Constraining Neogene Mantle Dynamics of Western Mediterranean Region Encompassing Iberia by Quantitative Modeling of Basalt Geochemistry

Dynamic topography is the surface expression of sub-plate mantle convective processes. In recent years, there has been considerable interest in combining a wide range of geophysical, geological and geomorphic observations with a view to determining the amplitude, wavelength and depth of mantle thermal anomalies. Here, we are interested in exploring how quantitative modelling of major, trace and rare earth elements can be used to constrain the depth and degree of asthenospheric melting for a mantle peridotitic source. Our focus is on a region that encompasses the Iberian Peninsula where previous research suggests that long-wavelength topography is supported by a significant sub-plate thermal anomaly which is manifest by reduced shear-wave velocities. Stratigraphic and fluvial studies imply that this dynamic support is a Neogene phenomenon. We analyzed 48 Neogene basaltic rocks that were acquired from Iberia in September 2019 and combined these analyses with previously published datasets. Both major element thermobarometry and rare earth element inverse modelling are used to determine the asthenospheric potential temperature and lithospheric thickness. These values are compared with those estimated from calibrated shear-wave tomographic models. Our geochemical results indicate that potential temperatures and lithospheric thicknesses are 1300-1375 °C and 50-80 km, respectively. These values broadly agree with calibrated tomographic models which yield values of 1300-1360 °C and 45-70 km. We conclude that a region encompassing Iberia is dynamically supported by a combination of warm asthenosphere and thinned lithosphere.