NSFGEO-NERC Proposal: Integrated Experimental and Dynamical Modeling of Top-down Crystallization in Terrestrial Cores: Implications for Core Cooling in the Earth

NSFGEO-NERC 提案：陆地核心自上而下结晶的综合实验和动态建模：对地球核心冷却的影响

• 批准号: 2152686
• 负责人: Anne Pommier
• 金额: $ 34万
• 依托单位: Carnegie Institution of Washington
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-07-01 至 2025-04-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2152686&HistoricalAwards=false
• 关键词: NSFGEO; NERC; Proposal; Integrated; Experimental

On Earth, the magnetic field generated in the core protects us from the Sun's harmful radiation. It plays a major role in the presence of life and it is therefore critical to understand how it is generated and can last through time. This project combines experiments and theory to understand if and how the cooling of the metallic core of planets generates a magnetic field and influences the core's evolution. In particular, the project aims to provide a "revised" standard model for the origin of the magnetic field in our planet. A novel aspect of this proposal is the constant interactions between experiments and theoretical models. Laboratory-based chemistry will be used to refine the models, and numerical results will then be used to motivate new experiments at specific compositions. The proposed study should improve the current understanding of core crystallization in the Earth and also in other planets such as Mercury and Mars. This work will be shared with the scientific community and will contribute to the training of students as well as postdoctoral researchers by the PIs both in the US and in the UK.The standard model describing the origin of the geodynamo posits that the field is maintained by slow cooling of the liquid iron core below a solid mantle and gradual bottom-up freezing of the solid inner core. This model is no longer tenable following the first calculations of the thermal conductivity of iron alloys at core conditions, which predict rapid cooling, a young inner core and pervasive melting of the lower mantle early in Earth's history. In this scenario it is presently unclear how the geodynamo was powered before inner core nucleation. Recent studies have argued that the ancient core could have crystallized from the top down. The central objective of this joint experimental-theoretical project is to understand if and how top-down crystallization generates magnetic fields and influences the thermochemical evolution of Earth's core. This project consists of two major interlinked components: experiments on core analogues and theoretical models of core evolution. Phase equilibria experiments will be carried out at pressure up to 30 GPa and temperature up to 2200degC in the multi-anvil apparatus at UCSD-SIO using NSF-COMPRES assemblies. The team will consider the Fe-S-Mg(-O) and Fe-S-O(-Si) systems, building on PI's recent experimental work in the Fe-S-O system. Chemical analyses of quenched products will be used to determine the chemistry of phases, the liquidus curve and the eutectic temperature for the investigated systems. Results will be applied to the Earth's pressure and temperature conditions using rigorous thermodynamic extrapolation, as is common in experimental petrology, and will also be directly applicable to small terrestrial planets. Experimental results will be incorporated to theoretical models of the Earth's core and other terrestrial bodies.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

在地球上，芯中产生的磁场可保护我们免受太阳的有害辐射。它在生活的存在中起着重要的作用，因此，了解它是如何产生并可以持续时间的至关重要的。该项目结合了实验和理论，以了解行星金属芯的冷却是否以及如何产生磁场并影响核心的演变。特别是，该项目旨在为我们星球中磁场的起源提供“修订的”标准模型。该提案的一个新方面是实验与理论模型之间的持续相互作用。基于实验室的化学将用于完善模型，然后使用数值结果来激励特定组成的新实验。拟议的研究应提高人们对地球核心结晶以及汞和火星等其他行星的当前理解。 这项工作将与科学界分享，并将为PIS在美国和英国的PIS培训以及博士后研究人员做出贡献。描述Geodynamo的起源的标准模型认为，该领域是通过在固体壁炉下方和固体内部核心逐渐稳固的固体底部稳固的液体铁芯来维持的。该模型不再是可以在核心条件下的铁合金的导热率的第一个计算，这可以预测快速冷却，年轻的内部核心以及地球早期下地幔的普遍融化。在这种情况下，目前尚不清楚Geodynamo如何在内部核心成核之前提供动力。最近的研究表明，古老的核心本可以从自上而下地结晶。该联合实验理论项目的核心目标是了解自上而下的结晶是否以及如何产生磁场并影响地球核心的热化学演化。该项目由两个主要相互联系的组成部分组成：核心类似物的实验和核心进化的理论模型。使用NSF-Compres组件，将在UCSD-SIO的多动型设备中以高达30 GPA的压力下进行相位平衡实验。该团队将考虑Fe-S-MG（-o）和Fe-S-O（-si）系统，该系统是基于PI最近在Fe-S-O系统中的实验性工作的。淬灭产物的化学分析将用于确定所研究系统的相位化学，液相曲线和共晶温度。结果将使用严格的热力学外推（在实验性岩石学上是常见）应用于地球的压力和温度条件，并且也将直接适用于小型陆地行星。实验结果将纳入地球核心和其他陆地机构的理论模型中。该奖项反映了NSF的法定任务，并认为使用基金会的知识分子优点和更广泛的影响审查标准，被认为值得通过评估。