Site 1277 is located on a basement ridge (Mauzy Ridge) beneath thin sediment cover (Figs. F8B, F9, and Fig. F20 in the "Site 1277" chapter). The main objective was to recover samples of basement, so the site was drilled without coring from 0 to 103.90 mbsf. It was predicted that the bit would be some tens of meters above the sediment/basement contact at that depth. During drilling, a "wash" core barrel was in place. When retrieved, this core barrel contained 2.29 m of fractured igneous rock and associated volcaniclastic sediments (Core 210-1277A-1W) that are indistinguishable from rock in the top of the next core, Core 2R. During drilling, hard zones were encountered at 85–89 and 97.5–100 mbsf. Thus, it is believed that the recovery in Core 210-1277A-1W comes from depths between 85 and 103.90 mbsf. We set the top of basement (Unit 1) at a nominal depth of 85 mbsf.
Two lithologic units are recognized (see Fig. F2 in the "Site 1277" chapter). Unit 1 is a succession of alternating basalt flows (~50%), coarse breccia units containing a wide variety of clasts of gabbro and serpentinite (~20%), and minor volcaniclastic and ferruginous sediments (~10%). There are also variably deformed gabbroic rocks (~20%) that may be very large clasts. All these rocks are fractured and have veins filled with mineral precipitates and detritus. The interpreted depth of this unit is 85–142.10 mbsf. The principal characteristic of Unit 1 is that it is a sedimentary and volcanic succession. The sedimentary units are derived entirely from rock types characteristic of the underlying basement at this site.
Lithologic Unit 2 (142.10 mbsf to the bottom of the hole at 180.30 mbsf) consists almost entirely of tectonized, altered ultramafic rocks including harzburgite, dunite, and serpentinite mylonite (see Fig. F2 in the "Site 1277" chapter). There is a gabbro cataclasite at the top of the unit. Unit 2 is cut pervasively by magmatic and hydrothermal veins that record several stages of fracturing and fluid precipitation. Many of the smaller veins cutting the serpentinized peridotite are composed of talc, magnetite, and calcite. There are no sediments or lavas in Unit 2 that would indicate formation in proximity to the seafloor. The rocks are interpreted as mantle that was exposed by tectonic extension and that was associated with pervasive deformation and hydrothermal alteration. During or after their exhumation, these serpentinites were buried by the lavas, allochthonous debris, and coarse sediments of Unit 1. The allochthonous debris was probably shed from local seafloor topography along the crest of the basement ridge.
No shipboard biostratigraphic analysis was conducted on the few sedimentary rocks recovered at Site 1277 because no suitable materials were recovered.
Agglutinated benthic foraminifers occur in a single piece of indurated ferruginous sediment (Sample 210-1277A-1W-1, 5–9 cm) overlying igneous rocks at Site 1277. The few poorly preserved specimens include planispirally coiled forms with numerous chambers and alveolar internal walls similar to those in the family Cyclamminidae. There are also encrusting(?) tubelike forms possibly belonging to the family Ammodiscidae. In addition, several tiny planktonic foraminifers were observed in a dark-colored sedimentary clast. No age-diagnostic taxa were observed.
We made pass-through magnetometer measurements and magnetic susceptibility measurements on the archive halves of all cores at 2-cm intervals. To isolate the ChRM, cores were subjected to alternating-field demagnetization up to 60 mT. We analyzed the results in Zijderveld diagrams (Zijderveld, 1967) and calculated ChRM direction using principal component analysis (Kirschvink, 1980). We also determined magnetic susceptibility on all whole cores at 2.5-cm intervals as part of the multisensor track analysis, and we measured split-core sections at 2-cm intervals with the point-susceptibility meter run on the archive multisensor track. No shipboard discrete samples were taken because of time constraints at the end of the leg.
Paleomagnetic data exhibit significant variations in demagnetization behavior among recovered lithologies. As at Site 1276, there was drilling-induced remagnetization, but at Site 1277 it was reduced in comparison. Greenish gabbro cataclasite in Core 210-1277A-2R has the lowest NRM intensity (~0.02–0.3 A/m), contrasting with stronger intensities in relatively fresh aphyric basalt in Cores 1R, 3R, and 5R (~1–4 A/m), gabbro at the base of Core 4R and in the lower part of Core 5R (0.2–0.5 A/m), and serpentinite in Core 9R (1–9 A/m). The basalts appear to record a stable component of magnetization with normal inclinations (~45°). The green gabbro cataclasite, on the other hand, displayed variable inclinations (from positive shallow to negative shallow). Gabbros and adjacent sediments have the same stable inclination values (~40°), similar to those of the basalt.
The serpentinized peridotites in different parts of long, coherent core pieces in Core 210-1277A-9R showed ChRM inclinations that cluster around a mean of 40°, generally in agreement with inclinations in the basalts and gabbros. Because NRM intensities of the serpentinized peridotites are on the order of 1–9 A/m, they could contribute significantly to the regional magnetic anomaly. There is a distinct difference between gabbro, with relatively low magnetic susceptibility and high median destructive field (MDF), and serpentinite, with high susceptibility and low MDF. This difference may be explained by either the finer grain size of the gabbros or their higher degree of low-temperature alteration, or both.
Because of time constraints at the end of the leg, no shipboard geochemical analyses were conducted on rocks from Site 1277.
Evaluation of physical properties at Site 1277 included nondestructive measurements of density, porosity, velocity, and thermal conductivity. Porosity varied between 2% and 25%, bulk density varied between 2.3 and 2.8 g/cm3, and grain density varied between 2.60 and 3.00 g/cm3. Compressional wave velocity ranged from 3300 to 6300 m/s. Velocity is lowest (~3270 m/s) in highly altered and veined breccias (Section 210-1277A-4R-2), and it is highest (6325 m/s) in a coarse-grained gabbro (Section 5R-3). Velocity in the serpentinized peridotites ranged from ~3300 to 4700 m/s. Thermal conductivity ranged from 1.6 to 2.25 W/(m·K), with no obvious trend in the values.