A mechanism for crustal thinning without lateral extension

In some continental regions thin crust is found without observing significant indications of extensional tectonics. We argue that in such regions upwelling mantle flows may give rise to sublithospheric loading stresses which may be able to squeeze out the ductile lower crust, but leave the upper crust and sub‐crustal lithosphere essentially unstretched. This model allows us to constrain the viscosity of the lower crust if the amount and time scale of crustal thinning is observed in any subsidence basin. We applied our model to the Pannonian Basin (Hungary) and found lower crustal viscosities between 10 20 and 10 21 Pa s. Comparing this viscosity with laboratory data of crustal rocks results in lower crustal temperatures of about 600 to 800°C, which are in good agreement with geothermal models. Our model might also help to understand the appearance of a very thick crust and lithosphere without any pronounced topography as it is found in Fennoscandia.