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1.
Charles R. Bentley 《Tectonophysics》1973,20(1-4):229-240
Seismic refraction profiles completed in the past twenty years reveal that the top of the basement complex generally lies near sea level in East Antarctica but typically 2 or 3 km below sea level in West Antarctica. Throughout much of East Antarctica the thickness of the layer overlying the basement complex is less than half a kilometer, although a Phanerozoic sequence more than 1 km thick probably underlies the ice at the South Pole. Throughout central West Antarctica, on the other hand, a section one to several kilometers thick generally overlies the basement complex. The observed sedimentary section is no more than one half kilometer thick on either side of the Transantarctic Mountains. Rocks with high seismic velocities typical of the lower continental crust occur within a few kilometers of the surface on both sides of the Transantarctic Mountains. This occurrence lends support to the hypothesis of an abrupt increase in crustal thickness between West and East Antarctica.
In 1969, deep seismic soundings were carried out by the 14th Soviet Antarctic Expedition near the coast of Queen Maud Land. The crustal thickness was found to be about 40 km near the mountains, decreasing to about 30 km near the coast. In the top 15 km of the crust there is a gradual downward increase in P-wave velocity from 6.0 to 6.3 km/sec. The average velocity through the crust is 6.4 km/sec and the measured velocity below the M-discontinuity is 7.9 km/sec.
At the southwestern margin of the Ronne Ice Shelf, near-vertical reflections from the M-discontinuity have been recorded. A mean P-wave velocity of 6 km/sec in the crust was measured, leading to an estimated depth to M of 24 km below sea level.
Seismic surface wave dispersion studies indicate a mean crustal thickness of about 30 km in West Antarctica and about 40 km in East Antarctica. The dispersion data also show that group velocities across East Antarctica are much closer to those along average continental paths than to those across the Canadian shield. The results thus support other indications that central East Antarctica is not a simple crystalline shield.
P′P′-reflections beneath the continent support the existence of a low-velocity channel for P-waves, but show no significant difference in deep structure between Antarctica and other continents. 相似文献
2.
中国岩石圈的基本特征 总被引：11，自引：2，他引：9
中国及邻区岩石圈结构构造十分复杂,并具有若干明显的特点:中国大陆地壳西厚东薄、南厚北薄,青藏高原地壳平均厚度为60~65 km,最厚达80 km;东部地区一般为30~35 km,南中国海中央海盆平均只有5 km;中国大陆地壳平均厚度为476 km,大大超过全球地壳392 km的平均厚度。中国大陆及邻区岩石圈亦呈西厚东薄、南厚北薄的变化趋势,青藏高原及西北地区岩石圈平均厚度为165 km,塔里木盆地中东部、帕米尔与昌都地区岩石圈厚度可达180~200 km。大兴安岭-太行山-武陵山以东,包括边缘海为岩石圈减薄区,厚度为50~85 km。西部岩石圈、软流圈“层状结构”明显,反映了板块碰撞汇聚的动力学环境;东部岩石圈、软流圈呈“块状镶嵌结构”,岩石圈薄,软流圈厚,反映了地壳拉张、软流圈物质上涌的特点,并在东亚及西太平洋地区85~250 km深处形成一巨型低速异常体。中国东部上、下地壳及地壳、岩石圈地幔之间普遍存在“上老下新”年龄结构。 相似文献
3.
中国大陆岩石圈厚度分布研究 总被引：11，自引：1，他引：10
利用不同物理性质所估计的岩石圈厚度可能具有不同的地球动力学意义。大陆岩石圈等效弹性厚度往往只与岩石圈内部的某些岩层相关,因此它可能不代表一般意义上的岩石圈厚度。地震学岩石圈厚度虽然有较高的精度,但依赖于人为地对岩石圈的定义;并且其具有的短时间尺度效应决定了它与长时间尺度的岩石圈概念不一致。热学岩石圈厚度体现了长时间尺度上的岩石圈热学作用,因此其厚度定义的标准是较合理的。地震-热学岩石圈厚度研究利用地震波速反演得到的温度数据按照热学岩石圈标准来对岩石圈厚度进行研究,具有地震学和热学岩石圈厚度两者的优点,是较合理的对岩石圈厚度的估计。中国大陆地震-热学岩石圈厚度分布有如下特点:(1)中国东部岩石圈较薄,厚度约100 km,其中包括中国东北、中朝克拉通、扬子克拉通东部和华南造山带;(2)青藏高原和塔里木克拉通以南地区的厚度变化较大,厚度约在160~220 km;(3)三大克拉通的岩石圈厚度有较大区别,扬子克拉通的核心最厚达约170 km,塔里木克拉通的核心厚度约140 km,中朝克拉通的厚度约100 km;(4)昆仑秦岭造山带的岩石圈上地幔内部较复杂,可能有大面积的部分熔融;(5)整个大陆岩石圈厚度分布并没有显示出与地壳年龄的线性相关关系,却表现出了与大地构造格局的直接关系。受板块碰撞强烈影响的地区,岩石圈较厚;受大洋俯冲带影响较强的地区,岩石圈较薄。 相似文献
4.
Tingdong Li 《地学前缘(英文版)》2010,1(1):45-56
<正>The lithospheric structure of China and its adjacent area is very complex and is marked by several prominent characteristics.Firstly,China's continental crust is thick in the west but thins to the east,and thick in the south but thins to the north.Secondly,the continental crust of the Qinghai—Tibet Plateau has an average thickness of 60—65 km with a maximum thickness of 80 km,whereas in eastern China the average thickness is 30—35 km,with a minimum thickness of only 5 km in the center of the South China Sea.The average thickness of continental crust in China is 47.6 km,which greatly exceeds the global average thickness of 39.2 km.Thirdly,as with the crust,the lithosphere of China and its adjacent areas shows a general pattern of thicker in the west and south,and thinner in the east and north.The lithosphere of the Qinghai—Tibet Plateau and northwestern China has an average thickness of 165 km, with a maximum thickness of 180—200 km in the central and eastern parts of the Tarim Basin,Pamir, and Changdu areas.In contrast,the vast areas to the east of the Da Hinggan Ling—Taihang—Wuling Mountains,including the marginal seas,are characterized by lithospheric thicknesses of only 50—85 km.Fourthly,in western China the lithosphere and asthenosphere behave as a "layered structure", reflecting their dynamic background of plate collision and convergence.The lithosphere and asthenosphere in eastern China display a "block mosaic structure",where the lithosphere is thin and the asthenosphere is very thick,a pattern reflecting the consequences of crustal extension and an upsurge of asthenospheric materials.The latter is responsible for a huge low velocity anomaly at a depth of 85—250 km beneath East Asia and the western Pacific Ocean.Finally,in China there is an age structure of "older in the upper layers and younger in the lower layers" between both the upper and lower crusts and between the crust and the lithospheric mantle. 相似文献
5.
详细的深部结构信息是深入认识华北克拉通显生宙改造和破坏的重要依据。基于密集流动地震台阵和固定台网记录的远震P波和S波接收函数资料,获得了跨越华北克拉通东、中、西部的3条剖面的岩石圈和上地幔结构图像,揭示了克拉通不同区域深部结构特征的显著差异。与东部普遍减薄的岩石圈(60～100km)相比,中、西部表现出厚、薄岩石圈共存的强烈横向非均匀性,既在稳定的鄂尔多斯盆地之下保留着厚达200km的岩石圈,又在新生代银川—河套和陕西—山西裂陷区存在厚度<100km的薄岩石圈,差异最大的厚、薄岩石圈仅相距约200km。岩石圈厚度在东、中部边界附近的约100km横向范围内显示出20～40km的迅速增加。岩石圈厚度的快速变化与地表地形从东向西的突然改变以及南北重力梯度带的位置大致吻合,并对应于地壳结构、地幔转换带厚度和660km间断面结构的快速变化。这种从地表到上地幔底部深、浅结构的耦合变化特征表明,东西两侧区域在显生宙可能经历了不同的岩石圈构造演化和深部地幔动力学过程。克拉通东部薄的地壳、岩石圈和厚的地幔转换带以及复杂的660km间断面结构可能与中生代以来太平洋板块深俯冲及其相关过程对这一地区岩石圈的改造和破坏有关;而中、西部存在显著减薄的岩石圈这一观测结果,并结合岩石、地球化学资料表明,克拉通岩石圈改造和减薄不仅发生在东部,而且可能影响了包括中、西部在内的更广泛的区域。岩石圈薄于100km的中、西部裂陷区可能与先前存在于岩石圈中的局部构造薄弱带相联系。这些古老岩石圈薄弱带可能经历了后期构造事件的多次改造,并在新生代印度—欧亚陆陆碰撞过程中被进一步弱化、减薄,最终造成地表裂陷。另一方面,中、西部总体较厚的地壳、岩石圈以及正常偏薄的地幔转换带表明,同太平洋深俯冲对东部的作用相比,包括印度—欧亚大陆碰撞在内的多期热-构造事件对该地区的构造演化影响相对较弱,不足以大范围改造和破坏高强度的克拉通岩石圈地幔根,从而造成了该地区现今岩石圈结构的高度横向不均匀。 相似文献
6.
E.V. Artyushkov 《Russian Geology and Geophysics》2012,53(6):566-582
As evidenced by plentiful data, most of the large recent positive topographic features formed as a result of a dramatically accelerated crustal uplift in the Pliocene–Quaternary after a relatively stable period (～100 Myr in most of the regions). The methods used are illustrated by the well-studied large neotectonic crustal uplifts on the Tibetan Plateau and in the Himalayas. Farther north, neotectonic uplifts with amplitudes of several hundred meters to several kilometers spread over a vast area from Central and Northeast China in the south to the Taimyr Peninsula and Northeastern Asia in the north. They are often attributed to the India–Asia plate collision which began ～50 Ma.Most of the uplifts in these regions have formed only during the last few Myr, unaccompanied by significant crustal shortening. Therefore, the large neotectonic crustal uplifts can be explained by a decrease in the lithospheric density. One of the causes was the rapid convective replacement of the lower part of the denser mantle lithosphere by the asthenosphere or mantle plume. This became possible owing to a drastic weakening of the mantle lithosphere under the influence of asthenospheric fluids. In some areas, a considerable asthenospheric top uplift is evidenced by seismic tomography data.The lower mantle lithosphere (～50–100 km thick) was replaced by the asthenosphere underneath the neotectonic crustal uplifts of ～1.0 km in Central Asia. Areas with a thick lithosphere were affected by relatively small neotectonic uplifts, strongly nonuniform in space. They point to metamorphism with mafic-rock expansion in the lower crust upon the infiltration of an asthenospheric fluid. The large crustal uplifts which formed on the continents in the Pliocene and Pleistocene indicate large-scale quasi-synchronic supply of the mantle fluid to their lithosphere. 相似文献
7.
D.Malleswari K.Veeraswamy K.K.Abdul Azeez A.K.Gupta Narendra Babu Prasanta K.Patro T.Harinarayana 《地学前缘(英文版)》2019,10(5):1915-1930
Broad-band and long period magnetotelluric measurements made at 63 locations along ～500 km long Chikmagalur-Kavali profile,that cut across the Dharwar craton(DC)and Eastern Ghat Mobile Belt(EGMB)in south India,is modelled to examine the lithosphere architecture of the cratonic domain and define tectonic boundaries.The 2-D resistivity model shows moderately conductive features that intersperse a highly resistive background of crystalline rocks and spatially connect to the exposed schist belts or granitic intrusions in the DC.These features are therefore interpreted as images of fossil pathways of the volcanic emplacements associated with the greenstone belt and granite suite formation exposed in the region.A near vertical conductive feature in the upper mantle under the Chitradurga Shear Zone represents the Archean suture between the western and eastern blocks of DC.Although thick(～200 km)cratonic(highly resistive)lithosphere is preserved,significant part of the cratonic lithosphere below the western DC is modified due to plume-continental lithosphere interactions during the Cretaceous—Tertiary period.A west-verging moderately conductive feature imaged beneath EGMB lithosphere is interpreted as the remnant of the Proterozoic collision process between the Indian land mass and East Antarctica.Thin(～120 km)lithosphere is seen below the EGMB,which form the exterior margin of the India shield subsequent to its separation from East Antarctica through rifting and opening of the Indian Ocean in the Cretaceous. 相似文献
8.
The Uralide orogen, in Central Russia, is the focus of intense geoscientific investigations during recent years. The international research is motivated by some unusual lithospheric features compared with other collisional belts including the preservation of (a) a collisional architecture with an orogenic root and a crustal thickness of 55–58 km, and (b) large volumes of very low-grade and non-metamorphic oceanic crust and island arc rocks in the upper crust of a low–relief mountain belt. The latter cause anomalous gravity highs along the thickened crust and the isostatic equilibrium inside the Uralides lithosphere as well as the overthrust high-metamorphic rocks. The integrated URSEIS '95 seismic experiment provides fundamentally new data revealing the lithospheric architecture of an intact Paleozoic collisional orogen that allows the construction of density models. In the Urals' lithosphere different velocity structures resolved by wide-angle seismic experiments along both the URSEIS '95- and the Troitsk profile. They can be used to constrain lithospheric density models: a first model consists of a deep subducted continental lower crust which has been highly eclogitized at depths of 60–90 km to a density of 3550 kg/m3. The second model shows a slightly eclogitized lower crust underlying the Uralide orogen with a crustal thickness of 60 km. The eclogitized lower crust causes a too-small impedance contrast to the lithospheric mantle resulting in a lack of reflectors in the area of the largest crustal thickness. Both models fit the measured gravity field. Analyzing the isostatic state of the southern Urals' lithosphere, both density models are in isostatic equilibrium. 相似文献
9.
Crustal structure of the Kaapvaal craton and its significance for early crustal evolution 总被引：1，自引：0，他引：1
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. 相似文献
10.
A determination of the seismic structure of the crust and uppermost mantle of East Antarctica, in the region of Casey station, Wilkes Land and Dumont DUrville station, Terre Adelie is presented. High-fidelity waveforms from teleseismic earthquakes recorded at stations CASY and DRV (1996-2001) are used to calculate the seismic receiver function, the signal produced as energy passes through layers in the seismic velocity structure under the receiving station. The receiver functions are stacked to improve the signal-to-noise ratio and then modelled using an inverse algorithm to find the structure that best fits the observed waveform at each station. Inferences are made regarding the tectonic structure, in particular, the crustal thickness and character of the seismic Moho.The crustal thickness under Casey Station is found to be 30 km (+/- 2 km) with a fairly sharp Moho, considerably less than Dumont D'Urville Station, where the crustal thickness is 42 km, and there IS a significant low velocity region the deep crust. The structure of the Wilkes Land lithosphere is comparable to that of the Albany-Fraser Orogen, Western Australia, part of its conjugate margin. This places a new constraint on the relative position of East Antarctica and Australia in the reconstruction of Gondwana, and earlier, supercontinents. A recent reinterpretation of Antarctic geology proposes tectonic province boundaries trending perpendicular to the coast with counterparts in southern Australia. Seismic techniques, determining structure beneath regions with no surface exposure, are vital tools in testing such tectonic hypotheses, towards the reconstruction of Gondwana to full lithospheric depth. 相似文献
11.
Marcelo Assumpo Meijian An Marcelo Bianchi George S.L. Frana Marcelo Rocha Jos Roberto Barbosa Jesús Berrocal 《Tectonophysics》2004,388(1-4):173
The Tocantins Province in Central Brazil is composed of a series of SSW–NNE trending terranes of mainly Proterozoic ages, which stabilized in the Neoproterozoic in the final collision between the Amazon and São Francisco cratons. No previous information on crustal seismic properties was available for this region. Several broadband stations were used to study the regional patterns of crustal and upper mantle structure, extending the results of a recent E–W seismic refraction profile. Receiver functions and surface wave dispersion showed a thin crust (33–37 km) in the Neoproterozoic Magmatic Arc terrane. High average crustal Vp/Vs ratios (1.74–1.76) were consistently observed in this unit. The foreland domain of the Brasília foldbelt, on the other hand, is characterized by thicker crust (42–43 km). Low Vp/Vs ratios (1.70–1.72) were observed in the low-grade foreland fold and thrust zone of the Brasília belt adjacent to the São Francisco craton. Teleseismic P-wave tomography shows that the lithospheric upper mantle has lower velocities beneath the Magmatic Arc and Goiás Massif compared with the foreland zone of the belt and São Francisco craton. The variations in crustal thickness and upper mantle velocities observed with the broadband stations correlate well with the measurements along the seismic refraction profile. The integration of all seismic observations and gravity data indicates a strong lithospheric contrast between the Goiás Massif and the foreland domain of the Brasília belt, whereas little variation was found across the foldbelt/craton surface boundary. These results support the hypothesis that the Brasília foreland domain and the São Francisco craton were part of a larger São Francisco-Congo continental plate in the final collision with the Amazon plate. 相似文献
12.
We present relative sea level （RSL） curves in Antarctica derived from glacial isostatic adjustment （GIA）predictions based on the melting scenarios of the Antarctic ice sheet since the Last Glacial Maximum （LGM）given in previous works.Simultaneously,Holocene-age RSL observations obtained at the raised beaches along the coast of Antarctica are shown to be in agreement with the GIA predictions.The differences from previously published ice-loading models regarding the spatial distribution and total mass change of the melted ice are significant.These models were also derived from GIA modelling; the variations can be attributed to the lack of geological and geographical evidence regarding the history of crustal movement due to ice sheet evolution.Next,we summarise the previously published ice load models and demonstrate the RSL curves based on combinations of different ice and earth models.The RSL curves calculated by GIA models indicate that the model dependence of both the ice and earth models is significantly large at several sites where RSL observations were obtained.In particular,GIA predictions based on the thin lithospheric thickness show the spatial distributions that are dependent on the melted ice thickness at each sites.These characteristics result from the short-wavelength deformation of the Earth.However,our predictions strongly suggest that it is possible to find the average ice model despite the use of the different models of lithospheric thickness.By sea level and crustal movement observations,we can deduce the geometry of the post-LGM ice sheets in detail and remove the GIA contribution from the crustal deformation and gravity change observed by space geodetic techniques,such as GPS and GRACE,for the estimation of the Antarctic ice mass change associated with recent global warming. 相似文献
13.
A dense seismic network (～100 stations) was operated in the Koyna-Warna region from January 2010 to May 2010, that allow us to collect 400 high-quality local earthquake data of magnitude less than 4. In this region, the fault structure and tectonic setting that accommodate the induced seismicity is not well understood. To investigate the seismotectonics of the region, we have inverted 7826 P- and 7047 S-P arrival times for 3-D Vp and Vp/Vs tomographic models along with hypocenters parameters in the region. Although, Dixit et al. (2014) have performed 3-D local earthquake tomography with double-difference tomography code using catalog differential time data. In this paper, Simulps14 code on the same data set is applied. For better approach P arrival time and S-P travel times are inverted directly for Vp, Vp/Vs variations and earthquake locations. High Vp ～5.9 to 6.5 and low to high Vp/Vs ～1.69-1.74 imaged in the hypocenter region. These features interpreted as a fluid bearing rock mass under high pore pressure. It is also observed that below the trap basement form a local topography depression between the Koyna and Warna Reservoirs. To the South of the Warna reservoir, intense seismic activity defines a major cluster of ～ 5 km width at 3 to7 km deep, located under the trap, where the basement is deepening. Such regions are inferred to be associated with the seismically active faults zones. The obtain velocity anomalies are reliable down to a depth of 10 km. This is also confirmed by the analysis of three resolution parameters viz. Hit count, Derivative Weight sum (DWS) and Resolution Diagonal Elements (RDE). 相似文献
14.
:Reactivation of metasomatized mantle lithosphere may occur during continental extension,which is an important component of plate tectonics.The lower most part of the metasomatized domains in the subcontinental mantle lithosphere can be locally enriched in CO2.Therefore,partial melting of these metasomatized domains may play a crucial role in the global carbon cycle.However,little is known about this process and up until now few numerical constraints are available.Here we address this knowledge gap and use a 2-D high resolution petrological-thermomechanical model to assess lithospheric rifting.CO2 degassing and melting.We test 4 lithospheric thicknesses:90,110,130 and 200 km with a 10 km thick metasomatized layer at the base using CO2 of 2 wt.%in the bulk composition.The carbonate enriched layer is stable below^3 GPa(>110 km)for a temperature of 1300℃;therefore,we only observe degassing patterns for lithospheric models that are 130 km and 200 km thick.The metasomatized layer for the 130 km thick lithosphere mostly comprises carbonatite melting,whereas in the 200 km thick scenario propagation of melt development from kimberlites to carbonatites occurs as the metasomatic mantle is exhumed during extension.The numerical models fit well into natural rifting zones of the European Cenozoic Rift System for young(shallow)and of the North Atlantic Rift for old(thick)lithosphere. 相似文献
15.
西藏及其周围地区地壳、地幔地震层析成像——印度板块大规模俯冲于西藏高原之下的证据 总被引：20，自引：1，他引：20
文中介绍有关西藏—喜马拉雅碰撞带的一项地震层析成像研究。根据一个用天然地震数据产生的全球波速模型 ,印度板块有可能以近水平状俯冲于整个西藏高原之下至 16 5～ 2 6 0km深度。西藏岩石圈具有低波速地壳和高波速下岩石圈 (75～ 12 0km深 )。在 12 0～ 16 5km深度范围 ,西藏岩石圈与俯冲的印度板块之间有一层低速软流圈物质。高原中部从地表到 310km深处有一低速体 ,说明地幔物质有可能穿过俯冲板块的脆弱部位上隆。这些结果以及野外实测的地壳缩短值说明高原的抬升得助于印度板块的近水平俯冲。我们推论俯冲印度板块的升温上浮以及上覆软流层的存在是造成西藏高原高海拔抬升以及内部地表仍相对平坦的主要原因。2 0 0 1年 1月 2 6日在印度西部发生的毁灭性大地震有可能是俯冲应力在印度板块后缘薄弱处引发的岩石圈大断裂。 相似文献
16.
天然地震S波和大地电磁测深给出了两种不同的藏北岩石圈厚度模型,两种测量结果的地质含义至今还不十分清楚。通过对地表高程与地壳厚度回归关系的研究,以回归直线的斜率和截距作为地壳和岩石圈地幔平均密度取值的约束,并考虑相变因素对软流圈密度的影响,采用均衡理论对藏北岩石圈厚度进行了计算。计算结果表明,在可能的软流圈温度取值范围内藏北岩石圈的平均厚度约为106～120km,地壳增厚前的岩石圈平均厚度约80km。藏北新生代火山作用和岩浆起源-分凝深度分析表明,藏北现今岩石圈厚度主要受金云母脱水深度所控制。增厚前岩石圈地幔底部温度高于橄榄岩湿固相线温度,并受闪石和金云母高压脱水作用的影响。加厚岩石圈地幔因其底部不断发生脱水低程度熔融而进入软流圈小尺度对流体系,使岩石圈加厚过程中伴随有底部的脉动减薄作用。 相似文献
17.
青藏高原东北缘是研究高原隆升和演化的理想场所,其岩石圈结构记录了高原向外扩展的岩石圈变形行为和演化过程,本研究利用一条跨青藏高原东北缘的宽频带观测剖面(红原-景泰剖面)和部分甘肃、青海区域台网的远震体波波形资料,通过S波接收函数方法获得了青藏高原东北缘的岩石圈-软流圈边界(LAB)图像。结果表明:1)松潘-甘孜地体东北部和西秦岭造山带下方的岩石圈较薄,略向北加厚,其LAB深度为110~130 km,昆仑断层下方无明显岩石圈错断,推测松潘-甘孜地块与西秦岭造山带的岩石圈可能具有亲缘性; 2)祁连地块下方的岩石圈厚度为135~150 km,其中祁连造山带东缘的LAB震相不聚焦,反映复杂的造山带型岩石圈属性; 3)阿拉善地块下方岩石圈略向南加厚, LAB深度为130~150 km,呈向祁连造山带下方汇聚的趋势,但尚未通过海原断裂带; 4)鄂尔多斯地块下方的岩石圈较厚, LAB深度为160~170 km,反映其稳定的克拉通型岩石圈属性。 相似文献
18.
中国东北地区地震空间分布与主要断裂带、深部构造及应力场关系 总被引：5，自引：1，他引：4
中国东北地区在北东东向应力场控制下, 地震有其特殊性。地震空间分布和深度统计结果表明, 东北地区地震主要受岩石圈断裂(开原-赤峰断裂带) 控制, 以44°N为界, 南北具有明显差异。北部地震发生的数量少于南部, 震源深度主要集中在4～6 km和8～12 km两个深度范围内; 而南部主要集中在8～12 km和28～30 km两个深度范围内。发震深度分析显示, 开原-赤峰、郯庐断裂带、大兴安岭断裂带下可能存在地温较低的区域, 使地震可以在深部孕育。地震分布的Vp和Vs剖面资料的研究暗示, 断裂与速度变化带、断裂与断裂的相交区域是地震易发生区域。 相似文献
19.
Conventional diamond exploration guidelines predict that economic diamond occurrences will be restricted to Archaean cratons, where the lithosphere is thick and cool, and diamond is the stable form of carbon in the lower portions of the lithosphere. However, Australia's current economic diamond deposits are not well predicted by these conventional exploration guidelines. Tomographic images show that Australia's economic diamond deposits lie at step changes in lithospheric thickness within dominantly cratonized Proterozoic provinces with thick (≥ 200 km) lithosphere. The thickest portions of the seismic lithosphere in Australia occur not under the major Archaean cratons, rather the central Proterozoic regions of the continent. We use a numerical code to show that such features are stable, and that the longevity of the diamond stability field is dependent on distance to the continent–ocean boundary, local depth of the chemical boundary layer (CBL), and proximity to changes in CBL depth. We also show that abrupt changes in lithospheric thickness focus lithospheric stress gradients, affecting melt migration paths, and that continental melt production is enhanced in regions adjacent to major cratons. Diamond pipes occur where conditions conducive to diamond stability and deep-seated alkaline volcanism (kimberlite or lamproite) occur simultaneously, and the common confluence of these factors at abrupt changes in lithospheric thickness marks them as potential exploration targets. 相似文献
20.
M. G. Bostock 《Lithos》1999,48(1-4):1-16
Discontinuities in physical properties within the continental lithosphere reflect a range of processes that have contributed to craton stabilization and evolution. A survey of recent seismological studies concerning lithospheric discontinuities is made in an attempt to document their essential characteristics. Results from long-period seismology are inconsistent with the presence of continuous, laterally invariant, isotropic boundaries within the upper mantle at the global scale. At regional scales, two well-defined interfaces termed H (60 km depth) and L (200 km depth) of continental affinity are identified, with the latter boundary generally exhibiting an anisotropic character. Long-range refraction profiles are frequently characterized by subcontinental mantle that exhibits a complex stratification within the top 200 km. The shallow layering of this package can behave as an imperfect waveguide giving rise to the so-called teleseismic Pn phase, while the L-discontinuity may define its lower base as the culmination of a low velocity zone. High-resolution, seismic reflection profiling provides sufficient detail in a number of cases to document the merging of mantle interfaces into lower continental crust below former collisional sutures and magmatic arcs, thus unambiguously identifying some lithospheric discontinuities with thrust faults and subducted oceanic lithosphere. Collectively, these and other seismic observations point to a continental lithosphere whose internal structure is dominated by a laterally variable, subhorizontal layering. This stratigraphy appears to be more pronounced at shallower lithospheric levels, includes dense, anisotropic layers of order 10 km in thickness, and exhibits horizontal correlation lengths comparable to the lateral dimensions of overlying crustal blocks. A model of craton evolution which relies on shallow subduction as a principal agent of craton stabilization is shown to be broadly compatible with these characteristics. 相似文献