Mesozoic subalkaline rocks of Central part of the Northern Caucasus: geodynamical typification, geochemistry and minerageny

Abstract

In Central part of the Northern Caucasus (leaf of the geological map К-38-VIII) on the territory of Kabardino-Balkarian republic in interfluves of the Chegem-Cherek Balkarsky the lava flows, sills and dykes of Mesozoic rocks, are occur. In this paper description of the most widespread modification of volcanic rocks which are represented by basaltic porphyrites, dolerites, diabases, trachytes and rhyolites was done. Results of its petrographical and geochemical (by XRF and ICP-MS methods) investigation was advanced. It is shown, that these rocks are subalkaline, high and moderate aluminiferous, among which there are high-potassic and highsodic varieties. It is found that rocks have higher level contents of Аg, Ве, LILe, LREE and Zr, Hf, Nb, Tа elements. Spectrums of incompatible elements, normalized on N-MORB and spectrums of REE, normalized on chondrite in basic rocks and trachytes have a appearance of a slanted lines, located between profiles ОIB and E-MORB. Value of Laн/Ybн ratio extend within 2,2‑6,5. It is supposedly, that initial melt was formed during melting of spinelian peridotites and was enriched by components of continental crust and subcontinental lithosphere. Evolutional alterations of melt at stage of trachytes and rhyolites generation, included such processes as fractionation of plagioclase, apatite, ilmenite and partial digestion with fusions which were generating during melting of metasediments. Based on geological assessment the suppositions that the polymetallic and Au-Ag mineralization associated with volcanic rocks have been generated by interact with cooling subvolcanic bodies with burial in Middel Jurassic carbon-bearing terrigenous blackshist series of vadose and sedimentaty water.