Fractures and veins are the principal structures developed in basalts from Hole 1163A. Veins are filled by cream-colored micritic carbonate and/or clay, pinkish brown finely crystalline sparry calcite, and white sparry calcite (see Fig. F16 and "Alteration"). The cream-colored micritic carbonate and/or clay appears to be derived from interpillow sediments. Therefore, most veins are considered to represent sediment-filled open fractures.
Fractures and veins are abundant in the lower part of Hole 1163A (Fig. F17). A plot of fracture + vein density (Fig. F17) on a section-by-section basis indicates a general increase in the abundance of fractures and veins downhole.
Fracture + vein density ranges from 4.5 to 38.5/m and averages 19.0/m (Fig. F17). The vein density ranges from 0 to 28.8/m and averages 11.4/m. The calculated vein volume percent ranges from 0 to 3.4 and averages 1.1.