DI015-0019
The Multifaceted Scandinavian Lithosphere – New Insights from Surface Waves and Ambient Noise

Friday, 11 December 2020
Poster
Alexandra Mauerberger, Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences, Potsdam, Germany, Valerie Maupin, University of Oslo, CEED, Oslo, Norway, Hamzeh Sadeghisorkhani, Isfahan University of Technology, Department of Mining Engineering, Isfahan, Iran, Olafur Gudmundsson, Uppsala University, Uppsala, Sweden and Frederik J Tilmann, Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Potsdam, Germany
Abstract:
The Scandes mountain chain runs parallel to the west coast of Norway; it originated 420 Ma and is now deeply eroded, lacking recent compressional forces.

Beamforming of Rayleigh waves yielded a sin(1θ) phase velocity variation with azimuth in northern and southern Scandinavia but not in the central study area. Such a variation is incompatible with azimuthal anisotropy.

By performing a 2D full-waveform modeling of the Rayleigh wave propagation, we were able to reproduce our observations which might emerge due to the interference of reflected surface wave energy at sharp transition in lithospheric structure.

We use a classic two step inversion scheme with a 1D transdimensional Bayesian method to invert the merged phase dispersion curves for the VSV structure.

While the southern and central Scandes lack a crustal root, we observe a minor root below the northern Scandes. The LAB is deepening from west to east with a sharp step and velocity drop both in the South (120 km depth) and the North (150 km depth), coinciding with the Caledonian belt. The central area shows rather smoothly varying structures from west to east. In consideration of different crustal structures, we assume distinct uplift mechanisms along the Scandes. The southern Scandes might sustain their topography due to dynamic support from the mantle, while the northern Scandes experience both crustal and lithosphere isostasy. In both cases, we suspect the influence of a small-scale edge-driven convection at the sharp LAB gradients. Additionally, we find low-velocity areas below 150 km depth beneath the Karelia craton in northern Finland and image the Norrbotten craton which separates the Karelia craton and the Caledonides.

The sharp gradients in the LAB imaged in southern and northern Scandinavia are consistent with the observed sin(1θ) phase velocity variation whereas the smoother velocity structure in the central study area explains the absence of such variations there.

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