A Structural and Dynamic Model of Subduction at the Middle American Trench, Central Mexico

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This project is advancing the conceptual and quantitative links between the state of subduction zones and the manner in which they evolve by exploring their dynamics with numerical experiments. Dynamic models are being related to subduction along the Middle America Trench (MAT). MAT is being used to constrain time-dependent models because of a clear progressive reorientation of the volcanic arc since the Oligocene. With models, present mantle structure is being linked with paleogeography. Our analysis study coincides with the Meso-American Subduction Experiment (MASE) -- a major international collaboration between Mexican and American scientists. A dense seismic experiment is currently deployed along a trans-Mexico transect from Acapulco to Tampico (through Mexico City) and provides critical parameters for subduction modeling -- the slab geometry and structure, and seismic proxies for viscosity of the mantle wedge. Construction of the geodynamic model is motivated by significant along-strike variations in slab structure despite simple variations in plate age and subduction velocity along the MAT. A variety of models are being brought to bear on a series of questions (including, how does the flat slab regime set in, how does the upper plate resist deformation by the flat slab, how can a younger plate have a steep dip, etc.). Structural, instantaneous geodynamic, and time-dependent geodynamic models are being integrated into a continuous suite in which the results of one are improving the others. This projects makes extensive use of the newly established Caltech Geosciences Computational Facility with its 2048 processor Dell Supercomputer. Some principal models include the following. The first are seismic models. Seismic data are being analyzed for crustal and slab structure and the viscosity structure of the mantle wedge using receiver functions, travel time & attenuation tomography, and full wavefield simulations. The second are instantaneous geodynamic models. Dynamic models are being found that are consistent with seismic structure, heat flow, topography, gravity and the dominate tensile stress of the horizontal slab with 2-D and 3-D viscous models. Determinations are underway to see what slab and mantle wedge viscosity models are consistent with these results. The third are paleogeographically consistent geodynamic models. The onset of flat slab subduction and the space-time changes in the pattern of Mexican volcanism are being addressed with a spherical convection model coupled to interactive plate reconstruction software (GPlates).This study is providing the opportunity for a postdoctoral researcher, Vlad Manea, to further his research career, particularly in geodynamics. The project also supports the training of one graduate student in geophysics. This funding for analysis of MASE data is enhancing collaboration between US and Mexican scientists.