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板块下方地幔的区域。在两个板块之间，上地幔的楔形部分经历了广泛的物理和化学变化。在冷却过程中，地幔楔的角部被脱水下沉板产生的流体剪切和水合。当岩石通过蛇纹石化过程变得水合时，楔形角变得更弱、更轻。蛇纹石化还会引起岩石膨胀和渗透率变化，进而影响俯冲带中的流体运移。由此产生的流体分布和减弱对重要的地质过程具有重大影响，例如俯冲带环境中的大地震和火山喷发。为了更好地约束楔角的物理特性，PI 将使用数值模型量化蛇纹石化的空间范围。这些模型将考虑在北美和日本俯冲带收集的地球物理观测结果，并纳入岩石变形和水合作用的实验数据。该项目的成果将进一步加深我们对俯冲带动力学的理解。它们还将帮助解释地震观测结果并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早期的女科学家、两名地球科学研究生的培训以及对 K-12 学生和教师以及公众的教育推广。从地震速度推断地幔楔角的蛇纹石化程度由于矿物叶蛇纹石具有很强的弹性各向异性，因此具有挑战性。叶蛇纹石是楔角蛇纹石化的主要产物。它通过其母矿物橄榄石的变形和拓扑生长形成晶体择优取向（CPO）。这可以使楔角高度各向异性，但该区域的叶蛇纹石 CPO 尚不清楚。楔角处的裂缝渗透率控制着蛇纹石化的程度。然而，背景应力和反应引起的应力对裂缝渗透率的影响还不清楚。为了量化楔角处的蛇纹石化作用，PI 将使用三类不同的数值模型：(1) 用于矿物结构演化的时间相关热机械模型，(2) 用于应力状态空间变化的机械模型，以及 ( 3）反应诱发裂缝发育的水力-化学-机械模型。这些模型将考虑三个俯冲带（卡斯卡迪亚、南海和日本东北部）弧前区域的地震、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的 CPO 和蛇纹石化程度。 它们还将提高我们对背景和反应引起的应力及其对蛇纹石化影响的理解。该项目对我们了解俯冲带动力学具有直接影响，并对板块边界附近地质灾害的评估具有更广泛的影响。它将支持一名职业生涯早期的女科学家、两名研究生以及对 K-12 学生和教师以及公众的教育推广。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优势和更广泛的评估进行评估，认为值得支持。影响审查标准。