CSEDI Collaborative Research: Integrating Seismological, Rheological and Petrological Studies of Melt Production in Subduction Zones

最具爆炸性、最致命的火山喷发发生在俯冲带。它们的发生和爆炸性与水和其他挥发物向深部的输送以及它释放到热地幔或沿板块边界密切相关。然而，了解从俯冲板块释放的挥发物如何在俯冲带的地幔楔子内产生熔融仍然是一个挑战。最近在俯冲带进行的一系列地震和岩石学项目以及实验室的结果极大地增加了关于这些过程的可用信息，对这些数据的初步分析已经开始对熔融的范围和深度、熔体输送的方式和地点之间的差异作出限制。这项提议计划采取下一步，整合地球物理观测、地球化学测量和流变模型，以解决有关地幔融化过程的基本问题。我们将比较尼加拉瓜-哥斯达黎加俯冲带的最新结果，该带在地球物理和地球化学观察中显示出强烈的沿走向变化，与马里亚纳群岛的结果相比较，在马里亚纳群岛，火山从弧前到活跃的弧后扩张中心进行跨走向采样。中美洲和马里亚纳群岛的宽带成像由地震衰减和P波速度指示了一个流动的热地幔区域，从剪切波分裂测量指示了地幔组构，从Vp/VS异常指示了熔体输送的几何形状。这些结果还显示了大多数参数沿走向的明显变化，可解释为板片水化、熔体输送和地幔楔形H2O含量的变化。在这两个地区，对火山产物的广泛采样和分析首次提供了岩浆水含量的直接测量，这似乎与中美洲板岩流体/沉积物的经典指标以及马里亚纳地区离弧前的距离不同。由于我们对水和熔体存在下的地幔流变学的理解有所进展，包括实验和理论上的突破，例如在剪切条件下熔体的行为、对颗粒大小的物理控制以及熔体组构的定量参数方面的突破，这些观察结果的整合将成为可能。我们的方法将是以一致的方式整合所有数据集，然后针对它们反复测试理论预测。结果应区分熔体产生和输送的模型，例如垂直多孔流动、倾斜流动或冷底辟上升模型。一旦校准，进行这些比较所需的关系将可用于解释全球其他俯冲带和熔体产生区的结构。整合不同的观察是让广大受众理解它们的关键一步，这种整合的多学科方法将在本科生课堂和研究生研讨会上进行测试。地震观测值和热力学熔融参数之间关系的校准应得到广泛应用，并有助于加强研究基础设施。

The most explosive, deadly volcanic eruptions occur in subduction zones. Their occurrence and explosivity is intimately tied to the transport of water and other volatiles to great depth, and its release into hot mantle or along the plate boundary. Yet, understanding how volatiles released from subducting plates produce melts within the mantle wedge of subduction zones remains a challenge. A series of recent seismic and petrologic projects in subduction zones and results from the laboratory have dramatically increased the available information on these processes, and preliminary analyses of these data have begun to place bounds on the extent and depths of melting, style of melt transport, and variations between sites. This proposal plans to take the next step, the integration of geophysical observations, geochemical measurements, and rheological models, to address fundamental problems regarding melting process in the mantle. We will compare recent results from the Nicaragua-Costa Rica subduction zone, which exhibits strong along-strike variations in geophysical and geochemical observations, with those from the Marianas where volcanoes sample across-strike from the arc front to active back-arc spreading center. Broadband imaging in Central America and the Marianas indicates a region of flowing hot mantle from seismic attenuation and P-wave velocities, mantle fabric from shear-wave splitting measurements, and the geometry of melt transport from Vp/Vs anomalies. These results also show clear along-strike variations in most parameters, interpretable as variations in slab hydration, melt transport, and mantle wedge H2O content. In both regions, extensive sampling and analysis of volcanic products has provided for the first time direct measurement of magmatic water content, which appears to vary in tandem with classic indicators of slab fluid/sediment in Central America, and with distance from the arc front in the Marianas. The integration of these observations will be made possible by advances in our understanding of mantle rheology in the presence of water and melt, including both experimental and theoretical breakthroughs, for example on the behavior of melt under shearing conditions and on the physical controls on grain size, and on quantitative parameterizations of melt fabric. Our approach will be to integrate all datasets in a consistent manner, then iteratively test theoretical predictions against them. Results should distinguish models of melt generation and transport, for example of vertical porous flow, inclined flow, or ascent of cold diapirs. Once calibrated, the relationships needed to make these comparisons will be made available to interpret structure in other subduction zones and regions of melt production globally. The integration of disparate observations is a key step in making them understandable to a wide audience, and this integrated multidisciplinary approach will be tested in undergraduate classrooms and graduate seminars. The calibration of relationships between seismic observables and thermodynamic melting parameters should be broadly applicable and serve to enhance infrastructure for research.