Three-Dimensional Modeling of Continental Subduction and the Evolution of Ultra High Pressure Metamorphism

该项目通过整合大陆俯冲和碰撞中物质的构造/岩石学演化的数值模拟，研究与大陆俯冲和超高压变质作用相关的驱动力和物质行为。挪威西部片麻岩的天然超高压和高压组合为建模提供了流变学、几何和地质年代学信息，而新西兰中部的活动斜辐合板块边界则是碰撞-俯冲过渡的现代模拟。大陆俯冲带是地壳-地幔相互作用从接近水平向以垂直为主转变的区域，突出了大陆演化过程中体力和粘性力的竞争影响。因此，这些带包含了关于控制大陆构造的基本驱动力和物质行为的丰富信息。挪威西部的超高压推覆带是少数几个穿越了大陆俯冲的脏器，并逃脱了后来事件的完全矿物学覆盖和构造肢解的地形之一。因此，它们可以提供碰撞时达到的深度和温度的基本信息，地壳物质在地幔运动传递到地壳时的瞬态流变行为，以及物质通过碰撞造山带的空间轨迹。这些特征确定了碰撞过程连贯力学建模所需的基本约束。在这些观测的条件下，斜向辐合的地球动力学模型提供了造山带范围内的速度和应变速率，并确定了斜向俯冲内应变分配的特征长度尺度。目前正在发展与实地结构观测重叠的比尺的运动学描述，将大比尺动态模型与露头水平上的观测联系起来。研究小组正在将这些数据集整合到大陆俯冲的三维动态和运动学模型中，该模型能够描述粒子的力学、变质和热演化的历史。由于研究人员同时解决了热量和物质流动模式，因此可以跟踪整个俯冲过程中物质的压力-温度和时间历史。这将提供与自然岩石学比较的模型粒子历史。

This project investigates driving forces and material behavior associated with continental subduction and ultra high-pressure metamorphism through an integration of numerical modeling of continental subduction and structural/petrological evolution of the material caught in the collision. The natural ultra high-pressure and high-pressure assemblages of the Western Gneiss of Norway provide rheological, geometric and geochronological information for the modeling, while the active obliquely convergent plate boundary of central New Zealand serves as a modern analog of a collision-subduction transition. Continental subduction zones represent regions where the crust-mantle interaction changes from nearly horizontal to dominantly vertical, accentuating the competing influences of body and viscous forces in the evolution of continents. Consequently, these zones contain a wealth of information on the basic driving forces and material behavior that control continental tectonics. The ultra high-pressure nappes of western Norway represent one of the few terrains that have traversed the viscera of continental subduction and escaped complete mineralogical overprinting and structural dismemberment of later events. Consequently, they can provide fundamental information on depth and temperature attained during collision, transient rheological behavior of crustal material where the motion in the mantle is transmitted to the crust, and on the spatial trajectories of material through a collisional orogen. These features identify the basic constraints required for coherent mechanical modeling of the collisional process. The geodynamic models of oblique convergence, conditioned by these observations, provide orogen-wide velocity and strain rates and identify the characteristic length scales of strain partitioning within oblique subduction. Kinematic descriptions at a scale that overlap with field structural observations are being developed that relate the large scale dynamic model to observations made at the level of an outcrop. The research group is integrating these data sets into a three-dimensional dynamic and kinematic model of continental subduction capable of describing particle histories as a function of mechanical, metamorphic and thermal evolution. Because the researchers solve simultaneously for thermal as well as material flow patterns, pressure- temperature and time history of material throughout the subduction process can be tracked. This will provide model particle histories for comparison with the natural petrology.