Zircons U-Pb Geochronology of the Ore-Bearing Plutons of Adjara-Trialeti Folded Zone, Lesser Caucasus and Analysis of the Magmatic Processes

摘要

Zircons of the major ore-bearing plutons (Merisi, Namonastrali, Vakijvari, Zoti, Okros-Ghele and Rkviana) of the Adjara-Trialeti Paleogene folded zone of the Lesser Caucasus were dated by the U-Pb method using the Laser Ablation ICP-MS tool at the isotope laboratory of the Department of Earth Sciences at the National Taiwan University. The results are almost identical and are as follows: Merisi (diorite), sm. #12Ge-03=43.42±0.61 Ma; Merisi (syenite) sm.#12Ge-04=42.78±0.65 Ma; Namonastrali (diorite) sm. #12Ge-05=42.42±0.5 Ma; Namonastrevi (diorite) sm.#12Ge-06=42.03±0.83 Ma; Vakijvari (syenite) sm.#12Ge-13=43.26±0.74 Ma; Zoti (syenite) sm. #12Ge-15 =43.86±0.43 Ma; Zoti (gabbro) sm.#12Ge-16=46.77±0.81 Ma; Okros-Ghele (syenite) sm. #12Ge=19-44.34±0.55 Ma; Rkviana (gabbro) sm. #12Ge-21=44.85±0.59 Ma. Based on the analysis of the results, it is obvious that the ore bearing plutons of the Adjara-Trialeti zone were intruded through the volcanic-sedimentary rocks within a short time interval, between 46-42 Ma. It should be noted that according to paleontological data, the peak of volcanic activity in the Ajara-Trialeti folded zone was similarly dated as the Middle Eocene. If we rely on these data and accept the results of the plutons zircons dating by U-Pb method above, we should assume that the volcanic activities in the region were shortly followed by plutonic injections. Proceeding from the above and the petrological-geochemical analysis of the rocks, we assert, that volcanic and plutonic formations of the Adjara-Trialeti zone are the products of the same magmatic source activity and their formation was not significantly separated in time.