Late Cenozoic Volcanic Activity in Western Georgia: Evidence from New Isotope Geochronological Data

摘要

The products of volcanic activity from the Kutaisi area and Guria (western Georgia) were studied in terms of isotope geochronology to determine the age of rocks and to confirm their attribution to Cenozoic formations. The results obtained show that the erupted rocks in the Kutaisi area were formed during the three pulses of Mesozoic volcanic activity: the Bajocian, Kimmeridgian-Tithonian, and Turonian-Santonian. It was shown that no displays of Late Cenozoic volcanism occurred in this region of the western Georgia. Because of this, its inclusion into the Central Georgian neovolcanic province, earlier supposed, seems to be improper. By the data of isotope geochronology, Guria is the only region of western Georgia where volcanic activity occurred in post-Paleogene period. Two pulses of young volcanism were revealed: of about 15.5 and 9-7.5 My. The former was related to the introduction of syenite intrusion, and the latter, to subaqueous exudation of subalka-line Neogene lavas. All the outcrops of Neogene rocks we found and dated in Guria fit within the well-pronounced sublatitudinal linear band which probably represents the occurrence in the Middle Miocene of a local zone of extension appearing under conditions of total compression during the collision of the Eurasian and Arabian lithospheric plates.