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: 1832462
• 负责人: Anne Pommier
• 金额: $ 34万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-05-15 至 2021-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1832462&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，地核产生的磁场保护我们免受太阳有害辐射的伤害。它在生命的存在中起着重要作用，因此了解它是如何产生并持续时间是至关重要的。该项目结合了实验和理论，以了解行星金属核心的冷却是否以及如何产生磁场并影响核心的演变。特别是，该项目旨在为地球磁场的起源提供一个“修订”的标准模型。这一提议的一个新方面是实验和理论模型之间的不断相互作用。将使用基于化学的方法来改进模型，然后将使用数值结果来激励特定组合物的新实验。这项拟议中的研究将提高目前对地球以及水星和火星等其他行星核心结晶的理解。 这项工作将与科学界分享，并将有助于美国和英国的专业研究人员对学生和博士后研究人员的培训。描述地球发电机起源的标准模型假设，该场是通过固体地幔下方液态铁核的缓慢冷却和固体内核自下而上的逐渐冻结来维持的。在第一次计算了铁合金在地核条件下的热导率之后，这个模型不再成立，它预测了地球历史早期的快速冷却，年轻的内核和下地幔的普遍熔化。在这种情况下，目前还不清楚地球发电机是如何在内核成核之前提供动力的。最近的研究认为，古老的核心可能是自上而下结晶的。这个联合实验-理论项目的中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核的热化学演化。该项目包括两个主要的相互关联的部分：核心类似物的实验和核心进化的理论模型。相平衡实验将在UCSD-SIO的多砧装置中使用NSF-COMPRES组件在高达30 GPa的压力和高达2200摄氏度的温度下进行。该团队将考虑Fe-S-Mg（-O）和Fe-S-O（-Si）系统，建立在PI最近在Fe-S-O系统中的实验工作基础上。淬火产品的化学分析将用于确定相的化学性质、液相线曲线和所研究系统的共晶温度。结果将适用于地球的压力和温度条件下使用严格的热力学外推，这是常见的实验岩石学，也将直接适用于小型类地行星。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。