Diaphthoresis

the repeated metamorphism of rocks during which the rocks that formed under conditions of deep-seated high-temperature metamorphism are then subjected to low-temperature metamorphism and changed into diaphthorites, that is, rocks of low degree of metamorphism (phyllites, green slates, and others) containing traces of the former deeper metamorphism. The term “diaphthoresis” was proposed in 1909 by the Austrian petrologist F. Becke. Diaphthoresis is sometimes considered to be a manifestation of regressive metamorphism that occurs as a result of the uplifting of rock from deeper and more heated zones of the earth’s crust to zones of lower temperatures and pressures.