PetrologyPetrology

The study of the properties of rocks and the The study of the properties of rocks and the

processes behind their formationprocesses behind their formation

Recognition and description of rocksRecognition and description of rocks

Interpretation of their origin and historyInterpretation of their origin and history

InstructorInstructor

Michael F. SheridanMichael F. Sheridan email:email:

• mfs@geology.buffalo.edumfs@geology.buffalo.edu

Homepage:Homepage:• http://www.eng.buffalo.edu/~mfshttp://www.eng.buffalo.edu/~mfs

Office hours:Office hours:• We & Th 1:00-2:00 PMWe & Th 1:00-2:00 PM

FundamentalsFundamentals

ClassificationClassification

Changing States (Equilibrium)Changing States (Equilibrium)

Plate Tectonics & PetrologyPlate Tectonics & Petrology

ThermodynamicsThermodynamics

KineticsKinetics

Magmatic Rock BodiesMagmatic Rock Bodies

Study of rocks in hand sampleStudy of rocks in hand sample

Descriptive PetrochemistryDescriptive Petrochemistry

Origin and evolution of magmasOrigin and evolution of magmas

Interpretative PetrochemistryInterpretative Petrochemistry

Study of rocks in hand sampleStudy of rocks in hand sample

FabricFabric

Rock forming mineralsRock forming minerals

ClassificationClassification

FabricFabric

PhaneriticPhaneritic

AphaniticAphanitic

GlassyGlassy

ClasticClastic

Sequence of mineral formationSequence of mineral formation

Degree of perfection of formDegree of perfection of form

Inclusion within other mineralsInclusion within other minerals

Chemical zonationChemical zonation

Signs of deformationSigns of deformation

Secondary growthSecondary growth

Alteration to secondary mineralsAlteration to secondary minerals

Rock forming mineralsRock forming minerals

FeldsparsFeldspars QuartzQuartz Pyroxenes Pyroxenes OlivinesOlivines AmphibolesAmphiboles MicasMicas FeldspathoidsFeldspathoids

ClassificationClassification

LeucocraticLeucocratic

FelsicFelsic

SilicicSilicic

MaficMafic

UltramaficUltramafic

Rock SuitesRock Suites

Mafic and ultramafic Mafic and ultramafic

Calc-alkalineCalc-alkaline

Highly alkalineHighly alkaline

Descriptive PetrochemistryDescriptive Petrochemistry

Chemical analysesChemical analyses

• Major elementsMajor elements

• Trace elementsTrace elements

Relation of chemistry to mineralogyRelation of chemistry to mineralogy

Chemical classificationChemical classification

Silica concentrationSilica concentration

• Acid >66%Acid >66%

• Intermediate 52-66%Intermediate 52-66%

• Basic 45-52%Basic 45-52%

• Ultrabasic <45%Ultrabasic <45%

Silica saturationSilica saturation

OversaturatedOversaturated

• compatible with quartzcompatible with quartz

SaturatedSaturated

• Neither undersaturated minerals nor quartzNeither undersaturated minerals nor quartz

UndersaturatedUndersaturated

• undersaturated mineralsundersaturated minerals

Alkali/Aluminum saturationAlkali/Aluminum saturation

Relative to feldspar compositionRelative to feldspar composition

• NaAlSiNaAlSi33OO88

PeralkalinePeralkaline

PeraluminousPeraluminous

Calc-alkalineCalc-alkaline

CIPW normCIPW norm

DefinitionDefinition

How calculatedHow calculated

Use in classificationUse in classification

Chemistry of rocksChemistry of rocks

Major elementsMajor elements

Trace elementsTrace elements

CIPW normCIPW norm

From Mineral Composition to From Mineral Composition to Rock CompositionRock Composition

Determine the minerals presentDetermine the minerals present

estimate their abundanceestimate their abundance

Calculate the rock composition using proper Calculate the rock composition using proper

weightingsweightings

Interpretative PetrochemistryInterpretative Petrochemistry

Models of crystallizationModels of crystallization

Concepts of magma movementConcepts of magma movement

Secondary alterationSecondary alteration

Ultramafic rock bodiesUltramafic rock bodies

Petrography of gabbroic and ultramafic Petrography of gabbroic and ultramafic

rocksrocks

Nature of PlutonsNature of Plutons

Oceanic subalkaline basaltic to ultramafic Oceanic subalkaline basaltic to ultramafic

associationsassociations

OphiolitesOphiolites

Petrography of gabbroic and Petrography of gabbroic and ultramafic rocksultramafic rocks

GeneralGeneral• phaneritic grain sizephaneritic grain size• may be nearly monomineralicmay be nearly monomineralic

– PyroxenePyroxene– OlivineOlivine– PlagioclasePlagioclase

FabricFabric• Slow sequential growthSlow sequential growth• Hypidiomorphic granularHypidiomorphic granular

Petrography of gabbroic and Petrography of gabbroic and ultramafic rocksultramafic rocks

ClassificationClassification

AlterationAlteration

• deuteric and hydrothermal alterationdeuteric and hydrothermal alteration

• SerpentineSerpentine

• Secondary iron oxideSecondary iron oxide

• brucite & talcbrucite & talc

Nature of Gabbroic PlutonsNature of Gabbroic Plutons

Dikes, sills, and plugsDikes, sills, and plugs

Layered intrusionsLayered intrusions

Slow shallow cooling of basaltic magmaSlow shallow cooling of basaltic magma