Crust-mantle boundary in the central Fennoscandian shield: constraints from wide-angle P- and S-wave velocity models and new results of reflection profiling in Finland

Our poster presents analyse of the crust-mantle boundary in the central Fennoscandian shield based on new P- and S-wave 2-D velocity models of SVEKA'81, SVEKA'91 and FENNIA wide-angle reflection and refraction profiles and on results of a new seismic reflection experiment in Finland (FIRE). In this area the crust is extremely thick and the Moho boundary is difficult to detect using methods based on interpretation of P-waves (near vertical profiling and wide-angle experiments). However, the S-wave reflections from the Moho boundary (SmS) are frequently more pronounced in wide-angle data than the P-wave reflections (PmP). In order to infer the crust-mantle transition, we developed new P- and S-wave velocity models using reprocessing of the old data and compared them to record sections of collocated reflection profiles and to Vp and Vp/Vs of main types of lower crustal and upper mantle rocks. Based on the lateral variations of Vp, Vp/Vs and reflectivity in the lower crust and upper mantle, three main types of the crust-mantle boundary were distinguished. The first type corresponds to eclogitized lower crust that overlies peridotitic upper mantle. In this case the Moho coincides with the litholigical crust-mantle boundary. The second type corresponds to lower crust composed of mafic garnet granulites overlying the peridotitic upper mantle, for which the Moho and the lithological crust-mantle boundary coincide as well. The third type corresponds to the mafic garnet granulites underlain by a layer of eclogitic upper mantle. In the latter case the lithological crust-mantle boundary is deeper than the Moho.