Calibrating olivine crystallographic preferred orientation as a mantle water detector

地球与其他行星的不同之处在于板块构造的出现和表面液态水的存在。固体地幔流动驱动板块构造旋回和地球深部水循环。研究人员将研究储存在橄榄石中的水和地幔中流动的水之间的相互作用。橄榄石是最丰富的上地幔矿物。微量的水以氢的形式出现在橄榄石晶格中，可以改变橄榄石晶格在流动过程中排列的方式。这种晶格排列转变的条件是在预期的上地幔水分含量和应力条件下进行的，但几乎没有对多晶橄榄石的实验室实验重现这些组构。为了解决这个问题，研究人员将把对橄榄石聚集体的实验室实验与对阿拉斯加塔尔基特纳洋内弧的地幔岩石的分析结合起来。进行实验室实验的过程将通过专为大学课程设计的视频和幻灯片来记录。该项目将包括一名博士后研究员的高级培训和一名本科生的暑期研究项目，该项目将机器学习算法应用于岩石。橄榄石等名义上无水矿物中的少量水可以极大地影响地幔的粘度、熔融温度、各向异性结构及其整体动力学。事实证明，解释地幔矿物中水丰度的测量具有挑战性，因为氢的扩散如此之快，以至于在地幔折返过程中，水含量可能会发生显着变化。以前的实验表明，变形诱导的组构发育对橄榄石水分含量很敏感，因此橄榄石组构可能对地幔矿物的水分含量提供独立的约束。该项目将通过在最近更新的高压实验装置中对橄榄石集合体进行变形实验，来约束与E型织物形成相关的水分和应力条件。将对实验样品和Talkeetna样品进行详细的微观结构分析，以评估它们的相似性，这将用于支持将实验结果外推到地球条件。该项目将解决以下问题：(1)生产E型橄榄石织物的有利条件是什么？(2)橄榄石E型织物是否可以用作天然样品中的地幔水探测器？该奖项反映了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。

The Earth is distinguished from other planets by the occurrence of plate tectonics and the presence of liquid water on its surface. Flow of the solid mantle drives the plate tectonic cycle and deep Earth water cycle. The investigators will study the interaction between water stored in olivine, the most abundant upper mantle mineral, and flow in the mantle. The occurrence of tiny amounts of water, in the form of hydrogen substituted into the olivine lattice, can modify the way in which the olivine crystal lattice aligns during flow. The conditions for this transition in crystal lattice alignment are within the expected water content and stress conditions of the upper mantle, but almost no laboratory experiments on polycrystalline olivine have recreated these fabrics. To address this, the investigators will combine laboratory experiments on olivine aggregates with analysis of mantle rocks from the Talkeetna intraoceanic arc in Alaska. The process of conducting laboratory experiments will be documented through a video and slideshow designed for university-level courses. The project will involve the advanced training of a postdoctoral researcher and a summer research project for an undergraduate student that will apply machine learning algorithms to rocks.Small amounts of water in nominally anhydrous minerals such as olivine can greatly influence the viscosity, melting temperature, and anisotropy structure of the mantle and its overall dynamics. Interpreting measurements of water abundances in mantle minerals has proven challenging as hydrogen diffusion is so fast that water contents can be significantly modified during exhumation of the mantle. Previous experiments suggest that deformation-induced fabric development is sensitive to olivine water content and therefore olivine fabrics may provide an independent constraint on the water content of mantle minerals. This project will constrain the water content and stress conditions associated with E-type fabric formation through deformation experiments on olivine aggregates in a recently updated high-pressure experimental apparatus. Detailed microstructural analysis of experimental samples and Talkeetna samples will be performed to evaluate their similarities, which will be used to support the extrapolation of experimental results to Earth conditions. This project will address the following questions: (1) What are the conditions favorable to producing an E-type olivine fabric? (2) Can olivine E-type fabrics be used as a mantle water detector in natural samples?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.