Early Permian post-collisional magmatism induced by extensive removal of the Variscan lithospheric mantle

Abstract

The tectonic re-equilibration after the Variscan orogeny coincided with widespread early Permian post-collisional magmatism in southern Europe. A full understanding of the origin of this magmatism in the South Variscan realm and its relationship to major tectonic events such as subduction, continental collision, rifting or lithospheric foundering hinges on high-precision geochronological data of the magmatic products. Here, we present new high-precision zircon U–Pb geochronological data obtained by chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-ID-TIMS) for the early Permian Athesian Magmatic District (AMD) in NE Italy. Our analysed zircons from felsic intrusive and volcanic rocks give ages spanning from ca. 281.8 to 277.2 Ma, suggesting that the lifetime of the AMD was significantly shorter than previously reported. Our data, when combined with recent high-precision ages from other South Variscan magmatic systems suggest that the Cisuralian (early Permian) post-collisional magmatism in the Southalpine domain occurred over more than 8 m.y. with the magmatic centres migrating from the western to the eastern Southern Alps. Geochemical and radiogenic isotope modelling of published data for magmatic rocks in the Southern Alps and the Corsica-Sardinia batholith suggest a subduction-enriched mantle source for the South Variscan post-collisional magmatism, with melting occurring under a relatively thin lithosphere at depths of ca. 60 km. Our results point to a significant post-orogenic delamination of the thick lithospheric mantle formed during the Variscan orogeny. In this scenario, the migration of the post-collisional magmatism within the Cisuralian district may be due to the lateral migration of the lithospheric foundering.