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1.
M.J.N. Remkes 《地学学报》1990,2(6):563-568
Tornographic images of the Mediterranean upper mantle P-wave velocity structure have been used to analyse the gravity potential in the vicinity of the Hellenic subduction zone. The velocity anomalies are assumed to be proportional to density variations according to Birch's law. The effect of the topography on the geoid in the region is also calculated. The results indicate that the upper mantle geoid signal probably has significant amplitudes of several metres, but it correlates poorly with the observed geoid. The geoid calculated from topography correlates well, but has an amplitude that is too large in comparison with the observed geoid. The results show that an improved understanding of the Hellenic subduction zone geoid requires refinement of the Moho topography, so that the effect of this topography can be separated from the upper mantle signature. 相似文献
2.
During summer 1975, a line of large shots was fired across the continental margin between the Rockall Trough and the Hebridean shelf along 58°N. Arrivals were observed at temporary seismic stations set up across Scotland and in northwestern Ireland. A clear P2 phase was observed to cross the margin and a converted phase P1 also seen on the records is interpreted as travelling in the sub-sedimentary oceanic crust of Rockall Trough and in the upper continental crust beneath the shelf.The continental crust beneath the Hebridean shelf is estimated to be 27 ± 2 km thick, with Pg = 6.22 ± 0.03 km/s and Pn = 8.01 ± 0.04 km/s as determined by time-term analysis. Pg delays on the outer shelf are interpreted in terms of a seaward thickening wedge of Mesozoic sediments which pre-date the split. Pn beneath the Rockall Trough was poorly determined at 8.20 ± 0.17 km/s and the Moho is estimated to be 18 ± 2 km deep at 58°N. This and other seismic and gravity work indicates a northward thickening of the crust along the Rockall Trough, accounting for the northward decrease in the height of the slope.Our results, and those of gravity interpretations, indicate a relatively abrupt transition between continental and oceanic crust, possibly correlating with the lack of major shelf subsidence. This is attributed to a relatively cool origin for this margin. The main thinning of the continental crust beneath the slope is attributed to outslip of continental crustal material into and beneath the newly forming oceanic crust during the first few million years after the split, possibly enhanced by pre-split stretching. 相似文献
3.
青藏高原地球物理特征分析 总被引：1，自引：0，他引：1
根据区域性航空磁测、重力区测及现代地震活动观察分析表明,青藏高原是一个十分独特和年青的巨大的构造单元。它具有薄的磁性壳层,透镜状的地壳结构,断块镶嵌的构造特征。高的热流和地震活动,以及地磁场的剧烈衰减和大面积分布的均衡重力异常,揭示出青藏高原目前仍然在升温上拱和推覆调整中。青藏高原地壳内部普遍发育低速低阻层,壳下发育壳幔混合层。地壳显示为两类不同特征的结构层:上部地壳以断错叠推增厚为特征,下部地壳因混入大量上地幔及软流圈物质而增生为透镜层。地壳挤压推叠破坏了岩石圆的均衡状态,而地幔混合层的发育则是对壳幔不均衡状态的补偿和调整。由于地壳深部的高温高压环境,古构造岩相痕迹被改造熔蚀,现今观察到的青藏高原地球物理特征主要反映的是新近发育和目前存在的构造特征。青藏高原是由两个不同历史演化的大陆板块碰撞缝合而成。航磁及其它地球物理测量表明,两大板块的结合带发育在金沙江—红河断裂带及南侧的唐古拉—三江构造带。在上述地带两边,区域磁场背景差别十分明显。 相似文献
4.
利用航磁、重力资料研究川滇地区大陆变形特征 总被引：1，自引：0，他引：1
利用航磁、重力资料对川滇地区大陆变形特征进行了研究。航磁异常揭示了研究区内的基底性质及其横向差异,研究区内的强烈地震主要集中在航磁异常突变带上,基底性质横向差异有利于应力的相对集中,成为地震孕育和发生的有利部位。康定—绵阳一带刚性基底的阻挡造成了青藏高原下地壳物质向东的塑性流动被迫转向南东—南南东方向,进而造成了川滇菱形块体内广泛的地壳增厚,布格重力异常等值线呈向南东伸出的舌状是其地壳增厚作用的直观反映。川滇地区的大陆变形特征既存在广泛的地壳增厚现象,同时在下地壳塑性流动的驱动下,中、上地壳破碎成大小不一的块体,变形特征表现出整体刚性,因而不能简单地套用“地壳增厚”或“大陆逃逸”模式。 相似文献
5.
Many ancient deformation belts, especially of Archean and Palaeoproterozoic age, show large areas marked by primary flat‐lying fabrics associated with rather monotonous metamorphic conditions of HTLP type and affected by steep transpressive zones involving vertical stretch. These features do not support strain localization along large‐scale thrusts and (or) extensional detachments, as common in modern orogens. Instead, they are consistent with hot and weak lithospheres where gravity‐driven horizontal flow may compete with distributed thickening from early stages of collisional processes. Relevant deformation features are reviewed and highlighted by lithosphere‐scale analogue models involving low‐viscosity lower crust and sub‐Moho mantle. Both nature and models argue that compression of such lithospheres may induce combined distributed thickening and lateral channel flow of the ductile crust accommodated by transpressive zones. 相似文献
6.
《Journal of Structural Geology》2001,23(2-3):455-472
The Aegean region constitutes the overriding plate of the Africa–Eurasia convergent plate system, in the eastern Mediterranean. To explain the fault kinematics and tectonic forces that controlled rift evolution in the Aegean area, we present fault-slip data from about 900 faults, and summarise the structural analyses of five key structural “provinces”. Five regional tectonic maps are used as the basis for a new stress map for the Aegean region and for discussions on regional geodynamics.Since the Late Miocene, the central Aegean has been affected by WNW- and NE-trending faults which transfer the motion of the Anatolian plate to the southwest, synchronous with arc-normal pull acting on the boundary of the Aegean plate. At the same time, the Hellenic Peninsula has suffered moderate extension by NW-trending grabens formed due to collapse of the Hellenic mountain chain.During intense extension in the southern Aegean in the Plio-Quaternary the arcuate shape of the Hellenic Trench was established. Arc-normal pull in the Aegean plate margin, combined with transform resistive forces along the Hellenic subduction gave rise to widespread strike-slip and oblique-normal faults in the eastern segment and moderate oblique extension in the western segment of the arc. To the north, subduction involves more continental crust and consequently the push of subduction is transmitted to the overriding plate (Hellenic Peninsula), resulting in the formation of NE-trending grabens. WNW-trending grabens in this area are considered to have propagated westward from the Aegean Sea to the Ionian Sea during Plio-Quaternary times, probably acting as pull-apart structures between stable Europe and the rapidly extending southern Aegean area. 相似文献
7.
Crustal structure under the central High Atlas Mountains (Morocco) from geological and gravity data 总被引：1，自引：0，他引：1
P. Ayarza F. Alvarez-Lobato A. Teixell M.L. Arboleya E. Tesn M. Julivert M. Charroud 《Tectonophysics》2005,400(1-4):67-84
Seismic wide angle and receiver function results together with geological data have been used as constraints to build a gravity-based crustal model of the central High Atlas of Morocco. Integration of a newly acquired set of gravity values with public data allowed us to undertake 2–2.5D gravity modelling along two profiles that cross the entire mountain chain. Modelling suggests moderate crustal thickening, and a general state of Airy isostatic undercompensation. Localized thickening appears restricted to the vicinity of a north-dipping crustal-scale thrust fault, that offsets the Moho discontinuity and defines a small crustal root which accounts for the minimum Bouguer gravity anomaly values. Gravity modelling indicates that this root has a northeasterly strike, slightly oblique to the ENE general orientation of the High Atlas belt. A consequence of the obliquity between the High Atlas borders and its internal and deep structure is the lack of correlation between Bouguer gravity anomaly values and topography. Active buckling affecting the crust, a highly elevated asthenosphere, or a combination of both are addressed as side mechanisms that help to maintain the high elevations of the Atlas mountains. 相似文献
8.
The upper part of the lithosphere has been actively involved in various exogenic and endogenic processes which have left their imprint on the gravity field on the Indian Peninsula and the Himalaya. Analysis of the gravity field over the Dharwar craton shows that the greenstone belts of this craton have been formed as a result of development of deep fractures in the earth's crust during Archaean times. Precambrian mountain ranges such as the Aravallies, Vindhyans, Satpura and Eastern Ghats are located peripheral to Archaean cratons. Most of these mountain belts are characterized by gravity highs suggesting that the underlying crust is of higher than normal density. These mountain ranges with the exception of the Eastern Ghats do not appear to be locally compensated. Regional compensation seems to prevail over all these areas. Eastern Ghats ranges are also underlain by a crust of higher than normal density relative to the Dharwar and Bastar cratons and exist with a sharp contact with the cratons in the West. Isostatic compensation in the Eastern Ghats appears to have been achieved by thickening of the underlying crust. The Himalaya has attained a fairly high degree of isostatic compensation. 相似文献
9.
A seismic refraction/wide-angle reflection experiment was undertaken in the Levant Basin, eastern Mediterranean. Two roughly east–west profiles extend from the continental shelf of Israel toward the Levant Basin. The northern profile crosses the Eratosthenes Seamount and the southern profile crosses several distinct magnetic anomalies. The marine operation used 16 ocean bottom seismometers deployed along the profiles with an air gun array and explosive charges as energy sources. The results of this study strongly suggest the existence of oceanic crust under portions of the Levant Basin and continental crust under the Eratosthenes Seamount. The seismic refraction data also indicate a large sedimentary sequence, 10–14 km thick, in the Levant Basin and below the Levant continental margin. Assuming the crust is of Cretaceous age, this gives a fairly high sedimentation rate. The sequence can be divided into several units. A prominent unit is the 4.2 km/s layer, which is probably composed of the Messinian evaporites. Overlying the evaporitic layer are layers composed of Plio–Pleistocene sediments, whose velocity is 2.0 km/s. The refraction profiles and gravity and magnetic models indicate that a transition from a two layer continental to a single-layer oceanic crust takes place along the Levant margin. The transition in the structure along the southern profile is located beyond the continental margin and it is quite gradual. The northern profile, north of the Carmel structure, presents a different structure. The continental crust is much thinner there and the transition in the crustal structure is more rapid. The crustal thinning begins under western Galilee and terminates at the continental slope. The results of the present study indicate that the Levant Basin is composed of distinct crustal units and that the Levant continental margin is divided into at least two provinces of different crustal structure. 相似文献
10.
《Journal of South American Earth Sciences》2000,13(6):479-489
We present a gravity model of the crustal structure in southern Mexico based on interpretation of a detailed marine gravity profile perpendicularly across the Middle America Trench offshore from Acapulco, and a regional gravity transect extending into continental Mexico across the Sierra Madre del Sur, the central sector of the Trans-Mexican Volcanic Belt, the Sierra Madre Oriental, the Coastal Plain, and into the Gulf of Mexico. The elastic thickness of the Cocos lithospheric plate was found to be 30 km. In agreement with a previous seismic refraction study, no major differences in crustal structure were observed on both sides of the O’Gorman Fracture Zone. The gravity high seaward of the trench is interpreted as due to the incipient flexure and crustal thinning. The gravity low at the axis of the trench is explained by the increase in water depth and the existence of low-density accreted or continental-derived sediments (2.25 and 2.40 g/cm3). A gravity high of 50 mGal extending about 100 km landward is interpreted as caused by local shoaling of the Moho. The crust attains a thickness of 42 km under the Trans-Mexican Volcanic Belt but thins beneath the Coastal Plain and the continental slope of the Gulf of Mexico. Gravity highs around the Sierra de Tamaulipas are interpreted in terms of relief of the lower–upper crustal interface, implying a shallow basement. 相似文献
11.
K. Hinz H.-U. Schlüter A.C. Grant S.P. Srivastava D. Umpleby J. Woodside 《Tectonophysics》1979,59(1-4)
In 1977 the Federal Institute for Geosciences and Natural Resources, Hannover, carried out a large scale multichannel reflection seismic survey in the Labrador Sea. This survey provided an opportunity for the direct comparison of the geologic structure of the Labrador and Greenland margins. The seismic records across the Labrador Shelf show a thick, prograding sedimentary wedge consisting of several seismic sequences onlapping an acoustic basement that dips steeply seaward. The surface of the acoustic basement is irregular below the continental slope, indicating Late Cretaceous—Early Tertiary faulting. The thick sedimentary section below the slope is divided by an unconformity, tentatively identified as Late Tertiary in age, into two seismic megasequencies which can be subdivided. The acoustic basement on the Greenland side is also strongly faulted but is overlain, in the south, by a thin sedimentary section. The sediment cover thickens on the Greenland Shelf to the north as the shelf becomes wider.As with more southerly parts of the western Atlantic margin, a positive free-air anomaly (30–50 mgal) lies landward of the shelf break off Labrador and a smaller negative anomaly follows the base of the slope. Similar, but generally narrower features are observed along the Greenland margin. West of the negative anomaly off the Greenland slope a narrow band of lower amplitude positive anomalies tends to be associated with an acoustic basement high observed in the reflection profiles. A landward negative gradient in the simple Airy isostatic anomaly across this margin suggests that the ocean—continent boundary is related to this high.Detailed magnetic measurements across the northern Labrador margin show that well-developed oceanic anomalies trending north-northwest lie east of the large Labrador Shelf gravity high, beyond the 2000 m isobath. Landward of these magnetic anomalies is a quiet magnetic zone within which the linear gravity high is parallel to the shelf break and correlates with a deep, sediment-filled basin. It is inferred that oceanic-type crust or greatly-attenuated continental crust underlies this basin and that continental crust thickens markedly westward of the gravity high over a distance of about 50 km. 相似文献
12.
A generalised crustal structure of Fiordland is proposed.Detailed mapping in part of Western Fiordland has led to the recognition of a basement granulite facies lower crustal material, probably Precambrian in age) separated by a regional thrust zone from a cover sequence (amphibolite facies gneisses, of Lower Paleozoic age). With the recognition of the basement—cover relationship and the aid of aeromagnetic anomalies Fiordland has been divided into four, generally north-northeast trending, regions. The Western Fiordland region is composed chiefly of basement rocks. The Central Fiordland and Southwestern Fiordland regions are made up predominantly of amphibolite and greenschist-facies metasediments and gneissic granodiorites of the cover sequence, which in Central Fiordland have a regional dip to the east, off the basement. The Eastern Fiordland region is characterised by a series of basic, intermediate and acid intrusive rocks. The more prominent magnetic anomalies in Eastern Fiordland, Southwestern Fiordland, and a large anomaly off the coast of Western Fiordland, are all considered to be caused by intrusive bodies. The presence of a positive gravity anomaly over Western Fiordland, coupled with a gravity low offshore, is consistent with the lower crust being uplifted and exposed in this area. Continuing shallow and intermediate-depth seismic activity beneath Fiordland, as well as the large size of the gravity anomaly, suggest that tectonic forces are currently acting to maintain Western Fiordland at its unusually high level.Fiordland thus displays a cross-section of continental crust: Precambrian(?) metaigneous granulites in the lower crust; Lower Paleozoic metasedimentary amphibolitefacies gneisses and melted equivalents in the middle crust; Mesozoic intrusives, and overlying Cretaceous and Tertiary sediments in the upper crust. 相似文献
13.
14.
T. Yegorova U. Bayer H. Thybo Y. Maystrenko M. Scheck-Wenderoth S.B. Lyngsie 《Tectonophysics》2007,429(1-2):133-163
We study the gravity signals from different depth levels in the lithosphere of the Central European Basin System (CEBS). The major elements of the CEBS are the Northern and Southern Permian Basins which include the Norwegian–Danish Basin (NDB), the North-German Basin (NGB) and the Polish Trough (PT). An up to 10 km thick sedimentary cover of Mesozoic–Cenozoic sediments, hides the gravity signal from below the basin and masks the heterogeneous structure of the consolidated crust, which is assumed to be composed of domains that were accreted during the Paleozoic amalgamation of Europe. We performed a three-dimensional (3D) gravity backstripping to investigate the structure of the lithosphere below the CEBS.Residual anomalies are derived by removing the effect of sediments down to the base of Permian from the observed field. In order to correct for the influence of large salt structures, lateral density variations are incorporated. These sediment-free anomalies are interpreted to reflect Moho relief and density heterogeneities in the crystalline crust and uppermost mantle. The gravity effect of the Moho relief compensates to a large extent the effect of the sediments in the CEBS and in the North Sea. Removal of the effects of large-scale crustal inhomogeneities shows a clear expression of the Variscan arc system at the southern part of the study area and the old crust of Baltica further north–east. The remaining residual anomalies (after stripping off the effects of sediments, Moho topography and large-scale crustal heterogeneities) reveal long wavelength anomalies, which are caused mainly by density variations in the upper mantle, though gravity influence from the lower crust cannot be ruled out. They indicate that the three main subbasins of the CEBS originated on different lithospheric domains. The PT originated on a thick, strong and dense lithosphere of the Baltica type. The NDB was formed on a weakened Baltica low-density lithosphere formed during the Sveco-Norwegian orogeny. The major part of the NGB is characterized by high-density lithosphere, which includes a high-velocity lower crust (relict of Baltica passive margin) overthrusted by the Avalonian terrane. The short wavelength pattern of the final residuals shows several north–west trending gravity highs between the Tornquist Zone and the Elbe Fault System. The NDB is separated by a gravity low at the Ringkøbing–Fyn high from a chain of positive anomalies in the NGB and the PT. In the NGB these anomalies correspond to the Prignitz (Rheinsberg anomaly), the Glueckstadt and Horn Graben, and they continue further west into the Central Graben, to join with the gravity high of the Central North Sea. 相似文献
15.
Along the Rio Muni transform margin, the transition from continental to oceanic crust occurs across a region of approximately 75-km width. The crust in this transition region, termed proto-oceanic crust (POC), is neither purely oceanic nor continental in composition and structure. Improved seismic reflection images from the PROBE deep-imaging dataset, combined with gravity modelling, have shed new light on the structural architecture of the margin and the composition of the POC. On these newly migrated seismic reflection sections, four fracture zones associated with large steps in the Moho are identified, splitting the POC into three segments. Models in which these segments are composed of oceanic or stretched continental crust do not provide satisfactory predictions of the gravity anomaly. A model of serpentinized peridotite for two segments of POC, with the third segment composed of oceanic crust in between, does satisfy the observed gravity anomaly. Three alternative geological scenarios are proposed to explain the segmentation and composition of the POC: (a) serpentinized upper mantle becoming unroofed and emplaced at basement surface level along detachment surfaces confined to discrete segments by the fracture zones, (b) oblique-slip on transform faults that allow the circulation of water into the mantle and emplacement of serpentinized upper mantle material; or (c) intense faulting of anomalous oceanic crust as a result of magma depletion allowing hydrothermal circulation and the emplacement of serpentinized peridotites. 相似文献
16.
Kiranmai Samudrala K A Kamesh Raju P Rama Rao 《Journal of Earth System Science》2016,125(8):1523-1542
High-resolution shipboard geophysical investigations along the Indian Ocean ridge system are sparse especially over the Carlsberg and Central Indian ridges. In the present study, the shipboard gravity and multibeam bathymetry data acquired over a 750 km long section of the Central Indian Ridge between 3 °S and 11 °S have been analysed to understand the crustal structure and the ridge segmentation pattern. The mantle Bouguer anomalies (MBA) and the residual mantle Bouguer anomalies (RMBA) computed in the study area have shown significant variations along the ridge segments that are separated by transform and non-transform discontinuities. The MBA lows observed over the linear ridge segments bounded by well-defined transform faults are attributed to the thickening of the crust at the middle portions of the ridge segments. The estimates of crustal thickness from the RMBA shows an average of 5.2 km thick crust in the axial part of the ridge segments. The MBA and relative RMBA highs along the two non-transform discontinuities suggests a thinner crust of up to 4.0 km. The most significant MBA and RMBA highs were observed over the Vema transform fault suggesting thin crust of 4 km in the deepest part of the transform fault where bathymetry is more than 6000 m. The identified megamullion structures have relative MBA highs suggesting thinner crust. Besides MBA lows along the ridge axis, significant off-axis MBA lows have been noticed, suggesting off-axis mantle upwelling zones indicative of thickening of the crust. The rift valley morphology varies from the typical V-shaped valley to the shallow valley floor with undulations on the inner valley floor. Segments with shallow rift valley floor have depicted well-defined circular MBA lows with persistent RMBA low, suggesting modulation of the valley floor morphology due to the variations in crustal thickness and the mantle temperature. These are supported by thicker crust and weaker lithospheric mantle. 相似文献
17.
Fission track and fault kinematics analyses for new insight into the Late Cenozoic tectonic regime changes in West-Central Sulawesi (Indonesia) 总被引：1，自引：0，他引：1
Olivier Bellier Michel Sbrier Diane Seward Thierry Beaudouin Michel Villeneuve Eka Putranto 《Tectonophysics》2006,413(3-4):201-220
A 3-D density model for the Cretan and Libyan Seas and Crete was developed by gravity modelling constrained by five 2-D seismic lines. Velocity values of these cross-sections were used to obtain the initial densities using the Nafe–Drake and Birch empirical functions for the sediments, the crust and the upper mantle. The crust outside the Cretan Arc is 18 to 24 km thick, including 10 to 14 km thick sediments. The crust below central Crete at its thickest section, has values between 32 and 34 km, consisting of continental crust of the Aegean microplate, which is thickened by the subducted oceanic plate below the Cretan Arc. The oceanic lithosphere is decoupled from the continental along a NW–SE striking front between eastern Crete and the Island of Kythera south of Peloponnese. It plunges steeply below the southern Aegean Sea and is probably associated with the present volcanic activity of the southern Aegean Sea in agreement with published seismological observations of intermediate seismicity. Low density and velocity upper mantle below the Cretan Sea with ρ 3.25 × 103 kg/m3 and Vp velocity of compressional waves around 7.7 km/s, which are also in agreement with observed high heat flow density values, point out at the mobilization of the upper mantle material here. Outside the Hellenic Arc the upper mantle density and velocity are ρ ≥ 3.32 × 103 kg/m3 and Vp = 8.0 km/s, respectively. The crust below the Cretan Sea is thin continental of 15 to 20 km thickness, including 3 to 4 km of sediments. Thick accumulations of sediments, located to the SSW and SSE of Crete, are separated by a block of continental crust extended for more than 100 km south of Central Crete. These deep sedimentary basins are located on the oceanic crust backstopped by the continental crust of the Aegean microplate. The stretched continental margin of Africa, north of Cyrenaica, and the abruptly terminated continental Aegean microplate south of Crete are separated by oceanic lithosphere of only 60 to 80 km width at their closest proximity. To the east and west, the areas are floored by oceanic lithosphere, which rapidly widens towards the Herodotus Abyssal plain and the deep Ionian Basin of the central Mediterranean Sea. Crustal shortening between the continental margins of the Aegean microplate and Cyrenaica of North Africa influence the deformation of the sediments of the Mediterranean Ridge that has been divided in an internal and external zone. The continental margin of Cyrenaica extends for more than 80 km to the north of the African coast in form of a huge ramp, while that of the Aegean microplate is abruptly truncated by very steep fractures towards the Mediterranean Ridge. Changes in the deformation style of the sediments express differences of the tectonic processes that control them. That is, subduction to the northeast and crustal subsidence to the south of Crete. Strike-slip movement between Crete and Libya is required by seismological observations. 相似文献
18.
Subduction zone roll‐back was recently put forward as a convincing model to explain the geometry and evolution of the Gibraltar Arc. For other subduction‐related arc systems of the Mediterranean, such as the Calabrian Arc and the Hellenic Arc, palaeomagnetic rotation data from Neogene extensional basins provided important constraints on geodynamic evolution models. Here, we present the results of a palaeomagnetic study of 13 continuous sections that are located in E–W transects across the Neogene sedimentary basins of Morocco and Spain. They provide evidence that no significant rotation about vertical axes has occurred in the Gibraltar Arc since the late Tortonian. Comparison with other Mediterranean arc systems shows strong similarities as regards geodynamic evolution. The timing of rotation in the Gibraltar Arc is markedly older than in the Calabrian and Hellenic arcs, and suggests that it is related to the first Neogene extensional phase of the western Mediterranean in which the Algerian–Provençal Basin opened. 相似文献
19.
The main target of the present study is an objective and automated regionalization of Rayleigh wave dispersion data for the Mediterranean basin, without a priori seismotectonic constraints, and to determine the corresponding regional shear-velocity structures. The database used is formed by almost 200 Rayleigh wavetrains corresponding to 42 regional events, with surface-wave magnitude greater than 4.5, recorded at the MedNet very-broad-band stations in the Mediterranean area. Path-averaged group velocities for the Rayleigh wave fundamental mode are derived for each available epicentre-station trajectory crossing the Mediterranean basin. After this, a principal component analysis and a clustering process are applied to local group velocities, obtained for 13 different periods from 10 to 70 s, in order to classify the Mediterranean basin into several homogeneous regions. The stochastic inversion of the averaged group velocity dispersion curve obtained for each region provides the respective shear-velocity structures, down to a depth of 150–160 km. The characteristics of these areas and their possible correlation with the main seismotectonic features of the Mediterranean region are discussed. The regional models reveal significant lateral changes in the elastic structure, with the main differences concerning particularly the upper 35–40 km. Within this depth range, low shear velocities, varying from 2.8 to 3.9 km s−1, characterize the Eastern Mediterranean, whereas higher velocities, ranging from 3.0 to 4.2 km s−1, are deduced for the Western Mediterranean. These results suggest a thicker crust in the eastern part, but with a greater thickness of sedimentary layers. However, for depths of between 80 and 110 km, lower shear velocities are obtained in the Western part, while higher shear velocities are derived for the Eastern Mediterranean Sea, in the Aegean Sea, Greece, the south of Italy, Sicily and Tunisia. This velocity pattern suggests an averaged thicker lithosphere under the latter areas, as the top of the asthenosphere is detected at a mean depth of 75 km for the remaining regions. This thicker lithosphere can be related to processes associated with the convergence of the Eurasian and African plates and subduction under the Calabrian and Hellenic Arcs. 相似文献
20.
川黔湘构造带可划分为4个不同的构造带,其中雪峰山构造带地理位置特殊,恰位于华南块体南北向重力梯度带上,两侧岩石圈厚度差异显著,其成因机制历来是争论的焦点。雪峰山构造带基底是一个花状结构,与川黔隔槽式褶皱带构成一个整体,为一个厚皮结构。雪峰山基底在沅麻盆地隆升最高,表现为压扭性构造特点。参考深反射剖面,绘制了研究区浅层与深部结构地质剖面。板块受挤压,中、上地壳与下地壳存在不同的耦合方式,对此分析了研究区下地壳的变形过程。雪峰山下地壳向下存在对冲,形成山根,但并没有俯冲至地幔。随地壳加厚,岩石圈发生弯曲,下地壳与上地幔存在瑞利泰勒不稳定性,并下沉至软流圈地幔。晚中生代,伸展背景下的软流圈上涌使雪峰山以东岩石圈发生拆沉,致使两侧岩石圈厚度出现差异。 相似文献