Ultramafic Rock BodiesUltramafic Rock BodiesBest, Chapter 5Pyroxene ClassificationPyroxene ClassificationTopicsTopics• Petrography - gabbroic & ultramafic rocks• Nature of plutons• Oceanic subalkaline associations• Ophiolites (treated with basalts in GLY206)AMF DiagramsAMF Diagrams• Initial compositions• Early iron enrichment• Later alkali enrichment• Tholeiitic vs. calc-alkali trendsPetrographyPetrography•FabricPhaneritic grain-size•Slow sequential growth•Hypidiomorphic granular•Cumulate textureMineralogyMineralogy•Plagioclase •An85to An50•Pyroxene•Ortho (Hypersthene)•Clino (Augite to Pigeonite)•Olivine•Fo85to Fo30PetrographyPetrography•Classification•Pl-Ol-Px •Olivine-Opx-CpxUltramafic RocksAlterationAlteration•Deuteric and hydrothermal alteration•Serpentine•Secondary iron oxide•Brucite & talcNature of PlutonsNature of Plutons• Dikes, sills, and plugs• Layered intrusions• Slow shallow coolingCooling & CrystallizationCooling & Crystallization• Sills• Progressive fractionation• Settling at bottom• Assimilation at top• Crystallization from marginsSequence of CrystallizationSequence of Crystallization• Olivine• Clinopyroxene• Plagioclase• Fe-Ti oxides• ApatiteReaction TexturesReaction Textures• Olivine surrounded by pyroxene• Quartz surrounded by pyroxene• Write the reactionsForm of BodiesForm of Bodies• Sills• Example of Red Hill, Tasmania• Form and zonation of bodyStillwater Intrusion, MontanaStillwater Intrusion, Montana• Layering• Zonation of mineralsStillwaterStillwaterTexturesTexturesSkaergaard Intrusion, GreenlandSkaergaard Intrusion, Greenland• General form of the body• Layering of the intrusion• Mineral zonation of layers• Hydrothermal alterationSkaergaard