CSEDI: Melt stability and dynamics in the deep Earth

该奖项是根据2009年《美国复苏和再投资法》(公法111-5)资助的。地球超低速带(ULVZ)相对较低的剪切模数和较高的温度意味着，这些位于核-地幔边界(CMB)的薄(5-40公里厚)区域可能是部分熔融的。为了保持通过对流驱动发电机所需的冷却速度，地球古老的核心一定比现在更热，因此最低的地幔可能会更广泛地融化。据推测，地幔最深处较高的熔体密度稳定了熔融层，形成了一个致密的基底岩浆海洋(BMO)，它在地球历史早期就出现了，其遗迹现在是ULVZ。BMO的存在对地球深处的动力学和分化有很大的影响。不相容的元素将通过分馏作用隔离到熔体中，而从BMO结晶的固体的化学特征将由相图决定。这种结晶特征应该出现在地球表面深地幔羽流的火山产物中。地球最下部地幔中的其他结构，如“化学堆积”，可能是由BMO结晶形成或修改的。BMO的存在还将增强相对于固体最低地幔的核-地幔化学相互作用的程度，可能导致在地核顶部形成富含轻元素的浮力层。该项目旨在通过建立一个两相动力学模型来进一步探索BMO的后果，该模型将被用来更好地约束BMO的动力学演化，解决BMO假说提出的几个问题，并开始用地球化学数据和地震学观测来检验这一假说。还将使用数值发电机模型来探索BMO和内核之间的反应在内核顶部形成的浮力层的影响，以测试这种内核中发电机的特征是否与地磁观测相一致。该项目将为一名博士后研究人员提供两年的支持，他将受益于跨学科培训，并涉及4个不同国家(美利坚合众国、英国、法国和加拿大)的研究人员之间的直接国际合作。大多数将是新的合作。两相流模型可以应用于其他学科的各种泥浆系统，如地壳岩浆室和火山系统的演化。该代码将在即将到来的基准练习中使用，这是代码开发和建模的一个耗时但必不可少的方面。该代码还将提供给更广泛的研究团体用于其他项目。地球超低速带(ULVZ)相对较低的剪切模数和较高的温度意味着，这些位于核-地幔边界(CMB)的薄(5-40公里厚)区域可能部分是熔融的。为了保持通过对流驱动发电机所需的冷却速度，地球古老的核心一定比现在更热，因此最低的地幔可能会更广泛地融化。据推测，相对于地幔最深处的固体，熔体的密度更高，稳定了这个熔融层，形成了一个致密的基底岩浆海洋(BMO)，它在地球历史早期就出现了，其遗迹目前是ULVZ。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)The relatively low shear modulus and high temperature of Earth's ultralow-velocity zones (ULVZ) imply that these thin (5-40 km thickness) regions at the core-mantle boundary (CMB) may be partly molten. In order to maintain the cooling rate necessary to drive a dynamo by convection, Earth's ancient core must have been hotter than at present and the lowermost mantle would therefore have been more extensively melted. It has been hypothesized that the higher density of melt relative to solids in the deepest mantle stabilized this molten layer, forming a dense basal magma ocean (BMO) that appeared early in Earth's history and whose remains are at present the ULVZs.The existence of a BMO has large effects on the dynamics and differentiation of the deep Earth. Incompatible elements would have been sequestered into the melt by fractionation, while the chemical signature of solids crystallized from the BMO would be governed by the phase diagram. This crystallization signature should appear at Earth's surface in volcanic products from deep-seated mantle plumes. Other structures in Earth's lowermost mantle such as "chemical piles" may be formed or modified by BMO crystallization. The presence of a BMO will also enhance the extent of core-mantle chemical interactions relative to a solid lowermost mantle, possibly leading to the formation of a buoyant layer at the top of the core that is enriched in light elements.This project aims to further explore the consequences of a BMO by developing a two-phase dynamics model that will be used to better constrain the dynamical evolution of a BMO, to address several questions raised by the BMO hypothesis, and to begin to test the hypothesis with geochemical data and seismological observations. The effects of a buoyant stratified layer at the top the core produced by reactions between the BMO and core will also be explored using a numerical dynamo model to test whether features of dynamos in such cores are compatible with geomagnetic observations.The project will provide two years of support for a post-doctoral researcher, who will benefit from interdisciplinary training, and involves direct international collaboration among researchers in 4 different countries (United States of America, United Kingdom, France, and Canada). Most will be new collaborations. The two-phase flow models can be applied to a large variety of mush-slurry systems in other disciplines, such as the evolution of crustal magma chambers and volcanic systems. The code will be used in upcoming benchmark exercises, a time consuming but essential aspect of code development and modeling. The code will also be made available to the broader research community for use in other projects.The relatively low shear modulus and high temperature of Earth's ultralow-velocity zones (ULVZ) imply that these thin (5-40 km thickness) regions at the core-mantle boundary (CMB) may be partly molten. In order to maintain the cooling rate necessary to drive a dynamo by convection, Earth's ancient core must have been hotter than at present and the lowermost mantle would therefore have been more extensively melted. It has been hypothesized that the higher density of melt relative to solids in the deepest mantle stabilized this molten layer, forming a dense basal magma ocean (BMO) that appeared early in Earth's history and whose remains are at present the ULVZs.