Principal petrographic characteristics and K-Ar isotope-geochronological data on samples from the Keli Volcanic Highland, Greater Caucasus

The paper reports newly obtained stratigraphic, petrographic, and isotope geochronology data on modern moderately acid lavas from the Keli Highland of the Greater Caucasus and presents a geological map of the territory, in which 35 volcanoes active in Late Quaternary time were documented by the authors. Total duration of volcanic activity at the highland was estimated at 250 ka. Volcanic activity was discrete and occurred in three phases: Middle Neopleistocene (245-170 ka), Late Neopleistocene (135-70 ka), and Late Neopleistocene-Holocene (<30 ka). Newly obtained lines of evidence indicate that certain volcanoes erupted in the latest Neopleistocene-Holocene. The first phase of volcanic activity was connected mainly with lava volcanoes, and eruptions during the later phases of volcanic activity in this part of the Greater Caucasus produced mainly lavas. The most significant eruptions are demonstrated to occur in the territory during the second phase. The major evolutionary trends of volcanic processes during the final phase in the Keli Highland are determined. It was also determined that overwhelming majority of volcanoes that were active less than 30 ka BP are spatially restricted to long-liven local magmatic zones, which were active during either all three or only the final two phases of activity. These parts of the territory are, perhaps, the most hazardous in terms of volcanic activity.

K-Ar ages of basalts from islands of the Franz Josef Land archipelago

New K-Ar age determinations of basalt samples from three drill holes and outcrops on the Franz Josef Land suggest that flood volcanism throughout the archipelago fits in a very narrow age interval (116±5 Ma). For 95% of the samples we studied, age scatter is within analytical uncertainty. New data on basaltic bulk-rock, trace element, and REE compositions point to mantle plume affinity for Early Cretaceous magmatism on the Franz Josef Land, which preceded the onset of seafloor spreading in the Canada Basin.