Dynamics of Slab Detachment

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This project is the first to explore slab detachment using fully-dynamic, numerical models of thermal convection, (in 2-D and 3-D spherical geometry), capable of treating both the process of detachment and its geological expression.Slab detachment (or break-off) may occur in subduction zones following an event such as continent or ridge collision with the trench, which prevents the existing slab from effectively pulling the unsubducted lithosphere into the mantle. However, even the most basic aspects of deformation accompanying slab detachment are not understood: for example, does the location detachmentinitiates in the slab (top or bottom surface) influence the resulting deformation?The slab detachment process provides a unique opportunity to place constraints on the upper mantle viscosity structure, one important aspect of understanding the rheologic controls on mantle convection and plate tectonics. The main focus of the project is to characterize the dependence of slab detachment dynamics on therheologic structure of the lithosphere, slab and upper mantle, including the importance of lateral changes in lithospheric/slab structure due to age, composition, subduction velocity and geometry. Broad 2-D modelling will be followed by 3-D models designed to explore the Miocene slab detachment event in southern Baja California.The 3-D models focused on the Baja California/western Mexico region are complementary to the current NARS-Baja seismic experiment (funded through the MARGINS program), which will provide the data for high resolution seismic tomographic images, possibly illuminating the shallow Farallon slab, and anisotropymeasurements providing constraints on regional flow in the mantle. In addition, this award will provide a graduate student with the experience and background necessary to participate in multi-disciplinary research by teaching both geodynamic modelling methods and the tectonic and geophysical implications of a variety ofgeological observations.