Geochemical Consequences of Melt Channelization: Exploring New Models for U-Series Variability

智力优势。地球化学家和地球物理学家面临的一个基本挑战是如何利用观测到的化学变化来推断地幔的性质和过程。铀系衰变链对推断地幔过程有着巨大的希望，因为这些核素对熔化和熔体输送的速率以及熔体和固体分布的几何形状（即孔隙度/沟道等）很敏感。然而，实现这一承诺仍然极具挑战性。U系列核素，其他微量元素和地球物理参数之间的相关性的新的观察模型的地方强有力的约束，并与其他研究一起，表明熔体在地幔中的运输是高度本地化的某种形式的通道化网络。因此，定量相关的观察到的U系列过剩地幔过程需要模型，结合耦合熔体和固体动力学与化学输运。该提案的目的是开发和系统地探索岩浆系统中稳定和放射成因示踪剂的下一代模型，以了解其对地幔过程的影响。具体而言，建议1）扩展反应性通道化流中稳定和U系列输运的当前模型，以包括现实的主要元素熔化和微量元素分配行为，以便模型可以直接与观测结果进行比较。2)利用这些模型，系统地探讨耦合稀土元素和铀系列行为可能的地幔过程的敏感性。3)扩展模型，以调查其他机制，如剪切诱导的机械不稳定性熔体本地化。4)为了提高计算精度，计算模型需要极高的空间和时间分辨率，这对于求解大尺度地质系统中的U系列响应非常重要。因此，本研究的另一个组成部分是开发下一代高性能计算模型，用于高分辨率熔体和化学输运。我们已经开始了这个过程，移植的主要组件的便携式可扩展工具包的科学计算（PETSC），这是一个核心技术的计算基础设施的地球动力学（CIG）。我们将与CIG密切合作，开发在更大的CIG框架内可互操作的公共访问的化学品传输模型。如果成功的话，这一提议将使人们更好地理解U系列观测的动态影响，并开发出灵活的建模工具，使整个地球化学和地球物理界受益。该项目将成为完成方延明研究生工作的主要资金来源，以便在应用数学和地球科学的交叉点工作。这项工作也应该在科学和工程中的一般应用，涉及渗透，反应和变形固体，如石油工程，水文和核废料的生产和处置的流体流动的问题。通过这项工作开发的所有代码和算法将通过CIG作为开源组件向公众提供。

Intellectual Merit. A fundamental challenge for geochemists and geophysicists is to understand how to use observed chemical variability to infer both properties and processes occurring in the Earth's mantle. The Uranium-series decay chains hold enormous promise for inferring mantle processes because these nuclides are sensitive to the rates of melting and melt transport as well as the geometry of melt and solid distribution (i.e. porosity/channeling etc.). Realizing this promise, however, remains extremely challenging. New observations of correlations between U-series nuclides, other trace elements and geophysical parameters place strong constraints on models and, together with other studies, suggest that melt transport in the mantle is highly localized into some form of channelized network. Thus, to quantitatively relate observed U-series excesses to mantle processes requires models that integrate coupled melt and solid dynamics with chemical transport. The purpose of this proposal is to develop and systematically explore the next generation of models for stable and radiogenic tracers in magmatic systems to understand their implications for mantle processes. Specifically, it is proposed to 1) Extend current models for stable and U-series transport in reactive channelized flows to include realistic major element melting and trace element partitioning behavior so that the models can be compared directly to observations. 2) Use these models to systematically explore the sensitivity of coupled REE and U-series behavior to possible mantle processes. 3) Extend the models to investigate other mechanisms for melt localization such as shear-induced mechanical instabilities. 4) Develop comprehensive U-series models for mid-ocean ridge geometries.For accuracy, the computational models require extremely fine spatial and temporal resolution, which becomes important when solving for U-series response in large-scale geological systems. Thus, another component of this research is to develop the next generation of high-performance computational models for high-resolution melt and chemical transport. We have begun this process by porting major components to the Portable Extensible Toolkit for Scientific Computation (PETSc) which is a core technology in the Computational Infrastructure for Geodynamics (CIG). We will work closely with CIG to develop publicly accessible chemical transport models that are interoperable within the larger CIG framework. If successful, this proposal will develop both a better understanding of the dynamic implications of U-series observations as well as flexible modeling tools that can benefit the entire geochemical and geophysical community.Broader Impacts. This project will form the primary source of funding to finish the graduate work of Yanming Fang to work at the intersection of Applied Mathematics and Earth Science. This work should also have general applications in science and engineering to problems involving the flow of fluids in permeable, reactive and deformable solids such as petroleum engineering, hydrology and nuclear waste production and disposal. All codes and algorithms developed through this work will be made available as open source components to the public through the CIG.