Some geological and petrological characteristics of the Eocene trachybasalt-trachyandesite- basalt-phonolite formation of the Talysh zone (Azerbaijan)

Abstract

This article discusses the stages of crystallization of the Eocene trachybasalt-tra- chyandesitebasalt-phonolith formation of the Talysh zone. Determination of the composi- tion of the primary magma, evolution and melting fraction of the initial melt of the Eocene volcanism of the Talysh zone within Azerbaijan. Eocene volcanism of the trachybasalt-tra-chyandesitebasalt-phonolith formation of the Talysh zone. Petrographic, petrochemical, geochemical studies of rocks, typomorphic features of mineral paragenesis, chemical composition of rocks were carried out by X-ray spectral and X-ray fluorescence analysis. The analyzes of the conducted studies show that the Talysh zone was formed in the Eocene time. Stages of evolution of the original magma and typomorphic features of mineral parageneses have been established. The distributions of microelements in mineral parageneses, which are direct participants in the crystallization processes that took place in intermediate chambers at different depths, have been studied. At present, the question arises of the need to clarify the typomorphic features of igneous complexes, as factors that determine the geodynamic regimes of their formation, and to determine the potential ore content. The petrographic and petrochemical characteristics of the volcanic rocks are given. It was found that if the process of differentiation in the Early-Middle Eocene was more distinct with the initial formation of more magnesian rock varieties (picrite-trachybasalts), and subsequently more ferruginous ones (trachyandesites and trachyandesitebasalts), then such accumulation of iron is not observed in porphyritic trachyandesites. This petrochemical feature is obviously associated with the duration of the break in volcanism, caused by the formation of a thick sedimentary-tuffaceous stratum, accompanied by the initiation and manifestation of an intermediate chamber of medium composition. Volcanism in the Late Eocene was undifferentiated and was not accompanied by the formation of medium differences. The appearance in the late Eocene of leucite phonolites, which represent an alkaline branch, and the absence of transitional varieties indicate the autonomous development of vit- robasalts and leucite phonolites. It is concluded that from the early phases of the manifestation of Eocene volcanism to the later phases, the change in the material composition along the lateral is expressed in the manifestation of more alkaline facies with a significant predominance of K over Na and with a greater correspondence to the differentials of the shoshonite series.