Final Report

Project number		Stand-alone Projects  P14895
Title		Dating thermal events in the Donbas Foldbelt (Ukraine)
Principal investigator		SACHSENHOFER Reinhard F.
Approval date		07.05.2001
University / Research institution		Institut für Geowissenschaften, Montanuniversität Leoben
Scientific field(s)
Keywords		UKRAINE, THERMAL HISTORY, DONBAS, BASIN INVERSION, FISSION-TRACK, HEAT FLOW
Homepage		http://unileoben.ac.at./~buero62/geologie/Sachsenh

The Donbas Foldbelt is a folded and inverted segment of the Dnjepr-Donets Basin. The basin fill comprises Devonian and Carboniferous sediments. The latter host one of the major coalfields of the world. Significant parts of the Carboniferous sediments were eroded during an early Permian uplift phase. The age of the compressional structures (Permian or late Cretaceous) is a matter of discussion.
Previous investigations have shown that paleo-heat flows during Permian maximum burial were in the range 40 to 75 mW/m² and provided evidence for an additional thermal event (100 - 200 mW/m²) with an unknown age.
Within the frame of the present project, apatite fission track (FT) data were used to determine the age of the "additional heat flow event" and to study the Mesozoic thermal history. Main study results include:

• The heating event in the Krasnoarmeisk area occurred during early/middle Triassic times (240-230 Ma). The areal extent of the event is larger than presumed earlier.
• The Permo-Triassic(?) event also occurred in the Donetsk-Makeevka region, but cannot be dated with the FT data. This is because of a relatively strong (90-100°C) Jurassic/Cretaceous thermal overprint. The latter is probably related to intraplate extension and magmatic activity during late Jurassic times.
• Although the southern Donbas area was affected by Permian alkaline magmatism, the thermal overprint is mild. This suggests that the Permian magmatic phase had only little influence on regional heat flow.
• Rocks in the southern and westernmost study area cooled below 60°C already during the Jurassic (140-160 Ma), whereas rocks in the Donets-Makeevka region remained at temperatures above 60°C till Cretaceous/Tertiary times (125-45 Ma). In the latter area, a correlation exists between the present-day depth of the samples and their cooling ages. This suggests that folding occurred before late Cretaceous times.

The results have implications for different scientific and applied aspects of the evolution of the basin including (1) the geodynamic evolution of the basin, (2) the timing of coal-bed methane generation, (3) the timing of epigenetic mercury, antimony and gold deposits in the Donbas Foldbelt.