It is well established that rock at depth can deform in either (or both) a ductile or brittle fashion in response to the passage of a more fluid material (magma, water, salt, etc.). Empirically, the greater the viscosity contrast between the host rock and the fluid moving around, the more likely one is to find the fluid in narrow cracks and dikes, and the less likely one is to find it in diapirs and plutions. Although this observation is intuitively appealing, as yet there has been little effort to quantify the role of host/fluid viscosity contrast in determining the geologic regimes under which dike intrusion is likely or possible. The PI will study the dike/diapir transition be treading dikes as propagating, fluid-filled cracks in viscoelastic host rock. The results, in addition to being of general geologic interest, should find particular application to a number of important questions and processes. These include the buoyant rise of granitic and serpentinite bodies along faults, the question of whether pluton/crustal viscosity contrasts are such that granities can ascend via a combination of fracture and flow, at rates greater than that of the Stoke's flow solution ( and hence traverse more of the crust before freezing), and the upwelling of buoyant asthenosphere between diverging (rifting) lithospheric blocks.
