3 The Lithosphere

3.1 Rocksand Minerals

Elements areatomswith a specificnumberof protons.All hydrogenatomshave oneproton,alloxygenatomshave8 protons.

Molecules arecombinationsof elements.Moleculesarethesmallestsubdivision of a substancethatretainsthatsubstances chemicalcomposition.Water(

) is a molecule.Thechemi-

calpropertiesof hydrogen(H) andoxygen(O) areverydifferentthanthechemicalpropertiesof water.

Bonds hold the elementstogether, makingmolecules.Elementsonly bondtogetherwhentheyform a stableelectronconfiguration.

Ionic bonds: thesebondsoccurwhenan electronis strippedfrom an elementby anotherelement,forming a cation and an anion. Chloride can strip electionsfrom sodium,creating and ions.Theseionsareelectricallyattractedto eachotherformingsalt(Halite)

Covalent bonds: thesebondsarecreatedwhenelementsshareelectrons.Oxygenoccursasin theatmosphere,thesetwo atomsaresharingelectrons

van der Walls bond: thesebondsareweakandresultfrom theelectricalattractioncausedby atomicasymmetry

Minerals arecompoundsor collectionsof molecules.Silicon andoxygenare the primary ele-mentsthatmakeupminerals.All mineralshavefivebasicproperties: crystalline:solid with regularstructure homogeneous:cant bemechanicallyseparatedinto differentchemicalcompounds natural definitechemicalcomposition inorganic:notmadeby abiologicalprocess

Therearemany differentgroupsof minerals (e.g.oxides,sulfides,carbonates).Thesilicatesarethedominantmineralgroup(silicon oxides).Thebuilding block for this groupof mineralsis . Thesecompoundshave a tetrahedralstructurethatcanbeisolated,make chains,planesor framework structures(Figure4-7 in text).

Shell (subshells) Max. Na ClK ( ) 2 2 2L ( ) 8 8 8M ( ) 18 1 7

Table1: Electronshellsin atoms.Theseshellscontrolhow thedifferentelementsinteract.

1

Mineral identification is doneby testingthephysicalandchemicalpropertiesof amineral.Thesepropertiesreflect the atomic structureand chemistryof a mineral. Thesepropertiesalsoinfluencethe impactof mineralson the environment(will a mineral increaseor decreaselandslidehazard,slow contaminantmigration,or alterwaterchemistry). cleavage hardness color streak crystalshape reactionto chemical(likeHCl) density opticalproperties

Rocks areaggregatesof minerals(aresomeexceptions:obsidian,coal).Thetextureandchemistryof rocksprovidesclueson theenvironmenttherock formedin. if time, passaroundrocksandaskstudentsto speculateon

wherethey formed

IgneousRocks: cooledfrom magma.Rockwascompletelymeltedbeforeif formed. Extrusive: cooledquickly nearsurfaceof theearth Intrusive: insulatedby surroundingrocksandcooledslowlySedimentaryRocks: formedfrom erodedpartsof rock. book defines another classification-biologicsedimentary

rocks,while coal easily falls in this group,otherrocksarenot aseasilyclassified,is coquina(rock madeof shell frag-ments)detrital,chemical,or biological?

Clastic or Detrital: formed from broken bits of materialcreatedby mechanicalweatheringandshowing evidenceof transport.Theserocksareclassifiedby grainsizeandincludesandstone,siltstone,andshale Chemical:formedfrom dissolvedmaterialthathasprecipitated Somerocksaredifficult to classify:coal,coquina

Metamorphic Rocks Rockthathasbeenalteredby heatandpressure(but not completelymelted) foliation impartedin rock: themineralgrainsareorientedrelative to astressfield specificmineralsform at differenttemperaturesandpressures

2

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H (93.5) O (46) Fe(35)He (6.3) Si (28) O (30)O (.06) Al (8) Si (15)C (.04) Fe(6) Mg (13)Ne (.01) Mg (4) Ni (2.4)

N Ca(2.4) S (1.9)Mg K (2.3) Ca(1.1)Si Na (2.1) Al (1.1)Fe

Table2: Abundanceof elements(%). Chemicalandphysicalprocesseshave differentiatedtheelementswithin theEarthandtheUniverse.

4

Figure1: Dif ferenttetrahedralstructuresformedby silicateminerals

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The Rock Cycle

Igneous Rocks

Compaction/Cementation

Sedimentary Rocks

Metamorphic Rocks

Heat and Pressure

Melting

Magma

Weathering and Erosion

Solidification

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3.2 Structure of the Earth TheEarthis madeupof layerswith differentchemicalandphysicalproperties.Temperatureandpressureincreasewith depth,resultingin phasechangeswithin the threemajor layers,thecrust,mantle,andcore.Thesethreelayerscontaindifferentchemicalcompositionsthatdifferentiatedwhentheearthformed.

CrustPoceaniccrustfrom 0 to 10 km, Mafic//basalticPcontinentalcrustfrom 0 to 40km, Sialic/granitic

UpperMantle: to 700k, maficsilicates,dividedinto partiallymoltenandsolid layers.

LowerMantle: to 2900km, maficsilicates,solid

OuterCore:to 4980km, iron, fluid

InnerCore:to 6370km, iron, solid Thecrustof theearthis brokeninto platesthatareslowly moving. ContinentalDrift wasfirstproposedin 1912by Wegenerbasedongeologiccorrelationof rocksondifferentcontinents. PlateTectonicsdevelopedout of this ideaand incorporatesmechanismsfor platemotion.Platesincludethecrustandasmallportionof themantle.

Subductionoccursalongconvergentplateboundaries.Denseroceaniccrustis forcedunderlessdensecontinentalcrustandinto themantle.

Mid-oceanridgesfoundat divergentplateboundaries.Magmarisesfrom theEarthsinterior andformsrockat thisboundary.

transformboundariesoccurwhereplatesslidepastoneanother

Plateboundariesarezonesof active faulting andfolding. Folding occurswherethe rocksbehaveplastically, typically atdepth,andfaultingoccursatshallow (lessthan30km) depths.

reversefault: compression

normalfault: tension

transformfault: lateralslip

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3.3 MainesVery General Geologic

3.3.1 GeologicHistory Theeventsthatcontrolledtheformationof Precambrianrocks(olderthan570million yearsbeforepresent)not well understood.Theoldestrocksin Maineareabout1.5 billion yearsold andarelocatedin northwesternMaine. Subductiontheoceanicplate(thentheIapetusOcean)underMaineoccurredduringtheearlyPaleozoic. During this time, small piecesof continentalcrustwithin the oceaniccrustareplasteredontotheMainecoastline.Eachdistinctremnantof thesesmallpiecesof continentalcrust are called terranes, and theseterranesappearas bandsof geologicmaterialon thegeologicmapof Maine. Thecollision of thesepiecesof continentalcrustproducedearthquakesandotherdeforma-tion in thecrustalrocksof Maine. Theseeventsareorogenies, mountainbuilding episodes.Orogeniesareidentifiedin the rock recordby igneousintrusions,rapiddepositionof sedi-mentsrelatedto theerosionof uplifted mountains,andmetamorphismof rocksdueto heatandpressureassociatedwith thecollision. In theDevonian,Europecollideswith MaineproducingtheAcadianorogeny, amajordefor-mationeventthatproducedtheAppalachianmountains. Uplift with associatederosionand igneousactivity continuesthroughthe Mississippian,Pennsylvanian,andPermian.Sebagoplutonandassociatedpegmatitesaredepositedin Mis-sissippian Europesplitsfrom North Americain LatePaleozoic.Fracturingandfaultingof rocksasso-ciatedwith this rifting occursthroughtheTriassic. Limited igneousactivity in thelateMesozoicandCenozoicandcontinuederosion. GlaciersadvanceacrossMaineseveraltimesin theQuaternary. This glaciationscouredthelandscape,mixing andredepositingsedimentsin new landforms.Glacial ice wasthousandsof feetthick andcoveredthehighestmountainsin Maine.Theweightof this icewarpedthecrust,locally loweredthebedrocksurface. Theglaciersbeganretreatedfrom Maineabout14,000yearsago(this retreatbeganlongbe-forethisbut it tookabout10,000yearsfor theicemargin to reachMaine).SeawaterfloodedtheMainelandscapethathadbeenloweredby theweightof theice. As theMainelandscapeslowly rebounded,thecoastlinemigratedfrom centralMaineto its currentposition.

3.4 Glacial Geology Till materialdepositeddirectlyby theglacier

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usuallypoorly sorted,composedof a materialwith a wide rangeof grain sizes(e.g.boulderyclay)

angularfragment,commonlywith striations(scratchescausedby rocksbeingrubbedagainsteachotherby themoving ice)canbefoundin thetill.

ablationtill is till thatformsat theice surface,it is theaccumulationof debristhathasmeltedoutof theice

lodgmenttill representsmaterialthat wasdepositedat the baseof the glacier. It ismaterialthatis plasteredagainstsediments/rocksby themoving ice

morainesare the accumulationof till. Terminalmorainesaremorainesdepositedattheendof a glacierwherethe influx of ice is balancedby melting,producinga ridgecomposedof till. Groundmorainesform when the capacityfor the glacier to carrysedimentis exceededand the glacier must drop someof this material,producingablanket of till.

StratifiedDrift Sedimentsdepositedby meltwater coming from the glacier. Thesesedimentsare sortedduringthetransportprocess.

contactdrift forms in contactwith the glacierwhile proglacialdepositsthat areem-placedat somedistancefrom theglacier

eskers,streamsedimentsdepositedin theice, form ridgesof coarsematerial

outwash,streamsedimentdepositedin from of theglacier.

kamesandkameterracesareformedfrom materialdepositedat theicemargin. Kamesaredeltadepositsthat form at thefront of theglacieror aredepositsthataccumulatedin stagnentzonesin theice andkameterracesarestreamsedimentsfrom streamsthatranalongthecontactbetweenavalley andtheglacier.

proglacialdeltas,proglaciallakesediment

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3.5 Earthquakes Earthquakesarecausedby suddenmotionalonga fault. This faultingis typically associatedwith plate motion. Stressbuilds up along fault followed by catastrophicfailure and thereleaseof energy storedin therocks. Thehypocenter is thelocationof earthquake in theearth(truelocationof theearthquake). The epicenter is the locationof the earthquake on the earths surface(projectionof earth-quakeontotheearths surface) A seismometeris usedto measuretheamplitudeandfrequency of wavesgeneratedby anearthquake Body wavesandsurfacewaves:

P-waves(Primarywaves)arecompressionalwavesandarethe fastestwaves( Y[Z]\_^a`ab ) generatedby anearthquake. Thesewavesstrikeanareafirst. S-waves(Secondarywaves)areshearingwavesthat travel at a rateof cdfegZ]\h^a`ab .

ThesewavesarriveaftertheP-waves

Surfacewavesarewavesthatmovealongthesurfaceof theEarth(SandPwavesmovethroughtheearthandarebothBody waves.)Thesearehigh amplitude,low frequencywaves. Seismicwaveshavebeenusedto developanunderstandingof theEarthsstructure To determinethepositionof anearthquake, the time differencesbetweenS andP wavesat

threelocationsareneeded. Differentscaleshavebeenproposedto quantifytheintensityof earthquakes: A Richter Scalelogarithmicscaleof thelargestwaveamplitudegeneratedby anearth-

quake. Eachunit increasein theRichterscalecorrespondsto a10-fold increasein waveamplitudeanda30-fold increasein earthquakeenergy.

TheModified Mercalli Intensity Scaleis basedon humanobservationof thedamagedoneby anearthquake. This intensityvarieswith distancefrom theearthquake andisdependenton thegeologicmaterialsandotherfactors.

TheMoment Magnitude Scaleis basedon theenergy releasedby anearthquakeat itshypocenter. Geologicmaterialsinfluencethedestructive impactof anearthquake.

seismicwavesareamplifiedin loosesediments

wet unconsolidatedsedimentscanliquefy Building structureinfluencesthe damagecausedby an earthquake: concreteandmasonrybuildingswill sustainandcausemoredamagethansteelor woodstructures.Concretefailsmorereadilythansteelandlight weightmaterialwill causelessdamagethanheavy material.

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Resonance:buildingshave a naturalperiod wherewave motion that correspondstothatperiodwill causeresonancein thebuilding. Theseismicwaveswill beamplifiedin thebuilding causingbuildingsof certainsizesto experiencemorestress.

A buildingscompressivestrengthis greaterthanits shearstrengthS-wavesandsurfacewavescausemostdamage. Planningcan reducingthe damagecausedby an earthquake by identify areaswith high

earthquake risk andpreventinginappropriatestructuresfrom beingbuilt in high risk areas.Whencharacterizingearthquake risk, thefollowing itemsareconsidered:

earthquakeprobabilityandstrength

geologicmaterials,strengthof bedrockor unconsolidatedmaterial

slopes/vegetativecover

distancefromthefault(earthquake): greaterdamageoccursnearanearthquakebecausewaveshave not beendampedby traveling throughrock anddifferentwavesarrive atsametimeexposingbuilding to forcesin many directionsat onetime.

distancefrom utilities (gaslines,electricallines) Humanscant predictearthquakesverywell but they canforecastearthquakes(identify highrisk areas,assignaprobabilitythatanearthquakewill occurin sometimeperiod). A varietyof changeshavebeenobservedbeforeandearthquakeandcouldbeusedto predictandearthquake. Noneof thesemethodsalonearevery reliable.

changein animalbehavior

changein electricalpropertiesof theearth,canmeasurechangesin electricalcurrentsin theearth

seismicgaps,reductionin seismicactivity

fore shocks

changesin gasemission(Radon) An earthquake with a magnitudeof 8.5 on the Richterscalehasthe energy of 10,000Hi-roshimaA-bombs Seismometersnow arealsousedto monitorfor nucleartesting. Somehumanactivitiescanincreaseearthquakeactivity

Injection of liquids: At Rocky Mountain Arsenal, liquid wastewas pumpedinto a3600m. deepwell. A correlationwasobservedbetweeninjectionrateandearthquakeactivity.

Loadingearthscrust: 600earthquakesover the10 yearsfollowing theconstructionoftheHooverDam,relatedto loadingandincreasewaterpressurein therocks.

Nuclearexplosions

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SecondaryEffectsof Earthquakes Landslides

Fires:brokenutilities linesignitefires

Tsunamis(Tidal Waves): oceanwatervertically displaced,waveshave low amplitudein deepwater(lessthan1m)but canreachheightsof 15 m in coastalwaters As we discussnaturaldisasters,the function of theseeventsshouldbe considered.Some

naturaldisastershave a service function and may benefithumansor the environmentinsomeway. It is difficult to think of aservicefunctionfor earthquakes,otherthannotingthatthey relievestressin theEarthscrust.

Amplitude

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Figure3: Thelag time betweentheP andS wavesof anearthquake canbeusedto definehow farawayanearthquake is from a seismicstation.

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Figure4: Threestationsareneededto identify the epicenterof an earthquake. The distanceanearthquake is from asinglestationdefinesacirclearoundthatstation.

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3.6 Volcanos Most (80%)volcanosareassociatedwith convergentplateboundaries,theremainderoccuralongdivergentplateboundariesor hot spots. A fracturein thecrustallows magmato risein thecrust.This rising magmaformsandfillsamagmachamber, pressureincreasesin this chamberuntil it ruptures. Theeruptivestyleof a volcanois influencesby thethechemicalcompositionof themagmaemittedfrom thevolcano.

Magmawith a high silica content(70%) hasa high viscosity. This materialmovesslowly andclogsthefracturesandfissuresassociatedwith avolcano.Eruptionsassoci-atedwith thismagmaareviolent. Bits of theviscouspyroclasticmaterialformvolcanicdomes, steepwalled,smallvolcanos.Thesevolcanosdont form asfrequentlyasothertypesbecausethemagmahasdifficulty rising throughthecrust.

Magmawith intermediatesilica composition(60%) form Stratovolcanos(compositevolcanos). Magmawith an andesiticcompositionreachthe surfacemoreoften thanfelsic magmas.Stratovolcanoshave a steepslopenearthe vent anda shallow slopefartheraway from thevent.Thesedifferentslopesreflecttheintermediatecompositionof the magma.Both pyroclasticdebrisandlava flows areemittedby stratovolcanos.Mt. St. Helensis astratovolcano.

Magmawith a low silica content(50%)hasthelowestviscosityandformsshield vol-canos. Thesearearealythe largesttypeof volcanoandhave shallow slopes.Kilaueais ashieldvolcano.Magmacoolsto form basalticrocks. Pyroclasticdebrisis calledtephraandincludesashfall, ashflows,andlargerfragments

ashfall: fine grainedmaterialthat settlesslowly out of the atmosphere.Thismaterialcanbecarriedgreatdistancesfrom thevolcano.

ashflows (Nuee ardante):mixture of hot gas,steamandashthat movesasa densityflow down thehillside. Thesedebrisflowscantravel atspeedsof 100 Z\o^qpr . Gasesare alsoemittedby volcanosduring eruptionsandduring dormantperiods. These

gasescanpoisonorganismsaroundthevolcanos. A Caldera is a cratercreatedfrom the collapseof rock into an emptiedmagmachamber.Eruptionsassociatedwith theformationof acalderaareveryviolentbut arerare. Secondaryeffectsof Volcaniceruption:

Lahars (Mudslides),thick depositsbecomesaturatedandmovedownslope.

fires

building failurefrom weightof ash Volcanic eruptionshave beenpredictedwith successthroughthe measurementof earth-quakes,changein thecompositionof gases,anddoming.

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Geologicmaterialassociatedwith volcaniceruptionscanbemapped,allowing the identifi-cationof hazardousareas.

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3.7 Mineral Resources As the populationgrows, larger quantitiesof mineral resourcesarerequiredto sustainit.As thereis a finite amountof mineral resourceson the Earth, it appearsthat the demandfor mineralresourceby anever increasinghumanpopulationwill eventuallyexceedsupply.Concernsoverresourcedepletionarealleviatedby improvementsin technologythatdecreasethecostof mining, improvewasterecovery, or allow alternativematerialsto beused. Thereis a largedisparityof thepercapitauseof resourcesbetweendifferentcountries. Mineral,rock,andsedimentdepositsareconcentratedby geologicprocesses.Thesedepositsareminedby humanswhenthe concentrationof the resourceallows it to be economicallyextracted(thevalueof thematerialexceedsthecostof mining,processing,andtransportingit). the concentrationfactor is ever changingdue to changing

valueandchangingmineralextractiontechnology

Theeconomicconcentration factor is theamountthata metalhasto beenrichedtomake it aneconomicallyviableresource( sutvwsuxyvwz|{}~z||tyvv{xyty{s xs tyvsuxyvz|{}~z|tvvsu{wuz ) Iron hasa concentrationof about50 g per kilogram in theEarths crust. To extract iron profitably, 500 gramsof iron

perkilogramof rock is required.Iron, therefore,hasaneco-nomicconcentrationfactorof 10. Economicmetaldepositsareassociatedwith plateboundaries.Heat(associatedwith plate

boundaries)is neededto concentratemany metalsin thecrust.

Metalsin mineralsaremeltedwith subductedrocks,segregatefrom the magma,andform concentratedmetaldeposits.

Hot seawatermovesthroughrock at spreadingcentersandleachesout metals.Whenthis fluid cools,metal-richmineralsprecipitate. Theconcentrationof mineralresourcescanberelatedto:

IgneousprocessesMetalsconcentratedin crystalsor densemagmathatsettleto bottomofmagmachamber;verycoarsegrainedigneousrocks(pegmatites)containrareelementsthat areincorporatedinto mineralsthat form in the late stagesof magmacrystalliza-tion (in easternMaine,beryllium is a componentof beryl (alsousedasthegemstonesemeraldandaquamarine)andtourmalineis avaluedgemstoneandusedin electronics(the Maine statemineral). Densecrystalsseparatefrom lighter materialin a magmachamberforming layerswhatareenrichedin someelements.

Metamorphic processeshigh tempandpressurecausesmovementof hot fluid or partialmelting of rock that preferentiallymobilizesmetals. This canbe relatedto contactmetamorphism, metamorphismthatoccursalongthecontactbetweenamagmacham-ber andthe rock it intrudes.Groundwatercanmigratethroughthemagmachamber,leachingmetals,andmove into the country rock depositingmetal-richveins(a hy-drothermaldeposit). Regional metamorphism refersto large-scalemetamorphism,dueto platecollision or other large scaleprocesses.The high temperatureandpres-surecanchangethemineralogycreatingimportantmineralssuchasasbestos,talc,andgraphite.

Hydr othermal processesrefer to the movementof materialby hot water. Metalscanbepartitionedinto waterandgasasthemagmacrystallizes;themetalsarethendeposited

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in fracturesandotheropeningsthat the fluids migrateinto the surroundingrock andcool. Similarly, Hot watercanleachmetalsfrom rockanddepositthemetalsin amoreconcentratedform.

Sedimentaryprocessesinclude1) theselective separationof densemineralsfrom movingwater(formingplacer deposits)(gold,diamonds)andevaporationof seawaterproduc-ing evaporitemineralssuchashaliteandgypsum.Bandediron formationsareauniquechemicalsedimentaryrockproducedfrom alternatingchemicalconditionsthatallowedsilica andhematiteor magnetite(iron ore)to bedepositedin alternatinglayersrelatedto changesin atmosphericchemistry. Manganesenodulesarefoundover muchof thedeepseafloor wheresedimentationratesare low. Thesenodulesreachdiametersofabout10cm andcontaincopper, nickel, cobalt,andplatinum,aswell asmanganese.

Weatheringprocessesreferto thepreferentialweatheringof rock or sediment,leaving be-hind importantmineralsthatareinsoluble,suchasgibsite(Al) andgeothite(Fe). New technologiesareimproving our ability to find mineraldeposits,increasingour ability

to extractthedeposits,andreducingenvironmentalimpact.

Remotesensinginvolvesusingsatellitesandairplanesto collectinformationover largeportionsof the Earth. Picturesare taken that capturedifferentwavelengthsof light.Theseimagesarethenusedto identify favorablelocationsfor mineralresourcesthatcanthenbeexploredin moredetail.

In situmining: performedby pumpingfluidsinto thegroundthatleachmetals,recover-ing thefluid, andextractingthemetals.Thereareproblemscontrollingthetoxic fluidsthatcouldbegeneratedby this method.

recycling is improving, reducingthe amountof mineral resourcesthat are needed.Thereis somespeculationon mining landfills.

Impactof mining on theenvironment Heapleachinginvolvespercolatinga cyanidesolutionthrougha pile of broken rock.

Thecyanidewill leachgold or othermetalsout of thepile of rock andthemetal-richsolutioncanbeprocessed.Whenimproperlymanaged,spills or leaksoccur, releasingcyanideandheavy metalsinto theenvironment

Mercuryis usedto to gather(amalgamate)goldandthetwo metalsarethenseparated.Mercuryis very toxic andhasbeenreleasedin gold-miningareas.

Smeltersreleasemetalsandsulfurassociatedwith themetalsinto theatmosphere.Par-ticulatesenrichedin metalsarecarriedfrom the smelteranddepositedon the nearbylandscape(10s of km downwind). Acid rain is generatedfrom thechemicalreactionof sulfur with oxygenandwaterin theatmosphere.

de^ Plantandanimallife canbedevastatednearsmelters.All coniferswerekilled within12 milesof a largesmelterin British Columbia.Smeltersthatareproperlyconstructedtodayhavemuchloweremissionsthanthoseconstructedjust20 yearsago.

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Mine spoilsarewastepilesleft from miningactivity. Rainwaterthatpercolatesthroughthesepiles canleachout heavy metalsthat thenentergroundwateror surfacewater.Dustis producedfrom thesepilesif not re-vegetated,spreadingmetalrich debris.

Acid minedrainageis producedfrom minespoilsandfrom mineexcavationsthatareleft open. Oxygenatedwaterthatcomesin contactwith sulfidemineralscanproducesulfuric acid that thenentersstreamsandgroundwater. This is associatedwith metalminesandcoalmines(coalcontainspyrite (iron sulfide))

alterationof thephysicalenvironment,ground-waterdewatering,inducederosion,col-lapseof undergroundmines

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resource Merritset al. Kellerstone 7905 9250sand 6658 8370

cement 659 792salt 383 440clay 375 550iron 1063 1300

aluminum 45 66copper 23 24zinc 11 15lead 9 15

Table3: U.S.A.percapitauseof minerals(in pounds).

1987 1988 1989aluminum 15.6 19.5 21.6

lead 54.7 56.4 60.3nickel 24.6 32.3 34.4

Table4: Metalsrecycledin U.S.aspercentof consumption.(U.S.Bureauof mines,1990)

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Magma ChamberFractures

Metal-Rich FluidsMigrate from magma

into country rock

Hydrothermal Mineral Deposits are formedby hot , metal-rich fluids

in sedimentary environmentsPlacer deposits are collections of dense minerals

River

Faster Current

Possible locationsof placer deposit

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