THE DEEP LITHOSPHERE IN THE ALPS - A MODEL INFERRED FROM P RESIDUALS

The tomographic studies of the Alps and their surroundings, based on the relative P residuals, indicated two lithosphere roots attaining depths over 200 km separated by an upwelling of the lithosphere-asthenosphere transition beneath the central part of this mountain range. The directional dependence of relative P velocities indicates an anisotropic wave propagation in the subcrustal lithosphere beneath the Alps and their surroundings. The presented model of the deep lithosphere structure suggests several phases of the tectonic development of this region: collision of a tip of the Adriatic plate with Europe in the eastern Alps and dextral strike-slip movement of the Adriatic ending with underthrusting of Europe beneath the western Alps and counterclockwise rotation. The latter contributes to a steep plunge of both plates beneath the eastern Alps and to stress accumulation in the Friuli region. A model with delamination of the rigid upper crust and its rotation resolves some of the inconsistencies between the near-surface and deep tectonics and also explains the distribution of seismicity. © 1990.