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

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。它在生命的存在中扮演着重要的角色，因此了解它是如何产生的，并能持续一段时间是至关重要的。这个项目将实验和理论结合起来，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。这项工作将与科学界共享，并将有助于美国和英国的pi培养学生和博士后研究人员。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液态铁核的缓慢冷却和固体内核的逐渐自下而上的冻结来维持的。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，目前尚不清楚地球发电机在内核成核之前是如何供电的。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。该项目包括两个主要的相互关联的部分：岩心类似物的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摄氏度，使用nsf - comppres组件。该团队将考虑Fe-S-Mg（-O）和Fe-S-O（-Si）系统，以PI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。结果将采用严格的热力学外推法，应用于地球的压力和温度条件，这在实验岩石学中很常见，也将直接适用于小型类地行星。实验结果将被纳入地核和其他地球天体的理论模型。该奖项反映了美国国家科学基金会的法定使命，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。

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.