Collaborative Research: Decoding thermal and magmatic history of mafic and ultramafic rocks through systematic studies of cation diffusion in pyroxene

斜方辉石和单斜辉石是地球上地幔和下地壳中的两种主要造岩矿物。 辉石的常量和微量元素组成已被广泛用于推断含辉石岩石经历的热历史和岩浆历史。 天然岩石中辉石的一个共同特征是存在出溶纹层。在存在出溶层片的情况下，没有阳离子在辉石中扩散的模型，这阻碍了含辉石岩石热历史的解释。本次合作研究的重点是铝，钙，锆，铪在辉石中的扩散。该项目包括三个主要任务：（1）辉石中出溶层对阳离子扩散作用的理论和数值研究;（2）辉石中Al、Ca、Zr和Hf扩散的实验研究;（3）地球化学应用。结果将是一组模型的扩散质量转移的辉石颗粒，有出溶层流。这些扩散模型具有通用性，也可用于岩石学和地球化学领域以外的复合材料化学和力学性质的研究。Al，Ca，Zr和Hf的扩散系数，然后将被应用到开发广义的质量传递模型，可用于量化稀土元素（REE）和高场强元素（HFSE）分馏不平衡熔融期间沿着地幔柱，然后亚固相线再平衡。将开发Ca-in-opx温度计和Al-in-opx温度计的闭合温度的新模型。这些新模型将用于研究不同构造背景下橄榄岩中辉石的稀土元素和高场强元素的分布和分馏。拟议工作的更广泛影响将侧重于研究生和本科生的培训和对高产女科学家的支持。在这个拟议的工作中开发的层压板中和通过层压板的扩散模型是通用的，可以用来研究地球科学以外的领域的复合材料的化学和力学性能。镁铁质和超镁铁质岩石中辉石的主量和微量元素分带现象是研究含辉石岩石热演化史和岩浆演化史的重要线索。 天然岩石中辉石的一个共同特征是存在出溶纹层。 尽管在量化稀土元素（REE）和高场强元素（HFSE）在辉石中的扩散方面取得了重大进展，但对铝在辉石中的扩散知之甚少。 有没有公开的数据，钙在斜方辉石中的扩散和阳离子扩散的模型，并通过辉石中存在的出溶laminate。本次合作研究的重点是辉石中Al、Ca和HFSE的扩散分布及其地球化学应用。 该项目包括三个主要任务：（1）辉石中出溶层对阳离子扩散作用的理论和数值研究;（2）辉石中Al、Ca、Zr和Hf扩散的实验研究;（3）地球化学应用。 大多数扩散实验将在1个大气压下进行。 压力对铝，钙锆，铪在辉石中扩散的潜在影响尚不清楚，但将进行一些更高压力的实验。 Al在实验装药中的扩散分布将用27 Al（p，gamma）28 Si核反应测量。 将使用卢瑟福背散射光谱法测量Ca、Zr和Hf的扩散分布。 任务1的结果是一组微观和宏观尺度的模型，在辉石颗粒具有出溶层流扩散传质。 这些扩散模型具有通用性，也可用于岩石学和地球化学领域以外的复合材料化学和力学性质的研究。 连同公布的分配和扩散数据，铝，钙，锆和铪的扩散系数从任务2将被用来开发广义的质量传递模型，可用于量化稀土元素和HFSE分馏不平衡熔融期间沿着的地幔柱，然后亚固相线再平衡。 作为任务3的一部分，将开发Ca-in-opx温度计和Al-in-opx温度计的闭合温度的新模型。 这些新模型将用于研究不同构造背景下橄榄岩中辉石的稀土元素和高场强元素的分布和分馏。拟议工作的更广泛影响将侧重于人力资源，其中包括研究生和本科生培训以及对一名高产女科学家的支持。 所提出的工作将构成研究生博士论文的主要部分。 该项目将为本科生提供实验室分析和计算机建模经验，并为高级论文项目提供研究机会。在这个拟议的工作中开发的层压板中和通过层压板的扩散模型是通用的，可用于研究地球科学以外领域的复合材料的化学和机械性能。这个奖项反映了NSF的法定使命，并被认为是值得支持的，通过使用基金会的知识价值和更广泛的影响审查标准进行评估。

Orthopyroxene and clinopyroxene are two major rock-forming minerals in the Earth’s upper mantle and lower crust. Major and trace element compositions of the pyroxenes have been widely used to infer thermal and magmatic histories experienced by pyroxene-bearing rocks. A common feature of pyroxene in natural rocks is the presence of exsolution lamellae. There is no model for cation diffusion in and through pyroxene in the presence of exsolution lamellae, which hinders the interpretation of thermal history of pyroxene-bearing rocks. The focus of this collaborative study is Al, Ca, Zr, and Hf diffusion in pyroxene. The project consists of three main tasks: (1) theoretical and numerical studies of the role of exsolution lamellae on cation diffusion in pyroxene; (2) experimental studies of Al, Ca, Zr, and Hf diffusion in pyroxene; and (3) geochemical applications. The outcome shall be a set of models for diffusive mass transfer across pyroxene grains that have exsolution lamellae. These diffusion models are general and can also be used to study chemical and mechanic properties of composite materials outside the field of petrology and geochemistry. Al, Ca, Zr and Hf diffusion coefficients will then be applied to develop generalized mass transfer models that can be used to quantify rare earth element (REE) and high-field strength element (HFSE) fractionation during disequilibrium melting along a mantle adiabat followed by subsolidus re-equilibration. New models for closure temperatures of the Ca-in-opx thermometer and the Al-in-opx thermometer will be developed. These new models will be used to study the distribution and fractionation of REE and HFSE in pyroxenes in peridotites from different tectonic settings. The broader impacts of the proposed work will focus on graduate and undergraduate training and support of a highly productive female scientist. Models for diffusion in and through laminates to be developed in this proposed work are general and can be used to study chemical and mechanic properties of composite materials in fields outside Earth science. Major and trace element zoning in pyroxene has often been observed in mafic and ultramafic rocks, which may provide important clues to the thermal and magmatic histories experienced by the pyroxene-bearing rocks. A common feature of pyroxene in natural rocks is the presence of exsolution lamellae. Although significant progress has been made in quantifying rare earth element (REE) and high field strength element (HFSE) diffusion in pyroxene, very little is known about Al diffusion in pyroxene. There are no published data for Ca diffusion in orthopyroxene and no model for cation diffusion in and through pyroxene in the presence of exsolution lamellae. The focus of this collaborative study is Al, Ca and HFSE diffusion and distribution in pyroxene and their geochemical applications. The project consists of three main Tasks: (1) theoretical and numerical studies of the role of exsolution lamellae on cation diffusion in pyroxene; (2) experimental studies of Al, Ca, Zr, and Hf diffusion in pyroxene; and (3) geochemical applications. The majority of the diffusion experiments will be conducted at 1-atm pressure. The potential effects of pressure on Al, Ca Zr, and Hf diffusion in pyroxene are not known, but some higher-pressure experiments will be conducted. Diffusion profiles of Al in experimental charges will be measured with the 27Al(p,gamma)28Si nuclear reaction. Diffusion profiles of Ca, Zr and Hf will be measured with Rutherford Backscattering Spectrometry. The outcome of Task 1 is a set of microscale and macroscale models for diffusive mass transfer across pyroxene grains that have exsolution lamellae. These diffusion models are general and can also be used to study chemical and mechanic properties of composite materials outside the field of petrology and geochemistry. Together with published partitioning and diffusion data, Al, Ca, Zr and Hf diffusion coefficients from Task 2 will be used to develop generalized mass transfer models that can be used to quantify REE and HFSE fractionation during disequilibrium melting along a mantle adiabat followed by subsolidus re-equilibration. As part of Task 3, new models for closure temperatures of the Ca-in-opx thermometer and the Al-in-opx thermometer will be developed. These new models will be used to study the distribution and fractionation of REE and HFSE in pyroxenes in peridotites from different tectonic settings. The broader impacts of the proposed work will focus on human resources, which include graduate and undergraduate training and support of a highly productive female scientist. The proposed work will constitute a major part of the graduate student’s PhD thesis. The project will provide laboratory analytical and computer modeling experiences for undergraduate students and research opportunities for senior thesis projects. Models for diffusion in and through laminates to be developed in this proposed work are general and can be used to study chemical and mechanic properties of composite materials in fields outside Earth science.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.