Abstract. 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 100øC increase in temperature, a decrease of 0.5-2% in Vp and 0.7-4.5% in Vs 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 Vp and Vs 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, Vp-and Vs-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 400øC below an average mantle adiabat at 100 km depth under the Russian Platform and a 300øC 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.

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Transition zone slab deformation influences Earth's thermal, chemical, and tectonic evolution.However, the mechanisms responsible for the wide range of imaged slab morphologies remain debated. Here we use 2-D thermo-mechanical models with a mobile trench, an overriding plate, a temperature and stress-dependent rheology, and a 10, 30, or 100-fold increase in lower mantle viscosity, to investigate the effect of initial subducting and overriding-plate ages on slab-transition zone interaction. Four subduction styles emerge: (i) a ''vertical folding'' mode, with a quasi-stationary trench, near-vertical subduction, and buckling/folding at depth (VF); (ii) slabs that induce mild trench retreat, which are flattened/''horizontally deflected'' and stagnate at the upper-lower mantle interface (HD); (iii) inclined slabs, which result from rapid sinking and strong trench retreat (ISR); (iv) a two-stage mode, displaying backward-bent and subsequently inclined slabs, with late trench retreat (BIR). Transitions from regime (i) to (iii) occur with increasing subducting plate age (i.e., buoyancy and strength). Regime (iv) develops for old (strong) subducting and overriding plates. We find that the interplay between trench motion and slab deformation at depth dictates the subduction style, both being controlled by slab strength, which is consistent with predictions from previous compositional subduction models. However, due to feedbacks between deformation, sinking rate, temperature, and slab strength, the subducting plate buoyancy, overriding plate strength, and upper-lower mantle viscosity jump are also important controls in thermo-mechanical subduction. For intermediate upper-lower mantle viscosity jumps (330), our regimes reproduce the diverse range of seismically imaged slab morphologies.

We map the thermal state of the North American mantle between depths of 50 and 250 km by inverting P and S velocities of three recent seismic tomographic models. In the well‐resolved regions, temperatures derived from P velocities agree with those derived from S velocities within the estimated uncertainties, and generally, the seismic temperatures are in agreement with those inferred from surface heat flow. Adiabatic mantle temperatures are found as shallow as 50 km under most of the Basin and Range. Warm, subsolidus mantle and known crustal structure can account for the high average elevation and large‐scale variations in topography of western North America. In the cratonic mantle beneath the stable eastern part of North America, temperatures at 50–100 km are on average 500°C cooler than under the tectonic western part of the continent and adiabatic mantle temperatures are not reached until 200–250 km depth. To balance the effect on topography of the thermally implied density increase for the North American craton, we infer a compositionally induced density decrease equivalent to a 1% depletion in iron over a depth interval of 50–250 km. In regions where TP differs significantly from TS we drop our assumption that variations in seismic velocity are only due to thermal structure. A discrepancy between TP and TS between 50 and 150 km depth under the Cascades and the Gulf of California can be accounted for by the presence of 1 to 2 vol % of fluids and/or melt. Another such discrepancy beneath Wyoming remains enigmatic.

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