Shallow mantle temperatures under Europe from P and S wave tomography

Temperature is one of the key parameters controlling lithospheric and mantle dynamics and rheology. Using recent experimental data on elastic parameters and anelasticity, we obtain models of temperature at 50 to 200 km depth beneath Europe from the global P wave velocity model of Bijwaard et al. [1998] and the regional S wave velocity model of Marquering and Snieder [1996], Forward modeling of seismic velocity allows us to assess the sensitivity of velocity to various parameters. In the depth range of interest, variations in temperature (when below the solidus) yield the largest effects. For a 100 degrees C increase in temperature, a decrease of 0.52% in V-P and 0.7-4.5% in V-S is predicted, where the strongest decrease is due to the large effect of anelasticity at high temperature, The effect of composition is expected to give velocity anomalies <1% for the shallow mantle and would therefore be difficult to resolve. At depths >80 km the relative amplitudes of the European V-P and V-S anomalies are consistent with a thermal origin. At shallower depths, variations in crustal thickness and possibly the presence of partial melt appear to have an additional effect, mainly on S wave velocity. In regions where both P and S anomalies are well-resolved, V-P- and V-S-derived thermal models agree well with each other and with temperatures determined from surface heat flow observations. Furthermore, the thermal models are consistent with known tectonics. The inferred temperatures Vary significantly, from around 400 degrees C below an average mantle adiabat at 100 km depth under the Russian Platform and a 300 degrees C increase from east to west across the Tornquist-Teisseyre zone to temperatures around the mantle adiabat in the depth range 50-200 km under areas with present surface volcanism. In spite of the uncertainties in the calculation of temperatures due to uncertainties in the experimental elastic parameters and anelasticity and uncertainties associated with tomographic imaging, we find that the tomographic models of the shallow mantle under Europe can yield useful estimates of the thermal structure.