The impossible Galapagos connection: geometric constraints for a near-American origin of the Caribbean plate

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.     

地球表层运动和变形的GPS描述

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。     

The paleomagnetism of eastern Nazca plate seamounts

Paleomagnetism of eastern Nazca plate seamounts defines Nazca and Farallon absolute plate motion during Cenozoic times. Magnetic and bathymetric surveys are presented for two eastern Nazca plate seamounts in the Chile Basin and they are used to calculate paleomagnetic poles with uniform and nonuniform magnetic modeling. The paleopole for Piquero-2 seamount is coincident with the earth's pole, suggesting a young seamount. The paleopole for Piquero-1 seamount indicates that the Nazca plate moved 23° northward during 0–50 ma. This is 13° more latitudinal motion than predicted by a Pacific hotspot reference frame and 20 ° more motion than predicted by DSDP sediment and basalt paleomagnetism.     

现今绝对板块运动

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。     

Multibeam bathymetry and sidescan imaging of the Rivera Transform–Moctezuma Spreading Segment junction, northern East Pacific Rise: New constraints on Rivera–Pacific relative plate motion

To better understand the recent motion of the Pacific plate relative to the Rivera plate and to better define the limitations of the existing Rivera–Pacific plate motion models for accurately predicting this motion, total-field magnetic data, multibeam bathymetric data and sidescan sonar images were collected during the BART and FAMEX campaigns of the N/O L'Atalante conducted in April and May 2002 in the area surrounding the Moctezuma Spreading Segment of the East Pacific Rise, located offshore of Manzanillo, Mexico, at 106°16′W, between 17.8°N and 18.5°N. Among the main results are: (1) the principle transform displacement zone of the Rivera Transform is narrow and well defined east of 107o15′W and these azimuths should be used preferentially when deriving new plate motion models, and (2) spreading rates along the Moctezuma Spreading Segment should not be used in plate motion studies as either seafloor spreading has been accommodated at more than one location since the initiation of seafloor spreading in the area of the Moctezuma Spreading Segment, or this spreading center is not a Rivera–Pacific plate boundary as has been previously assumed. Comparison of observed transform azimuths with those predicted by the best-fit poles of six previous models of Rivera–Pacific relative motion indicate that, in the study area, a significant systematic bias is present in the predictions of Rivera–Pacific motion. Although the exact source of this bias remains unclear, this bias indicates the need to derive a new Rivera–Pacific relative plate motion model.     

亚洲板块运动欧拉参数的确定及其板内形变的分析

板块运动的欧拉参数是表征板块运动的最基本特征。地质模型和独立空间技术实测资料建立的ITRF序列模型都将欧亚板块视为一个整体,由于80%的台站集中在西欧,因此整个欧亚作为一个背景场来研究亚洲区域形变,不能真正反映亚洲板内形变。本文利用国际地球自转服务(IERS)发布的ITRF2000速度场,独立确定亚洲区域板块运动欧拉参数,进而分析亚洲区域现今板内形变,并与地质模型NNR-NUVEL1A和ITRF2000VEL模型得到的结果进行比较,揭示亚洲区域现今运动特征:中南部形变最大,向北逐渐减小,东西向拉伸,南北向收缩;亚洲东部地区相对于亚洲是一稳定的区域;另外亚洲西伯利亚地区不属于亚洲区域块体,而属于独立的稳定的欧亚构造块体,具有刚性块体特征。     

Possible effects of collisions on plate motions

A large-scale collision at a plate boundary is expected to play an important role not only in the deformation at the boundary but also in the motion of the plate carrying the buoyant material to be accreted. Possible changes in rates and directions of such motions may be calculated provided that certain assumptions are made about the nature of the driving forces. In this model we shall assume basically that:

1. (1) an oceanic plate is driven by slab pull and ridge push, being resisted by basal asthenospheric drag and slab resistance; and

2. (2) because of detachment, slab pull is lost upon collision.

If, however, the calculated motion following collision has a convergent component at the boundary, a new subduction zone, with an increasing slab pull force, forms seaward of the accreting buoyant material.Calculations were first made on an idealized planar octagonal plate. Results indicated that, so long as the scale of collision is limited, changes in motion take place but the motion returns to the initial state. However, for large-scale collisions, the plate motion suffers a large directional change, which also changes the nature of some boundaries, and hence the motion approaches a new steady-state motion irreversibly. Calculations were then conducted on an idealized Philippine Sea plate on a spherical earth. For a sizable collision along the Taiwan-Philippine-Mindanao boundary, this boundary and perhaps the Bonin-Mariana boundary, may become a transform fault provided that slab pull-ridge push is the driving force. These results provide some support to Uyeda-McCabe model (1983) of episodic spreading of the Philippine Sea basins, as well as the predominance of strike-slip motion along collision boundaries. Finally, in agreement with prior studies, subduction of a ridge system, assumed to have been located along the southwestern rim of the Paleo-Pacific plate, was shown to be consistent with the change in direction of motion of that plate at 43 m.y.B.P.Calculations conducted in this study show that predicted changes are model dependent so that comparisons with observed or inferred motions may be useful as a means of estimating the relative importance of the various potential driving forces.     

对地球质心偏移及板块驱动力的讨论

支持宇宙力参与板块运动的观点,赞同地球质心偏移的论断,但对质心偏移的力源和成因提出不同的看法。数理推导表明,太阳斥力与万有引力常数G的变化综合作用、冰盖在一极的形成与消融等是质心偏移的主要力源。     

Neogene patterns of relative plate motion for Africa-Europe: some implications for recent central Mediterranean tectonics

A detailed relative motion picture for the Neogene Africa-Europe plate kinematics is presented. The kinematic reconstruction was carried out using the finite difference solution between the rotation parameters determined for Anomalies 7 to 2 in the Africa-North America-Europe plate motion circuit. The analysis shows a motion of Africa with respect to Europe which is NNE directed during Late Oligocene to Burdigalian times, becoming NNW trending from the Langhian to the early Tortonian; from upper Tortonian times onward, the motion changes to a clear north-west directed convergence. Major Late Neogene tectonic features of the central Mediterranean region can, to a large extent, be explained within the context of the reconstructed major plate motions. Late Tortonian to Recent Africa-Europe slip vectors are compatible with a variety of geological phenomenoa such as north-west directed subduction beneath Calabria, south-east translation of Calabria and extension in the Tyrrhenian Sea, north-west trending slip vectors from thrust earthquakes between Gibraltar and Sicily, and dextral strike-slip across the North African margin.     

Is northern Honshu a microplate?

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.     

Structure and development of the Sagami trough and the Boso triple junction

The Sagami trough is located at the particular plate margin where the Izu forearc is subducted underneath the Honshu forearc. At its southeastern end, the world's only known TTT-type triple junction (Boso triple junction) has developed. Several different kinds of basins occur in different segments along the Sagami trough and at the triple junction. The bathymetric, geologic, and geophysical data obtained during the Kaiko Project and from additional studies are summarized together with our onland studies. We suggest that the right-lateral oblique plate motion formed an eduction margin in the Sagami basin, while a normal subduction margin and an oblique subduction margin have been formed in the Middle Sagami trough basin. These tectonic phenomena resulted from the long-lasting compressional covergence between the Philippine Sea plate and Eurasian plate since the early or middle Miocene. The North basin on the northeasternmost margin of the Philippine Sea plate near the Boso triple junction has developed as a stretched basin due to the westward motion of the Philippine Sea plate with respect to the Eurasian plate.     

Rigid Indian plate: Constraints from GPS measurements

We analyze GPS data from 26 sites located on the Indian plate and along its boundary. The large spatial coverage of the Indian plate by these sites and longer data duration helped us in refining the earlier estimates of the Euler pole for the Indian plate rotation. Our analysis suggests that the internal deformation of the Indian plate is very low (< 1–2 mm/year) and the entire plate interior region largely behaves as a rigid plate. Specifically, we did not infer any significant difference in motion on sites located north and south of the Narmada Son failed rift region, the most prominent tectonic feature within the Indian plate and a major source of earthquakes. Our analysis also constrains the motion across the Indo-Burmese wedge, Himalayan arc, and Shillong Plateau and Kopili fault in the NE India.     

Hotspots in the Southern Oceans — an absolute frame of reference for motion of the Gondwana continents

The geometry and geochronology of aseismic ridges and oceanic islands in the southern oceans provide a good test of the proposition that hotspots remain fixed over long periods of time; that is, motion of an order of magnitude less than the relative motion between plate pairs. In most cases it is concluded that inter-hotspot movement cannot be discerned for the period 100 m.y. to Present and that widely distributed hotspots in the Atlantic and Indian Oceans provide a frame of reference for plate motions following the disintegration of Gondwanaland, which is independent of paleomagnetism. This frame of reference is “absolute” in that it gives the motion of the lithosphere with respect to the mantle (= hotspots). The absolute motion model indicates that Africa and Antarctica are now moving only very slowly, that there has been significant relative movement between East and West Antarctica since the Cretaceous, and prescribes the relative motion between the Somali and African plates.     

Evolution of the Eurasian Basin and its implications to the motion of Greenland along Nares Strait

A combined analysis of the recently collected aeromagnetic data from the Eurasian Basin with the magnetic data from the Labrador Sea, the Norwegian-Greenland Sea and the North Atlantic yields a plate kinematic solution for the Eurasian Basin which is consistent with the solution for the North Atlantic as a whole. It shows that the Eurasian Basin and Norwegian-Greenland Sea started to evolve at about anomaly 25 time, though active seafloor spreading did not start in either of these regions until anomaly 24 time. It further shows that the spreading in the Eurasian Basin has been a result of motion only between the North American and Eurasian plates since the beginning, with the Lomonosov Ridge remaining attached to the North American plate. The relative motion among the North American, Greenland and Eurasian plates as obtained from the plate kinematics of the North Atlantic shows that from Late Cretaceous to Late Paleocene (anomaly 34 to 25) Greenland moved obliquely to Ellesmere Island. It is suggested that most of this motion was taken up within the Canadian Arctic Islands resulting in little or no motion along Nares Strait between Greenland and Ellesmere Island. From Late Paleocene to mid-Eocene (anomaly 25-21) Greenland continued to move obliquely, resulting in a displacement of 125 km along and of 90 km normal to the Nares Strait. From mid-Eocene to early Oligocene another 100 km of motion took place normal to the Strait, which correlates well with the Eurekan Orogeny in the Canadian Arctic Island. During these times the relative motion between Greenland and Svalbard (Eurasian plate) was mainly strike-slip with a small component of compression. The implication of the resulting motion between the North American and the Eurasian plates onto the Siberian platform are discussed.     

运动方向的线状指示物与斑变晶中叶理交切轴(FIAs)的比较及其与板块相对运动方向的关系(英文)

过去还无人指出过板块相对运动的方向与缓倾斜叶理、逆断层和断层上的线状指示物有直接关系,这是因为缓倾斜构造上的运动方向只和变厚了的造山地层的重力塌陷有关,它们和俯冲板块传递给仰冲板块的推力没有关系。缓倾斜叶理上的运动方向的线状指示物和斑状变晶中的叶理弯曲或叶理交切轴（FIA）并无直接关系,这是因为FIA的指向受缓倾斜叶理和斑状变晶边缘上产生的、近乎垂直的叶理之间的交切面控制。在班状变晶边缘上形成的、近乎垂直的叶理在基质中的方位可能在较大范围内变动,因为它们会在稍早期间形成的叶理再活化作用影响下发生转动或遭到破坏。斑状变晶边缘上近乎垂直的叶理,与形成于早期或晚期的缓倾斜叶理的交线,在后期的生长中被圈闭在班状变晶里,此交线规定出了FIA的方位,而与叶理上的运动方向无关。从美国佛蒙特州阿巴拉契亚山脉采集的FIA资料指出,在125km×35km的一片地区内,在该地岩层所发生的多次变形中,从未曾使早期形成的FIA组的方位发生变动。这种情况要求：后来的每一代褶皱都是由于渐进的。总体不均匀缩短作用造成的。这种情况表明：FIA保存着原始的运动方向,此方向未因以后的变形而转动。非洲板块与欧洲板块的相对运动方向和由阿尔卑斯期变质岩中叶理交切轴（FIAs）所指示     

Earth's tectonic history revisited in the light of episodic misfits between plate network and mantle convection

Episodic plate reorganisations abruptly change plate boundary configurations. To illustrate their role, we review the plate reorganisations that appear in the present-day oceans and in the reconstructed Tethys ocean. These time periods cover the dispersal of the Pangea super-continent and the collisions with Eurasia that foreshadow a new super-continent. Plate reorganisations have played a fundamental role in the tectonic history of the Earth, being responsible for continental break-up and, after oceanic spreading, for continental collisions. As a result, they governed the formation and dispersal of super-continents. We observe a bulk polarity in plate motion that governs continental collision and the opposite bulk polarity in plate reorganisation that governs continental break-up. Such opposite polarities show in the tectonic history that we follow since the 550 Ma formation of the Gondwana super-continent.In order to decipher the rules that govern plate reorganisation, we investigate the distribution of spreading and subduction that derives from the current plate motion. We observe a mismatch between the evolution tendency of the plate boundary network and convection in the deep mantle. The actual network of plate boundaries illustrates a compromise between the two. Based on the opposite polarities in plate motion and plate reorganisation, we propose that this compromise is maintained by plate reorganisations that counterbalance free evolution of the network in abruptly changing its boundaries. We propose that plate reorganisations are basically caused by the mismatch between the free evolution of the plate boundary network and the current convection pattern in the deep mantle.Evidence on Proterozoic rifting and continent collisions allows dating the oldest known plate reorganisation around 2 Ga, which is the age of the oldest known super-continent. Based on the geology of the Archean before 3 Ga, mantle convection appears limited under a greenstone cover and different from the current mantle convection. The distribution of the diapiric granitoids that intrude this cover points to a honeycomb convection centred on downwelling sites separated by diffuse upwelling, which fits the theory on the early Earth mantle convection when plates did not cover the globe. We propose that the plate reorganisation regime appeared sometime between 3 and 2 Ga.     

Nares Strait—A suture zone: Geophysical and geological implications

The motion of Greenland relative to Ellesmere Island along Nares Strait is determined from poles of rotation which provide control for the motion independent of local geology and geophysics. The plate kinematics around the North Atlantic Ocean, the Norwegian and Greenland Seas and the Eurasian Basin of the Arctic Ocean constrain motion along Nares Strait. These motions are checked by examining the stability characteristics of the triple junctions. These junctions are found to be stable. The motion along Nares Strait between anomalies 34 and 13 is a combination of strike-slip and compression. The regional geology is found to support the plate reconstructions. The local geology of the Nares Strait area is reviewed and found not to refute the predicted motions. The geophysical and geological data are interpreted in terms of the Wilson cycle, the opening and closing of an ocean. The Nares Strait area has the characteristics of a cryptic suture, a join between regions of collided continental crust.     

Earliest Eocene (53 Ma) convergence in the Southwest Pacific: evidence from pre‐obduction dikes in the ophiolite of New Caledonia

Uncertainty about the timing and location of the initiation of convergence in the western and south‐western Pacific greatly hinders accurate plate tectonic reconstructions of subduction systems in that area. The chemistry and age of dikes intruding mantle peridotite in the ophiolite of New Caledonia infer that subduction‐related magmatism began before 53 Ma. These new results infer that obduction in the south‐west Pacific is unrelated to the reorientation of the Pacific plate motion that occurred c. 43 Ma and confirm new interpretations showing that changes in mantle flow, hotspot and plate motion may have occurred as soon as late Paleocene or early Eocene.     

全球应力场与构造分析

介绍了近年来全球构造应力研究方面的一些新进展并以“世界应力图”提供的资料为背景 ,结合一些最新的研究成果 ,阐述了全球构造应力场的分布特征及其与板块构造运动之间的联系。研究结果表明 :(1)全球存在大尺度的统一性构造应力场 ;(2 )全球大多数板块内部地区为挤压应力作用 ,其应力结构多为逆断型、走滑型或逆走滑型 ;(3)大陆板块内部的扩张区大多位于高海拔异常地区 ,其应力结构为正断型或正走滑型 ,如青藏高原、东非裂谷和贝加尔裂谷等 ;(4)全球大部分地区的地壳上部构造应力作用方向较为均一 ,存在区域统一应力场 ;(5 )全球大部分地区的最大水平主应力方向与板块绝对运动 (角速度 )迹线保持较好的一致性 ,反映出构造应力与板块运动的关系密切 ;(6 )板块汇聚、洋脊扩张可能是产生岩石圈上部构造应力的主要力源。     

Tectonic evolution along the northernmost border of the Philippine Sea plate since about 1 Ma

Recent structural, tephrochronologic and magnetostratigraphic studies conducted along the northernmost border of the Philippine Sea (PHS) plate enable us to reconstruct the precise tectonic evolution along the convergent boundary between the PHS plate and the Northeast Japan (NEJ) plate or the North American (NAM) plate since about 1 Ma. The authors of the present study split the tectonic evolution into five stages and present the characteristics of each stage. A plate tectonic interpretation is proposed, based upon the tectonic evolution, with special reference to the mode of convergent motion. In brief, our interpretations are as follows: the relative motion between the PHS and the NEJ plates was not recognized geologically within the area studied from about 1.0 to 0.9 Ma (Stage 1), suggesting either none or small influence from the coupling between the two plates during that period of time. Convergence between the PHS and the NEJ plates was possibly in N-S direction from 0.9 to 0.5 Ma (Stage II), and probably north-northwestward since 0.5 Ma (Stages III to V). The mode of the convergent motion was that of buoyant subduction in Stages II and III. The mode changed gradually from buoyant subduction during Stage IV to collision in Stage V (0.07 Ma to the present).