A MOHR CIRCLE CONSTRUCTION FOR THE OPENING OF A PREEXISTING FRACTURE

The opening of a fracture is dependent on the fluid pressure and the l ocal stress regime around the fracture. For a fracture to open, the fl uid pressure must exceed the normal stress acting on the fracture. The Mohr circle provides a useful tool allowing the visualization of thes e relationships. This construction determines the range of fracture or ientations that are able to open, as well as determining the opening d irection of these fractures. This is then used to produce ratios of th e magma pressure and the principal stresses for some dykes from the Li zard ophiolite, U.K. (C) 1997 Elsevier Science Ltd.