40Ar/39Ar laserprobe dating of mylonitic fabrics in a polyorogenic terrane of NW Iberia



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Gómez Barreiro, Juan and Wijbrans, Jan R. and Castiñeiras García, Pedro and Martínez Catalán, José R. and Arenas Martín, Ricardo and Díaz García, Florentino and Abati Gómez, Jacobo (2006) 40Ar/39Ar laserprobe dating of mylonitic fabrics in a polyorogenic terrane of NW Iberia. Journal of the Geological Society, 163 . pp. 61-73. ISSN 0016-7649

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The tectonothermal evolution of a polyorogenic terrane in the Variscan belt of NW Spain has been
constrained by 40Ar/39Ar laserprobe incremental heating experiments on mylonitic fabrics developed in major
structures. Transitional levels between HP–HT and IP upper units in the O´ rdenes Complex where
metamorphic and structural records demonstrate two cycles of burial and exhumation were selected for dating.
Two groups of ages have been defined: (1) Silurian–Early Devonian, obtained from mylonites of the Forna´s
extensional detachment, here considered as the minimum age for the start of tectonic exhumation of the HP–
HT units and an upper age-limit for the HP–HT event itself; (2) Early to Mid-Devonian, from structures
related to the Variscan convergence in the area, which include top-to-the-east thrusts and extensional
detachments. A single, younger Carboniferous age obtained from the uppermost allochthonous sequences
possibly reflects the final stages of emplacement of the allochthonous complexes. Our data indicate a
polyorogenic character for a part of the Iberian allochthonous complexes, including Variscan (sensu stricto)
and Early Variscan convergence, as well as an older, Early Palaeozoic cycle.

Item Type:Article
Uncontrolled Keywords:Polyorogenic terrane; Variscan belt; NW Iberian
Subjects:Sciences > Geology > Petrology
ID Code:14028
Deposited On:07 Dec 2011 10:35
Last Modified:07 Dec 2011 10:35

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