The paper presents authors’ original detailed data on rocks of the Archean Pon’goma-Navolok charnockite−enderbite complex in northern Karelia. The rocks practically have not been modified and are preserved within a rigid block among Paleoproterozoic zones of ductile deformations and metamorphism. The geochemistry of the rocks and their isotope−geochemical features indicate that the protolith from which the enderbite melts of the main phase of the massif were derived may have been amphibolites. The enderbite melts were derived from these amphibolites under the effect of K2O-, Na2O-, and SiO2-bearing fluids; and the enderbites were subsequently charnockitized with the involvement of fluids enriched in K2O and SiO2. Physicochemical modeling indicates that the enderbite melt was derived from the amphibolite protolith at a depth of about 45 km (P = 14.8 kbar, T = 1030−1080°C) under the effect of saline H2O−CO2 fluid. Comparison of the P−T parameters of the granulite-facies metamorphism of the metabasites and the parameters under which the enderbite melts were derived indicates that Archean granulite-facies metamorphism in the Belomorian belt in northern Karelia was of contact but not regional nature and was induced by the high-temperature field of an emplaced enderbite massif. The orthogneisses hosting the Pan’goma-Navolok massif inherit geochemical features of the unsheared, ungneissose, and unmetamorphosed enderbites. This means that enderbites analogous to those of the Pan’goma-Navolok massif may have served as the protolith of some of the orthogneisses, and that enderbites may have been spread more widely in the Archean than the currently preserved single enderbite massifs.

— The paper presents authors’ original detailed data on rocks of the Archean Pon’goma-Navolok charnockite−enderbite complex in northern Karelia. The rocks practically have not been modified and are preserved within a rigid block among Paleoproterozoic zones of ductile deformations and metamorphism. The geochemistry of the rocks and their isotope−geochemical features indicate that the protolith from which the enderbite melts of the main phase of the massif were derived may have been amphibolites. The enderbite melts were derived from these amphibolites under the effect of K 2 O-, Na 2 O-, and SiO 2 -bearing fluids; and the enderbites were subsequently charnockitized with the involvement of fluids enriched in K 2 O and SiO 2 . Physicochemical modeling indicates that the enderbite melt was derived from the amphibolite protolith at a depth of about 45 km ( P = 14.8 kbar, T = 1030−1080°C) under the effect of saline H 2 O−CO 2 fluid. Comparison of the P − T parameters of the granulite-facies metamorphism of the metabasites and the parameters under which the enderbite melts were derived indicates that Archean granulite-facies metamorphism in the Belomorian belt in northern Karelia was of contact but not regional nature and was induced by the high-temperature field of an emplaced enderbite massif. The orthogneisses hosting the Pan’goma-Navolok massif inherit geochemical features of the unsheared, ungneissose, and unmetamorphosed enderbites. This means that enderbites analogous to those of the Pan’goma-Navolok massif may have served as the protolith of some of the orthogneisses, and that enderbites may have been spread more widely in the Archean than the currently preserved single enderbite massifs.

The paper provides the first lithological and age data from the Ameghino segment of the Atlantic Patagonian Margin. The multiproxy study, which involves lithology, microfossils, magnetic susceptibility, color reflectance, and accelerator mass spectrometry radiocarbon (AMS-14C) dating, made it possible to establish the litho- and chronostratigraphic frame of six short (<1 m) sediment cores from the continental margin from a water depth range of 2–2.3 km. The units corresponding to marine oxygen-isotope stages (MIS) 1–3 are identified and distantly correlated with simultaneous units of reference core AI-3327 from the Piedra Buena Terrace. The unit thickness and sedimentation rates are estimated. The occurrence of glauconite in coarse-grained sediments of the last glacial, described earlier from coeval sediments on the Piedra Buena Terrace, has now been confirmed within the Ameghino segment of the continental margin. The occurrence of contourites in the sediment cores is also confirmed, suggesting that bottom currents were involved in sedimentation.

On August 6, 2021, the chief researcher of the IO RAS, Doctor of Geological and Mineralogical Sciences, Professor Ivar Oskarovich Murdmaa turned 90 years old. The main focus of I.O. Murdmaa is the study of bottom sediments of seas and oceans, their lithology, mineralogy, deposition processes, facies and formations, the theory of oceanic sedimentogenesis. He first distinguished marine volcanoterrigenous sediments and described the facies variability of modern sediments of island arcs. Ivar Murdmaa is known for his studies in mineralogy of oceanic sediments, processes of pelagic sedimentogenesis and associated iron-manganese nodules formation. Studying sediment formation in rift zones of mid-ocean ridges, he identified a new genetic type of sediments named edaphogeonus sediments, elaborated mineralogical criteria for their recognition and formation processes. In recent years I.O. Murdmaa is actively developing the theoretical concept of "sedimentosphere", paying special attention to a new direction – the study of the erosion-accumulative activity of bottom currents and the formation of contourites.

Herein we provide information on the sedimentological and paleoceanographic research on the Argentine Patagonian continental slope during cruise 79 of the R/V Akademik Mstislav Keldysh in March 2020. The preliminary scientific results are discussed.

Приведены сведения о литолого-палеоокеанологических исследованиях на континентальном склоне Аргентинской Патагонии в 79-м рейсе НИС “Академик Мстислав Келдыш” в марте 2020 г. Обсуждаются предварительные результаты.

Herein we provide information on the integrated geological, geophysical, sedimentological, paleoceanographic, hydrophysical and biological investigations in the Central Atlantic during the cruise 45 of the R/V "Akademik Nikolaj Strakhov" in October-November 2019. The preliminary scientific results are discussed.

Приведены сведения о комплексе геолого-геофизических, литолого-палеоокеанологических, гидрофизических и биологических исследований в Центральной Атлантике в 45-м рейсе НИС “Академик Николай Страхов” в октябре–ноябре 2019 г. Обсуждаются предварительные результаты экспедиции.

The paper presents newly obtained original data on the morphology, internal structure (as seen in cathodoluminescence images, CL), and composition of more than 400 zircon grains separated from gabbroids and plagiogranites (OPG) sampled at the axial zone of the Mid-Atlantic Ridge (MAR). The zircons were analyzed for REE by LA-ICP-MS and for Hf, U, Th, Y, and P by EPMA. Magmatic zircon in the gabbroids crystallized from differentiating magmatic melt in a number of episodes, as follows from systematic rimward increase in the Hf concentration, and also often from the simultaneous increase in the (U + Th) and (Y + P) concentrations. These tendencies are also discernible (although much less clearly) in zircons from the OPG. Zircon in the OPG is depleted in REE compared to the least modified zircons in the gabbro, which suggests that the OPG were derived via partial melting of gabbro in the presence of seawater-derived concentrated aqueous salt fluid. Another reason for the REE depletion might be simultaneous crystallization of zircon and apatite. The CL-dark sectors, which are found in practically all of the magmatic zircon grains, have Y/P (a.p.f.u.) ≫ 1 which most likely resulted from OH accommodation in the zircon structure, a fact suggesting that the OPG parental melt contained water. High-temperature hydrothermal processes induced partial to complete recrystallization of zircon (via dissolution-reprecepitation), a process that was associated with ductile and brittle deformations of the zircon-hosting rocks. The morphology of the hydrothermal zircons varies depending on pH and silica activity in the fluid from weakly corroded subhedral crystals with typical vermicular microtopography of the crystal faces to completely modified grains of colloform structure. Geochemically, the earlier hydrothermal transformations of the zircons resulted in their enrichment in La and other LREE, except only Ce, whose concentration, conversely, decreases compared to that of the unmodified magmatic zircons. The hydrothermal zircon displays a reduced Ce anomaly and its most altered domains typically host minute inclusions of xenotime, U and Th oxides and silicates, and occasionally also baddeleyite, which suggests that the hydrothermal fluid was reduced and highly alkaline. These features were acquired by the seawater-derived fluid when it circulated within the axial MAR zone area due to phase separation in the H2O–NaCl system and particularly as a result of fluid interaction with the abyssal peridotites of oceanic core complexes. Our data demonstrate that zircon is a sensitive indicator of tectonic and physicochemical processes in the oceanic crust.

The morphology and concentrations of trace elements and rare earth elements (REE) of zircon from a transitional layer of bentonite ash at the PaleoceneEocene boundary at a locality north of Salzburg in the Eastern Alps suggest a magmatic genesis of the zircon, and data on the REE distribution in the mineral testify to an oceanic nature of the magmas. A more reliable criterion of the nature of the magmatic source is data on the Li concentrations; the latter in some of the zircon grains are much lower than the minimum values typical of the continental crust. It is hypothesized that a zircon type exists that is related to plume magmatism.

This paper reports the results of detailed petrological-geochemical study of zircons and host rocks that were dredged from the Markov Deep area in the slow-spreading Mid-Atlantic ridge. The rocks are represented by variably cataclased gabbronorite with veinlets of oceanic plagiogranite (OPG) as well as leucocratic gabbro (primitive gabbro) and hornblende Fe-Ti oxide gabbronorite (ferrogabbro) without OPG. The studied zircons differ in morphology, inner structure, set of mineral inclusions (ingrowths), and content of trace elements. Compositional heterogeneity is also observed within individual grains. The REE distribution patterns in zircons are characterized by gentle growth from LREE to HREE, with prominent positive Ce anomaly and negative Eu anomaly, and in general fall in the range of zircons from magmatic rocks. Oceanic zircons clearly differ from continental populations in the U/Yb-Y and U/Yb-Hf discrimination diagrams, primarily, due to their lower U/Yb ratio at wide variations of Y and Hf contents. Zircons that contain inclusions of acid glass and hence, crystallized from OPG melt are relatively depleted in REE, especially HREE. This indicates that OPG was formed by partial melting of gabbro in the presence of concentrated water-salt fluid, which extracted REE from the plagiogranite melt. Zircons from gabbroids devoid of OPG inclusions have higher total REE contents than zircons from OPG. Late hydrothermal alterations of zircon are distinctly established by the formation of neogenic collomorphic (porous) texture and/or by composition of mineral inclusions and accompanied by significant enrichment in La. Heterogeneous distribution of Ti in zircon may be caused not only by a change in its crystallization temperature, but also variations in silica to titanium oxide activity ratios in the rocks during interaction with hydrothermal solution of variable acidity. A complex study of structural-morphological and geochemical features of oceanic zircons and phase composition of host rocks and inclusions provides insight into processes leading to the crystallization and subsequent evolution of this mineral in the rocks of oceanic lithosphere.

This report presents the main results of LA-ICPMS studies of zircon from metamorphosed magmatic rocks of the Fisher Massif in East Antarctica. The minimum age of crystallization for still unexplored granitoid intrusion in the southeastern part of the massif amounts to 1399 ± 11 Ma. The presence of inherited zircon of 1786 ± 23 Ma age in the rocks points to their fusion from a crustal source of Paleoproterozoic age. The time of the eruption of vulcanites of basite composition amounts to 1244 ± 11 Ma. The vulcanites contain xenogenic zircon of Late Archean and Middle Proterozoic age; hence, their initial melt interacted with the heterogeneous continental crust. The earliest metamorphism of the amphibolite facies proceeded 1213 ± 16 Ma ago, and was accompanied with intense shift deformations. The time of volcanism complies with the age of a large basite dike swarm in Vestfold Hills, intruded about 1250 Ma ago, which is associated with the destruction of the hypothetical Paleoproterozoic Nuna (Columbia) continent.