Middle-Jurassic volcanites of the Goitkhsko Achishkinsk folded zone of the North-Western Caucasus: geochemistry, geodynamical typification and minerageny

Abstract

Relevance. Within of southern part of Scythian platform there are areas with Early-Middle Jurassic volcanites and associated with it Au-Ag-polymetallic ore manifestations. Geochemical investigation of these volcanites should be adopted for refinement of peculiarities of this area development in this period of time. The aim of the research is to obtaine analytical data, refinement of geodynamical position and ore specialization of volcanites. Object of the research have been selected the effusive rocks and subvolcanic bodies in the Goitkhsko Achishkinsk folded zone of North-Western Caucasus. Methods. Petrographical description, quantative analysis by XRF and ICP-MS methods; calculation of geochemical characteristics; analysis of discriminatory charts; comparing values of average contents of elements with their content in rocks (standards) of close petrochemical type from various geodynamic settings. Results and its discussion. As a result of the study, was found that in the Goitkhsko-Achishkinsk folded zone the moderately alkalinity basic, middle and normal alkalinity rocks are spread. It is supposedly, that distributed here moderately titanium, low and moderately magnesian rocks of basic composition is effected by preliminary evolving of high alumina melt which formed during 1-5% melting of spinel peridotites. Shaping focuses of these melts happened in lithospheric mantle on the background of processes of back-arc extension in the rear part of the Transcaucasian volcanic belt. The elevated concentration of Li, Аg, Ве, Вi, LILe, LREE are characteristic for volcanites. Spectrums REE in basic rocks normalized to chondrite have a facies of sloping line close with E-MORB profile. On the multeelement spectrums there are negative anomalies of Nb and Ta. Acid rocks – this supersaturated by alumina rocks, comparison on concentrations of К, Rb, Ва, K/ Rb, Ba/Rb with granitoid of andesitic line. It was shown, that in regional plane investigated volcanites is clouse with rocks of Chegem-Cherekskogo and Karachaevskogo volcanic areas. It is established, that volcanites of the Goitkhsko-Achishkinsk folded zone according geochemical parameters are comparable with rocks of island-arc and marginal volcano-plutontc belts of active continental margins. The supposition about considerable zone of volcanite development on detection of gold-silver-polymetallic mineralization.