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THE CENTRAL IBERIAN ARC (VARISCAN BELT)

THE CENTRAL IBERIAN ARC (VARISCAN BELT). José R. Martínez Catalán. Paleoposition of the Iberian Massif. It is the last massif of the European Variscan belt to the SW It includes the core and the southern part of the Ibero-Armorican arc It consists of an authochtonous domain…

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THE CENTRAL IBERIAN ARC (VARISCAN BELT)

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  1. THE CENTRAL IBERIAN ARC (VARISCAN BELT) José R. MartínezCatalán

  2. Paleoposition of the Iberian Massif • It is the last massif of the European Variscan belt to the SW • It includes the core and the southern part of the Ibero-Armorican arc • It consists of an authochtonous domain… • and a large allochthon containing the suture of the Rheic Ocean • All units, except the ophiolitic, are of Gondwana derivation

  3. TheIberianMassif The Iberian Massif consists of five continuous parallel zones and a weirdo: Galicia-Trás-os-Montes Zone, the allochthonous stack including the suture

  4. Proposed name:Central Iberianarcbecause it is identified in the Central Iberian Zone (CIZ) An arc is delineated by the axial traces of D1 Variscan folds, which converge in a covered area. D3 folds are roughly coeval with the arc

  5. TheCentralIberianarc A key area in La Mancha, between Toledo and Ciudad Real, where the arc is well delineated by upright D1 folds of the CIZ

  6. TheCentralIberianarc D1 folds are delineated by the Armorican Quartzite (Early Ordovician) They rotate anticlockwise Eastward, from an E-W to a N-S attitude Source: Google Earth

  7. The arc was drawn by Du Toit (Our wandering continents: An hypothe- sis of continental drifting. Oliver and Boyd, Edinburgh, 366 pp., 1937)

  8. The arc is also marked by faint magnetic anomalies Source: Aeromagnetic Map of Spain, Instituto Geográfico Nacional (IGN)

  9. Noticed by Aerden (Journal of Structural Geology, 26, 177-196, 2004) Interpreted as due to interference of two folding phases, the second of which related with sinistral transpression

  10. TheCentralIberianarc Magnetic anomalies: High resolution aeromagnetic IGN data in Spain

  11. TheCentralIberianarc Magnetic highs and lows delineate the arc and show that it is bounded to the south by a straight negative magnetic anomaly

  12. TheCentralIberianArc The negative magnetic anomaly follows the limit between the Central Iberian and Ossa-Morena zones, and continues beneath the Betics

  13. TheCentralIberianArc Ollo de Sapo Fm: Cambro- Ordovician (495-483 Ma) felsic volcanism, in northern part of the CIZ. The Fm seems repeated in the Urra Fm (Portalegre area, southwestern CIZ) The allochthonous GTMZ occupies the core of the Central Iberian arc

  14. Allochthon: klippen cropping out in structural basins amonganatectic domes NW Iberiaand the Galicia-Trás-os-Montes Zone Autochthon: a Paleozoic sequence overlying non-metamorphic or very low-grade Cadomian basement

  15. The Galicia-Trás-os-Montes Zone consists of three groups of allochthonous units, plus an underlying thrust sheet:the Parautochthon, Lower allochthon or Schistose DomainRed lines: cross sections in next slide

  16. Threegroups of allochthonousunits: • Above the suture, a peri-Gondwanan island arc • Ophiolitic units mark the suture of the Rheic Ocean • Below the suture, the edge of the northern Gondwana margin • The Central Iberian arc is not evident in the allochthon : flat thrust sheets are not prone to fold about vertical axes. Probably, there is a compromise between oroclinal and upright folding

  17. TheCentralIberianArc The Central Iberian arc is limited to the S and W by wrench shear zones. The Porto-Tomar shear zone overprints all previous ones

  18. Strike-slip shear zones in the Variscan belt, crosscutting relationships: The PTSZ seems to overprint the whole Central Iberian arc (CIA) The PTSZ-SASZ-S is folded by the Ibero-Armorican arc (IAA), but less tightly than the zones of the Iberian Massif

  19. Strike-slip shear zones in the Variscan belt, crosscutting relationships: The Central Iberian arc is older, or at least, reached full development before than the Ibero Armorican arc

  20. Right-lateral wrench tectonics in the Variscan belt • A model of dominantly right-lateral strike-slip motion accounting for the present distribution of terranes and zones was proposed by MartínezCatalán et al. (GSA Memoir 200, 403-423, 2007) • The Central Iberian arc fits early dextral displacements on the main, large dextral shear zone

  21. CONCLUSIONS • The Central Iberian arc is an orocline delineated by the trend of the first Variscan foldsand by magnetic anomalies in the Central Iberian Zone of the Iberian Massif. The structure was known by DuToit (1937) and was noticed by Aerden (2004), but has been ignored by most due to the post-Paleozoic cover of its hinge zone and, perhaps, the faintness of the magnetic anomalies • The arc explains the width of the Central Iberian Zone (up to 400 km) by duplication of a strip initially half that width. Its sense of curvature is opposite to that of the Ibero-Armorican arc, and it makes more understandable the position of the allochthonous complexes of NW Iberia, which occupy its core, and which include the Rheic suture. The Ossa-Morena and South Portuguese zones do not appear involved in the Central Iberian arc • It is suggested that the origin of the arc is linked to a large intracontinental, strike-slip, dextral shear zone related with oblique convergence between Laurussia and Gondwana. This shear zone is presently hidden in Iberia, perhaps by Los Pedrochesgraniticlineament or by the Badajoz-Córdoba shear zone, and may continue in Central Europe by the Layale-Lubine fault

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