EXHUMATION OF HIGH-PRESSURE METAMORPHIC ROCKS

The exhumation of high-pressure metamorphic minerals necessitates the removal of overburden which was present at the time of metamorphism. Assuming metamorphism during an orogenic phase, and exhumation during an uplift phase, the model presented here is based on postulating continuous deformation at the active margin of an ocean-continent interaction. Accepting the conclusion that coesite-bearing eclogites and other high-pressure minerals were formed when a sliver of continental crust was subducted down to 100 km, I propose that their uplift was caused by a shift of the Benioff zone. The high-pressure slab now accreted to the continental lithosphere was lifted up the ramp of a Benioff zone, when ocean lithosphere was thrust under the continent. The geology of the western Alps illustrates this model.