The Uplift of Armorica and the Bretonian Movements of the Variscan Orogeny-New Insights From Detrital Zircons in the Early Carboniferous Terrigenous Rocks of the Laval Basin (Armorican Massif, France)
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引用次数: 0
Abstract
In the French Armorican Massif, the Bretonian phase of the Variscan orogeny has been defined by the Late Devonian (Famennian-Frasnian) erosion gap, and the Early Carboniferous (Tournaisian) syntectonic terrigenous deposits of the l’Huisserie formation in the Laval basin in the Central-North Armorican Domain, ascribed to the Armorica microcontinent. This phase is coeval with vertical (epeirogenic) movements. In addition to Neo-, and Paleo-Proterozoic peaks, ascribed to the Cadomian and Icartian events, respectively, the detrital zircon age populations of the l’Huisserie formation reveal the existence of a 388–358 Ma magmatic event previously recognized by the ca 367–360 Ma dolerite dyke swarms exposed in the N. part of the Central-North Armorican Domain. The isotopic (εHf) signature of these grains documents a pre-orogenic Variscan mantle contribution for the mafic magmatism interpreted here as the indication of the south-directed subduction of the Le Conquet-Teplá ocean, that is, a branch of the Rheic ocean, below the Armorica microcontinent during the Bretonian phase. The intraplate opening of the Laval, Ménez-Bélair, and Châteaulin basins was coeval with this subduction. In the Laval area, the final closure of the basin, accommodated by north-directed folds-and-thrusts, took place after the Bashkirian (ca 320 Ma).
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