板块俯冲动力学模拟及特征分析

发布时间：2018-04-28 10:51

本文选题：板块俯冲 + 地幔对流　；参考：《武汉大学》2016年博士论文

【摘要】：为了深入研究板块俯冲对重大地震事件、火山活动等区域性地质现象的深远影响,板块俯冲的动力学过程模拟已经发展成为地球科学的一个重要研究方向。本文运用二维数值模拟技术研究板块俯冲动力学与地幔对流的耦合作用,模拟不同俯冲模型的板块俯冲动力学过程,分析板块俯冲动力学演化的影响因素,探讨关键参数对于与板块俯冲相关的弧后变形及中深源地震等地质现象的影响,提炼西太平洋俯冲板块的俯冲动力学特征,解释西太平洋主要俯冲板块的俯冲形态及有关的地质现象。论文的主要工作和成果概括如下：利用有限差分方法,计算了全地幔对流模式和双层地幔对流模式下日本海沟俯冲板块热结构、浮力及P波速度异常分布,基于亚稳态橄榄石相变模型推测亚稳态橄榄石的存在范围。结果表明,双层地幔对流模式下模拟的P波速度异常分布与层析成像结果更为相符,也与深源地震的分布有较好的相关性。俯冲板块所受负浮力在400 km深度附近达到最大值,亚稳态橄榄石的存在使负浮力逐渐减小,甚至在板块内部产生正浮力,不利于俯冲板块穿透660 km间断面。运用Underworld 1.7数值模拟软件,探讨了全动力学俯冲模型和运动学-动力学俯冲模型的板块热结构与黏度演化、板块俯冲过程中的应力分布与地幔对流特征等。研究结果表明,在上下地幔密度差异的作用下,全动力学模型的板块俯冲表现为非稳定的俯冲过程,与新生代板块运动观测结果较为相符。上覆板块的应力状态在弧前和弧后区域表现出不同的变化特征,主要与上覆板块与俯冲板块的相互作用及上覆板块底部地幔流动有关。在板块的俯冲作用下,地幔中呈现出较为复杂的地幔对流模式,其变化对于板块俯冲形态及浅部的应力状态都有较大的影响。基于全动力学俯冲模型,讨论了不同参数对板块俯冲动力学的影响。模拟结果表明,当上下地幔密度差异或黏度差异较大时,在海沟后撤的作用下,板块能够形成平卧于660 km间断面之上的俯冲形态,但板块在黏度差异作用下俯冲过程趋于稳定。板块在俯冲至上下地幔交界面之前的俯冲倾角与板块强度及上覆板块的年龄有关。当板块俯冲至下地幔后,板块的俯冲倾角主要取决于海沟后撤的速度。俯冲板块的板块年龄对俯冲动力学的影响相对较小。上覆板块弧前区域均为挤压应力状态,而弧后区域的应力呈现出持续的拉伸应力作用或出现由拉伸应力向挤压应力的转变,与上覆板块年龄、海沟的运动模式及上覆板块底部的地幔流向有关。分析总结了板块俯冲的动力学特征,结合西太平洋俯冲板块的具体情况,针对西太平洋上较为典型的俯冲板块,对其俯冲形态、弧后变形及中深源地震成因给出了一定的解释。结果表明,700℃等温线深度与板块俯冲速率(或汇聚速率)呈现出一种对数增加的变化关系,俯冲板块上的深源地震可能是由于板块内部温度过低而发生橄榄石的亚稳态相变引起的。板块在抗弯作用下的应力状态与俯冲板块上所观测到的大多数双地震带分布范围及其震源机制有较好的一致性,因而能够较为合理的解释发生在俯冲板块上的中源地震,特别是双地震带的形成机制。西太平洋俯冲板块上不同的俯冲形态与海沟的后撤和推进作用有关。该区域弧后变形的间歇性变化是海沟运动、上覆板块年龄及大范围的地质构造活动共同作用的结果。
[Abstract]:In order to further study the profound influence of plate subduction on major seismic events, volcanic activity and other regional geological phenomena, the simulation of the dynamic process of plate subduction has become an important research direction of earth science. In this paper, the coupling effect of plate subduction and mantle convection is studied by two dimensional numerical simulation. The dynamic evolution process of plate subduction in different subduction models is used to analyze the influence factors of plate subduction dynamics, and to discuss the influence of key parameters on the geological phenomena such as post arc deformation and middle deep source earthquake related to plate subduction, to extract the subduction dynamics of the subduction plate of the Western Pacific, and to explain the subduction of the main subduction plates in the Western Pacific. The main work and results of this paper are summarized as follows: using the finite difference method, the thermal structure, buoyancy and P wave velocity of the subduction plate of the subduction plate of the Japanese trench under the full mantle convection model and the double mantle convection model are calculated. Based on the metastable olivan phase transformation model, the existence of the metastable olivine is speculated. The results show that the anomalous distribution of the P wave velocity simulated under the double layer mantle convection model is more consistent with the results of the tomography, and has a good correlation with the distribution of deep source earthquakes. The negative buoyancy under the subduction plate reaches the maximum near the depth of 400 km, the metastable olivine is deposited and the negative buoyancy is gradually reduced, even within the plate. The positive buoyancy can not help the subduction plate penetrate the 660 km cross section. Using the Underworld 1.7 numerical simulation software, the plate thermal structure and viscosity evolution of the fully dynamic subduction model and the kinematic dive model, the stress distribution and the mantle flow characteristics during the plate subduction are discussed. The results show that the upper and lower mantle density is close to the lower mantle. Under the action of the degree difference, the plate subduction of the fully dynamic model is an unstable subduction process, which is more consistent with the results of the Cenozoic plate motion observation. The stress state of the overlying plate shows different changes in the pre arc and back arc regions, mainly with the interaction between the overlying plate and the subducted plate and the bottom mantle of the overlying plate. Flow is related. Under the subduction of the plate, the mantle convection model is more complex in the mantle. The change has great influence on the plate subduction form and the shallow stress state. Based on the full dynamic subduction model, the influence of the different parameters on the plate subduction dynamics is discussed. The simulation results show that the upper and lower mantle density is shown. When the difference or viscosity varies greatly, the plate can form a subduction form above the 660 km cross section under the action of the trench, but the subduction process tends to stabilize under the effect of the viscosity difference. The subduction angle of the plate before subduction to the upper mantle interface is related to the strength of the plate and the age of the overlying plate. The subduction and dip angle of the plate mainly depends on the retreating velocity of the trench. The plate age of the subduction plate has a relatively small influence on the subduction dynamics. The pre arc region of the overlying plate is the state of extrusion stress, while the stress in the back arc region presents a continuous tensile stress or the transition from tensile stress to extrusion stress. The variation is related to the age of the overlying plate, the movement pattern of the trench and the mantle flow in the bottom of the overlying plate. The dynamic characteristics of the plate subduction are analyzed and summarized. The subduction plate, which is a typical subduction plate on the Western Pacific, has been given to the subduction form, the post arc deformation and the middle deep source earthquake. The results show that the depth of the isotherm at 700 C is associated with a logarithmic increase in the plate subduction rate (or convergence rate). The deep source earthquake on the subduction plate may be caused by the metastable phase transition of olivine due to the low temperature in the plate. The stress state of the plate and the subduction plate under the bending of the plate The distribution of most of the double seismic belts and its source mechanism have good consistency, so it is able to reasonably explain the middle source earthquakes occurring on the subduction plate, especially the formation mechanism of the double seismic belts. The different subduction forms on the subduction plate of the Western Pacific are related to the withdrawal and propulsion of the trenches. The intermittent change of post arc deformation is the result of the trench movement, the age of overlying plate and the large-scale tectonic movement.

【学位授予单位】：武汉大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P542

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