Serpentinization of olivine in gabbroic rocks from the Hess Deep Rift

Abstract

We report paragenesis and chemical compositions of serpentine and associated minerals in gabbroic rocks recovered during IODP Expedition 345. In contrast to that of peridotites, serpentine of gabbroic rocks shows no evidence for mixing with brucite but suggests local mixing with smectite. The observed variations of compositions such as Si/(Mg+Fe) and Mg/(Mg+Fe) ratios, and the abundance of coexisting magnetite or smectite can be explained as a result of variation in temperature, silica activity, oxygen fugacity and/or water/rock ratio during serpentinization.