TECTONOMAGMATIC EVOLUTION OF THE EOCENE VOLCANISM OF THE TALYSH ZONE (AZERBAIJAN)

Abstract

Link for citation: Karimov V.M. Tectonomagmatic evolution of the Eocene volcanism of the Talysh zone (Azerbaijan). Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2021, vol. 332, no. 11, рр. 200-211. In Rus. The relevance. At present, the question arises of the need to clarify the typomorphic features of magmatic complexes, as factors that determine the geodynamic regimes of their formation and to clarify the potential ore content. In this regard, the article examines the features of the Talysh magmatic complexes, which makes it possible to elucidate the tectonomagmatic evolution of this complexly constructed region in the Caucasus. Purpose of research is to clarify the tectonomagmatic evolution of the Eocene volcanism of the Talysh zone within Azerbaijan. Objects: Eocene volcanism, volcanogenic trachybasalt-trachyandesite-basalt-phonolite formation, petrochemical composition of rocks, evolution of the primary melt. Methods: petrographic studies of rocks, chemical composition of rocks by X-ray spectral analysis, isolation of magmatic complexes. In addition, the results of analyzes of the studied samples for petrogenic elements were used, both published in the literature and obtained by X-ray fluorescence analysis on a multichannel X-ray spectrometer SRM-25 at the Institute of Geology and Geophysics, Baku. Minerals were analyzed on a JXA-8200 JEOL (Japan) electron microprobe at the Karpinsky All-Russian Geo-logical Research Institute (St. Petersburg). Results. The analysis of the conducted studies shows that during the period from the Paleozoic to the Quaternary, inclusive, in the development of the structures of the Talysh fold zone, there is a certain sequence in its inception. In the structure of the zone, there are structural stages corresponding to the pre-collisional (Cretaceous–Eocene) and collisional (Oligocene–Miocene) periods of the region's development. Paleogene volcanic formations of Talysh make up the southeastern segment of the northern volcanoplutonic belt, in the structure of which the volcanic trachybasalt-basaltic trachyandesite-phonolite (Early-Middle and Late Eocene) and intrusive subalkaline ultrabasic (Late Eocene–Oligocene) formations are distinguished. The volcanic formation includes two complexes: (Early-Middle Eocene) absarokite-shoshonite-alkaline basaltic and (Late Eocene) basaltic trachyandesite-phonolite. The petrographic and petrochemical characteristics of the volcanic rocks that make up the first formation are given. It was found that if the process of differentiation in the Early-Middle Eocene had more distinct character with the initial formation of more magnesian rock varieties (picrite-trachybasalts), and subsequently more ferruginous (trachyandesites and basaltic trachyandesites), then such accumulation of iron is not observed in porphyry trachyandesites. This petrochemical feature is obviously associated with the duration of the break in volcanism caused by the formation of a thick sedimentary-tuffaceous sequence, accompanied by the formation and manifestation of an intermediate chamber of average composition. Volcanism in the Late Eocene was undifferentiated and had a contrasting character, i. e. was not accompanied by the formation of average differences. The appearance in the Late Eocene of leucite phonolites, which are an alkaline branch, and the absence of transitional differences indicate the autonomous development of vitrobasalts and leucite phonolites, possibly associated with the process of early decomposition of the initial melt under subcrustal conditions. It is concluded that from the early phases of the manifestation of Eocene volcanism to the later, the change in the material composition laterally is expressed in the manifestation of more alkaline facies with a significant predominance of K over Na and with a greater correspondence to the differentiates of the Shoshonite series.