Structural and stratigraphical significance of U–Pb ages from the Mora and Saldanha volcanic complexes (NE Portugal, Iberian Variscides)
Published:January 01, 2014
Ícaro Dias Da Silva, Pablo Valverde-Vaquero, Emilio González-Clavijo, Alejandro Díez-Montes, José R. Martínez Catalán, 2014. "Structural and stratigraphical significance of U–Pb ages from the Mora and Saldanha volcanic complexes (NE Portugal, Iberian Variscides)", The Variscan Orogeny: Extent, Timescale and the Formation of the European Crust, K. Schulmann, J. R. Martínez Catalán, J. M. Lardeaux, V. Janoušek, G. Oggiano
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Geological mapping and structural investigations were carried out in the eastern rim of the Morais Allochthonous Complex in NE Portugal (NW Iberian Massif) along the first-order tectonic boundary between the lower part of the Galicia–Trás-os-Montes Zone (the parautochthonous Schistose Domain) and the autochthonous Central Iberian Zone. The aim was to correlate the Palaeozoic stratigraphic pile of both domains, and to establish their pre- and synorogenic Variscan evolution.
An Early Palaeozoic volcanic complex forms part of the pre-orogenic record of the parautochthonous Schistose Domain. It includes two volcanic units, the oldest of which is described for the first time in this work and is named the Mora Volcanics. It is a bimodal volcanic suite with basic to acid rocks which has yielded a late Cambrian age (c. 493 Ma).
Above the Mora Volcanics, the Saldanha Volcanics show petrographic, geochemical and age (c. 483 Ma) similarities to the Ollo de Sapo Formation, a volcano-detritic ensemble found in the autochthonous domain of NW and Central Iberia. The stratigraphic record and the geochemical signatures of both volcanic units indicate that they were originated by fast partial melting induced by extension along the northern Gondwana margin at the Cambro-Ordovician boundary, coeval with the opening of the Rheic Ocean.
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The Variscan Orogeny: Extent, Timescale and the Formation of the European Crust
This volume summarizes the state of the art of Variscan geology from Iberia to the Bohemian Massif. The European Variscan belt consists of two orogens: the older, northern and the younger, southern. The northern Variscan realm was dominated by Late Devonian–Carboniferous rifting, subduction and collisional events as defined by sedimentary records, crustal growth, recycling of continental crust and large-scale deformations. In contrast, the southern European crust was reworked by major Late Carboniferous collision followed by Permian wrenching. The Late Carboniferous–Permian orogeny overprinted the previously accreted system in the north, but with much lower intensity, resulting in magmatic recycling and extensional tectonics.
These two main orogenic cycles do not reflect episodic evolution of a single orogenic system but a complete change in orientation of stress field, thermal regime, degree of reworking and recycling of European crust, reflecting a major switch in plate configurations at the Early–Late Carboniferous boundary.