Magma generation and transport throughout the Earth's mantle: ab initio simulation of silicate melts

岩浆在地幔中的生成和输送：硅酸盐熔体的从头计算模拟

• 批准号: NE/F017871/1
• 负责人: Lars Stixrude
• 金额: $ 36.77万
• 依托单位: University College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2009
• 资助国家: 英国
• 起止时间: 2009 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FF017871%2F1
• 关键词: Magma; generation; transport; throughout; Earth

Silicate liquids are primary agents of chemical and thermal evolution of the Earth. Because of the contrast in density, chemical diffusivity, viscosity, and bulk composition between silicate liquids and their source regions, the generation and transport of magma is one of the most efficient geological means of mass and heat transport. Magmatic processes are responsible for the origin and ongoing formation of the oceanic and continental crust, and for bringing to the surface one of our primary clues to the composition of the interior in the form of xenoliths. The physical properties of silicate liquids are expected to vary substantially over the magma genetic regime even in the present day Earth (up to ~100 km or 3 GPa), and these variations are expected to have important consequences for the role of silicate liquids in geochemical and geodynamical processes. The greater compressibility of liquids, and therefore diminishing density contrast with coexisting solids is thought to be accommodated by pressure-induced changes in liquid structure, including increases in the coordination number of major cations, although experimental data on liquids at elevated pressure is limited. Pressure-induced changes in liquid structure have been implicated in variations of transport properties and solid-melt element partitioning with pressure. Models of the Earth's thermal history, analysis of ancient lavas, and of deep mantle xenoliths lead us to consider a range of pressure and temperature much broader than that of present day magma genesis, and a range of melt compositions that may differ substantially from that of current primary mantle melts. The early Earth probably had a deep magma ocean that may have encompassed the entire mantle (to 2890 km or 136 GPa). Xenoliths have been brought to the surface by melts from depths as great as 400 km (14 GPa) or possibly much deeper. Komatiitic lavas may have been produced by mantle melting starting as deep as ~800 km depth (~30 GPa). Seismological investigations have found evidence for an ultra-low velocity zone at the base of the mantle that is thought to be partially molten, and which may provide important clues to the Earth's extensively molten past. Despite their importance in understanding Earth's thermal and chemical evolution, very little is known of silicate liquids throughout almost the entire mantle pressure regime. Measurements near ambient pressure of the volume and sound speeds are abundant, but do not permit unique extrapolation beyond a few GPa. Melting equilibria including solidus and liquids temperatures and liquid compositions, have been measured up to about 25 GPa. Dynamic compression studies on pre-heated samples have reached 40 GPa (i.e. one third that at the base of the mantle), and studies that produce melting on the Hugoniot have reached 200 GPa, although only on a small number of compositions. In situ measurements of liquid structure are so far limited to a few GPa. First principles simulations, primarily from our group, have made important progress, but have only been able to study a few relatively simple liquid compositions. Thus a key stumbling block to further progress is a lack of information regarding crucial properties of silicate liquids across most of the mantle pressure-temperature regime. The issues that we wish to address may be focused around three hypotheses that the proposed research will test: 1. Is there silicate melt at the base of the mantle, and if so, how much? 2. It is likely that Earth was largely or completely molten at some time during its early history, possibly as a result of the moon-forming impact. How would the evolution of a completely molten mantle proceed? And at what depth? Did crystallisation begin bottom-up as is generally thought, or at mid-mantle depths? 3. Basalt tends to segregate into the deep mantle; is this consistent with the seismic complexity observed near the core-mantle boundary?

硅酸盐液体是地球化学和热演化的主要媒介。由于硅酸盐液体与其源区之间的密度、化学扩散性、粘度和整体成分之间的差异，岩浆的产生和传输是质量和热量传输的最有效的地质手段之一。岩浆过程负责海洋和大陆地壳的起源和持续形成，并将我们以捕虏体形式了解内部组成的主要线索之一带到地表。即使在当今的地球上，硅酸盐液体的物理性质预计也会在岩浆成因体系中发生很大变化（高达约 100 km 或 3 GPa），并且这些变化预计将对硅酸盐液体在地球化学中的作用产生重要影响。和地球动力学过程。液体具有更大的可压缩性，因此与共存固体的密度对比减小，被认为是通过压力引起的液体结构变化来调节的，包括主要阳离子配位数的增加，尽管高压​​下液体的实验数据有限。压力引起的液体结构变化与传输特性和固熔元素随压力分配的变化有关。地球的热历史模型、对古代熔岩和深部地幔捕虏体的分析使我们考虑了比当今岩浆成因更广泛的压力和温度范围，以及可能与岩浆成因有很大不同的一系列熔体成分。当前的原生地幔融化。早期地球可能有一个深层岩浆海洋，可能包围了整个地幔（深达 2890 公里或 136 GPa）。包体是由深达 400 公里（14 GPa）或更深处的熔体带到地表的。科马提岩熔岩可能是由地幔融化产生的，起始深度可达约 800 公里（约 30 GPa）。地震学调查发现了地幔底部存在超低速区域的证据，该区域被认为是部分熔融的，这可能为地球过去广泛熔融的过程提供重要线索。尽管硅酸盐液体对于理解地球的热和化学演化很重要，但我们对几乎整个地幔压力范围内的硅酸盐液体知之甚少。接近环境压力的体积和声速测量非常丰富，但不允许进行超过几 GPa 的独特外推。测量到的熔化平衡（包括固相线和液体温度以及液体成分）高达约 25 GPa。对预热样品的动态压缩研究已达到 40 GPa（即地幔底部的三分之一），而在 Hugoniot 上产生熔化的研究已达到 200 GPa，尽管只针对少数成分。迄今为止，液体结构的原位测量仅限于几个 GPa。主要来自我们小组的第一原理模拟已经取得了重要进展，但只能研究一些相对简单的液体成分。因此，进一步进展的一个关键障碍是缺乏有关大部分地幔压力-温度范围内硅酸盐液体关键特性的信息。我们希望解决的问题可能集中在拟议研究将测试的三个假设上： 1. 地幔底部是否存在硅酸盐熔融物，如果存在，有多少？ 2. 地球很可能在其早期历史的某个时期大部分或完全熔化，这可能是月球形成撞击的结果。完全熔融的地幔的演化将如何进行？深度是多少？结晶是像人们普遍认为的那样自下而上开始的，还是在中地幔深处开始的？ 3. 玄武岩倾向于偏析到地幔深部；这与在核幔边界附近观察到的地震复杂性是否一致？

项目成果

First-principles calculation of the elastic moduli of sheet silicates and their application to shale anisotropy

片状硅酸盐弹性模量的第一性原理计算及其在页岩各向异性中的应用

• DOI: 10.2138/am.2011.3558
• 发表时间: 2024-09-14
• 期刊: American Mineralogist
• 影响因子: 3.1
• 作者: B. Militzer;H. Wenk;Stephen Stackhouse;Lars Stixrude
• 通讯作者: Lars Stixrude

Models of triplet self-trapped excitons in SiO 2 , HfO 2 , and HfSiO 4

SiO 2 、HfO 2 和 HfSiO 4 中三重态自俘获激子模型

• DOI: http://dx.10.1103/physrevb.85.024120
• 发表时间: 2012
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: Muñoz Ramo D

First principles viscosity and derived models for MgO-SiO 2 melt system at high temperature

高温MgO-SiO 2 熔体体系的第一原理粘度及推导模型

• DOI: http://dx.10.1029/2012gl054372
• 发表时间: 2013
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: Karki B

First-principles study of enhancement of transport properties of silica melt by water.

水增强二氧化硅熔体输运性能的第一性原理研究。

• DOI: 10.1103/physrevlett.104.215901
• 发表时间: 2010-05-28
• 期刊: Physical review letters
• 影响因子: 8.6
• 作者: B. Karki;L. Stixrude
• 通讯作者: L. Stixrude

Self-consistent thermodynamic description of silicate liquids, with application to shock melting of MgO periclase and MgSiO 3 perovskite

硅酸盐液体的自洽热力学描述，应用于MgO方镁石和MgSiO 3 钙钛矿的冲击熔化

• DOI: http://dx.10.1111/j.1365-246x.2009.04142.x
• 发表时间: 2009
• 期刊: Geophysical Journal International
• 影响因子: 2.8
• 作者: De Koker N