Volume 73, Nº 6 (2018)

The secondary (metachronous) magnetization components identified in the Precambrian complexes of the Karelian Craton have been analyzed. The average directions of high-temperature components (deviations from the true direction) have been calculated based on the contribution of secondary magnetization components resulting from tectonomagmatic events of uneven ages. The Precambrian key poles often coincide with the vector sum of the Phanerozoic magnetization components of uneven ages. The conclusion on the primary/secondary origin of the Precambrian paleomagnetic poles should be made on the basis of the integrated petro- and paleomagnetic and isotope data and geological correlations, rather than based on only the paleomagnetic reliability tests.

Numerous Riphean mafic dykes cross-cut Precambrian clastics and carbonates on the western slope of the Southern Urals. An andesite dyke with an isotope age of 71 ± 1 Ma (U–Pb SHRIMP II on zircons) encountered among metamorphic rocks of the Taratashskii complex (Archean–Early Proterozoic) at the northern terminus of the Bashkirian meganticlinorium along with two gabbro bodies with zircons of similar ages near the town of Bakal provides the first evidence of Mesozoic magmatism in this region.

The results of a study of wall-rock metasomatites are presented on the basis of a complex mineralogical–structural approach, including the study of numerous publications, as well as original macro- and microscopic and X-ray diffraction data. The rocks are classified and the metasomatic column is presented; conclusions are made based on studying the hydrothermal–metasomatic processes related to the discharge of endogenic energy and redistribution of flows of material in the upper part of the crust.

The mineralogical and geochemical patterns of platinum-bearing vein–impregnated and massive chromitite from dunite of the Svetloborsky, Veresovoborsky, and Kamenushensky clinopyroxenite–dunite massifs (Middle Urals) are reported. Platinum is characterized by an extremely uneven distribution in chromitite and is concentrated in the form of Pt–Fe intermetallic compounds. The structural and textural patterns of chromitite from these massifs, the PGE distribution in it, and the composition of chrome spinels are similar to those in well-studied chromitite from the zoned clinopyroxenite–dunite massifs of the Urals (Nizhny Tagil) and Koryakia (Gal’moenansky).

The leaching of aluminum with acidified riverine waters from minerals (hornblende, biotite, muscovite, microcline, labradorite, and albite) and rocks (granite, tuffosandstone, and crystalline schist) was studied experimentally. The relationship between the aluminum concentration and solution acidity was found: log[Al] = A–BpH, where the angular coefficient B was approximately equal for all the samples, 0.74 ± 0.06. It was concluded that polymeric hydroxocomplexes of aluminum prevailed in the solutions. The pH value below which the content of dissolved aluminum should exceed the maximum allowable concentration for fishery water bodies is 6.6 ± 0.3.

The use of IR spectrometry for examining the structural and group composition of chloroform bituminous components of dispersed organic matter in Mesozoic and Cenozoic deposits of the Azov–Kuban oil-and-gas basin resulted in obtaining significant information on the conditions of sedimentation and diagenesis of the deposits that enclose organic matter, as well as on its degree of katagenetic transformation. The IR spectra, which conformed to 15 genetic types of chloroform bitumen, allow one to distinguish the zones that contain no oil-and-gas source rocks, along with those with generation of hydrocarbons and those with completed processes.

A new deep-water hydrate-bearing structure, named after Moscow State University (MSU), has been discovered on July 29, 2018 during the geological-geophysical research of the Class@Baikal project. The structure lies on a fault scarp at the bottom of the central basin of Lake Baikal at a water depth of 1380 m (coordinates N 52°52′/E 107°07′). The “MSU” structure is sub-isometric in planar view, 500 m in diameter, and reveals a multi-summit morphology. Results of initial investigations show an active fluid seepage and gashydrate formation within the discovered structure. Laboratory analyses of the sampled gases indicate a significant concentration of thermogenic hydrocarbons.