THE RISE OF SOLID-STATE DIAPIRS

When magma inside a diapir solidifies it increases in density and beco mes a stiff power-law fluid. If the diapir is still positively (or neg atively) buoyant after solidification, it will continue to rise (or st art to sink). The results presented here suggest that solidified diapi rs may rise (sink) a distance of up to a few kilometres in geologicall y reasonable times. Rocks and bubble- and/or crystal-rich magmas behav e as power-law fluids. This paper compares numerical results of viscos ity and strain-rate profiles across power-law and Newtonian diapirs an d wall rocks. The comparison shows that the core of power-law diapirs deforms more slowly and the margins much faster than in Newtonian diap irs. This pattern of strain rate distribution leads to the often obser ved 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-l aw diapir resulting in similar strains on either side of the contact, and that power-law wall rocks, in contrast to Newtonian wall rocks, de form into a rim synform as the diapir rises.