Thermotectonic evolution of the Ukrainian Donbas Foldbelt revisited: new constraints from zircon and apatite fission track data

Abstract

The Donbas Foldbelt (DF) is the compressionally deformed segment of a large Late Palaeozoic rift cross-cutting the southern part of the East European Craton and is traditionally described as a classic example of an inverted intracratonic rift basin. Proposed formational models are often controversial and numerous issues are still a matter of speculation, primarily due to the lack of absolute time constraints and insufficient knowledge of the thermal evolution. We investigate the low-temperature thermal history of the DF by means of zircon fission track and apatite fission track (AFT) thermochronology applied to Upper Carboniferous sediments. In all samples, the AFT chronometer was reset shortly after deposition in the Early Permian (∼275 Ma). Samples contained kinetically variable apatites that are sensitive to different temperatures and using statistic-based component analysis incorporating annealing characteristics of individual grains assessed by Dpar , we identified several distinct age populations, ranging from the Late Permian (∼265 Ma) to the Late Cretaceous (∼70 Ma). We could thus constrain the thermal history of the DF during a ∼200 Myr long period following the thermal maximum. We found that earliest cooling of Permian and Permo-Triassic age is recorded on the basin margins whereas the central parts were residing in or slowly cooling through the apatite partial annealing zone during Jurassic and most of Cretaceous times, and then finally cooled to near-surface conditions latest around the Cretaceous/Palaeogene boundary. Our data show that Permian erosion was less significant and Mesozoic erosion more significant than generally assumed. Inversion and pop-up of the DF occurred in the Cretaceous and not in the Permian as previously thought. This is indicated by overall Cretaceous AFT ages in the central parts of the basin.