Volcanism and Other Igneous ProcessesVolcanism and Other Igneous Processes

March 8, 2010March 8, 2010

AgendaAgenda::

11

On Sunday, May 18, 1980, the largest volcanic eruption to occur in North American historic times transformed a picturesque volcano into a decapitated remnant. On this date in southwestern Washington State, Mount St. Helens erupted with tremendous force.

What happened??What happened??

•Approximately 1 kmApproximately 1 km3 3 of ash erupted.of ash erupted.•Summit decreased by 1,350 feet.Summit decreased by 1,350 feet.•Claimed 59 livesClaimed 59 lives•Ash propelled 11 miles into the atmosphere.Ash propelled 11 miles into the atmosphere.•Ash covered surrounding areas of Yakima, Tri-cities, and Ash covered surrounding areas of Yakima, Tri-cities, and northern Oregon for 3 days – Noon felt like night.northern Oregon for 3 days – Noon felt like night.• Feb. 1981- highest birth rate in Portland and surrounding Feb. 1981- highest birth rate in Portland and surrounding areas –TRUE FACTareas –TRUE FACT

Advice from the authorities: Advice from the authorities: If there is another major eruption, put your head between yourIf there is another major eruption, put your head between yourlegs and kiss your ash goodbye!legs and kiss your ash goodbye!

Mt. St. HelensMt. St. HelensMt. St. HelensMt. St. Helens

BeforeBefore AfterAfter

22

Goals for mastering this chapter:

•Describe factors that affect the nature of volcanic eruptions.

•What factors affect viscosity of magma?

•Describe the various types of materials associated with volcanic eruptions.

•Describe the major types of volcanoes recognized by volcanologists and their eruptive styles – the geomorphology.

•Describe magmatic differentiation and how it is related to Bowen’s reaction series.

•Describe various intrusive bodies associated with plutonic rocks.

•Understand the general relationship between volcanic activity and plate tectonics.

Goals for mastering this chapter:

•Describe factors that affect the nature of volcanic eruptions.

•What factors affect viscosity of magma?

•Describe the various types of materials associated with volcanic eruptions.

•Describe the major types of volcanoes recognized by volcanologists and their eruptive styles – the geomorphology.

•Describe magmatic differentiation and how it is related to Bowen’s reaction series.

•Describe various intrusive bodies associated with plutonic rocks.

•Understand the general relationship between volcanic activity and plate tectonics.

33

Why do volcanoes have different eruptiveWhy do volcanoes have different eruptivestyles???styles???Why do volcanoes have different eruptiveWhy do volcanoes have different eruptivestyles???styles???

Factors influencing eruptionsFactors influencing eruptions• dependant on the magma’s viscositydependant on the magma’s viscosity

• high viscosity –”pasty” explosivehigh viscosity –”pasty” explosive• low viscosity –”fluid” flows easily low viscosity –”fluid” flows easily

Factors influencing eruptionsFactors influencing eruptions• dependant on the magma’s viscositydependant on the magma’s viscosity

• high viscosity –”pasty” explosivehigh viscosity –”pasty” explosive• low viscosity –”fluid” flows easily low viscosity –”fluid” flows easily

Factors influencing viscosityFactors influencing viscosity• Temperature of magmaTemperature of magma

• T viscosity = fluid flowT viscosity = fluid flow• T viscosity = pasty flowT viscosity = pasty flow

Factors influencing viscosityFactors influencing viscosity• Temperature of magmaTemperature of magma

• T viscosity = fluid flowT viscosity = fluid flow• T viscosity = pasty flowT viscosity = pasty flow

• Chemical compositionChemical composition• SiOSiO22 content (high or low) content (high or low)

• Chemical compositionChemical composition• SiOSiO22 content (high or low) content (high or low)

mafic composition: (50% SiOmafic composition: (50% SiO22)=“fluid” flow)=“fluid” flowintermediate comp.: (60% SiOintermediate comp.: (60% SiO22))felsic composition: (70% SiOfelsic composition: (70% SiO22) =“pasty” flow) =“pasty” flow

mafic composition: (50% SiOmafic composition: (50% SiO22)=“fluid” flow)=“fluid” flowintermediate comp.: (60% SiOintermediate comp.: (60% SiO22))felsic composition: (70% SiOfelsic composition: (70% SiO22) =“pasty” flow) =“pasty” flow

•high viscosityhigh viscosity•high SiOhigh SiO22

•felsicfelsic•““pasty”pasty”•explosiveexplosive

•high viscosityhigh viscosity•high SiOhigh SiO22

•felsicfelsic•““pasty”pasty”•explosiveexplosive

•low viscositylow viscosity•low SiOlow SiO22

•maficmafic•““fluid”fluid”•non-explosivenon-explosive

•low viscositylow viscosity•low SiOlow SiO22

•maficmafic•““fluid”fluid”•non-explosivenon-explosive

AA

BB

44

The “buzzword” is VISCOSITYThe “buzzword” is VISCOSITYWhat is viscosity?What is viscosity?

Viscosity = how well a material flowsViscosity = how well a material flows

more viscous – flows very slowly(high viscosity)

more viscous – flows very slowly(high viscosity)

less viscous – flows quickly(low viscosity)

less viscous – flows quickly(low viscosity)

Does glass have viscosity?Does glass have viscosity?

55

Dissolved gasses – influencing the movement of magmaDissolved gasses – influencing the movement of magma(volatiles – water, CO(volatiles – water, CO22, SO, SO22….) ….) Dissolved gasses – influencing the movement of magmaDissolved gasses – influencing the movement of magma(volatiles – water, CO(volatiles – water, CO22, SO, SO22….) ….)

Silica contentSilica content and and volatilesvolatiles erupt two types of materials: erupt two types of materials:Silica contentSilica content and and volatilesvolatiles erupt two types of materials: erupt two types of materials:

magma magma lowlow in SiO in SiO22magma magma lowlow in SiO in SiO22

volatiles volatiles easilyeasily migrate upward migrate upwardvolatiles volatiles easilyeasily migrate upward migrate upward

lava flows fluidlylava flows fluidlylava flows fluidlylava flows fluidly

Gas charged lavaGas charged lavaexpands 100 times its volume expands 100 times its volume

Gas charged lavaGas charged lavaexpands 100 times its volume expands 100 times its volume

lava fountainslava fountainslava fountainslava fountains

magma high in SiO2magma high in SiO2

Volatiles migrate upwardswith difficulty

Volatiles migrate upwardswith difficulty

very explosivevery explosive

Gas chargedexpands 100 times its

volume

Gas chargedexpands 100 times its

volume

66

Magma chamberMagma chamber

volatilesvolatilesvolatilesvolatiles

15%15%15%15%

5%5%5%5%70%70%70%70%

SO2

5%5%5%5%

Carbon dioxideCarbon dioxideCarbon dioxideCarbon dioxidewater vaporwater vaporwater vaporwater vapor

sulfur dioxidesulfur dioxidesulfur dioxidesulfur dioxide> 1%> 1%> 1%> 1%

Dissolved gasses (volatiles)Dissolved gasses (volatiles)• 1-6% of total magma wt.1-6% of total magma wt.• contributes to atmospherecontributes to atmosphere

Dissolved gasses (volatiles)Dissolved gasses (volatiles)• 1-6% of total magma wt.1-6% of total magma wt.• contributes to atmospherecontributes to atmosphere

77

I I I I VOLCANOES.VOLCANOES.VOLCANOES.VOLCANOES.

I will get an A on my exams and quizzes.I will get an A on my exams and quizzes.

Discuss with a friend:Discuss with a friend:

1.1.What factors affect viscosity?What factors affect viscosity?

2. How does silica content (SiO2. How does silica content (SiO22) influence) influence the consistency of magma?the consistency of magma?

3.3.Name various volatiles that are typically Name various volatiles that are typically emitted from a volcanic eruption.emitted from a volcanic eruption.

88

PahoehoePahoehoePahoehoePahoehoe AaAaAaAa

Types of Basaltic Lava FlowsTypes of Basaltic Lava Flows(low silica (SiO(low silica (SiO22) content)) content)

Types of Basaltic Lava FlowsTypes of Basaltic Lava Flows(low silica (SiO(low silica (SiO22) content)) content)

• very fluid, thin, very fluid, thin, broad sheetsbroad sheets

• flows 10-300 km/hrflows 10-300 km/hr (30-900 ft/hr)(30-900 ft/hr)

•high volatile gas contenthigh volatile gas content

• smooth “skin,” ropeysmooth “skin,” ropey type flowtype flow

• very fluid, thin, very fluid, thin, broad sheetsbroad sheets

• flows 10-300 km/hrflows 10-300 km/hr (30-900 ft/hr)(30-900 ft/hr)

•high volatile gas contenthigh volatile gas content

• smooth “skin,” ropeysmooth “skin,” ropey type flowtype flow

• very “pasty,” sticky,very “pasty,” sticky, thick, cool flowsthick, cool flows

• flows 5-50 m/hrflows 5-50 m/hr (15-150 ft/hr)(15-150 ft/hr)

•low volatile gas contentlow volatile gas content

• rough, blocky, sharp,rough, blocky, sharp, angular type flowangular type flow

• very “pasty,” sticky,very “pasty,” sticky, thick, cool flowsthick, cool flows

• flows 5-50 m/hrflows 5-50 m/hr (15-150 ft/hr)(15-150 ft/hr)

•low volatile gas contentlow volatile gas content

• rough, blocky, sharp,rough, blocky, sharp, angular type flowangular type flow 99

Pyroclastic materialsPyroclastic materials

VolcanicBombs

BombsBombsBombsBombs

Lahars mud flows

LaharsLaharsLaharsLahars

Ash

AshAshAshAsh

Nuee-Ardente

Nuee-ArdenteNuee-ArdenteNuee-ArdenteNuee-Ardente

Ryholitic magmasRyholitic magmas• high silicahigh silica• very explosivevery explosive• thick, pastythick, pasty• high viscosityhigh viscosity• pyroclastic ejectionspyroclastic ejections

Ryholitic magmasRyholitic magmas• high silicahigh silica• very explosivevery explosive• thick, pastythick, pasty• high viscosityhigh viscosity• pyroclastic ejectionspyroclastic ejections

1010

Why are there various types of volcanoes???What factors govern the structure of volcanoes?? Features of a typical volcano:

flank

Magma Chamber

conduit

flank

crater

1111

CalderaCalderaCalderaCalderaCalderas are circularCalderas are circulardepressions created depressions created from the collapse of from the collapse of

material into the material into the volcano.volcano.

>1km in diameter >1km in diameter

Calderas are circularCalderas are circulardepressions created depressions created from the collapse of from the collapse of

material into the material into the volcano.volcano.

>1km in diameter >1km in diameter

CraterCraterCraterCrater Craters are funnel-Craters are funnel-shaped depressions shaped depressions where gas, tephra,where gas, tephra,

and lava are ejected.and lava are ejected.

““An active area of An active area of volcanism”volcanism”

<1km in diameter<1km in diameter

Craters are funnel-Craters are funnel-shaped depressions shaped depressions where gas, tephra,where gas, tephra,

and lava are ejected.and lava are ejected.

““An active area of An active area of volcanism”volcanism”

<1km in diameter<1km in diameter

1212

I I I I VOLCANOES.VOLCANOES.VOLCANOES.VOLCANOES.Discuss with a friend:Discuss with a friend:

1.1.Describe the differences between Describe the differences between aaaa and and pahoehoepahoehoe type basaltic flows. type basaltic flows.

2. Describe a pyroclastic type flow. Describe2. Describe a pyroclastic type flow. Describe 3 types of pyroclastic flows.3 types of pyroclastic flows.

3. Draw a typical volcano and label the3. Draw a typical volcano and label the common features.common features.4. What is the difference between a 4. What is the difference between a cratercrater and a and a calderacaldera??

1313

Three types of VolcanoesThree types of Volcanoes

ShieldShield

CompositeComposite(stratovolcano)(stratovolcano)

Cinder coneCinder coneExplain the differences.Explain the differences.

•Volcano type is dependant onVolcano type is dependant on SiOSiO22 content. content.

1414

Shield Volcano - HawaiiShield Volcano - HawaiiShield Volcano - HawaiiShield Volcano - Hawaii

Shield VolcanoesShield Volcanoes•Hawaiian Islands, Iceland, Galapagos IslandsHawaiian Islands, Iceland, Galapagos Islands•commonly rise from the deep ocean floorcommonly rise from the deep ocean floor

Shield VolcanoesShield Volcanoes•Hawaiian Islands, Iceland, Galapagos IslandsHawaiian Islands, Iceland, Galapagos Islands•commonly rise from the deep ocean floorcommonly rise from the deep ocean floor

•formed by the accumulation of fluid basaltic flowsformed by the accumulation of fluid basaltic flows•low silica content (basaltic composition)low silica content (basaltic composition)

•low viscositylow viscosity•less than 1% pyroclastic debrisless than 1% pyroclastic debris•non-explosive eruptionsnon-explosive eruptions

•pahoehoe flowspahoehoe flows•aa flowsaa flows

•formed by the accumulation of fluid basaltic flowsformed by the accumulation of fluid basaltic flows•low silica content (basaltic composition)low silica content (basaltic composition)

•low viscositylow viscosity•less than 1% pyroclastic debrisless than 1% pyroclastic debris•non-explosive eruptionsnon-explosive eruptions

•pahoehoe flowspahoehoe flows•aa flowsaa flows

Broad, low angle flanks

1515

StratovolcanoStratovolcanoComposite Cones (stratovolcanoes, stratacomposite)

•Western U.S. coast, Western South American coast, Japan• typically form in the ocean along continent convergent boundaries• found along the ring of fire

Composite Cones (stratovolcanoes, stratacomposite)•Western U.S. coast, Western South American coast, Japan• typically form in the ocean along continent convergent boundaries• found along the ring of fire

Steep high angle flanksSteep high angle flanks

•formed from layering deposits of ash, lava, and pyroclastic flows

•high silica content (70%)- (Rhyolitic composition)

•high viscosity flows

•abundant pyroclastic activity•deadly airborne debris

•explosive eruptions – very hazardous

•formed from layering deposits of ash, lava, and pyroclastic flows

•high silica content (70%)- (Rhyolitic composition)

•high viscosity flows

•abundant pyroclastic activity•deadly airborne debris

•explosive eruptions – very hazardous

Nuee Ardente gas cloud

Nuee Ardente gas cloudPyroclasticsPyroclasticsPyroclasticsPyroclastics

1616

The Ring of FireThe Ring of Fire

Cascade Mt. Range Cascade Mt. Range StratovolcanoesStratovolcanoes

1717

Old laharsOld lahars

1818

Cinder Cones•Exist all over the earth’s surface (by the 1000’s)•Located in volcanic fields (Flagstaff, AZ– about 600)

Cinder Cones•Exist all over the earth’s surface (by the 1000’s)•Located in volcanic fields (Flagstaff, AZ– about 600)

Very high, steep angled flanks30-40 degrees

Averages 100 ft – 1000 ft high

Very high, steep angled flanks30-40 degrees

Averages 100 ft – 1000 ft high

•Formed by gas rich basaltic flows (low viscosity, low silica) producing small sized material. Common rock scoria and volcanic glass

•Single eruptive episode lasting a short time

•Composed of scoria and loose pyroclastic material

•Formed by gas rich basaltic flows (low viscosity, low silica) producing small sized material. Common rock scoria and volcanic glass

•Single eruptive episode lasting a short time

•Composed of scoria and loose pyroclastic material

1919

Cinder ConesCinder Cones

2020

I see extensive lava flows, but where are the volcanoes?I see extensive lava flows, but where are the volcanoes?

Fissure type eruptions and lava plateaus

• very fluid basaltic lava erupted from fractures in the earth’s crust• lava fountains along “linear” fractures spreading out over wide areas• extrudes voluminous amounts of low silica basaltic lava• single flows can travel 100’s of kilometers

Fissure type eruptions and lava plateaus

• very fluid basaltic lava erupted from fractures in the earth’s crust• lava fountains along “linear” fractures spreading out over wide areas• extrudes voluminous amounts of low silica basaltic lava• single flows can travel 100’s of kilometers

Columbia River basalts• 11 m.y. flows

• very extensive –single flows from Idaho to Portland, Ore.

• 1 mile thick in southwest Washington

Columbia River basalts• 11 m.y. flows

• very extensive –single flows from Idaho to Portland, Ore.

• 1 mile thick in southwest Washington

Linear cracks (fissures)Linear cracks (fissures)

My study AreaMy study Area

2121

I I I I VOLCANOES.VOLCANOES.VOLCANOES.VOLCANOES.1.1. Fill in the following blanks given the chartFill in the following blanks given the chart below:below:

CompositionCompositionSiOSiO22

contentcontentViscosityViscosityPyro-Pyro-

clasticsclasticsVolcanoVolcano

typetype

Shield typeShield typeFlood basaltsFlood basalts

Composite typeComposite type

CompositeCompositeCider-coneCider-conepyroclasticpyroclastic

MaficMaficbasalticbasaltic

LowLow<50%<50%

LowLow NoneNone

IntermediateIntermediateApproxApprox60%60%

IntermediateIntermediatesomesome

Felsic Felsic rhyoliticrhyolitic

HighHigh70%70% highhigh highhigh

2222

Plates separate resulting from basaltic magma ascending into fractures. Shield type volcanoes form ridges and mountains below the ocean.

Plates separate resulting from basaltic magma ascending into fractures. Shield type volcanoes form ridges and mountains below the ocean.

Divergent plate volcanismDivergent plate volcanism

• Very fluid eruptions• Less than 50% SiO2 content• Shield type volcanoes• Basalt rocks

• Very fluid eruptions• Less than 50% SiO2 content• Shield type volcanoes• Basalt rocks

2323

Oceanic plate subducts beneath oceanic plate. Melting subducted plate ascends upward forming shield type volcanoes in the form of island arc systems “mountainous arcs” that rise above the ocean floor. – Japan, Aleutian Islands

Oceanic plate subducts beneath oceanic plate. Melting subducted plate ascends upward forming shield type volcanoes in the form of island arc systems “mountainous arcs” that rise above the ocean floor. – Japan, Aleutian Islands

Ocean – Ocean plate convergenceOcean – Ocean plate convergence

•Very fluid eruptions• Less than 50% SiO2 • Shield type volcanoes• Basalt rocks

•Very fluid eruptions• Less than 50% SiO2 • Shield type volcanoes• Basalt rocks

2424

BakerBaker

RainierRainier

St. HelensSt. Helens

AdamsAdams

HoodHood

JeffersonJefferson

Three SistersThree SistersNewberry VolcanoNewberry VolcanoNewberry VolcanoNewberry Volcano

Crater LakeCrater Lake

McLaughlinMcLaughlin

Medicine Lake VolcanoMedicine Lake VolcanoShastaShasta

Lassen PeakLassen Peak

Pacific PlatePacific PlatePacific PlatePacific Plate

NorthNorthAmericanAmericanPlatePlate

NorthNorthAmericanAmericanPlatePlate

Oceanic plate is subducted beneath continental plate. Melting plate ascends upward mixing with continental material.

Oceanic plate is subducted beneath continental plate. Melting plate ascends upward mixing with continental material.

Ocean to Continent convergence

Ocean to Continent convergence

• High SiO2 – High viscosity• explosive volcanoes• “pasty” lava flows• composite type volcanoes• andesite/rhyolite rocks

• High SiO2 – High viscosity• explosive volcanoes• “pasty” lava flows• composite type volcanoes• andesite/rhyolite rocks

2525

I I I I VOLCANOES.VOLCANOES.VOLCANOES.VOLCANOES.

I will get an A on my exams and quizzes.I will get an A on my exams and quizzes.

Discuss with a friend:Discuss with a friend:

1.1.Draw a diagram that shows how the Draw a diagram that shows how the shield and composite type volcanoes areshield and composite type volcanoes are related to their respective plate boundaryrelated to their respective plate boundary or “plate tectonic setting.”or “plate tectonic setting.”

2626

Why and How Rocks MeltWhy and How Rocks MeltWhy and How Rocks MeltWhy and How Rocks Melt

Granite/Shale (commonGranite/Shale (commonrocks) typically begin to rocks) typically begin to melt at 800melt at 80000C and turn toC and turn to

liquid at 1200liquid at 120000C.C.

Granite/Shale (commonGranite/Shale (commonrocks) typically begin to rocks) typically begin to melt at 800melt at 80000C and turn toC and turn to

liquid at 1200liquid at 120000C.C.

The range of temperature for complete melting of a rockThe range of temperature for complete melting of a rockis due to various individual mineral melting point is due to various individual mineral melting point characteristics. characteristics.

The range of temperature for complete melting of a rockThe range of temperature for complete melting of a rockis due to various individual mineral melting point is due to various individual mineral melting point characteristics. characteristics.

Amphibole (hornblende) melts Amphibole (hornblende) melts at around 900at around 90000C.C.

Amphibole (hornblende) melts Amphibole (hornblende) melts at around 900at around 90000C.C.

Feldspar (orthoclase) meltsFeldspar (orthoclase) meltsat around 700at around 70000C.C.

Feldspar (orthoclase) meltsFeldspar (orthoclase) meltsat around 700at around 70000C.C.

Quartz melts at around 600Quartz melts at around 60000C.C.Quartz melts at around 600Quartz melts at around 60000C.C.

Why a temperature range?Why a temperature range?Why a temperature range?Why a temperature range?

2727

What factors influence the melting points What factors influence the melting points of rocks?of rocks?What factors influence the melting points What factors influence the melting points of rocks?of rocks?

• Temperature:Temperature:• geothermal gradientgeothermal gradient

• Pressure:Pressure:• influence of pressure at depthinfluence of pressure at depth• pressure/temperature relationshippressure/temperature relationship

• Presence of water in the rocks:Presence of water in the rocks:• water in the subduction zonewater in the subduction zone• how water influences the melting pointhow water influences the melting point

• Temperature:Temperature:• geothermal gradientgeothermal gradient

• Pressure:Pressure:• influence of pressure at depthinfluence of pressure at depth• pressure/temperature relationshippressure/temperature relationship

• Presence of water in the rocks:Presence of water in the rocks:• water in the subduction zonewater in the subduction zone• how water influences the melting pointhow water influences the melting point

2828

Temperature inside the earthTemperature inside the earthTemperature inside the earthTemperature inside the earth

0000 500500500500 1000100010001000 1500150015001500 2000200020002000

Dep

th (

km

)D

ep

th (

km

)D

ep

th (

km

)D

ep

th (

km

)

100100100100

200200200200

300300300300

400400400400

5,0005,0005,0005,000

10,00010,00010,00010,000

15,00015,00015,00015,000

Pre

ssu

re (

mp

a)

Pre

ssu

re (

mp

a)

Pre

ssu

re (

mp

a)

Pre

ssu

re (

mp

a)

GeothermalGeothermalgradientgradient

GeothermalGeothermalgradientgradient

• the rate at whichthe rate at which temperature increasestemperature increases with depthwith depth

• the rate at whichthe rate at which temperature increasestemperature increases with depthwith depth

Continent gradientContinent gradient

• In thicker crust,In thicker crust, gradient increases.gradient increases.

• average 7average 7ooC/km rateC/km rate

• temperature increasestemperature increases gentlygently

Continent gradientContinent gradient

• In thicker crust,In thicker crust, gradient increases.gradient increases.

• average 7average 7ooC/km rateC/km rate

• temperature increasestemperature increases gentlygently

Oceanic gradientOceanic gradient

• Below the ocean floor,Below the ocean floor, temperature increasestemperature increases rapidly.rapidly.

• average 13average 1300C/kmC/km

Oceanic gradientOceanic gradient

• Below the ocean floor,Below the ocean floor, temperature increasestemperature increases rapidly.rapidly.

• average 13average 1300C/kmC/km2929

How does pressure influence the melting pointHow does pressure influence the melting pointof rock?of rock?How does pressure influence the melting pointHow does pressure influence the melting pointof rock?of rock?

Pressure inside the earth with depth.Pressure inside the earth with depth.Pressure inside the earth with depth.Pressure inside the earth with depth.

• Pressure/Temperature increase with depth.Pressure/Temperature increase with depth.

• Mantle (mesosphere) reaches temperaturesMantle (mesosphere) reaches temperatures beyond rock melting point, but the mantlebeyond rock melting point, but the mantle remains “solid!”remains “solid!”

• Increased pressures raise melting points.Increased pressures raise melting points.

• At a depth of 100 km, pressure is 35,000At a depth of 100 km, pressure is 35,000 times greater than at sea level.times greater than at sea level.

• Many minerals will begin melting at Many minerals will begin melting at temperatures above melting points attemperatures above melting points at sea level.sea level.

• Pressure/Temperature increase with depth.Pressure/Temperature increase with depth.

• Mantle (mesosphere) reaches temperaturesMantle (mesosphere) reaches temperatures beyond rock melting point, but the mantlebeyond rock melting point, but the mantle remains “solid!”remains “solid!”

• Increased pressures raise melting points.Increased pressures raise melting points.

• At a depth of 100 km, pressure is 35,000At a depth of 100 km, pressure is 35,000 times greater than at sea level.times greater than at sea level.

• Many minerals will begin melting at Many minerals will begin melting at temperatures above melting points attemperatures above melting points at sea level.sea level.

3030

How does the presence of water influence theHow does the presence of water influence therock’s melting point?rock’s melting point?How does the presence of water influence theHow does the presence of water influence therock’s melting point?rock’s melting point?

The presence of water or water vapor The presence of water or water vapor the rock’s melting point.the rock’s melting point.

• water present in subduction zoneswater present in subduction zones

The presence of water or water vapor The presence of water or water vapor the rock’s melting point.the rock’s melting point.

• water present in subduction zoneswater present in subduction zones

The introduction of waterdecreases melting pointsand creates melted platematerial that moves upward.

Magma stays liquid dueto the decrease in pressureas magma rises.

(decompression melting) Introduction ofIntroduction of

waterwater

3131

Cooling and Crystallization of MagmaCooling and Crystallization of Magma• What is magmatic differentiation?What is magmatic differentiation?

• What is the significance of Bowen’s reaction series?What is the significance of Bowen’s reaction series?

• How do you get a rhyolitic composition from a How do you get a rhyolitic composition from a basaltic magma?basaltic magma?

Cooling and Crystallization of MagmaCooling and Crystallization of Magma• What is magmatic differentiation?What is magmatic differentiation?

• What is the significance of Bowen’s reaction series?What is the significance of Bowen’s reaction series?

• How do you get a rhyolitic composition from a How do you get a rhyolitic composition from a basaltic magma?basaltic magma?

Put the following igneous rocks in the order ofPut the following igneous rocks in the order oftheir compositional equivalence.their compositional equivalence.Put the following igneous rocks in the order ofPut the following igneous rocks in the order oftheir compositional equivalence.their compositional equivalence.

granitegranite

dioritediorite

gabbrogabbro

granitegranite

dioritediorite

gabbrogabbro

basaltbasalt

rhyoliterhyolite

andesiteandesite

basaltbasalt

rhyoliterhyolite

andesiteandesite

Is it possible to Is it possible to create a granitecreate a granitecomposition fromcomposition froma basaltic magma?a basaltic magma?

Is it possible to Is it possible to create a granitecreate a granitecomposition fromcomposition froma basaltic magma?a basaltic magma?

3232

Magmatic differentiation:Magmatic differentiation:• the formation of many kinds of igneous rocks fromthe formation of many kinds of igneous rocks from a single magmaa single magma

Magmatic differentiation:Magmatic differentiation:• the formation of many kinds of igneous rocks fromthe formation of many kinds of igneous rocks from a single magmaa single magma

FeFeFeFe

Simple exampleSimple exampleSimple exampleSimple example

FeFeFeFeFeFeFeFe

FeFeFeFe MgMgMgMgMgMgMgMg

MgMgMgMg

MgMgMgMg

SiOSiO22SiOSiO22

SiOSiO22SiOSiO22

SiOSiO22SiOSiO22

SiOSiO22SiOSiO22

SiOSiO22SiOSiO22

SiOSiO22SiOSiO22

SiOSiO22SiOSiO22

SiOSiO22SiOSiO22

Liquid magmaLiquid magmaLiquid magmaLiquid magma Part liquid/solidPart liquid/solidPart liquid/solidPart liquid/solid

FeSiOFeSiO22

FeSiOFeSiO22MgSiOMgSiO22

FeSiOFeSiO22 MgSiOMgSiO22

FeSiOFeSiO22MgSiOMgSiO22

solidsolidsolidsolid

liquidliquidliquidliquid

SiOSiO22SiOSiO22

SiOSiO22SiOSiO22SiOSiO22SiOSiO22

SiOSiO22SiOSiO22

CoolingCooling

How has the liquid magma changed composition?How has the liquid magma changed composition?How has the liquid magma changed composition?How has the liquid magma changed composition?

As the liquid magma begins to cool, various minerals precipitate asAs the liquid magma begins to cool, various minerals precipitate assolids and become separated from the liquid melt. This separationsolids and become separated from the liquid melt. This separationof various chemistries changes the composition of the original magma.of various chemistries changes the composition of the original magma.

As the liquid magma begins to cool, various minerals precipitate asAs the liquid magma begins to cool, various minerals precipitate assolids and become separated from the liquid melt. This separationsolids and become separated from the liquid melt. This separationof various chemistries changes the composition of the original magma.of various chemistries changes the composition of the original magma.

3333

Three ways crystals separate from a melt:Three ways crystals separate from a melt:Three ways crystals separate from a melt:Three ways crystals separate from a melt:

Filter pressingFilter pressing::• Remaining melt is pushedRemaining melt is pushed through a fracture andthrough a fracture and separated from xlized melt.separated from xlized melt.

Filter pressingFilter pressing::• Remaining melt is pushedRemaining melt is pushed through a fracture andthrough a fracture and separated from xlized melt.separated from xlized melt.

Crystal settlingCrystal settling::• The first minerals to The first minerals to xlize are denser andxlize are denser and sink to the bottom.sink to the bottom.

Crystal settlingCrystal settling::• The first minerals to The first minerals to xlize are denser andxlize are denser and sink to the bottom.sink to the bottom.

Crystal floatationCrystal floatation• The first crystals areThe first crystals are less dense and riseless dense and rise to the top.to the top.

Crystal floatationCrystal floatation• The first crystals areThe first crystals are less dense and riseless dense and rise to the top.to the top.

3434

Which minerals form first, second, third…….etc.?Which minerals form first, second, third…….etc.?Bowen’s reaction seriesBowen’s reaction series

Which minerals form first, second, third…….etc.?Which minerals form first, second, third…….etc.?Bowen’s reaction seriesBowen’s reaction series

GabbroGabbro

DioriteDiorite

GraniteGranite

3535

I I I I crystallizing.crystallizing.crystallizing.crystallizing.

I will get an A on my exams and quizzes.I will get an A on my exams and quizzes.

Discuss with a friend:Discuss with a friend:

1.1.Why do rocks typically have a Why do rocks typically have a temperature range to become completelytemperature range to become completely melted?melted?2. Describe magmatic differentiation.2. Describe magmatic differentiation.3. Describe the three ways crystals are3. Describe the three ways crystals are separated.separated.4. What is Bowen’s reaction series?4. What is Bowen’s reaction series?

3636

What types of features areWhat types of features areformedformed

when magmawhen magmacools below the surface?cools below the surface?

3737

Tabular intrusive bodiesTabular intrusive bodiesforming below the earth’sforming below the earth’ssurfacesurface

DikesDikes

SillSill

TabularTabular

Batholith

Batholith

3838

Intrusive Bodies:Intrusive Bodies:

BatholithBatholith: intrusive body GREATER than 40 mi: intrusive body GREATER than 40 mi22

Stock: intrusive body LESS than 40 mi2

Dike: intrusive body cutting across strata (disconcordant)

Sill: intrusive/extrusive body parallel to strata (concordant)

Laccolith: “mushroom-shaped” intrusive body forming a dome-like structure

Intrusive Bodies:Intrusive Bodies:

BatholithBatholith: intrusive body GREATER than 40 mi: intrusive body GREATER than 40 mi22

Stock: intrusive body LESS than 40 mi2

Dike: intrusive body cutting across strata (disconcordant)

Sill: intrusive/extrusive body parallel to strata (concordant)

Laccolith: “mushroom-shaped” intrusive body forming a dome-like structure

3939

BatholithBatholithBatholithBatholith

LoccolithLoccolithLoccolithLoccolith

DikeDikeDikeDike

SillSillSillSill

StockStockStockStock

Intrusive BodiesIntrusive Bodies

4040

Sierra Nevada BatholithGranite/Diorite

Sierra Nevada BatholithGranite/Diorite

Melting magma rises andmixes with continentalmaterial (high SiO2) andsolidifies beneath the surface.

Melting magma rises andmixes with continentalmaterial (high SiO2) andsolidifies beneath the surface.

4141

I I I I intrusiveintrusiveintrusiveintrusive1.1.Given the block diagram below, describeGiven the block diagram below, describe the following plutonic (intrusive) typethe following plutonic (intrusive) type features:features:

rocks.rocks.

4242

SQ-9SQ-9SQ-9SQ-9