Alpine and Caledonide tectonics - a brief comparative study

The structure and tectonic evolution of the Alpine and Caledonide orogens s how several common features in addition to the many contrasts. These parall els, taken to imply a basic similarity in orogenic processes, form the star ting point for a brief comparative study. The Alpine transect used as refer ence is that through the Central Alps in eastern Switzerland, which coincid es with the trace of the European Geotraverse. In the Caledonides, the Sogn efjord transect in southern Norway, the subject of a recent structural comp ilation, is taken as illustration. Both are presented in the form of a tect onic map and crustal cross-section drawn at the same scale, with the tecton ic units in each case distinguished according to their pre-orogenic affilia tion: cratonic foreland, rifted continental margin and oceanic complex. In spite of the individually complicated pre-orogenic architectures, the oroge nic evolution of both orogens can be described in terms of a series of phas es with characteristic features: pre-collisional contraction, early collisi onal, late collisional and, in the case of the Caledonides, post-collisiona l (extensional collapse). A cross-fertilization of ideas and concepts is ac hieved due to the present structure representing different stages of orogen ic development and exhumation. This applies particularly to questions regar ding, for instance, the deep structure, the rheology of the lower crust, an d the role of gravity.