Present-day upper-mantle architecture of the Alps: insights from data-driven dynamic modelling

Abstract

Geodetic observations by the Global Navigation Satellite Systems (GNSS) show that the Alpine mountains are uplifting while their forelands to the north and south are subsiding (Figure 1, Serpelloni et al., 2022;Sternai et al., 2014). Vertical uplift also varies along strike, with higher rates in the Western and Central Alps (∼2-2.5 mm/yr) than in the Eastern Alps, similar to inferred erosion and exhumation rates (Fox et al., 2015). Horizontal velocities from GNSS show ∼2 mm/yr convergence between Adria and Europe in the Eastern Alps, being related to the counter-clockwise rotation of the Adria microplate with respect to Eurasia, while convergence is only minor, if not absent, in the Western Alps (Serpelloni et al., 2016). Seismicity is restricted to upper-crustal depths in the Alps compared to whole crustal seismicity in their forelands (Figure 1). Earthquakes below Moho (>40 km) occur only to the south, beneath the Northern Apennines. A combination of surface and/or mantle processes have been proposed to explain these observations, including: (a) isostatic response to the latest deglaciation, (b) long-term erosion, (c) crustal shortening, (d) delamination of the European lithosphere, (e) detachment of the Western Alpine slab, and, (f) mantle flow in the asthenosphere (Fox et al., 2015;Mey et al., 2016;Sternai et al., 2014). Quantifying the relative contribution of these processes to the present-day surface deformation is essential to understand the coupling between surface and mantle processes and the evolution of this complex orogen. Mey et al. (2016) proposed that ∼90% of rock uplift in the Alps could be due to crustal rebound following the Last Glacial Maximum, while mantle processes exert only a local influence (e.g., Rhone Valley and Eastern Alps). Recently, Sternai et al. (2019) critically revisited this hypothesis. They demonstrated how deglaciation and erosion account for a relatively larger proportion of uplift in the Eastern Alps (30%-60%