Middle Jurassic volcanogenic rocks of the southern margin of the Greater Caucasus and the Abkhazian-Racha zone of the Transcaucasian median massif: geodynamic typification and minerageny

Abstract

Relevance. On the southern margin of the Greater Caucasus (GC) and the adjacent Abkhaz-Racha zone of the Transcaucasian median massif, Middle Jurassic volcanic rocks and associated pyrite-polymetallic, copper-pyrrhotite and lead-zinc ore objects are common. The geochemical study of these volcanites is necessary to clarify the features of the development of the region during this time period. The aim of the study is to obtain analytical data, clarify the geodynamic position and ore specialization of volcanic rocks. The object of research was the Bajocian effusive rocks of the "Porphyrite Series", common in South Ossetia, Abkhazia and the Krasnodar Territory. Research methods included: petrographic description of rocks and their analysis by quantitative methods XRF, ISP-MS; calculations of geochemical characteristics, analysis of discrimination. Results. It has been established that the volcanic rocks of PS are moderately and low magnesian basalts, trachybasalts, andesite basalts, trachyandesite basalts with potassium and sodium types of alkalinity. Their initial melts were formed at 1-5% melting of spinel peridotites. The derivatives of these melts are close to E-MORB type basalts - Laн/Ybн = 1.3–5.4, but from which, on the multi-element diagrams of the concentrations of incompatible elements, they differ in the presence of negative Ta and Nb anomalies, positive K anomalies, as well as higher concentrations of large-ionic elements Rb, Ba, Th, U and Sr. On the discrimination diagrams, figurative rock points are grouped in the rock fields of island arcs and active continental margins. It is noted that PS volcanic rocks are similar in their characteristics to the rocks of the Middle Jurassic "Behind the arc" dike belt GC, but they were formed in a zone more enriched in fluid components.