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1.
《International Geology Review》2012,54(5):375-387
We use updated rotations within the Pacific-Antarctica-Africa-North America plate circuit to calculate Pacific-North America plate reconstructions for times since chron 13 (33 Ma). The direction of motion of the Pacific plate relative to stable North America was fairly steady between chrons 13 and 4, and then changed and moved in a more northerly direction from chron 4 to the present (8 Ma to the present). No Pliocene changes in Pacific-North America plate motion are resolvable in these data, suggesting that Pliocene changes in deformation style along the boundary were not driven by changes in plate motion. However, the chron 4 change in Pacific-North America plate motion appears to correlate very closely to a change in direction of extension documented between the Sierra Nevada and the Colorado Plateau. Our best solution for the displacement with respect to stable North America of a point on the Pacific plate that is now near the Mendocino triple junction is that from 30 to 12 Ma the point was displaced along an azimuth of ～N60°W at rate of ～33 mm/yr; from 12 Ma to about 8 Ma the azimuth of displacement was about the same as previously, but the rate was faster (～52 mm/yr); and since 8 Ma the point was displaced along an azimuth of N37°W at a rate of ～52 mm/yr. We compare plate-circuit reconstructions of the edge of the Pacific plate to continental deformation reconstructions of North American tectonic elements across the Basin and Range province and elsewhere in order to evaluate the relationship of this deformation to the plate motions. The oceanic displacements correspond remarkably well to the continental reconstructions where deformations of the latter have been quantified along a path across the Colorado Plateau and central California. They also supply strong constraints for the deformation budgets of regions to the north and south, in Cascadia and northern Mexico, respectively. We examine slab-window formation and evolution in a detailed re-analysis of the spreading geometry of the post-Farallon microplates, from 28 to 19 Ma. Development of the slab window seems linked to early Miocene volcanism and deformation in the Mojave Desert, although detailed correlations await clarification of early Miocene reconstructions of the Tehachapi Mountains. We then trace the post-20 Ma motion of the Mendocino slab window edge beneath the Sierran-Great Valley block and find that it drifted steadily north, then stalled just north of Sutter Buttes at ～4 Ma. 相似文献
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New data indicate that northeast-directed extensional faulting characterizes slip across the Brothers fault zone (BFZ), which marks the northern limit of the northwestern Basin and Range (NWBR) extensional province in southeastern Oregon. Structural separation across individual north-northeast striking NWBR faults decreases to zero south of the BFZ. Field relationships and cross-sections demonstrate limited kinematic linkage and independent evolution of the two fault systems since ∼7 Ma. West-directed extension accumulated on NWBR faults at 0.01 mm/yr and lengthened northward after 7.05 Ma. BFZ faults accumulated northeast-directed extension at rates of 0.01 mm/yr since 5.68 Ma. Deformation coincides with periods of heightened basaltic magmatism in the High Lava Plains, implying that volcanism weakened the crust and promoted extension in the BFZ. In a new model, we reconcile the observed northward diminishing rate and clockwise motion of the modern NWBR deformation field with regional geology. The BFZ defines a small circle about the pole of rotation and separates a stable block to the NE from the extending region to the south. Faults to the south are growing northward, consistent with the northward decrease in rate and magnitude of extension in the NWBR. 相似文献
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The reason for obduction, or tectonic transport of oceanic lithosphere onto continents, is investigated by two‐dimensional thermo‐mechanical numerical modelling based on the geology of the Anatolia–Lesser Caucasus ophiolites. Heating of the oceanic domain and extension induced by far‐field plate kinematics appear to be essential for the obduction of ~80‐Ma‐old oceanic crust over distances exceeding 200 km. Heating of the oceanic lithosphere by mantle upwelling is evidenced by a thick alkaline volcanic series emplaced on top of the oceanic crust 10–20 Ma before obduction, at the onset of Africa–Eurasia convergence. Regional heating reduced the negative buoyancy and strength of the magmatically old lithosphere. Extension facilitated the propagation of obduction by reducing the mantle lithosphere thickness, which led to the exhumation of eclogite‐free continental crust previously underthrusted beneath the ophiolites. This extensional event is ascribed to far‐field plate kinematics resulting from renewed Neotethys oceanic subduction beneath Eurasia. 相似文献
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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
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探测大陆岩石圈的属性、相态与物质运动: 固体地球物理学的新使命 总被引：1，自引：0，他引：1
20世纪大地构造物理学取得引人瞩目的进展。本文详细评述了探测地球大陆圈层的属性、相态与物质运动取得的进展和技术路线。并且指出,大陆地壳和海洋地壳结构上的最基本区别是后者是相对均匀和整体刚性的,内部不存在明显的物质运动。前者的下地壳部分区域是不均匀和流变的,其中的物质运动使大陆板内的地壳产生比较强烈的变形和岩浆活动。因此,当前发展板块构造学说的最焦点就是对地壳不均匀性和流变岩石进行三维成像,从下到上找出大陆地壳物质运动规律。同时,一定要坚持深层油气和地震预测方面的应用基础研究,为人类社会可持续发展作出更大的贡献。 相似文献
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Structure of the Transkei Basin and Natal Valley, Southwest Indian Ocean, from seismic reflection and potential field data 总被引：1，自引：0，他引：1
Marine geophysical data from the southern Natal Valley and northern Transkei Basin, offshore southeast Africa, were used to study the structure of the crust and sedimentary cover in the area. The data includes seismic reflection, gravity and magnetics and provides information on the acoustic basement geometry (where available), features of the sedimentary cover and the basin's development. Previously mapped Mesozoic magnetic anomalies over a part of the basin are now recognized over wider areas of the basin. The ability to extend the correlation to the southeast within the Natal Valley further confirms an oceanic origin for this region and provides an opportunity to amplify the existing plate boundary reconstructions.The stratigraphic structure of the southern Natal Valley and the northern Transkei Basin reflects processes of the ocean crust formation and subsequent evolution. The highly variable relief of the acoustic basement may relate to the crust formation in the immediate vicinity of the continental transform margin. Renewed submarine seismicity and neotectonic activity in the area is probably related to the diffuse boundary between the Nubia and Somalia plates.2.5-D crustal models show that a 1.7–3.2-km-thick sediment sequence overlies a 6.3±1.2-km-thick normal oceanic crust in the deep southern Natal Valley and Transkei Basin. The oceanic crust in the study area is heterogeneous, made up of blocks of laterally varying remanent magnetization (0.5–3.5 A/m) and density (2850–2900 kg/m3). Strong modifications of accretionary processes near ridge/fracture zone intersections may be a reason of such heterogeneity. 相似文献
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The structural setting beneath the Ligurian Sea resuJts from several tectonic events reflected in the nature of the crust. The central-western sector, called the Ligurian basin, is part of the northwestern Mediterranean. It is a marginal basin that was generated in Oligocene-Miocene time by subduction of the Adriatic plate beneath the European plate and by the eastward drift of the Corsica-Sardinia block. The eastern sector belongs to the Tyrrhenian basin system and is characterized by extensional activity which since Tortonian time superimposed an earlier compressional regime. Our effort has been addressed in particular towards simplifying the complex nature of the crust of the Ligurian basin by modelling its genesis using uniform extension and sea-floor depth variation with age. In the rift stage of the basin's evolution, the initial subsidence reaches the isostatic equilibrium level of the asthenosphere by a thinning factor of 3.15. The additional passive process, corresponding to the cooling of the lithosphere since 21 Ma, leads to a total tectonic subsidence of 3.4 km, representing the boundary of the extended continental crust. For values up to 4.1 km a transitional-type crust is expected, whereas for higher tectonic subsidence values a typical oceanic crust should exist. After setting these constraints, the boundaries of the different crust types have been drawn based on total tectonic subsidence observations deduced from bathymetry and post-rift sediment thickness. Although there is a general agreement with the previous reconstructions deduced from other experimental data, the oceanic realm has wider extent and more complex shape. The northernmost part of this realm shows crust of sub-oceanic type altemating basement highs with lower subsidence values. The observed surface heat flux is consistent with the predicted geothermal held in the Alpine-Provençal continental margin and in the oceanic domain. However, a characteristic thermal asymmetry is clearly visible astride the basin, due to the enhanced heat flux of the Corsica margin. Even if the uniform extension model accounts well at a regional level for the present basement depth, a remarkable tectonic subsidence excess has been found in the Alpine-Provençal continental margin. This evidence agrees with the reprise in compression of the margin; the direction of the greatest principal stress is N120°E on average. 相似文献
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南海北部陆缘地壳结构特征及其构造过程 总被引：5，自引：0，他引：5
根据“北部湾大陆缘地壳结构ＰＳ转换波测深”等地球物理测量结果,本文研究了南海北部陆缘的地壳结构特征,讨论了其白垩纪以来的构造过程。地球物理测量表明,由陆向海,南海北部陆缘地壳由陆壳、过渡壳变为洋壳,厚度由３４ｋｍ减薄至８ｋｍ左右。垂向上地壳为３层结构模式。陆壳、过渡壳和洋壳的下地壳Ｐ波速度普遍较高。地壳伸展系数的计算表明南海北部陆缘伸展主要发育于陆坡地区。结合区域地质研究,本文认为：南海北部陆缘及 相似文献
11.
Anshu K.Sinha 《地学前缘》2000,(Z1)
he 2500km long Indus\|Tsangpo Suture has been recognized as one of the best examples of continent to continent collisional Suture Zone. It has come into existence as a result of subduction followed by continental collision (55～60Ma) between Indian (Sinha, 1989, 1997; Sinha et al., 1999) and Eurasian plates. While considering the recent palaeogeographic reconstruction of Pangea during late Palaeozoic it appears that a southern belt of Asian microcontinents stretching from Iran and Afghanistan through southern Tibet to western Thailand, Malaysia and Sumatra, comprise several continental blocks and numerous fragments that have coalesced since the Mid\|Palaeozoic along with the closure of Tethys. The origin, migration, assembly and timing of accretion of all these blocks to their present geotectonic position is not well known and there is no Permo—Triassic crust left in the present day Indian Ocean. The oldest ocean crust adjacent to the west African and Antarctic margin is of early or middle Cretaceous age (approximately 140～100Ma) (Searle, 1991). The Karakoram\|Hindukush microplate in the west and the Qiangtang\|Lhasa block in the central and eastern segment of South Asia margin are among those blocks already welded with Asian plates around 120～130Ma ago, before the collision of India (55～60Ma) with the collage of plates forming Peri\|Gondwanian microcontinents. But the reconstruction of palaeogeographic configuration remain incomplete due to paucity of authentic geologic information available from Karakoram, Pamir and Western Tibet. Prior to our discovery no early Permian plant remains and palynomorphs were ever reported from Karakoram terrane. Our discovery of Early Permian remains and late Asselian (about 280～275Ma) palynomorphs provides crucial clue regarding the palaeogeographic reconstruction of the Karakoram\|Himalayan block in the Permian time. 相似文献
12.
Simon Williams Nicky M.Wright John Cannon Nicolas Flament R.Dietmar Müller 《地学前缘(英文版)》2021,12(2):769-780
Reconstructions of past seafloor age make it possible to quantify how plate tectonic forces,surface heat flow,ocean basin volume and global sea level have varied through geological time.However,past ocean basins that have now been subducted cannot be uniquely reconstructed,and a significant challenge is how to explore a wide range of possible reconstructions.Here,we investigate possible distributions of seafloor ages from the late Paleozoic to present using published full-plate reconstructions and a new,efficient seafloor age reconstruction workflow,all developed using the open-source software GPlates.We test alternative reconstruction models and examine the influence of assumed spreading rates within the Panthalassa Ocean on the reconstructed history of mean seafloor age,oceanic heat flow,and the contribution of ocean basin volume to global sea level.The reconstructions suggest variations in mean seafloor age of~15 Myr during the late Paleozoic,similar to the amplitude of variations previously proposed for the Cretaceous to present.Our reconstructed oceanic age-area distributions are broadly compatible with a scenario in which the long-period fluctuations in global sea level since the late Paleozoic are largely driven by changes in mean seafloor age.Previous suggestions of a constant rate of seafloor production through time can be modelled using our workflow,but require that oceanic plates in the Paleozoic move slower than continents based on current reconstructions of continental motion,which is difficult to reconcile with geodynamic studies. 相似文献
13.
A study based on computation of D-function anomalies (method of joint gravity and magnetic data analysis) along profiles in the Bering Sea has been performed in both the Aleutian Basin with oceanic crust and the Bering continental shelf. This study revealed extended faults that affect not only the Earth’s crust but also the upper mantle. This is supported by seismic profiling. The calculated palinspastic reconstructions of the position of North America relative to “immobile” Eurasia 80, 52–50, 50–47, and 15–20 Ma ago allowed us to show that the revealed strike-slip faults are probable relics of an echeloned transform boundary between the Eurasian and North American lithospheric plates. The formation of this boundary beginning from the Late Cretaceous was apparently related to opening of the North Atalantic, which determined the large rate of displacement of North America relative to Eurasia. 相似文献
14.
冈底斯斑岩铜矿成矿模式 总被引：35，自引：0，他引：35
已有的斑岩铜矿成矿模式都是建立在“B”型俯冲基础上的，而冈底斯斑岩铜矿成矿为18～12Ma，主碰撞期为65Ma，因此属于“A”型俯冲时期，即印度大陆壳俯冲到亚洲大陆壳之下的早期，此时夹于两者之间的新特提斯洋壳尚未消失掉，由此上地幔脱水和部分熔融提供了斑岩铜矿的主要成矿的物质来源。本文讨论了俯冲作用与斑岩铜矿的关系，通过驱龙和冲江两个代表性矿床的Nd、Sr同位素讨论了冈底斯斑岩铜矿成矿物质来源，通过矿带结构和成矿年代等制定了冈底斯斑岩铜矿成矿模式。 相似文献
15.
本文将华北板块和中亚-蒙古陆块缝合带中前人划分的"贺根山蛇绿岩套"划分为三个不同组分、不同成因的岩系:以含金刚石和其它幔源矿物的变质橄榄岩系为主,包括堆晶杂岩在内的镁铁-超镁铁岩系;含放射虫硅质岩夹层的玄武岩系;上覆的火山-沉积岩系。根据地质学与年代学证据,可以认为蛇绿岩形成于晚泥盆-早石炭世。在此基础上,本文重点讨论了三个问题:(1)结合不同尺度的构造研究,将含金刚石等幔源矿物的超镁铁岩看作源自地幔转换带的幔源熔-流体,在软流圈底辟体上涌的背景下持续上升,在板块对接的过程中构造侵位的岩石。据此,对现有的蛇绿岩概念提出了补充;同时提出贺根山在板块汇聚过程未发生明显的俯冲和碰撞,而是通过拼贴的方式连为一体的;(2)贺根山具有OIB特征的玄武岩与朝克山MORB的对比,表明不同来源的多地块的存在及板块闭合时间的差异均反映了陆间小洋盆的特征;(3)将上覆在玄武岩系之上的火山沉积岩系看作洋盆最后充填的产物,反映了古亚洲洋闭合过程中小洋盆直接从洋壳转化为陆壳的过程,最后从时空角度进一步讨论了小洋盆闭合的特征。 相似文献
16.
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
17.
Peter R. Dawes 《地学学报》2009,21(1):1-13
Nares Strait separating Greenland and northernmost Canada is floored by continental crust. Most palaeogeographic reconstructions of Laurentia and the North Atlantic region model the seaway as the site of massive sinistral strike–slip and/or compression/transpression, subduction and collision, the supposed manifestations of the hypothetical Wegener Fault. However, these reconstructions fail to take into account the bedrock geology that represents within-plate evolution. Both sides of Smith Sound, the southernmost part of Nares Strait, expose the same early Proterozoic to early Palaeozoic assemblages that are unaffected by seaway-related tectonism or thermal activity. Smith Sound is an intact crustal block or `linchpin' demonstrating that there was no independent Greenland plate. North-west Greenland was not a leading plate margin neither was Nares Strait the site of the plate boundary between Greenland and North America. The Wegener Fault does not exist. The Smith Sound linchpin constitutes a key constraint that must be respected in any palaeogeographic reconstruction of the region. 相似文献
18.
《Gondwana Research》2014,25(3-4):984-998
In recent years several tectonic reconstructions have been presented for Australia–Antarctica break-up, with each putting the Australian plate in a different location with respect to Antarctica. These differences reflect the different datasets and techniques employed to create a particular reconstruction. Here we show that some of the more recent reconstructions proposed for Australia–Antarctica break-up are inconsistent with both our current knowledge of margin evolution as well as the inferred match in basement terranes on the two opposing conjugate margins. We also show how these incorrect reconstructions influence the fit of the Indian plate against Antarctica if its movement is tied to the Australian plate. Such errors can have a major influence on the tectonic models of other parts of the world. In this case, we show how the position of the Australia plate can predetermine the extent of Greater India, which is (rightly or wrongly) used by many as a constraint in determining the timing of India–Asia, or India–Island Arc collisions during the closure of Tethys. We also discuss the timing of Australia–Antarctica break-up, and which linear magnetic features are a product of symmetric sea-floor spreading versus those linear magnetic features that result from rifting of a margin. The 46 Ma to 84 Ma rotational poles previously proposed for Australia–Antarctica break-up, and confined to transitional crust and the continent–ocean transition zone, more likely formed during earlier stages of rifting rather than during symmetric sea-floor spreading of oceanic crust. So rotation poles that have been derived from magnetic anomalies in such regions cannot be used as input in a plate reconstruction. A new reconstruction of the Australia–Antarctica margin is therefore proposed that remains faithful to the best available geological and geophysical data. 相似文献
19.
Applications of plate tectonic concepts to problems of continental geology are hampered by the lack of direct evidence from the sea floor of pre-Cretaceous plate motions, since oceanic crust is continually destroyed by subduction in trenches. Studies on the structural geometry of Jurassic ring-dike provinces in Africa and North America, however, reveal patterns closely correlated with predicted plate motions. These ring complexes are commonly discordant to major crustal structures and show many features indicative of deep-seated origin. Ring-dike provinces probably form when continents drift over fixed plumes (hot-spots) in the asthenosphere and thereby provide unique tracks of pre-Cenozoic continental plate motions. 相似文献
20.
S.P. Colman-Sadd 《Tectonophysics》1982,90(3-4):263-282
It is proposed that major continental collision normally causes two orogenies. The first is characterized by ophiolite obduction, and the second by widespread deformation, often accompanied by metamorphism and granite intrusion. The two orogenies are separated by a relatively quiescent orogenic pause of 40–60 Ma. The two stages of continental collision are illustrated by examples from the Paleozoic Newfoundland Appalachians, and the Mesozoic-Cenozoic Tethyan collision belts of the Zagros and Himalayas.
The stages of continental collision are explained in terms of the forces driving plate motions, which are dominated by the downward pull of subducting oceanic lithosphere and, to a lesser extent, by the outward push of spreading oceanic ridges.
The Taconic stage marks attempted subduction of continental crust. The buoyancy of continental crust offsets the negative buoyancy of subducting oceanic lithosphere and other driving forces so that plate motion is halted. Orogeny involves vertical buoyancy forces and is concentrated along the narrow belt of plate overlap at the subduction zone.
In a major collision the Taconic stage destroys a substantial proportion of the earth's subducting capacity. It is an event of such magnitude that it has global consequences, reducing sea-floor spreading and the rate of convection. This results in retention of heat within the earth and a consequent increase in the forces driving the plates. The orogenic pause represents the time taken for these forces to become strong enough to overcome the obstruction of buoyant continental crust and renew subduction at the collision zone.
The Acadian stage of collision occurs when renewed subduction is achieved by detachment of continental crust from its underlying lithosphere. As the subcrustal lithosphere is subducted, the crust moves horizontally. The result is crustal shortening with widespread deformation and generation of anatectic granitic magma, as well as subduction related volcanism.
The effects of continental collision on the rate of sea-floor spreading can be related to eustatic changes in sea level, glaciations, and mass extinctions. There may also be connections, through changes in the rate of mantle convection, to the earth's magnetic polarity bias and rotation rate. 相似文献