Some particularities of crustal structure in young orogenic systems

Abstract

During the last twenty years, the structure of the earth's crust and mantle of young orogenic systems has been investigated by means of seismic measurements. Therefore, it is possible now to discuss detailed problems. This paper deals with the crustal structure in the transition zone between the central part and the hinterland of an orogene. As demonstrated by three examples taken from the Western Alps, the Southern Apennines, and the Crimea, it can be stated that the crustal structure in these zones is anomalous. It is typical that, within the upper 20 km, a high-velocity layer exists which is separated from the crust/mantle boundary, being situated at a depth of 40–50 km, by an extreme low-velocity layer. Thus the existence of sialic material under basic material is indicated. The relation between the shallow high-velocity layer and the crust of the hinterland, no more than 20–30 km thick, is different in the cases described here. The crustal structure of the Eastern Alps and of the Caucasus is briefly discussed. Finally, this anomalous crustal structure and the tectonic development of an orogene are discussed.