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

Abstract

The European Variscan and Alpine mountain chains are collisional orogens, and are built up of pre-Variscan ''building blocks'' which, in most cases, originated at the Gondwana margin. Such pre-Variscan elements were part of a preOrdovician archipelago-like continental ribbon in the former eastern prolongation of Avalonia, and their present-day distribution resulted from juxtaposition through Variscan and/or Alpine tectonic evolution. The well-known nomenclatures applied to these mountain chains are the mirror of Variscan resp. Alpine organization. It is the aim of this paper to present a terminology taking into account their pre-Variscan evolution at the Gondwana margin. They may contain relics of volcanic islands with pieces of Cadomian crust, relics of volcanic arc settings, and accretionary wedges, which were separated from Gondwana by initial stages of Rheic ocean opening. After a short-lived Ordovician orogenic event and amalgamation of these elements at the Gondwanan margin, the still continuing Gondwana-directed subduction triggered the formation of Ordovician Al-rich granitoids and the latest Ordovician opening of Palaeo-Tethys. An example from the Alps (External Massifs) illustrates the gradual reworking of Gondwana-derived, pre-Variscan elements during the Variscan and Alpine/ Tertiary orogenic cycles.

The transition from Pangea amalgamation to fragmentation: Constraints from detrital zircon geochronology on West Iberia paleogeography and sediment sources

“…Continental collision started at approximately 365 Ma (Dallmeyer et al, 1997;Ribeiro et al, 2007), causing significant crustal shortening and the emplacement of voluminous igneous rocks (Fernández-Suárez et al, 2000;Jesus et al, 2007;Martínez Catalán et al, 2007). The basement of the South Portuguese Zone (SPZ) of the Variscan Iberian Massif is likely associated with one of the continental blocks that docked with Laurentia (i.e., Meguma or Avalonia) prior to Pangea amalgamation (e.g., Oliveira and Quesada, 1998;de la Rosa et al, 2002;von Raumer et al, 2003;Ribeiro et al, 2007;Braid et al, 2011). Hence, the contact zone between the Ossa Morena Zone (OMZ), a peri-Gondwana geotectonic unit, and the SPZ may be underlying a suture recording the final stages of the closure of the Rheic Ocean (Quesada et al, 1994;Matte, 2001).…”

Provenance of Pleistocene Rhine River Middle Terrace sands between the Swiss–German border and Cologne based on U–Pb detrital zircon ages

“…In the Penninic units, intracontinental rifting is documented at c. 500 Ma and followed by granitoid magmatism between 480 and 450 Ma (e.g., Guillot et al 2002;Schaltegger et al 2003). Stampfli et al (2002) and von Raumer et al ( , 2003 assign different units of the Alpine basement to the Gondwana-derived Hun Superterrane, which are now spread over different Alpine nappes and basement units (Schaltegger et al 2003). The Hun Superterrane includes all continental fragments, which were in lateral continuity with Avalonia along the Gondwana margin and accreted to Laurussia between the Late Devonian and Early Carboniferous.…”

Devonian magmatism in the western Sakarya Zone, Karacabey region, NW Turkey

“…von Raumer & Stampfli, 2008;Schät, Reischmann, Tait, Bachtadse, Bahlburg & Martin 2002). The initiation of subduction has been assigned to Silurian-Early Devonian Kröner & Romer, 2013;Matte, 2001;Reischmann & Anthes, 1996;Stampfli, 2000;von Raumer & Stampfli, 2008;von Raumer, Stampfli & Bussy, 2003) and almost in every region where the Variscan orogeny is defined, granitoids belonging to this interval have been reported. In the European Variscides, main arc-related magmatism is constrained between Devonian and Early Carboniferous (410-350 Ma, Kröner & Romer, 2013;Neubauer & Handler 2000) and magmatism between 325 and 310 Ma is regarded as post-collisional (Siebel, Chen, & Satır, 2003).…”