The paper presents new data on mineralogy, geochemistry, and Sr-Nd-Pb isotope systematics of Late Cenozoic eruption products of Uguumur and Bod-Uul volcanoes in the Tesiingol field of Northern Mongolia, with implications for the magma generation conditions, magma sources, and geodynamic causes of volcanism. The lavas and pyroclastics of the two volcanic centers are composed of basanite, phonotephrite, basaltic trachyandesite, and trachyandesite, which enclose spinel and garnet peridotite and garnet-bearing pyroxenite xenoliths; megacrysts of Na-sanidine, Ca-Na pyroxene, ilmenite, and almandine-grossular-pyrope garnets; and carbonate phases. The rocks are enriched in LILE and HFSE, show strongly fractioned REE spectra, and are relatively depleted in U and Th. The low contents of U and Th in Late Cenozoic volcanics from Northern and Central Mongolia represent the composition of a magma source. The presence of carbonate phases in subliquidus minerals and mantle rocks indicates that carbon-bearing fluids were important agents in metasomatism of subcontinental lithospheric mantle. The silicate-carbonate melts were apparently released from eclogitizied slabs during the Paleo-Asian and Mongol-Okhotsk subduction. The parent alkali-basaltic magma may be derived as a result from partial melting of Grt-bearing pyroxenite or eclogite-like material or carobantized peridotite. The sources of alkali-basaltic magmas from the Northern and Central Mongolia plot different isotope trends corresponding to two different provinces. The isotope signatures of megacrysts are similar to those of studied volcanic centers rocks. The P-T conditions inferred for the crystallization of pyroxene and garnet megacrysts correspond to a depth range from the Grt-Sp phase transition to the lower crust. Late Cenozoic volcanism in Northern and Central Mongolia may be a response to stress propagation and gravity instability in the mantle associated with the India-Asia collision.

The main subject of this article is research on the genetic relationships in the K–Na subalkaline series that occurs in the Belogolovsky volcanic center located in the back part of Sredinny Range. The differentiated rock series includes trachybasalts, trachyandesites, trachytes, comendite, trachytes, and comendites. Mass balance calculation and trace element modeling show that crystal fractionation is the main process in volcanic center evolution and the main fractionated mineral is feldspar. Trace element characteristics of rock-forming minerals (Fsp, Cpx, Bt, Ap, and Ol) obtained by LA–ICP–MS method allowed calculation of the “mineral/rock” partition coefficients for the Belogolovsky volcanic center genetic model representation to explain melt evolution. Genetic connections were established between trachyandesites, trachytes, comenditic trachytes and comendites, whereas no direct genetic connections between trachybasalts and trachyandesites were detected.

The index-species of calcareous nannoplankton in two cored wells, penetrating the Miocene rocks of the Alba Guyot, have been used to identify time intervals for deposition of the young (Pleistocene-to-modern, 7–13 Ma) basanite tuff, tuffite sublayer (18–24 Ma). There have been discovered young Fe-Mn crust sublayers of contrasting composition and growth rate: early, enriched in Mn, Ni, Cu, Nb, and late, substantially ferruginous, with high REE, Y, Be, Sc, V, Zn, Rb, Cs, Sr, Zr, Hf, Mo, Sb, Pb, Th and U contents. Disregarding the duration of a probable break in the deposition of ore matter (Fe-Mn oxyhydroxides), the young crust with a Co-chronometry-based thickness of ~4 mm was formed over a period of ~2.3 Ma with an average growth rate from 1.6 mm/Ma in the early sublayer to 2.2 mm/Ma in the late sublayer. A young Fe-Mn crust 4–8 mm thick began to form on Miocene rocks 4.5 to 2.3 Myr, when the guyot surface was at depths below the oxygen minimum zone in the ocean water column (>600–700 m). A contrasting change in the composition of the late sublayer (a significant increase in Fe, REE, Y, V, Zn, Sr, Zr, Hf, Mo, Sb, Pb, Th and U contents) could have been caused by a 500000-year-old rapid subsidence of the guyot to depths similar to present-day (1250–1500 m at the plateau level). The average Co concentration (0.8–1.0 wt. %) in the young Fe-Mn crust on Miocene rocks is almost twice that of the bulk composition of thick (multilayered) crusts in other parts of the guyot. Relatively small-scale distribution of the young Fe-Mn crust, anomalously enriched in Co, will apparently have an insignificant impact on the increase in inferred ore reserves on the Alba Guyot for this strategically important metal.

The first finds of the REE-bearing silicates in the Kamchatka island-arc system were reported from K-Na alkaline trachytes from a large volcanic body of Bolshoi volcano in the back-arc zone of the Sredinny Ridge volcanic belt (56°24′10″ N and 157°56′45″ E) of Kamchatka. Chevkinite microlites are found in a trachytic groundmass in association with microlites of ferropigeonite, ferroaugite, anorthoclase, Na-sanidine, richterite, apatite, Nb-bearing ilmenite, zirkelite, baddeleyite, and zircon. The chevkinites from the Bolshoi volcano trachytes have higher Nb and Zr and similar REE contents compared to the chevkinite-group minerals from igneous rocks formed in different geodynamic settings. The crystallization conditions for chevkinites from Bolshoi volcano were determined by comparing the compositions of trachytes and their mineral assemblages with those of trachytes from Belogolovskii volcano of Sredinny Ridge, Kamchatka. The results show that chevkinites were formed during prolonged crystallization of a trachytic magma under reducing conditions at \(\Delta \log f_{O_2 } \) ranging from −1.36 to −1.55 NNO, relatively low temperatures of 794–741°C, and moderate HF concentrations of magmatic fluids (0.003–0.0029 mol/dm³). These results, combined with the other data, are of crucial interest for studies of the REE budget during the evolution of high-alkaline magmas and can be used as indicators for determining the nature and role of different magma sources in the active continental margin setting of Kamchatka.

This study presents U-Pb dating results for zircon collected from the beaches of recreation zone "Peschanaya" (Sandy) on Lake Baikal. These beaches are formed exclusively by the erosion of Early Proterozoic rapakivi granites from the Primorsky Complex. Zircon from the granites yields a U-Pb age (ID-TIMS) of 1859±16 Ma, with an average U concentration of ~120 μg/g. Analysis of detrital zircon from the beaches of recreation zone "Peschanaya" was conducted using the ID-TIMS method on three aliquots and two in-situ methods – LA-ICP-MS and SHRIMP – on multiple (>600) individual grains. The new ID-TIMS and SHRIMP data are in complete agreement with each other, yielding ages of 1853.6±6.5 Ma and 1853.0±3.3 Ma, respectively. The LA-ICP-MS data, obtained in 7 Russian and 1 Chinese laboratory, are in general consistence with these results. Zircon from the beaches of the recreational zone "Peschanyа" is recommended as a secondary standard for U-Pb dating of early Precambrian samples.