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Hyperextended continental margins and unrooted complexes: the case of the West European Variscan belt

The Variscan belt of western Europe is characterized by the deformation of an anomalously wide continental passive margin, located in northern Gondwana, that acted as the lower plate during the upper Devonian – Carboniferous Variscan collision. Another feature in this collisional belt are the unrooted “allochthonous complexes” with lower crust and mantle rocks associated with dismembered ophiolite-like rocks, classically interpreted as sutures of putative oceanic realms (Rheic and/or Paleo Tethys oceans).

Many models have been built in the past decades to explain the architecture of the Variscan belt, generally using oversimplified geometries for the passive margin. When continents break apart, the lithosphere is thinned by stretching and “necking” through time. In rifted margins, the lower and upper continental crust become coupled and embrittled, causing major faults (i.e. extensional detachments) to propagate into mantle depths, and leading to mantle uplift. This process, “hyperextension”, is increasingly documented worldwide in recent passive margins and it may also be accompanied by magmatic activity derived from the decompression of the lowermost crustal components or even the mantle.

Two episodes of partial melting in lower crustal and/or mantle rocks can be identified during the long-lived evolution of the northern Gondwana passive margin, during Ordovician and lower Devonian, and can be associated with the margin stretching linked to ridge subduction. Inversion of a complex hyperextended margin depicting key magmatic features may explain most of the characteristics that can be observed nowadays in the West European Variscan Belt, including the unrooted nature of the complexes.

Details

Author
Gabriel Gutiérrez-Alonso1, Alicia López-Carmona2
Institutionen
1University of Salamanca, Spain; 2Complutense University of Madrid
Veranstaltung
GeoSaxonia 2024
Datum
2024
DOI
10.48380/epm8-2h06