Lithospheric contact of the Western Carpathians with the Bohemian Massif in the light of seismic and new AlpArray gravity data

The Bohemian Massif represents the largest exposure of rocks deformed during the Variscan orogeny. Western Carpathians form an arc-shaped mountain range related to the Alpine orogeny. In our study, the lithospheric structure of the key tectonic units in the area and their contact zone was analyzed by 2D gravity modelling along the NW-SE oriented CEL09 profile of the CELEBRATION 2000 seismic experiment. New gravity map compiled at the initiative of the AlpArray Gravity Research Group was used. This map is based on a uniform reprocessing of the national terrestrial gravimetric databases of ten countries of the wider Alpine region. The resultant 2D density model based on gravity data was constrainted by results of seismic reflection and refraction method. Applied densities were defined by transformation of the modelled P-wave velocities. A good correlation between the density and seismic models was shown. The resultant 2D density model consisting of five principal layers (sediments, upper crust, lower crust, lower lithosphere and asthenosphere) shows differences between the older, cooler and thicker Bohemian Massif (in average: ~32 km thick crust, and ~120 km thick lithosphere), and the younger, warmer and thinner Carpathian-Pannonian region (~28 km crust, ~95 km lithosphere). The detected contact is delimited by a change in the Moho and the LAB topography, and assumes an overthrusting of the Western Carpathians onto the Bohemian Massif by ~30 km resulting in a neo-transformation of the crust/mantle and related lithosphere after subduction.