Events in alpine deformation and metamorphism in the Northern Pennine Zone and Southern Gotthard massif regions, Switzerland

Abstract

The Pennine nappes consist of broad subrounded anticlinal cores of crystalline basement enveloped by a relatively thin cover of Mesozoic metasediments. They have been subsequently refolded by two more phases of deformation, F 2 and F 3, on a regional scale. The imprint of these deformations, F 2 and F 3, also occur in the southern part of the Gotthard massif and its Mesozoic cover. The main episode of Alpine metamorphism, producing principal porphyroblasts, has occurred after the formation of Pennine nappes as a result of heat emanating from the “thermic dome” of the Lepontine Alps. The study of metamorphic fabrics suggests that the Alpine metamorphism probably had a higher grade during the time of the rise of “thermic dome” than during the formation of Pennine nappes.