Modules 4-6

Chapter 4: Earth Materials: Minerals and Rocks

Lecture Outline

  • Minerals and Their Formation

  • Rock-Forming Minerals

  • Mineral ID with Physical Properties

  • Major Classes of Rocks

  • The Rock Cycle

  • Mineral Resources

Minerals: Building Blocks of Rocks

  • Homogenous: Minerals are uniform throughout.

  • Naturally occurring: Formed by natural geological processes.

  • Solid: Maintains its shape and volume.

  • Inorganic (usually): Not composed of organic molecules (some exceptions).

  • Crystalline: Possessing an ordered atomic structure.

  • Specific chemical composition: Defined by a chemical formula.

Elements: Building Blocks of Minerals

  • Atoms consist of protons, neutrons, and electrons.

  • Atomic number: Number of protons, which defines the element.

  • Atomic mass: Sum of protons and neutrons.

  • Isotopes: Variants of an element with different numbers of neutrons, thus different atomic masses.

Chemical Bonding

  • Chemical reaction: Interaction of atoms to form chemical compounds in fixed proportions.

  • Bonds are formed by electron transfer or sharing:

    • Ionic bonds: Electrons are transferred between atoms.

    • Covalent bonds: Electrons are shared between atoms.

Ionic Bonds

  • Occur when electrons are transferred. For example, sodium (Na) and chlorine (Cl) react.

  • Sodium atom loses one electron to become a positive ion (Na+).

  • Chlorine atom gains one electron to become a negative ion (Cl-).

  • Electrostatic attraction holds the ions together.

  • Na+Cl→Na++Cl−Na + Cl \rightarrow Na^+ + Cl^-

  • Most minerals are ionic compounds.

Covalent Bonds

  • Electrons are shared between atoms.

  • The carbon atoms in diamond are arranged in a tetrahedral structure where each carbon shares electrons with four neighbors.

  • Covalent bonds are generally very strong.

Formation of Minerals

  • Crystallization: Atoms in a gas or liquid arrange in a crystalline structure to form a solid substance, occurring in proper chemical proportions.

  • Lower a liquid to below its melting point

  • Supersaturate a solution

  • Cations: positively charged ions (e.g., Si4+Si^{4+}, A13+A1^{3+})

  • Anions: negatively charged ions (e.g. O2−O^{2-}, Cl^{-}$)

Rock-Forming Minerals

  • Minerals are grouped based on their chemical composition.

  • Only a few dozen minerals are commonly encountered and are known as rock-forming minerals.

Silicate Minerals

  • Most abundant group of minerals in Earth’s crust.

  • The silicon-oxygen tetrahedron (SiO_4)isthefundamentalbuildingblockofallsilicates.</p></li><li><p>Silicatetetrahedracanbearrangedinvariousstructures:</p><ul><li><p>Isolatedtetrahedra:e.g.,Olivine() is the fundamental building block of all silicates.</p></li><li><p>Silicate tetrahedra can be arranged in various structures:</p><ul><li><p>Isolated tetrahedra: e.g., Olivine ((Mg,Fe)2SiO4),nocleavageplane</p></li><li><p>Singlechains:e.g.,Pyroxene(), no cleavage plane</p></li><li><p>Single chains: e.g., Pyroxene ((Mg,Fe)SiO_3),2planesat90°cleavage</p></li><li><p>Doublechains:e.g.,Amphibole(), 2 planes at 90° cleavage</p></li><li><p>Double chains: e.g., Amphibole (Ca2(Mg,Fe)5Si8O{22}(OH)_2),2planesat60°and120°cleavage</p></li><li><p>Sheets:e.g.,Mica(Muscovite:), 2 planes at 60° and 120° cleavage</p></li><li><p>Sheets: e.g., Mica (Muscovite:KAl2(AlSi3O{10})(OH)2),1planecleavage</p></li><li><p>Three−dimensionalframeworks:e.g.,Feldspar(Orthoclase:), 1 plane cleavage</p></li><li><p>Three-dimensional frameworks: e.g., Feldspar (Orthoclase:KAlSi3O8,Plagioclase:, Plagioclase:(Ca,Na)AlSi2O8),2planesat90°cleavage</p></li></ul></li></ul><h4id="329d84e5−f217−4054−ab33−5f6a5f4c82b7"data−toc−id="329d84e5−f217−4054−ab33−5f6a5f4c82b7"collapsed="false"seolevelmigrated="true">CarbonateMinerals</h4><ul><li><p>Carbonateion(), 2 planes at 90° cleavage</p></li></ul></li></ul><h4 id="329d84e5-f217-4054-ab33-5f6a5f4c82b7" data-toc-id="329d84e5-f217-4054-ab33-5f6a5f4c82b7" collapsed="false" seolevelmigrated="true">Carbonate Minerals</h4><ul><li><p>Carbonate ion (CO_3^{2-})isabasicbuildingblock.</p></li><li><p>CommonmineralsformattheEarth′ssurface.</p></li><li><p>Carbonateandcalciumarearrangedinalternatingsheets,e.g.,Calcite() is a basic building block.</p></li><li><p>Common minerals form at the Earth's surface.</p></li><li><p>Carbonate and calcium are arranged in alternating sheets, e.g., Calcite (CaCO_3).</p></li></ul><h4id="eb39e7b4−add4−4e54−92c0−9ef8f6e04ef5"data−toc−id="eb39e7b4−add4−4e54−92c0−9ef8f6e04ef5"collapsed="false"seolevelmigrated="true">OxideMinerals</h4><ul><li><p>Oxygenanionisbondedtometalliccations.</p></li><li><p>Economicallyimportantasoresofmetals(iron,titanium,chromium).</p></li><li><p>Example:Hematite().</p></li></ul><h4 id="eb39e7b4-add4-4e54-92c0-9ef8f6e04ef5" data-toc-id="eb39e7b4-add4-4e54-92c0-9ef8f6e04ef5" collapsed="false" seolevelmigrated="true">Oxide Minerals</h4><ul><li><p>Oxygen anion is bonded to metallic cations.</p></li><li><p>Economically important as ores of metals (iron, titanium, chromium).</p></li><li><p>Example: Hematite (Fe2O3),anironore.</p></li></ul><h4id="3d5cc6f2−51e3−4e94−b878−73d56a4e4727"data−toc−id="3d5cc6f2−51e3−4e94−b878−73d56a4e4727"collapsed="false"seolevelmigrated="true">SulfideMinerals</h4><ul><li><p>Sulfideanionisbondedtometalliccations.</p></li><li><p>Economicallyimportantasoresofmetals(copper,zinc,nickel).</p></li><li><p>Example:Pyrite(), an iron ore.</p></li></ul><h4 id="3d5cc6f2-51e3-4e94-b878-73d56a4e4727" data-toc-id="3d5cc6f2-51e3-4e94-b878-73d56a4e4727" collapsed="false" seolevelmigrated="true">Sulfide Minerals</h4><ul><li><p>Sulfide anion is bonded to metallic cations.</p></li><li><p>Economically important as ores of metals (copper, zinc, nickel).</p></li><li><p>Example: Pyrite (FeS_2),fool’sgold.</p></li></ul><h4id="741a40a6−9a8d−4bf1−b060−565267ac793b"data−toc−id="741a40a6−9a8d−4bf1−b060−565267ac793b"collapsed="false"seolevelmigrated="true">SulfateMinerals</h4><ul><li><p>Sulfateanionisamajorbuildingblock.</p></li><li><p>Oftenassociatedwithevaporiticconditions.</p></li><li><p>Example:Gypsum(), fool’s gold.</p></li></ul><h4 id="741a40a6-9a8d-4bf1-b060-565267ac793b" data-toc-id="741a40a6-9a8d-4bf1-b060-565267ac793b" collapsed="false" seolevelmigrated="true">Sulfate Minerals</h4><ul><li><p>Sulfate anion is a major building block.</p></li><li><p>Often associated with evaporitic conditions.</p></li><li><p>Example: Gypsum (CaSO4 \cdot 2H2O).</p></li></ul><h4id="9ad7df2a−2439−438c−a199−3f1ada80450f"data−toc−id="9ad7df2a−2439−438c−a199−3f1ada80450f"collapsed="false"seolevelmigrated="true">MineralIDwithPhysicalProperties</h4><ul><li><p>Primarydiagnosticpropertiesaredeterminedthroughobservationandsimpletests.</p></li><li><p>Eachmineralhasdistinctphysicalproperties,sodeterminationofseveralpropertiescanidentifymineralsinhandsamples.</p></li></ul><h4id="c9bb178b−b13b−41c3−b2b4−d7f3a00d2c11"data−toc−id="c9bb178b−b13b−41c3−b2b4−d7f3a00d2c11"collapsed="false"seolevelmigrated="true">Hardness</h4><ul><li><p>Easewithwhichamineralsurfacecanbescratched.</p></li><li><p>Relatedtothestrengthofchemicalbonds.</p></li><li><p>GeologistsuseMohsScaleofHardness.</p></li></ul><h4id="8620a0a9−0dcc−4346−80f4−509510286d4a"data−toc−id="8620a0a9−0dcc−4346−80f4−509510286d4a"collapsed="false"seolevelmigrated="true">Cleavage</h4><ul><li><p>Tendencyofsomecrystalstosplitalongplanarsurfaces.</p></li><li><p>Occursalongplanesinwhichbondingisweak.</p></li><li><p>Cleavageanglesandthenumberofplanesareindicativeofspecificminerals.</p></li></ul><h4id="4489a2a9−ac41−4957−a059−56301692a51e"data−toc−id="4489a2a9−ac41−4957−a059−56301692a51e"collapsed="false"seolevelmigrated="true">ColorandStreak</h4><ul><li><p>Colorcanbevariableduetotraceimpurities.</p></li><li><p>Streakcolorisoftenlessambiguous.</p></li></ul><h4id="05a6228d−8f38−465a−b186−0c553929ebc8"data−toc−id="05a6228d−8f38−465a−b186−0c553929ebc8"collapsed="false"seolevelmigrated="true">CrystalHabit</h4><ul><li><p>Shapeinwhichanindividualcrystal(oraggregateofcrystals)grows.</p></li></ul><h4id="f508d66f−6e7c−458e−b779−dd43ed417ef5"data−toc−id="f508d66f−6e7c−458e−b779−dd43ed417ef5"collapsed="false"seolevelmigrated="true">OtherUsefulPhysicalProperties</h4><ul><li><p>Fracture:Tendencyforacrystaltobreakalongirregularsurfaces</p></li><li><p>Luster:Thewayinwhichthesurfaceofamineralreflectslight</p></li><li><p>Density:massperunitvolume(g/cc)</p></li></ul><h4id="a1bce735−0281−47ee−9729−50468163805f"data−toc−id="a1bce735−0281−47ee−9729−50468163805f"collapsed="false"seolevelmigrated="true">Rocks:NaturalAggregatesofMinerals</h4><ul><li><p>Rocksarecomposedofoneormoreminerals.</p></li><li><p>Example:Graniteconsistsoforthoclasefeldspar,quartz,biotite,andplagioclasefeldspar.</p></li></ul><h4id="2b2fac89−c960−491d−b769−7464631742fd"data−toc−id="2b2fac89−c960−491d−b769−7464631742fd"collapsed="false"seolevelmigrated="true">ThreeMajorClassesofRocks</h4><ul><li><p>Igneous:Formedbythecrystallizationofmagmaorlava.</p></li><li><p>Sedimentary:Formedbydeposition,burial,andlithificationofsediments.</p></li><li><p>Metamorphic:Formedbyrecrystallizationofnewmineralsinsolidstateunderhightemperaturesandpressures.</p></li></ul><tablestyle="min−width:75px"><colgroup><colstyle="min−width:25px"><colstyle="min−width:25px"><colstyle="min−width:25px"></colgroup><tbody><tr><thcolspan="1"rowspan="1"><p>Typeofrockandsourcematerial</p></th><thcolspan="1"rowspan="1"><p>Rock−formingprocess</p></th><thcolspan="1"rowspan="1"><p>Example</p></th></tr><tr><tdcolspan="1"rowspan="1"><p>IGNEOUSMeltingofrocks</p></td><tdcolspan="1"rowspan="1"><p>Crystallizationsolidificationofmagmaorlava</p></td><tdcolspan="1"rowspan="1"><p>Granite</p></td></tr><tr><tdcolspan="1"rowspan="1"><p>SEDIMENTARYWeatheringanderosionofrocks</p></td><tdcolspan="1"rowspan="1"><p>Deposition,burial,andlithification</p></td><tdcolspan="1"rowspan="1"><p>Sandstone</p></td></tr><tr><tdcolspan="1"rowspan="1"><p>METAMORPHICRocksunderhightemp/pressure</p></td><tdcolspan="1"rowspan="1"><p>Recrystallizationofnewmineralsinthesolidstate</p></td><tdcolspan="1"rowspan="1"><p>Gneiss</p></td></tr></tbody></table><h4id="ca72ed84−8e45−43d4−9af5−22fe816955e8"data−toc−id="ca72ed84−8e45−43d4−9af5−22fe816955e8"collapsed="false"seolevelmigrated="true">IgneousRocks</h4><ul><li><p>Extrusiveigneousrocks:Formwhenlavaeruptsatthesurfaceandcoolsrapidly,resultinginfine−grainedorglassytextures(e.g.,basalt).</p></li><li><p>Intrusiveigneousrocks:Formwhenmagmaintrudesintounmeltedrockandcoolsslowly,allowinglargecrystalstogrowandresultingincoarse−grainedtextures(e.g.,granite).</p></li></ul><h4id="9b48835f−4edf−4fcb−8abc−830049d7e322"data−toc−id="9b48835f−4edf−4fcb−8abc−830049d7e322"collapsed="false"seolevelmigrated="true">SedimentaryRocks</h4><ul><li><p>Formedfromparticlesanddissolvedsubstancescreatedbyweatheringanderosion.</p></li><li><p>Sedimentsaretransported,depositedinlayers,andlithifiedbycompactionandcementation.</p></li><li><p>Siliciclasticsediments:Rockfragments(e.g.,sandstone).</p></li><li><p>Chemicalandbiologicalsediments:Precipitatedfromseawaterorbyorganisms(e.g.,fossilizedcoralskeletons).</p></li></ul><h4id="9e61e08d−f955−4963−ac69−5622ae87206c"data−toc−id="9e61e08d−f955−4963−ac69−5622ae87206c"collapsed="false"seolevelmigrated="true">MetamorphicRocks</h4><ul><li><p>Formedbyalterationofpre−existingrocksunderhighpressure,temperature,andchemicalchanges.</p></li><li><p>Contactmetamorphism:Occursinlimitedareaswhereheatfromamagmaticintrusionmetamorphosesneighboringrock.</p></li><li><p>Regionalmetamorphism:Occurswherehighpressuresandtemperaturesextendoverlargeregions.</p></li><li><p>Ultra−high−pressuremetamorphism:OccursdeepinEarth′scrust.</p></li><li><p>High−pressure,low−temperaturemetamorphism:Occurswhereoceaniccrustissubductedbeneathacontinentalplate.</p></li></ul><h4id="2fea67cf−3fcd−4d2b−a5e4−4aa9222dde2c"data−toc−id="2fea67cf−3fcd−4d2b−a5e4−4aa9222dde2c"collapsed="false"seolevelmigrated="true">TheRockCycle</h4><ul><li><p>Allrockclassesareabletoundergonaturalprocessestoconverttoanotherrockclass.</p></li><li><p>Interactionsinvolvetheplatetectonicandclimatesystems.</p></li></ul><h4id="214e9b3f−e9cb−4371−8f7c−b4e6d2a10fef"data−toc−id="214e9b3f−e9cb−4371−8f7c−b4e6d2a10fef"collapsed="false"seolevelmigrated="true">MineralResources</h4><ul><li><p>Mineralsarevaluabletosociety,eitherbythemselvesorbyextractingimportantmetals.</p></li><li><p>Oftenhydrothermallydepositedinveins.</p></li><li><p>Examples:</p><ul><li><p>Metalsulfideores:Cinnabar(mercurysulfide),Pyrite(ironsulfide),Galena(leadsulfide),Sphalerite(zincsulfide).</p></li></ul></li></ul><h4id="805100df−f2db−46c0−a760−a7718d2f1f44"data−toc−id="805100df−f2db−46c0−a760−a7718d2f1f44"collapsed="false"seolevelmigrated="true">MineralResources:EnvironmentalCost</h4><ul><li><p>CopperoresandtheKennecottopen−pitmineinUtahexemplifiestheenvironmentalcost.</p></li></ul><h4id="085a9054−33c5−4576−8175−79d1e5e5ee99"data−toc−id="085a9054−33c5−4576−8175−79d1e5e5ee99"collapsed="false"seolevelmigrated="true">KeyTermsandConcepts</h4><ul><li><p>Atom,Bedding,Chemicalbond,Chemicalreaction,Cleavage,Color,Contactmetamorphism,Crystal,Crystalhabit,Crystallization,Density,Erosion,Extrusiveigneousrock,Foliation,Fracture,Hardness,Hydrothermalsolution,Igneousrock,Intrusiveigneousrock,Ion,Isotope,Lithification</p></li></ul><h4id="adc49770−6a74−4d71−93f4−7f102056f376"data−toc−id="adc49770−6a74−4d71−93f4−7f102056f376"collapsed="false"seolevelmigrated="true">Module5:IgneousProcessesandVolcanism</h4><h4id="731d7764−457c−4c6a−bb1d−5a0c71134cdb"data−toc−id="731d7764−457c−4c6a−bb1d−5a0c71134cdb"collapsed="false"seolevelmigrated="true">LectureOutline</h4><ul><li><p>IgneousRockIntroductionandEnvironments</p></li><li><p>MagmaFormation</p></li><li><p>MagmaDifferentiation</p></li><li><p>IgneousIntrusions</p></li><li><p>MagmaticProcesses</p></li><li><p>VolcanicProcesses</p></li><li><p>VolcanicLandforms</p></li><li><p>VolcanicHazards</p></li></ul><h4id="2079d5ee−5bf0−4788−8421−f532fd159ac9"data−toc−id="2079d5ee−5bf0−4788−8421−f532fd159ac9"collapsed="false"seolevelmigrated="true">IgneousRocks</h4><ul><li><p>Rockformedfromthesolidificationofmagma.</p></li><li><p>Intherockcycle,arockmustbemeltedandthencrystallizedtoproduceanigneousrock.</p></li></ul><h4id="20ada939−8f4c−43c6−b8fa−22e17897566e"data−toc−id="20ada939−8f4c−43c6−b8fa−22e17897566e"collapsed="false"seolevelmigrated="true">IgneousRocksandPlateTectonics</h4><ul><li><p>Atocean−oceanconvergentboundaries,magmasgiverisetovolcanicislandarcseruptingmostlybasalticlavas.</p></li><li><p>Magmasformedatocean−continentconvergentboundarieseruptandesiticlavas.</p></li><li><p>Plateseparationatamid−oceanridgeresultsinbasalticvolcanism.</p></li><li><p>Platemotionoverhotspotscreatesmidplatechainsofbasalticvolcanicislands.</p></li></ul><h4id="c31433b6−b384−4ea2−abd4−bc194611428e"data−toc−id="c31433b6−b384−4ea2−abd4−bc194611428e"collapsed="false"seolevelmigrated="true">IgneousEnvironmentsandRockTextures</h4><ul><li><p>ExtrusiveigneousrockscoolrapidlyonEarth′ssurfaceandarefine−grained(e.g.,basalt,rhyolite).</p></li><li><p>IntrusiveigneousrockscoolslowlyinEarth′sinterior,allowinglarge,coarsecrystalstoform(e.g.,gabbro,granite).</p></li><li><p>Extrusivepyroclastsforminviolenteruptions.</p></li><li><p>PorphyriticcrystalsstarttogrowbeneathEarth′ssurface.Somecrystalsgrowlarge,buttheremainingmeltcoolsfaster,formingsmallercrystals.</p></li></ul><h4id="6348439a−faa1−469b−9217−2cdd7f805964"data−toc−id="6348439a−faa1−469b−9217−2cdd7f805964"collapsed="false"seolevelmigrated="true">IgneousClassification</h4><p></p><ul><li><p><br></p></li><li><p>Classifiedbasedontextureandmineralcomposition.</p></li><li><p><br></p></li><li><p>Felsic(Feldspar−Silica)–dominatedbysilica,sodium,potassium</p></li><li><p><br></p></li><li><p>Mafic(Magnesium−Ferric)–dominatedbyiron,magnesium,calcium<br></p><p></p><tablestyle="min−width:100px"><colgroup><colstyle="min−width:25px"><colstyle="min−width:25px"><colstyle="min−width:25px"><colstyle="min−width:25px"></colgroup><tbody><tr><thcolspan="1"rowspan="1"><p>Composition</p></th><thcolspan="1"rowspan="1"><p>Coarse−grained</p></th><thcolspan="1"rowspan="1"><p>Fine−grained</p></th><thcolspan="1"rowspan="1"><p><br></p></th></tr><tr><tdcolspan="1"rowspan="1"><p>FELSIC</p></td><tdcolspan="1"rowspan="1"><p>Granite</p></td><tdcolspan="1"rowspan="1"><p>Rhyolite</p></td><tdcolspan="1"rowspan="1"><p><br></p></td></tr><tr><tdcolspan="1"rowspan="1"><p>INTERMEDIATE</p></td><tdcolspan="1"rowspan="1"><p>Granodiorite</p></td><tdcolspan="1"rowspan="1"><p>Dacite</p></td><tdcolspan="1"rowspan="1"><p><br></p></td></tr><tr><tdcolspan="1"rowspan="1"><p>MAFIC</p></td><tdcolspan="1"rowspan="1"><p>Gabbro</p></td><tdcolspan="1"rowspan="1"><p>Basalt</p></td><tdcolspan="1"rowspan="1"><p><br></p></td></tr><tr><tdcolspan="1"rowspan="1"><p>ULTRAMAFIC</p></td><tdcolspan="1"rowspan="1"><p>Peridotite</p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td></tr><tr><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td></tr><tr><tdcolspan="1"rowspan="1"><p>Trends:</p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td></tr><tr><tdcolspan="1"rowspan="1"><p>∗Orthoclasefeldspar</p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td></tr><tr><tdcolspan="1"rowspan="1"><p>∗Quartz</p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td></tr><tr><tdcolspan="1"rowspan="1"><p>∗Plagioclase</p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td></tr><tr><tdcolspan="1"rowspan="1"><p>∗Potassium</p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td></tr><tr><tdcolspan="1"rowspan="1"><p>∗Sodium</p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td></tr><tr><tdcolspan="1"rowspan="1"><p>∗Calcium</p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td></tr><tr><tdcolspan="1"rowspan="1"><p>∗Viscosity</p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td></tr><tr><tdcolspan="1"rowspan="1"><p>Density</p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td></tr><tr><tdcolspan="1"rowspan="1"><p>∗Temperatureatmeltingstarts</p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td><tdcolspan="1"rowspan="1"><p></p></td></tr></tbody></table><h4id="404e5eb1−e04b−4e46−a501−28ff7aa0cc83"data−toc−id="404e5eb1−e04b−4e46−a501−28ff7aa0cc83"collapsed="false"seolevelmigrated="true">IgneousClassification</h4><ul><li><p>Felsic:dominatedbysilica,sodium,potassium;higherviscosity,lowermeltingtemperature.</p></li><li><p>Mafic:dominatedbyiron,magnesium,andcalcium;lowerviscosity,highermeltingtemperature.</p></li></ul><h4id="9775f242−82f4−4b3d−9ab8−faed654b724a"data−toc−id="9775f242−82f4−4b3d−9ab8−faed654b724a"collapsed="false"seolevelmigrated="true">ToMeltRock…</h4><ul><li><p>Magmaconsistsof:</p><ul><li><p>Liquidportion=melt</p></li><li><p>Solids=silicateminerals</p></li><li><p>Volatiles=dissolvedgases(H2O,CO2,SO2).</p></li></ul></li></ul><h4id="334fde8d−86cc−45fd−beac−e3f7ee894794"data−toc−id="334fde8d−86cc−45fd−beac−e3f7ee894794"collapsed="false"seolevelmigrated="true">ToMeltRock…</h4><ul><li><p>Maficminerals(rocks)havehighermeltingtemperaturesthanfelsicminerals(rocks).</p></li><li><p>Foragivenrock,meltingcanoccurby:</p><ul><li><p>Addingheat</p></li><li><p>Reducingpressure(decompressionmelting)</p></li><li><p>Addingvolatiles(e.g.,water).</p></li></ul></li></ul><h4id="36d552c2−ab95−4ccd−a514−4aae9cdb0dd6"data−toc−id="36d552c2−ab95−4ccd−a514−4aae9cdb0dd6"collapsed="false"seolevelmigrated="true">MagmaticDifferentiation</h4><ul><li><p>Rocksofvaryingcompositioncanarisefromauniformparentmagma.</p></li><li><p>Processisaresultofthefactthatmineralshavedifferingcrystallizationtemperatures.</p></li></ul><h4id="be2cfaf6−7947−4c6f−9ceb−691f0777f8b6"data−toc−id="be2cfaf6−7947−4c6f−9ceb−691f0777f8b6"collapsed="false"seolevelmigrated="true">MagmaticDifferentiation</h4><ul><li><p>Bowen’sReactionSeries:amodelfordifferentiation.</p></li><li><p>Fractionalcrystallization:Ultramafic/maficmineralscrystallizefirstandaresegregatedfromthemelt.</p></li><li><p>Asmagmacools,mineralscrystallizeatdifferenttemperaturesandsettleoutofthemagmainaparticularorder</p></li><li><p>Processesoffractionalcrystallizationandpartialmeltingleadtoprogressivelymorefelsicmelts.</p></li></ul><h4id="a2710f36−c638−4504−a9a5−8d62dce52990"data−toc−id="a2710f36−c638−4504−a9a5−8d62dce52990"collapsed="false"seolevelmigrated="true">MagmaticDifferentiation</h4><ul><li><p>Formationofdifferentmagmas:</p><ul><li><p>Basaltic(mafic)magmas:Rocksintheuppermantleundergopartialmelting.</p></li><li><p>Andesitic(intermediate)magmas:Mixturesofsedimentaryandbasalticoceanicrocksundergopartialmelting.</p></li><li><p>Rhyolitic(felsic)magmas:Mixturesofsedimentary,igneous,andmetamorphiccontinentalcrustalrocksundergopartialmelting.</p></li></ul></li></ul><h4id="be423d72−adf9−476e−8757−8def74b5d1f7"data−toc−id="be423d72−adf9−476e−8757−8def74b5d1f7"collapsed="false"seolevelmigrated="true">IgneousStructures</h4><ul><li><p>Dikescutacrosslayersofcountryrock.</p></li><li><p>Sillsrunparalleltothelayers.</p></li><li><p>Batholithsarethelargestformsofplutons,coveringatleast100).</p></li></ul><h4 id="9ad7df2a-2439-438c-a199-3f1ada80450f" data-toc-id="9ad7df2a-2439-438c-a199-3f1ada80450f" collapsed="false" seolevelmigrated="true">Mineral ID with Physical Properties</h4><ul><li><p>Primary diagnostic properties are determined through observation and simple tests.</p></li><li><p>Each mineral has distinct physical properties, so determination of several properties can identify minerals in hand samples.</p></li></ul><h4 id="c9bb178b-b13b-41c3-b2b4-d7f3a00d2c11" data-toc-id="c9bb178b-b13b-41c3-b2b4-d7f3a00d2c11" collapsed="false" seolevelmigrated="true">Hardness</h4><ul><li><p>Ease with which a mineral surface can be scratched.</p></li><li><p>Related to the strength of chemical bonds.</p></li><li><p>Geologists use Mohs Scale of Hardness.</p></li></ul><h4 id="8620a0a9-0dcc-4346-80f4-509510286d4a" data-toc-id="8620a0a9-0dcc-4346-80f4-509510286d4a" collapsed="false" seolevelmigrated="true">Cleavage</h4><ul><li><p>Tendency of some crystals to split along planar surfaces.</p></li><li><p>Occurs along planes in which bonding is weak.</p></li><li><p>Cleavage angles and the number of planes are indicative of specific minerals.</p></li></ul><h4 id="4489a2a9-ac41-4957-a059-56301692a51e" data-toc-id="4489a2a9-ac41-4957-a059-56301692a51e" collapsed="false" seolevelmigrated="true">Color and Streak</h4><ul><li><p>Color can be variable due to trace impurities.</p></li><li><p>Streak color is often less ambiguous.</p></li></ul><h4 id="05a6228d-8f38-465a-b186-0c553929ebc8" data-toc-id="05a6228d-8f38-465a-b186-0c553929ebc8" collapsed="false" seolevelmigrated="true">Crystal Habit</h4><ul><li><p>Shape in which an individual crystal (or aggregate of crystals) grows.</p></li></ul><h4 id="f508d66f-6e7c-458e-b779-dd43ed417ef5" data-toc-id="f508d66f-6e7c-458e-b779-dd43ed417ef5" collapsed="false" seolevelmigrated="true">Other Useful Physical Properties</h4><ul><li><p>Fracture: Tendency for a crystal to break along irregular surfaces</p></li><li><p>Luster: The way in which the surface of a mineral reflects light</p></li><li><p>Density: mass per unit volume (g/cc)</p></li></ul><h4 id="a1bce735-0281-47ee-9729-50468163805f" data-toc-id="a1bce735-0281-47ee-9729-50468163805f" collapsed="false" seolevelmigrated="true">Rocks: Natural Aggregates of Minerals</h4><ul><li><p>Rocks are composed of one or more minerals.</p></li><li><p>Example: Granite consists of orthoclase feldspar, quartz, biotite, and plagioclase feldspar.</p></li></ul><h4 id="2b2fac89-c960-491d-b769-7464631742fd" data-toc-id="2b2fac89-c960-491d-b769-7464631742fd" collapsed="false" seolevelmigrated="true">Three Major Classes of Rocks</h4><ul><li><p>Igneous: Formed by the crystallization of magma or lava.</p></li><li><p>Sedimentary: Formed by deposition, burial, and lithification of sediments.</p></li><li><p>Metamorphic: Formed by recrystallization of new minerals in solid state under high temperatures and pressures.</p></li></ul><table style="min-width: 75px"><colgroup><col style="min-width: 25px"><col style="min-width: 25px"><col style="min-width: 25px"></colgroup><tbody><tr><th colspan="1" rowspan="1"><p>Type of rock and source material</p></th><th colspan="1" rowspan="1"><p>Rock-forming process</p></th><th colspan="1" rowspan="1"><p>Example</p></th></tr><tr><td colspan="1" rowspan="1"><p>IGNEOUS Melting of rocks</p></td><td colspan="1" rowspan="1"><p>Crystallization solidification of magma or lava</p></td><td colspan="1" rowspan="1"><p>Granite</p></td></tr><tr><td colspan="1" rowspan="1"><p>SEDIMENTARY Weathering and erosion of rocks</p></td><td colspan="1" rowspan="1"><p>Deposition, burial, and lithification</p></td><td colspan="1" rowspan="1"><p>Sandstone</p></td></tr><tr><td colspan="1" rowspan="1"><p>METAMORPHIC Rocks under high temp/pressure</p></td><td colspan="1" rowspan="1"><p>Recrystallization of new minerals in the solid state</p></td><td colspan="1" rowspan="1"><p>Gneiss</p></td></tr></tbody></table><h4 id="ca72ed84-8e45-43d4-9af5-22fe816955e8" data-toc-id="ca72ed84-8e45-43d4-9af5-22fe816955e8" collapsed="false" seolevelmigrated="true">Igneous Rocks</h4><ul><li><p>Extrusive igneous rocks: Form when lava erupts at the surface and cools rapidly, resulting in fine-grained or glassy textures (e.g., basalt).</p></li><li><p>Intrusive igneous rocks: Form when magma intrudes into unmelted rock and cools slowly, allowing large crystals to grow and resulting in coarse-grained textures (e.g., granite).</p></li></ul><h4 id="9b48835f-4edf-4fcb-8abc-830049d7e322" data-toc-id="9b48835f-4edf-4fcb-8abc-830049d7e322" collapsed="false" seolevelmigrated="true">Sedimentary Rocks</h4><ul><li><p>Formed from particles and dissolved substances created by weathering and erosion.</p></li><li><p>Sediments are transported, deposited in layers, and lithified by compaction and cementation.</p></li><li><p>Siliciclastic sediments: Rock fragments (e.g., sandstone).</p></li><li><p>Chemical and biological sediments: Precipitated from seawater or by organisms (e.g., fossilized coral skeletons).</p></li></ul><h4 id="9e61e08d-f955-4963-ac69-5622ae87206c" data-toc-id="9e61e08d-f955-4963-ac69-5622ae87206c" collapsed="false" seolevelmigrated="true">Metamorphic Rocks</h4><ul><li><p>Formed by alteration of pre-existing rocks under high pressure, temperature, and chemical changes.</p></li><li><p>Contact metamorphism: Occurs in limited areas where heat from a magmatic intrusion metamorphoses neighboring rock.</p></li><li><p>Regional metamorphism: Occurs where high pressures and temperatures extend over large regions.</p></li><li><p>Ultra-high-pressure metamorphism: Occurs deep in Earth's crust.</p></li><li><p>High-pressure, low-temperature metamorphism: Occurs where oceanic crust is subducted beneath a continental plate.</p></li></ul><h4 id="2fea67cf-3fcd-4d2b-a5e4-4aa9222dde2c" data-toc-id="2fea67cf-3fcd-4d2b-a5e4-4aa9222dde2c" collapsed="false" seolevelmigrated="true">The Rock Cycle</h4><ul><li><p>All rock classes are able to undergo natural processes to convert to another rock class.</p></li><li><p>Interactions involve the plate tectonic and climate systems.</p></li></ul><h4 id="214e9b3f-e9cb-4371-8f7c-b4e6d2a10fef" data-toc-id="214e9b3f-e9cb-4371-8f7c-b4e6d2a10fef" collapsed="false" seolevelmigrated="true">Mineral Resources</h4><ul><li><p>Minerals are valuable to society, either by themselves or by extracting important metals.</p></li><li><p>Often hydrothermally deposited in veins.</p></li><li><p>Examples:</p><ul><li><p>Metal sulfide ores: Cinnabar (mercury sulfide), Pyrite (iron sulfide), Galena (lead sulfide), Sphalerite (zinc sulfide).</p></li></ul></li></ul><h4 id="805100df-f2db-46c0-a760-a7718d2f1f44" data-toc-id="805100df-f2db-46c0-a760-a7718d2f1f44" collapsed="false" seolevelmigrated="true">Mineral Resources: Environmental Cost</h4><ul><li><p>Copper ores and the Kennecott open-pit mine in Utah exemplifies the environmental cost.</p></li></ul><h4 id="085a9054-33c5-4576-8175-79d1e5e5ee99" data-toc-id="085a9054-33c5-4576-8175-79d1e5e5ee99" collapsed="false" seolevelmigrated="true">Key Terms and Concepts</h4><ul><li><p>Atom, Bedding, Chemical bond, Chemical reaction, Cleavage, Color, Contact metamorphism, Crystal, Crystal habit, Crystallization, Density, Erosion, Extrusive igneous rock, Foliation, Fracture, Hardness, Hydrothermal solution, Igneous rock, Intrusive igneous rock, Ion, Isotope, Lithification</p></li></ul><h4 id="adc49770-6a74-4d71-93f4-7f102056f376" data-toc-id="adc49770-6a74-4d71-93f4-7f102056f376" collapsed="false" seolevelmigrated="true">Module 5: Igneous Processes and Volcanism</h4><h4 id="731d7764-457c-4c6a-bb1d-5a0c71134cdb" data-toc-id="731d7764-457c-4c6a-bb1d-5a0c71134cdb" collapsed="false" seolevelmigrated="true">Lecture Outline</h4><ul><li><p>Igneous Rock Introduction and Environments</p></li><li><p>Magma Formation</p></li><li><p>Magma Differentiation</p></li><li><p>Igneous Intrusions</p></li><li><p>Magmatic Processes</p></li><li><p>Volcanic Processes</p></li><li><p>Volcanic Landforms</p></li><li><p>Volcanic Hazards</p></li></ul><h4 id="2079d5ee-5bf0-4788-8421-f532fd159ac9" data-toc-id="2079d5ee-5bf0-4788-8421-f532fd159ac9" collapsed="false" seolevelmigrated="true">Igneous Rocks</h4><ul><li><p>Rock formed from the solidification of magma.</p></li><li><p>In the rock cycle, a rock must be melted and then crystallized to produce an igneous rock.</p></li></ul><h4 id="20ada939-8f4c-43c6-b8fa-22e17897566e" data-toc-id="20ada939-8f4c-43c6-b8fa-22e17897566e" collapsed="false" seolevelmigrated="true">Igneous Rocks and Plate Tectonics</h4><ul><li><p>At ocean-ocean convergent boundaries, magmas give rise to volcanic island arcs erupting mostly basaltic lavas.</p></li><li><p>Magmas formed at ocean-continent convergent boundaries erupt andesitic lavas.</p></li><li><p>Plate separation at a mid-ocean ridge results in basaltic volcanism.</p></li><li><p>Plate motion over hot spots creates midplate chains of basaltic volcanic islands.</p></li></ul><h4 id="c31433b6-b384-4ea2-abd4-bc194611428e" data-toc-id="c31433b6-b384-4ea2-abd4-bc194611428e" collapsed="false" seolevelmigrated="true">Igneous Environments and Rock Textures</h4><ul><li><p>Extrusive igneous rocks cool rapidly on Earth's surface and are fine-grained (e.g., basalt, rhyolite).</p></li><li><p>Intrusive igneous rocks cool slowly in Earth's interior, allowing large, coarse crystals to form (e.g., gabbro, granite).</p></li><li><p>Extrusive pyroclasts form in violent eruptions.</p></li><li><p>Porphyritic crystals start to grow beneath Earth's surface. Some crystals grow large, but the remaining melt cools faster, forming smaller crystals.</p></li></ul><h4 id="6348439a-faa1-469b-9217-2cdd7f805964" data-toc-id="6348439a-faa1-469b-9217-2cdd7f805964" collapsed="false" seolevelmigrated="true">Igneous Classification</h4><p></p><ul><li><p><br></p></li><li><p>Classified based on texture and mineral composition.</p></li><li><p><br></p></li><li><p>Felsic (Feldspar-Silica) – dominated by silica, sodium, potassium</p></li><li><p><br></p></li><li><p>Mafic (Magnesium-Ferric) – dominated by iron, magnesium, calcium<br></p><p></p><table style="min-width: 100px"><colgroup><col style="min-width: 25px"><col style="min-width: 25px"><col style="min-width: 25px"><col style="min-width: 25px"></colgroup><tbody><tr><th colspan="1" rowspan="1"><p>Composition</p></th><th colspan="1" rowspan="1"><p>Coarse-grained</p></th><th colspan="1" rowspan="1"><p>Fine-grained</p></th><th colspan="1" rowspan="1"><p><br></p></th></tr><tr><td colspan="1" rowspan="1"><p>FELSIC</p></td><td colspan="1" rowspan="1"><p>Granite</p></td><td colspan="1" rowspan="1"><p>Rhyolite</p></td><td colspan="1" rowspan="1"><p><br></p></td></tr><tr><td colspan="1" rowspan="1"><p>INTERMEDIATE</p></td><td colspan="1" rowspan="1"><p>Granodiorite</p></td><td colspan="1" rowspan="1"><p>Dacite</p></td><td colspan="1" rowspan="1"><p><br></p></td></tr><tr><td colspan="1" rowspan="1"><p>MAFIC</p></td><td colspan="1" rowspan="1"><p>Gabbro</p></td><td colspan="1" rowspan="1"><p>Basalt</p></td><td colspan="1" rowspan="1"><p><br></p></td></tr><tr><td colspan="1" rowspan="1"><p>ULTRAMAFIC</p></td><td colspan="1" rowspan="1"><p>Peridotite</p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td></tr><tr><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td></tr><tr><td colspan="1" rowspan="1"><p>Trends:</p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td></tr><tr><td colspan="1" rowspan="1"><p>*Orthoclase feldspar</p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td></tr><tr><td colspan="1" rowspan="1"><p>*Quartz</p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td></tr><tr><td colspan="1" rowspan="1"><p>*Plagioclase</p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td></tr><tr><td colspan="1" rowspan="1"><p>*Potassium</p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td></tr><tr><td colspan="1" rowspan="1"><p>*Sodium</p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td></tr><tr><td colspan="1" rowspan="1"><p>*Calcium</p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td></tr><tr><td colspan="1" rowspan="1"><p>*Viscosity</p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td></tr><tr><td colspan="1" rowspan="1"><p>Density</p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td></tr><tr><td colspan="1" rowspan="1"><p>*Temperature at melting starts</p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td><td colspan="1" rowspan="1"><p></p></td></tr></tbody></table><h4 id="404e5eb1-e04b-4e46-a501-28ff7aa0cc83" data-toc-id="404e5eb1-e04b-4e46-a501-28ff7aa0cc83" collapsed="false" seolevelmigrated="true">Igneous Classification</h4><ul><li><p>Felsic: dominated by silica, sodium, potassium; higher viscosity, lower melting temperature.</p></li><li><p>Mafic: dominated by iron, magnesium, and calcium; lower viscosity, higher melting temperature.</p></li></ul><h4 id="9775f242-82f4-4b3d-9ab8-faed654b724a" data-toc-id="9775f242-82f4-4b3d-9ab8-faed654b724a" collapsed="false" seolevelmigrated="true">To Melt Rock…</h4><ul><li><p>Magma consists of:</p><ul><li><p>Liquid portion = melt</p></li><li><p>Solids = silicate minerals</p></li><li><p>Volatiles = dissolved gases (H2O, CO2, SO2).</p></li></ul></li></ul><h4 id="334fde8d-86cc-45fd-beac-e3f7ee894794" data-toc-id="334fde8d-86cc-45fd-beac-e3f7ee894794" collapsed="false" seolevelmigrated="true">To Melt Rock…</h4><ul><li><p>Mafic minerals (rocks) have higher melting temperatures than felsic minerals (rocks).</p></li><li><p>For a given rock, melting can occur by:</p><ul><li><p>Adding heat</p></li><li><p>Reducing pressure (decompression melting)</p></li><li><p>Adding volatiles (e.g., water).</p></li></ul></li></ul><h4 id="36d552c2-ab95-4ccd-a514-4aae9cdb0dd6" data-toc-id="36d552c2-ab95-4ccd-a514-4aae9cdb0dd6" collapsed="false" seolevelmigrated="true">Magmatic Differentiation</h4><ul><li><p>Rocks of varying composition can arise from a uniform parent magma.</p></li><li><p>Process is a result of the fact that minerals have differing crystallization temperatures.</p></li></ul><h4 id="be2cfaf6-7947-4c6f-9ceb-691f0777f8b6" data-toc-id="be2cfaf6-7947-4c6f-9ceb-691f0777f8b6" collapsed="false" seolevelmigrated="true">Magmatic Differentiation</h4><ul><li><p>Bowen’s Reaction Series: a model for differentiation.</p></li><li><p>Fractional crystallization: Ultramafic/mafic minerals crystallize first and are segregated from the melt.</p></li><li><p>As magma cools, minerals crystallize at different temperatures and settle out of the magma in a particular order</p></li><li><p>Processes of fractional crystallization and partial melting lead to progressively more felsic melts.</p></li></ul><h4 id="a2710f36-c638-4504-a9a5-8d62dce52990" data-toc-id="a2710f36-c638-4504-a9a5-8d62dce52990" collapsed="false" seolevelmigrated="true">Magmatic Differentiation</h4><ul><li><p>Formation of different magmas:</p><ul><li><p>Basaltic (mafic) magmas: Rocks in the upper mantle undergo partial melting.</p></li><li><p>Andesitic (intermediate) magmas: Mixtures of sedimentary and basaltic oceanic rocks undergo partial melting.</p></li><li><p>Rhyolitic (felsic) magmas: Mixtures of sedimentary, igneous, and metamorphic continental crustal rocks undergo partial melting.</p></li></ul></li></ul><h4 id="be423d72-adf9-476e-8757-8def74b5d1f7" data-toc-id="be423d72-adf9-476e-8757-8def74b5d1f7" collapsed="false" seolevelmigrated="true">Igneous Structures</h4><ul><li><p>Dikes cut across layers of country rock.</p></li><li><p>Sills run parallel to the layers.</p></li><li><p>Batholiths are the largest forms of plutons, covering at least 100km^2$$.
    *Stock
    *Lava flow
    *Ash falls and pyroclastics
    *Volcano
    *Pluton

Magmatic Processes

  • Three dominant locations for magma generation:

    • Mid-ocean ridges

    • Subduction zones

    • Mantle plumes

Magmatic Processes: Mid-Ocean Ridges

  • Decompression melting of peridotite occurs as plates separate.

  • Partial melting alters the composition of melt to basaltic.

  • Basaltic magma feeds volcanic activity and leads to intrusive (gabbro) and extrusive (basalt) layers.

Magmatic Processes: Subduction Zones

  • Fluid-induced melting of oceanic crust occurs as plate is subducted.

  • Composition of melt is variable.

  • Fractional crystallization in magma chambers leads to higher silica content and andesitic magmas.

Magmatic Processes: Mantle Plumes

  • Decompression melting of ultramafic material occurs as plume ascends.

  • Partial melting leads to basaltic composition of melt.

  • Since plume is essentially fixed in space, trails of basaltic volcanoes are produced as plates move over the plume location.

Volcanic Processes

  • Volcanoes are features in which magma is transported to the surface via a plumbing system that feeds one or more vents.

  • Volcanoes are often related to plate tectonic features, and therefore the magma type and eruptive style of a given volcano are often somewhat predictable.

Volcanic Processes

  • Viscosity of magma is an important factor that affects magma behavior and eruptive style.

  • Factors that affect viscosity:

    • Composition of melt (more silica = more viscous) à Basalt – Andesite – Rhyolite (low – high viscosity)

    • Temperature (warmer = less viscous)

    • Volatile content (more dissolved = less viscous). Volatiles break chemical bonds in the melt.

Volcanic Processes: Basaltic Eruptions

  • Low-silica basaltic magma has low viscosity and can therefore flow relatively easily.

  • Rarely explosive

  • Lava flows are common.

  • Divergent boundaries, hotspots

Volcanic Processes: Andesitic Eruptions

  • Intermediate-silica andesitic magma has higher viscosity and therefore flows with more difficulty.

  • Often explosive

  • Pyroclastic material is common.

  • Subduction zones

Volcanic Processes: Rhyolitic Eruptions

  • High-silica rhyolitic magma has very high viscosity and flows with great difficulty.

  • Very explosive

  • Pyroclastic material

  • Locations in which large volumes of continental crust are melting from mantle heat

Eruptive Style Dictates Volcanic Landforms

  • Shield volcano- lavas pile up over the vent.

  • Volcanic dome- Central vent. A dome has been growing within the center of Mount St. Helens since its 1980 Eruption.

  • Cinder cone volcano- Successive layers of ejected pyroclasts drip away from the crater at the summit. The vent may become filled with volcanic debris.

  • Stratovolcano- Central vent filled with lava from the previous eruption. Lava that has solidified in fissures forms radiating dikes that strengthen the cone.

  • Caldera- results when a violent eruption empties a volcano's magma chamber, which then cannot support the overlying rock. It collapses, leaving a large, steep-walled basin.
    Volcano Landforms:
    *Shield Volcano
    *Volcanic Dome
    *Cinder-Cone Volcano
    *Stratovolcano
    *Caldera

Volcanic Hazards

  • Lava dome collapse and pyroclastic flow

  • Lahar (mud or debris flow)

  • Lava flow

  • Eruption cloud

  • Eruption column

  • Bombs

  • Pyroclastic flow

  • Ash fall

  • Landslide (debris avalanche)
    *Fumeroles
    *Groundwater
    *Acid rain
    Prevailing wind
    Crack
    Magma

Volcanic Hazards

*Tsunamis
*Floods
*Debris avalanches
*Gas emissions
*Lava flows
*Lahars
*Ash falls
*Pyroclastic flows
Lightning
*Unknown
Laki
Kelut
Unzen
Tambora
Krakatau
Pelee
Nevado del Ruiz

Volcanic Hazards in the United States

*Silverthorne
*Bridge River
*Meager Mountain
*Mount Cayley
*Mount Garibaldi
*Mount Baker
*Glacier Peak
*Mount Rainier
*Mount St. Helens
*Mount Adams
*Three Sisters
*Yellowstone Caldera
*Mount Jefferson
*Newberry volcano
*Crater Lake
*Mount McLoughlin
*Lassen Peak
*Clear Lake volcanoes
*Mono-Inyo Craters
*Mount Shasta
*Medicine Lake
*Vidako
*Mount Hood
*Long Valley Caldera
*Coso volcanoes
*Socorro
San Francisco Peak

Key Terms and Concepts (1 of 2)

  • Andesite, Basalt, Batholith, Bomb, Breccia, Caldera, Country rock, Crater, Dacite, Decompression melting, Dike, Diorite, Felsic rock, Fluid-induced melting, Fractional crystallization, Gabbro, Granite, Granodiorite, Hot spot, Intermediate igneous rock, Lahar, Lava

Key Terms and Concepts (2 of 2)

  • Mafic rock, Magma chamber, Magmatic differentiation, Mantle plume, Obsidian, Partial melting, Pegmatite, Peridotite, Pluton, Porphyry, Pumice, Pyroclast, Pyroclastic flow, Rhyolite, Shield volcano, Sill, Stock, Stratovolcano, Tuff, Ultramafic rock, Vein, Viscosity, Volcanic ash, Volcano

Module 6: Sedimentation: Rocks Formed by Surface Processes

Lecture Outline

  • Sedimentary Rock Introduction and Processes

  • Weathering and Surface Processes

  • Sediment Type

  • Sediment Structures

  • Sedimentary Environments

  • Sedimentary Basins

  • Burial and Diagenesis

  • Classification of Sedimentary Rocks

Sedimentary Rocks

  • Sediment is solid, fragmental material deposited on Earth’s surface after transport by physical, chemical, or biological processes.

  • After deposition and burial, sediments are lithified to produce sedimentary rocks.

Sedimentary Processes

  • Weathering breaks down rocks physically and chemically.

  • Erosion carries away particles produced by weathering.

  • Transportation moves particles downhill via streams, glaciers, and wind.

  • Deposition occurs when particles settle out or dissolved minerals precipitate.

  • Burial occurs as layers of sediment accumulate and compact previous layers.

  • Diagenesis lithifies the sediment to make sedimentary rocks.

Weathering

  • Physical weathering: Solid rock is fragmented by mechanical processes.

  • Chemical weathering: Solid rock is chemically altered and dissolved.

Weathering: Production of Sediment

  • Siliciclastic sediment: Sediments composed of solid silicate minerals: boulders, pebbles, sand, silt, and clay

  • Chemical and biological sediment: Precipitation of chemical weathering products either abiotically or biotically

Sediment Erosion and Transport

  • Siliciclastic sediment is eroded when forces initiate the movement of particles.

  • Transport by water, wind, ice, and gravity move “down” to a sedimentary basin.

  • Ions from chemical weathering are dissolved in water and transported by flow.

Siliciclastic Sediment Transport

  • Stronger currents are needed to transport larger particles.

  • As sediments spend more time moving through environments, they become more mature.

  • Maturity can be deduced from sorting and roundness:

    • Poorly sorted: Immature

    • Well sorted: Mature

Sedimentary Structures

  • During transport and deposition, surface and internal features called sedimentary structures are formed.

  • Bedding is produced when distinct layers of sediments are deposited on one another.

  • Many structures form in specific environments.

Sedimentary Structures: Ripples and Cross Bedding

  • Ripples are small ridges of sediment that form due to currents of wind or water.

  • Symmetrical: wave (oscillatory) motion

  • Asymmetrical: unidirectional flow
    Former lee slopes are preserved internally as cross beds.

Sedimentary Structures: Bedding Sequences

  • Vertically stacked beds of different sediments.

Sedimentary Environments

  • Geographic location characterized by a particular combination of conditions and processes (climatic, physical, chemical, and biological) that accumulates sediment deposits.

  • Sediment type, structures, and fossils can be indicative of a particular environment.
    Glacier
    Desert Lake
    Desert
    Rivers
    Lake
    Tidal Flat
    Beach
    Delta
    Continental Margin/Slope
    Continental Shelf
    Organic Reef
    Turbidity Currents
    Deep Sea

Sedimentary Basins

  • Large-scale regions of thick sediment deposition and preservation resulting from sedimentation and subsidence.

  • These basins contain Earth’s primary oil and gas reserves.

  • Three specific types:

    • Rift basins (divergent margins)

    • Thermal subsidence basins (passive margins)

    • Flexural basins (convergent margins)

Burial and Diagenesis

*Different sediments result in different sedimentary rocks.
*TEMPERATURE and PRESSURE
*Compaction
*Cementation by burial

Different depths is Earth's crust. Lithification
Heat to 90 to 120 °C
*Compaction by Burial squeezes out water
Shell-Shale
Sand- Sandstone
Cargravel - Conglomerate
Plant matter- coal

Classification and Distribution of Sedimentary Rocks

*Shale/Mudstone etc- 75%
*Carbonate Rocks 14%
*Conglomerate/sandstone 11%

Classification: Siliciclastic Sediments


  • Classified based on grain size

    Grain Size

    Sediment

    Rock


    Gravel (>2mm)

    Conglomerate


    Sand (0.062-2mm)

    Sandstone

    Conglomerate


    Mud (<0.062mm)

    Mud

    Shale

    Classification: Chemical and Biologic Sediments

    • Classified based on chemical composition

    • Major players include carbonates, evaporites, and organic sediments.

    • Example: Reef carbonates → Calcite → Limestone

    Example: Carbonate Platform System & Marine Evaporite Environment

    The Bahamas are a Carbonate platform, where Reefs are built in warm shallow seas, organic sediments form quickly and sedimentation much slower
    In a Marine Evaporite system water entered the Mediterranean through Evaporation.
    As the basin became more saline, and formed gypsum and halite crystals.

    Key Terms

    Key Terms and Concepts (1 of 2)
    *Bedding, Bedding sequence, Bioclastic sediment, Biological sediment, Bioturbation, Carbonate rock, Carbonate sediment, Cementation, Chemical and biological sedimentary environment, Chemical sediment, Chemical weathering, Chert, Clastic sediment, Clay, Claystone, Coal, Compaction, Conglomerate, Continental shelf, Cross-bedding, Diagenesis, Dolostone, Evaporite rock, Evaporite sediment, Flexural basin, Graded bedding

    Key Terms and Concepts(2 of 2)
    Gravel, Limestone, Lithification, Mud, Mudstone, Physical weathering, Porosity, Reef , Rift basin, Ripple, Salinity, Sand, Sandstone, Sedimentary basin, Sedimentary environment, Sedimentary structure, Shale, Siliciclastic sediment, Siliciclastic sedimentary environment, Silt, Siltstone, Sorting, Thermal subsidence basin, Weathering