Deep-reaching geodynamic processes in the Alps

Summary The Alps are a deep-reaching crust-mantle structure in Europe situated at the northernmost tip of the Adriatic promontory of the African plate. In that region the contact against the Eurasian plate is presently characterized by a NW-SE oriented compressional stress regime. A detailed regional analysis of seismic surface-wave dispersion and of P-wave travel time residuals (‘seismic tomography’) as well as long-range seismic refraction measurements and the interpretation of ‘stripped’ residual gravity anomalies have revealed a rather anomalous structure within the uppermost mantle under the Alpine arc. As a result of the massive continent-continent collision, parts of the lithosphere have been delaminated — a process which has led to ‘flaking’ in the upper crust, combined with a thickening of the entire crust and the formation of a pronounced relatively cold, dense and slowly subsiding ‘lithospheric root’ beneath the mountain chain. In this still continuing plate collision the lower parts of the lithosphere apparently have penetrated into the asthenosphere to a depth of 130 to 200 km in a steep zone of ‘subfluence’ (‘Verschluckung’). On this scale the presently measurable uplift of the Alpine chain (about 0.1 cm per year) is a secondary effect due to isostatic rebound of less dense crustal masses which previously had been forced to greater depths. A configuration of this type generates regionally a compressive dynamics of its own on which — within a wider framework — rotational processes may be superimposed.