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The results of 230Th/U dating of massive sulfides and metalliferous sediments (288 and 245 analyses, respectively) of hydrothermal sites in the northern equatorial area of the Mid-Atlantic Ridge (MAR) from 12° to 20° N are presented. The maximum and average ages of sulfides are 223 ± 38.2 and 80.5 ka, respectively. The comparison of ages of massive sulfides from various MAR hydrothermal sites showed asynchronous stages of hydrothermal activity along the ridge axis indicating the features of tectonic activity and magmatism, which control the hydrothermal activity within each region. The glaciation periods, which record the activation and low- and high-temperature hydrothermal activity, are an exception. A direct positive correlation between the age of a hydrothermal site and its distance from the axial ridge zone is typical of mafic-related hydrothermal sites in contrast to ultramafic-related hydrothermal sites, which is related to the different scenarios of the formation of these two types of sulfide mineralization within slow-spreading ridges. The ages of sulfides and sediments have been jointly analyzed based on the example of the Pobeda and Semenov hydrothermal sites. The interpretation of data on sediments indicates the continuous character of hydrothermal activity, which is partly supported by the age of sulfides. [ABSTRACT FROM AUTHOR]

The variety of information obtained during scientific research and exploration of seafloor massive sulfide (SMS) deposits include significant data on the morphology of orebodies formed in various geological settings. On the example of hydrothermal vent fields in the Northern Mid-Atlantic Ridge, different hydrothermal ore structures are described, from the most common mound-shaped to rarely encountered "smoking craters." The processes that govern the morphology of orebodies are analyzed, including alterations during the evolution of hydrothermal ore-forming systems. In contrast to the study of SMS deposits outcropping on the seafloor, the internal structure and formation models are mostly hypothetical. In particular, this concerns assumptions on the presence of massive sulfides and their formation mechanism below the paleo/subseafloor surface. Obviously, the results of drilling planned in the near future will make it possible to confirm or refute existing models and change the resource assessments, which are currently based on surface sampling of SMS deposits. [ABSTRACT FROM AUTHOR]

Sea level changes during of Earth's glacial periods the reduce hydrostatic pressure on the ocean bottom. The decrease in hydrostatic pressure increases magmatic activity and, as a result, could lead to the formation of hydrothermal systems [9, 19]. Thus, a correlation between glacial periods and the origin of circulating hydrothermal systems is possible. To test the hypothesis about the relationship between the formation of hydrothermal systems and glacial periods, we compared the 230Th/U age dates of sulfide ores in the northern near-equatorial zone of the Mid-Atlantic Ridge and marine isotopic stages, which reflect glacial and interglacial periods. The comparison shows that the glacial periods coincide only with the onset of formation of ore objects associated with basalts within magmatic segments of the Mid-Atlantic Ridge. Conversely, the periods of formation of ore objects associated with tectonic segments of the ridge within oceanic complexes are unrelated to glaciation. We hypothesize that the relationship between glaciations and the origin of hydrothermal systems is determined by differences in the geological conditions for the formation of seafloor massive sulfides within slow-spreading ridges. [ABSTRACT FROM AUTHOR]

radiochemical study was carried out on massive sulfides from Semyenov hydrothermal district at the Mid-Atlantic Ridge. New and published results provide evidence that Th/U ages obtained for massive sulfides are reliable. The sulfide deposits from the West, North-West, North-East, and East hydrothermal sites at the Semyenov hydrothermal district were formed between ∼124 ka and ∼37 ka ago. The hydrothermal activity might have started in the eastern part of the district and moved to the west by episodic ore formation. [ABSTRACT FROM AUTHOR]