Preprints
https://doi.org/10.5194/se-2020-126
https://doi.org/10.5194/se-2020-126

  21 Aug 2020

21 Aug 2020

Review status: this preprint was under review for the journal SE but the revision was not accepted.

A first estimation of the contraction related to vertical axis rotation: the case of the Ibero-Armorican Arc formation

Josep Maria Casas1, Joan Guimerà1,2, Joaquina Alvarez-Marron3, and Ícaro Días da Silva4,5 Josep Maria Casas et al.
  • 1Dpt. de Dinàmica de la Terra i de l'Oceà, Universitat de Barcelona, Martí Franquès s/n, 08028 Barcelona, Spain
  • 2Institut de recerca GEOMODELS, Martí Franquès s/n, 08028 Barcelona, Spain
  • 3Dpt. of Earth Structure and Dynamics, and Crystallography, Institute of Earth Sciences, Jaume Almera, CSIC, Lluís Solé i Sabarís s/n, 08028 Barcelona, Spain
  • 4Instituto Dom Luiz (IDL), Faculdade de Ciências, Universidade de Lisboa, Campo Grande, Edif. C1, Piso 1, 1749-9016 Lisboa, Portugal
  • 5Dpto. de Geologia, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal

Abstract. Different models have been proposed to explain the formation of the Ibero-Armorican Arc, which require significant vertical axis rotations, at the end of the Variscan orogeny. Estimates of the amount of contraction (horizontal shortening) needed for these rotations range from 54 % to 91 % perpendicularly to the arc. These estimates are compared with coeval deformational structures developed in two areas of the orogen, one in the autochthonous hinterland underlying the Galicia-Trás-os-Montes Zone in the southern branch of the arc, and the other in the Cantabrian Zone foreland in the core of the arc. From this analysis it follows that the late Variscan deformation together with the subsequent Alpine contraction is not sufficient to explain the formation of the Ibero-Armorican Arc as a secondary structure by means of vertical axis rotations. Our analysis suggests this arc is mainly a primary, or non-rotational curve, slightly modified by ca. 10 % of superposed contraction during late Carboniferous and/or Alpine times. Moreover, we propose that the assumptions underlying the interpreted geometry of the arc be re-evaluated, and we discuss the role of late-Variscan regional strike-slip faults in the Iberian and in the Armorican massifs that probably acted consecutively before and during the contraction of the arc.

Josep Maria Casas et al.

 
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Status: closed
Status: closed
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Josep Maria Casas et al.

Josep Maria Casas et al.

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Short summary
Many orogenic belts exhibit arcuate form in map view. We deal with the different models proposed to explain the formation of the Ibero-Armorican Arc in the western European Variscan Belt. We suggest this arc is primary slightly modified by superposed contraction during late Carboniferous and/or Alpine times. We discuss the role of late-Variscan regional strike-slip faults in the Iberian and in the Armorican massifs that probably acted consecutively before and during the contraction of the arc.