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

智力上的功绩。地球化学家和地球物理学家面临的一个根本挑战是了解如何利用观测到的化学可变性来推断地幔中发生的性质和过程。铀系衰变链在推断地幔过程方面具有巨大的前景，因为这些核素对熔融和熔体迁移的速度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，实现这一承诺仍然具有极大的挑战性。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察对模型施加了强烈的限制，并与其他研究一起表明，熔体在地幔中的运输高度局限于某种形式的沟道化网络。因此，要将观察到的U系列过量与地幔过程定量地联系起来，需要将耦合的熔体和固体动力学与化学传输相结合的模型。这项提议的目的是开发和系统地探索岩浆系统中稳定示踪和放射性成因示踪的下一代模型，以了解它们对地幔过程的影响。具体地说，建议1)扩展反应槽道化流动中稳定和U系列输运的现有模型，以包括真实的常量元素熔化和微量元素分配行为，以便模型可以直接与观测进行比较。2)利用这些模型系统地探讨了REE和U系列的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，如剪切引起的机械不稳定性。4)开发用于大洋中脊几何形状的综合U系列模型。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下一代高性能计算模型，用于高分辨率熔体和化学物质的传输。我们已经开始了这一进程，将主要组件移植到可移植可扩展科学计算工具包(PETSC)，这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框架内互操作的公众可访问的化学品运输模型。如果成功，这项建议将使人们更好地理解U系列观测的动态影响，并开发灵活的建模工具，使整个地球化学界和地球物理界受益。该项目将成为完成方燕明在应用数学和地球科学交叉点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广泛应用于石油工程、水文学和核废料生产和处置等涉及渗透性、反应性和可变形固体中流体流动的问题。通过这项工作开发的所有代码和算法将作为开放源码组件通过CIG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.