共查询到20条相似文献，搜索用时 31 毫秒
1.
The results of synchronous measurements of temperature variations in a near-bottom thermocline, as well as microdeformations
of the Earth’s crust and atmospheric pressure pulsing, recorded on-shore with the help of a laser strainmeter and laser nanobarograph,
are presented. A string containing 20 thermosensors spaced at 0.5 m was used; it was placed by an anchored buoy in a place
with 21-m depth and 500 m away from the shore. A good correlation between microdeformations and atmospheric pressure variations
was observed for periods longer than 6 h. Quantitative estimates and spectral analysis via the Gilbert-Huang method for investigation
of nonstationary and nonlinear processes lead to the conclusion that, on temporal scales from tidal to several minutes, the
predominant way of formation of microdeformations in the Earth’s crust can be breaking of internal waves in a thermocline
that leads to shallow water (i.e., in the zone of “internal breakers”). 相似文献
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Stepanov et al. (Contrib Mineral Petrol, 2017) question our conclusion that the UPVs in southern Tibet were derived by partial melting of an old, metasomatized subcontinental lithospheric mantle (SCLM) of the subducted Indian plate. Instead, they propose that these ultrapotassic volcanic rocks (UPVs) are shoshonitic and were generated in two steps: direct melting of crustal rocks first, and then the melts interacted with mantle peridotite. However, the trace element, isotopic, thermal, structural, and seismic evidence is consistent with the xenolith evidence (Wang et al in Contrib Mineral Petrol 172:62, 2016) for hybridisation of ascending Indian subcontinental lithospheric mantle-derived UPV magmas with the deep, isotopically unevolved, Tibetan crust. This necessitates a model whereby partial melting of subducting Indian SCLM generates the UPV suite of southern Tibet. 相似文献
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Dolgikh G. I. Budrin S. S. Dolgikh S. G. Ovcharenko V. V. Pivovarov A. A. Samchenko A. N. Shvyrev A. N. Chupin V. A. Yaroshchuk I. O. 《Doklady Earth Sciences》2017,475(1):811-815
On the basis of experimental data obtained during a comprehensive experiment in Vityaz Bay of the Sea of Japan using onshore laser strainmeters and a low-frequency hydroacoustic emitter generating complex phase-manipulated signals with a central frequency of 33 Hz, we developed the basic principles of contactless tomography of the Earth’s crust in the shelf regions of various seas, including those covered by ice, making it possible to determine efficiently the structure and composition of the upper Earth’s crust under seas.
相似文献5.
《Gondwana Research》2013,23(3-4):1060-1067
Convergence between the Indian plate and the Eurasian plate has resulted in the uplift of the Tibetan Plateau, and understanding the associated dynamical processes requires investigation of the structures of the crust and the lithosphere of the Tibetan Plateau. Yunnan is located in the southwest edge of the plateau and adjacent to Myanmar to the west. Previous observations have confirmed that there is a sharp transition in mantle anisotropy in this area, as well as clockwise rotations of the surface velocity, surface strain, and fault orientation. We use S receiver functions from 54 permanent broad-band stations to investigate the structures of the crust and the lithosphere beneath Yunnan. The depth of the Moho is found to range from 36 to 40 km beneath southern Yunnan and from 55 to 60 km beneath northwestern Yunnan, with a dramatic variation across latitude 25–26°N. The depth of the lithosphere–asthenosphere boundary (LAB) ranges from 180 km to less than 70 km, also varying abruptly across latitude 25–26°N, which is consistent with the sudden change of the fast S-wave direction (from NW–SE to E–W across 26–28°N). In the north of the transition belt, the lithosphere is driven by asthenospheric flow from Tibet, and the crust and the upper mantle are mechanically coupled and moving southward. Because the northeastward movement of the crust in the Burma micro-plate is absorbed by the right-lateral Sagaing Fault, the crust in Yunnan keeps the original southward movement. However, in the south of the transition belt, the northeastward mantle flow from Myanmar and the southward mantle flow from Tibet interact and evolve into an eastward flow (by momentum conservation) as shown by the structure of the LAB. This resulting mantle flow has a direction different from that of the crustal movement. It is concluded that the Sagaing Fault causes the west boundary condition of the crust to be different from that of the lithospheric mantle, thus leading to crust–mantle decoupling in Yunnan. 相似文献
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Polyansky O. P. Korobeynikov S. N. Babichev A. V. Reverdatto V. V. Sverdlova V. G. 《Doklady Earth Sciences》2009,429(1):1380-1384
A new point of view describing processes of partial melting and development of gravitational instability in a thickening crust
with increased thickness of the granite layer is suggested. Numeral experiments support the following main conclusions. The
critical volume of partially melted material should be formed for the beginning of flotation in a gravitational field. Due
to model estimations, the height of the melting area in the granite crust should be not less than 6–7 km. A mushroom-shaped
form of the floating body was observed in all models regardless of the thermal source size (fixed or variable width): the
high temperature channel (magma leader) and head body of the diapir are formed. The height of diapir floating depends on rheological
features of the surrounding crust: 10 times increase in the yield strength (from 1 to 10 MPa) while temperature decrease confines
the possible level of rising to a depth of 15–16 km. An elevation of about 750 m is formed in the day surface relief above
the axis part of the diapir. 相似文献
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We present the results of tectonophysical reconstruction of natural stresses of the Earth's crust in the Altai–Sayan mountain region using cataclastic analysis of fault slips and seismic data on the focal mechanisms of earthquakes. This method allows one to obtain the parameters of the total stress tensor by invoking additional data: generalized experimental data on the brittle fracture of rocks, seismic data on the released stress of strong earthquakes, and data on the topography and density of rocks. Results of the tectonophysical reconstruction of stresses showed significant inhomogeneity of the stress state, which is manifested not only in the variation of the strike and dip of the principal axes of the stress tensor, determining changes in the geodynamic regime of the Earth's crust, but also in the close location of the regions of high and low isotropic tectonic pressure in relation to the lithostatic pressure. The variance of the ratio of tectonic pressure to lithostatic pressure is in the range of 0.59–1.31, with an average value for the region close to unity. This paper discusses internal or external mechanisms capable of generating the stress field obtained by the tectonophysical reconstruction. 相似文献
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Doklady Earth Sciences - 相似文献
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A new numerical model of generating electric pulses in the Earth’s crust with use of a system of electric dipoles that are
located uniformly over an active surface of the structural block relaxing after its constrained turn is developed. Electric
moments of dipoles change with time according to the amplitude of differential movements. It is shown that the amplitude of
electric pulses and the degree of their attenuation with distance to the source are in agreement with the data of results
of instrumental observations. 相似文献
13.
Keith A. W. Crook 《Australian Journal of Earth Sciences》2013,60(1-2):215-232
A new general model describing the extended evolution of fore‐arc terrains is used to analyse the evolution of the southern Tasman Geosyncline and the concomitant growth and kratonisation of the continental crust of southeast Australia during the Palaeozoic. The southern Tasman Geosyncline comprises ten arc terrains (here defined), most of which are east‐facing, and several features formed by crustal extension. Each arc terrain consists of several strato‐tectonic units: a volcanic arc, subduction complex and fore‐arc sequence formed during subduction; and an overlying post‐arc sequence which post‐dates subduction and is composed of flysch, neritic sediments or subaerial volcanics. When these materials attained a thickness of c. 20 km their internal heat‐balance caused partial melting of the subduction complex and the hydrated oceanic lithosphere trapped beneath it, to yield S‐ and I‐type granitic magma. The magma rose, inducing pervasive deformation of each arc terrain and emplacement of granitoid plutons at high levels in the evolving crust. Transitional basins then developed in many terrains on top of their volcanic arcs or the thinner parts of the buried accretionary prisms. After deformation of the transitional sequences, platform cover accumulated, marking the completion of kratonisation. Analysis of each arc terrain in terms of the above units leads to a predicted ‘stratigraphy’ for the continental crust of southeast Australia. The crust is complexly layered, with lateral discontinuities reflecting the boundaries of arc terrains which were successively accreted, principally back‐arc to fore‐arc, during crustal development. 相似文献
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《Russian Geology and Geophysics》2014,55(3):376-389
The paper is focused on recent displacement rates in the Altai-Sayan region, obtained by hydroleveling, leveling, and satellite geodesy. Effective elastic moduli and viscosity parameters of the crust are used in the modeling of coseismic and tectonic processes. The elastic moduli are determined from measurements of periodic vertical displacements during seasonal loadings of the Sayano-Shushenskaya hydropower plant. We present the results of the modeling of coseismic displacements during the earthquakes of 10 February 2011 (M = 6.1) and 27 December 2011 (M = 6.7) in Tuva and West Sayan. The results of GPS determinations for postseismic displacements in the Chuya earthquake zone (Gorny Altai, 27 September 2003, M = 7.5) are analyzed; models for the geologic medium are selected; and its effective viscosity is estimated. The tectonic component of the recent crustal displacements in the Altai-Sayan region is defined. 相似文献
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E. V. Mikhal’sky 《Geotectonics》2008,42(6):413-429
Geological, geochemical, and isotopic data (U-Pb for zircon and Sm-Nd for whole-rock samples) are summarized for Proterozoic and Early Paleozoic geological complexes known from various regions of East Antarctica. The main events of tectonothermal and magmatic activity are outlined and correlated in space and time. The Paleoproterozoic is characterized as a period of rifting in Archean blocks, their partial mobilization, and formation of a new crustal material over a vast area occupied by present-day East Antarctica. In most areas, this material was repeatedly reworked at the subsequent stages of evolution (1800–1700, 1100–1000, 550–500 Ma). Complexes of Mesoproterozoic juvenile rocks (1500, 1400–1200, 1150–1100 Ma) arising in convergent suprasubduction geodynamic settings are established in some areas (basalt-andesite and tonalite-granodiorite associations with characteristic geochemical signatures). The evolution of the Proterozoic regions in East Antarctica may be interpreted as a Wilson cycle with the destruction of the Archean megacontinent 2250 Ma ago and the ultimate closure of the secondary oceanic basins by 1000 Ma ago. The Mesoproterozoic regions make up a marginal volcanic-plutonic belt that combines three provinces of different ages corresponding to consecutive accretion of terranes 1500–1150, 1400–950, and 1150–1050 Ma ago. The Neoproterozoic and Early Paleozoic tectonomagmatic activity developed nonuniformly. In some regions, it is expressed in ductile deformation, granulite-facies metamorphism, and postcollision magmatism; in other regions, a weak thermal effect and anorogenic magmatism are noted. The evolution of metamorphic complexes in the regime of isothermal decompression and the intraplate character of granitoids testify to the collision nature of the Early Paleozoic tectonomagmatic activity. 相似文献
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The catastrophic Shikotan earthquake of October 4 (5), 1994, occurred in the Pacific Ocean. Its focus was located 80 km eastward of Shikotan Island. The stress state of the Earth’s crust in this area was estimated by the method of the cataclastic analysis of the whole range of the earthquake mechanisms. The performed reconstruction of the parameters of the current stress state of the Earth’s crust and the upper mantle in the area of the Southern Kuril Islands made it possible to establish that this area is characterized, on the one hand, by the presence of extensive areas of steady behavior of the stress tensor parameters and, on the other hand, by the presence of local sections of anomalously fast changes in these parameters. 相似文献
19.
V. I. Usikov 《Russian Journal of Pacific Geology》2011,5(6):492-508
The analysis of 3D relief models of the lower Amur region and several adjacent areas suggested that the structure of the region
is related to the horizontal tectonic layering of the upper part of the Amur plate. When it was dislocated to the northwest
at the terminal Cretaceous, some fragments of the upper layers were displaced not strictly synchronously but with some lag
relative to the whole plate. This scenario was responsible for the formation of the main morphostructural elements of the
region: river valleys, mountain ranges, and graben series. These inferences are supported by field observations and some geological
data. The proposed hypothesis can also be applied for several other regions. 相似文献
20.
We have conducted a paleomagnetic investigation on the Middle–Upper Jurassic marine strata exposed in the hanging wall of the Tanggula Thrust system near the Yanshiping area, northern Tibet. Progressive demagnetization experiments successfully isolated stable magnetization over a broad spectrum of demagnetization temperatures. The mean direction of the characteristic remanent magnetizations for the Middle–Late Jurassic Yanshiping Group in stratigraphic coordinates (D/I (Declination/Inclination) = 5.6°/60.3°, k = 22.9, α95 = 12.9°, N = 7 s) is much more clustered than the mean direction in geographic coordinates (D/I = 345.5°/37.2°, k = 2.5, α95 = 48.4°), indicating magnetization was not acquired after folding. Although the conventional fold test is positive, incremental untilting test on the characteristic remanent magnetization reveals that a maximum value of precision parameter k occurs at 82.1 ± 4.6% untilting (D/I = 3.3°/57.8°, k = 43.9, α95 = 9.2°), which indicates the ChRMs are probably acquired during Late Cretaceous folding. This synfolding magnetization component is therefore secondary. The corresponding pole position (84.4°N, 119.4°E with dp/dm = 13.5/9.9°) is inconsistent with Jurassic–Early Cretaceous paleopoles of the region, but the paleolatitude is consistent with the Late Cretaceous paleolatitude observed in the Qiangtang terrane and its periphery. The synfolding component is carried by both magnetite and hematite, which were identified by isothermal remnant magnetization acquisition experiments, unblocking temperatures of stable magnetic components, and Curie temperature determination and correlated with observed hydrothermal veins. Available geological evidences indicate that the synfolding magnetization is probably the result of chemical remagnetization caused by orogenic fluids or hydrothermal sources during the early uplift of the Tibetan Plateau. 相似文献