| Text Description: |
Approximately 50’ thick flow with a glassy top surface at the very top of South Pass. Fine grained, vesicular, hypocrystalline, intersertal, seriate porphyritic with a matrix of brown glass, opaque, plagioclase, orthopyroxene and clinopyroxene. Plagioclase phenocrysts (An48 - An63) are up to 4.32 mm and some have normal zoning, occasionally there is oscillatory zoning; melt inclusions are common in larger grains. Olivine phenocrysts are up to 0.5 mm and some have coronas of small orthopyroxene crystals. Orthopyroxene phenocrysts are up to 0.7 mm. May be some clinopyroxene? present. |