Time and place in Alpine orogenesis — the Fermor Lecture

Summary Alpine geologists have suggested that the main structures of the Alps have been formed by a late Eocene event, which lasted at most a few million years. Data on earlier and later deformations have been interpreted as the evidence of Eoalpine and Neoalpine phases. The supposedly episodic nature of the Alpine orogenesis has been considered to be a fundamental contradiction of the seafloor spreading which predicts slow and gradual movement. The purpose of this contemplation on time and place in Alpine orogenesis is to point out that the paradox is man-made: the interpretation of the episodic nature of orogeny is a relic of the defunct catastrophic theory of orogeny of Elie de Beaumont (1831). Divorced from that discredited assumption, the orogenic data in the Alps are consistent with a postulate of continuous orogenic deformation since the early Cretaceous. The Alps is a collision-type of orogen. Using the late Eocene collision-event as a time marker, we can recognize two major stages of deformation: the Eoalpine subduction, and the Neoalpine post-collisional. The geological evidence is consistent with the postulate of a gradual build-up of the Alpine edifice, consequent upon the approach between two continental blocks since the early Cretaceous and continuing deformation after the late Eocene collision. The Eoalpine subduction should have started 130 Ma ago, some 50 Ma before the approach of the African and European Plates. This and other geological evidence necessitates an assumption of relative movements among 3 plates to explain the Alpine orogenesis; the middle Mediterranean Plate (M-plate) had movements independent of Africa since 130 Ma bp . The kinematics of plate displacements in the Alpine-Mediterranean region have been reconstructed, using the data on Atlantic magnetic lineations to fix the positions of Africa and Europe, and geological evidence to guide the movement of the M-Plate. This kinematic analysis, harmonized with geological data, indicates that the Alpine Orogenesis resulted from the relative movement between the European- and M-Plates at rates of about 1 centimetre per year. There is no contradiction between Alpine geology and the plate-tectonic theory.