Investigation of fluids and hydrated mantle in subduction zones, with a focus on Cascadia

地球上最具破坏性的地震和火山喷发发生在俯冲带板块边界，那里的海洋岩石圈下降到地幔。例如，2011年3月11日，日本东北发生里氏9.0级俯冲带地震，造成19000人死亡，估计损失2350亿美元。卡斯卡迪亚俯冲带沿着北美西海岸从温哥华岛延伸到加利福尼亚州北部，绵延1000公里。卡斯卡迪亚板块边界的破裂每隔500年就会发生一次9级大地震，最后一次发生在公元1700年1月26日。破坏性的卡斯卡迪亚地震也发生在俯冲的胡安德富卡和俯冲的北美板块内。 俯冲带地震与富水流体的生成、运输和再吸收有关。了解板块边界的力学行为，从而了解地震潜力，需要了解沿边界的含水矿物和流体的分布。最近的研究表明，地震在上覆板块中的分布与板块边界的渗透性以及在深部产生的流体逃逸到上覆地壳中的程度有关。在更深的层面上，从俯冲板块释放的流体使上覆地幔水化，形成蛇纹石、滑石和其他弱矿物。 我的五年研究计划支持了我更好地了解俯冲地带的长期目标，并利用了我之前的建模工作。我的短期目标是研究渗入地幔楔体的俯冲带流体。具体地说，我建议(1)建立地幔楔体的矿物学图，作为主体成分和H2O含量的函数，(2)进行野外岩石学研究，以限制水化地幔岩石中H2O平衡的空间尺度(S)，以及(3)发展一个受地震活动启发的卡斯卡迪亚俯冲带流体流动的综合模型。将结合数值传热学和热力学模型，将结果与地震观测相结合，构建矿物学地图。野外工作将集中在不列颠哥伦比亚省和华盛顿州暴露的超镁铁质岩石上。 我建议培训一个多元化的HQP小组，由三名研究生(1名博士和2名硕士)和1名本科生组成，采用公平和包容的招聘和指导做法。热-岩石学建模技术和变质岩石学的研究培训将为这些学生追求学术和技术职业生涯提供坚实的基础。 拟议的研究计划的结果将进一步加深我们对俯冲带流体和地震的了解，潜在地开辟了改进地震危险性长期预测的新途径。研究成果将在国际地球科学会议和研讨会上发表，并在高质量的同行评议期刊上发表。

Earth's most damaging earthquakes and volcanic eruptions occur along subduction-zone plate boundaries where oceanic lithosphere descends into the mantle. For example, the magnitude (M) 9.0 subduction-zone earthquake that struck Tohoku, Japan on March 11, 2011 resulted in the loss of >19,000 lives and estimated damages of US$235B. The Cascadia subduction zone extends for >1,000 km along the west coast of North America from Vancouver Island to northern California. Rupture of the Cascadia plate boundary has resulted in great M9 earthquakes every ~500 years, with the last one occurring on January 26, 1700 AD. Damaging Cascadia earthquakes also occur within the subducting Juan de Fuca and overriding North American plates. Subduction-zone earthquakes are linked to the generation, transport, and resorption of water-rich fluids. Understanding the mechanical behaviour of the plate boundary, and therefore the seismic potential, requires understanding the distribution of hydrous minerals and fluids along the boundary. Recent work has demonstrated that the distribution of earthquakes in the overriding plate is linked to the permeability of the plate boundary and the extent to which fluids generated at depth escape into the overlying crust. At deeper levels, fluids released from the subducting plate hydrate the overlying mantle forming serpentine, talc, and other weak minerals. My five-year program of research supports my long-term objective to better understand subduction zones and leverages my previous modelling efforts. My short-term objectives focus on subduction-zone fluids that infiltrate the mantle wedge. Specifically, I propose to (1) construct mineralogical maps of the mantle wedge as a function of bulk composition and H2O content, (2) conduct field-based petrologic studies to constrain the spatial scale(s) of H2O equilibrium in hydrated mantle rocks, and (3) develop an integrated model of fluid flow in the Cascadia subduction zone as illuminated by seismicity. The mineralogical maps will be constructed by combining numerical heat transfer and thermodynamic models, integrating the results with seismological observations. Field work will focus on ultramafic rocks exposed in British Columbia and Washington state. I propose to train a diverse HQP group consisting of three graduate students (1 PhD and 2 MSc) and one undergraduate student using equitable and inclusive recruitment and mentoring practices. Research training in thermal-petrologic modelling techniques and metamorphic petrology will provide a strong foundation for these students to pursue academic and technical careers. The results of the proposed program of research will further our understanding of subduction zone fluids and earthquakes, potentially opening up new avenues to improve long-term forecasting of seismic hazards. Research results will be presented at international geoscience meetings and workshops, and published in high-quality peer-reviewed journals.