Synchrotron deformation experiments of olivine under the deep upper mantle conditions: Transient creep, plastic anisotropy, and the role of grain-boundary sliding.

上地幔深部条件下橄榄石的同步加速变形实验：瞬态蠕变、塑性各向异性和晶界滑动的作用。

• 批准号: 2322719
• 负责人: Jennifer Girard
• 金额: $ 46.61万
• 依托单位: Yale University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-09-01 至 2026-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2322719&HistoricalAwards=false
• 关键词: Synchrotron; deformation; experiments; olivine; under

The Earth’s mantle dynamics are governed by the mechanical properties of its constituent materials. These dynamics include geological processes with human impacts, such as surface deformations that occur after earthquakes and ice ages, with consequences on sea-level rise. Olivine is the most abundant mineral in the upper mantle, and it is likely the weakest mineral. Therefore it is olivine’s mechanical properties that control small vertical displacements of the crust and mantle due to the melting of ice caps after the last ice age. This vertical displacement, called post-glacial rebound, is a time dependent deformation arising from the transient creep of the mantle, and is used to estimate mantle viscosity. In contrast, the convection of the mantle is a steady-state phenomenon, frequently resulting in a different effective viscosity. Determining transient creep of olivine will therefore allow accurate constraint of mantle viscosity across time scales, but studies on olivine transient creep are limited. This project will perform deformation experiments of olivine with and without dissolved water under the conditions of the Earth’s upper mantle. The results will be interpreted from a materials science point of view to interpret how the mineral deforms under transient and steady-state creep for a more complete application to geophysical processes such as post-glacial rebound and post-seismic relaxation. This is the first NSF proposal for the PI, who is also the Director of the Yale Earth Materials Characterization Center (EMC2); this project will broaden and support the mission of EMC2 with further outreach, training, and educational opportunities for students and postdoctoral scholars. The PIs actively participate in all levels of STEM training; specifically, this project will train an undergraduate student and a post-doctoral researcher on synchrotron high-pressure deformation experiments, giving them valuable experience in state-of-the-art techniques. In this project, the PI will address geophysically important questions such as post-glacial rebound and post-seismic relaxation which require understanding of transient creep mechanisms at small strains. Deformation in the transient creep regime is controlled by the rate of formation and motion of linear crystal defects produced during deformation. Pressure and water content has been shown to affect the motion of linear defects differently in the steady state, and therefore will most likely also affect transient creep. As creep involves multiple microscopic processes, the rheological properties inferred from short-term deformation may differ from those relevant to long-term deformation. Studies on transient creep have been limited, especially in elucidating the relative roles of inter-granular versus intra-granular deformation mechanisms. This study will provide new deformation experiments on olivine to bridge transient and steady-state creep regimes. This work will include analysis of the roles of inter- and intra-granular deformation mechanisms, and how they are affected by the variations in pressure and water content. The project further includes a set of experiments where grain-boundary sliding will be studied using a bi-crystal to estimate the effect of grain-boundary sliding on viscosity. All results from olivine aggregate and single crystals will be interpreted using materials physics and microstructural characterization, and implications on geophysical processes such as post-glacial rebound and post-seismic relaxation will be determined.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.

地球地幔动力学受其组成材料的机械特性控制，这些动力学包括受人类影响的地质过程，例如地震和冰河时代后发生的地表变形，从而影响海平面上升。在上地幔中，它可能是最弱的矿物，因此，由于最后一个冰河时代后冰盖的融化，橄榄石的机械特性控制着地壳和地幔的小垂直位移。冰川后回弹是地幔瞬态蠕变引起的与时间相关的变形，用于估计地幔粘度，相反，地幔对流是稳态现象，经常导致不同的有效粘度。因此，确定橄榄石的瞬态蠕变将允许在不同时间尺度上准确地约束地幔粘度，但对橄榄石瞬态蠕变的研究是有限的，该项目将进行有或没有橄榄石的变形实验。地球上地幔条件下溶解水的结果将从材料科学的角度进行解释，以解释矿物在瞬态和稳态蠕变下如何变形，以便更完整地应用于地球物理过程，例如冰期后的回弹。这是国家科学基金会向 PI 提出的第一个提案，PI 也是耶鲁大学地球材料表征中心 (EMC2) 的主任，该项目将通过进一步的推广、培训和教育来扩大和支持 EMC2 的使命；机会针对学生和博士后学者积极参与各级STEM培训；具体来说，该项目将培训一名本科生和一名博士后研究员进行同步加速器高压变形实验，为他们提供宝贵的经验。在这个项目中，PI 将解决地球物理上的重要问题，例如冰川后回弹和地震后松弛，这些问题需要了解小应变下的瞬时蠕变机制。瞬时蠕变状态中的变形是由形成速率控制的。变形过程中产生的线性晶体缺陷的运动已被证明对稳态下线性缺陷的运动有不同的影响，因此很可能也会影响瞬态蠕变，因为蠕变涉及多个微观过程，因此流变特性。从短期变形推断的结果可能与与长期变形相关的研究有所不同，特别是在阐明晶间变形机制与晶内变形机制的相对作用方面。橄榄石变形实验以桥接瞬态和稳态蠕变状态。这项工作将包括分析晶粒内和晶粒内变形机制的作用，以及它们如何受到压力和含水量变化的影响。一系列实验将使用双晶来研究晶界滑动，以估计晶界滑动对粘度的影响。橄榄石聚集体和单晶的所有结果都将使用材料物理和微观结构进行解释。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优点和更广泛的影响审查标准进行评估，被认为值得支持。