Petrology of ultramafic nodules from São Tomé Island, Cameroon Volcanic Line (oceanic sector)

摘要: Ultramafic xenoliths were found in recent alkali basalts from Sao Tome Island. These include spinel peridotites (lherzolites, harzburgites and dunites) pyroxenites (orthopyroxenites clinopyroxenites). Textures mineral compositions indicate that originated crystal/liquid separation processes operating on magmas similar to those giving rise their present host rocks whereas peridotite had an accidental origin; Fo (>89) Ni (>0.36 wt.%) contents olivines, Mg# (91–95) of orthopyroxenes low Ti clinopyroxene (primary crystals: TiO2 1150 °C) is compatible with a long period pre-entrainment cooling supporting Fitton's [Tectonophysics 94 (1983) 473] hypothesis proposes oceanic lithosphere uprising the Cameroon Volcanic Line prior initiation current thermal regime, related magmatism. The association upper mantle (peridotite) igneous cumulates (pyroxenites) suggests suite uppermost above magma storage zone(s), probably region high strain rate, near boundary between overlying crust.