A basalt-carbonate breccia was recovered from the upper part of Hole 1156A (Core 187-1156A-2R). The breccia consists of basalt, basaltic glass/palagonite, and pink micritic calcite fragments in a light gray micritic calcite matrix, described in "Alteration", as first- and second-generation calcite, respectively. The relative abundances of basalt, first-generation calcite, and second-generation calcite in the breccia are shown in Figure F15. Calcite that fills the veins and vugs (third-generation calcite) is a minor breccia constituent and is not included in the figure.
As mentioned in "Alteration", at least two brecciation events have taken place. In some cases the second-generation calcite crosscuts basalt and first-generation calcite, forming a jigsaw puzzle that can be fitted together (Fig. F16). Because of this, the second brecciation may have occurred nearly in situ with little or no displacement.
The fracture + vein density and vein density for Hole 1156A average 14.8 and 4.8/m, respectively. These values are significantly lower in Core 187-1156A-2R than in Core 3R (Fig. F17). This variability reflects differences in the rock types recovered in these cores. Core 187-1156A-3R is almost exclusively basalt fragments, whereas Core 2R contains fragments of basaltic breccia with abundant matrix material (Fig. F18). The veins and fractures are much more common in basalt fragments than in breccia matrix.
Fractures and veins are the principal structures developed in basalts from Hole 1156B. Their distributions are uneven, and they are concentrated in some pieces or in Sections 187-1156B-4R-2 (Piece 1), 5R-1 (Piece 1), and 6R-1 (Pieces 1 and 7). The fracture + vein density ranges from 2.4 to 29.1/m and averages 15.2/m (Fig. F17). The vein density ranges from 1.5 to 26.2/m and averages 10.4/m. The calculated volume percent of veins ranges from 0.04 to 1.96 and averages 0.86.