Seismic refraction evidence for crustal structure in the central part of the Trans-European Suture Zone in Poland

Abstract

AbstractThe results of seismic investigations obtained for the Trans-European Suture Zone (TESZ) show the presence of relatively low velocity rocks (Vp < 6.1 kms−1), of sedimentary, metamorphic or volcanic origin, down to a depth of 20 km; high velocity (Vp = 6.8–7.3 kms−1) lower crust, the Moho at a depth of approximately 30–33 km; and a high-velocity (Vp > 8.3 kms −1) uppermost mantle. The transition of the crustal structure is seen across a 200 km wide zone. The three-layered crystalline crust of Baltica changes over this distance into the two-layered crust of Palaeozoic (Variscan) Europe, due to the disappearance of the lowest layer (Vp ∼ 7.1 kms−1) and tapering off of the Baltican/cratonic wedge. The seismic profiles suggest that the lower crust (Vp ∼ 7.1 kms−1) in the transition zone represents the attenuated Baltica margin underthrust towards the SW beneath the Avalonian accretionary wedge. The latter corresponds to the low-velocity upper crust (Vp < 6.1 kms−1) characteristic of the German-Polish Caledonides. Consequently, the high-velocity reflective lower crust of Baltica affinity extends approximately 200 km to the SW of the Teisseyre-Tornquist Zone within the basement of the Palaeozoic Platform. The Avalonian upper/middle crust is confined in the SW against the WNW-ESE trending Dolsk Fault. To the SW of the Odra Fault, a typical Variscan crust is detected which shows two-layer structure and relatively low P-wave velocities. The WNW-ESE Odra Fault, approximately parallel to the Dolsk Fault, splits the Variscan domain into the Variscan externides buried beneath the Palaeozoic Platform in the NE and the Variscan internides of the Sudetes in the SW. We interpret both the Odra and Dolsk Faults as dextral strike-slip features that cross cut the NE termination of the Variscan Orogen parallel to the Teisseyre-Tornquist Zone. In a relatively small area, they juxtapose three crustal domains representing, successively, the Variscan internides, externides and the Variscan foreland.