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

Journal Title

Journal ISSN

Volume Title

Publisher

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.

Description

Keywords

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

Citation

Source

Lithos

Type

Journal article

Book Title

Entity type

Access Statement

License Rights

DOI

10.1016/j.lithos.2009.12.013

Restricted until

2037-12-31