The Palaeozoic evolution in the Alps: from Gondwana to Pangea

Abstract

More than 50% of the Alps expose fragments of Palaeozoic basement which were assembled during the Alpine orogeny. Although the tectonic and metamorphic history of the basement units can be compared to that of the Variscan crust in the Alpine foreland, most of the basement pieces of the Alps do not represent the direct southern continuation of Variscan structural elements evident in the Massif Central, the Vosges-Black Forest or the Bohemian massif. The basement units of the Alps all originated at the Gondwana margin. They were derived from a Precambrian volcanic arc suture fringing the northern margin of Gondwana, from which they were rifted during the Cambrian-Ordovician and Silurian. A short-lived Ordovician orogenic event interrupted the general rifting tendency at the Gondwana active margin. After the Ordovician, the different blocks drifted from the Gondwana margin to their Pangea position, colliding either parallel to Armorica with Laurussia or with originally peri-Gondwanan blocks assembled presently in Armorica. From the Devonian onwards, many basement subunits underwent the complex evolution of apparently oblique collision and nappe stacking. Docking started in the External massifs, the Penninic and Lower and middle Austroalpine units in approximately Devonian/early Carboniferous times, followed by the Upper Austroalpine and the South Alpine domains, in the Visean and the Namurian times, respectively. Wrenching is probably the best mechanism to explain all syn and postcollisional phenomena since the Visean followed by postorogenic collapse and extension. It explains the occurrence of strike-slip faults at different crustal levels, the formation of sedimentary troughs as well as the extrusion and intrusion of crustal and mantle-derived magmas, and allows for contemporaneous rapid uplift of lower crustal levels and their erosion. From the Stephanian onwards, all regions were deeply eroded by large river systems.

Modélisation géométrique 3D des granites stéphaniens du massif du Pelvoux (Alpes, France)

“…Their structural and metamorphic evolution are related to the Variscan orogeny and correlated to the French Massif Central, Vosges and Bohemian massif [18]. The tectonic evolution of these Palaeozoic domains begins with the formation of an ocean during Cambrian and Ordovician.…”

“…However this study highlights difference during the late stage of the Palaeozoic evolution. The French Massif Central granites are characterised by dome shape and laccoliths geometry emplaced during N-S extension direction in a context of crustal thinning [8,15] Ces terrains représentent des fragments de la chaîne Paléozoïque Européenne [18], réactivés lors des compressions alpines le long de grandes discontinuités structurales puis exhumés il y a environ 15 Ma [20].…”

Gondwana-derived microcontinents — the constituents of the Variscan and Alpine collisional orogens

“…2) separated from Gondwana, during the Early Ordovician, drifting was hampered in the former easterly situated continental blocks (Cadomia, IntraAlpine Terranes) by the still existing oceanic ridge of Proto-Tethys. The Ordovician collision of the detaching terranes with Gondwana triggered the consumption of the embryonic eastern Rheic ocean and the amalgamation of volcanic arcs and continental ribbons with Gondwana in a rather short-lived orogenic pulse (von Raumer, 1998, with references therein). The cordillera, resulting from mid-ocean ridge subduction during the Ordovician, started to collapse already during the Late Ordovician leading to the opening of the Paleo-Tethys rift, followed by the Late Silurian drift of the composite Hun-superterrane (Stampfli, 2000).…”

“…the External Massifs), such orthogneisses can be easily distinguished from Late Variscan granites, as they carry the imprint of Variscan anatectic remelting (e.g. Aiguilles Rouges and Mont-Blanc external massifs, von Raumer, 1998). In such cases, all transitions from shear-bands containing newly formed sillimanite to stringers of melt following the foliation produced during strike-slip to a microgranular new granitoid are observed, where former K-feldspars appear as black coloured, preserved relics, and the former foliation as ghost structure.…”

Bimodal magmatism as a consequence of the post-collisional readjustment of the thickened Variscan continental lithosphere (Aiguilles Rouges–Mont Blanc Massifs, Western Alps)

“…These syntectonic melts are associated with major transcurrent faults and seem to constitute an 'isochron belt' throughout Europe Von Raumer 1998), although the exact geometry of the latter is unknown due to potential Late-Carboniferous transcurrent displacement. This belt probably reflects a major geotectonic structure, where partial melting of the lithospheric mantle and lower crust would have been favoured for a short time (Visean extension), possibly controlled by lithosphericscale transcurrent faults.…”