The Variscan subduction inheritance in the Southern Alps Sub-Continental Lithospheric Mantle: Clues from the Middle Triassic shoshonitic magmatism of the Dolomites (NE Italy)

Although often speculated, the link between theMiddle Triassic shoshonitic magmatismat the NE margin of the
Adria plate and the subduction-related metasomatismof the Southern Alps Sub-Continental Lithospheric Mantle
(SCLM) has never been constrained. In this paper, a detailed geochemical and petrological characterization of the
lavas, dykes and ultramafic cumulates belonging to the shoshonitic magmatic event that shaped the Dolomites
(Southern Alps) was used tomodel the composition and evolution of the underlying SCLMin the time comprised
between the Variscan subduction and the opening of the Alpine Tethys. Geochemical models and numerical simulations
enabled us to define that 5–7% partial melting of an amphibole + phlogopite-bearing spinel lherzolite,
similar to the Finero phlogopite peridotite, can account for the composition of the primitive Mid-Triassic SiO2-
saturated to -undersaturated melts with shoshonitic affinity (87Sr/86Sri = 0.7032–0.7058; 143Nd/144Ndi =
0.51219–0.51235; Mg # ~ 70; ~1.1 wt% H2O). By taking into account the H2O content documented in mineral
phases from the Finero phlogopite peridotite, it is suggested that the Mid-Triassic SCLM source was able to
preserve a significant enrichment and volatile content (600–800 ppm H2O) for more than 50 Ma, i.e. since the
slab-related metasomatismconnected to the Variscan subduction. The partialmelting of a Finero-like SCLM represents
the exhaustion of the subduction-related signature in the Southern Alps lithosphere that predated the
Late Triassic-Early Jurassic asthenospheric upwelling related to the opening of the Alpine Tethys.