HORIZONTAL STRUCTURES IN GRANULITE TERRAINS - A RECORD OF MOUNTAIN BUILDING OR MOUNTAIN COLLAPSE

Abstract

In many high-temperature (>800°C) granulite terrains, the development of characteristic horizontal structures occurred during the metamorphic culmination and was followed by isobaric cooling. The absolute magnitude of isobaric cooling (commonly >300°C) implies cooling intervals of the order of the thermal time constant of the continental lithosphere (~100 m.y.). Such prolonged isobaric cooling implies that no significant erosional denudation followed the development of the horizontal structures and thus precludes the prograde deformation being responsible for significant crustal thickening. Rather, the prograde deformation more probably records bulk crustal thinning during extensional collap..