Lasha Sukhishvili, Adam Matthew Forte , Giorgi Merebashvili, Joel Leonard, Kelin X. Whipple, Zurab Javakhishvili, Arjun Heimsath, Tea Godoladze

Since the Plio-Pleistocene, southward migration of shortening in the eastern part of the Greater Caucasus (GC) into the Kura foreland basin has progressively formed the Kura-Fold Thrust belt (KFTB) and Alazani piggyback basin, which separates the KFTB from the GC. Previous work argued for an eastward propagation of the KFTB, implying that the western portion in Georgia is the oldest, but this hypothesis was based on coarse geologic maps and speculative ages for units within the KFTB. Here we investigate this hypothesis and focus on the Gombori Range (GR), which defines NW edge of the belt. Previous work divided the sediments of northern flank of the range into three facies. The rock types in the older and middle facies suggest a GC source provenance, despite the modern drainage network in the NE GR, which is dominated by NE flowing rivers.
Paleocurrent analyses of the alluvial conglomerates of the oldest and youngest syntectonic units indicate a switch from dominantly SW directed paleocurrents in the oldest unit to paleocurrents more similar to the modern drainage network in the youngest unit. A single successful 26Al-10Be burial date indicates these syntectonic sediments are 1±1 Ma, which while not a precise age, is consistent with original mapping suggesting these sediments are Akchagyl-Apsheron (2.7-0.88 Ma) age. Tectonic geomorphologic analyses indicate that western GR is the most active. Given its close proximity to the capital city of Tbilisi, this suggests that active structures within the Gombori range pose seismic hazard to this city of 1.2 million people.