Epicratonic Orogeny

(also, postcratonic orogeny), the resumption of crustal movements and mountain building in a region that until then had long developed as a platform and had a flat topography. Regions that have experienced epicratonic orogeny are characterized by arched block structure, equal in height to epigeosynclinal orogens, which arise directly on the site of geo-synclines, for example, the Caucasus and the Alps. Unlike the latter, the intermontane and submontane depressions of epicratonic orogenic regions are filled with detrital deposits, called molasses, and manifestations of magmatic activity are usually confined to outflows of basalt, which is often alkaline.

Epicratonic orogeny has occurred most strongly in recent and Oligocene through Anthropogenic times; however, it had also occurred periodically at earlier times, beginning in the Middle Precambrian. Spatially, the regions of epicratonic orogeny have been linked chiefly to the periphery of the geosynclinal belts and oceans and appear to have been caused by deep-seated processes beneath the oceans. Among the mountain structures resulting from epicratonic orogeny are the Tien-Shan, the Altai Mountains, the Saians, and the Hindu Kush. Epicratonic orogens are frequently complicated by rifts, such as the Baikal rift system and the Great Rift Valley in Africa.

The processes of epicratonic orogeny are linked with the formation of deposits of nonferrous metals and, in intermontane and submontane depressions, with the formation of deposits of coal, oil shale, petroleum, and gas.