The CFZ consists of left-lateral strike-slip faults bearing fault gouge formed in the uppermost 5?km of the crust. The faults cut metamorphic basement and folded post-orogenic sediments and volcanic rocks, and acted as a conduit for calc-alkaline volcanic rocks rising to the surface. NW of the CFZ, a series of unconformities and deformation episodes affect successive sedimentary formations of upper Miocene age. The CFZ is interpreted as part of a transform fault system separating NE-SW stretched and NW-SE shortened crust deformed above a south-westward retreating subducted slab, from a less deformed terrain lying to the south-east. Total offset on the CFZ may be up to 40?km but is at least 15?km.