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1.
A recent re-evaluation of the Late Mesozoic and Cenozoic sea-floor spreading data in the eastern Pacific has allowed us to make a new interpretation of the timing and sequence of the tectonic events which produced the present configuration of the plates (Whitman and Harrison, 1981; Whitman, 1981). Rotation parameters specifying the relative motion between all pairs of plates in the ocean basin have been calculated from the best fit of oceanic magnetic anomalies, with additional input from bathymetry and crustal ages of the Deep Sea Drilling Project sites. The rotation parameters for the relative motion between the Pacific and Antarctic plates are taken from Weissel et al. (1977) and the continental rotation parameters are from Barron et al. (1981).Plate motions have been determined back to 74 Ma. This time marks the initiation of spreading at the Pacific-Antarctic Ridge which caused the separation of the Campbell Plateau from Antarctica (Barron et al., 1981). Thus, this time is the earliest fix on the position of the Pacific plate relative to the continents surrounding the Pacific Ocean basin using sea-floor spreading. Since it is not possible to derive quantitative information about the relative motion between two plates separated by a trench, all rotations for the oceanic plates of the Pacific basin have been calculated relative to the Pacific plate and then relative to North America through the plate circuit: Pacific-Antarctica-Africa-North AmericaSince we also know the relative position of North America with respect to the other continents, we can show the relative position of the Pacific plate and the other oceanic plates with respect to all of the continental plates surrounding the Pacific Ocean basin. 相似文献
2.
The oldest portions of the Indian Ocean formed via the breakup of Gondwana and the subsequent fragmentation of East Gondwana. We present a constrained plate model for this early Indian Ocean development for the time period from Gondwana Breakup until the start of the Cretaceous Normal Superchron. The motions of the East Gondwana terranes are determined using new geophysical observations in the Somali Basin and existing geophysical interpretations from other coeval Indian Ocean basins. Within the Somali Basin, recent satellite gravity data clearly resolve traces of an east–west trending extinct spreading ridge and north–south oriented fracture zones. A thorough compilation of Somali Basin ship track magnetic data allows us to interpret magnetic anomalies M24Bn through M0r about this extinct ridge. Our magnetic interpretations from the Somali Basin are similar in age, spreading rate, and spreading directions to magnetic anomalies previously interpreted in the neighboring Mozambique Basin and Riiser Larsen Sea. The similarity between the two magnetic anomaly datasets allows us to match both basin's older magnetic anomaly picks by defining a pole of rotation for a single and cohesive East Gondwana plate. However, following magnetic anomaly M15n, we find it is no longer possible to match magnetic picks from both basins and maintain plausible plate motions. In order to match the post-M15n geophysical data we are forced to model the motions of Madagascar/India and East Antarctica/Australia as independent plates. The requirement to utilize two independent plates after anomaly M15n provides strong circumstantial evidence that suggests East Gondwana breakup began around 135 Ma. 相似文献
3.
M. Meschede 《International Journal of Earth Sciences》1998,87(2):200-205
Geometric constraints derived from the present plate configuration and from plate motion vectors of the Caribbean as well as the North and South American plates within a hotspot reference frame indicate that the thickened Caribbean oceanic crust was formed in a near-American position rather, than at the Galapagos hotspot. A lateral displacement of more than 1000 km between the Caribbean plate and the North and South American plates is related to differences in plate motion velocities during the Cenozoic era. The differential motion between the Caribbean and the American plates results from trench-parallel mantle flow as a response to the westward motion of the American plates. 相似文献
4.
Recent high-resolution models of past plate motions and their comparison with plate motion models inferred from space geodetic techniques reveal a number of short-term variations in global plate velocities over the past 10 Myrs. Such variations serve as powerful probe into the nature and magnitude of plate boundary forces, because they are unlikely to originate from changes in mantle buoyancy forces, which evolve on longer time scales. Here we explore the constraints of the velocity record using a novel coupled modeling-approach of global neo-tectonic simulations combined with realistic plate driving forces obtained from mantle circulation models (MCMs) to arrive at simple global budgets of mantle, lithosphere and plate boundary forces. We focus on three plate boundary systems along the Nazca/South America plate margin, the Aleutian trench and the India/Australia plate boundary to show that gravitational spreading from high topography in the Andes and Tibet contributes substantially to the global plate tectonic force balance and that this contribution is sufficient to explain some 35% of recent velocity changes over the Earth's surface, including among others the observed 30% convergence reduction between the Nazca/South America plates. Our models make a number of specific predictions such as significant lateral variations in plate coupling forces along a given margin revealed by trench-parallel gravity and bathymetry anomalies and the occurrence of large earthquakes, as well as differences by as much as a factor of five from margin to margin. They also support the notion of a relatively young plate boundary separating the India and Australia plates, which has been previously suggested based on independent observations. Importantly, we find that the modeled Nazca/South America convergence reduction explains recent spreading-rate variations in the South Atlantic and South Pacific, which points to the importance of far field effects on the adjacent continents in explaining the spreading record of oceanic basins. Our numerical results demonstrate (a) that detailed budgets of forces acting upon plates can be obtained and (b) support the notion of strong forcing along weak plate boundaries. 相似文献
5.
全球地壳运动的背景场及其研究进展 总被引：1，自引：0，他引：1
全球地壳运动是在全球地壳运动背景场中发生的，其背景场的运动参数是表征地壳运动的最基本特征。由于现今板块运动模型ITRF序列均忽略板块边界部分，并且板块以NUVEL1A模型来划分，由此建立的全球板块运动模型不能作为一个严格的全球地壳运动背景场。利用区域速度场和ITRF2000速度场建立一个包括非刚体的板块边界区域和刚体板块的全球地壳运动模型，其板块总角动量ΙLΙ＝0．131°/Ma，即不为零，存在整体旋转，由此建立无整体旋转（NNR）模型，并评述其研究进展。 相似文献
6.
地球表层运动和变形的GPS描述 总被引：3，自引：1，他引：3
利用IERS所公布的分在全球各大构造板块上的 6 5 7个GPS、SLR和VLBI连续观测站在ITRF框架下的速度场资料 ,采用刚体板块运动 +板块整体均匀应变 +板块内局部不均匀应变的变形分析模型 ,研究了全球各主要板块的运动和变形。结果表明板块的整体变形在统计上均不显著。在一级近似上板块间表现出来的整体相对运动显著 ,根据这些运动参数定量研究了板块边界的相对运动的大小和性质。认为地球的双重不对称变形可能主要表现为南北、东西两半球所含的板块边界的运动方式不同所致。板块内的局部不均匀变形明显 ,为板块内部可能应划分成次一级的活动地块提供了佐证。由于观测点分布的密度和均匀性不足 ,本文未能就板内不均匀变形作进一步的深入讨论。 相似文献
7.
R.L. Carlson 《Tectonophysics》1983,99(2-4)
Largely because of the wide variety of observational constraints which must be satisfied, the search for a viable driving mechanism is perhaps the most perplexing problem related to plate tectonics. The mechanism must be compatible with the rigid behavior of lithospheric plates, and with a wide range of plate sizes, shapes and motions. It must be consistent with complex configurations of plate boundaries and equally complex boundary interactions, such as the destruction of ridges at subduction zones. The mechanism must produce steady-state relative and absolute plate motions which persist for tens of millions of years, but must also account for sudden dramatic changes. Finally, the plate driving mechanism must be consistent with the non-Newtonian properties of olivine and with the fabrics of upper mantle peridotites.Mounting evidence suggests that plate motions result from forces associated with plate boundaries and that the principal resisting force is drag at the base of the lithosphere, particularly beneath continents Several investigators have suggested that gravitational forces acting on thermally-induced, lateral density variations in the upper mantle are the principal driving forces for plate tectonics. If so, plate motions are ultimately controlled by the temperature distribution in the upper mantle, and plate tectonics represents a state of dynamic equilibrium in which plate motions are both the cause and the consequence of temperature and density variations in the mantle. This concept requires that average absolute plate velocities be predictable from the characteristics of individual plates, and that plates tend to move down horizontal temperature gradients.A simple linear relation which includes contributions from ridge push (RP), slab pull (SP), trench suction (TS) and continental drag (CD): (cm/y) = (2.6 ± 0.4) + (4.8 ± 1.8) RP + (14.3 ± 1.7) SP +(3.5 ± 2.5) TS−(5.1 ±0.7) CD predicts plate velocities with an rms error of 0.44 cm/y, and a correlation coefficient of 0.98. That plate velocities can be accurately predicted from their own boundary configurations and proportions of continental lithosphere is strong evidence that plate motions result from negative buoyancy forces associated with plate boundaries. 相似文献
8.
Both the system of plate motions and the global gravity field or the geoid are now so precisely known that it seems worthwhile to look for quantitative relationships. Some aspects, such as the general occurrence of positive gravity and geoid anomalies in regions of plate convergence, have long been known. Our aim is to describe the gravitational field in terms of plate-kinematic parameters and we present a preliminary step in this direction: for four plates (Pacific, Nazca, Indian, American) we have computed the correlation of the Gem 8 geoid heights (with reference to an ellipsoid of 1/298.255 ellipticity) with distance from the poles of motion and distance from the axes in an “absolute” frame. The geoid tends first to drop from the ridge axes to at least 10° distance and then to rise toward the convergence zones. This trend is strongest for the Indian plate in collision with Eurasia, is smaller, but very clear for the oceanic Pacific and Nazca plates, and is not developed for the American plate which does not subduct. We did not find a consistent relationship for the geoid with distance from the pivots. A possible interpretation of the results is the return flow of the large-scale mantle circulation. 相似文献
9.
Tetsuzo Seno 《Tectonophysics》1985,115(3-4)
Seismic slip vectors along the Japan Trench, the eastern margin of the Japan Sea and the Sagami Trough are compared with global relative plate motions (RM2, Minster and Jordan, 1978) to test a new hypothesis that northern Honshu, Japan, is part of the North American plate. This hypothesis also claims that the eastern margin of the Japan Sea is a nascent convergent plate boundary (Kobayashi, 1983; Nakamura, 1983).Seismic slip vectors along the Japan Trench are more parallel to the direction of the Pacific-North American relative motion than that of the Pacific-Eurasian relative motion. However, the difference in calculated relative motions is too small avoid to the possibility that a systematic bias in seismic slip vectors due to anomalous velocity structure beneath island arcs causes this apparent coincidence. Seismic slip vectors and rates of shortening along the eastern margin of the Japan Sea for the past 400 years are also consistent with the relative motion between the North American and Eurasian plates calculated there. Seismic slip vectors and horizontal crustal strain patterns revealed by geodetic surveys in south Kanto, beneath which the Philippine Sea plate is subducting, indicate two major directions; one is the relative motion between the North American and Philippine Sea plates, and the other that between the Eurasian and Philippine Sea plates.One possible interpretation of this is that the eastern margin of the Japan Sea may be in an embryonic stage of plate convergence and the jump of the North American-Eurasian plate boundary from Sakhalin-central Hokkaido to the eastern margin of the Japan Sea has not yet been accomplished. In this case northern Honshu is a microplate which does not have a driving force itself and its motion is affected by the surrounding major plates, behaving as part of either the Eurasian or North American plate. Another possibility is that the seismic slip vectors and crustal deformations in south Kanto do not correctly represent the relative motion between plates but represent the stresses due to non-rigid behaviors of part of northern Honshu. 相似文献
10.
The Olyutorsky–Kamchatka foldbelt formed as a result of two successive collisions of the Achaivayam–Valaginsky and Kronotsky–Commander island arcs with the Eurasian margin where the two terranes docked after a long NW transport. We model their motion history from the Middle Campanian to Present and illustrate the respective plate margin evolution with ten reconstructions. In this modeling the arcs are assumed to travel on the periphery of the large plates of Eurasia, North America, Pacific, and Kula, for which the velocities and directions of motion are known from published data. The model predicts that the Achaivayam–Valaginsky arc was the leading edge of the Kula plate from the Middle Campanian to the Middle Paleocene and then moved slowly with the Pacific plate as long as the Middle Eocene when it accreted to Eurasia. The Kronotsky arc initiated in the Middle Campanian on the margin of North America and was its part till the latest Paleocene when the terrane changed polarity to move northwestward with the Pacific plate and eventually to collide with Eurasia in the Late Miocene. The predicted paleolatitudes of the Achaivayam–Valaginsky and Kronotsky–Commander island arcs for the latest Cretaceous and Paleogene are consistent with nine (out of eleven) reliable paleomagnetic determinations for samples from the two arcs. Additional changes imposed on the initial model parameters (kinematics of the large plates, relative position of the Kula–Pacific Ridge and the Emperor seamount chain, or time of active volcanism within the arcs) worsen the fit of the final reconstructions to available geological and paleomagnetic data. Therefore, the suggested model appears to be the most consistent one at this stage of knowledge. 相似文献
11.
A.O. Alothman R. M. Fernandes M.S. Bos S. Schillak B. Elsaka 《Arabian Journal of Geosciences》2016,9(8):529
We compute the secular tectonic motion of the Arabian plate, based on two different sets of Global Navigation Satellite System (GNSS) observations. The first set is formed by continuous GNSS (cGNSS) observations from 10 stations that are being operated since 2000 and have a data time span of at least 3.5 years. The cGNSS is supplemented with a second set of GNSS observations from 11 episodic stations (eGNSS) acquired between 2003 and 2009 (having at least six reoccupations). In order to evaluate the robustness of the solutions, we have estimated three different solutions using different parameterizations concerning the error models as follows: (a) estimating the velocities based only on the cGNSS sites; (b) combining the cGNSS and eGNSS, where the errors for the eGNSS solutions were rescaled to be consistent with those estimated for the cGNSS solutions; and (c) giving the same weight to all cGNSS and eGNSS solutions. Our conclusions show that case (b) is the preferred solution when the uncertainties of the eGNSS solutions are multiplied by a scale factor (4.1× in this particular case), since the inclusion of the eGNSS solutions allows to have a larger number of points with a better spatial distribution. Finally, we compare our angular velocity model with other models, in particular the most recent global models: GEODVEL (geodetic) and MORVEL (geophysical). We find that GEODVEL provides inaccurate predictions for the Arabian tectonic plate, whereas the MORVEL model shows a slightly better agreement with our solution. Our proposed model shows a significant improvement to model the present-day kinematics of Arabian plate. Thus, it is suggested to be used instead of the global models. As corollary, we also advocate that global models for present-day tectonic motions should be carefully verified for each modeled plate, so that dedicated regional models can provide better results. 相似文献
12.
Seismic coupling and uncoupling at subduction zones 总被引：1，自引：0，他引：1
Seismic coupling has been used as a qualitative measure of the “interaction” between the two plates at subduction zones. Kanamori (1971) introduced seismic coupling after noting that the characteristic size of earthquakes varies systematically for the northern Pacific subduction zones. A quantitative global comparison of many subduction zones reveals a strong correlation of earthquake size with two other variables: age of the subducting lithosphere and convergence rate. The largest earthquakes occur in zones with young lithosphere and fast convergence rates, while zones with old lithosphere and slow rates are relatively aseismic for large earthquakes. Results from a study of the rupture process of three great earthquakes indicate that maximum earthquake size is directly related to the asperity distribution on the fault plane (asperities are strong regions that resist the motion between the two plates). The zones with the largest earthquakes have very large asperities, while the zones with smaller earthquakes have small scattered asperities. This observation can be translated into a simple model of seismic coupling, where the horizontal compressive stress between the two plates is proportional to the ratio of the summed asperity area to the total area of the contact surface. While the variation in asperity size is used to establish a connection between earthquake size and tectonic stress, it also implies that plate age and rate affect the asperity distribution. Plate age and rate can control asperity distribution directly by use of the horizontal compressive stress associated with the “preferred trajectory” (i.e. the vertical and horizontal velocities of subducting slabs are determined by the plate age and convergence velocity). Indirect influences are many, including oceanic plate topography and the amount of subducted sediments.All subduction zones are apparently uncoupled below a depth of about 40 km, and we propose that the basalt to eclogite phase change in the down-going oceanic crust may be largely responsible. This phase change should start at a depth of 30–35 km, and could at least partially uncouple the plates by superplastic deformation throughout the oceanic crust during the phase change. 相似文献
13.
According to the hypothesis of global plate tectonics the surface motions of the earth are now known in considerable detail, but very little is known about the three-dimensional flow in the earth and about the forces which maintain the motions. The motions at depth are difficult to study because they produce few surface effects. For instance, there is now no reason to believe that ridges are the surface evidence for rising convection currents at depth. Only the plate motions themselves and the gravity field observed by satellites must be consequences of three-dimensional flow beneath the plates. Other observations, such as the high heat flow near ridges or deep earthquakes beneath trenches, now appear to be explained by the production and destruction of plates. 相似文献
14.
We have computed motions of the major plates (seven large plates and seven medium‐sized plates) and 38 microplates relative to the hotspot reference frame, and present velocities of these 52 plates. Moreover, using updated plate boundaries for the present, we have computed new geometrical factors for plates and microplates, useful for kinematic calculations and to obtain the net‐rotation of the lithosphere and plate velocities in the mean‐lithosphere reference frame. Instead of a continuum or gradational distribution of the plates by size, the plates clearly partition into three groups each having their own characteristics. For the seven large plates, rotation poles generally lie in high latitudes; the seven medium‐sized plates have rotation poles in a restricted equatorial area; the 38 small plates show the greatest scatter. Moreover subsets of the 52 plates reveal differing fractal behaviour: the large, middle and small groupings each have a characteristic fractal dimension, suggestive of microplate clustering. The highest angular velocities occur for some of the smallest plates, with the location of their rotation poles closeby. Terra Nova, 18, 276–281, 2006 相似文献
15.
Paul Edwin Potter 《Earth》2009,96(4):279-799
An amazing congruence of seemingly unrelated, diverse global events began in the Middle and Upper Miocene and established our modern world. Two global orogenic belts were active, mostly in the Middle and Upper Miocene, while backarc basins formed along the eastern margin of Asia. Coincident with these events global temperatures cooled in both the ocean and atmosphere, desertification occurred from Central Asia into and across most of northern Africa and also in Australia, and in southern South America. Coincident with the expansion of the Antarctic ice cap at 14 Ma, there was initial widespread deep sea erosion and changes in patterns of deep sea sedimentation. Muddy pelagic sedimentation increased six-fold in the North and Central Atlantic and Pacific Oceans and global changes in circulation lead to more diatomites in the Pacific and fewer in the Atlantic. By the end of the Miocene most of the Mediterranean Sea had evaporated. Broadly coincident with these events, many old, large river systems were destroyed and new ones formed as much of the world's landscape changed. Collectively, these global on-shore tectonic and ocean-atmospheric events provide the foundation for our modern world—a mixture of new and rejuvenated orogenic belts and their far-field effects (distant epiorogenic uplift, rain-shadow deserts, large alluvial aprons, and distant deltas) as inherited Gondwanan landscapes persisted remote from plate boundaries. Thus at the end of the Miocene much of the world's landscape, except for that changed by Pleistocene continental glaciation, would be recognizable to us today.We argue that all of these events had the same ultimate common cause-an internal Earth engine-that drove plate motions in two broad ways: first, the opening and closing of seven key gateways to deep-water oceanic currents radically altered global heat transfer and changed a lingering Greenhouse to an Icehouse world; secondly, these events were in part coincident with renewed heat flow in the African and Pacific Superplumes that energized global plate motions in the Middle and Upper Miocene. We hope this global synthesis will stimulate more research on the many global events of the Miocene—to understand better both our modern world and earlier global orogenies. 相似文献
16.
魏子卿 《西安地质学院学报》2009,(4):331-343
根据热点假设,热点对于中间层是固定的。相对热点的板块运动叫做绝对板块运动。绝对板块运动模型可以通过反演火山链传播的速率和走向数据以确定相对板块运动在角速度空间的原点来得到。利用一组近来（0～7．8Ma）全球分布的热点的迁移速率和走向数据,结合板块运动模型NNR—NUVELIA,已研制出一个叫做APM2的现今绝对板块运动模型。按照该模型,太平洋板块围绕60．063°S、102．210°E处的极以（0．8330°±0．0133°）／Ma的速率运动,非洲板块围绕46．849°N、44．372°W的极以（0．1015°±0．0134°）／Ma的速率运动,南极板块的运动则以46．871°N、146．942°E为极,速率为（0．0846°±0．0177°）／Ma,欧亚板块的运动更慢,极为27．291°N、171．925°W,速率为（0．0655°±0．0206°）／Ma。这一模型表明,岩石圈相对深部地幔有一个以49．423°S、90．625°E为极,速率为（0．1983°±0．0135°）／Ma的净旋转。表明太平洋热点同印度-大西洋热点不一致,显示太平洋热点的运动也不一致。为了分析和比较,还给出了仅用全球分布的热点的走向数据和仅用印度一大西洋热点的走向数据得到的板块绝对运动的角速度。 相似文献
17.
18.
Michael Bevis 《Mathematical Geology》1987,19(6):561-569
Standard models of present-day plate motions are framed in terms of rates and poles of rotation, in accordance with the well-known theorem due to Euler. This article shows how computation of relative plate velocities from such models can be viewed as a simple problem in spherical trigonometry. A FORTRAN subroutine is provided to perform the necessary computations.EDITOR'S NOTE: Teaching geomathematics and geostatistics is a particularly difficult task. It requires a good knowledge of the mathematical theory and of its applications in the earth sciences. Good textbooks are relatively rare. So finding suitable examples and easy-to-follow proofs is time-consuming.This Teacher's Aide Column has been initiated to help get teaching material into circulation, and to act as a forum for exchanging questions and answers. Readers' suggestions are most welcome.Margaret ArmstrongAssociate Editor 相似文献
19.
A. Kröner 《Precambrian Research》1977,4(2):163-213
The classical model of continental accretion and progressive cratonization, starting with an ancient nucleus onto which younger orogenic belts are welded (onion skin tectonics), has dominated geotectonic research for many years and has received new impetus with the general acceptance of the theory of plate tectonics. It has also been applied to the geotectonic evolution of large Precambrian crustal segments such as Africa.It is demonstrated, however, that new structural, geochronological and paleomagnetic data from Africa provide strong evidence for the existence of large cratonic continental plates since at least the Early Proterozoic which were later transected by linear mobile belts and thus partly destroyed. Crustal reworking and rejuvenation in these belts now gives the impression of younger orogens surrounding ancient “nuclei”.The geotectonic evolution of Africa is therefore characterized by plate destruction rather than by plate accretion with progressive cratonization, and only the “nuclei” have escaped this process.Many phenomena in the African mobile belts seem to indicate processes involving little or no relative motion of crustal plates or crustal shortening between them, and there is as yet no evidence of former oceanic plates to have been generated or consumed. It is therefore suggested that large-scale dispersive movements of major continental fragments were uncommon or absent in the Early and Middle Precambrian.Widespread drift may only have begun during the Late Precambrian/Early Paleozoic Pan African Tectogenesis, eventually leading to a crustal evolution as envisaged by the modern theory of global tectonics. 相似文献
20.
The focal mechanisms for 86 selected earthquakes (3.0 mb 5.5) located in central Alaska have been investigated from P-wave first motions; the data were gathered by local seismic networks. The results show a depth-dependent characteristic to the fault-plane solutions. For earthquakes having focal depths shallower than 60–70 km, the focal mechanisms indicate either strike-slip or normal faults, while for earthquakes with foci at intermediate depths the focal mechanisms correspond to thrust faults. The nature of the seismicity indicates the hinge line of the Pacific lithospheric plate under the study area to be striking N17°E from Cook Inlet towards interior Alaska. The comparison of the focal mechanisms with the seismicity shows that the strike-slip and normal faults are the predominant processes of stress release along the shallow section of the plate. The earthquakes with intermediate foci systematically occur along the inclined section of the plate. If the gently dipping nodal planes for these earthquakes are chosen as the fault planes, the focal mechanisms correspond to underthrust motions at the foci. In these, the slip vectors are oriented either to the west or north with the resultant being in the N30°W direction. The tension axes for the underthrust solutions are also found to be parallel to the local dip of the plate, indicating that the subducted plate in interior Alaska is undergoing gravitational sinking. 相似文献