Vol 69, No 11 (2024)

The results of study of chilled glasses sampled during 45-th cruise of R/V “Professor Logachev” at the top of the submarine volcano Puy-des-Folles are presented. Puy-des-Folles Volcano is located in the axial part of Rift Valley of the Mid-Atlantic Ridge (MAR) at 20°31′N.Unlike typical volcanic axial highs which usually does n ot exceed several hundred meters the summit of the Puy-des-Folles volcano is located a depth of 1950 m and rises 1800 meters above the bottom of the Rift Valley. The data on geochemistry and isotope composition of chilled glasses examined allow to come to a number of conclusions that expanded existing ideas about magmatic and rectjnic processes conducted in the Rift Valley of the Slow Spreading Ridges. Chilled glasses sampled at the top of the Puy-des-Folles volcano are originated from a very depleted melt formed by partial melting of the DM reservoir. Puy-des-Folles volcano was formed as result of trhe activity of a long-lived magma chamber located below the Rift Valley axis. It is possible that in addition to the DM reservoir mantle source enriched in incompatible elements may have participated in the formation of the parenatl melts for studied chilled glasses.Weak geoichemical signal of contamination of perental melt with a hydrothermal component in chilled glasses was established. Signs of staganation in the spreading of the oceanic crust in the Rift Valley segment studied in thic work have been established.

The Early Proterozoic gabbros of the Velimyaki intrusion of the Northern Ladoga region contain titanomagnetite ore, the development of which was carried out at the end of the 19th century. The peculiarity of horizons with titanomagnetite mineralization is the high concentration of phosphorus in the form of apatite, the content of which reaches up to 10 vol. %. Isotopic analysis of lead apatite indicates the redeposited nature of this mineral, presumably during superimposed metamorphism approximately 100 Ma after the stage of magmatic crystallization of gabbroids and clinopyroxene-titaniummagnetite ores. Mineralogical, petrological and isotope-geochemical criteria for the superimposed nature of mineral formation with recrystallization of apatite are the connection of this mineral with the formation of other metamorphic minerals (hornblende, biotite, acid plagioclase), the isotopic age of apatite (1790 ± 5 Ma) and low temperature (620–710 °C) of its formation in comparison with the crystallization temperatures (900–1260 °C) of igneous minerals from the melt. The Pb-Pb age of apatite coincides with the age of metamorphic minerals of the late Svecofennian stage from other rocks in the region, as well as with the Rb-Sr ages of biotite and amphibole from the direct host supracrustal rocks. Based on the data obtained, a conclusion was made about the recrystallization of apatite and re-equilibration of the U-Pb system in it during the Late Svecofennian regional metamorphism.

Within the framework of the problem of establishing the biogeochemical features of Precambrian petroleum-derived organic matter (OM) and naphthides generated by it, the distribution of biomarker hydrocarbons in samples from Ust-Mayskaya-366 well of the Aldano-Maya depression of the Siberian platform has been studied at a detailed modern level. In order to correlate OM and assess the effect of migration on biomarker parameters, allochthonous and mixed bitumens (AllB and MB), as well as extracted from the undivided rock open-pore bitumens (OPB) of the Neryuen, Ignikan, Kandyk, Ust-Kirbin (Riphean) and Sardana (Vendian) Formations were studied in comparison with autochthonous bitumen (AutB), of the Neryuen Formation’s oil-source-rock horizon in samples from the Ust-Mayskaya-366 well of the Aldan-Maya depression. Saturated cyclanes and aromatic fraction compounds for this well were analyzed for the first time. Neryuen mudstones are enriched with organic matter (TOC > 1%) accumulated in clays (in steranes βα/(αα + ββ)=0.5), which survived diagenesis in reducing environments without excess H2S (in homohopanes C₃₅/C₃₄=0.4) and thermally transformed within MC2-MC31 (T_max – 452–465 °C). The maximum in tricyclanes C_19–31 in almost all studied samples is C23, as well as in the Neryuen AutB. Even homologues of a number of 3,7-dimethylalkanes present in the Neryuen AutB and Ust-Kirbin MB, as well as those observed in trace amounts in the Neryuen and Ignikan MBs and in the OPBs of the Sardana formation, apparently disperse at migration. 12- and 13-monomethylalkanes are recorded in all bitumens, and they are especially abundant in the Kandyk OPBs – probably these compounds can accumulate during migration. Migrated bitumens differ from AutB by an increase in the proportion of steranes C₂₉ (to C₂₉/nC₂₇ > 2) and the ratio nC₂₇/nC₁₇ (to > 1). A relationship with the bitumen coefficient was found for: Pr/Ph, nC₂₇/nC₁₇, ΣnC_i/ΣizoC_i in acyclic hydrocarbons, C₂₉/C₂₇ in steranes, C₃₅/C₃₄ in homohopanes, hopane/tricyclane ratios – these parameters are likely subject to migration effects. Probably, the Riphean bitumens have their source mainly in the carbonaceous Neryuen horizon, variations in characteristics are associated with catagenesis and migration processes of accumulation or dispersion of low molecular weight mobile compounds. The OPBs of the Sardana Formation differ from the Riphean ones. The upper 2 bitumens are immature parautochthonous, the rest are probably a mixture of Riphean and Vendian bitumens, which were influenced by the effects of solutions from the located southeast stratiform polymetallic deposits Sardana (about 35 km) and Perevalnoye (about 20 km) with mineralization in the Vendian.

The contents of 25 elements were established in reference materials candidates — black shales SChS-1A and SLg-1A using a developed analysis technique based on fusing samples with lithium metaborate and determining elements by external calibration with an internal standard on an ELEMENT high-resolution mass spectrometer. The passport characteristics of the Russian reference materials of magmatic and sedimentary rocks – SG-3, SGD-2, ST-2A, SI-2, BIL-1 and technical standards – ZUK-1 and ZUA-1 have been clarified. New data of rare earth elements were obtained for SI-2 and ZUA-1, which were missing during certification. Based on the ICP-MS analysis of standards SG-3, SI-2 from 2005 to 2024, their applicability now has been confirmed. The new ICP-MS results obtained make it possible to expand the number of certified parameters of reference materials, clarify their results, and can be used in analytical practice.