Collaborative Research: Experimental and computational constraints on the isotope fractionation of Mossbauer-inactive elements in mantle minerals

合作研究：地幔矿物中穆斯堡尔非活性元素同位素分馏的实验和计算约束

• 批准号: 2246686
• 负责人: Dongzhou Zhang
• 金额: $ 27.49万
• 依托单位: University of Hawaii
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-07-01 至 2026-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2246686&HistoricalAwards=false
• 关键词: Collaborative; Research; Experimental; computational; constraints

Isotope compositions of deep-earth minerals provide crucial constraints on the earth’s internal structure and chemical evolution. The isotope compositions of deep-earth minerals are controlled by a process named isotope fractionation, in which different isotopes redistribute between different minerals under various pressures and temperatures. There are three conventional ways to constrain equilibrium isotope fractionation in deep-earth minerals, namely theoretical calculation, mass spectroscopy, and nuclear resonance scattering. However, each method has its own challenges. Theoretical calculation is limited by physical approximations used in the model and has to be benchmarked by experiments; mass spectroscopy has difficulty in determining the attainment of equilibrium and is time-consuming; and nuclear resonance scattering can only be applied to the few Mössbauer-active elements. This proposal describes a novel multidisciplinary study on the isotope fractionations of deep-earth minerals that are difficult to be constrained by conventional experimental approaches, through collaborative and synergetic efforts by combining state-of-the-art X-ray spectroscopy with theoretical calculations. The researcher's approach is experimentally benchmarked, time-efficient, directly reflects the equilibrium isotope fractionation, and can be applied to nearly all elements. They aim to answer the following questions with their proposed study: 1) How do the Mössbauer-inactive elements in deep-earth minerals redistribute with pressure, temperature, and crystal structure? 2) How to constrain the fractionation of Mössbauer-inactive elements in deep earth solid solutions efficiently? and 3) How does vibrational anharmonicity affect the isotope fractionation in mantle silicates? The project will support three early to mid-career researchers to continue their research at the University of Hawaii at Maona (Zhang and B. Chen) and Purdue University (M. Chen). Through this project, the team will develop both experimental instruments at a national user facility and open-source codes for computation, and the research suite will be available to domestic and international researchers in earth sciences and beyond. Undergraduate assistants and postdoc scholars will be involved in this project. This project is also committed to establishing the career development pathways for the involved early-career researchers, pushing for the gender and racial equality in geoscience, and broadening the participation in STEM of traditionally underrepresented minorities.The fractionation of the isotopes of constituent elements of mantle minerals at high P-T conditions are considered the ramifications of the differentiation of the Earth, offering crucial clues for the mantle’s composition and chemical evolution. Previous studies on the isotope fractionation of Mössbauer-inactive elements between minerals were either measured using mass spectroscopy in which the attainment of equilibrium requires additional caution, or estimated from theoretical calculations without corroboration from experiments. The researchers have demonstrated that the reduced partition function ratio (β-factor) of tetracoordinated Si can be constrained by theoretical-calculation-calibrated in-situ high-T SXD experiments. In this proposed project, they will extend the method to determine experimentally constrained β-factors of hexacoordinated Si in non-quenchable deep-earth minerals for the first time. They will also tackle challenges to establish an efficient approach to determine β-factors in solid solutions by theoretical calculations, which are to be benchmarked by SXD experiments and thus allows them to investigate the isotope fractionation of hexacoordinated Ti in deep-earth minerals. Their proposed combined approach circumvents direct theoretical modeling of solid solutions, which significantly reduces computational costs. Using the combined approaches of experiments and theoretical modeling, the correction to Si β-factor in hydrous phyllosilicates induced by the vibrational anharmonicity will be investigated. The proposed experimentally benchmarked machine learning framework to establish a highly accurate yet efficient model will allow them to provide reliable estimations of Si β-factor in anharmonic mineral systems. Though they only propose to study select Mössbauer-inactive elements (Si & Ti) in this proposal, the same approach can be extended to other elements such as C, O, Mg, and Ca. All the three proposed tasks will build the foundation for a complete landscape of isotope distribution in mantle minerals, and will enhance understanding of the Earth’s isotopic composition and in turn its chemical evolution. This project is jointly funded by Cooperative Studies of the Earth's Deep Interior (CSEDI) and the Established Program to Stimulate Competitive Research (EPSCoR).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.

深地球矿物质的同位素组成对地球的内部结构和化学演化提供了重要的限制。深地球矿物质的同位素组成由一个名为同位素分馏的过程控制，其中在各种压力和温度下，不同矿物质之间的不同同位素重新分布。有三种常规方法可以约束深地球矿物质中等效的同位素分馏，即理论计算，质谱和核共振散射。但是，每种方法都有自己的挑战。理论计算受模型中使用的物理近似的限制，必须通过实验进行基准测试。质谱很难确定同等的属性，并且耗时。核共振散射只能应用于少数莫斯鲍尔活性元素。该提案描述了一项关于深地球矿物质的同位素分馏的新的多学科研究，这些研究很难通过将先进的X射线光谱谱与理论计算相结合，这是通过常规实验方法，通过协作和协同努力来限制的。研究人员的方法是通过实验基准的，时间效率的，直接反映了等效的同位素分馏，并且可以应用于几乎所有元素。他们的目的是通过提出的研究回答以下问题：1）深地球矿物质中的莫斯鲍尔无效元素如何与压力，温度和晶体结构重新分配？ 2）如何有效地限制在深层固定溶液中Mössbauer-In活性元素的分馏？ 3）振动非谐度如何影响地幔硅硅硅硅硅的同位素分馏？该项目将支持三名至中期研究人员在夏威夷大学（Zhang and B. Chen）和普渡大学（M. Chen）的夏威夷大学继续研究。通过该项目，团队将在国家用户设施和开源计算代码中开发实验仪器，研究套件将为地球科学及其他地区的国内和国际研究人员提供。本项目将参与本科助理和博士后学者。该项目还致力于为参与的早期研究人员建立职业发展途径，推动地球科学中的性别和种族平等，并扩大了传统上代表性不足的少数群体的参与。 进化。先前关于矿物质之间Mössbauer不活跃元件的同位素分馏的研究要么使用质谱法测量，在质谱上，在没有实验中辅助的情况下，同等的均质需要额外谨慎，要么从理论计算中估计。研究人员已经证明，四核Si的分区函数比（β因子）可以受到理论计算量化的位置高-T-T SXD实验的约束。在这个拟议的项目中，他们将扩展该方法，以确定第一次在不可降低的深地球矿物中实验限制的己二氏链球化的β因子。他们还将应对通过理论计算来确定固定溶液中β因子的有效方法的挑战，该计算应通过SXD实验进行基准测试，从而使他们能够研究深度地球矿物中己二酸己二的同位素分馏。他们提出的组合方法规定了实心解决方案的直接理论建模，从而大大降低了计算成本。使用实验和理论模型的组合方法，将研究由振动非谐波诱导的液压纤维硅酸盐中Siβ因子的校正。提出的实验基准的机器学习框架以建立高度准确但有效的模型，将使他们能够在Anharmonic矿物系统中对Siβ因子的可靠估计。尽管他们只建议在此提案中研究某些Mössbauer-In活性元素（SI＆TI），但可以将相同的方法扩展到C，O，MG和CA等其他元素。所有提议的任务将为地幔矿物质的同位素分布的完整景观奠定基础，并将增强对地球同位素组成和化学演化的理解。该项目由对地球深层内部（CSEDI）的合作研究以及刺激竞争性研究的既定计划（EPSCOR）共同资助。该奖项反映了NSF的法定任务，并通过基金会的知识分子优点和更广泛的影响标准通过评估来诚实地对支持进行评估。

项目成果

Externally Heated Diamond ANvil Cell Experimentation (EH-DANCE) for studying materials and processes under extreme conditions

外部加热金刚石砧室实验 (EH-DANCE)，用于研究极端条件下的材料和工艺

• DOI: 10.1063/5.0180103
• 发表时间: 2023
• 期刊: Review of Scientific Instruments
• 影响因子: 1.6
• 作者: Wang, Siheng;Berrada, Meryem;Chao, Keng-Hsien;Lai, Xiaojing;Zhu, Feng;Zhang, Dongzhou;Chariton, Stella;Prakapenka, Vitali B.;Sinogeikin, Stanislav;Chen, Bin
• 通讯作者: Chen, Bin