ALBERT

Description: Summary The Bathymetrists Seamounts (BSM) are located north of the volcanic Sierra Leone Rise in the eastern Atlantic between 6° and 9°N. The three W-E, N-S and NE-SW striking directions of the seamounts indicate a clear structural control for the emplacement of these volcanoes. The origin of the melts, their relationship to the Sierra Leone Rise and the role of the faults in the formation of the melts are unknown as the BSM could be explained by plume related volcanism or decompression melting beneath deep (transform) faults. The SEDIS-cruise M152/2 of RV METEOR strove for a better understanding of the life cycle of submarine volcanoes and their effect on the oceanic lithosphere in the oceanic intraplate setting of the BSM and the relationship to the Sierra Leone Rise. The aims were: 1) to understand the interaction between crustal thickness, tectonics and volcanic phases, 2) to investigate the structural, chronological and petrological evolution of individual seamounts and seamount chains, 3) to review slope failures and resulting mass flow processes. We addressed these objectives by more than 4000 km highresolution reflection seismic and more than 5000 km of parametric echosounder, multi-beam, and gravity and magnetic profiles. Rock samples for ground truthing and geochemical research have been collected during 14 dredge stations. We further determined the concentrations in surface seawater and air and the state of air-sea exchange of a number of nowadays globally banned pesticides, polychlorinated biphenyls, brominated flame retardants, polycyclic aromatic hydrocarbons and their derivatives. Zusammenfassung Die Bathymetrists Seeberge liegen nördlich der Sierra Leone Schwelle, einer vulkanischen Plattform im östlichen Atlantik zwischen 6° und 9° N. Diese submarinen Vulkane gruppieren sich entlang W-E, N-S und NE-SW Trends, was eine strukturelle Kontrolle der Vulkanentstehung indiziert. Die Schmelzentstehung sind unbekannt und können mit PlumeVulkanismus oder Dekompressionsschmelzen unter bisher nicht untersuchten Störungen und tiefen Transformstörungen zusammenhängen. Der Bezug zur Sierra Leone Schwelle ist ebenfalls unbekannt. Im Zuge der SEDIS-Expedition M152/2 mit FS METEOR wurde der Lebenszyklus von Unterwasservulkanen und deren geochemischen Einfluss auf die ozeanische Lithosphäre der Bathymetrists Seeberge untersucht. Anhand der profilhaften geophysikalischer Messungen und Dredge-Proben wollen wir 1) die Wechselwirkung zwischen Krustenmächtigkeit, Tektonik und Vulkanismus verstehen, 2) die strukturelle, chronologische und petrologische Entwicklung von Vulkanen und Vulkanketten untersuchen, und 3) Auslösemechanismen, Transportprozesse und Volumina von Hangrutschungen studieren. Zur Bearbeitung der wissenschaftlichen Fragen sammelten wir mehr als 4000 km mehrkanal-reflexionsseismischer und mehr als 5000 km parametrische Sedimentecholot, Fächerlot, Schwere und Magnetik-Profile. Für die geochemischen Arbeiten sammelten wir an 14 Stationen Gesteinsproben unter Einsatz einer Dredge. Die regelmäßige Beprobung der Luft und des Oberflächenwassers diente der Bestimmung der Konzentration von heute weltweit verbotenen Pestiziden, polychlorierten Biphenylen, bromierten Flammschutzmitteln, polyzyklischen aromatischen Kohlenwasserstoffen und deren Derivaten und um den Austausch zwischen Luft und Meer weiter zu verstehen.

Description: Intraplate volcanism, in contrast to mid-ocean-ridge (MOR) oceanic crustal basalts, is formed by low degrees of deep mantle melting and has a unique and distinct major and trace element and isotopic composition. Intraplate magmatism can therefore significantly alter the composition of the lithosphere, but may also trigger local structural changes and fluid flow causing large-scale hydrothermal activity, which would also modify the original composition of the lithosphere. The BATHYCHEM (MSM70, Dec 2017-Febr 2018) cruise aimed to study the effect of the magmatism of the, so far poorly researched, Bathymetrists and Grimaldi Seamounts intraplate volcanic province on the Atlantic oceanic plate. The Bathymetrists Seamounts were formed on oceanic crust that has a wide range of ages from 30 to 〉100 Ma and thus has been exposed to variable degrees of seafloor alteration. This project aims at characterizing the structure, age and composition of the Bathymetrists Seamounts and adjacent areas to understand their origin and formation mechanism, which will allow a better assessment of how intraplate volcanism modifies the structure and composition of oceanic lithosphere through time. To achieve these aims the MSM70 expedition undertook high-resolution mapping and dense rock sampling of the intraplate Bathymetrists Seamount Chain and its corresponding N-bounding fracture zones; Cape Verde Ridge and Kane Gap. Hydro-acoustic models could be greatly improved to a resolution of 50 m and the position of 40 named and unnamed seamounts could be refined. The bathymetric maps reveal a complicated pattern of emplacement and indicate that most of the seamounts (62%) resemble guyots capped by carbonated platforms. A total of 65 dredge-tows recovered volcanic samples, carbonates, phosphorites, mudstones and manganese crusts and nodules. Volcanic samples from 27 seamounts revealed dense basaltic samples and vesicular volcanoclastic material of mafic origin containing pyroxenes, amphiboles and biotite.