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doi:10.2204/iodp.proc.345.107.2014 Igneous petrologyCoring in Hole U1415G recovered five different igneous lithologic intervals from lithologic Unit I (surficial rubble) at Site U1415 (Fig. F1). GabbroGabbro defines two intervals (Intervals 2 and 4) from Unit I in Hole U1415G. In general, the gabbro is medium-grained equigranular rock. Modally, the gabbro consists of plagioclase (29%–50%) and clinopyroxene (50%–70%), with trace amounts of olivine, orthopyroxene, and oxide. Plagioclase is medium grained and subhedral to euhedral with a tabular-shaped habit. Clinopyroxene is medium grained and anhedral with an interstitial to oikocrystic habit. Clinopyroxene oikocryst-bearing troctoliteClinopyroxene oikocryst-bearing troctolite occurs as a single piece recovered from Unit I in Interval 3 (Section 345-U1415G-1R-1) (Fig. F2). The clinopyroxene oikocryst-bearing troctolite is medium-grained equigranular rock, with well-developed magmatic modal layering and foliation. The strong foliation is formed by the alignment of tabular plagioclase. Modally, the rock consists of olivine (20%), plagioclase (76%), and clinopyroxene (4%), with trace oxide minerals. Olivine is fine grained and subhedral to anhedral with an irregular, elongate amoeboid habit. Despite their irregular habit, the long axes of the olivines are subparallel to the foliation, defined by the plagioclase in the troctolitic matrix (Fig. F3). Plagioclase is fine grained and subhedral to euhedral with a tabular habit. Overall, plagioclase shows no obvious zoning. Clinopyroxene occurs as large anhedral oikocrysts (as large as 15 mm) that contain a distinctive population of subhedral to euhedral, lath-shaped, partially resorbed plagioclase chadacrysts (Fig. F2). The plagioclase chadacrysts have random orientations within the oikocryst in sharp contrast to the surrounding strongly foliated plagioclase fabric. Olivine is conspicuous by its absence as a chadacryst in the oikocrysts. Olivine gabbroOlivine gabbro defines one interval from Unit I. The olivine gabbro is a medium-grained equigranular granular rock. Modally, the olivine gabbro consists of olivine (10%), plagioclase (60%), and clinopyroxene (30%), with trace amounts of oxide. Olivine is fine grained and euhedral to subhedral with a subequant habit. Plagioclase is medium grained and subhedral to euhedral with a lath-shaped habit. Clinopyroxene is medium to coarse grained and anhedral with an oikocrystic habit. Orthopyroxene-bearing olivine gabbroOrthopyroxene-bearing olivine gabbro defines Interval 4 in Unit I. The orthopyroxene-bearing olivine gabbro is a medium-grained equigranular granular rock. Modally, the orthopyroxene-bearing olivine gabbro consists of olivine (10%), plagioclase (70%), clinopyroxene (17%), and orthopyroxene (3%), with trace amounts of oxide. Olivine is fine grained and euhedral to subhedral with a subequant habit. Plagioclase is medium grained and euhedral to subhedral with a tabular habit. Clinopyroxene is medium grained and anhedral with an irregular interstitial habit. Orthopyroxene is subhedral with a prismatic habit. Orthopyroxene-bearing gabbroOrthopyroxene-bearing gabbro defines Interval 5 in Unit I. The orthopyroxene-bearing gabbro is a medium-grained equigranular granular rock displaying a strong magmatic foliation (Fig. F4). Modally, the orthopyroxene-bearing gabbro consists of plagioclase (60%), clinopyroxene (36%), and orthopyroxene (4%). Plagioclase is medium grained and subhedral with a tabular habit defining a magmatic foliation. Clinopyroxene is medium grained and subhedral to anhedral with a prismatic habit. Orthopyroxene is subhedral to euhedral with a prismatic to poikilitic habit. |
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