EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

From the Finero phlogopite peridotite to the shoshonitic magmatism of the Dolomites: unveiling the evolution of the Sub-Continental Lithospheric Mantle beneath the Southern Alps (Northern Italy)

Federico Casetta1, Massimo Coltorti1, Ryan B. Ickert2, Darren F Mark3, Pier Paolo Giacomoni1, Costanza Bonadiman1, Theodoros Ntaflos4, and Alberto Zanetti5
Federico Casetta et al.
  • 1University of Ferrara, Department of Physics and Earth Sciences, Ferrara, Italy (
  • 2Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN 47907
  • 3Scottish Universities Environmental Research Centre, Rankine Avenue, East Kilbride, G75 0QF, UK
  • 4Department of Lithospheric Research, University of Vienna, Althanstraße 14 (UZA II), 1090 Wien, Austria
  • 5Istituto di Geoscienze e Georisorse - C.N.R., Unità di Pavia (Italy)

The Mid-Triassic emplacement of shoshonitic magmas at the NE margin of the Adria plate in concomitance with extensional/transtensional tectonics is one of the most intriguing and peculiar aspects typifying the geodynamic evolution of the Western Tethyan realm. Although often hypothesized, the link between this magmatic event and the metasomatised Southern Alps Sub-Continental Lithospheric Mantle (SCLM) has never been constrained.

Geochemical and petrological analyses of lavas, dykes and ultramafic cumulates belonging to the shoshonitic magmatism of the Dolomites, coupled with pre-existing data on peridotite massifs (i.e. Finero, Balmuccia, Baldissero), were used to reconstruct the evolution of the Southern Alps SCLM between Carboniferous and Triassic. According to our model, a metasomatised amphibole + phlogopite-bearing spinel lherzolite, similar to the Finero phlogopite peridotite and likely generated by interaction between a depleted mantle and slab-derived components during the Variscan subduction, was able to produce magmas with orogenic-like affinity during Mid-Triassic. In this context, partial melting degrees of ca. 5-7% were required for producing primitive 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). As testified by the H2O content in mineral phases from the Finero phlogopite peridotite (Tommasi et al., 2017), the modelled Mid-Triassic fertile lithospheric mantle could have been able to preserve a significant enrichment and volatile content (600-800 ppm H2O) for more than 50 Ma, i.e. since the Variscan subduction-related metasomatism. During the Mid-Triassic partial melting event, the modelled Finero-like mantle exhausted the subduction-related signature inherited during the Variscan subduction. Around 20 Ma later, the same lithosphere portion was affected by an asthenospheric upwelling event related to the Late Triassic-Early Jurassic opening of the Alpine Tethys (Casetta et al., 2019).

Casetta, F., Ickert, R.B., Mark, D.F., Bonadiman, C., Giacomoni, P.P., Ntaflos, T., Coltorti, M., 2019. The alkaline lamprophyres of the Dolomitic Area (Southern Alps, Italy): markers of the Late Triassic change from orogenic-like to anorogenic magmatism. Journal of Petrology 60(6), 1263-1298.

Tommasi, A., Langone, A., Padrón-Navarta, J.A., Zanetti, A., Vauchez, A., 2017. Hydrous melts weaken the mantle, crystallization of pargasite and phlogopite does not: Insights from a petrostructural study of the Finero peridotites, Southern Alps. Earth and Planetary Science Letters 477, 59-72.

How to cite: Casetta, F., Coltorti, M., Ickert, R. B., Mark, D. F., Giacomoni, P. P., Bonadiman, C., Ntaflos, T., and Zanetti, A.: From the Finero phlogopite peridotite to the shoshonitic magmatism of the Dolomites: unveiling the evolution of the Sub-Continental Lithospheric Mantle beneath the Southern Alps (Northern Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10137,, 2021.