Professor Logachev Research Articles

Geochemical Signature of Basalts of the MAR Rift Valley at 20°31′ N: Origin Conditions of the Anomalous Volcanic Center of Puy des Folles in the Axial Zone of the Mid-Atlantic Ridge

The results of a study of chilled glasses sampled during the 45th cruise of the R/V Professor Logachev at the top of the submarine volcano Puy des Folles are presented. The Puy des Folles volcano is located in the axial part of the rift valley of the Mid-Atlantic Ridge (MAR) at 20°31′ N. Unlike typical volcanic axial highs which usually does not exceed several hundred meters the summit of the Puy des Folles volcano is located a depth of 1950 m and rises 1800 m above the bottom of the rift valley. The data on geochemistry and isotope composition of chilled glasses examined allow us to come to a number of conclusions that expanded existing ideas about magmatic and tectonic 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 the activity of a long-lived magma chamber located below the rift valley axis. It is possible that, in addition to the DM reservoir, a mantle source enriched in incompatible elements may have participated in the formation of the parental melts for the studied chilled glasses. A weak geochemical signal of contamination of the parental melt with a hydrothermal component in chilled glasses was established. Signs of stagnation in the spreading of the oceanic crust in the rift valley segment studied in this work have been established.

ПЛАВАЮЩИЙ МОРСКОЙ МУСОР В СЕВЕРО-ВОСТОЧНОЙ АТЛАНТИКЕ ОСЕНЬЮ 2022 г.

Ship-borne observations of floating marine litter in the northeastern region of the Atlantic Ocean were carried out during the 45th cruise of the R/V “Professor Logachev”. The route of the vessel covered the waters of the Baltic, North Seas, the English Channel, the northeastern region of the Atlantic Ocean. A small amount of floating marine litter was found in the surveyed water areas. In total, 37 objects 5–40 cm in size were noted, which were found in single quantities, there were no litter accumulations. Plastic made up 89 % of the total amount of recorded litter items. Basically, these are various plastic pieces 2.5–50 cm in size, plastic bags including pieces and other plastic items. The distribution of floating marine litter was uneven along the vessel’s route. It was not found in the Baltic and North Seas. Its concentration in the English Channel was 1.52 items/km2; in general, in the water area of the northeastern Atlantic – 1.08 items/km2; off the coast of Portugal and west of the Canary Islands – 1.41 and 6.43 items/km2 respectively. Thus, it has been shown that the open part of the Atlantic Ocean in the Northern Hemisphere far from the coast and outside the subtropical circulation is not characterized by pollution by floating marine litter. A significant increase in concentration was noted only in the outer region of the accumulation zone, due to the North Atlantic gyre. In addition, the importance of adopting and complying with the rules of international and regional conventions in the field of waste management was noted.

Discovery of New Hydrothermal Ore Fields “Korallovoe” (13°07′ N) and “Molodezhnoe” (13°09′ N) in the Middle Atlantic Ridge

During the 41th scientific cruise of the R/V “Professor Logachev” in 2019, two new ore fields were discovered within the Russian exploration area of the Mid-Atlantic Ridge. The “Korallovoye” ore field is located in the middle part of the rift valley ridge and lies on a gentle slope in the depth range of 2800–2850 m. The “Molodezhnoye” ore field is located at a distance of approximately 5 km northeast of the “Korallovoye” field and lies on a less steeper section of the slope between 3500 and 3550 m in depth. The “Korallovoye” and “Molodezhnoye” fields are confined to the outcrop of a gabbro-peridotite massif on the western side of the Mid-Atlantic Rift valley. The total number of discovered ore fields in the Russian exploration area has been increased to 14 sites.

Минералы группы атакамита из рудопроявлений на дне Атлантического океана

The study of samples with minerals of the atacamite group from the ore fields of the Atlantic Ocean made it possible to reveal their genetic features and hydrothermal nature. The objects were observed with the help of underwater television directly on the ocean floor. The lifted samples were initially studied under binoculars aboard the R/V Professor Logachev. Due to their characteristic rich bluish-green color, atacamites were easily recognized among other minerals, and their diagnosis was further confirmed by the results of studying optical properties in transparent polished sections, under an electron microscope, and during X-ray diffraction analysis.

Identification of Two New Hydrothermal Fields and Sulfide Deposits on the Mid-Atlantic Ridge as a Result of the Combined Use of Exploration Methods: Methane Detection, Water Column Chemistry, Ore Sample Analysis, and Camera Surveys

In 2018–2020 the research vessel (R/V) Professor Logachev (cruises 39 and 41) carried out geological and geochemical studies in the bottom waters of the Mid-Atlantic Ridge hydrothermal fields at 14°45’ N, 13°07’ N, and 13°09’ N. Two new hydrothermal fields were discovered—the Molodezhnoye and Koralovoye. Standard conductivity, temperature, and depth (CTD) sounding with a methane sensor was accompanied by video surveillance and sampling of rocks and water. The rocks were characterized by a zonal composition with opal and sulfides of copper and zinc. An increase in methane concentration values was accompanied by CTD anomalies in the bottom waters. The methane anomaly was formed within the hydrothermal plume of both high-temperature and low-temperature systems. Methane was almost absent in the plume of neutral buoyancy and was associated in all the studied manifestations with the ascending flow of hot waters over the hydrothermal vents. The hydrothermal plumes were characterized by increased Cu, Zn, and Fe concentrations at background Mn concentrations. Signs of low-temperature hydrothermal activity were also observed. Different sources and mechanisms are required to explain the elevated concentrations of base metals and methane in the hydrothermal plumes.

New records of Recent brachiopods (Terebratulida) from the northern Mid-Atlantic Ridge

ABSTRACT Five species of Recent brachiopods (Terebratulida), i.e. Xenobrochus parvus (Cooper, 1977), Chlidonophora incerta (Davidson, 1878), Eucalathis ergastica Fischer & Œhlert, 1890, Nanacalathis atlantica Zezina 1991, and Leptothyrella incerta (Davidson, 1880) have been identified in the material collected during the 39th cruise of the RV Professor Logachev in the Russian Exploration Area in the central part of the northern Mid-Atlantic Ridge in February–March 2018. Only Chlidonophora incerta is numerous, the remaining species are very rare. This is the first confirmed occurrence of the genus Xenobrochus from the Atlantic Ocean. The distribution of the studied fauna and its comparison with adjacent regions are also discussed.

The influence of fluids on the species composition and preservation of microfossils in biogenic carbonate sediments by hydrothermal cluster “Pobeda” (Mid-Atlantic ridge)

The species composition, distribution and preservation of carbonate shells of nanno and microfossils of biogenic bottom sediments within the hydrothermal cluster Pobeda (1707.451708.7 n) were studied on the basis of materials obtained in flight No. 37 of NIS Professor Logachev in the Russian exploration area (Mid-Atlantic ridge). Physical-chemical parameters and the total carbonate content of sediments were measured, their changes in column sections were revealed. For complexes of coccoliths studied precipitation is attributed to the top (acme) biostratigraphic zone of Emiliania huxleyi. It is established that within the zone of hydrothermal activity (ore cluster Pobeda) the total number of microorganisms decreases and their species diversity decreases, as a rule, in the lower part of the columns. Down the column section also decreases the Eh, pH and carbonate precipitation. These changes are explained by the influence of diffuse hydrothermal fluids.

Ecological studies of the Russian exploration area on the Mid-Atlantic ridge on the 39th cruise of RV Professor Logachev

During the 39th cruise of RV Professor Logachev ecological studies of the Russian exploration area in the Central part of the Northern Mid-Atlantic Ridge were conducted. New data on the composition and structure of benthic communities as well as composition and distribution of ichthyofauna were obtained.

Ecological Studies of the Russian Exploration Area on the Mid-Atlantic Ridge on the 39th Cruise of RV Professor Logachev

Ecological Studies of the Russian Exploration Area on the Mid-Atlantic Ridge on the 39th Cruise of RV Professor Logachev

Influence of hydrothermal-metasomatic processes on the formation of present-day sulfide ores in carbonate bottom sediments of the mid-Atlantic Ridge (19°–20° N)

Based on materials obtained in Cruises 33 and 34 of the R/V Professor Logachev, the paper addresses formation conditions, morphology, structures, mineral composition of the present-day oceanic sulfide ores, and their relationships with the host (biogenic carbonate) bottom sediments in the 19°–20° N MAR (Zenith-Victoria and Petersburg hydrothermal fields) region. The grain size distribution, mineral composition of the carbonate (background) and ore-hosting sediments, as well as physicochemical parameters of their interstitial waters, are examined. The results suggest a significant role of hydrothermal-metasomatic processes in the formation of ores and ore-bearing sediments. A model is proposed for the formation of sulfide mineralization in oceanic sediments at the geochemical barrier in the zone of their interaction with the acid hydrothermal (diffuse-type) ore-bearing solutions delivered from rocks of the ocean floor.

Redescription of Nanacalathis atlantica Zezina, 1991 (Brachiopoda: Chlidonophoridae) from the North Atlantic

The chlidonophorid brachiopod species Nanacalathis atlantica Zezina, 1991 has been identified in material from the north tropical Mid-Atlantic Ridge, between 16°56’ – 16°51’N at the depth range 3227–3474 m, collected during the 37th cruise of the RV Professor Logachev in February-March 2015. This rich new material allows us to redescribe and properly illustrate this poorly known, deep-water species that was established on the basis of one empty shell. The spiculation within the lophophore and tentacles is heavy with the pattern characteristic for the subfamily Eucalathinae.

First data on benthic and fish communities from the Mid-Atlantic Ridge, 16°40′− 17°14′N

The first ecological survey in the tropical part of the northern Mid-Atlantic Ridge (MAR) was conducted between 17°14′N and 16°40′N in February–March 2015 during the 37th cruise of the RV Professor Logachev. Significant effort of the survey was aimed at studies of benthic non-vent soft sediment fauna at depths from 2270m to 3900m. Samples of this fauna at seven stations revealed ~780 specimens and at least 136 species. The most common species was the hermit crab Parapagurus cf. nudus. Also common were the ophiuroids Ophiotypa simplex and Ophiomusium cf. lymani. Most benthic organisms were <3cm in size. Collection of fish taken in the depth range from 0 to 3850m included 1128 specimens represented by 48 species from 16 families. The highest number of species was in the families Myctophidae (18), Gonostomatidae (9) and Sternoptychidae (5). In the course of the cruise, two new fields of massive sulphide deposits were discovered on the south-western slope of the seamount on the eastern flank of the rift valley, one at 17°08.7′N and second at 17°07.45′N. During video profiling in this area indications of modern hydrothermal activity were recorded. Extensive fields of shells of Bathymodiolus puteoserpentis and Thyasira sp. were discovered and samples of bivalves were taken using the TV-grab and geological square corer. Surprisingly high concentration of drowned pelagic algae Sargassum sp. (Phaeophyceae, Fucales) in different state of degradation was observed at TV transects at the seafloor both on soft and hard substrates. Thalli of Sargassum fluitans appeared in trawl catches. Massive aggregations of Sargassum also were abundant at the sea surface in the area from December 2014 to April 2015.

Petrogenetic conditions at 18°–20° N MAR: Interaction between hydrothermal and magmatic systems

The paper presents petrological and geochemical data on mantle peridotite, basalt, and metamorphic rocks sampled in Cruise 36 of the R/V Professor Logachev at the MAR axial zone between 17° and 20° N. These data are interesting not only as providing new information on the inner structure of the oceanic crust in the still-poorly known axial MAR segment but also in the context of the fundamental problem of interaction between magmatic and hydrothermal systems in slow-spreading mid-oceanic ridges. The MAR axial zone between 17° and 20° N was determined to host both weakly and strongly depleted residual peridodites, which suggests that the degree of mantle source melting significantly varied along the ridge axis in this segment. The MAR crest zone comprises slabs of serpentinized peridotite brought to the seafloor surface at various time. The most strongly depleted mantle peridotites likely uplifted later than the mildly and weakly depleted rocks in the same areas. A mantle reservoir beneath the MAR axial zone at 20° N is not isotopically related to the mantle source of the parental MORB melts, and high-Mg metabasites exposed at 17°56- N were derived from a crustal source that was modified near the root zone of a high-temperature hydrothermal system. The studied area seems to display traces of an extinct hydrothermal field and likely an ore occurrence related to it.

New chemical and isotopic data for basalts from the axial segment of the Mid-Atlantic ridge between the Vema and Mercury fracture zones

The whole-rock geochemistry and isotopic composition of the basalts dredged from the Mid-Atlantic Ridge (MAR) segment between the Mercury and Vema fracture zones during cruise 32 of the R/V Professor Logachev were studied. In addition to typical basalts with moderate petrochemical parameters, there are high-Ca and low-Na types of basalts representing higher degree melts and high-Fe varieties generated at great depths. The basalts derived by high degrees of melting exhibit a close spatial association with the central portions of three on-axis rises on the rift valley, which reach a height of 300–500 m above the floor of the valley and represent the loci of the subaxial mantle upwelling. The position of the Northern rise at the northern intersect of the Mercury transform fault is inconsistent with focused upwelling. The basalts with a more radiogenic Nd, Sr, and Pb composition are identified above the loci of the subaxial upwelling. They are compositionally similar to basalts, which have HIMU-like affinities and are interpreted to be derived under the influence of the 14° N plume between the Marathon and Cape Verde fracture zones. The relatively high isotopic ratios of these basalts anti-correlate with their low (La/Sm)n values typical of the depleted N-MORB-type basalts. The results show that enriched melts contributing to basalts from the central portions of on-axis rises are associated with one of the flows of plume material channeled from the 14° N anomaly to these rises. The partial melting of the rising plume material causes the formation of localized accumulation of magmas at structural barriers and creates new centers of upwelling, which, being enhanced by the regular upwelling, lead to increased magma production and changes in the composition of basalts.

Hydrothermal metasomatic alteration of carbonate bottom sediments in the Ashadze-1 field (13° N Mid-Atlantic Ridge)

We have performed the first detailed study of hydrothermal alteration of the Holocene-upper Pleistocene sediments in the recent Ashadze-1 hydrothermal field sampled during the 26th cruise of R/V Professor Logachev in 2005. It has been established that alterations in mineralogy and geochemistry are caused by the dissolution of calcite shells in bottom sediments and their metasomatic replacement with sulfides and other hydrothermal minerals. A zone of sediments enriched in magnesian hydrothermal minerals has been revealed in the sediments of the MAR for the first time. It is suggested that metasomatism is related to diffuse percolation of hydrothermal fluids through sediments.

Mineralogical and geochemical zoning of sediments at the Semenov cluster of hydrothermal fields, 13°31′-13°30′ N, Mid-Atlantic Ridge

New material from eight columns recovered during Cruise 32 of the R/V Professor Logachev in 2009 was used to explore the lithological facies, biostratigraphy, mineralogy, and geochemistry of sediments from the northwestern (active) and eastern (inactive) hydrothermal vent fields of the Semenov cluster. Mineral types of sediments were distinguished, and a general scheme was proposed for the vertical structure of the hydrothermal-sedimentary sequence overlying massive sulfide ores. It was found that the ore-bearing sediments exhibit a vertical zoning in the distribution of mineral assemblages, which are controlled by oxygen activity. The mechanisms of the formation of atacamite, CuCl2 · 3Cu(OH)2, which is a widespread mineral in red iron-oxide bodies replacing sulfides (gossans), were evaluated.

Large, enigmatic foraminiferan-like protists in the eastern part of the Clarion-Clipperton Fracture Zone (abyssal north-eastern subequatorial Pacific): biodiversity and vertical distribution in the sediment

Komokiaceans and similar large (millimetre-sized to centimetre-sized) testate protists resembling Foraminifera are a ubiquitous and often dominant component of abyssal macrofaunal assemblages. Yet they are often overlooked and many forms are undescribed, often at the genus or higher taxon level. As a result, they represent a major source of unknown biodiversity in the deep sea. We studied the diversity and vertical distribution of these delicate, often fragmentary organisms in sediment samples (0- to 6-cm layer) collected from three sites in the eastern part of the Clarion-Clipperton polymetallic nodule field (subequatorial NE Pacific) during the 1997 cruise of the RV Professor Logachev organised by the Interoceanmetal Joint Organization (IOM). A total of 102 morphospecies and morphotypes was recorded (28-69 per station), indicating an extremely diverse assemblage. Although most were found in the uppermost 2 cm, deeper sediment layers also yielded some species. This is one of only a few studies of komokiaceans and related organisms in this part of the Pacific. It contributes to baseline knowledge of abyssal communities in an area targeted for future commercial nodule mining operations.

Accumulation history of the metalliferous and ore-bearing sediments of the Krasnov hydrothermal field (MAR 16°38′N) for last 80 Ka: Part II

The lithological-facies, biostratigraphic, and geochemical studies of ore-bearing and metalliferous sediments were carried out using original material from six cores taken in the MAR 16°38′N area during 28th Cruise of the R/V Professor Logachev.

Peculiarities of present-day sulfide mineralization at 19°15′—20°08′ N, Mid-Atlantic Ridge

Based on studies conducted on the 33rd cruise of the R/V Professor Logachev in 2010, a new type of sulfide mineralization of the mid-oceanic ridges has been established. It was formed in the present-day organic sediments due to diffuse penetration of hydrothermal fluids that emanated along the fractures in basalts on the slopes of the Mid-Atlantic Ridge.

Distribution, Composition, and Vertical Fluxes of Particulate Matter in Bays of Novaya Zemlya Archipelago, Vaigach Island at the End of Summer

An analysis of suspended particulate matter (SPM) and phytoplankton distribution, composition and vertical particle fluxes in Russkaya Gavan’ Bay (Northern Island of the Novaya Zemlya), Bezymyannaya Bay (Southern Island of the Novaya Zemlya), Dolgaya Bay (northwestern part of the Vaigach Island) in comparison with the data from the Svalbard Archipelago is presented. Field studies were carried out by the authors during the 9th expedition of the RV “Professor Logachev” in September 1994, the 11th, 13th, and 14th expeditions of the RV “Akademik Sergey Vavilov” in September-October 1997 and August-September 1998. The data about Spitsbergen fjords are from literature. Our results show that, on the bays of the Barents Sea islands, most SPM stays in the bays (fjords) and only small part of it reaches the open sea. This is due to the hydrodynamic conditions in the bays, the large size of the particles, flocculation, and often to the morphological barriers in the relief at the bay entrances. It is important for ecological purposes to map out migration pathways of the SPM with pollutants from bays to the open sea. Results of our investigation indicate that the western bays of the Novaya Zemlya act as traps for SPM derived from glaciers and coastal abrasion.