Collaborative Research: A Combined Observational and Theoretical Investigation of Thermal and Chemical Transport in Subduction Zones and the Evolution of Active Continental

小行星9219796 俯冲和岩浆作用在大陆地壳生长和壳幔系统演化中的作用早已被认识，但对俯冲旋回的详细、过程性认识一直是个谜。 在这个项目中，主要研究人员将把联合收割机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数值方法结合起来，研究板片和地幔楔的热结构和大规模对流，以及弧环境中熔体和流体迁移的多孔流动模型。 热流和各种地震数据的分析，主要来自日本弧，将限制的热结构和流变学特性中使用的初始计算（2-D和一些3-D）的流在板和地幔，使用温度依赖的粘度。 为地震限制最强的日本开发的模型将用作中美洲和喀斯喀特山脉的基础，那里有一个年轻的热板块正在俯冲，条件远非稳定状态。 在板块附近的含水流体的运输模型，并通过地幔的熔体将使用热和对流模拟的应力和流场计算。 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岩浆的深源;流体和熔体输送过程将这些元素的一部分转移回地壳建造岩浆的表面。 在流体/熔体迁移模型中，将有文献记载的板片源元素，如10 Be（1.5 Ma半衰期）、B和U（75 ka半衰期的不平衡系列）作为化学示踪剂，结合通量、输运路径和特征参数， 运输时间受到亚导电沉积物和喷发熔岩化学的限制。 对关键要素的流体分配研究将进一步限制对迁移模型的输入。 将把从热、对流和迁移耦合模型中得出的关于熔岩沿着弧长和弧宽的空间分布、特征和化学性质的预测与观测值进行比较，并根据观测到的弧与弧之间俯冲参数的变化进行评价，以得出俯冲周期及其在地壳生长和地幔演化中的作用的综合模型。 ***

9219796 Kincaid 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 con strain 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. ***