地质专业英语教材.docx
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地质专业英语教材.docx
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地质专业英语教材
1.TheEarth
TheEarthisanearlysphericalplanet.Ithasacircumferenceofapproximately25,000miles(40,000km),apolardiameterofabout7900miles(12,714km),andanequatorialdiameterof7927miles(12,756km).
ThethreemainunitsoftheEarth’sinteriorarecore,mantle,andcrust.Thediameterofthecoreisabout4300miles(6900km),andironisprobablyitschiefingredient.Thecoreconsistsofaninnerpartthatseemssolidandanouterpartthatappearsfluid.Themantleisnearly1800miles(2900km)thickandmakesupabout84%ofthevolumeoftheEarth.Sincethevolumeofthecoreisabout16%,thecrustactuallymakesupaverysmallpartoftheEarthasawhole.Themantleandcrustaresolidexceptforrelativelysmallmassesofmagmathatdevelopoccasionallywithinafewtensofmilesofthesurface.
Ontheaverage,thecrustisaboutsixtimesasthickbeneaththecontinentsasbeneaththeoceanfloors---approximately20to25miles(32to40km)vs.3to4miles(5to6.5km).However,thecontinentalcrustismuchthickerthanaveragebeneaththegreatmountainbelts.Asthetermhasbeenusedrecently,thelithosphereisthesolidoutershelloftheEarth,about35to60miles(50to100km)ormoreinthickness.
Therockmostabundantintheupperpartofthecrustbeneaththecontinentsappearstobesimilartograniteinchemicalcompositionandspecificgravity(2.7).Aheavierrock,probablysimilartobasaltinchemicalcompositionandspecificgravity(3.0),isthoughttounderliethefloorsoftheoceansandalsothegraniticrocksofthecontinents.Thusthetwo-partcontinentalcrustdiffersfundamentallyfromtheone-partoceaniccrust;infact,thedifferenceaccountsfortheexistenceofcontinentsandoceanbasins.
Theuppersurfaceofthecrustmaybecoveredbywater,byunconsolidatedsediments,bysoilandvegetation,oritmaybeexposedatthesurface.
2.TheOuterPartoftheEarth’sCrust
Bedrockisthesolidrockthatisexposedatthesurfaceorimmediatelyunderliessoilandloosesurfacedebris.Regolithistherelativelythincoveringofsoilandunconsolidatedrockwastethathidesthebedrockinmostareas.Bedrockiscontinuousandmayconsistofanykindofrock,whereasregolithisdiscontinuous,althoughgenerallypresent.Regolithtendstobeafewtensoffeetthickorless,butmaybemuchthicker,Itmaydevelopinplacebythedecayanddisintegrationofbedrockorconsistoftransportedmaterials.Soilreferstotheupperportionoftheregolithwhichhasbeensoalteredbyphysicalchemical,andbiologicalprocessesthatitcansupportrootedvegetation.However,soilmaybeabsentfromanarea.
Bydirectobservation,manhasaccesstoonlyaverythinouterpartofthecrust,thedeepestminespenetratelessthan2miles(3km)beneaththesurface,andthedeepestwellsabout5miles(8km).However,certainrocksnowexposedatthesurfacemayoncehavebeenburiedseveralmilesbelowit.
Chemicalanalyseshavebeenforrocksofvarioustypes,andtheproportionsoftheelementsintheouter10-mile(16km)zoneofthelithospherehavebeenestimated.Eightelementsapparentlyconstitutemorethan98%byweightofthiszone:
oxygen(mostabundant),silicon,aluminium,iron,calcium,sodium,potassium,andmagnesium(leastabundant).Thefollowingmnemonicexpressionarrangestheseeightelementsintheorderoftheirrelativeabundances:
“OnlySillyArtistsInCollegeStudyPastMidnight”.Ifthematerialsintheatmosphereandhydrosphereareaddedtothoseofthe10-milezone,percentagesarechangedonlyslightly.
Oftheseeightelementsoxygenandsiliconcombinedassilica(SiO2)makeupaboutthree-fourthsofthetotal.Thusthesilicatemineralsarethemostabundantinthecrust,especiallythefeldspars,pyroxenes,amphiboles,micasandquartz.
3.TheWorkofRunningWater
Fromtheatmosphere,watermoleculesfallupontheEarth’ssurfaceasrain,snow,hail,andsleet.Somewaterevaporatesoristakenupbyplants,somerunsoffimmediatelyintostreams,andtheremaindersinksintotheground.Muchgroundwaterlateremergesatthesurfaceataloweraltitudeandbecomesrunoff.Streamscarryexcesswaterfromthelandtothesea.Indoingso,theyerodevalleysandhelpshapetheEarth’ssurface.Theytransportrockdebrisanddissolvedmaterials,andeventuallytheydepositmostoftheirsedimentintheoceans.Streamactivity,incombinationwithweatheringandmasswastingpredominatesbyfaroverothertypesoferosionsuchaswind,ice,ormarine.
Streamsareimportanttomanwhetherheusesthemassourcesofdrinkingwater,irrigation,orelectricpower,orasplacesinwhichtofish,swim,ordumpsewage.Valleysfurnishthemostconvenientcoursesformanyroadsandrailroads.Thelocationofanumberofimportantcitiesdependeduponthenavigabilityoflargerivers.Civilizationflourishedfirstonfertilefloodplains.Bridges,dams,andreservoirshavetobebuilt.Frequentfloodsthatcauselossoflifeanddestructionofpropertyemphasizetheimportanceofstreamstoman.
4.WeatheringandSoils
Theprincipalsignificanceofthedifferentclimatictypestothestudentofgeologyliesintheirinfluenceonsoilformationandonerosion.Eachclimaticenvironmentplacesitsownstampuponthesoilsdevelopedthere,andeachinfluences,throughitscontrolovervegetation,amountofrainfall,andevaporationlosses,thegeologicalprocessesinvolvedinmoldingthedetailsoftheearth’ssurface.Erosion,theprocessofremovalofrockwaste,willbediscussedinlaterchapters;here,wewillexaminetheinfluenceofseveraldifferentclimaticenvironmentsupontheweatheringofdifferentrocktypes.
Themostfamiliarexampleofweatheringistheetchinganddiscolorationofthesurfaceofanunpaintedboardleftout-of-doors.Rock,exposedintheearth’ssurface,alsodecaysandleaches,butmuchmoreslowly.Iftheproductofrockdecayismerelybrokenanddiscolored,itiscalledmantlerock;butifitislooseandporousenoughforplantstofindafoothold,itiscalledsoil.
Soilismorecommonthanrockattheearth’ssurface.Almostalloutcropsofrockarelessfirm---moreeasilycrumbledandbroken--thanisthesamerockatadepthof20or100feet.Manyrocksthatareblackorsteelgraywherepenetratedinmines,wells,ordeepquarriesareyelloworbrowninoutcrops.Insome,theyellowcolorinamerestainonornearcracks,butinothersitismorepervasiveandisaccompaniedbydrasticchangesinmineralcompositionoftherock.Thatthechangesresultfromweatheringisshownbyobservationonbuildingstones.Forexample,theexposedfacesofthesandstoneusedintheolderbuildingsatStamfordUniversityturnedyellowin5to10years,andwhereexposedtorepeatedwettings,begantocrumblein20to30years.
5.Minerals
Mostmineralsarechemicalcompounds;thatis,theyconsistoftwoormoreelementsincombination.Ofcoursethereareexceptions,suchasgold,copper,sulphur,andcarbon,whichmayoccuraselementsbythemselvesaswellasinchemicalcompounds.Mineralsarenaturallyoccurringsubstances.Thisstatementrulesoutlaboratorycreations.Mineralshaveareasonablydefinitechemicalcomposition.Sincetheyarenaturallyoccurringsubstances,andnetlaboratoryproducts,onlyrarelyaretheychemicallypurecompounds.Forthisreason,suchpropertiesascolormayvaryoverarangeaswideasfromblacktowhite,dependingonthepercentageofelementspresentforanymineral.Mineralsalsohavecertainphysicalproperties,determinedbytheirchemicalcompositionandbythegeometricarrangementoftheatomscomposingthem.Itisthisatomicarrangementthatdeterminesthecrystalformofamineral.Otherpropertiesincludesuchthingsascolor,hardness,andspecificgravity.
Insummary,then,amineralmaybedefinedas
(1)anaturallyoccurringsubstancewith
(2)afairlydefinitechemicalcompositionand(3)characteristicphysicalpropertiesbywhichitmaybeidentified.Inshort,atypicalmineralisacrystallinesolidandisaninorganicsubstance.Mostarechemicalcompounds,butafew,suchasthediamond,mayconsistofasingleelement.
Beforewediscussthecharacteristicsofindividualmineralsweshouldlearnoftheessentialpropertieswhicharethechiefmeansoftheiridentification.Physicalpropertiesarethethingswecansee,orfeel,orforsuchmineralsashalite(rocksalt),taste.Trueenough,thechemicalcompositionispossiblythemostdiagnosticpropertyamineralpossesses,butfewofusaregoingtopackalongafullyequippedchemicallaboratorytobeusedformineralidentificationonafieldtrip.Sinceoneofthecriticaldifferencesbetweenmineralsandrocksisthatmineralsareapproximatelyhomogeneoussubstances,andmostrocksarenot,thismeansthatonepieceofquartzwillbeaboutashardasanotherpiece,thatitwillhavethesamespecificgravity,andifformedinasimilarenvironment,itwillhaveaboutthesamecrystalform.
6.CommonMinerals
(1)
Onthebasisofphysicalandchemicalproperties,some2000differentmineralshavebeenrecognizedanddescribedbymineralogists.However,thisgreatnumberneednotdiscourageusfromattemptingtounderstandtheearth’smaterials.Mostofthe2000mineralsarerareandofinterestmainlytospecialists.Actually,fewerthantwodozenareabundant,andaknowledgeofonlytenmineraltypesisanadequatebasisforageneralizedunderstandingofthebulkofrockswhicharemostfrequentlyencountered.
FeldsparThemostabundantmineraltype,feldspar,composesover60%oftherockmaterialsintheearth’scrust.Strictlyspeaking,thetermfeldsparreferstoagroupofcloselyrelatedmineralshavinggenerallysim
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