This is the Heating stage. The Uplift phase begins as an isostatic response to the lower density of the sediments and to heating which further decreases the density. During this stage, at least initially, the temperature continues to rise even as the pressure on the system drops. The Unroofing phase sees a rapid drop in both temperature and pressure as weathering removes the overlying rock cover. While most orogenic belts seem to be characterized by this clockwise trend, older granulite terrains seem to have evolved in a different manner, the reverse or counterclockwise trend.
Magma rises and pods above the metamorphic rocks.
Upon solidification of the igneous rocks pressure on the underlying metamorphics increases. This thermal inversion produces slow cooling due to the blanketing effect of the igneous rocks. A compressional event, probably related to collision, increases pressure on the system and initiates uplift. Uplift and Unroofing occur much as they did in the previous model with pressure dropping more rapidly than temperature. Metamorphism of Convergent Margins Miyashiro was the first to recognize that paired metamorphic belts were a common occurrence in the Japanese Islands.