Ch04 igneousrocksfall2007-140227222125-phpapp02
- 2. Rocks are made of MineralsRocks are made of Minerals (Minerals in Granite)(Minerals in Granite)
- 3. Three Types of RocksThree Types of Rocks 1.1. IgneousIgneous – Crystallized from hot, molten– Crystallized from hot, molten rock.rock. • ExamplesExamples: granite, basalt: granite, basalt 2.2. SedimentarySedimentary – Fragments of sediment laid– Fragments of sediment laid down by water or wind become compresseddown by water or wind become compressed or cemented into layers over time.or cemented into layers over time. • ExamplesExamples: sandstone, shale, limestone: sandstone, shale, limestone 3.3. MetamorphicMetamorphic – Rocks changed by heat– Rocks changed by heat and/or pressure or chemical activity.and/or pressure or chemical activity. • ExamplesExamples: gneiss, schist, slate, marble: gneiss, schist, slate, marble
- 4. Proportions ofProportions of Rock Types on the EarthRock Types on the Earth Igneous & Metamorphic Rocks = Crystalline RocksIgneous & Metamorphic Rocks = Crystalline Rocks
- 5. The Rock Cycle:The Rock Cycle: Part of the Earth SystemPart of the Earth System • The loop that involves theThe loop that involves the processes by which rocksprocesses by which rocks originate and change tooriginate and change to other rocks.other rocks. • Illustrates the variousIllustrates the various processes and paths asprocesses and paths as rocks change both on therocks change both on the surface and inside thesurface and inside the Earth.Earth. • IllustratesIllustrates interrelationship amonginterrelationship among many parts of the Earthmany parts of the Earth System.System.
- 7. What Can IgneousWhat Can Igneous Minerals/Rocks Tell Us?Minerals/Rocks Tell Us? 1.1. Magma Composition, Viscosity, Temperatures,Magma Composition, Viscosity, Temperatures, PressuresPressures 2.2. Volcano Types and Eruptive BehaviorVolcano Types and Eruptive Behavior 3.3. Tectonic SettingTectonic Setting 4.4. MagnetismMagnetism 5.5. PaleomagnetismPaleomagnetism 6.6. Latitude – Magnetic DeclinationLatitude – Magnetic Declination 7.7. Polar Reversals – Orientation of Earth’s Magnetic FieldPolar Reversals – Orientation of Earth’s Magnetic Field and Timing of Reversalsand Timing of Reversals 8.8. Seafloor SpreadingSeafloor Spreading 9.9. Plate MovementsPlate Movements 10.10. Changes in Atmospheric Chemistry – OxygenChanges in Atmospheric Chemistry – Oxygen 11.11. Radiometric Age DatingRadiometric Age Dating
- 8. Origin ofOrigin of Igneous RocksIgneous Rocks
- 9. How Do Igneous Rocks Form?How Do Igneous Rocks Form? Igneous rocksIgneous rocks form from theform from the cooling andcooling and crystallizationcrystallization of magma orof magma or lava (moltenlava (molten rock)rock)..
- 10. MagmaMagma isis molten rockmolten rock that isthat is generated ingenerated in deep in thedeep in the Earth.Earth. Magma thatMagma that reaches thereaches the surface issurface is calledcalled lavalava..
- 11. How Does Magma Originate?How Does Magma Originate? • MagmaMagma originates fromoriginates from partialpartial meltingmelting of rocks at various levels inof rocks at various levels in the Earth’sthe Earth’s crustcrust andand upper mantle.upper mantle. • Plate tectonicsPlate tectonics plays a majorplays a major role in therole in the generation ofgeneration of most magma.most magma.
- 12. Generating Magma fromGenerating Magma from Solid RockSolid Rock 1.1. Role of HeatRole of Heat 2.2. Role of PressureRole of Pressure 3.3. Role of VolatilesRole of Volatiles
- 13. Generating Magma from Solid RockGenerating Magma from Solid Rock • Role of Heat:Role of Heat: – Temperature increasesTemperature increases within Earth’s upper crustwithin Earth’s upper crust (called the(called the geothermalgeothermal gradientgradient) average between) average between 2020oo C to 30C to 30oo C per kilometer.C per kilometer. – Rocks in the lower crustRocks in the lower crust and upper mantle are nearand upper mantle are near their melting points.their melting points. – Any additional heat mayAny additional heat may induce melting:induce melting: 1.1. from rocks descending intofrom rocks descending into the mantlethe mantle 2.2. heating or frictionheating or friction 3.3. or rising heat from theor rising heat from the mantlemantle
- 14. • Role of Pressure:Role of Pressure: – A reduction in confining pressure causes theA reduction in confining pressure causes the lowering of a rock’s melting temperature.lowering of a rock’s melting temperature. Generating Magma from Solid RockGenerating Magma from Solid Rock – When confiningWhen confining pressures drop,pressures drop, decompressiondecompression meltingmelting occurs.occurs. – May occur when aMay occur when a rock ascends as arock ascends as a result ofresult of convectiveconvective upwellingupwelling..
- 15. Decompression MeltingDecompression Melting Insert Mantle Melting and Plate Tectonics: Decompression Melting Animation #52
- 16. Affect of Pressure and VolatilesAffect of Pressure and Volatiles Insert Mantle Melting Pressure-Temperature Graphs Animation #53
- 17. • Role of Volatiles:Role of Volatiles: – Volatiles (primarily water) cause rocks to melt atVolatiles (primarily water) cause rocks to melt at lower temperatureslower temperatures.. Generating Magma from Solid RockGenerating Magma from Solid Rock – Effect ofEffect of volatiles isvolatiles is magnified bymagnified by increasedincreased pressure.pressure.
- 18. Affect of Pressure and VolatilesAffect of Pressure and Volatiles Insert Mantle Melting Pressure-Temperature Graphs Animation #53
- 19. Role of Volatiles – Wet MeltingRole of Volatiles – Wet Melting • Effect of volatiles is magnified by increasedEffect of volatiles is magnified by increased pressure.pressure. • This is particularly important where oceanicThis is particularly important where oceanic lithosphere descends into the mantle.lithosphere descends into the mantle. • Increased heat andIncreased heat and pressure drive waterpressure drive water from the subductingfrom the subducting slab.slab. • These volatiles are veryThese volatiles are very mobile and migrate intomobile and migrate into the wedge of hot mantlethe wedge of hot mantle – lowering the melting– lowering the melting temperature andtemperature and causing melting.causing melting.
- 20. • Mantle-derived basaltic magma buoyantlyMantle-derived basaltic magma buoyantly rises due to itsrises due to its lesser densitylesser density (hotter).(hotter). • In a continental setting, basaltic magma mayIn a continental setting, basaltic magma may ““pondpond” beneath crustal rocks, which have a” beneath crustal rocks, which have a lower density.lower density. Role of Volatiles – Wet MeltingRole of Volatiles – Wet Melting • Crustal rocks areCrustal rocks are near their meltingnear their melting point.point. • Increased heatIncreased heat fromfrom basaltic magmabasaltic magma causes melting ofcauses melting of crustal rockscrustal rocks.. • Forms secondaryForms secondary silica-rich magmas.silica-rich magmas.
- 21. Wet MeltingWet Melting Insert Mantle Melting and Plate Tectonics: Decompression Melting Animation #52
- 23. Three Components of MagmaThree Components of Magma 1.1. AA liquidliquid portion, calledportion, called meltmelt, that is composed, that is composed of mobile ions.of mobile ions. 2.2. SolidsSolids, if any, are silicate, if any, are silicate mineralsminerals that havethat have already crystallized from the melt.already crystallized from the melt. 3.3. VolatilesVolatiles, which are, which are gases dissolvedgases dissolved in thein the melt that are confinedmelt that are confined under immenseunder immense pressurepressure exerted by overlying rocks.exerted by overlying rocks. • water vapor (Hwater vapor (H22O)O) • carbon dioxide (COcarbon dioxide (CO22)) • sulfur dioxide (SOsulfur dioxide (SO22))
- 24. Crystallization ofCrystallization of Magma:Magma: Formation of IgneousFormation of Igneous RocksRocks
- 25. Crystallization of Magma:Crystallization of Magma: Formation of Igneous RocksFormation of Igneous Rocks 1.1. Cooling of magma results in theCooling of magma results in the systematic arrangement of ions intosystematic arrangement of ions into orderly patterns.orderly patterns. 2.2. As heat is lost, ions lose their mobilityAs heat is lost, ions lose their mobility (vibrate less vigorously) and begin to(vibrate less vigorously) and begin to pack closer and closer together until thepack closer and closer together until the forces of chemical bonds will confineforces of chemical bonds will confine them to and orderly crystallinethem to and orderly crystalline arrangement.arrangement.
- 26. 3.3. When magma cools, silicon and oxygenWhen magma cools, silicon and oxygen atoms link together first to formatoms link together first to form Si-OSi-O tetrahedratetrahedra.. 4.4. Further cooling – Tetrahedra bond withFurther cooling – Tetrahedra bond with other ions to formother ions to form embryonic crystalembryonic crystal nucleinuclei.. 5.5. Further cooling –Further cooling – Nuclei growNuclei grow as ions loseas ions lose their mobility and join the crystallinetheir mobility and join the crystalline network.network. 6.6. The silicate minerals resulting fromThe silicate minerals resulting from crystallization form in a predictable order.crystallization form in a predictable order. Crystallization of Magma:Crystallization of Magma: Formation of Igneous RocksFormation of Igneous Rocks
- 27. • Bowen’s Reaction SeriesBowen’s Reaction Series explains this predictable order ofexplains this predictable order of crystallization of silicate minerals and how this relates tocrystallization of silicate minerals and how this relates to the evolution of magma and igneous compositions.the evolution of magma and igneous compositions. • Demonstrates that as a magma cools, minerals crystallizeDemonstrates that as a magma cools, minerals crystallize in a systematic fashion based on theirin a systematic fashion based on their melting pointsmelting points..
- 28. Bowen’s Reaction Series explains the evolutionBowen’s Reaction Series explains the evolution of magma and igneous rock compositionsof magma and igneous rock compositions
- 29. Evolution of MagmasEvolution of Magmas • Bowen’s Reaction Series:Bowen’s Reaction Series: Divided into twoDivided into two branches:branches: discontinuous seriesdiscontinuous series andand continuous seriescontinuous series • Discontinuous Reaction SeriesDiscontinuous Reaction Series – The upper left branch indicates that as magma cools,The upper left branch indicates that as magma cools, olivineolivine is the first mineral to crystallize.is the first mineral to crystallize. – Olivine chemically reacts with the remaining melt to formOlivine chemically reacts with the remaining melt to form pyroxenepyroxene.. – Single tetrahedra of olivine link together with additionalSingle tetrahedra of olivine link together with additional tetrahedra to form single-chains structures of thetetrahedra to form single-chains structures of the pyroxene mineral.pyroxene mineral. – Pyroxene reacts with the remaining melt to form thePyroxene reacts with the remaining melt to form the double-chain structure ofdouble-chain structure of amphiboleamphibole.. – Amphibole reacts to form the sheet structure ofAmphibole reacts to form the sheet structure of biotitebiotite.. – Discontinuous – each step forms a different silicateDiscontinuous – each step forms a different silicate structure.structure.
- 30. Evolution of MagmasEvolution of Magmas • Bowens Reaction Series shows thatBowens Reaction Series shows that during crystallization, the compositionduring crystallization, the composition of the liquid portion of the magmaof the liquid portion of the magma continually changes.continually changes. – Composition changes due to removal ofComposition changes due to removal of elements by earlier-forming minerals.elements by earlier-forming minerals. – Minerals remain in contact with theMinerals remain in contact with the remaining melt and will chemically reactremaining melt and will chemically react and evolve into the next mineral in theand evolve into the next mineral in the sequence.sequence.
- 31. • TheThe silicasilica componentcomponent of the melt becomesof the melt becomes enrichedenriched asas crystallizationcrystallization proceeds.proceeds. • Forms increasinglyForms increasingly complex silicatecomplex silicate structures.structures.
- 32. Evolution of MagmasEvolution of Magmas • Bowen’s Reaction SeriesBowen’s Reaction Series Continuous Reaction Series:Continuous Reaction Series: – The right branch indicates Ca-The right branch indicates Ca- rich plagioclase feldspar reactsrich plagioclase feldspar reacts with Na ions in the melt towith Na ions in the melt to become progressively more Na-become progressively more Na- rich.rich. – Na ions diffuse into feldsparNa ions diffuse into feldspar crystals and replace Ca ions incrystals and replace Ca ions in the crystal lattice.the crystal lattice. – Continuous – no steps, sameContinuous – no steps, same silicate structure, same family ofsilicate structure, same family of minerals –minerals – solid solution seriessolid solution series – Rapid cooling prohibits completeRapid cooling prohibits complete replacement producing zonedreplacement producing zoned crystals with Ca-rich cores andcrystals with Ca-rich cores and Na-rich rims.Na-rich rims. – ““Mini”-continuous reactionMini”-continuous reaction series occurs within each step ofseries occurs within each step of the discontinuous series – olivine,the discontinuous series – olivine, pyroxene, amphibole.pyroxene, amphibole.
- 33. • Magmatic Differentiation byMagmatic Differentiation by Crystal Settling (FractionalCrystal Settling (Fractional Crystallization)Crystallization) – More dense, early-formed crystalsMore dense, early-formed crystals sink toward the bottom of the magmasink toward the bottom of the magma chamber.chamber. – Separation of a melt from earlierSeparation of a melt from earlier formed crystalsformed crystals halts the chemicalhalts the chemical reaction process along BRSreaction process along BRS.. – Produces one or more stages ofProduces one or more stages of crystallization.crystallization. – Forms of one or moreForms of one or more secondarysecondary magmasmagmas from a singlefrom a single parentalparental magmamagma.. Processes ResponsibleProcesses Responsible for Deviations from BRSfor Deviations from BRS BRS is highly idealized, assumes magmaBRS is highly idealized, assumes magma cools slowly in an unchanging environmentcools slowly in an unchanging environment
- 34. Fractional CrystallizationFractional Crystallization Insert Fractional Crystallization Animation #33
- 35. • AssimilationAssimilation – Changing a magma’s composition by the incorporation ofChanging a magma’s composition by the incorporation of foreign matterforeign matter into a magma (into a magma (xenolithsxenoliths).). Processes Responsible forProcesses Responsible for Deviations from BRSDeviations from BRS – In near surfaceIn near surface environments, the force ofenvironments, the force of injecting magma mayinjecting magma may fracture surrounding brittlefracture surrounding brittle rocksrocks ((host rockhost rock). Dislodged). Dislodged blocks become incorporatedblocks become incorporated into the magma.into the magma. – In deeper environments,In deeper environments, magma may be hot enoughmagma may be hot enough toto melt and assimilatemelt and assimilate hosthost rock near its meltingrock near its melting temperature.temperature.
- 36. Processes Responsible forProcesses Responsible for Deviations from BRSDeviations from BRS – Two chemicallyTwo chemically distinct magmas maydistinct magmas may produce anproduce an intermediateintermediate compositioncomposition quitequite different from eitherdifferent from either original magma.original magma. – MixingMixing aided byaided by convective flowconvective flow in thein the magma chamber.magma chamber. • Magma MixingMagma Mixing – Involves two bodies of magma intrudingInvolves two bodies of magma intruding one another.one another.
- 37. Magma compositions willMagma compositions will vary depending on thevary depending on the source materialsource material that isthat is melted and themelted and the eventsevents (history)(history) that affectthat affect crystallization alongcrystallization along BRS.BRS.
- 38. Origin of Magma CompositionsOrigin of Magma Compositions 1.1. Silica-Poor Magmas (Basaltic)Silica-Poor Magmas (Basaltic) – Primary/Primitive MagmasPrimary/Primitive Magmas • Partial Melting of Mantle (Asthenosphere)Partial Melting of Mantle (Asthenosphere) 2.2. Silica-Rich and Intermediate MagmasSilica-Rich and Intermediate Magmas (Andesitic and Rhyolitic)(Andesitic and Rhyolitic) – Secondary/Evolved to Highly EvolvedSecondary/Evolved to Highly Evolved MagmasMagmas • Partial Melting of CrustPartial Melting of Crust • Fractional Crystallization of Basaltic MagmaFractional Crystallization of Basaltic Magma • Assimilation or Magma MixingAssimilation or Magma Mixing
- 39. • Most originate from directMost originate from direct partial meltingpartial melting (incomplete melting) of(incomplete melting) of ultramafic rockultramafic rock (peridotite) in the(peridotite) in the mantlemantle.. • Not evolved.Not evolved. • Primary/PrimitivePrimary/Primitive Magmas –Magmas – earliest stagesearliest stages along BRS – olivine,along BRS – olivine, pyroxene, Ca-plagioclase.pyroxene, Ca-plagioclase. • Basaltic magmas form atBasaltic magmas form at mid-ocean ridges and riftmid-ocean ridges and rift zoneszones byby decompressiondecompression meltingmelting or ator at subductionsubduction zoneszones byby wet meltingwet melting.. Origin of Basaltic MagmasOrigin of Basaltic Magmas
- 40. • Mantle-derived basalticMantle-derived basaltic magmas migrates upward,magmas migrates upward, melts, andmelts, and assimilates moreassimilates more silica-rich rockssilica-rich rocks in the crustin the crust generating magma ofgenerating magma of andesitic composition.andesitic composition. • Andesitic magma may alsoAndesitic magma may also evolve byevolve by magmaticmagmatic differentiationdifferentiation (crystal(crystal settling).settling). • Evolved Magmas.Evolved Magmas. • Secondary Magmas –Secondary Magmas – intermediate stages alongintermediate stages along BRS – pyroxene,BRS – pyroxene, amphibole, biotite,amphibole, biotite, plagioclase, and minorplagioclase, and minor quartz.quartz. Origin of Andesitic MagmasOrigin of Andesitic Magmas
- 41. • Most likely form as theMost likely form as the endend product of crystallization ofproduct of crystallization of andesitic magmaandesitic magma.. • Or product ofOr product of partial meltingpartial melting of silica-rich continentalof silica-rich continental rocksrocks.. • Highly Evolved Magmas.Highly Evolved Magmas. • Secondary/Teritary Magmas –Secondary/Teritary Magmas – late stages along BRS –late stages along BRS – orthoclase, quartz, muscovite,orthoclase, quartz, muscovite, plagioclase, biotite, and lesserplagioclase, biotite, and lesser amphibole.amphibole. • Higher in silica and thereforeHigher in silica and therefore more viscous than othermore viscous than other magmas.magmas. • Because of their viscosity, theyBecause of their viscosity, they lose their mobilitylose their mobility beforebefore reaching the surface.reaching the surface. • Tend to produceTend to produce largelarge plutonic structuresplutonic structures.. Origin of Granitic MagmasOrigin of Granitic Magmas
- 42. Classification ofClassification of Igneous RocksIgneous Rocks
- 43. Classification of Igneous RocksClassification of Igneous Rocks • Igneous rocks are typically classified byIgneous rocks are typically classified by – TextureTexture – Mineral CompositionMineral Composition • TheThe environmentenvironment during crystallizationduring crystallization can be roughly inferred fromcan be roughly inferred from texturetexture.. • TheThe source and historysource and history can be roughlycan be roughly inferred from theinferred from the mineral compositionmineral composition..
- 45. Igneous TexturesIgneous Textures • TextureTexture in igneous rocks isin igneous rocks is determined by thedetermined by the – sizesize,, – shapeshape, and, and – arrangementarrangement of mineral grains.of mineral grains.
- 46. Igneous TexturesIgneous Textures • Factors Affecting Crystal SizeFactors Affecting Crystal Size 1.1. Rate of cooling – TimeRate of cooling – Time 2.2. Amount ofAmount of silicasilica (SiO(SiO22) present) present 3.3. Amount ofAmount of dissolved gasesdissolved gases 4.4. FluidsFluids (water and other volatiles)(water and other volatiles) presentpresent
- 47. Rate of CoolingRate of Cooling • The rate of cooling is determined by theThe rate of cooling is determined by the environment:environment: – ExtrusiveExtrusive:: Rocks formed fromRocks formed from lavalava at theat the surface are classified assurface are classified as extrusiveextrusive oror volcanicvolcanic rocks.rocks. – IntrusiveIntrusive:: Rocks formed fromRocks formed from magmamagma thatthat crystallizes at depth are termedcrystallizes at depth are termed intrusiveintrusive, or, or plutonic rocks.plutonic rocks.
- 48. The rate of cooling is determined by the environment:The rate of cooling is determined by the environment: – ExtrusiveExtrusive:: Cools quickly at surface –Cools quickly at surface – fine-grainedfine-grained – IntrusiveIntrusive:: Cools slowly subsurface –Cools slowly subsurface – course-grainedcourse-grained
- 49. Rapid Rate of CoolingRapid Rate of Cooling Aphanitic (Fine-Grained) TextureAphanitic (Fine-Grained) Texture • RapidRapid rate of cooling ofrate of cooling of lava or magma.lava or magma. • Causes ions to quicklyCauses ions to quickly lose mobility and readilylose mobility and readily combine with existingcombine with existing crystals.crystals. • Promotes development ofPromotes development of numerous embryonicnumerous embryonic nucleinuclei that all competethat all compete for available ions.for available ions. • FormsForms many microscopicmany microscopic crystalscrystals.. • Commonly characterizedCommonly characterized by color –by color – lightlight,, intermediateintermediate,, or darkor dark..
- 50. Vesicular Texture –Vesicular Texture – Rapid Cooling W/ VolatilesRapid Cooling W/ Volatiles Vesicular Basalt • Aphaniutic RocksAphaniutic Rocks may containmay contain vesiclesvesicles (voids from(voids from gas bubbles).gas bubbles). • Form in the upperForm in the upper zone of the lavazone of the lava flow where…flow where… • rapid coolingrapid cooling “freezes” the lava“freezes” the lava preserving openingpreserving opening produced byproduced by expanding gasexpanding gas bubbles.bubbles.
- 51. • Very Fast RateVery Fast Rate –– molten material ismolten material is quenched suchquenched such that ions arethat ions are unable to arrangeunable to arrange into a crystallineinto a crystalline network.network. • FormsForms glassglass rock –rock – obsidian, scoria, orobsidian, scoria, or pumicepumice.. Very Fast Rate of CoolingVery Fast Rate of Cooling Glassy TextureGlassy Texture Obsidian
- 52. Pyroclastic TexturesPyroclastic Textures • Various fragments ejected during a violentVarious fragments ejected during a violent volcanic eruption:volcanic eruption: – Very fine-grainedVery fine-grained ashash – CrystalsCrystals,, glass fragmentsglass fragments,, pumicepumice – BombsBombs –– streamlined molten blobsstreamlined molten blobs thatthat solidified in air.solidified in air. – BlocksBlocks –– large angular fragmentslarge angular fragments torn from thetorn from the walls of the vent.walls of the vent. • Textures often appear to more similar toTextures often appear to more similar to sedimentary rocks (sedimentary rocks (clasticclastic).).
- 53. Pyroclastic RocksPyroclastic Rocks • TuffTuff – Composed of ash-sized fragments that– Composed of ash-sized fragments that solidified before impact and cemented later.solidified before impact and cemented later. • Welded TuffWelded Tuff – Composed hot, fine glass shards– Composed hot, fine glass shards that fused together upon impact.that fused together upon impact. • Volcanic BrecciaVolcanic Breccia – Particles larger than ash.– Particles larger than ash.
- 54. • Slow RateSlow Rate of coolingof cooling magma.magma. • Permits movement of ionsPermits movement of ions until they join an existinguntil they join an existing crystalline structure.crystalline structure. • Promotes the growth ofPromotes the growth of fewer but larger crystalsfewer but larger crystals.. • Mass of intergrownMass of intergrown crystals.crystals. • Large, visible crystals canLarge, visible crystals can be identified without abe identified without a microscope.microscope. Slow Rate of CoolingSlow Rate of Cooling Phaneritic (Coarse-Phaneritic (Coarse- Grained) TextureGrained) Texture
- 55. • Exceptionally coarse-Exceptionally coarse- grainedgrained igneousigneous rocks.rocks. • Large crystal sizeLarge crystal size generated by slowgenerated by slow cooling rates andcooling rates and dissolved fluids.dissolved fluids. • Crystals are allCrystals are all largerlarger than 1 cm inthan 1 cm in diameterdiameter.. • Crystals can be asCrystals can be as large as 1 meter orlarge as 1 meter or more.more. Very Slow Rate of Cooling w/ VolatilesVery Slow Rate of Cooling w/ Volatiles Pegmatitic TexturePegmatitic Texture
- 56. • Pegmatites form inPegmatites form in late stages of crystallization oflate stages of crystallization of granitic magmasgranitic magmas (highly evolved).(highly evolved). • Water and volatilesWater and volatiles are present in unusually largeare present in unusually large percentage:percentage: – Chlorine, fluorine, and sulfurChlorine, fluorine, and sulfur • Also contain significant amounts rare elements:Also contain significant amounts rare elements: – lithium, cesium, boron, berylium, uranium,lithium, cesium, boron, berylium, uranium, • Ion migration is enhanced in this fluid-richIon migration is enhanced in this fluid-rich environment forming large crystals.environment forming large crystals. • Magma “stewing in its own juices.”Magma “stewing in its own juices.” • May produce semi-precious gems such as beryl,May produce semi-precious gems such as beryl, topaz, and tourmaline.topaz, and tourmaline. Very Slow Rate of Cooling w/ VolatilesVery Slow Rate of Cooling w/ Volatiles Pegmatitic TexturePegmatitic Texture
- 57. • Minerals form byMinerals form by differentdifferent cooling ratescooling rates.. • Large crystals, calledLarge crystals, called phenocrystsphenocrysts, are embedded in a, are embedded in a matrix of smaller crystals, calledmatrix of smaller crystals, called thethe groundmassgroundmass.. • A rock with porhyritic texture isA rock with porhyritic texture is called acalled a porphyryporphyry.. • This type of rock typically has aThis type of rock typically has a 2-phase cooling history that2-phase cooling history that affected the rate ofaffected the rate of crystallization.crystallization. Two-Phased CoolingTwo-Phased Cooling Porphyrytic TexturePorphyrytic Texture
- 58. The texture of a particularThe texture of a particular igneous rock is ultimatelyigneous rock is ultimately determined by thedetermined by the environmentenvironment from which it crystallized.from which it crystallized.
- 59. Mineral CompositionsMineral Compositions of Igneous Rocksof Igneous Rocks
- 60. Bowen’s Reaction Series explains the order of silicateBowen’s Reaction Series explains the order of silicate mineral crystallization and the how this governs themineral crystallization and the how this governs the evolution of magma and igneous rock compositionsevolution of magma and igneous rock compositions
- 62. Igneous CompositionsIgneous Compositions • UltramaficUltramafic Composition:Composition: – Rare composition that is high in magnesium andRare composition that is high in magnesium and iron.iron. • Low silica content –Low silica content – approximatelyapproximately 45%45%.. • Main constituent ofMain constituent of thethe upper mantleupper mantle..
- 63. Ultramafic RocksUltramafic Rocks:: PeridotitePeridotite • Ultramafic igneous rocksUltramafic igneous rocks are composed entirely ofare composed entirely of dark (ordark (or ferromagnesianferromagnesian)) silicate minerals:silicate minerals: – OlivineOlivine – Pyroxene (Augite)Pyroxene (Augite) – Minor Ca-PlagioclaseMinor Ca-Plagioclase
- 64. Igneous CompositionsIgneous Compositions • BasalticBasaltic (or(or MaficMafic) Composition:) Composition: – MaficMafic ((mamagnesium andgnesium and feferrum, for iron)rrum, for iron) – Silica deficient –Silica deficient – approximatelyapproximately 50 percent50 percent.. – MoreMore densedense than graniticthan granitic rocks.rocks. – Comprise theComprise the ocean floorocean floor as well as manyas well as many volcanicvolcanic islandsislands.. – Also found on continents.Also found on continents.
- 65. Mafic RocksMafic Rocks:: GabbroGabbro,, BasaltBasalt • Mafic igneous rocks areMafic igneous rocks are composed primarily ofcomposed primarily of dark (ordark (or ferromagnesianferromagnesian)) silicate minerals:silicate minerals: – OlivineOlivine – Pyroxene (Augite)Pyroxene (Augite) – Amphibole (Hornblende)Amphibole (Hornblende) – Ca-PlagioclaseCa-Plagioclase
- 66. Igneous CompositionsIgneous Compositions • AndesiticAndesitic (or(or IntermediateIntermediate) Composition:) Composition: – Intermediate silica content (Intermediate silica content (~60%~60%) between granite) between granite (65%) and basalt (50%).(65%) and basalt (50%). • Contain at least 25Contain at least 25 percent dark silicatepercent dark silicate minerals.minerals. • Associated withAssociated with explosive volcanicexplosive volcanic activityactivity nearnear continental margins.continental margins.
- 67. Intermediate RocksIntermediate Rocks:: DioriteDiorite,, AndesiteAndesite • Intermediate igneous rocks are composed of darkIntermediate igneous rocks are composed of dark and light silicate minerals:and light silicate minerals: – Pyroxene (Augite)Pyroxene (Augite) – Amphibole (Hornblende)Amphibole (Hornblende) – Biotite MicaBiotite Mica – PlagioclasePlagioclase – Minor QuartzMinor Quartz
- 68. Igneous CompositionsIgneous Compositions • GraniticGranitic or (or (FelsicFelsic) Composition:) Composition: – FelsicFelsic ((felfeldspar anddspar and sisilica).lica). – Contains highContains high amounts of silicaamounts of silica (SiO(SiO22) –) – 65 percent65 percent or more.or more. – Major constituentsMajor constituents ofof continental crustcontinental crust..
- 69. Felsic RocksFelsic Rocks:: GraniteGranite,, RhyoliteRhyolite • Felsic igneous rocks are composed of primarilyFelsic igneous rocks are composed of primarily light with fewer dark silicate minerals:light with fewer dark silicate minerals: – QuartzQuartz – Muscovite and Biotite MicasMuscovite and Biotite Micas – Plagioclase and Orthoclase FeldsparsPlagioclase and Orthoclase Feldspars – Amphibole (Hornblende)Amphibole (Hornblende)
- 70. Igneous Rock ClassificationIgneous Rock Classification FelsicFelsic IntermediateIntermediate MaficMafic UltramaficUltramafic FF ii nn ee RhyoliteRhyolite AndesiteAndesite BasaltBasalt CC oo aa rr ss ee GraniteGranite DioriteDiorite GabbroGabbro PeridotitePeridotite
- 71. The mineral composition of aThe mineral composition of a particular igneous rock isparticular igneous rock is ultimately determined by theultimately determined by the composition of the magmacomposition of the magma (source material and history)(source material and history) from which it crystallized.from which it crystallized.
- 72. Glossary ofGlossary of Igneous RocksIgneous Rocks
- 73. Naming Igneous RocksNaming Igneous Rocks
- 74. Naming Igneous RocksNaming Igneous Rocks
- 75. Igneous Rock ClassificationIgneous Rock Classification FelsicFelsic IntermediateIntermediate MaficMafic UltramaficUltramafic FF ii nn ee RhyoliteRhyolite AndesiteAndesite BasaltBasalt CC oo aa rr ss ee GraniteGranite DioriteDiorite GabbroGabbro PeridotitePeridotite
- 76. Igneous Rock ClassificationIgneous Rock Classification
- 77. GraniteGranite • IntrusiveIntrusive andand phaneriticphaneritic.. • Over 25 percent quartz, about 65Over 25 percent quartz, about 65 percent or more feldspar.percent or more feldspar. • Other minor silicates muscovite,Other minor silicates muscovite, biotite, amphibole comprise lessbiotite, amphibole comprise less than 10 percent.than 10 percent. • May exhibit a porphyritic texture.May exhibit a porphyritic texture. • Very abundant as it is oftenVery abundant as it is often associated with mountainassociated with mountain building.building. • The term granite covers a wideThe term granite covers a wide range of mineral compositions.range of mineral compositions.
- 78. RhyoliteRhyolite • ExtrusiveExtrusive equivalent ofequivalent of granite.granite. • AphaniticAphanitic texture.texture. • May contain glassMay contain glass fragments and vesicles.fragments and vesicles. • May containMay contain phenocrystsphenocrysts of orthoclase, mica, andof orthoclase, mica, and quartz.quartz. • TypicallyTypically red to reddish-red to reddish- purplepurple to gray in color.to gray in color. • Less common and lessLess common and less voluminous than granite.voluminous than granite.
- 79. Other GraniticOther Granitic (Felsic) Rocks(Felsic) Rocks • ObsidianObsidian – Extrusive with glassy textureExtrusive with glassy texture – High silica contentHigh silica content – Dark colored due to presence ofDark colored due to presence of metallic ionsmetallic ions • PumicePumice – Extrusive with glassy textureExtrusive with glassy texture – Vesicular texture (more voids thanVesicular texture (more voids than rock)rock) – Frothy appearance with numerousFrothy appearance with numerous voidsvoids – Void shape is typically elongatedVoid shape is typically elongated • ScoriaScoria – Extrusive with glassy textureExtrusive with glassy texture – Vesicular texture (more rock thanVesicular texture (more rock than voids)voids) – Void shape is typically moreVoid shape is typically more roundedrounded
- 80. AndesiteAndesite • Volcanic origin –Volcanic origin – extrusiveextrusive.. • AphaniticAphanitic texture.texture. • Often resemblesOften resembles rhyolite.rhyolite. • Typically medium-Typically medium- gray.gray. • May containMay contain phenocrystsphenocrysts ofof plagioclase andplagioclase and hornblende.hornblende.
- 81. DioriteDiorite • PlutonicPlutonic equivalent ofequivalent of andesite.andesite. • Coarse-grained orCoarse-grained or phaneriticphaneritic.. • Intrusive.Intrusive. • Composed mainly of Na-Composed mainly of Na- rich plagioclaserich plagioclase (intermediate) feldspar(intermediate) feldspar and amphibole withand amphibole with lesser amounts of biotite.lesser amounts of biotite. • Salt and pepperSalt and pepper appearance.appearance.
- 82. BasaltBasalt • Volcanic origin –Volcanic origin – extrusiveextrusive.. • AphaniticAphanitic texture.texture. • Composed mainly of pyroxeneComposed mainly of pyroxene and calcium-rich plagioclaseand calcium-rich plagioclase feldspar with lesser amounts offeldspar with lesser amounts of olivine and amphibole.olivine and amphibole. • Very dark green to black inVery dark green to black in color.color. • May containMay contain phenocrystsphenocrysts ofof plagioclase and olivine.plagioclase and olivine. • May exhibit vesicular texture.May exhibit vesicular texture. • Most common extrusive igneousMost common extrusive igneous rock.rock.
- 83. GabbroGabbro • IntrusiveIntrusive equivalentequivalent of basalt.of basalt. • PhaneriticPhaneritic texturetexture consisting ofconsisting of pyroxene andpyroxene and calcium-richcalcium-rich plagioclase.plagioclase. • Makes up aMakes up a significant percentagesignificant percentage of the oceanic crust.of the oceanic crust.
- 84. PyroclasticPyroclastic • Composed of fragments (Composed of fragments (tephratephra) ejected) ejected during a volcanic eruption.during a volcanic eruption. – TuffTuff – ash-sized fragments that solidified before– ash-sized fragments that solidified before impact and cemented later.impact and cemented later. – Welded TuffWelded Tuff – Composed hot fine glass shards– Composed hot fine glass shards that fused together upon impact.that fused together upon impact. – Volcanic BrecciaVolcanic Breccia – Particles larger than ash.– Particles larger than ash. • BombsBombs – streamlined fragments that solidified in air.– streamlined fragments that solidified in air. • Large angularLarge angular blocksblocks torn from the walls of the vent.torn from the walls of the vent. • Crystals, glass fragments, pumice, ash.Crystals, glass fragments, pumice, ash.
- 85. Interlayered Tuff and ObsidianInterlayered Tuff and Obsidian
- 86. 1996 Eruption of Mount Ruapehu, New Zealand –1996 Eruption of Mount Ruapehu, New Zealand – Intermediate to Felsic composition magmasIntermediate to Felsic composition magmas
Editor's Notes
- #2: To begin our introduction to rocks, we will start with igneous rocks, but first I want to go over the rock cycle from Chapter 1. Show Rock cycle tutorial from Chapter 1 of the Goede Earth CDROM.
- #3: <number>
- #10: So, where does the heat source come from that drives this melting process of the crust and upper mantle. This was addressed during the last class during our discussions from Chapters 1 and 2.
- #11: So, where does the heat source come from that drives this melting process of the crust and upper mantle. This was addressed during the last class during our discussions from Chapters 1 and 2.
- #12: So, where does the heat source come from that drives this melting process of the crust and upper mantle. This was addressed during the last class during our discussions from Chapters 1 and 2.
- #24: Show Introduction to Igneous Rocks Tutorial from Chapter 4 of the Geode Earth CDROM.
- #26: Remember these concepts from Chapter 3 on Minerals.
- #27: Remember Bowen’s Reaction Series: Show slide of BRS and go over the progression of mineral crystallization again. Show the crystalline structure figure: Go over how BSR relates to silicate crystalline structures again and thus mineral physical properties (cleavage, crystal form, hardness, etc.).
- #28: Hopefully by now you have a pretty good understanding of BRS and the processes it embodies. Now, lets look at it a little more deeply as it relates to the evolution of the magma chamber.
- #29: You can superimpose Bowen’s Reaction Series over this igneous rock identification chart.
- #32: Use this chart along with Bowen’s Reaction Series to discuss common silicate minerals. I will progress through the minerals along Bowen’s Reaction Series.
- #44: Last bullets are very important concepts to this chapter. These characteristics will help you (1) determine the history of the rock – where it came from, its source material, how it was formed, and one a bigger-picture scale – what plate tectonic environment was occurring at the time in that area. Now, I am going to discuss in more detail each of these characteristics that we use to classify igneous rocks, texture and mineral composition.
- #47: (2) What is the composition of the building material available, (3&4) dissolved gases and fluids can accelerate crystal grow because they can enhance the rate of ion circulation.
- #48: These will be important concepts for rock identification.
- #49: These will be important concepts for rock identification.
- #61: Hopefully by now you have a pretty good understanding of BRS and the processes it embodies. Now, lets look at it a little more deeply as it relates to the evolution of the magma chamber.
- #63: Composed of minerals that formed very early along Bowen’s Reaction Series – Very High Temperature, Ultramafic melt – predominantly mafic (dark) ions like Fe, Mg, very little Silica content.
- #65: Composed of minerals that formed early along Bowen’s Reaction Series – High Temperature, Mafic melt – high in mafic (dark) ions like Fe, Mg, Ca, Lower in Silica – SiO4. Manifested in typical dark color of the rock.
- #67: Composed of minerals that formed along the middle of Bowen’s Reaction Series – Moderate Temperature, Intermediate melt composition composed of light and dark ions, Intermediate Silica content. Manifested in typical intermediate (gray or peppered) color of the rock.
- #69: Composed of minerals that formed later along Bowen’s Reaction Series – Lower Temperature, silicious melt – high in felsic (light) ions like Si, O, K, Na, Higher in Silica – SiO4. Manifested in typical light color of the rock.
- #74: This is just another version of the same chart. I like this one because it illustrates the rock color, which gives you a general visual guide for identifying these rocks in hand sample. I also like the pictures of the textures, which again give you a visual guide for how these rocks generally appear in hand sample.
- #75: You can superimpose Bowen’s Reaction Series over this igneous rock identification chart.
- #77: You can superimpose Bowen’s Reaction Series over this igneous rock identification chart.