The Variscan structural and metamorphic evolution of the eastern Southalpine basement

Abstract

The basement of the Southern Alps (northern Italy) belongs to the southernmost part of the European Variscan mountain belt. In contrast to other areas of the Alps, the post-Variscan metamorphic and tectonic overprint is weak and therefore permits the unravelling of the Variscan tectonometamorphic evolution of this region. Overprinting criteria and the mapping of the penetrative structural elements (S2 and L2) allow three deformational events to be distinguished. Major Variscan deformation (D2) in the Southern Alps commenced in the Carboniferous and lasted until the end of the Late Carboniferous. Tectonic movement during D2 was north-directed and was accompanied and followed by greenschist facies metamorphism. Peak metamorphic conditions reached 450–550°C and 5–6.5 kbar in the Brixen area and decreased in a southeasterly direction. Tectonic movement during D2 followed subduction of the Plankogel terrane and collision of the Noric terrane (northernmost part of Gondwana) with Laurasia and is interpreted to result from late orogenic extensional collapse of the Variscan mountain chain. Extensional deformation caused exhumation of the basement rocks as evidenced by greenschist facies basement pebbles, which show no substantial retrograde overprint, in Late Carboniferous/Early Permian conglomerates.