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

知识价值。地球化学家和地球物理学家面临的一个基本挑战是了解如何利用观察到的化学变化来推断地幔的性质和过程。铀系列衰变链对推断地幔过程具有巨大的希望，因为这些核素对熔化速率和熔体输送以及熔体和固体分布的几何形状（即孔隙度/通道等）很敏感。然而，实现这一承诺仍然极具挑战性。对u系列核素、其他微量元素和地球物理参数之间相关性的新观测对模型施加了强烈的限制，并与其他研究一起表明，地幔中的熔体运输高度局限于某种形式的通道化网络。因此，为了定量地将观测到的u系列过剩与地幔过程联系起来，需要将熔体和固体动力学与化学输运结合起来的模型。本提案的目的是开发和系统地探索岩浆系统中稳定和放射性成因示踪剂的下一代模型，以了解它们对地幔过程的影响。具体而言，建议1)扩展当前反应通道化流动中稳定输运和u系列输运的模型，以包括现实的主要元素熔化和微量元素分配行为，以便将模型直接与观测结果进行比较。2)利用这些模型系统探讨稀土元素和铀系耦合行为对可能的地幔过程的敏感性。3)扩展模型以研究熔体局部化的其他机制，如剪切诱导的机械不稳定性。4)开发大洋中脊几何形状的综合u系列模型。为了计算精度，计算模型需要非常精细的空间和时间分辨率，这在求解大规模地质系统中的u系列响应时变得非常重要。因此，这项研究的另一个组成部分是开发高分辨率熔体和化学物质传输的下一代高性能计算模型。我们通过将主要组件移植到可移植可扩展科学计算工具包（PETSc）开始了这一过程，PETSc是地球动力学计算基础设施（CIG）的核心技术。我们将与CIG密切合作，开发可在更大的CIG框架内互操作的可公开访问的化学运输模型。如果成功，这一建议将使人们更好地理解u系列观测的动态含义，并开发灵活的建模工具，使整个地球化学和地球物理界受益。更广泛的影响。该项目将成为方彦明完成应用数学与地球科学交叉方向的研究生工作的主要资金来源。这项工作还应在科学和工程中具有普遍的应用，以解决涉及渗透、反应性和可变形固体中的流体流动的问题，如石油工程、水文学和核废料的产生和处置。通过这项工作开发的所有代码和算法将通过CIG作为开源组件提供给公众。

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.