CAREER: Deformational Evolution and Serpentinization of the Mantle Wedge Corner in Subduction Zones

事业：俯冲带地幔楔角的变形演化和蛇纹石化

• 批准号: 1847612
• 负责人: Ikuko Wada
• 金额: $ 54.64万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1847612&HistoricalAwards=false
• 关键词: CAREER; Deformational; Evolution; Serpentinization; Mantle

Subduction zones are regions where one tectonic plate sinks into the mantle beneath another plate. In between the two plates, a wedge-shaped piece of the upper mantle experiences extensive physical and chemical transformations. While cooling down, the corner of the mantle wedge is sheared and hydrated by fluids that arise from the dehydrating sinking plate. As rocks become hydrated through a process called serpentinization, the wedge corner becomes weaker and lighter. Serpentinization also causes rock expansion and changes in permeability which in turn affects fluid migration in subduction zones. The resulting fluid distribution and weakening have strong implications for important geological processes, such as great earthquakes and volcanic eruptions in subduction-zone settings. To better constrain the physical properties of the wedge corner, the PI will quantify the spatial extent of serpentinization using numerical modeling. The models will account for geophysical observations collected in subduction zones in North America and Japan and incorporate experimental data on rock deformation and hydration. The project outcomes will further our understanding of subduction-zone dynamics. They will also help interpreting seismic observations and assessing geohazards near plate boundaries. This project will support an early-career female scientist, the training of two graduate students in Earth Science, and educational outreach toward K-12 students and teachers, and the public.Inferring the extent of serpentinization in the mantle-wedge corner from seismic velocities is challenging because of the strong elastic anisotropy of the mineral antigorite. Antigorite is the main product of serpentinization in the wedge corner. It develops crystal-preferred orientations (CPOs) through deformation and topotactic growth from its parent mineral olivine. This can make the wedge corner highly anisotropic, but antigorite CPOs in this region are not well understood. Fracture permeability in the wedge corner controls the extent of serpentinization. However, the effect of background and reaction-induced stresses on fracture permeability is also unclear. To quantify serpentinization in the wedge corner, the PI will use three distinct classes of numerical models: (1) a time-dependent thermo-mechanical model for mineral texture evolution, (2) a mechanical model for spatial variations in the stress state and (3) a hydraulic-chemical-mechanical model for the development of reaction-induced fractures. The models will account for seismological, geodetic, gravity and magnetic observations in the forearc regions of three subduction zones (Cascadia, Nankai, and NE Japan). The PI will also integrate in the modeling experimental results on the rheology and microstructures of the relevant minerals. Model outcomes will help to constrain CPOs in the mantle wedge corner and the degree of serpentinization. They will also improve our understanding of background and reaction-induced stresses and their effects on serpentinization. This project has direct implications for our understanding of subduction zone dynamics and broader implications for the assessment of geohazards near plate boundaries. It will support an early-career female scientist, two graduate students and educational outreaches toward K-12 students and teachers, and the public.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.

俯冲带是一个区域，一个构造板沉入另一板下方的地幔。在这两个板之间，上地幔的楔形部分经历了广泛的物理和化学转化。冷却时，地幔楔的一角由脱水下沉板产生的流体剪切和水合。随着岩石通过称为蛇纹石化的过程变得水分，楔形角变得越来越弱和更轻。蛇纹石化还会导致岩石膨胀和渗透率变化，进而影响俯冲带中的流体迁移。所得的流体分布和弱化对重要地质过程具有很大的影响，例如俯冲区环境中的大地震和火山喷发。为了更好地限制楔形角的物理特性，PI将使用数值建模来量化蛇形化的空间范围。这些模型将考虑在北美和日本俯冲带中收集的地球物理观察结果，并纳入有关岩石变形和水合的实验数据。该项目的结果将进一步了解俯冲区动力学。他们还将帮助解释地震观测并评估板界附近的地球阵得到。该项目将支持一位早期职业女性科学家，对地球科学的两名研究生的培训，以及对K-12学生和老师的教育外展，以及公众。从塞斯维斯速度的地幔叶角中，蛇形角度的程度是具有挑战性的，因为矿物质抗抗物的强烈弹性各向异性。抗果石是楔形角中蛇纹石化的主要产物。它通过其父矿物橄榄石的变形和拓扑生长来发展晶体偏爱的方向（CPO）。这可以使楔形角度高度各向异性，但是该地区的抗牙CPO尚不清楚。楔形角中的断裂渗透性控制着蛇形化的程度。然而，背景和反应诱导的应力对断裂渗透性的影响尚不清楚。为了量化楔形角中的蛇纹石化，PI将使用三种不同的数值模型：（1）用于矿物质纹理演化的时间依赖性热机械模型，（2）应力状态中空间变化的机械模型和（3）用于反应诱发的琐事开发的水力化学模型模型。这些模型将解释三个俯冲区（Cascadia，nankai和NE Japan）前臂区域中的地震，大地，重力和磁观测。 PI还将集成在相关矿物质的流变学和微观结构的建模实验结果中。模型结果将有助于限制地幔楔角和蛇形化程度的CPO。 他们还将提高我们对背景和反应引起的压力及其对蛇纹膜化的影响的理解。该项目对我们对俯冲带动力学的理解有直接的影响，并对板界附近的地球阵得到的评估产生了更广泛的影响。它将支持一位早期职业女性科学家，两名研究生和对K-12学生和老师的教育宣传，公开奖。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的知识分子优点和更广泛影响的评估评估标准的评估来支持的。