CAREER: When Subduction Fails - Dynamical Models of Oceanic Plateau Collision and Crustal-Fragment Accretion

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Most studies of subduction dynamics attempt to determine the processes responsible for sustaining long-term subduction of typical oceanic lithosphere. While active subducting slabs have seismicity evident of intense internal deformation to various depths, the slab continues to directly transmit stresses to the surface plate. Only under special conditions does the slab become sufficiently weak or the positive buoyancy of the surface plate sufficiently large to cause subduction to fail. By looking at cases when subduction fails we can learn about the processes required to sustain longterm subduction. Three-dimensional thermo-mechanical models are being used to address two processes of subduction failure: 1) How does attempted oceanic plateau subduction cause subduction to fail? 2) How does crustal-fragment loss occur during normal subduction? These studies focus on the first-order, essential processes, such as the basic rheologic layering of the oceanic plate and localization processes, phase transformations that change rheology and/or density, the size and geometry of structures, and obliquity of convergence. The educational components of this project build directly on the research objectives, by using the dynamical model results as synthetic data sets to help students master 3D spatial thinking skills. Laboratory and homework exercises are being developed from the numerical model results that ask students to create a cross section of the subsurface structure from mapped data of structure orientations (strike, dip) taken from the synthetic 3D models. This part of the exercise simulates the interpretive exercise students normally carry out with actual mapped data taken in the field. However, unlike the field experience, the students are then given the opportunity to correct their initial cross section after exploring the actual 3D structure using visualization software, which allows them to create cross sections of any orientation and view the 3D structures as isosurfaces. In addition, a new feature is being added to the visualization software that allows the surface of the 3D numerical data to be sliced with any pre-defined 2D topographic surface (instead of a simple plane). This tool allows students to explore directly how topography influences the surface outcrop of 3D subsurface structures (e.g., intersection of a dipping fault with a valley versus a ridge).