Carboniferous high-pressure metamorphism of Ordovician protoliths in the Argentera Massif (Italy), Southern European Variscan belt
Date
2010
Authors
Rubatto, Daniela
Ferrando, Simona
Compagnoni, Roberto
Lombardo, Bruno
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Elsevier
Abstract
The age of high-pressure metamorphism is crucial to identify a suitable tectonic model for the vast Variscan orogeny. Banded HP granulites from the Gesso-Stura Terrain in the Argentera Massif, Italy, have been recently described (Ferrando et al., 2008) relicts of high-pressure metamorphism in the western part of the Variscan orogen. Bulk rock chemistry of representative lithologies reveals intermediate silica contents and calc-alkaline affinity of the various cumulate layers. Enrichment in incompatible elements denotes a significant crustal component in line with intrusion during Ordovician rifting. Magmatic zircon cores from a Pl-rich layer yield scattered ages indicating a minimum protolith age of 486 ± 7 Ma. Carboniferous zircons (340.7 ± 4.2 and 336.3 ± 4.1 Ma) are found in a Pl-rich and a Pl-poor layer, respectively. Their zoning, chemical composition (low Th/U, flat HREE pattern and Ti-in-zircon temperature) and deformation indicate that they formed during the high-pressure event before decompression and mylonitisation. The proposed age for high-pressure metamorphism in the Argentera Massif proves that subduction preceded anatexis by less than 20 Ma. The new data allow a first-order comparison with the Bohemian Massif, which is located at the eastern termination of the Variscan orogen. Similarities in evolution at either end of the orogen support a Himalayan-type tectonic model for the entire European Variscides.
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Keywords: anatexis; Carboniferous; chemical composition; granulite; Hercynian orogeny; lithology; mylonitization; Ordovician; protolith; subduction; ultrahigh pressure metamorphism; uranium-lead dating; zircon; Argentera Massif; Bohemian Massif HP granulites; U-Pb geochronology; Variscan belt; Zircon
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2037-12-31
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