New Data on the Composition and Age of Rocks from the Bathymetrists Seamounts (Eastern Margin of the Equatorial Atlantic)

The petrology, geochemistry, and isotope ratios of volcanics dredged during the 43rd cruise of R/V Academik Ioffe on the Bathymetrists Seamounts in the eastern equatorial Atlantic have been studied. These are alkaline volcanics of basic and ultramafic compositions. Spider diagrams of the trace elements of volcanic rocks demonstrate strong fractionation, indicating formation of their primary melts from an enriched mantle source at garnet depth facies. Considering the isotope ratio values of Nd-143/Nd-144, Pb-206/Pb-204, Pb-207/Pb-204, Pb-208/Pb-204, and Sr-87/Sr-86 and the character of their variations, the volcanic mantle source was chemically heterogeneous: for various volcanic rocks it was a mixture of the mantle components HIMU with EM-1 or EM-2. Limestones dredged together with the volcanics yielded microfossils suggesting a Middle Eocene age of their formation in a carbonate platform environment.