The two igneous units recovered from Transect EG66 are significantly different. Unit I-1 in Holes SEG01A and SEG01B is a fine-grained, plagioclase-olivine-augite phyric to glomerocrystic basalt interpreted to be a lava flow. Typical glomerocrystic textures involving interlocking euhedral to subhedral, 1–3 mm plagioclase and clinopyroxene are shown in Figure F3. Plagioclase and clinopyroxene phenocrysts compose 10% and 6%, respectively, of the rock based on point-counting, whereas olivine is completely replaced by iddingsite and lizardite. Oscillatory zoning is common in plagioclase. The groundmass is composed of 55% plagioclase, 24% clinopyroxene, and 6% Fe-Ti oxide minerals. Fe-Ti oxides are commonly found associated with overgrowing or partially overgrowing glomerocrysts. Unit I-1 is massive with sparse vesicles and amygdules, suggesting that the core sample is from a flow interior.
Unit I-1 in Hole SEG02A is an aphyric to sparsely plagioclase phyric basalt with a fine-grained groundmass of plagioclase (50%), clinopyroxene (27%), and Fe-Ti oxides (3%). The unit is massive with sparse ellipsoidal vesicles from 1 to 3 mm in diameter and partially filled by secondary material. Unit I-1 in Hole SEG02A also lacks distinguishing features related to primary emplacement, except for weak decimeter-scale banding oriented approximately normal to the core axis and possibly originating by flow. The highly fractured character of this unit coupled with abundant slickensides on fracture surfaces suggests that drilling penetrated a shallow fault zone.