Résumé
This paper presents alteration data for basalts from Ocean Drilling Program (ODP) Sites 1183, 1185, 1186, and 1187 drilled on the Ontong Java Plateau during Leg 192. The entire sequence of recovered basaltic basement has undergone low-temperature water-rock interactions. Alteration and vein logs were compiled for each hole from visual core descriptions made aboard the ship. These logs quantify the alteration types, provide a consistent alteration characterization of the samples, and provide a method for estimation of downhole variations in basalt alteration and vein abundance/mineralogy. The three main alteration types identified include gray basalt, black or dusky green halos, and brown or olive halos. Secondary minerals, in order of decreasing abundance, include phyllosilicates, calcite, pyrite, chalcedony, quartz, Fe oxyhydroxides, and zeolites. Veins commonly contain smectite and/or celadonite, Fe oxyhydroxide or pyrite, and calcite. Alteration of basalts from the Ontong Java Plateau is similar to that observed from other Deep Sea Drilling Program/ODP sites drilled into the upper oceanic crust.