Petrological and geochemical features of the gabbrodolerites of the Paleozoic Yurmatau complex (Southern Urals)

The features of the chemical and mineralogical compositions of two converging gabbro dikes with a thickness of up to ~20 m are considered, which stretch for ~6 km in the central part of the Bashkir meganticlinorium in the zone of the Tukan fault and break through the sediments of the Malyi Inzer Subformation of the Avzyan Formation of the Middle Riphean. It has been established that, according to the petrogeochemical parameters, the gabbro of the western and eastern dikes of the Tukan section correspond to the gabbrodolerites of the Paleozoic Jurmatau complex. The studied intrusive rocks correspond to the tholeiitic petrochemical series and belong to the sodium and sodium-potassium types of alkalinities. At the same time, they show a weak removal of mobile alkaline elements, which indicates secondary transformations that led primarily to a decrease in potassium concentrations in gabbro. Their decrease occurs zonally in both dikes from west to east, in the west — from the center to the marginal parts. In the same directions, there is a sharp increase in the Na2O / K2O ratio. Gabbro contains high concentrations of Cl, Li, and Cu, which on average exceed clark by 2.0–3.6 times. As rocks of the Paleozoic Jurmatau complex, they differ from the Middle Riphean magmatic formations of the Bashkirian meganticlinorium in high concentrations of Li and low concentrations of Rb, as well as in the absence of a positive relationship between the concentrations of these elements. The enrichment of intrusive rocks of the Tukan section with lithium has been established for the first time. It is assumed that the lithium in them is mainly associated with chlorite and, possibly, partially with plagioclase. It is concluded that it is necessary to continue research in order to identify a possible genetic relationship between the magmatic formations of the Jurmatau complex and the occurrences of Cu and Li-enrichment zones in the Riphean sediments of the Bashkirian meganticlinorium. Analysis of geochronological data on igneous rocks of the Jurmatau complex shows that they are currently scarce and sometimes contradictory. The views on geodynamic models of the genesis and evolution of Devonian magmatism are not completely unambiguous. It is concluded that the Paleozoic magmatic occurrences of the Bashkirian meganticlinorium are insufficiently studied.