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The Geological Society of America (GSA)South-Central Section–40th Annual Meeting (6–7 March 2006)CRYSTALLIZATION DYNAMICS OF THE MT. SHERIDAN ROOSEVELT GABBRO, WICHITA MOUNTAINS, OKLAHOMAThree texturally distinct rock types in the Mt. Sheridan Roosevelt Gabbro suggest distinct modes of crystallization. The vertically stratified pluton is composed of layered gabbro in the lower elevations (the growing cumulate pile) which is overlain by homogenous quartz gabbro (the active magma chamber). Felsic pegmatite is present, and locally abundant, throughout the pluton (see McEllen et al., this session). These three rock types, though texturally distinct, are genetically linked during crystallization of the magma chamber. Reverse zoning in plagioclase and the repetition of olivine-bearing and quartz-bearing rocks vertically within the pluton indicates the magma chamber received multiple mafic replenishments during crystallization (Lasco et al. 2004). Isolation and extreme fractionation of the mafic magma could produce a felsic melt that, if kept isolated from the active chamber, would be preserved as pegmatite.
I apologize for my first post being a question and not something of value, but I'm pretty desperate. My grandfather gave me this rock when I was a small child, and I've never known what it was. I live in Oklahoma, but the rock could have been from anywhere. Unfortunately, I don't have the ability to ask exactly where it came from.It is pretty hard, is mainly black, but has large green fleck throughout.Any help is greatly appreciated. Greg
Is there any chance saamsuun's specimen is a breccia?