CHARACTERISTICS OF THE CRUST IN THE CONTINIUM FROM OROGENIC BELT TO CRATON : EXAMPLE OF THE SCANDINAVIAN MOUNTAINS AND THE BALTIC SHIELD

Understanding the evolution of the crust after different orogenic episodes is an important study in order to better explain the evolution of our landscape. At the largest scale, topography is controlled by variations in crustal and lithospheric structure related to tectonic events, and the underlying mantle dynamics. More locally, if the erosion controls the relief, it seems that the variations in the surface rock density also play an important role. Given this complex relationship between subsurface structure and present day landscape it is clear that characterising the properties of the crust in term of thickness, Poisson’s ratio and velocity will bring us more information.

The Scandinavian passive margin is a good place for studying the linkage between crustal properties and the present day topography. The Scandinavian Mountains are a topographic anomaly on the North-East Atlantic passive margin. With heights above 1km adjacent to the low-lying Baltic Shield (average altitude of 500 m), this mountain range has undergone a rejuvenation by an uplift event during the Neogene. The absence of a crustal root expected from Airy isostasy calculations, the variation of gravity anomaly and the possibility of a low velocity zone in the upper crust suggest variations in density within the crust. This mechanism will explain the (isostatic) equilibrium of the mountain range. With this perspective two passive seismic experiments were deployed in 2007-2009 (SCANLIPS2) and 2013-2014 (SCANLIPS3D) across the Northern Scandinavian Mountains and the Baltic Shield.

We choose to use the P-receiver functions and the ambient seismic noise for a study of the crust across the Northern Scandinavian Mountains and the Baltic Shield. Here we will show a new 2D Moho map compiled from our new results together with previous studies in this region. This map shows a crustal thickening from West to East (40 km to 50 km) without any obvious influence of the transition from the Scandinavian Mountains to the Baltic Shield. We will also show a new 3D shear wave velocity map derived from our surface wave ambient noise tomography. These two maps give us the new perspective in the understanding of this topographic anomaly and the contribution of the crust in the dynamic topography.