Rheology and microstructural evolution of serpentine

蛇纹石是一组含水矿物，通常形成于地球上的断层和其他界面上，在那里水能够与其他无水矿物发生反应。由于蛇纹石具有许多不同寻常的物理性质，人们推测蛇纹石类矿物在构造板块之间的边界动力学中起着至关重要的作用。此外，蛇纹岩可能控制地震可能发生或不可能发生的地方。然而，蛇纹石只能在狭窄的压力和温度条件下保持稳定，这阻碍了解释其行为的实验努力。这项研究将包括两组新颖的实验，以阐明蛇纹岩在类似地球的变形条件下如何改变形状或结构。更广泛的影响包括研究生的培训，可视化实验室的教育和推广模块的开发，以及跨学科的科学影响。该项目的目标是进一步澄清反辉石的流变学和相关的变形微结构，蛇纹石的高压和温度阶段。提出了两套实验方案。第一组实验将利用位于圣路易斯的华盛顿大学的大体积扭转(LVT)仪器，研究多晶蛇纹石的微观结构随应变的演变。这些实验的目的是表征由变形产生的晶体择优取向(CPO)，并确定产生稳态微结构的条件。为了解释可能存在蛇纹岩的地区的地震波速和地震各向异性，需要获得关于反蛇纹岩CPO的瞬时演化的数据。第二组实验将使用微机械方法，包括纳米压痕和微柱压缩测试，精确测量高达600摄氏度的反辉石的塑性流变学。这些数据将被用来在与俯冲带相关的条件下约束反辉石的流动规律，并可能在未来的努力中用于模拟板材界面的变形。这一奖项反映了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。

Serpentine is a group of hydrous minerals that is commonly formed along faults and other interfaces in Earth where water is able to react with other anhydrous minerals. Because serpentine has a number of unusual physical properties, it is hypothesized that serpentine-group minerals play an essential role in the dynamics of boundaries between tectonic plates. Furthermore, serpentine may control where earthquakes can or cannot occur. However, serpentine is only stable through a narrow range of pressure and temperature conditions, which has hindered experimental efforts to unravel its behavior. This study will involve two sets of novel experiments to elucidate how serpentine changes shape or structure when Earth-like deformation conditions are applied. Broader Impacts include training of a graduate student, development of educational and outreach modules in a visualization laboratory, and cross-disciplinary science impact.The objective of this project is to clarify further the rheology and associated deformation microstructures of antigorite, the high pressure and temperature phase of serpentine. Two sets of experiments are proposed. The first set of experiments will investigate microstructural evolution of polycrystalline serpentine as a function of strain, using the Large Volume Torsion (LVT) apparatus at Washington University in St. Louis. The purpose of these experiments is to characterize the crystallographic preferred orientation (CPO) generated by deformation and determine the conditions at which steady-state microstructures are produced. The data that will be obtained on the transient evolution of antigorite CPO are needed to interpret seismic wave-speeds and seismic anisotropy in regions where serpentine is inferred to be present. The second set of experiments will use micromechanical methods, including nanoindentation and micropillar compression testing, to measure precisely the plastic rheology of antigorite up to 600 degrees C. These data will be used to constrain flow-laws for antigorite at conditions relevant to subduction zones, and may be used in future efforts to model deformation at the slab interface.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.