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

Casetta, F., Ickert, R.B. , Mark, D.F. , Giacomoni, P.P., Bonadiman, C., Ntaflos, T., Zanetti, A. and Coltorti, M. (2021) The Variscan subduction inheritance in the Southern Alps Sub-Continental Lithospheric Mantle: clues from the Middle Triassic shoshonitic magmatism of the Dolomites (NE Italy). Lithos, 380-81, 105856. (doi: 10.1016/j.lithos.2020.105856)

Abstract

Although often speculated, the link between the Middle Triassic shoshonitic magmatism at the NE margin of the Adria plate and the subduction-related metasomatism of 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 to model the composition and evolution of the underlying SCLM in 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 metasomatism connected to the Variscan subduction. The partial melting 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.

• Item Type: Articles
• Additional Information: This work was supported by The University Institute for Higher Studies (IUSS) Mobility Research Programme of the University of Ferrara [grant numbers 570, 571] for Long Period, 2016/2017 to [FC], and the Italian National Research Program [PRIN_2017 Project 20178LPCPW] to [MC].
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Mark, Professor Darren and Ickert, Dr Ryan
• Authors: Casetta, F., Ickert, R.B., Mark, D.F., Giacomoni, P.P., Bonadiman, C., Ntaflos, T., Zanetti, A., and Coltorti, M.
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Lithos
• Publisher: Elsevier
• ISSN: 0024-4937
• ISSN (Online): 1872-6143
• Published Online: 29 October 2020
• Copyright Holders: Copyright © 2020 Elsevier B.V.
• First Published: First published in Lithos 380-381: 105856
• Publisher Policy: Reproduced in accordance with the publisher copyright policy