Lithospheric structure along wide-angle seismic profile GEORIFT 2013 in Pripyat–Dnieper–Donets Basin (Belarus and Ukraine)
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The GEORIFT 2013 (GR'13) WARR (wide-angle reflection and refraction) experiment was carried out in 2013 in the territory of Belarus and Ukraine with broad international co-operation. The aim of the work is to study basin architecture and deep structure of the Pripyat–Dnieper–Donets Basin (PDDB), which is the deepest and best studied Palaeozoic rift basin in Europe. The PDDB is located in the southern part of the East European Craton (EEC) and crosses Sarmatia—one of the three segments of the EEC. The PDDB was formed by Late Devonian rifting associated with domal basement uplift and magmatism. The GR’13 extends in NW–SE direction along the PDDB strike and crosses the Pripyat Trough (PT) and Dnieper Graben (DG) separated by the Bragin Uplift (BU) of the basement. The field acquisition along the GR'13 (of 670 km total length) involved 14 shots and recorders deployed every ∼2.2 km for several shot points. The good quality of the data, with first arrivals visible up to 670 km for several shot points, allowed for construction of a velocity model extending to 80 km depth using ray-tracing modelling. The thickness of the sediments (Vp < 6.0 km s−1) varies from 1–4 km in the PT, to ∼5 km in the NW part of the DG, to 10–13 km in the SE part of the profile. Below the DG, at ∼330–530 km distance, we observed an upwarping of the lower crust (with Vp of ∼7.1 km s−1) to ∼25 km depth that represents a rift pillow or mantle underplate. The Moho shallows southeastwards from ∼47 km in the PT to 40–38 km in the DG with mantle velocities of 8.35 and ∼8.25 km s−1 in the PT and DG, respectively. A near-horizontal mantle discontinuity was found beneath BU (a transition zone from the PT to the DG) at the depth of 50–47 km. It dips to the depth of ∼60 km at distances of 360–405 km, similar to the intersecting EUROBRIDGE’97 profile. The crust and upper mantle structure on the GR'13 may reflect varying intensity of rifting in the PDDB from a passive stage in the PT to active rifting in the DG. The absence of Moho uplift and relatively thick crystalline crust under the PT is explained by its tectonic position as a closing unit of the PDDB, with a gradual attenuation of rifting from the southeast to the northwest. The most active stage of rifting is evidenced in the DG by a shallower Moho and by a presence of a rift pillow caused by mafic and ultramafic intrusions during the active phase. The junction of the PT and the DG (the BU) locates just at its intersection with the NS regional tectonic zone Odessa-Gomel. Most likely, the ‘blocking’ effect of this zone did not allow for further propagation of active rifting to the NW.