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The European portion of the Eurasian plate formed as a result of a complex series of tectonic events that included the Caledonian, Variscan, and Carpathian orogenies. These orogenic events occurred along the western margin of the East European craton (a portion of the paleocontinent Baltica). In recognition of the complexity of the rifting that formed this margin in the Neoproterozoic-Cambrian and the subsequent tectonic events along it, the region adjacent to this margin has been called the Trans-European suture zone. In order to understand the processes at work during these tectonic events, a series of large integrated geophysical and geological investigations built around large seismic refraction-experiments (POLONAISE'97, CELEBRATION 2000, ALP 2002, and SUDETES 2003) were conducted between 1997 and 2003. In this study, we compare the results of the two longest seismic profiles and their tectonic implications. These studies showed that lithospheric structure of the East European craton directly inboard of its margin is relatively uniform, and the crust consists of three layers below the sedimentary cover, and it is ∼45 km thick. The lithospheric mantle contains several reflectors, and its velocity is ∼8.2 km/s.

In the Variscides (Paleozoic platform) of northern Poland along the Trans-European suture zone, the consolidated crust beneath the sedimentary cover consists of two distinct layers, and the total crustal thickness is 30–35 km. Within the core region of the Trans-European suture zone, the crust is ∼40 km thick, but most of its upper half is the sedimentary fill of the late Paleozoic and Mesozoic Polish trough, which is underlain by a thick sequence of older continental-margin volcanic and sedimentary units. The lithospheric mantle structure is complex and indicative of a plate collision under the Trans-European suture zone region, and it has seismic velocities that are generally higher than those of the East European craton.

In the Carpathian region, the effects of younger collisions are present in addition to evidence of the Variscan orogeny. It is somewhat surprising that the crustal thickness beneath the Carpathians is 30–40 km, but it is not surprising that beneath the Pannonian Basin, an extensional feature, the crust is only 24–28 km thick. The thickest crust in this region (∼50 km) occurs under the rifted margin of the East European craton. The sedimentary cover in this region varies greatly in age and thickness. It is 1–3 km thick beneath the East European craton, 10 km thick the beneath Polish Basin/Lublin trough region, ∼18 km thick in the Carpathian foredeep, and 5–8 km thick beneath the Pannonian Basin. The velocity in the lithospheric mantle is 8.1–8.25 km/s beneath the East European craton, 8.2–8.4 km/s beneath the Variscides–Trans-European suture zone, and 7.8–8.0 km/s beneath Carpathian-Pannonian area. The crust and features in the lithospheric mantle appear to dip northward in this area.

In northern Poland, the rifted southwestern margin of the East European craton is abruptly bounded by the Trans-European suture zone and ultimately the Variscides over a region that is only ∼100 km wide, while the collisional zone between the East European craton and the Carpathian-Pannonian area is ∼300 km wide. In both areas, the lithospheric structure observed suggests that the Caledonian, Variscan, and Carpathian orogenies in this area were relatively “soft” collisions that left the East European craton passive margin largely intact. The structural model of the transition between the Pannonian Basin–Carpathians and the East European craton indicates northward “old” subduction under Baltica (Jurassic–Early Cretaceous). However, the thinning of the Pannonian lithosphere could be explained as the result of extension and high heat flow, with “young” southward subduction or slab rollback to the east, which took place in the Tertiary (Miocene).

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