Igneous Rocks/EPCC/LM4

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Igneous Rocks/EPCC/LM4

  1. 1. Igneous RocksIgneous Rocks Chapter 4Chapter 4
  2. 2. Just a quick review:Just a quick review:
  3. 3. What is a rock?What is a rock?  A rock (is most often)is hard andA rock (is most often)is hard and made up of minerals.made up of minerals.  Why most often?Why most often? What is coal?What is coal? What is obsidian?What is obsidian? Rock Gypsum?Rock Gypsum?  The are criteria has exceptions!The are criteria has exceptions!
  4. 4. Types of RocksTypes of Rocks IgneousIgneous SedimentarySedimentary MetamorphicMetamorphic
  5. 5. The Rock CycleThe Rock Cycle
  6. 6. The Rock CycleThe Rock Cycle
  7. 7. The Rock CycleThe Rock Cycle
  8. 8. Chapter 4Chapter 4 Igneous Rocks: Product ofIgneous Rocks: Product of Earth’s Internal FireEarth’s Internal Fire
  9. 9. Igneous Rocks
  10. 10. What Is an Igneous Rock?What Is an Igneous Rock? Igneous rocks vary greatly.Igneous rocks vary greatly. – Some contain large mineral grains.Some contain large mineral grains. – Others contain grains so small they can barely beOthers contain grains so small they can barely be seen under a high power microscope.seen under a high power microscope. – Igneous rocks also vary greatly in color.Igneous rocks also vary greatly in color.  All igneous rocks are formed through theAll igneous rocks are formed through the cooling and solidification of magma/lava.cooling and solidification of magma/lava.
  11. 11. Mode of FormationMode of Formation Intrusive versus ExtrusiveIntrusive versus Extrusive
  12. 12. Intrusive Versus Extrusive IgneousIntrusive Versus Extrusive Igneous RocksRocks  Intrusive igneous rocks form when magmaIntrusive igneous rocks form when magma cools within existing rocks in Earth’scools within existing rocks in Earth’s crust.crust.
  13. 13. Intrusive Versus Extrusive IgneousIntrusive Versus Extrusive Igneous RocksRocks  Extrusive igneous rocks form when magmaExtrusive igneous rocks form when magma cools on Earth’s surface, where they havecools on Earth’s surface, where they have been “extruded.”been “extruded.”
  14. 14. TextureTexture Intrusive versus ExtrusiveIntrusive versus Extrusive
  15. 15. Textures in Igneous RocksTextures in Igneous Rocks Texture – size, shape and orientation of theTexture – size, shape and orientation of the crystals within a rockcrystals within a rock Sizes of mineral grains:Sizes of mineral grains: – Intrusive rocks are coarse-grained. (Phaneritic)Intrusive rocks are coarse-grained. (Phaneritic)  Magma that solidifies in the crust cools slowly and hasMagma that solidifies in the crust cools slowly and has sufficient time to form large mineral grains.sufficient time to form large mineral grains.
  16. 16. Coarse GrainedCoarse Grained
  17. 17. Textures in Igneous RocksTextures in Igneous Rocks – Extrusive rocks are fine-grained.Extrusive rocks are fine-grained. Lava that solidifies on the surface usuallyLava that solidifies on the surface usually cools rapidly, allowing insufficient timecools rapidly, allowing insufficient time for large crystals to grow.for large crystals to grow. – Fine-grained igneous rock is called anFine-grained igneous rock is called an aphaniticaphanitic
  18. 18. Fine GrainedFine Grained
  19. 19. Textures in Igneous RocksTextures in Igneous Rocks – AA porphyryporphyry is an igneous rock in which 50% or moreis an igneous rock in which 50% or more of the rock is coarse mineral grains scattered through aof the rock is coarse mineral grains scattered through a mixture of fine mineral grains.mixture of fine mineral grains. – Porphyritic texturePorphyritic texture – The isolated large grains areThe isolated large grains are phenocrystsphenocrysts..
  20. 20. PorphyriticPorphyritic Phenocrysts
  21. 21. Textures in Igneous RocksTextures in Igneous Rocks  Glassy rocks.Glassy rocks. – Atoms lack time to organize themselves intoAtoms lack time to organize themselves into minerals.minerals. – Extrusive igneous rocks that are largely or whollyExtrusive igneous rocks that are largely or wholly glassy are called obsidianglassy are called obsidian.. They display a distinctive conchoidal fracture (smooth,They display a distinctive conchoidal fracture (smooth, curved surface).curved surface).
  22. 22. Figure 4.5
  23. 23. Textures in Igneous RocksTextures in Igneous Rocks – Another common variety of igneous rock is pumice,Another common variety of igneous rock is pumice, a mass of glassy bubbles of volcanic origin.a mass of glassy bubbles of volcanic origin. – Texture is vesicular – the bubbles have “popped”Texture is vesicular – the bubbles have “popped” and left a vesicleand left a vesicle – Volcanic ash is also mostly glassy because theVolcanic ash is also mostly glassy because the fragments of magma cooled too quickly tofragments of magma cooled too quickly to crystallizecrystallize..
  24. 24. Vesicular TextureVesicular Texture Pumice Basalt
  25. 25. TexturesTextures  Intrusive Igneous RocksIntrusive Igneous Rocks 1) Coarse grained or phaneritic1) Coarse grained or phaneritic  Extrusive Igneous RocksExtrusive Igneous Rocks 1) Fine grained or aphanitic1) Fine grained or aphanitic 2) Porphyritic2) Porphyritic 3) Glassy3) Glassy 4) Vesicular4) Vesicular
  26. 26. Solidification of MagmaSolidification of Magma Bowen’s Reaction SeriesBowen’s Reaction Series
  27. 27. Solidification of MagmaSolidification of Magma  A magma of a given composition canA magma of a given composition can crystallize into many different kinds ofcrystallize into many different kinds of igneous rock.igneous rock.  Solidifying magma forms several differentSolidifying magma forms several different minerals which start to crystallize from theminerals which start to crystallize from the cooling magma at different temperaturescooling magma at different temperatures..
  28. 28. Solidification of MagmaSolidification of Magma  Crystal-melt separation can occur in aCrystal-melt separation can occur in a number of ways:number of ways: – Compression can squeeze melt out of a crystal-meltCompression can squeeze melt out of a crystal-melt mixture.mixture. – Dense, early crystallized minerals may sink to theDense, early crystallized minerals may sink to the bottom of a magma chamber, thereby forming a solidbottom of a magma chamber, thereby forming a solid mineral layer covered by melt.mineral layer covered by melt.  However a separation occurs, theHowever a separation occurs, the compositional changes it causes are calledcompositional changes it causes are called magmatic differentiation by fractionalmagmatic differentiation by fractional crystallizationcrystallization..
  29. 29. Bowen’s Reaction SeriesBowen’s Reaction Series  Canadian-born scientist N. L. BowenCanadian-born scientist N. L. Bowen (1887-1956) first recognized the(1887-1956) first recognized the importance ofimportance of magmatic differentiation bymagmatic differentiation by fractional crystallization.fractional crystallization.  Bowen argued that a single magma couldBowen argued that a single magma could crystallize into both basalt and rhyolitecrystallize into both basalt and rhyolite because of fractional crystallizationbecause of fractional crystallization..
  30. 30. Bowen’s Reaction SeriesBowen’s Reaction Series  Bowen knew that plagioclases thatBowen knew that plagioclases that crystallize from basaltic magma are usuallycrystallize from basaltic magma are usually calcium-rich (anorthitic).calcium-rich (anorthitic).  Plagioclases formed from rhyolitic magmaPlagioclases formed from rhyolitic magma are commonly sodium-rich (albitic).are commonly sodium-rich (albitic).  Bowen called such a continuous reactionBowen called such a continuous reaction between crystals and melts a continuousbetween crystals and melts a continuous reaction series.reaction series.
  31. 31. Bowen’s Reaction SeriesBowen’s Reaction Series  Bowen identified several sequences ofBowen identified several sequences of reactions besides the continuous reactionreactions besides the continuous reaction series of the feldspars.series of the feldspars.  When basalt cools down, one of theWhen basalt cools down, one of the earliest minerals to form is olivine.earliest minerals to form is olivine. – Olivine contains about 40 percent SiOOlivine contains about 40 percent SiO22 by weight.by weight. – Basaltic magma contains 50 percent SiOBasaltic magma contains 50 percent SiO22..  Crystallization of olivine will leave theCrystallization of olivine will leave the residual liquid a little richer in silica.residual liquid a little richer in silica.
  32. 32. Bowen’s Reaction SeriesBowen’s Reaction Series  The solid olivine reacts with silica in the meltThe solid olivine reacts with silica in the melt to form a more silica-rich mineral, pyroxene.to form a more silica-rich mineral, pyroxene.  The pyroxene in turn can react to formThe pyroxene in turn can react to form amphibole.amphibole.  Amphibole can react to form biotite.Amphibole can react to form biotite.  Such a series of reactions is called aSuch a series of reactions is called a discontinuous reaction seriesdiscontinuous reaction series..
  33. 33. Bowens Reaction SeriesBowens Reaction Series
  34. 34. Bowens Reaction SeriesBowens Reaction Series
  35. 35. Mineral AssemblagesMineral Assemblages What it tells usWhat it tells us
  36. 36. Mineral Assemblage In IgneousMineral Assemblage In Igneous RocksRocks  Once the texture of an igneous rock isOnce the texture of an igneous rock is determined, its name will depend on itsdetermined, its name will depend on its mineral assemblage. All common igneousmineral assemblage. All common igneous rocks consist largely of:rocks consist largely of: – Quartz.Quartz. – Feldspar (both potassium feldspar and plagioclase).Feldspar (both potassium feldspar and plagioclase). – Mica (both muscovite and biotite).Mica (both muscovite and biotite). – Amphibole.Amphibole. – Pyroxene.Pyroxene. – Olivine.Olivine.
  37. 37. ColorColor  The overall lightness or darkness of a rockThe overall lightness or darkness of a rock is a valuable indicator of its makeup.is a valuable indicator of its makeup. – Light-colored rocks are:Light-colored rocks are: Quartz.Quartz. Feldspar.Feldspar. Muscovite.Muscovite. – Dark-colored rocks are:Dark-colored rocks are: Biotite.Biotite. Amphibole.Amphibole. Pyroxene.Pyroxene.
  38. 38. Igneous RocksIgneous Rocks One more lookOne more look
  39. 39. Intrusive (Coarse-grained) IgneousIntrusive (Coarse-grained) Igneous RocksRocks  GraniteGranite is quartz-bearing rock in whichis quartz-bearing rock in which potassium feldspar is at least 65 percent bypotassium feldspar is at least 65 percent by volume of the total feldspar present.volume of the total feldspar present.
  40. 40. Intrusive (Coarse-grained) IgneousIntrusive (Coarse-grained) Igneous RocksRocks  DioriteDiorite:: — The chief mineral in diorite is plagioclase.The chief mineral in diorite is plagioclase. — Either or both amphibole and pyroxene are invariablyEither or both amphibole and pyroxene are invariably present.present.
  41. 41. Intrusive Igneous RocksIntrusive Igneous Rocks  Dark-colored diorite grades intoDark-colored diorite grades into gabbro.gabbro. — In gabbro, dark-colored minerals pyroxene and olivineIn gabbro, dark-colored minerals pyroxene and olivine exceed 50 percent of the volume of the rockexceed 50 percent of the volume of the rock..  A coarse-grained igneous rock in whichA coarse-grained igneous rock in which olivine is the most abundant mineral isolivine is the most abundant mineral is called a peridotite.called a peridotite.  Gabbros and peridodites can be found inGabbros and peridodites can be found in both the oceanic and the continental crust.both the oceanic and the continental crust.
  42. 42. Extrusive Igneous RocksExtrusive Igneous Rocks  RhyolitesRhyolites are quartz-bearing.are quartz-bearing.  Rhyolites contain a predominance ofRhyolites contain a predominance of potassium feldspar.potassium feldspar.
  43. 43. Extrusive Igneous RocksExtrusive Igneous Rocks  Andesite:Andesite: – Compositionally equal to a dioriteCompositionally equal to a diorite – Named for the Andes.Named for the Andes.  Basalt:Basalt: – Compositionally equivalent to coarse-grainedCompositionally equivalent to coarse-grained gabbro, fine-grained basalt is the most common kindgabbro, fine-grained basalt is the most common kind of extrusive igneous rock.of extrusive igneous rock. – The dominant rock of the oceanic crustThe dominant rock of the oceanic crust..
  44. 44. Granite RhyoliteFigure 4.7 A
  45. 45. Diorite Andesite
  46. 46. Gabbro Basalt Figure 4.7 C
  47. 47. Pyroclasts, Tephra, And TuffsPyroclasts, Tephra, And Tuffs  A fragment of rock ejected during a volcanicA fragment of rock ejected during a volcanic eruption is called aeruption is called a pyroclastpyroclast.. – Rocks formed from pyroclasts are pyroclasticRocks formed from pyroclasts are pyroclastic rocksrocks..  Geologists commonly refer to a deposit ofGeologists commonly refer to a deposit of pyroclasts aspyroclasts as tephratephra, a Greek name for ash., a Greek name for ash. – Tephra is a collective term for all airborne pyroclasts.Tephra is a collective term for all airborne pyroclasts.
  48. 48. Pyroclasts, Tephra, And TuffsPyroclasts, Tephra, And Tuffs  Tephra particles are categorized by size:Tephra particles are categorized by size: – Bombs: greater than 64 mm in diameterBombs: greater than 64 mm in diameter – Lapilli: between 2 and 64 mmLapilli: between 2 and 64 mm – Ash: smaller than 2 mm.Ash: smaller than 2 mm.  Tephra is igneous when it goes up butTephra is igneous when it goes up but sedimentary when it comes down.sedimentary when it comes down.
  49. 49. Pyroclasts, Tephra, And TuffsPyroclasts, Tephra, And Tuffs  Pyroclastic rocks are transitional betweenPyroclastic rocks are transitional between igneous and sedimentary rocks.igneous and sedimentary rocks.  When bomb-sized tephra are transformed intoWhen bomb-sized tephra are transformed into a rock they are calleda rock they are called agglomeratesagglomerates..  They are calledThey are called tuffstuffs when particles are eitherwhen particles are either lapilli or ash.lapilli or ash.
  50. 50. Figure 4.8 B
  51. 51. Igneous BodiesIgneous Bodies
  52. 52. PlutonsPlutons  All bodies of intrusive igneous rock,All bodies of intrusive igneous rock, regardless of shape or size, are calledregardless of shape or size, are called plutons,plutons, after Pluto, the Greek god of the underworld.after Pluto, the Greek god of the underworld.  Plutons are given special names depending onPlutons are given special names depending on their shapes and sizes.their shapes and sizes.
  53. 53. Figure 4.11
  54. 54. Minor Plutons: Dikes, Sills, andMinor Plutons: Dikes, Sills, and LaccolithsLaccoliths  AA dikedike is a tabular, sheet-like (thin butis a tabular, sheet-like (thin but laterally extensive) body of igneous rock thatlaterally extensive) body of igneous rock that cuts across the layering or fabric of the rockcuts across the layering or fabric of the rock into which it intrudes.into which it intrudes.  AA SillSill is tabular and sheet-like, like a dike,is tabular and sheet-like, like a dike, but runs parallel to the layering or fabric ofbut runs parallel to the layering or fabric of the rocks into which it intrudes.the rocks into which it intrudes.
  55. 55. Dikes and SillsDikes and Sills
  56. 56. Minor Plutons: Dikes, Sills, andMinor Plutons: Dikes, Sills, and Laccoliths (2)Laccoliths (2)  AA laccolithlaccolith is parallel to the layering of theis parallel to the layering of the rocks into which it intrudes, but forces therocks into which it intrudes, but forces the layers of rock above it to bend, forming alayers of rock above it to bend, forming a dome.dome.  AA volcanic pipevolcanic pipe is the roughly cylindricalis the roughly cylindrical conduit that once fed magma upward to aconduit that once fed magma upward to a volcanic vent.volcanic vent.
  57. 57. LaccolithLaccolith Mt. Cristo Rey in El PasoMt. Cristo Rey in El Paso
  58. 58. Volcanic NeckVolcanic Neck
  59. 59. Major PlutonsMajor Plutons  AA batholithbatholith is the largest kind of pluton. It isis the largest kind of pluton. It is an intrusive igneous body of irregular shapean intrusive igneous body of irregular shape that cuts across the layering or other fabric ofthat cuts across the layering or other fabric of the rock into which it intrudes.the rock into which it intrudes. – The largest batholith in North America,The largest batholith in North America, approximately 1500 km long, is the Coast Rangeapproximately 1500 km long, is the Coast Range batholith of British Columbia and southern Alaska.batholith of British Columbia and southern Alaska. – The magma from which a batholith forms intrudesThe magma from which a batholith forms intrudes upward from its source deep in the continental crust.upward from its source deep in the continental crust.
  60. 60. Figure 4.14

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