3-D gravity analysis of the Dniepr–Donets Basin and Donbas Foldbelt, Ukraine

• Published in: Tectonophysics 1999-11, Vol.313 (1), p.41-58
• Main Authors: Yegorova, T.P, Stephenson, R.A, Kozlenko, V.G, Starostenko, V.I, Legostaeva, O.V
• Format: Article
• Language: English
• Subjects: 3-D gravity modelling; crust–upper mantle structure; Dniepr–Donets Basin; Donbas Foldbelt
• ISSN: 0040-1951; 1879-3266
• DOI: 10.1016/S0040-1951(99)00189-4

The Dniepr–Donets Basin (DDB) is a linear, NW–SE trending, late Palaeozoic and younger sedimentary basin on the East European Platform separating the Ukrainian Shield from the Voronezh Massif. Its northwestern (Dniepr) segment has the characteristics of a typical rift basin. To the southeast, through a transition zone of approximately 200 km length, the DDB is progressively uplifted and compressionally deformed into the correlatable Donbas Foldbelt (DF). Along the axis of the Dniepr segment a series of gravity highs has been previously explained by high-density crystalline crust beneath the axis of the basin caused by intrusion of mafic and ultramafic rocks. In this paper, the results of a 3-D gravity analysis, using a gravity backstripping technique, is described that investigates the crustal and upper mantle structure in the region of the DDB–DF transition zone and DF. A residual gravity field I, obtained by subtracting the gravity influence of the sedimentary succession of the DDB from the observed field, reveals a distinct positive anomaly along the axis of the rift basin increasing in amplitude to the southeast in concert with increasing sedimentary thickness. A residual gravity field II, derived by removing the gravity effects of a modelled homogeneous crystalline crust from residual field I, reaches 200 and 100 mGal amplitude in the DF for two respective Moho models based on different interpretations of the published crust and upper mantle seismic velocity models. The first of these (model A) assumes crustal thickening beneath the transition zone and DF (to a Moho depth up to 50 km) whereas the second (model B) assumes a Moho shallowing (to depths in the range 35–37 km) along the whole basin axis. For each residual anomaly II, the best-fitting 3-D distribution of average density in the crystalline crust has been computed. Both models indicate the existence of a high-density body in the crystalline crust along the DDB axis, increasing in density from the Dniepr segment to the DF, with higher average crustal density required in the case of Moho model A (3.17×10 3 kg m −3 versus 3.06×10 3 kg m −3 for model B). The preferred interpretation of the density models is one in which the denser crystalline crust underlying the DDB–DF transition zone and DF is explained by intrusion of mafic and ultramafic rocks during late Palaeozoic rifting processes. Invocation of processes related to the uplift and inversion in the DF are not required to explain the observe