Magmatic to Solid-State Fabric Transition in a Post-Tectonic Tonalite Pluton

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Johnson0087661Magma chambers are an essential component in the construction of oceanic and continental lithosphere, and profoundly influence the thermal and mechanical behavior of the crust and mantle. The mechanical properties of a magma chamber change during cooling and crystallization, as accommodation of deformation changes from magmatic flow to solid-state processes. Thus, to understand the thermo-mechanical evolution of magma chambers, it is crucial to understand the relative importance of magmatic and solid-state flow, and the nature of the transition between them. This project is investigating such a transition preserved in the San Jose pluton, Baja California, Mexico. The pluton postdates the regional deformation, and so the transition from magmatic to solid-state flow reflects internal magma-chamber dynamics. Such transitions are rarely observed in post-tectonic plutons, and our results will benefit others who are working in more complex syntectonic examples. Detailed mapping and collection of spatially oriented samples is taking place along four transects in the pluton. X-ray compositional mapping, microstructural analysis and electron backscatter diffraction studies are being employed to track the chemical evolution of the deforming and crystallizing pluton, and to evaluate deformation mechanisms and the origins of the magmatic foliations. The project is supporting a PhD student, and several senior undergraduates at the University of Maine will participate as part of their Capstone Experience.