A term first used by D. S. Coombs in 1961 to describe metamorphic recrystallization during epeirogenic as opposed to orogenic earth movements. Sediments and volcanic rocks in a developing basin gradually become buried during sagging of the crust in response to the weight of the accumulating rock column above, so that temperatures, even at great depth, are much lower than those experienced during plate collision, when forcible depression of the rock mass to regions of much higher temperature and pressure cause metamorphic changes characteristic of regional metamorphism. See metamorphic rock.