The rise of solid-state diapirs

When magma inside a diapir solidifies it increases in density and becomes a stiff power-law fluid. If the diapir is still positively (or negatively) buoyant after solidification, it will continue to rise (or start to sink). The results presented here suggest that solidified diapirs may rise (sink) a distance of up to a few kilometres in geologically reasonable times. Rocks and bubble- and/or crystal-rich magmas behave as power-law fluids. This paper compares numerical results of viscosity and strain-rate profiles across power-law and Newtonian diapirs and wall rocks. The comparison shows that the core of power-law diapirs deforms more slowly and the margins much faster than in Newtonian diapirs. This pattern of strain rate distribution leads to the often observed isotropic or weakly deformed core surrounded by a strongly sheared margin. Furthermore, the results suggest that the strain rate of the ambient fluid (wall rock) is imposed across the contact into a power-law diapir resulting in similar strains on either side of the contact, and that power-law wall rocks, in contrast to Newtonian wall rocks, deform into a rim synform as the diapir rises.