Ocean Drilling Program (ODP) Hole 735B is the first and only long, continuous section of lower oceanic crust ever sampled. It is located on the Southwest Indian Ridge at 57°E and begins near the top of the gabbroic section, extending nearly to its bottom (Dick et al., 1991; Dick et al., 2000; Dick et al., 1999). This 1500-m-long section has proven quite useful for studies involving the igneous evolution of the oceanic crust, its metamorphic evolution, and its post-subduction role as a reservoir of trace elements within the mantle (Snow et al., 1999, unpubl. data). This paper reports on the major and trace element compositions of 60 gabbroic samples from the drill core. These analyses lay the groundwork for further study of the core by bulk geochemical means.
Hole 735B consists of one or more cumulate stacks of nearly cotectic olivine-plagioclase-clinopyroxene cumulates with minor orthopyroxene in some sections that lack olivine (Dick et al., 1991). This cumulate stack is reintruded by highly evolved liquids that crystallized further plagioclase and pyroxene, along with large amounts of iron and titanium oxides. The cumulate sequences are themselves cut by primitive olivine microgabbros and by late-stage silicic melts (Dick et al., 2000, 1999).