Thermal conductivity of lower mantle minerals and outer core alloys studied by combined fast pulsed laser and optical spectroscopy techniques

结合快速脉冲激光和光谱技术研究下地幔矿物和外核合金的热导率

• 批准号: 2049127
• 负责人: Alexander Goncharov
• 金额: $ 30.8万
• 依托单位: Carnegie Institution of Washington
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-04-01 至 2024-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2049127&HistoricalAwards=false
• 关键词: Thermal; conductivity; lower; mantle; minerals

Thermal convection in the Earth’s mantle drives plate tectonics. This process transports heat from within the planet, in its core and mantle, to the surface. Heat transport through the mantle is crucial for maintaining the geodynamo in the Earth's core, and the magnetic field which shields the surface from the solar wind. Mantle dynamics depends on the rate of heat transfer by convection, conduction (contact), and radiation (e.g., light). Quantifying the thermal conductivity of mantle and core materials is, thus, critical for understanding Earth’s thermal system, dynamics, and evolution. It is, however, challenging because of the extreme pressures and temperatures prevailing in Earth’s deep interior. Here, the researchers measure the thermal conductivity of lower-mantle minerals and core Fe-rich alloys. They carry out experiments on synthetic materials compressed at the tips of two opposing diamonds, which produces the relevant high pressures. They use high-power lasers to heat up the specimens and vary their temperature. Conductive and radiative thermal properties are extracted using state-of-the-art spectroscopic techniques previously developed by the team. The project gradually unveils the physics of thermal transport at extreme conditions. It advances the Earth Sciences field, as well as adjacent fields in Materials Sciences with potential energy applications. It provides support and training to one postdoctoral associate at Carnegie Institution of Washington, and outreach towards undergraduate and high-school students. The project also fosters an international collaboration with European scientists. The thermal conductivity of materials in Earth’s interior is a key parameter in controlling the thermal history and dynamics of the planet. Thermal properties constrain processes involved in planetary accretion and differentiation, the thermal evolution of mantle and core, and the generation of Earth’s magnetic field. Here, the team focusses on constraining more accurately the heat flow through the outer core and core-mantle boundary (CMB). Experiments in the laser-heated diamond anvil cell (DAC) are combined with modeling of deep Earth temperature profiles. The team applies transient heating and broad band optical spectroscopy, two novel techniques they previously develop; these allow quantifying the conductive and radiative conductivities of the thermal boundary layer. The researchers develop a new technique – the "pulsed electric conductivity" technique – which applied in combination with transient heating allows quantifying the thermal conductivity of the outer core. These experiments are performed on Fe-rich alloys (including the melts), and high-quality relevant minerals (e.g., single crystals of bridgmanite) synthesized in large-volume devices or in situ in the DAC. The starting materials are highly homogeneous glasses fused together in a gas-mixing aerodynamic levitation laser furnace. The project outcomes will provide accurate and consistent estimates of the heat flux through the core and the CMB. These results have strong implications for the understanding of the present-day heat flux at the CMB, the thermal history of Earth and heat transport mechanisms at the bottom of the lower mantle (e.g., via superplumes).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.

地幔中的热对流驱动着板块构造。这个过程将热量从行星内部的核心和地幔输送到地球表面。通过地幔的热传输对于维持地核中的地球发电机和保护地表免受太阳风影响的磁场至关重要。地幔动力学依赖于对流、传导(接触)和辐射(例如光)的传热率。因此，定量地幔和地核物质的导热系数对于理解地球的热系统、动力学和演化至关重要。然而，这是具有挑战性的，因为地球深处普遍存在极端的压力和温度。在这里，研究人员测量了下地幔矿物和核心富铁合金的热导率。他们对在两颗相对的钻石尖端压缩的合成材料进行实验，这会产生相应的高压。他们使用高功率激光来加热样本并改变它们的温度。导热和辐射热特性是使用该团队先前开发的最先进的光谱技术提取的。该项目逐渐揭开了极端条件下热传输的物理学面纱。它推进了地球科学领域，以及材料科学中具有潜在能源应用的邻近领域。它为华盛顿卡内基研究所的一名博士后助理提供支持和培训，并向本科生和高中生提供服务。该项目还促进了与欧洲科学家的国际合作。地球内部物质的导热系数是控制地球热历史和动力学的关键参数。热性质制约着涉及行星吸积和分化、地幔和地核的热演化以及地球磁场产生的过程。在这里，研究小组专注于更准确地限制通过外核和核-地幔边界(CMB)的热流。在激光加热的金刚石顶压室(DAC)中的实验与深部地球温度分布的模拟相结合。该团队应用了瞬变加热和宽带光学光谱，这是他们之前开发的两项新技术；这些技术可以量化热边界层的传导和辐射传导性。研究人员开发了一种新技术--“脉冲电导”技术--它与瞬变加热相结合，可以量化外核的热导率。这些实验是在大容量装置中或在DAC中原位合成的富铁合金(包括熔体)和高质量的相关矿物(如桥锰矿单晶)上进行的。起始材料是高度均匀的玻璃，在混合气体的空气动力悬浮激光熔炉中熔合在一起。项目成果将对通过堆芯和CMB的热通量提供准确和一致的估计。这些结果对理解CMB的现今热通量、地球的热历史和下地幔底部的热传输机制(例如，通过超强热柱)具有很大的影响。这一奖项反映了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。

项目成果

Radiative thermal conductivity of single-crystal bridgmanite at the core-mantle boundary with implications for thermal evolution of the Earth

核幔边界处单晶桥锰矿的辐射热导率对地球热演化的影响

• DOI: 10.1016/j.epsl.2021.117329
• 发表时间: 2022
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Murakami Motohiko;Goncharov Alexander F.;Miyajima Nobuyoshi;Yamazaki Daisuke;Holtgrewe Nicholas
• 通讯作者: Holtgrewe Nicholas

Thermal conductivity of materials under pressure

• DOI: 10.1038/s42254-022-00423-9
• 发表时间: 2022-02
• 期刊: Nature Reviews Physics
• 影响因子: 38.5
• 作者: Yan Zhou;Zuo-Yuan Dong;W. Hsieh;A. Goncharov;Xiao-Jia Chen

Contrasting opacity of bridgmanite and ferropericlase in the lowermost mantle: Implications to radiative and electrical conductivity

• DOI: 10.1016/j.epsl.2021.116871
• 发表时间: 2021-05
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: S. Lobanov;F. Soubiran;N. Holtgrewe;J. Badro;Jung‐Fu Lin;A. Goncharov

Structure and properties of two superionic ice phases

• DOI: 10.1038/s41567-021-01351-8
• 发表时间: 2021-10
• 期刊: Nature Physics
• 影响因子: 19.6
• 作者: V. Prakapenka;N. Holtgrewe;S. Lobanov;A. Goncharov