Do thermomechanical heterogeneities in the upper mantle control crustal deformation?

The architecture of the crust in intracontinental Western and Central Europe is well constrained by multidisciplinary geoscientific data. This low-strain intraplate setting is known for its widely distributed seismicity with earthquake localization, however, being difficult to explain by the observed crustal configuration. Also, observed variations in crustal thickness do not provide clear evidence to explain lateral shifts in depositional and erosional centers over geological time. This raises questions regarding the underlying forces controlling crustal tectonics in this region, located far from active plate boundaries. Shear-wave velocity models obtained from seismic full waveform inversion methods show that the upper mantle is strongly heterogeneous pointing to thermomechanical contrasts that potentially could impact crustal tectonics. Therefore, we convert mantle shear-wave velocities to thermodynamically consistent temperature and density configurations by following a Gibbs's free energy minimization approach. We find spatial correlations between lithospheric thickness, respectively shallow lithospheric temperature and density variations, and crustal deformation patterns (including seismicity). This indicates that thermomechanical instabilities in the mantle could be the origin of relative vertical movements which would (i) cause laterally variable surface uplift and/or subsidence and (ii) facilitate strain localization in the mantle (ductile shear movements) above which the overlying crust would locally respond by brittle deformation.