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 b Homepage: b Office hours: We & Th 1:00-2:00 PMWe & 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 elementsMajor elements Trace elementsTrace elements b Relation of chemistry to mineralogy

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

Silica saturation b Oversaturated compatible with quartzcompatible with quartz b Saturated Neither undersaturated minerals nor quartzNeither undersaturated minerals nor quartz b Undersaturated undersaturated mineralsundersaturated minerals

Alkali/Aluminum saturation b Relative to feldspar composition NaAlSi 3 O 8NaAlSi 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 sizephaneritic grain size may be nearly monomineralicmay be nearly monomineralic –Pyroxene –Olivine –Plagioclase b Fabric Slow sequential growthSlow sequential growth Hypidiomorphic granularHypidiomorphic granular

Petrography of gabbroic and ultramafic rocks b Classification b Alteration deuteric and hydrothermal alterationdeuteric and hydrothermal alteration SerpentineSerpentine Secondary iron oxideSecondary iron oxide brucite & talcbrucite & talc

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