Calibrating olivine crystallographic preferred orientation as a mantle water detector

地球与其他行星的区别在于板块构造的发生和其表面液态水的存在。固体地幔的流动驱动着板块构造旋回和深部水循环。研究人员将研究储存在橄榄石（最丰富的上地幔矿物）中的水与地幔流动之间的相互作用。少量水的存在，以氢的形式取代到橄榄石晶格中，可以改变橄榄石晶格在流动过程中排列的方式。晶格排列的这种转变的条件是在预期的水含量和上地幔的应力条件，但几乎没有多晶橄榄石的实验室实验重新创建这些织物。为了解决这个问题，研究人员将联合收割机对橄榄石聚集体的实验室实验与阿拉斯加塔尔凯特纳洋内弧的地幔岩分析相结合。进行实验室实验的过程将通过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。名义上无水矿物（如橄榄石）中的少量水可以极大地影响地幔的粘度，熔融温度和各向异性结构及其整体动力学。解释地幔矿物中水丰度的测量结果已被证明是具有挑战性的，因为氢扩散如此之快，以至于在地幔的折返过程中，水含量会发生显着变化。以前的实验表明，变形引起的组构的发展是敏感的橄榄石水含量，因此橄榄石组构可能提供一个独立的地幔矿物的水含量的约束。该项目将通过在最近更新的高压实验装置中对橄榄石聚集体进行变形实验来限制与E型组构形成相关的含水量和应力条件。将对实验样品和塔尔凯特纳样品进行详细的显微结构分析，以评价它们的相似性，这将用于支持将实验结果外推到地球条件。本项目将解决以下问题：（1）形成E型橄榄石组构的有利条件是什么？(2)橄榄石E型组构能否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，并被认为是值得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的支持。

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.