Collaborative Research: Diffusion of High Field Strength Elements (HFSE) and Rare Earth Elements (REE) in Pyroxenes and Pyroxene-bearing Rocks

合作研究：高场强元素 (HFSE) 和稀土元素 (REE) 在辉石和含辉石岩石中的扩散

• 批准号: 0738830
• 负责人: Yan Liang
• 金额: $ 15.01万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-03-01 至 2012-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0738830&HistoricalAwards=false
• 关键词: Collaborative; Research; Diffusion; Field; Strength

Intellectual Merit. The abundance and distribution of high field strength elements (HFSE) and rare earth elements (REE) in mafic and ultramafic rocks provide important clues to understanding the origin and evolution of igneous rocks. While the distribution of such trace elements between coexisting minerals and melt in many magmatic processes can be understood in terms of equilibrium fractionation, there are occasions where substantial chemical disequilibria between coexisting phases might provide unique and important insights into the time scales of geological processes. To better understand the various processes that give rise to disequilibrium distributions of HFSE and REE in the mantle and mantle derived rocks, partition coefficients and diffusion coefficients of these trace elements in major rocking-forming minerals are needed. Mineral-melt and mineral-mineral HFSE and REE partition coefficients for important mafic minerals such as clinopyroxene (cpx) and orthopyroxene (opx) are available for a range of temperatures, pressures, and melt and crystal compositions. There exists no HFSE diffusion data for any pyroxene compositions, while REE diffusion data in pyroxene is only available for the near endmember diopside and enstatite. It is not known how strongly REE and HFSE diffusion rates in pyroxenes depend on pyroxene compositions. In order to establish a database for studying kinetic fractionations of HFSE and REE in pyroxene-bearing rocks during magmatic and subsolidus processes, a three-year collaborative research program is proposed that consists of two major components: (1) laboratory studies of HFSE and REE diffusion in pyroxenes; and (2) ion probe and numerical studies of HFSE and REE zoning in coexisting cpx and opx in peridotites from the Trinity ophiolite. A range of pyroxene compositions common in the origin and differentiation of mafic and ultramafic rocks will be explored. Diffusion profiles from most diffusion experiments will be measured with Rutherford Backscattering Spectrometry (RBS). Trace element concentration profiles in coexisting cpx and opx will be measured by ion probe. Together with published partition and diffusion data, diffusion coefficients of HFSE and REE in pyroxenes obtained from this study will be used to develop generalized geospeedometry models that can be used to understand the processes and time scales of melt-rock reaction, via dissolution and reprecipitation, and subsolidus reequilibration experienced by the Trinity peridotites.Broader Impacts. Diffusion is a fundamental mass transfer process in solid-Earth systems and hence a very general topic. Diffusion coefficients obtained from this work will be widely applicable to pyroxenes and pyroxene bearing rocks from the Earth, Moon, Mars, and various meteorites. The dissolution-reprecipitation model to be developed will be useful to a range of practical applications beyond Earth Sciences. Results from this study will also provide valuable information for a diverse group of petrologists, geochemists, geochronologists, and cosmochemists, promoting cross-discipline integration in Earth Sciences. Results will be disseminated to a broader audience through public lectures and undergraduate and graduate courses. Finally, the proposed project will provide hands-on experience for undergraduates, research opportunities for senior thesis work, and experimental, computational, and educational experience for graduate students.

智力优势。镁铁岩和超镁铁岩中高场强元素（HFSE）和稀土元素（REE）的丰度和分布特征为认识火成岩的成因和演化提供了重要线索。虽然在许多岩浆过程中，这种微量元素在共存矿物和熔体之间的分布可以从平衡分馏的角度来理解，但有时共存相之间的大量化学不平衡可能为地质过程的时间尺度提供独特而重要的见解。为了更好地理解导致地幔和幔源岩中HFSE和REE不平衡分布的各种过程，需要这些微量元素在主要造岩矿物中的分配系数和扩散系数。矿物熔体和矿物矿物HFSE和稀土元素分配系数的重要镁铁质矿物，如单斜辉石（cpx）和斜方辉石（opx）的范围内的温度，压力，熔体和晶体成分。不存在任何辉石组合物的HFSE扩散数据，而辉石中的REE扩散数据仅适用于近端元透辉石和顽火辉石。目前还不清楚辉石中稀土元素和高场强稀土元素的扩散速率对辉石成分的依赖程度。为了建立含辉石岩石在岩浆和亚固相过程中HFSE和REE动力学分馏研究的数据库，提出了一个为期三年的合作研究计划，包括两个主要部分：（1）实验室研究辉石中HFSE和REE的扩散;（2）Trinity蛇绿岩橄榄岩中cpx和opx共存的HFSE和REE分带的离子探针和数值研究。将探讨镁铁岩和超镁铁岩的起源和分异过程中常见的一系列辉石成分。大多数扩散实验的扩散曲线将采用卢瑟福背散射光谱法（RBS）进行测量。用离子探针测量了共存的cpx和opx中微量元素的浓度分布。连同公布的分区和扩散数据，从这项研究中获得的辉石HFSE和稀土元素的扩散系数将被用来开发广义geospeedometry模型，可用于了解熔融岩石反应的过程和时间尺度，通过溶解和再沉淀，和subsolidus再平衡经历的Trinity橄榄岩。扩散是固体-地球系统中的一个基本传质过程，因此是一个非常普遍的话题。从这项工作中获得的扩散系数将广泛适用于辉石和辉石轴承岩石从地球，月球，火星和各种陨石。溶解-再沉淀模型的开发将是有用的，地球科学以外的一系列实际应用。这项研究的结果也将为岩石学家、地球化学家、地质年代学家和宇宙化学家提供有价值的信息，促进地球科学的跨学科整合。研究结果将通过公开讲座以及本科生和研究生课程向更广泛的受众传播。最后，该项目将为本科生提供实践经验，为高级论文工作提供研究机会，为研究生提供实验，计算和教育经验。