Serpentinization of olivine in troctolites and olivine gabbros from the Hess Deep Rift

摘要: Abstract To understand the similarity and diversity of serpentinization processes in different rock systems, gabbroic rocks recovered from IODP Site U1415 at Hess Deep Rift were examined compared with peridotites adjacent ODP 895. Textural observations, micro-Raman spectroscopic analyses electron microprobe indicated that most olivine-replacing serpentine lack mixing brucite, which is common peridotites. At least three stages are observable rocks; each generation characterized by submicroscopic mixtures or solid solutions sheet silicates: 1) Mg-Fe2 + lizardite + ferri-lizardite + chlorite, 2) lizardite + ferri-lizardite, 3) lizardite + ferri-lizardite + saponite. The first third generations mixed minerals relatively Fe-rich, whereas second Fe-poor associated abundant magnetite pyrrhotite. major difference between alteration peridotitic systems probably best explained iron content modal abundance primary olivine rock-dominated fluid compositions a high silica activity due to plagioclase rocks. mineralogical variations reported silicates can be ascribed and/or oxygen activities fluids under decreasing temperature conditions. abrupt increase crystallization during could caused oxidation SiO2 without olivine-serpentine-brucite buffering assemblage.