A 3-D gravity modeling of the crustal structure of the Dnieper-Donets basin and Donbas. II. Inhomogeneties of the crystalline crust
© Yegorova T.P., Stephenson R.A., Kozlenko V.G., Starostenko V.I.,
Zavorot'ko A.N., Legostaeva O.V.
Results of 3-D gravity modeling based on gravity back-strippong analysis, with the objective of studying the crustal structure of the Dnieper-Donets Aulacogen (DDA) and Donbas are presented. In the residual gravity field I, obtained by subtracting the effect of the sediments from the observed field, a stripe of positive anomaly thickness of amplitudeincreasing in SE direction in correspondence with total sediments has been distinguished along the rift axis. The residual anomaly II, formed by removing the effect of the homogeneous crystalline crust from the residual field I, reaches its maximal amplitude of 200 and 100 mgal in Donbas for two alternative crustal models. In the first model (version A), crustal model thickening to 50 km under the transition zone and Donbas is considered; in the second one (version B), Moho elevation to 35-37 km along the axis of the whole aulacogen is assumed. For both versions 3-D density models of the consolidated crust (as average-density distribution) compensating the residual anomaly II have been calculated by trial and error method. As a result of the calculations, an anomalous body whose density increases from the Dnieper graben to Donbas with higher densities (3,17 g/cm3) in the model A than in the model B (3,06 g/cm3) has been traced under the whole aulacogen along its axis. The rwvealed dense body is generally explained by intrusion of basic and ultrabasic rocks into the crystalline crust during rifting.