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1.
The geological-geophysical and petrological-geochemical studies of the Earth’s crust and upper mantle are combined to estimate the state of the lithosphere at the junction zone of Tarim and Tien Shan. The laboratory measurements of electric conductivity in the rocks sampled from the upper mantle and lower crust considered against the geoelectrical and thermal models revealed lherzolite, granulite, and eclogite massifs in the deep section of the Tarim and Tien Shan junction zone. The experimental results suggest that the crustal thickness in the southern Tien Shan attained 35–40 km 70 Ma ago. 相似文献
2.
天山造山带作为世界上陆内最大的造山带之一,现今地震活动频繁,造山运动强烈,是开展陆内造山和内陆地震活动研究的天然试验场.本文利用整个天山造山带地区国内及国际台网的108个地震台站连续三年的背景噪声资料,提取了8~50 s周期的瑞利面波相速度频散曲线,并构建了整个天山造山带地区的二维瑞利面波相速度与方位各向异性分布图像.结果表明：浅部结构与地表的地质构造单元具有较大的相关性.低波速异常主要分布于沉积层厚度较大的盆地地区,而高波速异常主要分布于构造活动比较活跃的山脉地区.东天山地区中下地壳存在比较弱的低波速异常,而塔里木盆地和准噶尔盆地汇聚边缘的上地幔区域则表现为明显的高波速异常,各向异性快波方向呈现近NS向的特征,暗示着塔里木盆地和准噶尔盆地的岩石圈已经俯冲至东天山的下方.中天山地区的中下地壳至上地幔区域均呈现为明显的低波速异常,且各向异性快波方向变化比较复杂,表明中天山地区的整个岩石圈结构已经弱化,热物质上涌可能对介质的方位各向异性有一定的影响.西天山及帕米尔高原的上地幔区域存在低波速异常,各向异性表现为NW-SE方向,可能与欧亚板块的大陆岩石圈南向俯冲有关.塔里木盆地内部存在相对弱的低波速异常,推测塔里木盆地可能已经受到上涌的地幔热物质的侵蚀和破坏. 相似文献
3.
根据横跨中国境内天山的库车—奎屯宽频带流动地震台阵和区域地震台网记录的近震和远震P波走时数据，利用地震层析成像方法重建了沿该地震台阵剖面下方400 km深度范围内地壳上地幔的P波速度结构.结果表明：沿新疆库车—奎屯剖面，天山地壳具有明显的横向分块结构，且南、北天山地壳显示了较为强烈的横向变形特征，表明塔里木地块对天山地壳具有强烈的侧向挤压作用；在塔里木和准噶尔地块上地幔顶部有厚度约60～90 km的高速异常体，塔里木—南天山下方的高速异常体产生了较为明显的弯曲变形，而准噶尔—北天山下方的高速异常体向南一直俯冲到中天山南侧边界下方300 km的深度，两者形成了不对称对冲构造；在塔里木和准噶尔地块下方150～400 km深度存在上地幔低速体，其中塔里木地块一侧的上地幔低速物质上涌到南天山地块的下方；在塔里木—南天山200～300 km深度范围的上地幔存在高速异常体，它可能是地幔热物质向上迁移过程融断的塔里木岩石圈的拆离体. 上述结果表明，塔里木地块的俯冲可能涉及整个岩石圈深度，但其前缘仅限于南天山的北缘；青藏高原隆升的远程效应可能不但驱动塔里木岩石圈向北俯冲，同时还造成天山造山带南侧上地幔物质的涌入；天山造山带上地幔广泛存在的低速异常有助于其上地幔的变形，而上地幔物质的强烈非均匀性应有助于推动天山造山带上地幔小尺度地幔对流的形成；根据研究区地壳上地幔速度结构特征推断，新近纪以来天山快速隆升的主要力源来自青藏高原快速隆升的远程效应，相对软弱的上地幔为加速天山造山带的变形和隆升创造了必要条件. 相似文献
4.
Shear velocity structure of crust and uppermost mantle in China from surface wave tomography using ambient noise and earthquake data 总被引：1，自引：0，他引：1
We present a 3D model of shear velocity of crust and upper mantle in China and surrounding regions from surface wave tomography.We combine dispersion measurements from ambient noise correlation and traditional earthquake data.The stations include the China National Seismic Network,global networks,and all the available PASSCAL stations in the region over the years.The combined data sets provide excellent data coverage of the region for surface wave measurements from 8 to 120 s,which are used to invert for 3D shear wave velocity structure of the crust and upper mantle down to about150 km.We also derive new models of the study region for crustal thickness and averaged S velocities for upper,mid,and lower crust and the uppermost mantle.The models provide a fundamental data set for understanding continental dynamics and evolution.The tomography results reveal significant features of crust and upper mantle structure,including major basins,Moho depth variation,mantle velocity contrast between eastern and western North China Craton,widespread low-velocity zone in midcrust in much of the Tibetan Plateau,and clear velocity contrasts of the mantle lithosphere between north and southern Tibet with significant E–W variations.The low velocity structure in the upper mantle under north and eastern TP correlates with surface geological boundaries.A patch of high velocity anomaly is found under the eastern part of the TP,which may indicate intact mantle lithosphere.Mantle lithosphere shows striking systematic change from the western to eastern North China Craton.The Tanlu Fault appears to be a major lithosphere boundary. 相似文献
5.
利用宽频带流动地震台阵GHENGIS和吉尔吉斯地震台网KNET记录的地震波走时数据，反演了中天山地区的Pn波速度结构和各向异性.结果表明，中天山上地幔顶部平均速度偏低，具有构造活动地区的特点和明显的横向非均匀性；中天山南部地幔上涌区的Pn波速度非常低，表明存在较高的热流活动.Pn波速度的变化与地震分布有着密切的对应关系：地震大都发生在中天山北部Pn波高速区上方，而南部的Pn波低速区上方几乎没有地震.这一现象说明地幔上涌引起高温极大地降低了岩石层地幔的强度，并以热传导的方式进入地壳使其失去地震破裂强度而发生韧性变形.中天山北部和南部的各向异性也存在一定的差异，南部各向异性的快波方向为近南北方向，与SKS波的各向异性特征基本一致，反映了地幔物质的迁移方向；北部各向异性的快波方向呈向南凸出的旋转趋势，估计与哈萨克地台南缘楚河盆地地壳块体向天山挤入造成应力场的改变和岩石层变形有关. 相似文献
6.
A new combined satellite-terrestrial model of the gravity field is used together with seismic data for construction of a density model of the lithosphere of the Central Tien Shan and for estimation of its isostatic balance. The Tien Shan is one of the most active intraplate orogens in the world, located about 1,500 km north of the convergence between Indian and Eurasian plate, and surrounded by stable Kazakh platform to the north and the Tarim block to the south. Although this area was extensively studied during recent decades, several principal problems, related to its structure and tectonics, remain unsolved up to now: (1) various geodynamic scenarios have been discussed so far to explain tectonic evolution, such as direct “crustal shortening,” intracontinental subduction and some others, but no definite evidence for any of them has been found. (2) Still, it is not clear why Tien Shan grows so far from the plate boundary at the Himalayan collision zone. Gravity modeling can provide valuable constraints to resolve these questions. The results of this study show that: (1) there exists a very strong deflection of the Tien Shan lithosphere from isostatic equilibrium. At the same time, the patterns of the isostatic anomalies are very different in the Western and Central Tien Shan. The latter one is characterized by much stronger variations. The best fit of the modeling results is found for the model according to which the Tarim plate partially underthrusts the Central Tien Shan; (2) negative density anomalies in the upper mantle under the central block possibly relate to magmatic underplating during the initial stage of the tectonic evolution. Therefore, the weak lithosphere could be the factor that initiates mountain building far away from the collision zone. Alternatively, this might be a gap after detachment of the eclogised lower crust and lithospheric lid, which is filled with the hot asthenospheric material. 相似文献
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对人工地震测深及天然地震面波体波三维层折反演数据进行统一处理，建立了中国及其邻区地球三维结构初始模型．此模型图像表明，中国及其邻区地球各圈层横向变化明显．岩石圈及软流圈内速度分布主要反映这一区域自古生代以来板块及地块拼合模式．各主要板块或地块（塔里木、扬子、中朝、青藏、哈萨克斯坦、印度、印度支那）岩石圈增厚或有很深的地慢根，板块或地块间的造山带岩石圈减薄，软流圈速度降低。下地幔底部及核幔边界D″层出现高速异常，表明古太平洋及古特提斯洋俯冲板块因重力坍塌已进入地球深层，形成亚洲超级下降地幔柱。这一下降地幔柱引起地球表层物质向中亚、东亚地区集中，印度半岛、青藏高原、新疆、蒙古至贝加尔一带，成为全球岩石圈最大的汇聚场所． 相似文献
8.
利用文登—阿拉善左旗长观测距地震宽角反射/折射剖面东段资料,辩识出4组地壳震相和3组地幔盖层震相.采用二维射线追踪走时反演和正演拟合交替计算方法,得到了包括鲁东隆起和华北裂陷盆地在内的地壳和地幔盖层二维速度结构.研究结果表明:华北裂陷盆地基底深达6km以上,研究区壳内界面C1埋深约15km,C2界面深约25km,Moho面平均埋深约35km.上地壳速度6.0~6.1km·s-1,且横向变化较大;中地壳速度相对均匀约为6.2~6.4km·s-1;下地壳速度为6.5~7.0km·s-1,速度梯度较大.地壳平均速度与隆起和坳陷构造相关.研究区岩石圈底界面一般为75~80km,西端接近太行隆起构造时深至90km左右,向西呈明显加深趋势,地壳厚度呈现相同的增厚特征.地幔盖层上部速度8.0~8.2km·s-1,具明显正梯度特征.岩石圈平均速度在郯庐断裂带附近显著偏低.PmP和PLP震相存在不同程度的复杂性,意味着在本地区Moho界面和岩石圈界面有较为复杂的结构,可能具有一定厚度或过渡带性质.结合其他研究结果认为,地幔盖层和下地壳速度梯度、界面性质差异与华北克拉通破坏相关,意味着破坏是一个渐变、缓慢和不均匀的过程.郯庐断裂带附近的低速应是其为软弱带的证据. 相似文献
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LIU Qiyuan Rainer Kind CHEN Jiuhui YUAN Xiaohui LI Shuncheng GUO Biao Kurt Wylegalla & LAI Yuangen . State Key Laboratory of Earthquake Dynamics Institute of Geology China Earthquake Administration Beijing China . GeoForschungZentrum Potsdam Telegrafenburg A Potsdam D- Germany 《中国科学D辑(英文版)》2005,48(7)
The Dabie Shan is located on the eastern side of the Qinling-Dabie orogenic belt, which marks a geological boundary between the Sino-Korean and Yangtze cra- ton. Since the 1980s, the discovery of coesite and mi- crodiamond in the Dabie Shan orogen motivates an extensive interest to the ultra-high pressure (UHP)metamorphism and its exhumation[1,2]. Many results about them were published, which deal with different disciplines, including tectonics, petrology and chro- nology[3?8]. Up to now,… 相似文献
10.
近年来新的研究成果反应出鄂尔多斯地块岩石圈并不是一个具有深根的完整的刚性块体,尤其在鄂尔多斯北部以及河套地堑发现有大范围的下地壳-上地幔低速低阻物质,如果这一情况属实,那么人们对鄂尔多斯地块的认识将发生大的变化.为此,我们在华北克拉通西部布设了一条穿过鄂尔多斯地块、河套地堑和阴山造山带的南北向大地电磁剖面,试图通过深部电性结构的探测提供更多信息.该剖面全长约850 km,共布设54个宽频测点和17个长周期测点.二维和三维反演结果均表明:鄂尔多斯地块内部以38°N为界,南部和北部电性结构存在明显差异.鄂尔多斯地块南部地壳至上地幔150 km深度范围内整体表现为高阻,具有刚性克拉通的特征;鄂尔多斯地块北部到河套地堑之间下地壳出现低阻层,特别是鄂尔多斯北端与河套地堑接壤地段,深部存在一个规模较大的下地壳-上地幔低阻异常体,该异常体从河套地堑开始,横向上向南延伸到鄂尔多斯地块内部约200 km,纵向上从下地壳向下延伸到上地幔(约100 km深度).根据该异常体的空间特征,参考该区地震波低速异常体的分布,我们认为鄂尔多斯北部及河套地堑中下地壳到上地幔存在热物质,其原因与深部的构造活动有关(软流圈热物质上涌、侧向流动等),这一情况可能反映出鄂尔多斯地块北部岩石圈深部正处于被改造(或者破坏)阶段,这对进一步认识青藏高原东北缘与华北克拉通之间的深部关系具有一定的启示作用. 相似文献
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I. V. Nizkous I. A. Sanina E. Kissling L. I. Gontovaya 《Izvestiya Physics of the Solid Earth》2006,42(4):286-296
Arrival times of P and S waves from local earthquakes in the Kamchatka area of the Kurile-Kamchatka Island Arc are used for calculating a spatial model of the elastic wave velocity distribution to a depth of 200 km. The lithosphere is shown to be strongly stratified in its velocity properties and laterally heterogeneous within the mantle wedge and seismic focal zone. A lower velocity layer (an asthenospheric wedge) is identified at depths of 70–130 km beneath the Eastern Kamchatka volcanic belt. The morphology of the Moho interface and the velocity properties of the crust are studied. The main tectonic structures of the region are shown to be closely interrelated with deep velocity heterogeneities. Regular patterns in the statistics of the earthquakes are analyzed in relation to variations in the elastic wave velocities in the focal layer. A mechanism of lithospheric block displacements along weakened zones of the lower crust and upper mantle is proposed. 相似文献
12.
本文利用天然地震面波记录和层析成像方法,研究了南北地震带及邻近区域的岩石圈S波速度结构和各向异性特征.结果表明南北地震带的东边界不但是地壳厚度剧变带,也是地壳速度的显著分界.其西侧中下地壳的S波速度显著低于东侧,强震大多发生在低速区内部和边界.青藏高原东缘中下地壳速度显著低于正常大陆地壳,在松潘甘孜地块和川滇地块西部大约25～45 km深度存在壳内低速层;这些低速特征与高原主体的低速区相连,有利于下地壳物质的侧向流动.地壳的各向异性图像与下地壳流动模式相符,即下地壳物质绕喜马拉雅东构造结运动,东向的运动遇到扬子坚硬地壳阻挡而变为向南和向北东的运动.面波层析成像结果支持青藏高原地壳运动的下地壳流动模型.南北地震带的岩石圈厚度与其东侧的扬子和鄂尔多斯地块相似但速度较低.川滇西部地块上地幔顶部(莫霍面至88 km左右)异常低速;松潘甘孜地块上地幔盖层中有低速夹层(约90～130 km深度).岩石圈上地幔的速度分布图像与地壳显著不同,在高原主体与川滇之间存在北北东向高速带,可能会阻挡地幔物质的东向运动.上地幔各向异性较弱且与地壳的分布图像显然不同.因此青藏高原岩石圈地幔的构造运动具有与地壳不同的模式,软弱的下地壳提供了壳幔运动解耦的条件. 相似文献
13.
《中国科学:地球科学(英文版)》2017,(10)
As one of the world's most active intracontinental mountain belts, Tien Shan has posed questions for researchers regarding the formation of different tectonic units and active shallow seismicity. Here, we used a huge data set comprising of 7094 earthquakes from local, regional and teleseismic seismic stations. We used waveform modeling and multi-scale double-difference earthquake relocation technique to better constrain the source parameters of the earthquakes. The new set of events provided us with better initial earthquake locations for further tomographic investigation. We found that reverse-faulting earthquakes dominate the whole study area while the fault plane solutions for earthquakes beneath the northwestern Tarim Basin and the Main Pamir Thrust are diverse. There is a low-velocity anomaly beneath Bashkaingdy at depth of 80 km, and high-velocity anomalies beneath central Tien Shan at shallower depths. These observations are the keys to understand the mechanism of Tien Shan's formation because of Tarim Basin northward and Kazakh Shield's southward subduction in the south and north respectively. Velocities beneath western Tien Shan are relatively high. We thus infer that the Western Tien Shan is relatively less deformed than the eastern Tien Shan primarily due to a relatively brittle mantle. 相似文献
14.
本文利用瑞利波群速度频散资料和层析成像方法,研究了中国西部及邻近区域(20°N—55°N,65°E—110°E)的岩石圈S波速度结构.结果表明这一地区存在三个以低速地壳/上地幔为特征的构造活动区域:西蒙古高原—贝加尔地区,青藏高原,印支地区.西蒙古高原岩石圈厚度约为80 km,上地幔低速层向下延伸至300 km深度,说明存在源自地幔深部的热流活动.缅甸弧后的上地幔低速层下至200 km深度,显然与印度板块向东俯冲引起俯冲板片上方的热/化学活动有关.青藏高原地壳厚达70 km,边缘地区厚度也在50 km以上并且具有很大的水平变化梯度,与高原平顶陡边的地形特征一致.中下地壳的平均S波速度明显低于正常大陆地壳,在中地壳20~40 km深度范围广泛存在速度逆转的低速层,这一低速层的展布范围与高原的范围相符.这些特征说明青藏高原中下地壳的变形是在印度板块的北向挤压下发生塑性增厚和侧向流动.地幔的速度结构呈现与地壳显著不同的特点.在高原主体和川滇西部地区上地幔顶部存在较大范围的低速,低速区范围随深度迅速减小;100 km以下滇西低速消失,150 km以下基本完全消失.青藏高原上地幔速度结构沿东西方向表现出显著的分段变化.在大约84°E以西的喀喇昆仑—帕米尔—兴都库什地区,印度板块的北向和亚洲板块的南向俯冲造成上地幔显著高速;84°E—94°E之间上地幔顶部速度较低,在大约150~220 km深度范围存在高速板片,有可能是俯冲的印度岩石圈,其前缘到达昆仑—巴颜喀拉之下;在喜马拉雅东构造结以北区域,存在显著的上地幔高速区,可能阻碍上地幔物质的东向运动.川滇西部岩石圈底界深度与扬子克拉通相似,约为180 km,但上地幔顶部速度较低.这些现象表明青藏高原岩石圈地幔的变形/运动方式可能与地壳有本质的区别. 相似文献
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16.
《Earth and Planetary Science Letters》2006,241(3-4):901-912
We have constrained the shear-wave structure of crust and upper mantle beneath Iceland by analyzing fundamental mode Rayleigh waves recorded at the ICEMELT and HOTSPOT seismic stations in Iceland. The crust varies in thickness from 20 to 28 km in western and northern Iceland and from 26 to 34 km in eastern Iceland. The thickest crust of 34–40 km lies in central Iceland, roughly 100 km west to the current location of the Iceland hotspot. The crust at the hotspot is ∼32 km thick and is underlain by low shear-wave velocities of 4.0–4.1 km/s in the uppermost mantle, indicating that the Moho at the hotspot is probably a weak discontinuity. This low velocity anomaly beneath the hotspot could be associated with partial melting and hot temperature. The lithosphere in Iceland is confined above 60 km and a low velocity zone (LVZ) is imaged at depths of 60 to 120 km. Shear wave velocity in the LVZ is up to 10% lower than a global reference model, indicating the influence of the Mid-Atlantic Ridge and the hotspot in Iceland. The lowest velocities in the LVZ are found beneath the rift zones, suggesting that plume material is channeled along the Mid-Atlantic Ridge. At depths of 100 to 200 km, low velocity anomalies appear at the Tjornes fracture zone to the north of Iceland and beneath the western volcanic zone in southwestern Iceland. Interestingly, a relatively fast anomaly is imaged beneath the hotspot with its center at ∼135 km depth, which could be due to radial anisotropy associated with the strong upwelling within the plume stem or an Mg-enriched mantle residual caused by the extensive extraction of melts. 相似文献
17.
长320 km横跨鲁西地区的聊城－连云港宽角反射地震剖面揭示了鲁西地区的地壳结构，上地壳为二层结构，总厚18～20 km，速度5.4～6.2 km/s；下地壳也分为二层结构，总厚度13～15 km，速度6.4～6.7 km/s.Moho深度33～35 km.Pn 速度为7.9 km/s.地壳速度分布在横向上有较大变化，且平均速度为6.2～6.5 km/s，较正常值偏高.研究结果发现地壳内有两个近直立的高速体.从下地壳延伸到上地壳并直达沉积盆地的底部.可能是幔源岩浆大量侵入地壳，使得地壳的局部平均速度增高.近直立的高速体可能是幔源岩桨上涌的通道.鲁西地壳结构的研究对于探讨古地台的裂解与沉陷机制具有一定的意义. 相似文献
18.
Records of deep-focus Hindu Kush earthquakes in the depth ranges 70–110 and 190–230 km made by 45 digital and analogue seismic stations were analyzed to study the attenuation field of short period seismic waves in the lithosphere of central Tien Shan. The dynamic characteristics studied include the ratio of peak amplitudes in S and P waves (S/P) and the ratio of the S-wave maximum to the coda level in the range t = 400 ± 5 s, where t is the lapse time (S/c400) for 1.25 Hz. Comparatively high values of S/P are shown to prevail in most of the area, corresponding to lower S-wave attenuation. Upon this background is a band of high and intermediate attenuation in the west of the area extending along the Talas-Fergana fault in the south and afterwards turning north-northeast. The rupture areas of the two largest (M ≥ 7.0) earthquakes which have occurred in Tien Shan during the last 25 years are confined to this band. Abnormally high values of S/c400 were obtained for stations situated in the rupture zone of the August 19, 1992, magnitude 7.3 Suusamyr earthquake and around it. For two of the stations we found considerable time variations in the coda envelope before the earthquake. The effective Q was derived from compressional and shear wave data for the entire area, as well as for the band of high attenuation. Comparison with previous data shows that the attenuation field in the area has changed appreciably during 20–25 years, which can only be due to a rearrangement of the fluid field in the crust and uppermost mantle. It is hypothesized that a large earthquake is very likely to occur in the northern part of the attenuating band. 相似文献
19.
天山构造带位于中国大陆西北部,是典型的岩石圈陆内缩短造山带.本文利用新疆区域数字地震台网2009年1月至2014年12月的近场小地震波形资料,采用剪切波分裂分析对天山构造带及邻区的地壳各向异性特征进行研究,获得了研究区域内39个台站的快剪切波偏振方向和慢剪切波时间延迟.剪切波分裂参数的空间特征显示,研究区上地壳各向异性具有分区性,各向异性特征与局部构造、地壳介质变形和应力分布有关.天山构造带的快剪切波偏振呈现出两个优势方向的特点,第一优势方向大致平行于台站附近断裂和天山构造带的走向,与断裂构造和应力的综合影响有关,另一个优势方向反映了主压应力的直接作用.北天山山前断裂带东段的断裂弯折部位和南天山局部地区的剪切波分裂参数与东、西两侧不同,与准噶尔盆地、塔里木盆地的南北向挤压作用密切相关.快剪切波偏振优势方向的剧烈变化揭示,在准噶尔盆地和塔里木盆地双向挤压隆起的过程中,天山构造带产生了强烈的局部不均匀变形.塔里木盆地西侧快剪切波偏振具有两个优势方向,一个为NNE方向,与帕米尔高原受到印度一欧亚板块碰撞产生的北向挤压作用有关,另一个为NW方向,指出了塔里木盆地区域主压应力方向.准噶尔盆地北部也存在NE和NW两个快波偏振优势方向,主要与断裂的影响有关.天山构造带区域内的慢剪切波时间延迟总体上低于塔里木盆地西侧和准噶尔盆地北部,同时慢剪切波时间延迟的结果也进一步证实了天山构造带的局部强烈变形. 相似文献
20.
J. Pim C. Peirce A.B. Watts I. Grevemeyer A. Krabbenhoeft 《Earth and Planetary Science Letters》2008,272(1-2):422-428
The Cape Verde Islands are located on a mid-plate topographic swell and are thought to have formed above a deep mantle plume. Wide-angle seismic data have been used to determine the crustal and uppermost mantle structure along a ~ 440 km long transect of the archipelago. Modelling shows that ‘normal’ oceanic crust, ~ 7 km in thickness, exists between the islands and is gently flexed due to volcano loading. There is no direct evidence for high density bodies in the lower crust or for an anomalously low density upper mantle. The observed flexure and free-air gravity anomaly can be explained by volcano loading of a plate with an effective elastic thickness of 30 km and a load and infill density of 2600 kg m− 3. The origin of the Cape Verde swell is poorly understood. An elastic thickness of 30 km is expected for the ~ 125 Ma old oceanic lithosphere beneath the islands, suggesting that the observed height of the swell and the elevated heat flow cannot be attributed to thermal reheating of the lithosphere. The lack of evidence for high densities and velocities in the lower crust and low densities and velocities in the upper mantle, suggests that neither a crustal underplate or a depleted swell root are the cause of the shallower than expected bathymetry and that, instead, the swell is supported by dynamic uplift associated with the underlying plume. 相似文献