陆壳熔融与流变的数值模拟及其地质约束研究

发布时间：2018-06-14 07:54

本文选题：陆壳熔融 + 岩石流变　；参考：《吉林大学》2017年博士论文

【摘要】：地壳内部过程的不可观测性,是诸多重大地质问题长期争论的根本原因,陆壳熔融及其流变机制问题即为其中之一。数值模拟技术与超级计算技术的发展,为地壳内部地质过程,包括花岗岩形成过程的数字重建提供了可能性。由于花岗岩“深熔-侵入”模型的数值模拟,已进行过大量研究,本论文拟在“深熔-对流”地质模型的基础上,借助大型模拟软件Underworld和天河2号超级计算机,对花岗岩形成的热动力过程,以及这一过程引起的地壳变形效应,开展进行数值模拟研究。论文选题不但对于花岗岩形成过程的数字重建有重要意义,更是大数据时代的地质学研究走向量化过程的重要一环。为了解部分熔融岩石的流变行为,作者在综合分析各种岩石在部分熔融过程中的强度变化与熔体分数关系的实验数据的基础上,提出研究陆壳深熔作用应使用岩石“综合强度”的认识。在此基础上,重新厘定已知的“熔体连通转换”(MCT)和“固-液转换”(SLT)所对应的熔体分数(MF),同时发现在MF=25%处,岩石综合强度存在显著突降,并将其命名为“框架熔融转换”(FMT)。、通过对粤西福湖岭混合岩-混合花岗岩剖面的实地测量和室内计算处理,获得了该剖面各种混合岩和混合花岗岩的浅色体比例。实验资料分析获知的岩石流变行为,与福湖岭剖面的地质资料结合,实现了实验结果与地质观察之间的双向约束。在此基础上,建立了受流变转换点SLT约束的岩石熔融过程的数学表达,并据此对“深熔-对流”地质模型描述的壳内熔融过程及其引起的效应进行数值模拟,以验证模型的可能性和普适性。本次研究获得的主要结论如下:(1).岩石在熔融过程中,其综合强度在固、液相线之间存在三个突降点或流变转换点,即MCT、FMT和SLT,三者对应的熔体分数百分比分别为8%,25%和40%;(2).通过实验流变转换点与粤西福湖岭混合岩-花岗岩野外剖面的对比研究发现,在地壳熔融过程中,MCT是粒间熔体从岩石孔隙空间向面理(层理、片理等)空间转移的标志,它导致部分熔融岩石原岩结构转变为层状或条带状结构;FMT标志部分熔融岩石的固体框架从压缩到熔融的转换,化学上标志岩石熔融从易熔组份到难熔组份的转换;SLT是岩石固体框架解体,即岩石的整体状态从固态到液态(岩浆)转换的标志。在地壳岩石部分熔融(深熔)过程中,SLT所处深度之下的硅铝质陆壳,应该存在层状花岗岩浆,而不是连续成层的硅铝质岩石;(3).上部陆壳熔融过程的数值模拟结果,揭示SLT之下岩浆对流作用的存在,且对流作用可导致陆壳熔融层不断增厚;岩浆对流速度依赖于模型底部边界温度,底部边界温度739.6℃是岩浆对流作用发生的必要条件;线性底部边界温度,可导致岩浆对流作用从独立涡流向整体环流发展;(4).岩浆流动对盖层岩石的拖曳作用,不但引起了陆壳熔融层顶部界面波动起伏,而且导致了盖层出现挤压与拉张相间的水平应力环境。前者反映盖层变形对岩浆流动的响应,后者说明固体盖层水平应力变化,可以是熔融层内岩浆对流的结果而不一定是引起岩浆流动的原因;模拟结果表明对流岩浆的侧向流动与盖层之间的剪切作用,可引起熔融层之上部分熔融岩石的变形,揭示了部分熔融岩石的变形作用,可以单纯起因于岩浆流动而不一定需要区域构造动力;(5).对含熔融层的地壳挤压过程的数值模拟,揭示岩浆流体在各方向上的速度差异可引起盖层的不均匀变形,熔融层顶界面的起伏与地面起伏存在同向关系;揭示了“深熔-对流”地质模型有关花岗岩和混合岩穹隆或背斜的形成机理;(6).数值模拟结果证实“深熔-对流”地质模型符合物理学的基本规律,对于相关地质现象的解释具有普适性。
[Abstract]:The unobservability of the internal process in the crust is the fundamental reason for the long argument of many major geological problems. The problem of the continental crust melting and its rheological mechanism is one of them. The development of the numerical simulation technology and super computing technology provides the possibility for the digital reconstruction of the internal geological process of the crust, including the granitic formation process. The numerical simulation of the rock "deep penetration intrusion" model has been studied. On the basis of the "deep melting and convection" geological model, this paper is to carry out numerical simulation of the thermal dynamic process of granite formation and the crustal deformation effect caused by this process on the basis of the "deep melt convection" geological model, with the aid of large simulation software Underworld and Tianhe No. 2 supercomputer. Research is important not only for the digital reconstruction of granite formation, but also an important part of the quantitative process of geological research in the era of large data. In order to understand the rheological behavior of some molten rocks, the author analyzes the relationship between the intensity changes and the melt fraction of various rocks in the partial melting process. On the basis of the data, the understanding of the "comprehensive strength" of the rock should be used to study the "comprehensive strength" of the rock. On this basis, the known melt fraction (MF) corresponding to the known "MCT" and "solid liquid conversion" (SLT) is redefined. At the same time, it is found that at the MF=25%, the comprehensive strength of the rock has a significant drop, and it is named as the rock. "Frame melting conversion" (FMT). Through field measurement and indoor calculation of the Fuhu ridge mixed granite mixed granite section in western Guangdong Province, the proportion of different mixed rocks and mixed granites in this section is obtained. The rheological behavior of the rocks and the geological data of the Fuhu ridge section are combined with the experimental data to realize the experimental knot. On this basis, the mathematical expression of the process of rock melting under the constraints of the rheological transition point SLT is established, and a numerical simulation of the inner shell melting process and its effect on the "deep melt convection" geological model is carried out to verify the possibility and universality of the model. The main conclusions are as follows: (1) during the melting process of the rock, the comprehensive strength of the rock is solid, and there are three drop points or rheological transition points between the liquidus, that is, MCT, FMT and SLT, the percentage of the corresponding melt fraction of the three are 8%, 25% and 40%, respectively, (2). It is found that in the process of crustal melting, MCT is a symbol of the spatial transfer of intergranular melt from the pore space to the surface (bedding, cleavage, etc.), which leads to the transformation of the protolith structure of partially molten rock into layered or strip structure, and the solid frame of the part of the molten rock from FMT marks the transition from compression to melting, chemically marking the melting of rocks from the melt. The conversion of components to refractory components; SLT is a sign of rock solid framework disintegration, that is, the whole state of rock from solid to liquid (Yan Jiang) conversion. In the process of partial melting (deep melting) of the crustal rocks, the silicalite crust under the depth of SLT should exist in layered granite, rather than a continuous layer of aluminosilicate; (3) upper land. The numerical simulation of the process of shell melting reveals the existence of magma convection under SLT, and the convection can cause the thickening of the continental crust melting layer, and the convection velocity of the magma depends on the bottom boundary temperature of the model. The temperature of the bottom boundary is 739.6 C as a necessary condition for the convection of the magma, and the linear bottom boundary temperature can lead to the convection of the magma. The action of the action from the independent vortex flow to the overall circulation; (4) the drag of the magma flow to the caprock rocks not only causes the fluctuation of the interface fluctuation at the top of the crust melting layer, but also leads to the horizontal stress environment of the cover layer between the extruding and stretching phases. The former reflects the response of the cover deformation to the flow of the rock slurry, and the latter indicates that the level of the solid cover should be horizontal. The change of force can be the result of magmatic convection in the molten layer and not necessarily the cause of the flow of magma. The simulation results show that the shear action between the lateral flow of the convective magma and the cover can cause the deformation of the partially molten rock above the molten layer, revealing the deformation of the partially molten rock, and can be simply caused by the flow of magma. It does not necessarily need regional tectonic dynamics; (5) the numerical simulation of the crustal extrusion process containing the molten layer reveals that the difference in the velocity of the magmatic fluid in all directions can cause the uneven deformation of the cover layer, the undulation of the top interface of the melting layer and the ground fluctuation, and reveals that the "deep melting convection" geological model is related to the granite and mixing. The formation mechanism of the rock dome or anticline; (6) the results of numerical simulation confirm that the "deep melting convection" geological model accords with the basic laws of physics, and it is universally suitable for the interpretation of related geological phenomena.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P542

【相似文献】