Igneous units were recovered from seven holes representing a total of 3.46 m of core. The longest units were recovered from Holes SEG10B (1.02 m) and SEG05B (1.04 m). The following synthesis is based on the observations from the igneous units ("I" units), with additional information drawn from basaltic clast units ("C" units) judged to represent basement. Information obtained from inspection of five thin sections prepared from these igneous units is also incorporated.
The contact between the sediment cover and the underlying basaltic basement is not preserved in any of the holes drilled from Transect EG68. The igneous units have irregular, blocky, fractured, and weathered surfaces and massive flow morphologies with few internal structural features. In most cores, vesicles are irregularly distributed or concentrated in patches. Unit I-1 in Hole SEG10B was the only core displaying flow banding (perpendicular to the core axis) defined by variations in the proportion of mesostasis, elongated vesicles, and planar orientation of groundmass plagioclase laths.
Igneous units from Transect EG68 range from aphyric basalt (Holes SEG04A and SEG10B) to moderately to highly plagioclase-olivine-clinopyroxene phyric basalts (Holes SEG05B and SEG12A), sparsely to highly plagioclase-clinopyroxene phyric basalts (Holes SEG4B and SEG11A), and moderately plagioclase-clinopyroxene-olivine phyric basalt (Hole SEG13C). Plagioclase typically occurs in a glomerocrystic intergrowth with or without clinopyroxene (Fig. F5A). Euhedral olivine with inclusions of chromian spinel occur in some samples (Fig. F5B).
In general, the lavas are fine grained, and seriate textures are most common (Fig. F5C). In one sample (Unit I-1, Hole SEG10B), a trachytic texture is evident. The groundmass is typically intergranular to intersertal (Fig. F5C) and composed of an assemblage of plagioclase, clinopyroxene, oxides, mesostasis (altered to palagonite), and rarely olivine. Thin section examination usually confirmed the visual core description. A common exception was the recognition of small amounts of olivine in thin section (Fig. F5B); however, this was not reported during the visual core descriptions.
Cored basalt clasts were recovered from a number of holes. The petrography of these clasts varies widely from aphyric (Holes SEG08A, SEG10A, SEG13A, and SEG18A) to sparsely olivine phyric (Hole SEG14A), sparsely plagioclase phyric (Holes SEG07A and SEG09B), sparsely clinopyroxene phyric (Hole SEG04A), moderately clinopyroxene-plagioclase phyric (Holes SEG16A and SEG19B), sparsely to highly plagioclase-clinopyroxene phyric (Holes SEG06A, SEG09B, SEG11C, and SEG19A), and sparsely to highly plagioclase-clinopyroxene-olivine phyric (Holes SEG05D and SEG13C). Such a large variation in phenocryst assemblages is difficult to reconcile with the more restricted assemblage reported for in situ basement (plagioclase-clinopyroxene and plagioclase-clinopyroxene-olivine basalt) from the outer area of Transect EG68. This suggests that most of the cored clasts probably are not samples of local basement. There are, however, two noteworthy exceptions: (1) clasts from Hole SEG05D (Unit C-1) that closely resemble the highly plagioclase-olivine-clinopyroxene phyric basalt of Unit I-1 in Hole SEG05B and (2) clasts of sparsely plagioclase-clinopyroxene-olivine phyric basalt recovered initially from Hole SEG13C that are practically indistinguishable from the moderately plagioclase-clinopyroxene-olivine phyric basalt core from the basement of the same hole.
Vesicles are unfilled or partially to completely filled by secondary minerals, including gray, green, and blue-gray clays, quartz, carbonate, and zeolite. Zoning in the vesicle fillings is commonly observed (Fig. F5C). Fractures are typically lined or filled by clay and carbonate. The phenocryst assemblages are variably altered to clay; however, often the groundmass appears relatively unaltered (Fig. F5A, F5C).