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.

俯冲带是一个构造板块沉入另一个板块之下的地幔的区域。在两个板块之间，一块楔形的上地幔经历了广泛的物理和化学变化。在冷却过程中，地幔楔的一角被脱水下沉板块产生的流体剪切和水合。当岩石通过一个叫做蛇纹岩化的过程被水化时，楔角变得更弱、更轻。蛇纹岩化作用还引起岩石膨胀和渗透性的变化，这反过来又影响俯冲带中的流体迁移。由此产生的流体分布和减弱对重要的地质过程有很大的影响，例如俯冲带环境中的大地震和火山爆发。为了更好地约束楔形角的物理特性，PI将使用数值建模来量化蛇形化的空间范围。这些模型将考虑到在北美和日本俯冲带收集的地球物理观测数据，并纳入岩石变形和水合作用的实验数据。项目成果将进一步加深我们对俯冲带动力学的理解。它们还将有助于解释地震观测和评估板块边界附近的地质灾害。该项目将支持一名职业生涯初期的女科学家，培训两名地球科学研究生，并向K-12学生和教师以及公众提供教育推广。由于矿物叶蛇纹石具有很强的弹性各向异性，因此从地震速度推断地幔楔角的蛇纹石化程度具有挑战性。叶蛇纹石是楔角蛇纹石化作用的主要产物。它通过变形和从其母体矿物橄榄石的拓扑生长来发展晶体择优取向（CPOs）。这可以使楔角高度各向异性，但叶蛇纹石CPO在这一地区没有得到很好的理解。楔形角部的裂缝渗透率控制着蛇纹化的程度。然而，背景应力和反作用应力对裂缝渗透率的影响也不清楚。为了量化楔角中的蛇纹石化，PI将使用三种不同类别的数值模型：（1）矿物结构演化的时间依赖性热-力学模型，（2）应力状态空间变化的力学模型和（3）反应诱导裂缝发展的水力-化学-力学模型。这些模型将解释三个俯冲带（卡斯卡迪亚、南海和日本东北部）弧前地区的地震、大地测量、重力和磁力观测。PI还将整合相关矿物流变学和微观结构的模拟实验结果。模型结果将有助于限制地幔楔角中的CPO和蛇纹石化程度。 它们还将提高我们对背景和反应诱导的应力及其对蛇纹石化的影响的理解。该项目对我们理解俯冲带动力学有直接影响，对评估板块边界附近的地质灾害有更广泛的影响。该奖项将支持一名职业生涯初期的女科学家、两名研究生以及面向K-12学生和教师以及公众的教育推广活动。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。