Structure of a diffuse suture between Fennoscandia and Sarmatia in SE Poland based on interpretation of regional reflection seismic profiles supported by unsupervised clustering

Abstract

The Paleoproterozoic suture between Sarmatia and Fennoscandia (SFS), two major components of the East European Craton, extends SW-ward from Russia through Belarus to SE Poland. The exact character of this suture remains speculative, despite the results of the wide-angle reflection and refraction (WARR) soundings. Here, we show results of newly reprocessed deep reflection seismic data of the PolandSPAN™ survey, portraying the whole crust and uppermost mantle in SE Poland. Their interpretation is supported by the unsupervised clustering of seismic reflectivity patterns. From the integration of PolandSPAN™ data with both magnetic and WARR data, we conclude that the SFS cannot be interpreted as a localised lithospheric discontinuity coincident with the Minsk Fault. Instead, we observe a so-called diffuse cryptic suture zone, c. 150 km wide, where materials from two colliding plates are mixed over large distances to form a unified continental crust. The suture-related reflections are interpreted as a thrust-wedge rooted at the lower-middle crust interface underneath the Ivanowo-Borisov zone. We support Bogdanova et al. (2015) view that the Okołowo-Holeszów Belt and Belarus-Podlasie Granulite Belt have affinities to the NW margin of Sarmatia. We interpret both units as belonging to the diffuse SFS.