Active deformation and Plio-Pleistocene fluvial reorganization of the western Kura fold-thrust belt, Georgia: implications for the evolution of the Greater Caucasus Mountains

Since Plio-Pleistocene time, southward migration of shortening in the eastern part of the Greater Caucasus into the Kura foreland basin has progressively formed the Kura fold-thrust belt and Alazani piggyback basin, which separates the Kura fold-thrust belt from the Greater Caucasus. Previous work argued for an eastward propagation of the Kura fold-thrust belt, but this hypothesis was based on coarse geological maps and speculative ages for units within the Kura fold-thrust belt. Here we investigate the initiation of deformation within the Gombori range in the western Kura fold-thrust belt and evaluate this eastward propagation hypothesis. Sediments exposed in the Gombori range have a Greater Caucasus source, despite the modern drainage network in the NE Gombori range, which is dominated by NE-flowing rivers. Palaeocurrent analyses of the oldest and youngest syntectonic units indicate a switch happened between similar to 2.7 Ma and 1 Ma from dominantly SW-directed flow to palaeocurrents more similar to the modern drainage network. A single successful Al-26-Be-10 burial date indicates the youngest syntectonic sediments are 1.0 +/- 1.0 Ma, which, while not a precise age, is consistent with original mapping suggesting these sediments are of Akchagylian-Apsheronian (2.7-0.88 Ma) age. These results, along with recent updated dating of thrust initiation in the eastern Kura fold-thrust belt, suggest that deformation within the Kura fold-thrust belt initiated synchronously or nearly synchronously along-strike. We additionally use topographic analyses to show that the Gombori range continues to be a zone of active deformation.