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

NSFGEO-NERC：陆地核心自上而下结晶的综合实验和动力学模型：对地球核心冷却的影响

• 批准号: NE/T003855/1
• 负责人: Christopher Davies
• 金额: $ 26.8万
• 依托单位: University of Leeds
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FT003855%2F1
• 关键词: NSFGEO; NERC; Integrated; Experimental; Dynamical

Earth's magnetic field is generated almost 3000 km below our feet in the liquid iron core by a process known as the geodynamo. The field protects the surface environment and low-orbiting satellites from solar radiation; its existence for at least the last 3.5 billion years therefore has broad implications for the presence of life and the operation of modern global communications. The standard model describing the origin of the geodynamo posits that the field is maintained by slow cooling of the liquid 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 the inner core formed some 0.5-1 billion years ago. Recent studies have argued that the ancient core could have crystallized from the top down. The central aim 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. The 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 2200 C in the multi-anvil apparatus at UCSD-SIO using NSF-COMPRES assemblies. We will consider the Fe-S-Mg(-O) and Fe-S-O(-Si) systems, building on our 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 and will also be directly applicable to small terrestrial planets. In parallel we will develop a new theoretical model that describes the thermal and chemical evolution of two-phase regions at the top of Earth's core using techniques that were recently employed to study the Martian core. The model will predict the properties of the two-phase region and the evolution of the magnetic field, which can be tested using a variety of observations, and will therefore provide a coherent description of Earth's core evolution over the past 3.5 billion years.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 will significantly improve the current understanding of core crystallization in the Earth and also in other planets such as Mercury and Mars.

地球磁场是在我们脚下近3000公里的液态铁核中通过一种被称为地球发电机的过程产生的。该场保护地面环境和低轨道卫星免受太阳辐射；因此，至少在过去35亿年里，它的存在对生命的存在和现代全球通信的运作有着广泛的影响。描述地球发电机起源的标准模型假定，磁场是通过固体地幔下的液体地核缓慢冷却和固体内核的逐渐自下而上冻结来维持的。在对铁合金在地核条件下的热导率进行了首次计算之后，这个模型就不再站住脚了。这些计算预测了地球历史早期的快速冷却、年轻的内核和普遍的下地幔融化。在这种情况下，目前尚不清楚在大约5亿至5亿年前内核形成之前，地球发电机是如何提供动力的。最近的研究认为，古代地核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。该项目由两个相互关联的主要部分组成：岩心类似物实验和岩心演化的理论模型。相平衡实验将在UCSD-SIO的多砧仪器中进行，压力高达30 GPa，温度高达2200℃，使用nsf - comppres组件。我们将考虑Fe-S-Mg（-O）和Fe-S-O（-Si）系统，以我们最近在Fe-S-O系统中的实验工作为基础。淬火产物的化学分析将用于确定所研究体系的相化学、液相曲线和共晶温度。结果将通过严格的热力学外推法应用于地球的压力和温度条件，也将直接适用于小型类地行星。与此同时，我们将开发一个新的理论模型，利用最近用于研究火星核心的技术，描述地球核心顶部两相区域的热和化学演化。该模型将预测两相区域的特性和磁场的演变，这可以通过各种观测来测试，因此将提供过去35亿年地球核心演变的连贯描述。这个建议的一个新颖方面是实验和理论模型之间不断的相互作用。以实验室为基础的化学将用于改进模型，然后数值结果将用于激发特定成分的新实验。这项提议的研究将大大提高目前对地球以及水星和火星等其他行星的核心结晶的理解。

项目成果

Powering Earth's ancient dynamo with silicon precipitation

用硅沉淀为地球古老的发电机提供动力

• DOI: 10.31223/x5h34m
• 发表时间: 2022
• 作者: Wilson A

Thermo-Chemical Dynamics in Earth's Core Arising from Interactions with the Mantle

地核与地幔相互作用产生的热化学动力学

• DOI: 10.31223/x5mw4g
• 发表时间: 2021
• 作者: Davies C

Influence of Thermal Stratification on the Structure and Evolution of the Martian Core

• DOI: 10.1029/2021gl095198
• 发表时间: 2021-11-28
• 期刊: GEOPHYSICAL RESEARCH LETTERS
• 影响因子: 5.2
• 作者: Greenwood, Sam;Davies, Christopher J.;Pommier, Anne
• 通讯作者: Pommier, Anne