Petrology b The study of the properties of

Petrology b The study of the properties of rocks and the processes behind their formation b Recognition and description of rocks b Interpretation of their origin and history

Instructor b Michael F. Sheridan b email: • mfs@geology. buffalo. edu b Homepage: • http: //www. eng. buffalo. edu/~mfs b Office hours: • We & Th 1: 00 -2: 00 PM

Fundamentals b Classification b Changing States (Equilibrium) b Plate Tectonics & Petrology b Thermodynamics b Kinetics

Magmatic Rock Bodies b Study of rocks in hand sample b Descriptive Petrochemistry b Origin and evolution of magmas b Interpretative Petrochemistry

Study of rocks in hand sample b Fabric b Rock forming minerals b Classification

Fabric b Phaneritic b Aphanitic b Glassy b Clastic

Sequence of mineral formation b Degree of perfection of form b Inclusion within other minerals b Chemical zonation b Signs of deformation b Secondary growth b Alteration to secondary minerals

Rock forming minerals b Feldspars b Quartz b Pyroxenes b Olivines b Amphiboles b Micas b Feldspathoids

Classification b Leucocratic b Felsic b Silicic b Mafic b Ultramafic

Rock Suites b Mafic and ultramafic b Calc-alkaline b Highly alkaline

Descriptive Petrochemistry b Chemical analyses • Major elements • Trace elements b Relation of chemistry to mineralogy

Chemical classification b Silica concentration • Acid >66% • Intermediate 52 -66% • Basic 45 -52% • Ultrabasic <45%

Silica saturation b Oversaturated • compatible with quartz b Saturated • Neither undersaturated minerals nor quartz b Undersaturated • undersaturated minerals

Alkali/Aluminum saturation b Relative to feldspar composition • Na. Al. Si 3 O 8 b Peralkaline b Peraluminous b Calc-alkaline

CIPW norm b Definition b How calculated b Use in classification

Chemistry of rocks b Major elements b Trace elements b CIPW norm

From Mineral Composition to Rock Composition b Determine the minerals present b estimate their abundance b Calculate the rock composition using proper weightings

Interpretative Petrochemistry b Models of crystallization b Concepts of magma movement b Secondary alteration

Ultramafic rock bodies b Petrography of gabbroic and ultramafic rocks b Nature of Plutons b Oceanic subalkaline basaltic to ultramafic associations b Ophiolites

Petrography of gabbroic and ultramafic rocks b General • phaneritic grain size • may be nearly monomineralic – Pyroxene – Olivine – Plagioclase b Fabric • • Slow sequential growth Hypidiomorphic granular

Petrography of gabbroic and ultramafic rocks b Classification b Alteration • deuteric and hydrothermal alteration • Serpentine • Secondary iron oxide • brucite & talc

Nature of Gabbroic Plutons b Dikes, sills, and plugs b Layered intrusions b Slow shallow cooling of basaltic magma