Tracking sodium in Earths deep mantle

钠集中在地球内部流体循环的区域，以及下沉并与地幔混合的海洋地壳中。因为钠会影响岩石的融化，增加流体的导电性，所以它在地球内部高压和高温下的化学性质对了解地球深处的碳和水循环非常重要。这项研究将观察地球最大的层，即下地幔中钠的数量和矿物形式。实验和计算机模拟将测试钠在地球上最丰富的氧化矿物中的储存情况，氧化矿物与岩盐具有相同的原子结构。该项目将支持培训一名研究生和本科生助理，并与密歇根州立大学博物馆合作，为公众制作、展示和评估盐地质学和晶体结构的模块化展览。地幔中钠的寄主相和容量对于模拟地球深层挥发物循环和解读板块构造的地幔记录具有重要意义。（Mg,Fe）O铁方长石可能是地球内部钠的主要寄主。系统实验使用激光加热的金刚石砧细胞将测量钠饱和条件下（Mg,Fe）O中钠的浓度，并与其他主要的下地幔相桥辉石和/或davemaoite平衡。互补密度泛函理论计算将测试钠在下地幔相溶解机制的相对有利性。这些方法将用于确定钠的下地幔主相和含钠下地幔的地震性质。改进的钠高压矿物学约束可用于更新地幔的热力学和地球物理建模，以更准确地确定地幔的组成和非均质性。将碱金属钠加入到（Mg,Fe）O氧化物中也将对盐的系统和高压下的键合产生深刻的见解。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。

Sodium is concentrated in regions of the Earth where fluids cycle within the planet as well as in oceanic crust sinking and mixing into the mantle. Because sodium affects melting of rocks and increases electrical conductivity of fluids, its chemistry at high pressures and temperatures of Earth’s interior is important to understanding deep Earth carbon and water cycles. This study will observe the quantity and mineral forms of sodium in the Earth’s largest layer, the lower mantle. Experiments and computer simulations will test sodium storage in the most abundant oxide mineral in the planet, which has the same atomic structure as rock salt. The project will support training for a graduate student and undergraduate assistant and a partnership with the MSU Museum to produce, present, and evaluate modular exhibits on salt geology and crystal structures for a public audience. The host phase and capacity for sodium in Earth’s mantle are important for modeling deep Earth cycles of essential volatiles and reading the mantle record of plate tectonics. (Mg,Fe)O ferropericlase may be the major host for sodium in Earth’s interior. Systematic experiments using laser-heated diamond anvil cells will measure the concentration of sodium in (Mg,Fe)O under sodium-saturated conditions and in equilibrium with the other major lower mantle phases bridgmanite and/or davemaoite. Complementary density functional theory calculations will test the relative favorability of mechanisms for dissolving sodium in lower mantle phases. In combination these methods will be used to determine the dominant lower-mantle host phase for sodium and the seismic properties of Na-bearing lower mantle. Improved constraints on the high-pressure mineralogy of sodium can be applied to update thermodynamic and geophysical modeling of the mantle for more accurate determination of mantle composition and heterogeneity. The incorporation of archetypal alkali metal sodium into (Mg,Fe)O oxide will also produce insights into systematics of salts and bonding at high pressure.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.