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

点击翻译按钮获取中文摘要

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.