General Characteristics of Metamorphic Terrains

Abstract

Contact metamorphism is due to a temperature rise in rocks adjacent to magmatic intrusions of local extent which penetrate relatively shallow and cold regions of the crust. The majority of magmatic intrusions are of granitic composition. The most frequent depth (distance from the earth’s surface at the time of solidification) of granitic intrusions was estimated by Schneiderhöhn (1961) to be 3 to 8 km, corresponding to a load pressure of 800 to 2100 bars. There are, of course, intrusions which solidified at greater or shallower depth; a depth of 1 km corresponds to a load pressure of 250 bars. Consequently, the load pressures effective during contact metamorphism range from 200 to 2000 bars, and they probably were less than 2000 bars in most cases. By way of contrast, load pressures prevailing during regional metamorphism are considerably greater.