Imaging the warm lithospheric mantle in the Mediterranean-Alpine region: integrated thermochemical inversion of surface wave dispersion, heat flow and elevation data

Here we investigate the thermal structure of the lithosphere in the Alpine-Mediterranean region. We focus on areas characterized by negative velocity anomalies according to a lithosphere-upper mantle surface-wave tomography study (El-Sharkawy et al., 2020) to analyze possible lithospheric thinning and melting. Surface-wave, phase-velocity curves were determined by interstation cross-correlation measurements and inverted for a set of phase-velocity maps, spanning a broad period range. We invert fundamental mode Rayleigh and Love dispersion curves together with surface elevation and heat flow for the 1D thermochemical lithospheric structure in 13 columns. The inversion is framed within an integrated geophysical-petrological setting where mantle seismic velocities and densities are computed thermodynamically as a function of the in situ temperature and compositional conditions (Fullea et al., 2021). We analyze the presence of small amounts of melt in the vicinity of the lithosphere-asthenosphere boundary. We conduct sensitivity tests to asses the uncertainties associated with alternative experimental results accounting for the effect of melt and water on seismic velocities. Our results show that the lithosphere is thin (60-90 km) over the whole negative velocity anomaly area in the Alpine-Mediterranean region. We find the thinnest lithosphere in the Pannonian and Tyrrhenian basins (60-70 km), while the thickest lithosphere is located in the Iberia and Central Europe (80-90 km). Our thermal models show the presence of melting near the LAB (1300 ºC isotherm) in some of the columns (e.g. Pannonian and Tyrrhenian basins) associated with a pronounced drop in Vs velocities.