Die tektonische Baugeschichte von Süd-Devonshire als Beispiel einer mehrphasigen variszischen Prägung

Five movement-phases during the Variscan tectogenesis shaped the structural cast of the Devonian rocks in South Devon. The first movement-phase, i. e. the main tectonic phase, resulted in the mappable fold system trending E-W or ENE-WSW in the west accompanied by related minor folds, and the first cleavage (s ₁) parallel to the axial planes. The cleavage planes dip to the south as far as the line Slapton-Bigbury, while farther to the south they dip to the north and finally to the south again, thus forming a huge fanning. In the second movement-phase a second cleavage (s ₂) with E-W strike associated with minor folds, was superimposed on the older structures south of the line Berry Head-Cornworthy. The trend of these folds is, more or less E-W. Furthermore the second cleavage shows a fanning which does not coincide with that of the first cleavage. South-vergent minor folds of bedding and cleavage planes, associated with small-scale southward thrusts represent structures of a third movement-phase. The fourth movement-phase was the kinking of mainly the first cleavage in the southern part of South Devon. There are two groups: one shows flat-lying kink-bands affecting mainlys ₁; seldoms ₂, and having a southward thrusting sense of movement while the other consists of nearly vertical kink-bands trending N-S which displace to the south on their eastern sides. Subsequently with the commencement of the New Red deposition, repeated tectonic stretching took place, resulting in N-S and WSW--ENE trending faults. The succession of the different tectonic events led to occasionally very complicated superimpositions. The rocks in the middle and southern part of South Devon suffered a regional metamorphosis that increases slowly towards the south. Finally, the tectonic structures of South Devon are compared with those in South Cornwall where the same movements-phases caused a completely different structural style.