Petrological Evidence of Magma Chambers Beneath the South Atlantic Ridge

Detailed studies of melt inclusion and matrix glass suggest multi-stage melting beneath the South Atlantic Ridge axis. Primary glass, with an approximate composition of MgO=12,5wt % Ti02 = 0.4 wt % and Mg# = 75, may have formed by a first stage of melting, and Mg-quartz tholeiite be a second stage of melting. Most of the matrix glass from basalts, erupted along the ridge, lies along the evolved part of the liquid line of descent of olivine and plagioclase fractionation, which suggests presence of a magma chamber beneath the South Atlantic Ridge. More primitive liquid were recorded in melt inclusions trapped in xenocrysts of plagioclase in almost every dredge hole along the Ridge. Independent of the offset size, some fracture zone, such as Ascension F.Z., 9.75°S F.Z. and Bode Verde F.Z. in the South Atlantic correspond to a boundary for chemical elements. Therefore, it seems that a magma chamber are a cornman feature beneath the South Atlantic Ridge.