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1.
大洋板块俯冲到地幔转换带,进而可形成不同的形态:板块可以停滞在660km不连续面,抑或穿过地幔转换带进入下地幔.这些不同的俯冲模式可进一步影响到海沟的运动.为更好地理解上地幔中俯冲板片的变形行为以及俯冲过程与海沟运动之间的关系,本文通过建立一系列高精度二维热-力学自由俯冲的数值模型,揭示了俯冲板块在上地幔中的变形方式及其与地幔转换带之间的相互作用过程.模拟结果显示,在俯冲板块与地幔转换带的相互作用过程中,其动力学过程可以分为以海沟后撤主导、海沟前进主导以及稳定型海沟等三种主要动力学类型.对于年龄较老,厚度较大的俯冲板块容易形成海沟后撤型俯冲,俯冲板块停滞在660km不连续面.相反,年龄较小,塑性强度较小的板块容易形成海沟前进型俯冲,俯冲板块穿越660km不连续面. 相似文献
2.
A two-dimensional numerical convection model in cartesian geometry is used to study the influence of trench migration on the ability of subducted slabs to penetrate an endothermic phase boundary at 660 km depth. The transient subduction history of an oceanic plate is modelled by imposing plate and trench motion at the surface. The viscosity depends on temperature and depth. A variety of styles of slab behaviour is found, depending predominantly on the trench velocity. When trench retreat is faster than 2–4 cm/a, the descending slab flattens above the phase boundary. At slower rates it penetrates straight into the lower mantle, although flattening in the transition zone may occur later, leading to a complex slab morphology. The slab can buckle, independent of whether it penetrates or not, especially when there is a localised increase in viscosity at the phase boundary. Flattened slabs are only temporarily arrested in the transition zone and sink ultimately into the lower mantle. The results offer a framework for understanding the variety in slab geometry revealed by seismic tomography. 相似文献
3.
汤加的俯冲板块结构复杂,板块形态的起因和形成机制不是很清晰.为了探索其演化,我们借助于板块运动学、海底年龄和关键的大地构造特征,用地球动力学模型模拟了本区域40 Ma之后的俯冲历史.通过研究我们发现,沿着海沟的分布位置,不同的黏度、流体的吸力与浮力比特征控制着板块的力学强度,从而影响着板块的俯冲角度和形态.我们的模型显示在俯冲板块形成前,研究区表面西侧的黏度剖面形成的弱化带为水平低黏度区,它对俯冲的发生有一定的引导作用,高黏度的上覆板块的存在和俯冲导致的地幔流体的吸力降低了俯冲板块的倾角,15°S附近的俯冲板块的分离发生在16-8 Ma之间.最后我们通过匹配实际的构造特征,包括贝尼奥夫带和波速结构剖面,用所得的相关性最佳的模型对本区的地幔结构随时间演化提供探索. 相似文献
4.
本文采用依赖温度的黏度结构以及考虑海洋板块和大陆板块厚度差异等特征,以太平洋板块向欧亚板块会聚速率作为板块速度的主要约束,通过变化海沟后撤速度模型,数值模拟西太平洋板块向中国东北的俯冲过程.结果表明,要产生类似于中国东北之下低角度的板片俯冲,海沟后撤是重要条件;而上下地幔黏度的较大差异是决定俯冲板片不穿透660 km相变面的决定因素;西太平洋板块向欧亚板块的俯冲应早于70 Ma B.P.,海沟后撤速度可能小于一些地质学家估计的45 mm/a, 而且可能是分阶段变化的;速度场表明运动学模型的反过程：大陆岩石圈之下物质的不断水平向东的流动和推挤可能成为海沟后撤的力源之一,地幔物质的这种东向流动可能与印度板块挤压碰撞欧亚板块有关,沿欧亚板块东缘的扩张构造可能是太平洋-欧亚板块运动和印度-欧亚板块运动的综合效应. 相似文献
5.
6.
琉球海沟的构造和运动特征 总被引：3，自引：3，他引：3
琉球海沟是欧亚板块与菲律宾海板块之间的边界，海沟西坡是大陆性质的琉球岛弧，东坡是大洋性质的菲律宾海地壳．海底地震反射探测和地震震源定位表明，菲律宾海板块沿海沟向琉球岛弧下俯冲，俯冲角度与深度沿海沟走向变化．有证据显示，由于俯冲板前缘的横向移动，海沟和岛弧正朝大洋方向后退，弧后盆地-冲绳海槽发生拉张变形．最近一次的海沟后退与冲绳海槽扩张可能是从上新世末(2Ma前)开始的，岛弧的后退移动和弧后拉张在南部与海沟走向垂直，在中部和北部与海沟走向斜交，总体上向南的运动分量占优势、与海沟后退相关的弧后拉张集中在冲绳海槽，没有证据表明对其西侧的中国东海陆架盆地产生影响、海沟后退的原因可能与俯冲板的动力不平衡以及它与周围地幔的相互作用有关． 相似文献
7.
A detailed comparison between fully dynamic and kinematic plate formulations has been made in models of mantle convection. Plate velocity is computed self-consistently from fully dynamic plate models with temperature- and stress-dependent viscosity and preexisting mobile faults. In fully dynamic models, the flow is driven solely by internal buoyancy, while in kinematic models the flow is driven by a combination of the prescribed surface velocity and internal buoyancy. Only a temperature-dependent viscosity, close to the effective viscosity determined from the fully dynamic models, is used in the kinematic models. The two types of models give very similar temperature structures and slab evolutionary histories when the effective viscosity and surface velocity are nearly identical. In kinematic plate models, the additional work introduced by the prescribed velocity boundary condition is apparently dissipated within the lithosphere and has little influence on the convection under the lithosphere. In models with periodic lateral boundary conditions, slabs sink into the lower mantle at an oblique angle and this contrasts with the vertical sinking which occurs with reflecting boundary conditions. Models show that we can simulate fully dynamic models with kinematic models under either periodic boundary conditions or reflecting boundary conditions. 相似文献
8.
According to the experimental studies on the rheology of two important mantle rocks (eclogite and harzburgite), the rheological properties of the deep subducted oceanic lithosphere are investigated by assuming a simplified harzburgite type slab model with moderate thickness of basaltic layer. When the mantle convergence rate is small or the subducting slab has been trapped in the mantle for an enough long time, the strength profile of the slab is characterized by a strong subducting crustal component lying on a weak subducting upper mantle. However, if the convergence rate is large enough, the subducting slab will be featured only by a rigid cold center. Our study suggests that the detachment of the subducting crust component from the underlying upper mantle is only likely to happen in hot slow subducting slabs, but not the cold fast subducting lithosphere. Rheological properties of the harzburgitic and the eclogitic upper mantle vary with depths. The eclogitic upper mantle is stronger than the peridotitic upper mantle across the upper mantle. Transition zone is the high strength and high viscosity layer in the upper mantle except the lithosphere. 相似文献
9.
通过反演562891个纵波和156321个横波走时数据,第一次同时获得了阿拉斯加地区地壳及上地幔的纵波与横波速度以及泊松比图像,为更好地认识阿拉斯加地区的深部地震结构、太平洋板块与亚库塔特板块的俯冲几何形态提供了科学依据.成像结果表明P波和S波速度图像与泊松比结构具有很好的一致性,强的高速度和低泊松比异常沿着阿拉斯加俯冲带延伸至200 km深度,该高速度和低泊松比异常体与俯冲带的地震空间分布吻合,因此,我们认为该高速体为俯冲的太平洋板块和亚库塔特板块.从地震空间分布发现,大部分大地震（M>6.5）发生在高速度与低速度异常交界处,可能反映了俯冲板块之间强耦合作用.在俯冲带的地幔楔显示出广泛的低速度和高泊松比异常,并且这些异常与岛弧火山的位置相对应,这与大洋板块俯冲所形成的岩浆入侵作用有关.研究结果表明在南阿拉斯加俯冲带,俯冲板块的俯冲角度从兰格尔块体下方的平坦变成在布里斯托尔湾下方的陡峭,这与亚库塔特板块俯冲在兰格尔块体下方和太平洋板块俯冲在布里斯托尔湾下方有关.在基奈半岛和科迪亚克岛连接处的上地幔位置存在强烈的低速与高泊松比异常体,使该处的大洋俯冲板块变薄.这一现象可能与亚库塔特板块和太平洋板块相互碰撞作用以及软流圈强烈的上升流入侵有关. 相似文献
10.
S. Goes F.A. Capitanio G. Morra M. Seton D. Giardini 《Physics of the Earth and Planetary Interiors》2011,184(1-2):1-13
The dynamics of plate tectonics are strongly related to those of subduction. To obtain a better understanding of the driving forces of subduction, we compare relations between Cenozoic subduction motions at major trenches with the trends expected for the simplest form of subduction. i.e., free subduction, driven solely by the buoyancy of the downgoing plate. In models with an Earth-like plate stiffness (corresponding to a plate–mantle viscosity contrast of 2–3 orders of magnitude), free plates subduct by a combination of downgoing plate motion and trench retreat, while the slab is draped and folded on top of the upper-lower mantle viscosity transition. In these models, the slabs sink according to their Stokes’ velocities. Observed downgoing-plate motion–plate-age trends are compatible with >80% of the Cenozoic slabs sinking according to their upper-mantle Stokes’ velocity, i.e., subducting-plate motion is largely driven by upper-mantle slab pull. Only in a few cases, do young plates move at velocities that require a higher driving force (possibly supplied by lower-mantle–slab induced flow). About 80% of the Cenozoic trenches retreat, with retreat accounting for about 10% of the total convergence. The few advancing trench sections are likely affected by regional factors. The low trench motions are likely encouraged by low asthenospheric drag (equivalent to that for effective asthenospheric viscosity 2–3 orders below the upper-mantle average), and low lithospheric strength (effective bending viscosity ～2 orders of magnitude above the upper-mantle average). Total Cenozoic trench motions are often very oblique to the direction of downgoing-plate motion (mean angle of 73°). This indicates that other forces than slab buoyancy exert the main control on upper-plate/trench motion. However, the component of trench retreat in the direction of downgoing plate motion (≈ slab pull) correlates with downgoing-plate motion, and this component of retreat generally does not exceed the amount expected for free buoyancy-driven subduction. High present-day slab dips (on average about 70°) are compatible with largely upper-mantle slab-pull driven subduction of relatively weak plates, where motion partitioning and slab geometry adjust to external constraints/forces on trench motion. 相似文献
11.
日本俯冲带与IBM俯冲带位于太平洋板块、菲律宾海板块和欧亚板块三者的交汇地带,是典型的"俯冲工厂"地区,具有重要的研究意义.本文利用震源分布资料与卫星重力数据对日本俯冲带与IBM俯冲带进行了研究.通过空间重力异常反映了俯冲带地区的区域构造形态,在此基础上基于艾利模式计算了均衡异常以反映地壳均衡特征.利用震源分布资料,分别从垂直俯冲带走向与沿俯冲带走向划定了横截剖面(cross-sections)进行了地震提取,讨论了俯冲带地区的Wadati-Benioff带形态特征,并借助于俯冲带地震等深线图直观描述了俯冲带的俯冲形态.在日本俯冲带与伊豆—小笠原俯冲带各选取了一条典型剖面进行了重力2.5D反演,研究了俯冲带地区的壳幔结构特征.研究结果表明,九州—帕劳海脊与IBM岛弧在均衡异常上存在差异,前者已逐渐趋向于地壳均衡.IBM的Wadati-Benioff带存在明显的南北差异,反映出伊豆—小笠原俯冲板片停留在了660km转换带中,而马里亚纳俯冲板片很可能垂直穿过了这一转换带,造成这种南北差异的原因与板块相对运动、岩石圈黏性和年龄差异以及俯冲板片的重力效应等因素有关.在IBM的中部和南部存在板片撕裂现象.日本俯冲带的俯冲洋壳密度随俯冲深度变化较小,洋幔存在一定程度的蛇纹岩化,地幔楔蛇纹岩化作用不典型,海沟处有一范围较小的含水畸变带;伊豆—小笠原俯冲带俯冲洋壳密度随深度增大而明显增大,洋幔蛇纹岩化程度较日本俯冲带低,地幔楔蛇纹岩化作用强烈,板块交汇处存在明显的蛇纹岩底辟.日本俯冲带与IBM俯冲带一线自北向南板片俯冲变陡,两侧板块耦合度降低,与俯冲带两侧的板块运动速率差异有关. 相似文献
12.
智利三联点(CTJ)位于纳兹卡板块、南极洲板块与南美板块的交界处,由南极洲—纳兹卡板块之间的智利洋脊俯冲到智利海沟而形成.巴塔哥尼亚板片窗的发展是智利洋脊长期扩张俯冲的结果之一.随着纳兹卡板块的不断东向俯冲,纳兹卡板块范围逐渐变小,CTJ同时向北移动.本文采用数值模拟方法,建立了关于洋脊海沟碰撞的简单二维模型,来研究智利三联点南部扩张洋脊俯冲区域岩石层的热结构.模拟结果表明,洋脊的位置、板块相对汇聚速度及上覆大陆板块的存在均对俯冲区域海洋板块的温度结构有着很大影响,并且大陆板块下方海洋板块温度变化最大的位置距洋脊的水平距离与洋脊到板片窗范围的水平距离两者之间具有较好的一致性.同时,当存在两两板块间的相对汇聚时,洋脊右侧大陆板块下表面的温度升高,俯冲带内海洋板块温度接近于地幔温度.纳兹卡板块以7.8 cm·a~(-1)的速度急速俯冲于南美板块之下的过程中,同时伴随着智利洋脊的持续扩张俯冲,在智利三联点南部,南美板块之下纳兹卡板块的温度因而可以更快地达到地幔软流层的约1300℃温度,并最终消亡于地幔之中. 相似文献
13.
地震层析成像研究清晰给出了地球深部俯冲板片的大尺度形态,但与俯冲过程相关的地幔流动特征仍不明确.在俯冲地幔楔系统中,前人观测到了与海沟平行和垂直的快波偏振方向.本文研究了西北太平洋俯冲板片在地幔过渡带中停滞形成的"大地幔楔"中的各向异性特征.对具有长期稳定观测数据的MDJ台站SKS震相和区域深源地震的直达S波震相进行了... 相似文献
14.
Seismic imaging of the entire arc of Tohoku and Hokkaido in Japan using P-wave, S-wave and sP depth-phase data 总被引：3，自引：0，他引：3
In order to better understand seismic structure and seismotectonics of the entire arc of Tohoku and Hokkaido in Japan, we combined arrival time data from earthquakes beneath Tohoku and Hokkaido land areas, and beneath the Pacific Ocean to determine the three-dimensional (3D) velocity structures (Vp and Vs) under the entire Northeast (NE) Japan-Kuril arc. We adopted 176,431 P-wave and 110,953 S-wave arrival times, from 5123 local earthquakes, and 2843 sP depth-phase data from 385 events that occurred beneath the Pacific Ocean. The 385 suboceanic events were accurately relocated by using P-wave, S-wave and sP depth-phase arrival time data jointly. The obtained results confirmed the major features delineated by previous studies and revealed some new features of the structural heterogeneity beneath NE Japan and the Kuril forearcs. High-velocity anomalies of the cold subducting Pacific slab and low-velocity anomalies in the hot mantle wedge were imaged clearly. Strong lateral heterogeneities were revealed on the upper boundary of the Pacific slab under the forearc region, which showed a good correlation with the spatial distribution of large interplate earthquakes. These results indicated that strong coupling sections (or asperities) and weak-coupled or decoupled patches might exist along the upper boundary of the Pacific slab. Widespread low-velocity anomalies were visible in the forearc mantle above the subducting Pacific slab, which might reflect serpentinization of the forearc mantle associated with the dehydration process of the subducting slab. Our results also showed a general tendency for seismic coupling in the asperities to be located around low-velocity areas on the slab boundary under the suboceanic region. 相似文献
15.
自3 Ma至现今,在欧亚东缘太平洋、菲律宾海板块以较大速率朝NWW方向运动,并沿海沟向欧亚大陆俯冲;同时欧亚板块以较小速率朝SEE方向移动,构成双方向的板块汇聚格局.沿日本岛弧东侧,海洋板片以较小的倾角插入欧亚大陆下面,在浅部产生的挤压变形扩展到日本海东边缘.琉球岛弧的中、北部,菲律宾海俯冲板片的倾角较大,其西南段由NE向转变为EW向,正经历活动的海沟后退与弧后扩张.台湾是3种板块汇聚的交点:欧亚沿马尼拉海沟向东俯冲,吕宋弧与台湾碰撞,使台湾岛陆壳东西向缩短与隆升,形成年轻的造山带,菲律宾海板块沿琉球海沟的西南段向北俯冲到欧亚下面.位于南海与菲律宾海之间的菲律宾群岛是宽的变形过渡带,两侧被欧亚向东、菲律宾海向西俯冲夹击,中间是大型左旋走滑断层.总体上,现今时期的太平洋、菲律宾海板块的西向俯冲运动所产生的变形主要分布在俯冲板片内部及岛弧,未扩散到弧后地区,可能这种俯冲运动产生的水平应力较小,不能阻挡欧亚大陆的向东移动,对大陆内部的现今构造没有明显的影响. 相似文献
16.
The Role of History-Dependent Rheology in Plate Boundary Lubrication for Generating One-Sided Subduction 总被引：1，自引：0，他引：1
Michio Tagawa Tomoeki Nakakuki Masanori Kameyama Fumiko Tajima 《Pure and Applied Geophysics》2007,164(5):879-907
We have developed a two-dimensional dynamical model of asymmetric subduction integrated into the mantle convection without
imposed plate velocities. In this model we consider that weak oceanic crust behaves as a lubricator on the thrust fault at
the plate boundary. We introduce a rheological layer that depends on the history of the past fracture to simulate the effect
of the oceanic crust. The thickness of this layer is set to be as thin as the Earth's oceanic crust. To treat 1-kilometer
scale structure at the plate boundary in the 1000-kilometer scale mantle convection calculation, we introduce a new numerical
method to solve the hydrodynamic equations using a couple of uniform and nonuniform grids of control volumes. Using our developed
models, we have systematically investigated effects of basic rheological parameters that determine the deformation strength
of the lithosphere and the oceanic crust on the development of the subducted slab, with a focus on the plate motion controlling
mechanism. In our model the plate subduction is produced when the friction coefficient (0.004–0.008) of the modeled oceanic
crust and the maximum strength (400 MPa) of the lithosphere are in plausible range inferred from the observations on the plate
driving forces and the plate deformation, and the rheology experiments. In this range of the plate strength, yielding induces
the plate bending. In this case the speed of plate motion is controlled more by viscosity layering of the underlying mantle
than by the plate strength. To examine the setting of the overriding plate, we also consider the two end-member cases in which
the overriding plate is fixed or freely-movable. In the case of the freely-movable overriding plate, the trench motion considerably
changes the dip angle of the deep slab. Especially in the case with a shallow-angle plate boundary, retrograde slab motion
occurs to generate a shallow-angle deep slab. 相似文献
17.
本文利用区域地震初至波到时数据,通过地震层析成像研究获得了东北日本俯冲带上地幔（深至约150 km）的P波速度（VP）、S波速度（VS）、VP/VS和P波各向异性结构.结果表明,低速及高VP/VS比异常体主要分布在火山下方的下地壳和地幔楔中,其与低频地震的分布吻合,该区域与俯冲板块脱水所释放的流体及其导致的部分熔融密切相关;俯冲的太平洋板块内可能由于脱水脆化导致的双层地震带区域则没有表现出整体的高VP/VS值,其可能与俯冲板块内部含水矿物含量有关;俯冲板块内双重地震带区域及上覆地幔楔薄层主要表现为与海沟平行的方位各向异性和正的径向各向异性,其可能是由于含水矿物的脱水使橄榄石晶格结构发生了从A型到B型的变化所引起的.我们研究表明,结合地震波速度和各向异性结构能够加深对俯冲带内水运移过程的认识. 相似文献
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俯冲板块的深部脱水使得上覆地幔含水, 从而降低含水地幔的熔点, 导致上覆地幔部分熔融。 部分熔融的地幔柱一旦喷发到地表就是俯冲带火山, 也形成新的地壳。 相对于周围的地幔来讲, 具有较小密度和黏度的部分熔融地幔的时空活动性就控制着俯冲带火山的时空分布特征。 本文主要回顾近年来运用三维热力学岩石力学模型数值模拟研究与板片脱水相关的俯冲带火山活动的时空分布特性。 结果表明, 部分熔融地幔的有效黏度和密度是影响俯冲板片之上的三维地幔柱横向分布特征的主要因素。 高黏度的部分熔融地幔(1020~1021 Pa·s )易于形成近平行于海沟的、 长波长(70~100 km)的、 薄的波状地幔柱; 低黏度(1018~1019 Pa·s )的熔融地幔易于形成平行于海沟的, 短波长(30~50 km)的蘑菇状地幔柱和垂直于海沟的山脊状地幔柱。 当部分熔融地幔和周围地幔的密度相差小于50 kg/m3时, 在俯冲板片之上只能形成长波长低幅度(宽50~100 km, 高10~15 km)的地幔山丘。 岩浆产率随着时间的变化反映了火山活动的生命周期性。 板块俯冲速度会影响地幔柱形成的深度和范围大小。 高效率熔融提取会增加新地壳增长总量。 低的板块俯冲速度和低的熔融提取效率会增加上地壳(花岗岩质)和中地壳(英安岩质)化学成分的比例。 数值模拟结果可以很好地解释如日本东北、 新西兰、 南阿拉斯加俯冲区火山的横向分布特征。 相似文献
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Tomographic structure of East Asia:Ⅱ.Stagnant slab above 660 km discontinuity and its geodynamic implications 
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下载免费PDF全文 P-wave arrival times of both regional and teleseismic earthquakes were inverted to obtain mantle structures of East Asia.No fast(slab) velocity anomalies was not find beneath the 660-km discontinuity through tomography besides a stagnant slab within the transition zone.Slow P-wave velocity anomalies are present at depths of 100-250 km below the active volcanic arc and East Asia.The western end of the flat stagnant slab is about 1 500 km west to active trench and may also be correlated with prominent surface topographic break in eastern China.We suggested that active mantle convection might be operating within this horizontally expanded "mantle wedge" above both the active subducting slabs and the stagnant flat slabs beneath much of the North China plain.Both the widespread Cenozoic volcanism and associated extensional basins in East Asia could be the manifestation of this vigorous upper mantle convection.Cold or thermal anomalies associated with the stagnant slabs above the 660-km discontinuity have not only caused a broad depression of the boundary due to its negative Clapeyron slope but also effectively shielded the asthenosphere and continental lithosphere above from any possible influence of mantle plumes in the lower mantle. 相似文献
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《Earth and Planetary Science Letters》2006,241(3-4):789-803
We present a combined method, using sP depth-phase data and double-difference arrival times, to determine the precise hypocenter locations of earthquakes that occur under the Pacific Ocean outside of the area covered by the land-based seismic network. We assess the effectiveness of the combined method using a data set of P- and S-wave arrival times and sP depth phase from suboceanic earthquakes recorded by both land-based seismic stations and offshore seismic stations (OFS). The hypocenters of the offshore earthquakes relocated using the combined method are consistent with those determined using the standard location method and OFS data. The differences in the hypocenters relocated by the two methods are less than 4 km. We applied the method to the subduction region that underlies the Kanto district, central Japan, and located a large number of earthquakes that occurred beneath the Pacific Ocean. We then determined the detailed 3D seismic velocity structure by inverting a large number of arrival times of P- and S-waves and sP depth phase from the relocated earthquakes in the study region. High-velocity anomalies related to the cold subducting Pacific slab and low-velocity anomalies related to the hot mantle wedge are clearly imaged. Beneath active volcanoes, low-velocity zones are visible from the surface to a depth of 100 km, reflecting fluids released by dehydration of the subducting Pacific slab. Strong lateral heterogeneities are revealed on the upper boundary of the Pacific slab beneath the forearc region. The low-velocity areas under the offshore region are associated with low seismicity and weak interplate coupling. A low-velocity layer is imaged along the upper boundary of the Philippine Sea slab in the northern part of Kanto district, which may reflect dehydration of the slab. Our tomographic images indicate that the overlaying Philippine Sea plate has effects on the spatial distribution of active volcanoes related to the subducting Pacific slab in the study region. 相似文献