The mid-ocean ridge system is the largest feature on the surface of the Earth. It is also the site of much active faulting, and of most of the Earth's volcanic activity. The production of new seafloor by the process of seafloor spreading is a fundamental process that shapes the planet's surface. A half-century's research has revealed much about the mid-ocean ridge system, and an increasingly important tool for understanding the workings of mid-ocean ridges is numerical modeling. Though the ridge system is three dimensional, such models have, up to now, been limited to two dimensions owing to computing limitations. This project represents an ambitious collaborative effort to build the first genuinely 3D models of faulting and magmatism (volcanic processes) over a global range of mid-ocean ridge settings. This project has a variety of broader impacts. The results of this study and the development of a new 3D visco-elasticplastic tectonics code will benefit studies of long-term lithospheric deformation generally, with broad applications in Earth (e.g., GeoPRISMS and Earthscope programs) as well as planetary science. In addition, 3D time-dependent visualizations will make exceptionally stimulating and intuitive illustrations for use in ongoing classroom instructional and K-12 outreach activities. Most of the budget will support two talented and promising graduate students. Finally, the PIs will work with the Computational Infrastructure for Geodynamics (CIG) to document, benchmark, and disseminate both our 2D and 3D codes, thereby contributing the the scientific infrastructure.