| Text Description: |
Approximately 5-10’ thick bifurcating dike trending N85°W and cutting silicic material from Dome C at Site 7 . Fine-grained, vesicular, hypocrystalline, intersertal, intergranular, porphyritic to glomeroporphyritic with a matrix of brown glass, plagioclase (An33 - An57), clinopyroxene and opaque. Many vesicles have dark brown, glassy rinds with plagioclase needles. A few vesicles are lined with yellowish alteration. Plagioclase phenocrysts (An30 - An54) have two populations: 3.7-0.2 mm and all large grains have sieve textured cores with thin overgrowth rims that are oscillatory zoned, and a few have poikilitic orthopyroxene; 0.2-0.05 mm, thin euhedral to subhedral laths, some with undulatory extinction. Orthopyroxene phenocrysts are 1.1-0.2 mm, and a few have thin clinopyroxene rims or sieve to spongy textured zones. Clinopyroxene phenocrysts are up to 1.05 mm and are frequently twinned; grains 0.1 - 0.05 mm in length are needle-like. Opaque phenocrysts are up to 0.08 mm. |