Collaborative Research: A Combined Observational and Theoretical Investigation of Thermal and Chemical Transport Subduction Zones, and the Evolution of Active Convergent...

9219434萨克斯俯冲和岩浆作用在大陆地壳生长和地壳/地幔系统演化中的作用早已得到承认，但对俯冲旋回的详细、注重过程的理解一直难以捉摸。在这个项目中，主要研究人员将把实验岩石学和地球化学、观测地震学、同位素和微量元素地球化学以及实验室对流实验与板岩和地幔楔体的热结构和大范围对流的数值方法以及弧形环境中熔体和流体迁移的多孔流模型相结合。热流和对主要来自日本弧区的地震数据的各种分析，将使用依赖于温度的粘性来约束在板块和地幔中流动的初始计算(2-D和一些3-D)中使用的热结构和流变性。为地震约束最强的日本开发的模型将被用作中美洲和喀斯喀德的基础，在那里，年轻的热板块正在俯冲，条件远未达到稳定状态。将使用来自热和对流模拟的应力场和流动场来计算板材附近的含水流体以及熔体通过地幔的输送模型。板块尺度的物质输送将来自大陆地壳、水圈和岩石圈的化学元素输送到弧形岩浆的深层来源；流体和熔体输送过程将这些元素中的一部分重新转化到地壳建造岩浆的表面。10Be(1.5 Ma半衰期)、B和U(75ka不平衡半衰期系列)等板片衍生元素将作为化学示踪剂纳入流体/熔体迁移模型，其通量、迁移路径和特征迁移时间受次传导沉积物和喷发熔岩的化学约束。对关键元素的流体分配研究将进一步保持对运移模型的输入。热、对流和输运耦合模型所作的关于熔岩沿弧长和跨弧宽的空间分布、性质和化学的预测将与观测值进行比较，并根据观测到的俯冲参数在弧间的变化进行评估，以得出俯冲循环及其在地壳增长和地幔演化中的作用的综合模型。***

9219434 Sacks The role of subduction and magmatism in the growth of the continental crust and the evolution of the crust/mantle system has long been recognized, but a detailed, process-oriented under- standing of the subduction cycle has been elusive. In this project the principal investigators will combine experimental petrology and geochemistry, observational seismology, isotope and trace element geochemistry and laboratory convection experiments with numerical approaches to the thermal structure and large-scale convection of the slab and mantle wedge, and porous flow models for melt and fluid migration in the arc environment. Heat flow and various analyses of seismic data, from primarily the Japan arc, will constrain the thermal structure and rheological properties used in the initial calculations (2-D and some 3-D) of flow in the slab and mantle, using a temperature-dependent viscosity. Models developed for Japan, where seismic constraints are strongest, will be used as a base for Central America and for the Cascades, where a young hot plate is subducting and conditions are far from steady state. Models for transport of hydrous fluids in the vicinity of the slab, and of melts through the mantle will be calculated using the stress and flow fields from the thermal and convection modeling. Plate scale mass transport delivers chemical elements derived from the continental crust, hydrosphere and lithosphere to the deep source of arc magmas; fluid and melt transport processes translate some fraction of these elements back to the surface in crust building magmas. Documentably slab-derived elements such as 10Be (1.5 Ma half-life), B and U (75 ka half-life in disequilibria series) will be incorporated as chemical tracers in fluid/melt migration models, with fluxes, transport paths and characteristic transport times constrained from chemistry of subconducting sediments and erupting lavas. Fluid partitioning studies on key elements will further const rain input to migration models. Predictions from coupled thermal, convection and transport models regarding spatial distribution, character and chemistry of lavas along the length and across the width of arcs will be compared with observed values, and evaluated against observed variations in subduction parameters from arc to arc to arrive at an integrated model of the subduction cycle and its role in crustal growth and evolution of the mantle. ***