New data on the rock composition of the Bahia Seamounts (Brazil Basin,South Atlantic Ocean)

During the 28th cruise of R/V Akademik Sergei Vavilov in 2009, five different mountains belonging to the northern chain of the Baia Seamounts, located in the Brazil Basin, were dredged. Igneous rocks, limestones, and Fe-Mn crusts were collected. Igneous rocks are greatly altered resulting from halmyrolithic and/or low-temperature hydrothermal processes; the main secondary minerals are smectite, iron hydroxide, and phillipsite. Igneous rocks are subdivided into two groups, namely, trachybasalts and trachyandesites. Trachybasalts are aphyric rocks, consisting of basal plagioclase microlites, Fe-Ti ore mineral, olivine, and clinopyroxene. Trachyandesites are rarely porphyre rocks. Inclusions in trachyandesite are represented by acidic plagioclase, olivine, biotite, and zircon. The main mass is formed by acidic plagioclase and a small quantity of clinopyroxene.