Apart from abundant veins, rocks obtained from Holes 1185A and 1185B exhibit relatively few structural features. The sediments that overlie the basaltic basement are characterized by horizontal bedding planes and appear to be unaffected by either tilting or faulting (see "Lithostratigraphy"). No ductile or cataclastic fault zones or tectonic breccias were encountered in the cores.
Location, vein width, and mineral filling have been documented for 2350 veins in the vein-structure log for this site. True dip was measured for 110 veins. For an additional 890 veins, we calculated true dip from measurements of apparent dip. The graphic presentation of fracture density, vein abundance, and true dip in Figures F68 and F69 provides some information about the relationship between vein characteristics and basement depth. The fracture density has been calculated per meter of core section. A vein thickness of 0.25 mm has been assumed to be a representative average for veins described as hairline veins in calculating vein abundance.
Basement penetration in Hole 1185A was 20.2 m. The data presented in Figure F68 are characterized by a random distribution and indicate significantly higher fracture and vein densities than those recorded for Hole 1183A (Fig. F68).
Hole 1185B yielded a 216.6-m-thick sequence of alternating pillow basalts and massive basalt flows subdivided into 12 basement units (see "Igneous Petrology"). The outer parts of pillows have much higher fracture densities than the inner parts or than the massive flows. The pillows are characterized by two types of vein orientations: concentric veins, which are located toward pillow margins, and radial veins, which extend from the center toward the pillow margin. Massive lava flows and the inner parts of large pillows are characterized by low fracture density, with veins oriented between 0° and 30°.
The relationship between depth in basement and dip inclination is random (Fig. F69). However, fracture density and vein abundance show some variation with depth, unlike those observed in Hole 1183A. These parameters reflect the presence of either pillow or massive flow sequences and show a general correlation with the 12 basement units (see "Igneous Petrology"). Massive flows typically have a fracture density of 20 veins/m and a vein abundance of 20 mm/m. Pillow lavas have fracture densities between 30 and 65 veins/m and vein abundances of 60-100 mm/m.
The absence of downhole logging information and structural marker planes (e.g., sedimentary or basaltic layering) precludes reorientation of the measured veins and the calculation of dip azimuths. Paleomagnetic results may enable reorientation of some of the veins on larger pieces during shore-based analysis of the data (see "Paleomagnetism") and allow the calculation of dip azimuths.