地质专业英语教材.docx

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