息。根据浙江地区位场的多尺度分解结果，可以将浙江省上地壳细分为六个构造单元：下扬子南部浙北陆沿带、江山- 绍兴古陆块碰撞拼合带、古华夏陆块北沿带、丽水- 余姚早古生代陆缘俯冲带、浙东侏罗纪白垩纪火山岩带和杭嘉地块。在上地壳的六个构造单元中，江山- 绍兴古陆块碰撞拼合带、浙东火山岩带和杭嘉地块具有高密度强磁性的属性；而下扬子南部浙北陆沿带、古华夏陆块北沿带和丽水- 余姚早古生代陆缘俯冲带具有低密度的属性，与它们在古生代受安第斯型大洋俯冲作用有关。浙江省下地壳只有西—西南部低密度区、中部杭州- 嵊州- 苍南中密度带和杭嘉- 舟山群岛- 滨海高密度带三个构造区。东部的中生代陆缘火山弧和杭嘉地块在中下地壳连为一体；江山- 绍兴古陆块碰撞拼合带和古华夏陆块北沿带也连为一体。浙江省中下地壳的格局主要受西太平洋俯冲带向东后撤的影响。     

中国大陆主要地质构造单元岩石圈地热特征

根据中国大陆的800余个大地热流值数据，作者研究了中国大陆主要地质构造单元的地热特征。中国大陆热流的空间分布以及其他岩石圈热状态参数均表现出明显的横向变化；这些特征源于太平洋板块俯冲和印度-亚洲碰撞导致的新生代构造热活动。中国大陆各构造单元的地壳生热率亦表现出横向非均匀性，这意味着各构造单元的地壳平均成分存在显著的横向变化。研究表明，各主要构造单元的地壳力学强度和地震活动性均受其地热特征的影响。     

广西地区岩石圈表层与深部构造之关联性:源于岩石圈密度与磁性结构的解读

广西地处华南地块、印支地块与西太平洋板块的汇合部位,因特殊的构造部位,广西区内大地构造单元归属、构造单元边界等许多基础地质问题一直存在争议.自新生代以来的板块构造运动对岩石圈的改造,广西地壳与上地幔在地震波速度及温度结构方面具有显著差异.应用卫星重、磁异常数据以及区域重力和航磁资料对广西地区岩石圈密度和磁化率结构及其与上地壳构造的关系开展了研究,结果显示广西地区地壳密度和上地壳磁性结构与现今地表构造较为契合,但下地壳密度结构与上地幔存在不连续现象;此外,岩石圈磁化率结构指示中下地壳存在不同范围和程度的解耦.对广西岩石圈密度与磁性结构的解读认为,在中生代以来岩石圈被大规模改造的背景下,幔源物质上侵至上地壳的规模和范围都有限,这可能是整个广西地区上地幔结构与地壳构造不对应的主要原因.      

龙门山多层分层拆离地壳结构:新构造变形与深部构造证据

2008年5.12汶川地震发生后,对于龙门山地壳结构及其与汶川地震的成生联系成为构造地质学研究极为关注的科学问题。然而,现有的多种龙门山地壳结构模式在综合解释表层构造变形及深部构造时与调查和探测资料均有不符。利用前人地球物理探测成果,结合穿过龙门山主要发震构造单元彭灌杂岩及雪隆包岩体的综合构造剖面,将地表构造与深部地壳探测资料结合进行了综合解释,认为龙门山逆冲构造带中的多重冲断推覆构造由约10 km深处的拆离断层分隔,因而应该只是浅层次构造变形的组合样式;在中、下地壳韧性流壳层的主导下,扬子地块基底被动?入并形成多层拆离的韧性流变构造组合。5.12汶川地震及余震是由于以彭灌杂岩和雪隆包岩体为代表的刚性体,在上部韧性流壳层前端的持续推挤作用下,发生破裂而形成的。     

Relationship between Crustal Structure and Tin Mineralization in South China

ＩＮＴＲＯＤＵＣＴＩＯＮＳｏｕｔｈＣｈｉｎａ,ｗｈｉｃｈｉｎｃｌｕｄｅｓＹａｎｇｔｚｅｐａｒａｐｌａｔｆｏｒｍａｎｄＳｏｕｔｈＣｈｉｎａＣａｌｅｄｏｎｉａｎｆｏｌｄｂｅｌｔ（ｏｒＣａｔｈａｙｓｉａ）,ｉｓｓｉｔｕａｔｅｄｉｎｔｈｅｊｕｎｃｔｕｒｅｏｆ...     

Seismic Velocity Structure and Composition of the Continental Crust of Eastern China

On the basis of a one-by-one latitude-longitude grid three-dimensional seismic velocity model, the crustal P-wave velocity structure in eastern China (105-125°E and 18-41°N) is obtained, and a set of geotherms for each grid is established for P-T correction on P-wave velocities. The average depths of sub-crustal layers and their average P-wave velocities of 18 tectonic units in eastern China are exhibited. Our result presents a 32-34 km thick crust beneath eastern China, which is thinner than previous studies, with an average velocity of 6.54 km/s, corresponding to a 5 kg/m3 variation in crustal mean density. The thicker upper but thinner middle and lower crust results in a lower average seismic velocity of eastern China. An intermediate crustal composition with a SiO2 content of 59.7 wt% has been estimated. However, there exists a significant lateral variation in the crustal structures among the tectonic units of eastern China. The structure and composition features of some regions in eastern China in     

辽宁西部地区地壳结构及其稳定性的初步研究

本文利用现有各种地球物理资料、地震地质资料,探讨了重磁场特征、地壳结构、活动断裂与地震的关系,进而总结出地震震中在地壳介质中的空间分布规律。在此基础上建立了地壳稳定性评价分级指标,并对本区的地壳稳定性进行了评价。     

准噶尔造山带地壳结构初探

准噶尔造山带地壳结构复杂 ,构造形态多样。根据地球物理资料 ,特别是国家“30 5”项目可可托海至阿克塞地学大断面反映出 ,准噶尔造山带至少由四个不同时代、不同性质的地质块体拼合而成。地体间为深断裂或超岩石圈深断裂分隔。在地块内部不同层次之间也常有巨型水平剪切或滑脱带存在 ,造成了准噶尔造山带在垂向上有明显的分层性 ,在横向上具有不均一性和不连续性。     

Crustal structure of the Kaapvaal craton and its significance for early crustal evolution

High-quality seismic data obtained from a dense broadband array near Kimberley, South Africa, exhibit crustal reverberations of remarkable clarity that provide well-resolved constraints on the structure of the lowermost crust and Moho. Receiver function analysis of Moho conversions and crustal multiples beneath the Kimberley array shows that the crust is 35 km thick with an average Poisson's ratio of 0.25. The density contrast across the Moho is 15%, indicating a crustal density about 2.86 gm/cc just above the Moho, appropriate for felsic to intermediate rock compositions. Analysis of waveform broadening of the crustal reverberation phases suggests that the Moho transition can be no more than 0.5 km thick and the total variation in crustal thickness over the 2400 km² footprint of the array no more than 1 km. Waveform and travel time analysis of a large earthquake triggered by deep gold mining operations (the Welkom mine event) some 200 km away from the array yield an average crustal thickness of 35 km along the propagation path between the Kimberley array and the event. P- and S-wave velocities for the lowermost crust are modeled to be 6.75 and 3.90 km/s, respectively, with uppermost mantle velocities of 8.2 and 4.79 km/s, respectively. Seismograms from the Welkom event exhibit theoretically predicted but rarely observed crustal reverberation phases that involve reflection or conversion at the Moho. Correlation between observed and synthetic waveforms and phase amplitudes of the Moho reverberations suggests that the crust along the propagation path between source and receiver is highly uniform in both thickness and average seismic velocity and that the Moho transition zone is everywhere less than about 2 km thick. While the extremely flat Moho, sharp transition zone and low crustal densities beneath the region of study may date from the time of crustal formation, a more geologically plausible interpretation involves extensive crustal melting and ductile flow during the major craton-wide Ventersdorp tectonomagmatic event near the end of Archean time.     

哈尔滨地区地壳稳定性研究

客观评价城市区域地壳稳定性,对于城市安全与可持续发展有着极其重要的意义.哈尔滨城市地质调查系统地研究了哈尔滨地区的莫霍面深度、地球物理场、火成岩特征及历史地震记录,并开展大地电磁测深、钻探及汞气测量研究,认为哈尔滨地区地壳结构连续、完整、稳定,不会发生中等强度及以上地震活动.     

The crustal structure of the western Arabian platform from the spectral analysis of long-period P-wave amplitude ratios

The crustal structure of the western Arabian platform is derived using the spectral analysis of long-period P-wave amplitude ratios. The ratio of the vertical to the horizontal component is used to obtain the crustal transfer function based on thickness variations, crustal velocities, densities and the angle of emergence at the lower crust and upper mantle interface. Eleven well-defined earthquakes recorded at the long-period RYD station during the period from 1985 to 1994 were selected for analysis based on the following criteria: focal depths with a range between 7 and 89 km, body-wave magnitudes greater than 4.7, epicentral distances with a range from 8.8° to 26.5°, and back azimuthal coverage from 196° to 340°. Spectral analysis calculations were based on the comparison of the observed spectral ratios with those computed from theoretical P-wave motion obtained using the Thomson–Haskell matrix formulation for horizontally layered crustal models. The selection of the most suitable model was based on the identification of the theoretical model which exhibits the highest cross-correlation coefficient with the observed transfer function ratio. By comparing the spectral peak positions of the observed and theoretical values, the thickness and velocity can be resolved within 3 km and 1 km/s, respectively, of the observed values. The spectral analysis of long-period P-waves can detect a thin layer near the surface of about 1.6 km thick and a velocity contrast of about 10% with that of the underlying layer. A strong velocity gradient of about 0.05 km/s per km was found in the upper crust and 0.02 km/s per km in the lower crust. The derived crustal model is not unique due to the theoretical assumptions (horizontal layering, constant densities and velocities in each layer), quality of the data and complexities of the crustal structure. The crustal model suggests that the crust consists of five distinct layers. The upper crustal layer has a P-wave velocity of about 5.6 km/s and is about 1.6 km thick. The second layer has a velocity of about 6.2 km/s and is 10.2 km thick. The third layer shows a velocity of 6.6 km/s and is 6.8 km thick. The fourth layer has a velocity of about 6.8 km/s and is 12.3 km thick. The lower crustal layer has a velocity of about 7.5 km/s and is 9.3 km thick. The Mohorovicic discontinuity beneath the western Arabian platform indicates a velocity of 8.2 km/s of the upper mantle and 42 km depth.     

Crustal complexity in the Lachlan Orogen revealed from teleseismic receiver functions

There is an ongoing debate about the tectonic evolution of southeast Australia, particularly about the causes and nature of its accretion to a much older Precambrian core to the west. Seismic imaging of the crust can provide useful clues to address this issue. Seismic tomography imaging is a powerful tool often employed to map elastic properties of the Earth's lithosphere, but in most cases does not constrain well the depth of discontinuities such as the Mohorovi?i? (Moho). In this study, an alternative imaging technique known as receiver function (RF) has been employed for seismic stations near Canberra in the Lachlan Orogen to investigate: (i) the shear-wave-velocity profile in the crust and uppermost mantle, (ii) variations in the Moho depth beneath the Lachlan Orogen, and (iii) the nature of the transition between the crust and mantle. A number of styles of RF analyses were conducted: H-K stacking to obtain the best compressional–shear velocity (V _P /V _S) ratio and crustal thickness; nonlinear inversion for the shear-wave-velocity structure and inversion of the observed variations in RFs with back-azimuth to investigate potential dipping of the crustal layers and anisotropy. The thick crust (up to 48 km) and the mostly intermediate nature of the crust?mantle transition in the Lachlan Orogen could be due to the presence of underplating at the base of the crust, and possibly to the existing thick piles of Ordovician mafic rocks present in the mid and lower crust. Results from numerical modelling of RFs at three seismic stations (CAN, CNB and YNG) suggest that the observed variations with back-azimuth could be related to a complex structure beneath these stations with the likelihood of both a dipping Moho and crustal anisotropy. Our analysis reveals crustal thickening to the west beneath CAN station which could be due to slab convergence. The crustal thickening may also be related to the broad Macquarie volcanic arc, which is rooted to the Moho. The crustal anisotropy may arise from a strong N–S structural trend in the eastern Lachlan Orogen and to the preferred crystallographic orientation of seismically anisotropic minerals in the lower and middle crust related to the paleo-Pacific plate convergence.     

江西省大地构造演化特征与基本规律

本文根据江西大地构造在时空演化上的不平衡性,以及各不同地区在地壳结构、沉积建造、变质建造、岩浆建造、构造型相、成矿作用以及深部构造等方面的种种差异,将江西大地构造划分为2个Ⅰ级构造单元、4个Ⅱ级构造单元、8个Ⅲ级构造单元和39个Ⅳ级构造单元。