An investigation of how intracratonic rifting is “seeded”: Case study of the Late Devonian Dniepr-Donets Basin rift within the East European Craton

Abstract

This paper analyses the role of pre-existing Precambrian structures for the localisation of the intracratonic rifts from a case study of the Dniepr-Donets Basin (DDB) in Ukraine. The DDB was formed as a result of Late Palaeozoic rifting in the Archaean-Paleoproterozoic Sarmatian segment of the East European craton (EEC). It separates the Ukrainian Shield (UkS) to its southwest from the Voronezh Massif (VM) to its northeast. The Donbas Foldbelt (DF) constitutes the tectonically inverted part of the DDB in its southeastern extent and has been imaged by coincident wide-angle reflection and refraction seismic as well as deep near-vertical reflection seismic profiles (project “DOBRE”). It is almost completely filled with a highly indurated succession of upper Palaeozoic sediments and metasediments, up to some 20 km in thickness, now exposed at the surface. Here, a crustal and upper mantle structural-compositional model that is tightly constrained by the seismic data and gravity anomalies along the profile is used to search for Precambrian pre-rift crustal features that could have played a role in localising Late Palaeozoic rifting. The results suggest that there may be a different tectonic history for Sarmatian crystalline crust on either side of the DF. Density isolines in the AM crust are shallower than corresponding ones of equal value in the VM crust and, accordingly, the mean density of the crust of the AM is higher. This effect, calibrated on the DOBRE profile, is expressed along the margins of the entire DDB with a higher background level of the gravity field seen generally for the UkS than for the VM. The associated gravity gradient coinciding with the location of Palaeozoic rifting means that there is a perturbation to the horizontal deviatoric stress in this position that likely predates rifting. Further, a well-constrained upper crustal low-density granitic body beneath the northeastern flank of the DF produces a significant negative gravity anomaly superimposed upon the background gravity gradient. This adds a significant additional extensional component to the ambient deviatoric stress field. It cannot be concluded with certainty that either of these crustal features was necessary or sufficient for “seeding” Late Palaeozoic rifting but modern passive seismology surveys across the DDB as well as new bedrock geological studies would help test such a hypothesis.