Tracking sodium in Earths deep mantle

钠集中在地球内部流体循环的区域，以及下沉并混合到地幔中的洋壳中。因为钠会影响岩石的熔融并增加流体的电导率，所以它在地球内部高压和温度下的化学作用对于了解地球深处的碳循环和水循环很重要。这项研究将观察地球上最大的一层，即下地幔中钠的数量和矿物形态。实验和计算机模拟将测试地球上最丰富的氧化物矿物中的钠存储，这种矿物具有与岩盐相同的原子结构。该项目将支持对研究生和本科生助理的培训，以及与密歇根州立大学博物馆的合作，为公众制作、展示和评估关于盐地质和晶体结构的模块展品。地幔中钠的宿主相和容量对于模拟地球深部挥发分循环和读取板块构造的地幔记录是重要的。(Mg，Fe)O铁方镁石可能是地球内部钠的主要宿主。利用激光加热的钻石顶压室进行的系统实验将测量在钠饱和条件下以及与其他主要的下地幔相布里格马利特和/或达维毛石平衡时(Mg，Fe)O中的钠的浓度。互补密度泛函理论计算将检验在下地幔相中溶解钠的机制的相对有利程度。这些方法相结合，将被用来确定钠的优势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模型，以便更准确地确定地幔成分和不均质性。将典型的碱金属钠加入到(Mg，Fe)O氧化物中也将产生对盐的系统学和高压结合的见解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.