Tectonics of the crystalline Basement of the Dolomites in North Italy

Abstract

The present thesis deals with a number of crystalline regions around the Dolomites in North Italy. The geographic position is shown on sheet I, which is depicted in fig. 105. The Dolomites proper consist mainly of Permotriassic, overlying a transgression plane, which cuts off the studied crystalline rocks. The tectonics of this crystalline basement have been scarcely studied hitherto, in contradistinction with the overlying sediments, the Alpine tectonics of which are rather wellknown. The complexity of the geometry of the crystalline basement, which may have caused this apparent lack of interest, is due to several factors. In the first place, a general stratigraphy of these uniform and for the greater part mesozonal micaschists has not been established. Therefore, it is necessary to base the tectonic interpretation almost entirely on the schistosity and the generally present minor folds. The age of these tectonical elements is generally pre-Permian. It can be proved that originally subhorizontal schistOsity-planes have been folded twice during the Hercynian orogenesis. In the second place, this Hercynian folded basement was deformed intensively during the Alpine orogenesis. A clear distinction between Hercynian and Alpine orogenesis is possible only by studying the pure Alpine tectonics of the adjacent Permotriassic sediments. For this reason, and because the existing geologic maps appeared to be inadequate, certain parts of these sediments have been mapped again. The fundamental tectonical values are scattered around the mean of the group to which they belong. Only the mean of a number of single values is a basis for regional tectonics. The means vary from place to place. Many measurements had to be made to determine the geometry of the means. A methodology had to be developed for calculating the means and for constructing the structure maps.