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板块俯冲时海沟位置存在不变、前进和后撤 3种情况 ,后撤俯冲可能造成弧后扩张 .层析成像等资料显示 :太平洋板块低角度俯冲到欧亚板块之下后没有穿透 670km相变界面 ,而是平卧于该界面之上 .这种平卧过程可能始于 2 8Ma前 .地球动力学计算表明 :俯冲板片前缘触及上下地幔相变界面而受阻平卧时 ,有利于形成后撤俯冲和弧后扩张 .中国东北火山形成很可能属于这种后撤俯冲、远离海沟陆内弧后引张、地幔热物质上涌、减压熔融的情况 . 相似文献
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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
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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
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西太平洋板块俯冲与华北克拉通破坏 总被引：1，自引：0，他引：1
华北克拉通破坏与西太平洋板块俯冲相关是学界的重要共识,但西太平洋板块何时开始向东亚大陆俯冲、早白垩世西太平洋俯冲带在何处、东亚大地幔楔何时形成、晚中生代西太平洋俯冲板块如何演化等重要科学问题一直没有很好地解决.文章通过综合分析与研究,认为西太平洋板块起始俯冲的时间早达早侏罗世;早白垩世西太平洋俯冲带位于东亚大陆边缘,比现今西太平洋板块俯冲带靠西2200km;与此相对应,欧亚大陆自早白垩世以来向东漂移了大约900km.西太平洋俯冲板块后撤始于～145Ma,说明东亚大地幔楔开始形成于早白垩世;西太平洋板块俯冲作用对华北克拉通的影响可能是通过地幔楔增大过程中物质和能量的迁移和交换来实现的.利用地质构造事件反演了大洋板块在俯冲到地球内部之前的演化过程,提出燕山运动A幕和B幕发生的原因分别是西太平洋板块向东亚大陆边缘以高速低角度俯冲和俯冲角度逐渐变低两种不同的地球深部动力学过程新观点.在早白垩世大约130～120Ma期间,西太平洋板块可能已经转变为高角度俯冲、回转与后撤速率达到最大、最终在地幔过渡带产生滞留体.这个过程可能显著改变了所在区域和上覆地幔的物性和黏滞度,导致上覆地幔楔产生非稳态流动,从而导致岩石圈地幔中熔/流体含量急剧增加、黏滞度降低以及岩石圈伸展/减压,并使其转变为年轻地幔——克拉通破坏.这些认识对揭示西太平洋俯冲板块与华北克拉通岩石圈地幔之间相互作用过程具有重要意义. 相似文献
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晚中生代以来,华南地区同时受到印度—欧亚板块碰撞和太平洋—菲律宾板块俯冲及后撤作用的影响,壳幔结构复杂.深入了解华南地区深部地幔流模式和地幔各向异性特征是认识华南复杂的深部构造演化过程与动力学机制的基础.本文采用三维全球地幔对流模型,从软流圈剪切变形的角度计算了软流圈的各向异性,尝试探讨了华南地区各向异性的起源和深部地幔流特征.华南地块东部,软流圈各向异性呈NW-SE向,各向异性主要来源于软流圈,壳幔具有垂直连贯的变形特征;南北构造带的中段,软流圈各向异性大致为N-S向,这一区域的造山作用虽然对岩石圈造成了巨大变形,但是并未显著影响软流圈变形,并且各向异性的主要来源可能是岩石圈地幔;在南北构造带中,30°N可能是地幔各向异性的过渡带,30°N以南的川滇地区,软流圈各向异性的方向出现了环形特征;菲律宾板块向欧亚板块下的俯冲到达地幔转换带,这种俯冲可能带动了西太平洋地幔向华南块体下的流动;华南地区的软流圈流场自西向东显示出顺时针旋转的特征,并在扬子板块东部与来自菲律宾板块下的西南向的地幔流相遇. 相似文献
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西太平洋俯冲带对中国东部构造的影响 总被引：5，自引：1，他引：5
本文在对西太平洋海沟—岛弧—弧后体系与中国东部中新生代构造进行对比的基础上,分析了大洋板块俯冲对大陆构造影响的几个不同阶段。始新世太平洋板块运动方向的改变影响了中国东部的应力场,使左旋剪切变为右旋。中新世前后海沟东撤之后,俯冲对华北的影响变小了。虽然诱发对流消亡了,过剩的重力势引起了地幔物质由洋向陆的侧向流动。蠕变流的数值模拟结果表明中国东部引张与挤压交替的格局是地幔侧向流动的结果。西北太平洋地区的地震旋回可能与这样一种流动的周期性有关。 相似文献
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本文通过地震层析成像研究获得了华北克拉通及其东邻地区（30°N-50°N,95°E -145°E）1°×1°的P波速度扰动图像.结果显示,在西太平洋俯冲带地区,上地幔中西倾的板片状高速异常体与其上方的低速异常区构成俯冲带与上覆地幔楔的典型速度结构式样.俯冲板片高速体在约300~400 km深度范围内被低速物质充填,暗示俯冲板片可能发生了断离.在华北克拉通地区的上地幔中发现三个东倾排列的高速异常带.在此基础上,本文构建了华北克拉通及其东邻西太平洋活动大陆边缘地区的上地幔速度结构模式图,并据此探讨克拉通岩石圈减薄与西太平洋活动大陆边缘的深部动力学联系.本文认为,太平洋板片的俯冲（断离）,触发热地幔物质上涌并在上覆地幔楔中形成对流,使克拉通岩石圈受到改造（底侵与弱化）.随着俯冲板片后撤,地幔楔中的对流场以及对岩石圈改造的影响范围均随之东移,最终导致华北克拉通岩石圈自下而上、从西向东分三个阶段依次拆沉减薄.这一模式能很好地解释现今克拉通岩石圈自西向东呈台阶状减薄的深部现象. 相似文献
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西太平洋地壳年龄较老,因而岩石层较冷和比重较大,俯冲带的角度也较大,活动和成熟的弧后盆地则较多;条件与之相反的东太平洋弧后盆地则较少.本文探讨这种相关关系的力学成因,计算了俯冲板块诱生的弧后上涌地幔流动.计算表明,俯冲角度大及存在后撤俯冲时,有利于在弧后地区产生明显的上涌地幔流,这种深部热物质的上涌会导致弧后扩张.反之,年龄较轻的海洋地块较热和较轻,俯冲角度一般也较小,不易诱生上涌地幔物质流动和弧后扩张.大陆地壳密度小于地幔物质,大陆碰撞区就更不具备弧后扩张的条件. 相似文献
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Introduction Northeastem China has the most strong Cenozoic volcanism in China (Liu, 1999), where dis-tributes more than 500 Cenozoic volcanoes, including sleeping volcanoes of Tianchi Lake (Celes-tial Pond) of Changbai Mountain, and Wudalianchi (Five linked Lakes) (LIU, 1999). Vo lcano ofTianchi Lake of Changbai Mountain consists of basaltic rocks of shield-forming stage andtrachytes and pantellerites in cone-forming stage. It is suggested by study of REE, incompatibleelements a… 相似文献
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There are three cases of variation of trench location possible to occur during subduction: trench fixed, trench advancing,
and trench retreating. Retreat of trench may lead to back-arc extension. The Pacific plate subducts at low angle beneath the
Eurasia plate, tomographic results indicate that the subducted Pacific slab does not penetrate the 670 km discontinuity, instead,
it is lying flat above the interface. The flattening occurred about 28 Ma ago. Geodynamic computation suggests: when the frontier
of the subducted slab reaches the phase boundary of lower and upper mantle, it may be hindered and turn flat lying above the
boundary, facilitates the retreat of trench and back-arc extension. Volcanism in northeastern China is likely a product of
such retreat of subduction, far field back-arc extension, and melting due to reduce of pressure while mantle upwelling.
Foundation item: National Natural Science Foundation of China (40234042 and 40174027). 相似文献
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以GPS观测资料和地震学研究成果为约束，针对不同流变参数的中国大陆岩石圈模型，数值模拟了岩石粘度与中国大陆板块边界作用强度的关系，探讨了陆-陆碰撞对中国大陆分层岩石圈运动的驱动机制．给出了陆-陆碰撞驱动力、附加地形与山根浮力及热浮力对中国大陆构造运动的驱动特点．印度板块、太平洋板块和菲律宾板块对中国大陆驱动的边界作用强度之比约是4：1．25：1，所引起的水平主压应力主要集中在坚硬岩石层；而附加地形等垂直方向作用力在水平方向产生的最大主压应力则主要集中在软弱岩石层．这种垂直方向上的作用力在高原南部地区阻碍陆-陆碰撞向北的推挤运动，在高原东北部增加对其它块体的推挤作用。 相似文献
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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
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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
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Satoru Honda 《Earth and Planetary Science Letters》2009,277(1-2):112-122
A simple kinematic-dynamic model of mantle flow around the slab-edge is constructed in order to understand the flow complexity there. The flow velocity on the top and the small boundary region around the shallow plate boundary is kinematically imposed in order to achieve a subduction-like feature and the flow in other part is dynamically calculated. The geometry of the plate mimics the region around the junction of Aleutian Islands and Kamchatka, that are examples of the convergent-transform fault plate boundaries. In a simple model in which the overlying plate is almost stationary, the lateral flow from the mantle under the subducting slab to the mantle under the neighboring plate is of minor importance, once the slab penetrates into the high viscosity layer where the downward flow encounters the resistance. Similar situation was found when the trench is advancing, that is, the trench moves toward the overlying plate. For the case with retreating trench, that is, the trench moves toward the subducting plate, a lateral flow exists even after the slab penetrates into the high viscosity layer, although its magnitude is significantly smaller than that of the plate velocity. The presence of a low viscosity layer just beneath the subducting plate may promote the emergence of lateral flow. A significant lateral flow is observed when the high temperature anomaly, that is, buoyant and low viscosity block carried by the movement of subducting plate, approaches the slab. These results may have important implications for the possible existence of trench parallel flow in the sub-slab mantle. 相似文献
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中国东北地区处于古亚洲构造域、蒙古—鄂霍茨克构造域和环太平洋构造域叠加作用最为显著的地区,是地学研究的热点区域.为了探析欧亚大陆下西太平洋板片的俯冲形态以及揭示该区域深部地球动力学机制,利用卫星重力数据通过预处理共轭梯度快速密度反演算法获得了包含东北地区、华北部分地区及日本海海域在内的研究区域上地幔三维密度结构,结合天然地震三维层析成像结果共同揭示太平洋板片的俯冲形态和深部动力机制.俯冲的太平洋板片在日本海沟处呈高密度异常,向西横向持续扩张,深度方向上有逐渐增加趋势.不连续的高密度体俯冲至地幔转换带(410～660km)后继续水平西向俯冲,部分滞留板片可能进入下地幔;在大兴安岭断裂带下面转换带中同样发现水平分布的高密度体,推断是大兴安岭断裂带下方地幔岩石圈拆沉的结果,横向不均匀分布的俯冲板片边缘已抵至大兴安岭造山带附近,这对于研究东北地区深部动力学机制具有重要的意义. 相似文献
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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