Deep temperatures and lithospheric thickness along the European Geotraverse

Abstract

One-dimensional, steady-state heat conduction models in the crust and upper mantle for 24 areas along the European Geotraverse (EGT) show that temperatures are higher beneath young geological regions; at the Moho they range from 450° to 825°C. Heat flowing out from the mantle varies from 18 to 72 mW/m 2 and the contribution of crustal heat-flow density, evaluated by the correlation between seismic velocity and the abundance of radioactive elements, accounts for about 48% of the surface heat-flow density. The temperature gradient below Moho (from about 5 to 23 mK/m) is low where the surface heat-flow density reaches its minimum values. The depth at which the geotherms reach 0.85 of the mantle melting temperature is greater in the Precambrian and Caledonian areas, with a maximum value of about 195 km under the Early Proterozoic Scandinavian Shield. In the Hercynian and Alpine areas, this depth is generally lower. Higher values (maximum 150 km) coincide with the orogenic belts and the continental block of Sardinia and Corsica; under the Ligurian Sea and the Sardinian Channel, the lithospheric thickness decreases remarkably to about 50 km. Globally, the lithosphere thickness is controlled by the mantle heat-flow density which decreases, according to a power law, with an increase in the lithosphere-asthenosphere depth.