Hole 1163A was rotary cored into igneous basement from 161 to 208.1 mbsf, and we recovered 15.7 m of core, which is 33.3% recovery (Cores 187-1163A-2R through 11R). Lavas from this hole were assigned to two lithologic units. Unit 1 (Section 187-1163A-2R-1 through Section 3R-1 [Piece 14]) is a medium gray, moderately plagioclase-olivine phyric basalt. Unit 2 (Sections 187-1163A-3R-1 [Piece 15] through 11R-2) is a medium gray aphyric basalt. We interpret this hole as having sampled intact pillow lavas, based on the high percentage of pieces with arcuate chilled margins (57 of 265 basalt pieces, equal to 21.5%) (Fig. F1) and on the presence of radial fractures. Pillows from Unit 2 are larger than most pillows encountered earlier on this leg, based on the lengths of individual pieces (as long as 70 cm) (Section 187-1163A-9R-1 [Piece 9]).
Ten pieces of interpillow sediment are interspersed with Unit 2 basalts in Sections 187-1163A-5R-2 through 11R-2. They range from clayey calcarenite to calcareous, clay-cemented hyaloclastite breccia (Fig. F2). Similar sediment is also present as patchy coatings up to several millimeters thick on the outsides of some basalt pieces (Fig. F3).
Unit 1 is a slightly to moderately altered (see "Alteration") medium gray, plagioclase-olivine phyric basalt. Phenocrysts include 1%-2% euhedral to subhedral equant olivine (as large as 4 mm) and 2% subhedral prismatic to tabular plagioclase (as large as 5 mm). Plagioclase is commonly twinned with some of the larger phenocrysts displaying discontinuous zoning and sieve-textured cores. Approximately 15% (in Sections 187-1163A-2R-1 and 2) to 25% (in Section 3R-1) of phenocrysts are included in glomerocrysts made up of several small (~1 mm) prismatic plagioclase and/or equant olivine grains (Fig. F4).
Eight pieces (i.e., 17% of the pieces recovered) have chilled margins ± glass/palagonite rinds ranging from <1 to 7 mm thick (e.g., Section 187-1163A-3R-1 [Piece 3]). Inward from these rinds, a zone of discrete spherulites as wide as 3 mm (e.g., Section 187-1163A-3R-1 [Piece 3]) is followed by a zone of coalesced spherulites as wide as 1.5 cm (e.g., Section 187-1163A-2R-1 [Piece 5]) before the more crystalline interior of the pillow is reached. Vesicles (<1%) are present in only three pieces (e.g., Section 187-1163A-2R-2 [Piece 3]). These are spherical, ~0.3 mm in diameter, and lined with either bluish gray cryptocrystalline silica or light gray clay.
The microcrystalline groundmass texture is intersertal, dominated by ~50% mesostasis with ~40% plagioclase and ~2% each of olivine, clinopyroxene, and opaque minerals. The plagioclase is seriate and ranges from sheaf quench textures to lath-shaped microphenocrysts as long as ~1 mm. Olivine is also seriate and ranges from quench morphologies to equant skeletal microphenocrysts as large as ~1 mm. Olivine seldom occurs as discrete crystals in the groundmass but rather in association with groundmass plagioclase. Clinopyroxene ranges from plumose quench texture in the groundmass to euhedral elongate crystals as long as 0.25 mm in miarolitic cavities. The opaque minerals are generally small (~2 µm in diameter) and spherical but may be as large as 30 µm in diameter in miarolitic cavities. Cr spinel (as large as 0.3 mm) is present in trace amounts and as inclusions in several olivine phenocrysts (e.g., Section 187-1163A-2R-2, Piece 3).
Unit 2 is a slightly to moderately altered (see "Alteration") medium gray aphyric basalt. Prismatic plagioclase phenocrysts as long as 3 mm are present throughout the unit but are rare (e.g., Section 187-1163A-5R-2 [Piece 8]). Chilled margins ± glass/palagonite rinds occur on 49 pieces (i.e., 22.4% of the pieces recovered). These rinds range from <1 to 8 mm thick (e.g., Section 187-1163A-7R-2 [Piece 1B]) and commonly contain plagioclase microlites. Inward from these rinds, a zone of discrete spherulites as wide as 4 mm (e.g., Section 187-1163A-11R-2 [Piece 4]) is followed by a zone of coalesced spherulites as wide as 5 mm (e.g., Section 187-1163A-5R-1 [Piece 3]) before the more crystalline interior is reached. The unit contains ~2% spherical vesicles, on average 0.3 mm in diameter, with variable filling (see "Alteration") and ~3% miarolitic cavities (as large as 0.8 mm across) with euhedral elongate clinopyroxene (as large as 0.1 mm).
The microcrystalline groundmass texture is intersertal, dominated by ~35% each of mesostasis and plagioclase. Plagioclase ranges from sheaf quench textured (Fig. F5) to prismatic microphenocrysts on average 0.6 mm long (but as large as 1.5 mm). Clinopyroxene (~20%) occurs mainly as plumose quench textures (Fig. F6), except in miarolitic cavities, where it forms euhedral elongate crystals as long as 0.1 mm (Fig. F7). The remaining groundmass consists of ~5% skeletal to equant olivine as large as 1 mm and <1% opaque minerals. The opaque minerals are generally small (~2 µm in diameter) and spherical. The larger, lath-shaped plagioclase and skeletal olivine (~30% of the crystals) are microphenocrysts that commonly form glomerocrysts (Fig. F8).
Ten pieces of sediment that range from pinkish tan clayey calcarenite with pink sparry calcite (e.g., Section 187-1163A-7R-1 [Piece 3]) to pinkish tan calcareous clay-cemented hyaloclastite breccia (e.g., Section 187-1163A-8R-1 [Piece 5]) were recovered along with the basalt of Unit 2. The breccia is poorly sorted with ~50% angular to subangular clasts of basaltic chilled margins and glass/palagonite rind fragments that range in size from 1 mm to 4.5 cm. The glass/palagonite fragments commonly contain microlites of plagioclase, similar to the pillow rinds in the Unit 2 aphyric basalt, suggesting that the fragments were derived from the pillows. The glass fragments also have concentric rims of palagonite, indicating that this alteration occurred within the sediment. Thirty-eight pieces of aphyric basalt from Unit 2 have patchy coatings of similar sediment, ranging in thickness from <1 mm (e.g., Section 187-1163A-7R-2 [Piece 5]) to 2.2 cm (e.g., Section 187-1163A-6R-1 [Piece 9]).