Geological evidence shows that over hundreds of millions of years, Earth's continents drift across the denser mantle, floating like icebergs. This drift sometimes brings the continents together into larger aggregates, and it sometimes rifts them apart, creating ocean basins between them. This process of rifting creates sedimentary basins, surface topography, volcanic activity, and continental shelves, all of which are important to human evolution, resources, hazards, and economic development. Rifting is also a fundamental part of plate-tectonic theory, and hence essential to our understanding of the mechanics of Earth. Rifting is almost always associated with magmatism: melting of rocks at depth and injection of the liquid through cracks toward (and sometimes onto) the surface. This liquid and the heat it carries are understood to modify the mechanical properties of the system, weakening it significantly. Hence magmatism plays an essential role in the mechanics and evolution of rifts, and yet models of rifts have not been able to quantify this except in the simplest of terms. The purpose of this project is to apply a careful theoretical analysis to this problem, to assess the magmatic controls on rifting, and hence on plate tectonics. The objectives of the project are as follows: (1) to derive mathematical theory based on the physics of partially molten poro-viscoelastic-brittle rocks. To model brittle failure, we will use plasticity theory. (2) To incorporate this theory into numerical models that can capture the forces and motions associated with rifts. (3) To model continental rifting process for various configurations of thermal and mechanics forcing. (3) To model oceanic rifting (mid-ocean ridges) for over a range of spreading rates, magma supply rates, and variance in supply. (4) To interpret the model outputs in terms of observations of rifts, including topography, seismic structure, gas emissions, and heat flow.
A particular focus of the research will be on the relationship between dikes and fault, and how this is expressed in the topography of rifts. This has a bearing on the question of whether variations in magma supply are recorded in the topography of abyssal hills, which flank mid-ocean ridges.
A more societally relevant consideration of the project is how magmatism interacts with continental rifting to shape the formation of sedimentary basins, and potentially to localise hydrothermal circulation and the deposition of mineral resources.
