大洋俯冲和大陆碰撞模式的数值模拟研究

发布时间：2018-04-22 17:04

  本文选题：大洋俯冲 + 板片倾角　； 参考：《中国科学院研究生院(广州地球化学研究所)》2016年博士论文

【摘要】：本文选择大洋俯冲和大陆碰撞的动力学演化过程作为主题,利用系统的数值模拟实验深入分析了各主要动力学参数如何影响大洋板片倾角及大陆俯冲模式。通过研究将影响大洋俯冲动力学过程的参数分为与俯冲大洋板片浮力相关、与板间耦合作用相关、与洋-陆汇聚速率相关和与俯冲带流变性质相关等四类。而板片正浮力作用(例如年轻大洋或增厚洋壳的俯冲)、俯冲板块和上覆板块之间的强耦合作用(例如低的初始俯冲角度或厚的上覆大陆岩石圈)、较高的上覆大陆向洋的绝对逆冲速率和大洋绝对俯冲速率之比以及有利于板片弯折的俯冲带流变性质等都是造成大洋低角度俯冲的有利因素。模拟结果表明,并不存与平板俯冲发育呈充分必要关系的特定参数条件。平板俯冲的发生与否不能归功于某一个或是某一类参数的单独作用,而往往与多类因素多个参数的共同作用相关。大洋平板俯冲的发生必须要满足一些“异常”的动力学条件,而这很可能就是平板俯冲难以产生的主要原因。结合模型实验结果和现今平俯冲区域的统计资料,我们认为由年轻的或含增厚洋壳的大洋俯冲所导致的俯冲板片正浮力作用是导致大洋平板俯冲的主导因素,其它因素也会在大洋俯冲过程中进一步促进平板俯冲发生。通过力学分析方法,俯冲板片的几何形态在力学本质上受控于板片重力矩和吸力矩的合力矩大小和方向,通过调节板片重力矩或吸力矩的大小最终影响大洋俯冲型式。基于模型中俯冲大陆板片的演化特征,将大陆俯冲分为大陆稳定俯冲和大陆非稳定俯冲。大陆稳定俯冲表现为俯冲至软流圈深度的大陆板片仍能保持较高流变强度而以特定角度持续俯冲至地幔深部;根据大陆板片倾角,又可进一步分为大陆陡俯冲和大陆平俯冲两个亚类。而在大陆非稳定俯冲中,大陆板片不能保持其几何和力学完整性,碰撞区域的重力不稳定受控于俯冲大陆板片断离或增厚岩石圈拆沉。根据俯冲大陆板片的形变特征,大陆非稳定俯冲表现为“多阶段断离”、“持续性流入”和“大规模拆沉”三种类型。模型实验表明,中-高速大陆汇聚和低-中温岩石圈热结构有利于大陆稳定俯冲的产生,而具体发育何种类型(大陆陡俯冲或平俯冲)则主要由大陆地壳的流变性质控制。大陆非稳定俯冲的三种不同类型(“多阶段断离”、“持续性流入”和“大规模拆沉”)分别与低汇聚速率、中-高速汇聚下的岩石圈高温热结构和低汇聚速率下的中等-高流变强度地壳有关。对于具中等-高流变强度地壳的大陆岩石圈发生非稳定俯冲时,无论分几个演化阶段以及前期演化阶段的类型如何,一般都会以碰撞区域增厚岩石圈地幔的大规模拆沉终止。大陆平俯冲型式的发育必须满足两个条件:高地壳流变强度和高速俯冲,两者缺一不可。高地壳流变强度一方面增加随大陆岩石圈地幔进入俯冲通道乃至软流圈的地壳体积,减小大陆板片的平均密度;另一方面提高大陆板片的整体流变强度,两方面的共同作用有利于大陆平俯冲的产生。大陆高速俯冲减少大陆板片在软流圈浅部的滞留时间,减弱大陆板片在软流圈内的热传导增温效应,从而使板片保持相对高的流变强度而有利于大陆平俯冲产生。针对印度-亚洲碰撞的模型实验结果表明,要造成上覆亚洲大陆的强烈缩短变形以及现今青藏高原造山带的岩石圈结构,上覆亚洲大陆相对较低的地壳流变强度和相对高温的岩石圈热状态是其必要条件。基于模型实验结果,识别出了两种不同的大陆平俯冲型式:第一种型式是俯冲大陆岩石圈直接垫置于上覆大陆岩石圈地幔之下,第二种型式是俯冲大陆岩石圈直接垫置于上覆大陆地壳之下。前者需要俯冲侧和上覆侧大陆都具较高的流变强度,后者要求上覆大陆具备比俯冲大陆低的流变强度。但不论是何种类型,都需要俯冲大陆具较高流变强度和较高俯冲速率。藏南动力学演化的数值模拟研究表明,该地区大陆动力学演化过程与第二种大陆平俯冲型式类似。印度大陆的持续向北俯冲促使亚洲大陆岩石圈地幔逐渐与上部地壳发生拆离并进入软流圈内,最终导致在藏南地区印度大陆直接垫置于亚洲大陆地壳之下。此过程伴随青藏高原造山带区域的中下地壳软弱层的广泛发育、碰撞区域内异常厚地壳的形成以及由深埋印度地壳物质重熔溢出而导致的高喜马拉雅地体内强烈岩浆作用,这些在第二类模型演化过程中都能得到体现。另外,综合多方面模型实验结果,我们推测喜马拉雅造山带东西向岩石圈结构差异可能由多种因素造成,包括印度大陆力学性质差异性、亚洲大陆温度场差异性、印度与亚洲初始碰撞时的聚速率差异性以及青藏北缘岩石圈结构差异性等。
[Abstract]:In this paper, the dynamic evolution process of ocean subduction and continental collision is chosen as the theme, and the numerical simulation experiments of the system are used to analyze how the main dynamic parameters affect the dip angle of Ocean plate and the continental subduction mode. It is related to the interplate coupling, related to the oceanic and continental convergence rate and the relationship with the rheological properties of the subduction zone, which are related to four types. The plate positive buoyancy (such as the subduction of the young ocean or thickened oceanic crust), the strong coupling between the subducted and overlying plates (such as low initial subduction angle or thick overlying continental lithosphere), higher overlying The absolute thrust rate of the continent and the ratio of the absolute subduction rate of the ocean and the rheological properties of the subduction zone, which benefit the bending of the plate, are all favorable factors for the low angle subduction of the ocean. It is often related to the interaction of a number of parameters in one or a certain class of parameters. The occurrence of an ocean plate subduction must satisfy some "abnormal" dynamic conditions, which is probably the main reason for the difficulty of the flat subduction. We believe that the positive buoyancy of the subduction plate caused by the young or thickened oceanic subduction is the leading factor in the subduction of the ocean plate, and the other factors will further promote the subduction of the plate in the process of ocean subduction. The geometric form of the subduction plate is in the mechanical nature by the mechanical analysis. The size and direction of the resultant force moment controlled by the plate heavy moment and the suction moment will affect the ocean subduction pattern by adjusting the plate gravitational torque or the suction moment. Based on the evolution characteristics of the subduction continental plate in the model, the continental subduction is divided into continental stable subduction and continental unstable subduction. The continental stable subduction is manifested by subduction to soft subduction. The continental plates with the depth of the flow still maintain high rheological strength and continue to subduction to the deep mantle in a particular angle. According to the dip angle of the continental plate, they can be further divided into two subsubduction subduction subduction and continental subduction. In the non stable subduction of the continent, the continental plate can not hold its geometric and mechanical integrity, the gravity of the collision region. The instability of the continental plate is controlled by the deformation characteristics of the subducted continental plate. The unstable subduction of the continent is characterized by three types of "multi stage disconnection", "continuous inflow" and "large scale disintegration". The model experiments show that the thermal structure of middle and high speed large land convergence and low middle temperature lithosphere is beneficial to the model. The formation of the continental stable subduction, and what type of specific development (Continental steep subduction or flat subduction) is controlled mainly by the rheological properties of the continental crust. Three different types of continental unstable subduction ("multi stage disconnection", "continuous inflow" and "mass delamination") and low convergence rate respectively, and the lithosphere under middle and high speed convergence. During the unstable subduction of the continental lithosphere with moderate to high rheological strength, the high temperature thermal structure and the low convergence rate are related to the crust of the continental lithosphere with medium high rheological strength. The development of the terrestrial subduction type must meet two conditions: the rheological strength of the highland shell and the high speed subduction, both of which are indispensable. The rheological strength of the highland shell increases with the continental lithosphere mantle entering the subduction channel and the soft flow circle, and reduces the average density of the continental plate, on the other hand, the overall rheological strength of the continental plate is improved. The common effect of the two aspects is beneficial to the emergence of the continental flat subduction. The continental high speed subduction reduces the retention time of the continental plate in the shallow part of the asthenosphere and reduces the heat transfer effect of the continental plates in the asthenosphere, thus making the plates relatively high in rheological strength and is beneficial to the horizontal subduction of the mainland. The India Asian collision The results of the model experiment show that, in order to cause the strong shortening of the overlying Asian continent and the lithosphere structure of the present orogenic belt of the Qinghai Tibet Plateau, the relatively low crust rheology intensity and the relatively high temperature of the lithosphere are the necessary conditions to overlay the Asia continent. Based on the experimental results, two different continental subductions have been identified. Type 1: the first type is subducted continental lithosphere under the overlying continental lithosphere mantle, and the second type is subducted continental lithosphere under the overlying continental crust. The former needs both the subduction side and the overlying continent with high rheological strength, and the latter requires the overlying continent to have a lower rheology than the subduction continent. The dynamic evolution of Zangnan's continental dynamics is similar to that of second types of continental subduction. The continuous northward subduction of the mainland of India has led to the gradual and upper mantle of the lithosphere in the Asian continent. The crustal crust is detached and entered into the asthenosphere, which eventually leads to the direct cushion of the India continent in the Zangnan region under the continental crust of the Asian continent. This process is accompanied by the extensive development of the weak layer of the middle and lower crust in the Tibetan Plateau orogenic zone, the formation of the abnormal thick crust in the collision area and the overflow of the crust material remelting of the deep buried India. The strong magmatism in the high Himalaya area can be reflected in the evolution of the second types of models. In addition, we speculate that the structural differences in the East-West lithosphere in the Himalaya orogenic belt may be caused by a variety of factors, including the differences in the mechanical properties of the mainland of India and the temperature field in the Asian continent. The difference is the convergence rate of initial collision between India and Asia and the difference of lithospheric structure in the northern margin of Qinghai Tibet Plateau.

【学位授予单位】：中国科学院研究生院(广州地球化学研究所)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P542
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本文编号：1788123