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Download Petrology Instructor Fundamentals Magmatic Rock Bodies Study of
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Petrology • The study of the properties of rocks and the processes behind their formation • Recognition and description of rocks • Interpretation of their origin and history Fundamentals • Classification • Changing States (Equilibrium) • Plate Tectonics & Petrology Instructor Michael F. Sheridan email: [email protected] Homepage: http://www.eng.buffalo.edu/~mfs Office hours: We & Th 1:00-2:00 PM Magmatic Rock Bodies • Study of rocks in hand sample • Descriptive Petrochemistry • Thermodynamics • Origin and evolution of magmas • Kinetics • Interpretative Petrochemistry Study of Rocks in Hand Sample • Fabric • Rock forming minerals • Classification Fabric • Phaneritic • Aphanitic • Glassy • Clastic Sequence of Mineral Formation • Degree of perfection of form • Inclusion within other minerals • Chemical zonation • Signs of deformation • Secondary growth • Alteration to secondary minerals Classification • Leucocratic Rock forming minerals • • • • • • • Feldspars Quartz Pyroxenes Olivines Amphiboles Micas Feldspathoids Rock Suites • Mafic and ultramafic • Felsic • Silicic • Mafic • Calc-alkaline • Highly alkaline • Ultramafic Descriptive Petrochemistry • Chemical analyses – Major elements – Trace elements • Relation of chemistry to mineralogy Chemical classification • Silica concentration – Acid >66% – Intermediate 52-66% – Basic 45-52% – Ultrabasic <45% Silica Saturation • Oversaturated – compatible with quartz • Saturated – Neither undersaturated minerals nor quartz • Undersaturated – undersaturated minerals CIPW norm • Relative to feldspar composition NaAlSi3O8 • Peralkaline • Peraluminous • Calc-alkaline Chemistry of Rocks • Definition • Major elements • How calculated • Trace elements • Use in classification • CIPW norm From Mineral Composition to Rock Composition • Determine the minerals present • Estimate their abundance • Calculate the rock composition using proper weightings Alkali/aluminum Saturation Fundamentals • Classification • Changing States (Equilibrium) • Plate Tectonics & Petrology • Thermodynamics • Kinetics Magma to Rock Concepts • Magma • Components – liquid – hot – chills to glass – End member chemical species • Phases • Rock – generally minerals in rocks – solid – cool – consists of crystals Compatible Elements • Ionic radius and charge similar to major • States – solid, liquid, and gas Major Elements in Rocks Coordination 4 element • Fractionate with the major elements • Example – Ba follows Ca by substitution in plagioclase Interpretative Petrochemistry • Models of crystallization • Concepts of magma movement valence 4 4 TiO2 4 4 or 6 Al2O3 3 4 or 6 Fe2O3 3 6 6 6 8 or 12 FeO MgO CaO Na2O 2 2 2 1 8 or 12 K 2O 1 Ultramafic Rock Bodies • Petrography of gabbroic and ultramafic rocks • Nature of plutons • Oceanic subalkaline basaltic to ultramafic associations • Secondary alteration element SiO2 • Ophiolites Petrography of gabbroic and ultramafic rocks • General – Phaneritic grain size – May be nearly monomineralic • Pyroxene • Olivine • Plagioclase • Fabric – Slow sequential growth – Hypidiomorphic granular Nature of Gabbroic Plutons • Dikes, sills, and plugs • Layered intrusions • Slow shallow cooling of basaltic magma Petrography of Gabbroic and Ultramafic Rocks • Classification • Alteration – Deuteric and hydrothermal alteration – Serpentine – Secondary iron oxide – Brucite & talc
