Chapter4 igneousrocks-110708161910-phpapp02

Essentials of GeologyEssentials of Geology
33rdrd
EditionEdition
Chapter 4
Norton Media LibraryNorton Media Library

Up from the Inferno: Magma
and Igneous Rocks
Prepared by:Prepared by:
Ronald ParkerRonald Parker,, Senior GeologistSenior Geologist
Fronterra GeosciencesFronterra Geosciences
Houston, Oklahoma City, Denver, Anchorage, Dallas, Midland, Aberdeen, Vienna, Buenos Aires, NeuquénHouston, Oklahoma City, Denver, Anchorage, Dallas, Midland, Aberdeen, Vienna, Buenos Aires, Neuquén
www.fronterrageosciences.comwww.fronterrageosciences.com

Essentials of Geology, 3rd
edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous Rocks
Igneous RocksIgneous Rocks
 Volcano – A vent where molten rock comes out of Earth.Volcano – A vent where molten rock comes out of Earth.
 Example: Kilauea Volcano, Hawaii.Example: Kilauea Volcano, Hawaii.
Hot (~1,200Hot (~1,200oo
C) lava pools around the volcanic vent.C) lava pools around the volcanic vent.
Hot, syrupy lava runs downhill as a lava flow.Hot, syrupy lava runs downhill as a lava flow.
The lava flow slows, loses heat and crusts over.The lava flow slows, loses heat and crusts over.
Finally, the flow stops and cools, forming an igneous rock.Finally, the flow stops and cools, forming an igneous rock.

 Solidified molten rock that freezes at high temp.Solidified molten rock that freezes at high temp.
 1,100°C to 650°C.1,100°C to 650°C.
 Temp depends on composition.Temp depends on composition.
 Earth is mostly igneous rock.Earth is mostly igneous rock.
 Magma – Subsurface melt.Magma – Subsurface melt.
 Lava – Melt at the surface.Lava – Melt at the surface.
 Volcanoes erupt magma.Volcanoes erupt magma.

 Melted rock can cool above or below ground.Melted rock can cool above or below ground.
 Intrusive igneous rocks – Cool slowly underground.Intrusive igneous rocks – Cool slowly underground.
 Extrusive igneous rocks – Cool quickly at the surface.Extrusive igneous rocks – Cool quickly at the surface.
Lava – Cooled liquid.Lava – Cooled liquid.
Pyroclastic debris – Cooled fragments.Pyroclastic debris – Cooled fragments.
Volcanic ash.Volcanic ash.
Fragmented lava.Fragmented lava.
 Many types of igneous rocks.Many types of igneous rocks.
 All oceanic crust.All oceanic crust.
 Most continental crust.Most continental crust.

Sources of HeatSources of Heat
 Sources of heat to the early Earth:Sources of heat to the early Earth:
 Planetesimal and meteorite accretion.Planetesimal and meteorite accretion.
 Gravitational compression.Gravitational compression.
 Differentiation.Differentiation.
 Decay of radioactive minerals.Decay of radioactive minerals.
 Tidal pull of the Sun and Moon.Tidal pull of the Sun and Moon.
 The crust does NOT float on aThe crust does NOT float on a
sea of molten rock.sea of molten rock.

Magma FormationMagma Formation
 Magma forms in special settings that melt existing rocks.Magma forms in special settings that melt existing rocks.
 Partial melting occurs in the crust and upper mantle.Partial melting occurs in the crust and upper mantle.
 Melting is caused by…Melting is caused by…
 Pressure release.Pressure release.
 Volatile addition.Volatile addition.
 Heat transfer.Heat transfer.

 Geothermal gradient – The Earth is hot inside.Geothermal gradient – The Earth is hot inside.
 Crustal temperature (T) averages 25°C / km of depth.Crustal temperature (T) averages 25°C / km of depth.
 At the base of the lithosphere T ~ 1280°C.At the base of the lithosphere T ~ 1280°C.
 The geothermal gradient varies from place to place.The geothermal gradient varies from place to place.

 Pressure release.Pressure release.
 Base of the crust is hot enough to melt mantle rock.Base of the crust is hot enough to melt mantle rock.
 Due to high pressure, the rock does not melt.Due to high pressure, the rock does not melt.
 A drop in pressure initiates “decompressional melting.”A drop in pressure initiates “decompressional melting.”
Pressure drops when hot rockPressure drops when hot rock
rises to shallower depths.rises to shallower depths.

Addition of VolatilesAddition of Volatiles
 Volatiles lower the melting T of a hot rock.Volatiles lower the melting T of a hot rock.
 Common volatiles include water and carbon dioxide.Common volatiles include water and carbon dioxide.
 Subduction introduces water to the mantle, melting rock.Subduction introduces water to the mantle, melting rock.

 Heat transfer.Heat transfer.
 Rising magma carries mantle heat with it.Rising magma carries mantle heat with it.
 This raises the T in nearby crustal rock, which then melts.This raises the T in nearby crustal rock, which then melts.

What is Magma Made of?What is Magma Made of?
 Magmas have three components (solid, liquid and gas).Magmas have three components (solid, liquid and gas).
 Solid – Solidified mineral crystals are borne by the melt.Solid – Solidified mineral crystals are borne by the melt.
 Liquid – The melt itself is comprised of mobile ions.Liquid – The melt itself is comprised of mobile ions.
Dominantly Si and O; lesser Al, Ca, Fe, Mg, Na, and K.Dominantly Si and O; lesser Al, Ca, Fe, Mg, Na, and K.
Other ions present to a lesser extent.Other ions present to a lesser extent.
 Different mixes of elements yield different magmas.Different mixes of elements yield different magmas.

What is Magma Made of?What is Magma Made of?
 Gas – Magmas contain abundant dissolved volatile gas.Gas – Magmas contain abundant dissolved volatile gas.
Dry magma – Scarce volatiles.Dry magma – Scarce volatiles.
Wet magma – To 15% volatiles.Wet magma – To 15% volatiles.
Water vapor (HWater vapor (H22O)O)
Carbon dioxide (COCarbon dioxide (CO22))
Sulfur dioxide (SOSulfur dioxide (SO22))
Nitrogen (NNitrogen (N22))
Hydrogen (HHydrogen (H22))

Magma CompositionsMagma Compositions
 There are four major magma types based on silica (SiOThere are four major magma types based on silica (SiO22))
percentage.percentage.
 Felsic (feldspar and silica)Felsic (feldspar and silica) 66 to 76% SiO66 to 76% SiO22..
 IntermediateIntermediate 52 to 66% SiO52 to 66% SiO22..
 Mafic (Mg and Fe-rich)Mafic (Mg and Fe-rich) 45 to 52% SiO45 to 52% SiO22..
 UltramaficUltramafic 38 to 45% SiO38 to 45% SiO22..

Magma CompositionsMagma Compositions
 Composition controls magma density, T, and viscosity.Composition controls magma density, T, and viscosity.
 The most important factor is silica (SiOThe most important factor is silica (SiO22) content.) content.
Silica-rich magmas are thick and viscous.Silica-rich magmas are thick and viscous.
Silica-poor magmas are thin and “runny.”Silica-poor magmas are thin and “runny.”
 These characteristics govern eruptive style.These characteristics govern eruptive style.
Type Density Temperature Viscosity
FelsicFelsic Very lowVery low Very low (600 to 850Very low (600 to 850°°C)C) Very High: Explosive eruptions.Very High: Explosive eruptions.
IntermediateIntermediate LowLow LowLow High: Explosive eruptions.High: Explosive eruptions.
MaficMafic HighHigh HighHigh Low: thin, hot runny eruptions.Low: thin, hot runny eruptions.
UltramaficUltramafic Very highVery high Very high (up to 1300Very high (up to 1300°°C)C) Very low.Very low.

Magma VariationMagma Variation
 Why are there different magma compositions?Why are there different magma compositions?
 Magmas vary chemically due to…Magmas vary chemically due to…
 Initial source rock compositions.Initial source rock compositions.
 Partial melting.Partial melting.
 Assimilation.Assimilation.
 Fractional crystallization.Fractional crystallization.

Magma VariationMagma Variation
 The source of the melt dictates the initial composition.The source of the melt dictates the initial composition.
 Mantle source – Ultramafic and mafic magmas.Mantle source – Ultramafic and mafic magmas.
 Crustal source – Mafic, intermediate, and felsic magmas.Crustal source – Mafic, intermediate, and felsic magmas.

Partial MeltingPartial Melting
 Upon melting, rocks rarely dissolve completely.Upon melting, rocks rarely dissolve completely.
 Instead, only a portion of the rock melts.Instead, only a portion of the rock melts.
 Silica-rich minerals melt first.Silica-rich minerals melt first.
 Silica-poor minerals melt last.Silica-poor minerals melt last.
 Partial melting, then, yields a silica-rich magma.Partial melting, then, yields a silica-rich magma.
 Removing a partial melt from its source creates…Removing a partial melt from its source creates…
 Felsic magma.Felsic magma.
 Mafic residue.Mafic residue.

 Magma melts the country rock it passes through.Magma melts the country rock it passes through.
 Blocks of country rock (xenoliths) fall into magma.Blocks of country rock (xenoliths) fall into magma.
 Assimilation of these rocks alters magma composition.Assimilation of these rocks alters magma composition.
AssimilationAssimilation

Magma MixingMagma Mixing
 Different magmas may blend in a magma chamber.Different magmas may blend in a magma chamber.
 The result combines the characteristics of the twoThe result combines the characteristics of the two
magmas.magmas.
 Often magma mixing is incomplete, resulting in blobs ofOften magma mixing is incomplete, resulting in blobs of
one rock type suspended within the other.one rock type suspended within the other.

Magma MigrationMagma Migration
 Magma doesn’t stay put; it tends to rise upward.Magma doesn’t stay put; it tends to rise upward.
 Magma may move upward in the crust.Magma may move upward in the crust.
 Magma may breach the surface – a volcano.Magma may breach the surface – a volcano.
 This transfers mass from deep to shallow parts of Earth.This transfers mass from deep to shallow parts of Earth.
 A crucial process in the Earth System.A crucial process in the Earth System.
 Provides the raw material for soil, atmosphere, and ocean.Provides the raw material for soil, atmosphere, and ocean.

 Magma moves by…Magma moves by…
 Injection into cracks.Injection into cracks.
 Melting overlying rocks.Melting overlying rocks.
 Squeezed by overburden.Squeezed by overburden.
 Low viscosity eases movement. Lower viscosity from…Low viscosity eases movement. Lower viscosity from…
 Higher T.Higher T.
 Lower Silica content.Lower Silica content.
 Higher volatile content.Higher volatile content.

 Viscosity depends on T, volatiles, and silica.Viscosity depends on T, volatiles, and silica.
 Temperature:Temperature:
Hotter – Lower viscosityHotter – Lower viscosity
Cooler – Higher viscosity.Cooler – Higher viscosity.
 Volatile content:Volatile content:
More volatiles – Lower viscosity.More volatiles – Lower viscosity.
Less volatiles – Higher viscosity.Less volatiles – Higher viscosity.
 Silica (SiOSilica (SiO22) content:) content:
Less SiOLess SiO22 (Mafic) – Lower viscosity.(Mafic) – Lower viscosity.
More SiOMore SiO22 (Felsic) – Higher viscosity.(Felsic) – Higher viscosity.

Cooling RatesCooling Rates
 Cooling rate – How fast does magma cool?Cooling rate – How fast does magma cool?
 Depth: Deep is hot; shallow is cool.Depth: Deep is hot; shallow is cool.
Deep plutons lose heat very slowly and cool slowly.Deep plutons lose heat very slowly and cool slowly.
Shallow flows lose heat rapidly and cool quickly.Shallow flows lose heat rapidly and cool quickly.
 Shape: Spherical bodies cool slowly; tabular bodies cool faster.Shape: Spherical bodies cool slowly; tabular bodies cool faster.
 Ground water: Ground water removes heat.Ground water: Ground water removes heat.

Fractional CrystallizationFractional Crystallization
The original melt is mafic. As early-formed minerals settle,
the melt becomes more felsic.
 As magma cools, early crystals settle by gravity.As magma cools, early crystals settle by gravity.
 Melt composition changes as a result.Melt composition changes as a result.
 Fe, Mg, and Ca are removed in early settled solids.Fe, Mg, and Ca are removed in early settled solids.
 Si, Al, Na, and K remain in melt and increase in abundance.Si, Al, Na, and K remain in melt and increase in abundance.

Fractional CrystallizationFractional Crystallization
 Felsic magma can evolve from mafic magma.Felsic magma can evolve from mafic magma.
 Progressive removal of mafics depletes Fe, Mg, and Ca.Progressive removal of mafics depletes Fe, Mg, and Ca.
 Remaining melt becomes enriched in Na, K, Al, and Si.Remaining melt becomes enriched in Na, K, Al, and Si.

Bowen’s Reaction SeriesBowen’s Reaction Series
 N. L. Bowen, in the 1920s, ran experiments with melts.N. L. Bowen, in the 1920s, ran experiments with melts.
 He found with cooling, early-forming crystals settled out.He found with cooling, early-forming crystals settled out.
 Settling removed elements from the remaining melt.Settling removed elements from the remaining melt.
 He discovered that minerals solidify in a specific series.He discovered that minerals solidify in a specific series.
 Continuous – Plagioclase changed from Ca-rich to Na-rich.Continuous – Plagioclase changed from Ca-rich to Na-rich.
 Discontinuous – Minerals that solidify in a narrow T range.Discontinuous – Minerals that solidify in a narrow T range.
OlivineOlivine
PyroxenePyroxene
AmphiboleAmphibole
BiotiteBiotite

Igneous EnvironmentsIgneous Environments
 Two major categories – Based on cooling site.Two major categories – Based on cooling site.
 Extrusive settings – Cool at or near the surface.Extrusive settings – Cool at or near the surface.
Cool rapidly.Cool rapidly.
Chill too fast to grow big crystals.Chill too fast to grow big crystals.
 Intrusive settings – Cool at depth.Intrusive settings – Cool at depth.
Lose heat slowly.Lose heat slowly.
Crystals grow large.Crystals grow large.
 Most mafic magmas extrude.Most mafic magmas extrude.
 Most felsic magmas don’t.Most felsic magmas don’t.

Extrusive SettingsExtrusive Settings
 Lava flows – Cool as blankets that often stack vertically.Lava flows – Cool as blankets that often stack vertically.
 Lava flows exit volcanic vents and spread outward.Lava flows exit volcanic vents and spread outward.
 Low-viscosity lava (basalt) can flow long distances.Low-viscosity lava (basalt) can flow long distances.
 Detail on extrusive igneous rocks appears in Chapter 5.Detail on extrusive igneous rocks appears in Chapter 5.

Extrusive SettingsExtrusive Settings
 Explosive ash eruptions.Explosive ash eruptions.
 High-viscosity felsic magma builds volcanic pressure.High-viscosity felsic magma builds volcanic pressure.
 Violent eruptions yield huge volumes of volcanic ash.Violent eruptions yield huge volumes of volcanic ash.
 Ash can cover large regions.Ash can cover large regions.

Intrusive SettingsIntrusive Settings
 Intrusive rocks cool at depth; they don’t surface.Intrusive rocks cool at depth; they don’t surface.
 Magma invading colder country rock initiates…Magma invading colder country rock initiates…
 Thermal (heat) metamorphism and melting.Thermal (heat) metamorphism and melting.
 Inflation of fractures which wedges the country rock apart.Inflation of fractures which wedges the country rock apart.
 Incorporation of country rock fragments (xenoliths).Incorporation of country rock fragments (xenoliths).
 Hydrothermal (hot water) alteration.Hydrothermal (hot water) alteration.

Intrusive SettingsIntrusive Settings
 Intrusive contacts preserve evidence of high heat.Intrusive contacts preserve evidence of high heat.
 Baked zone – Rim of heat-altered country rock.Baked zone – Rim of heat-altered country rock.
 Chill margin – Quenched magma at contact = tiny crystals.Chill margin – Quenched magma at contact = tiny crystals.
 Xenolith – Altered country rock fragment in magma.Xenolith – Altered country rock fragment in magma.
 Magma cooled before xenolith could be assimilated.Magma cooled before xenolith could be assimilated.

Intrusive ActivityIntrusive Activity
 Magma intrudes into other rocks in two ways.Magma intrudes into other rocks in two ways.
 As planar, tabular bodies (dikes and sills)As planar, tabular bodies (dikes and sills)
 As balloon-shaped blobs (plutons).As balloon-shaped blobs (plutons).
 Size varies widely.Size varies widely.
 Plutons can be massive.Plutons can be massive.
 Dikes and sills tend toDikes and sills tend to
be smaller.be smaller.

Tabular IntrusionsTabular Intrusions
 Tend to have a uniform thickness.Tend to have a uniform thickness.
 Can be traced laterally.Can be traced laterally.
 Two major subdivisions.Two major subdivisions.
 Sill – Parallels rock fabric.Sill – Parallels rock fabric.
 Dike – Crosscuts rock fabric.Dike – Crosscuts rock fabric.

 Dikes and sills modify invaded country rock.Dikes and sills modify invaded country rock.
 They cause the rock to expand and inflate.They cause the rock to expand and inflate.
 They thermally alter the country rock.They thermally alter the country rock.
 Dikes…Dikes…
 Cut across preexisting layering (bedding or foliation).Cut across preexisting layering (bedding or foliation).
 Spread rocks sideways.Spread rocks sideways.
 Dominate in extensional settings.Dominate in extensional settings.

 Sills…Sills…
 Are injected parallel to preexisting layering.Are injected parallel to preexisting layering.
 Are usually intruded close to the surface.Are usually intruded close to the surface.
 Both dikes and sills exhibit wide variability in...Both dikes and sills exhibit wide variability in...
 Size.Size.
 Thickness (or width).Thickness (or width).
 Lateral continuity.Lateral continuity.

 SillsSills
 This basalt sill (dark band) was intruded into sandstonesThis basalt sill (dark band) was intruded into sandstones
(light colored rock) in Antarctica.(light colored rock) in Antarctica.
 When intruded, itWhen intruded, it
lifted the entirelifted the entire
landscape above it.landscape above it.

Plutonic ActivityPlutonic Activity
 Most magma is emplaced at depth in the Earth.Most magma is emplaced at depth in the Earth.
 A large, deep, igneous body is called a pluton.A large, deep, igneous body is called a pluton.
 Plutonic intrusions modify the crust.Plutonic intrusions modify the crust.
 Push aside preexisting rock.Push aside preexisting rock.
 Add new material.Add new material.
 Add heat.Add heat.

Plutonic ActivityPlutonic Activity
 Plutons sometimes coalesce to form a larger batholith.Plutons sometimes coalesce to form a larger batholith.
 Plutons are created above subduction zones.Plutons are created above subduction zones.
 Magma generation may occur over tens of millions ofMagma generation may occur over tens of millions of
years.years.
 A long subduction history is linkedA long subduction history is linked
to the genesis of large batholiths.to the genesis of large batholiths.

Intrusive and ExtrusiveIntrusive and Extrusive
 Intrusive and extrusive rocks commonly co-occur.Intrusive and extrusive rocks commonly co-occur.
 Magma chambers feed overlying volcanoes.Magma chambers feed overlying volcanoes.
 Magma chambers may cool to become plutons.Magma chambers may cool to become plutons.
 Many igneous geometries are possible.Many igneous geometries are possible.

Intrusive and ExtrusiveIntrusive and Extrusive
 With erosion, progressively deeper features are exposed.With erosion, progressively deeper features are exposed.
 Dikes.Dikes.
 Sills.Sills.
 Laccoliths – Mushroom-shaped intrusions.Laccoliths – Mushroom-shaped intrusions.

Influence on LandscapeInfluence on Landscape
 Continued uplift and erosion exposes the pluton.Continued uplift and erosion exposes the pluton.
 Intrusive rocks are commonly more resistant to erosion.Intrusive rocks are commonly more resistant to erosion.
 Thus, intrusive rocks often stand high on the landscape.Thus, intrusive rocks often stand high on the landscape.
 ““Unroofing” takes long periods of geologic time.Unroofing” takes long periods of geologic time.

Interlocking or crystalline texture
Igneous TexturesIgneous Textures
 The size, shape, and arrangement of the minerals.The size, shape, and arrangement of the minerals.
 Interlocking – Mineral crystals fit like jigsaw puzzle pieces.Interlocking – Mineral crystals fit like jigsaw puzzle pieces.
 Fragmental – Pieces of preexisting rocks, often shattered.Fragmental – Pieces of preexisting rocks, often shattered.
 Glassy – Made of solid glass or glass shards.Glassy – Made of solid glass or glass shards.
 Texture directly reflects magma history.Texture directly reflects magma history.
Glassy texture
Fragmental texture

Crystalline Igneous TexturesCrystalline Igneous Textures
 Texture reveals cooling history.Texture reveals cooling history.
 Aphanitic (finely crystalline).Aphanitic (finely crystalline).
Rapid cooling.Rapid cooling.
Crystals do not have time to grow.Crystals do not have time to grow.
Extrusive.Extrusive.
 Phaneritic – (coarsely crystalline).Phaneritic – (coarsely crystalline).
Slow cooling.Slow cooling.
Crystals have a long time to grow.Crystals have a long time to grow.
Intrusive.Intrusive.

Crystalline TexturesCrystalline Textures
 Texture reveals cooling history.Texture reveals cooling history.
 Porphyritic texture – A mixture of coarse and fine crystals.Porphyritic texture – A mixture of coarse and fine crystals.
Indicates a two-stage cooling history.Indicates a two-stage cooling history.
Initial slow cooling creates large phenocrysts.Initial slow cooling creates large phenocrysts.
Subsequent eruption cools remaining magma more rapidly.Subsequent eruption cools remaining magma more rapidly.

Igneous ClassificationIgneous Classification
 Classification is based upon composition and texture.Classification is based upon composition and texture.
 Composition – Felsic, intermediate, mafic, and ultramafic.Composition – Felsic, intermediate, mafic, and ultramafic.
 Texture – Fine (aphanitic); coarse (phaneritic).Texture – Fine (aphanitic); coarse (phaneritic).
TypeType Aphanitic (fine)Aphanitic (fine) Phaneritic (coarse)Phaneritic (coarse)
FelsicFelsic RhyoliteRhyolite GraniteGranite
IntermediateIntermediate AndesiteAndesite DioriteDiorite
MaficMafic BasaltBasalt GabbroGabbro
UltramaficUltramafic Very highVery high Very high (up to 1300Very high (up to 1300°°C)C)
A B
A B
C2 C1
C2C1

 Composition.Composition.
 Texture.Texture.
 A specific composition mayA specific composition may
occur as different textures.occur as different textures.
Example: The finely crystalline equivalentExample: The finely crystalline equivalent
of a coarse granite is a rhyolite.of a coarse granite is a rhyolite.
 A specific texture may beA specific texture may be
found in varying compositions.found in varying compositions.
Example: Finely crystalline mafics are basalts;Example: Finely crystalline mafics are basalts;
finely crystalline felsics are rhyolites.finely crystalline felsics are rhyolites.
Crystalline ClassificationCrystalline Classification

PegmatitesPegmatites
 Coarse mineral crystals found in dikes.Coarse mineral crystals found in dikes.
 Large crystals are not due to slow cooling.Large crystals are not due to slow cooling.
 Instead, pegmatites form from water-rich melts.Instead, pegmatites form from water-rich melts.
 Many unusual minerals are found in pegmatites.Many unusual minerals are found in pegmatites.
 Some pegmatites are rich in prized minerals.Some pegmatites are rich in prized minerals.

 Form by very rapid cooling of lava in water or air.Form by very rapid cooling of lava in water or air.
 Glassy textures are more common in felsic magmas.Glassy textures are more common in felsic magmas.
 They often preserve gas bubbles (vesicles).They often preserve gas bubbles (vesicles).
 Underwater, basalt lava quenches into “pillows.”Underwater, basalt lava quenches into “pillows.”
Glassy TexturesGlassy Textures

Glassy ClassificationGlassy Classification
 Glassy Igneous Rocks.Glassy Igneous Rocks.
 Obsidian – Volcanic glass from rapidly cooled lava.Obsidian – Volcanic glass from rapidly cooled lava.
Quenching – Lava flowing into water.Quenching – Lava flowing into water.
High silica lavas – These can make glass without quenching.High silica lavas – These can make glass without quenching.
 Pumice – Frothy felsic rock full of vesicles; it floats.Pumice – Frothy felsic rock full of vesicles; it floats.
 Scoria – Glassy, vesicular, mafic rock.Scoria – Glassy, vesicular, mafic rock.

Fragmental TexturesFragmental Textures
 Preexisting rocks that were shattered by eruption.Preexisting rocks that were shattered by eruption.
 After fragmentation, the pieces fall and are cemented.After fragmentation, the pieces fall and are cemented.

Fragmental ClassificationFragmental Classification
 aka Pyroclastic – Fragments of violent eruptions.aka Pyroclastic – Fragments of violent eruptions.
 Tuff – Volcanic ash that has fallen on land and solidified.Tuff – Volcanic ash that has fallen on land and solidified.
 Volcanic breccia – Made of larger volcanic fragments.Volcanic breccia – Made of larger volcanic fragments.

Igneous Activity DistributionIgneous Activity Distribution
 Igneous activity tracks tectonic plate boundaries.Igneous activity tracks tectonic plate boundaries.

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Essentials of GeologyEssentials of Geology
33rdrd
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