CEE 437 CEE 437 Rocks!Rocks!

Thomas DoeThomas Doe

Silica TetrahedronSilica Tetrahedron

Feldspar StructureFeldspar Structure

All tetrahedra All tetrahedra corners occupiedcorners occupied

Both Si and Al Both Si and Al tetrahedratetrahedra

Cations in voids of Cations in voids of structure to structure to balance chargebalance charge

(a)

(b)

diad axis

T1T1 T1

T1T1 T1

T2 T2 T2

T2T2T2

b

Feldspar CompositionsFeldspar Compositions

aa

KAlSi3O8

NaAlSi3O8 albite

CaAl2Si2O8 anorthite

Plagioclase feldspars

sanidineorthoclasemicrocline

Clay MineralsClay Minerals

Extremely Important Mineral GroupExtremely Important Mineral Group SealsSeals StabilityStability Pore pressurePore pressure Chemical interactionChemical interaction SwellingSwelling SlakingSlaking

Confusion as both “Size” and Confusion as both “Size” and “Mineral” Classification“Mineral” Classification

Clay SourcesClay Sources

WeatheringWeathering Hydrothermal AlterationHydrothermal Alteration DepositionDeposition Clay TransformationsClay Transformations

Feldspar Feldspar Illite, Kaolinite Illite, Kaolinite Ferro-Magnesian Ferro-Magnesian Chlorite Chlorite Volcanics (alkaline conditions) Volcanics (alkaline conditions) Smectite Smectite Volcanics (acidic conditions) Volcanics (acidic conditions) Kaolinite Kaolinite

Bentonite: plastic, highly swellingBentonite: plastic, highly swelling

Clay UnitsClay Units

From West, Geology Applied to Engineering, Prentice Hall, 1995)

Two and Three-Layer Clay Two and Three-Layer Clay StructureStructure

From West, Geology Applied to Engineering, Prentice Hall, 1995)

Mixed Layer ClaysMixed Layer Clays

From West, Geology Applied to Engineering, Prentice Hall, 1995)

Clay Viewed from Clay Viewed from Electron MicroscopeElectron Microscope

Northwest Igneous and Northwest Igneous and Metamorphic RocksMetamorphic Rocks

Columbia River Basalts

(miocene)

Snake River Basalts

(pliocene)

Yellowstone Region Acidic Volcanics (Pleistocene to

recent)

Cascade Volcanoes (recent)

Recent Basaltic Volcanism (Newberry Crater)

Cascade Batholiths (Felsic, Cret-Miocene)

Geologic Settings for Geologic Settings for Igneous RocksIgneous Rocks

OceanicOceanic Hi Fe, Mg, Ca, low SiHi Fe, Mg, Ca, low Si basalt, gabbrobasalt, gabbro

Continental Continental Hi Si, Na, KHi Si, Na, K granite, rhyolite, andesitegranite, rhyolite, andesite

Igneous OriginsIgneous Origins

IntrusiveIntrusive Batholithic or plutonic: phaneriticBatholithic or plutonic: phaneritic Dikes or sills that chill rapidly: aphaniticDikes or sills that chill rapidly: aphanitic

ExtrusiveExtrusive deposition as melt (lava)deposition as melt (lava) pyroclasticpyroclastic

tufftuff tephratephra pyroclastic flowspyroclastic flows

Identifying Igneous Identifying Igneous RocksRocks

ChemistryChemistry Acidic: Basic (more Si, less Si)Acidic: Basic (more Si, less Si)

TextureTexture Aphanitic: crystals not visibleAphanitic: crystals not visible Phaneritic: made of visible crystal Phaneritic: made of visible crystal

componentscomponents Porphyritic: Larger crustals in aphanitic Porphyritic: Larger crustals in aphanitic

or phaneritic ground massor phaneritic ground mass

Igneous Rock Igneous Rock ClassificationClassification

SERPENTINITE

Acidic, Felsic Basic, Mafic Ultramafic

Magma Generation on Magma Generation on Continental MarginsContinental Margins

Magma Generation in Magma Generation in Convergent Continental Convergent Continental

Plate MarginsPlate Margins

ExtrusivesExtrusives

Viscosity varies with Si and water Viscosity varies with Si and water contentcontent Basalt — low viscosityBasalt — low viscosity Rhyolite — high viscosityRhyolite — high viscosity

Rhyolite flows relatively unusual as Rhyolite flows relatively unusual as rhyolite does not flow wellrhyolite does not flow well ExplosiveExplosive Tuffs, pyroclasticsTuffs, pyroclastics

Volcano TypesVolcano Types

Basaltic: low viscosity — Hawaii, Columbia Plateau

Andesitic/Rhyolitic

Structures of Basalt Structures of Basalt FlowsFlows

Lava TubesLava Tubes Flow StratigraphyFlow Stratigraphy

collonadecollonade entablatureentablature flow top breccia/scoriaflow top breccia/scoria

Hawaii Basalt FlowsHawaii Basalt Flows

Basalt Flow StructuresBasalt Flow Structures

Eruptions of Acid-Rock Eruptions of Acid-Rock VolcanoesVolcanoes

Rhyolite DomeRhyolite Dome

CalderaCaldera

Mt. St. Helen’s Blast Mt. St. Helen’s Blast ZoneZone

Mt. Mazama Ash Mt. Mazama Ash DistributionDistribution

Basic Metamorphic Basic Metamorphic TypesTypes

Quartz Sandstone Quartz Sandstone Quartzite Quartzite Limestone, Dolomite Limestone, Dolomite Marble Marble Shale Shale

Slate — cleavage, no visible xl’sSlate — cleavage, no visible xl’s Phyllite — foliation, mica sheen but xl’s not Phyllite — foliation, mica sheen but xl’s not

visiblevisible Schist — clear foliation, visible micaSchist — clear foliation, visible mica Gneiss — like granite but with Gneiss — like granite but with

foliation/gneissosityfoliation/gneissosity Basalt Basalt greenschist, amphibolite greenschist, amphibolite

Non-foliated Non-foliated Metamorphic RocksMetamorphic Rocks

Sandstone —> QuartziteSandstone —> Quartzite Limestone —> MarbleLimestone —> Marble Dolomite —> Dolomitic MarbleDolomite —> Dolomitic Marble

Foliated Metamorphic Foliated Metamorphic RocksRocks

Shale/MudstoneShale/Mudstone SlateSlate Phyllite (Greek for leaves e.g. phyllo Phyllite (Greek for leaves e.g. phyllo

dough)dough) SchistSchist GneissGneiss

Origin of Foliation Origin of Foliation (gneissosity, schistosity)(gneissosity, schistosity)

Engineering PropertiesEngineering Properties

Anisotropy of strength and elastic Anisotropy of strength and elastic propertiesproperties

Preferred failure on foliationPreferred failure on foliation

SlateSlate

PhyllitePhyllite

SchistSchist

Chlorite SchistChlorite Schist

GneissGneiss

Banded GneissBanded Gneiss

Metamorphic GradeMetamorphic Grade

Subduction-Zone Subduction-Zone MetamorphismMetamorphism

Metamorphism at Metamorphism at Continental CollisionsContinental Collisions

Contact MetamorphismContact Metamorphism

Sedimentary RocksSedimentary Rocks

Clastics, Siliciclastics, and Clastics, Siliciclastics, and EvaporitesEvaporites

Clastic rocks, depositional medium, Clastic rocks, depositional medium, and energyand energy

Diagenesis — chemical changes Diagenesis — chemical changes after depositionafter deposition

Rock CycleRock Cycle

Metamorphic Rocks

Sedimentary Rocks

Igneous Rocks

Sediments

Lithification

Magma

Weathering, Erosion

Burial, metamorphism, recrystallization

Melting

Crystallization at depth or extrusion at surface

Burial, metamorphism, recrystallization

Sediment SourcesSediment Sources

Clastic Sedimentary Clastic Sedimentary RocksRocks

Clastic — broken like iconoclast)Clastic — broken like iconoclast) Often referred to as Siliciclastics as Often referred to as Siliciclastics as

having Si based rock forming mineralshaving Si based rock forming minerals Based on grain size and to a lesser Based on grain size and to a lesser

extent compositionextent composition Grain size related to energy of Grain size related to energy of

depositional environmentdepositional environment Relationship of medium velocity to Relationship of medium velocity to

maximum grain size)maximum grain size)

Clastic Sedimentary Clastic Sedimentary RocksRocks

Clay, muds Clay, muds shales, mudstones, shales, mudstones, claystones (difference based on claystones (difference based on fissility)fissility)

Silts Silts siltstones siltstones Sands Sands sandstones sandstones Gravels Gravels Conglomerates (Breccia if Conglomerates (Breccia if

angular, breccia may also be a term angular, breccia may also be a term for tectonically fragmented rock) for tectonically fragmented rock)

Weathering CycleWeathering Cycle

Clastic SedimentsClastic Sediments

Clay MineralsClay Minerals

Sheets of linked silica tetrahedra sandwiching Sheets of linked silica tetrahedra sandwiching octahedral layers of gibbsite composition, octahedral layers of gibbsite composition, AlAl22(OH)(OH)66, or brucite Mg, or brucite Mg33(OH)(OH)66

Major Clay GroupsMajor Clay Groups kaolinite: single gibbsite layerkaolinite: single gibbsite layer montmorillonite:weak water bonding between montmorillonite:weak water bonding between

layers, moderated by Ca, Na, or K (near-shore layers, moderated by Ca, Na, or K (near-shore environments)environments)

illite: K bonds between layers (off-shore illite: K bonds between layers (off-shore environments)environments)

bentonite: highly expansive, volcanic-derived, Na-bentonite: highly expansive, volcanic-derived, Na-rich montmorilloniterich montmorillonite

Clay StructureClay Structure

Clay Structure Cont’d.Clay Structure Cont’d.

Kaolinite

Illite

Montmorillonite

LithificationLithification

CementationCementation deposition of a material different from clastsdeposition of a material different from clasts

CrystallizationCrystallization crystal growth on clasts to fill pore spacecrystal growth on clasts to fill pore space

CompactionCompaction DiagenesisDiagenesis

Early post-depositional chemical Early post-depositional chemical transformation of sediments, e.g. calcite to transformation of sediments, e.g. calcite to dolomitedolomite

CarbonatesCarbonates

Generally like siliciclastics — Generally like siliciclastics — carbonate muds, sands, etc.carbonate muds, sands, etc.

Often deposited in reefsOften deposited in reefs Major portion of world oil depositsMajor portion of world oil deposits Properties depend strongly on post-Properties depend strongly on post-

depositional pore chemistrydepositional pore chemistry CementationCementation DissolutionDissolution

Karst topography, cave formationKarst topography, cave formation

Carbonate EnvironmentsCarbonate Environments

EvaporitesEvaporites

Rock salt (NaCl), Gypsum-Anhydrite Rock salt (NaCl), Gypsum-Anhydrite (CaSO(CaSO44), Sylvite (KCl)), Sylvite (KCl)

Deposition in regions where Deposition in regions where evaporation exceeds rechargeevaporation exceeds recharge desert lakesdesert lakes restricted seas (Mediterranean)restricted seas (Mediterranean) lagoons, back-reef areaslagoons, back-reef areas

Subject to flow and diapirismSubject to flow and diapirism

Other Sedimentary RocksOther Sedimentary Rocks

Chert: finely crystalline silicaChert: finely crystalline silica as replacement/diagenetic nodulesas replacement/diagenetic nodules as bedded material from silica-shelled as bedded material from silica-shelled

biotabiota CoalCoal

Derived from vegetationDerived from vegetation Banded Iron FormationBanded Iron Formation

Likely bacteria derived, mainly Pre-Likely bacteria derived, mainly Pre-CambrianCambrian

Sedimentary Rocks and Sedimentary Rocks and Rock PropertiesRock Properties

Properties for a given geologic Properties for a given geologic description vary wildly based on description vary wildly based on cementation, porosity and other cementation, porosity and other diagenetic factors.diagenetic factors.

Properties can be strongly Properties can be strongly anisotropic and heterogeneous anisotropic and heterogeneous based on beddingbased on bedding

Depositional Depositional EnvironmentsEnvironments

Synchroneity of deposition of different Synchroneity of deposition of different rock typesrock types

Sedimentary faciesSedimentary facies A rock unit is not everywhere the same age: A rock unit is not everywhere the same age:

Bright Angel ShaleBright Angel Shale Related to energy of environmentRelated to energy of environment

(example channels and banks in fluvial (example channels and banks in fluvial systems)systems)

Energy related to topography, climate, Energy related to topography, climate, and tectonic activityand tectonic activity

Sediment SortingSediment Sorting

Sedimentary Structure — Sedimentary Structure — Cross BeddingCross Bedding

Fluvial and Lacustrine Fluvial and Lacustrine EnvironmentsEnvironments

FluvialFluvial ChannelizationChannelization Complex and close interrelationship of fine Complex and close interrelationship of fine

and course sedimentsand course sediments Challenge for characterization due to high Challenge for characterization due to high

variabilityvariability Special examples: glacial environmentsSpecial examples: glacial environments

LacustrineLacustrine Deltaic deposits at margins, finer materials in Deltaic deposits at margins, finer materials in

lake bedslake beds

Deltaic EnvironmentsDeltaic Environments

Variability based on proximity to Variability based on proximity to sourcesource

Stratigraphy effected by Stratigraphy effected by progradationprogradation

Deltaic Development and Deltaic Development and Sedimentary FaciesSedimentary Facies

Continental Slope Continental Slope EnvironmentsEnvironments

Turbidites and turbidity currentsTurbidites and turbidity currents Graded beddingGraded bedding

poor sortingpoor sorting vertical zonation with fining upwardsvertical zonation with fining upwards

Turbidites and Turbidity Turbidites and Turbidity CurrentsCurrents

Metamorphic Metamorphic ClassificationClassification

Original MaterialOriginal Material sandstone, limestone, shale, basalt)sandstone, limestone, shale, basalt)

Metamorphic Grade (Temperature, Metamorphic Grade (Temperature, Pressure)Pressure)

Source of Metamorphism (Regional, Source of Metamorphism (Regional, Contact)Contact)

K. Troost

Glacial EnvironmentsGlacial Environments