EASC 116 Ch. 3 Igneous Rx
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EASC 116 Ch. 3 Igneous Rx






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EASC 116 Ch. 3 Igneous Rx EASC 116 Ch. 3 Igneous Rx Presentation Transcript

  • Igneous RocksIgnis = “fire”Form from cooling & crystallization of magma (molten rock)Lava = molten rock at surface
  • Igneous RocksClassified by texture & compositionTexture = crystal size of mineralsComposition = minerals present
  • Changes of State of MatterAdd heat (melting):Rx Magma (atoms faster)Remove heat (crystallize):Rx (atoms slower) Magma
  • Texture of Igneous RocksDepends on magma’s cooling rate1) Cools slowlyAtoms can move through liquid - crystals grow (large, small)
  • Magma’s Cooling Rate2) Cools quicklyForms a solid faster than atoms can move around - crystals are (large, small)
  • Texture (Crystal Size)Two environments where magma cools:1) At surface or shallow burial2) Deep underground
  • Types of Texture1) Aphanitic - crystals invisible to naked eye - magma cooled ___________ - extrusive/volcanic
  • Types of Texture2) Vesicular- aphanitic rock w/many holes (vesicles) in it- gas trapped as magma cools very quick
  • Types of Texture3) Phaneritic - crystals easily visible - magma cooled ___________ - intrusive/plutonic
  • Types of Texture4) Porphyritic - two size crystals in same rockLarge crystals = phenocrystsSmall crystals = groundmass
  • Porphyritic Texture2-stage cooling process:1st stage = slow cooling at depth_______________ are formed2nd stage = rapid cooling of remaining magma_______________ are formed
  • Types of Texture5) Glassy - no crystalline structureEx: Obsidian; pumice
  • Types of Texture6) PegmaticAll minerals larger than 1 cmForms during later stage of crystallization- large percentage of liquid allows ions to migrate easier
  • Types of Texture7) Pyroclastic“pyro” = fire; “clastic” = piecesConsolidated rock fragments ejected during violent volcanic eruptions
  • Pyroclastic textureFragments can be volcanic ash, blobs of magma, or angular blocks- not composed of interlocking crystals!
  • Igneous Rock CompositionThe most abundant elements of Earth’s crust are _____ & ______Magma is mostly silica with varying amounts of other six elements
  • CompositionOther elements collect in water at top of magma chamberCreates hydrothermal solution- cools in fractures as highly concentrated ore deposits
  • Igneous CompositionsMafic- 45-50% silica (“silica-poor”)- rich in magnesium, iron (Fe), & calcium- dark-colored: black, dark gray, brownish-red
  • Igneous CompositionsFelsic (feldspar & silica)- 60-75% silica (“silica rich”)- rich in aluminum, potassium, & sodium- light-colored: light gray, pinkish
  • Igneous CompositionsIntermediateAphanitic: medium grayPhaneritic: black & white crystals
  • Importance of Igneous RocksCompose 90% of Earth’s crustTwo types of crust: oceanic crust = basalt continental crust = granite
  • Question:Why different igneous rock compositions if only 8 elements?N.L. Bowen experimented with mafic magmas
  • Results:** Same sequence of minerals crystallized from magmaReferred to as Bowen’s Reaction Series (Fig. 3.16)
  • Bowen’s Reaction SeriesDiscontinuous series (left) vs. continuous series (right)Discontinuous series:- each mineral has a unique silicate structure
  • Continuous seriesDifferent compositions of plagioclase feldspars- ions of Ca2+ and Na+ can interchange within crystalline structure
  • Bowen’s Reaction SeriesAs magma crystallizes:First mineral to form = maficComposition of remaining magma changes
  • Bowen’s Reaction SeriesBiotite uses last mafic elements in magma- remaining magma becomes more “silica rich”
  • Bowen’s Reaction SeriesMinerals that form in same temp. conditions are found together in same igneous rockQUESTION: Which mineral would you expect to form phenocrysts in a porphyritic basalt?
  • Phenocryst Mineral:a) Quartzb) Potassium feldsparc) Biotited) Calcium-rich plagioclase f-spare) Sodium-rich plagioclase f-spar
  • Felsic magmaFelsic minerals melt at cooler temp’s- magma not as hot as mafic magma- felsic magma not as buoyant
  • Felsic magmaMagma doesn’t reach surfaceEx: Continental crust = granite
  • Important ConceptsA mineral is stable if the environmental conditions are similar to where it formedEx: temperature, pressure, water- content
  • Example:Mafic minerals are stable in ____ temperaturesFelsic minerals are stable in ____ temperatures
  • Important ConceptsIf a mineral is put under different environmental conditions, it becomes unstable- mineral has to react to new environment by changing
  • New EnvironmentalConditions:If at the surface, weathering occursIf within the crust, metamorphism occurs