Geochronology of miocene volcanism in the northern part of the Lesser Caucasus (Erusheti Highland, Georgia)

Abstract

Study of epochs of tectonomagmatic activity of the Earth in different parts of the planet and under various geodynamic environments suggests as one of the main tasks of such investigations establishment of their age, duration, evolution dynamics, spatial–age regularities of volcanic focus migration, and other characteristics allowing one to reconstruct the history of magma gen� esis for concrete regions on the level of individual time lags of the geochronological scale. In this paper we discuss the results of the study of geochronology of Miocene volcanism in the northern part of neovolcanic province in the Lesser Caucasus, which allows us to determine the time of beginning and total duration of the Late Cenozoic epoch of tec� tonomagmatic activization in this sector of the Cauca� sian–Anatolian segment of the Alpine foldbelt. Products of the earliest impulses of Neogene– Quaternary volcanism within the northern end of the mountain system of the Lesser Caucasus, as is evident from the results of geological and stratigraphic investi� gations [1], are abundant in the upper reaches of the Kura River on its left bank, where they form the exten� sive (60 × 30 km) Erusheti volcanic highland on the territory of Georgia and Turkey (Fig. 1). They are united in the Goderdzi Formation in the Georgian part of the region. The lower parts of sections of the formation are composed of the pyroclastic series with a thickness of up to 700 m represented by welded and loose layered tuff, breccia, and agglutinate, in which thin lava flows of dacitic or more basic composition are sometimes observed. Numerous volcanic edifices (Gumbati, Shalosheti, Digra, and others) significantly destroyed and smoothed by erosion, their dacite lava flows forming a sheet with a thickness of up to several hundred meters, and overlying pyroclastic formations on most of the region are located on the surface of the Erusheti highland. The maximal heights within the highland reach 3000 m (on the territory of Turkey); its basement is entirely composed of sedimentary and volcanogenic series of Eocene age. Effusive rocks of the Goderdzi Suite in the east in valleys of the Kura River and its right tributary Paravani are overlain by mainly basic Pliocene lavas of the Dzhavakheti high� land (3.7–1.6 Ma [2]) and further, in the latitudinal direction most likely entirely thin out in sections within the area of western ends of the Samsari ridge, where Quaternary lavas occur directly on rocks of the Early Cenozoic–Mesozoic basement [3]. The available concepts on the age of rocks of the Goderdzi Formation were mainly based on the results of investigations of plant and fossil remains in horizons of diatomic clays, which are known and were previ� ously mined in some locations at the bottom of the young effusive series in the Erusheti Highland [1, 4]. These data allowed us to establish the possible age range of the formation of pyroclastic rocks and lavas of the formation as Late Miocene–Early Pliocene. !"# !"$ !"% !"" !"& $# $$ $% !"’ !"( !&) !&* !&! + , .