構(gòu)造地質(zhì)學(xué)雙語(yǔ) 1 primarystructure

Chapter1PrimarystructureKEYWORDSStructuralgeology構(gòu)造地質(zhì)學(xué)Crossbeds交錯(cuò)層理Kinematics運(yùn)動(dòng)學(xué)Dynamics動(dòng)力學(xué)Tectonics大地構(gòu)造PrimarystructuressecondarystructuresEmplacementDetritalTopset原生構(gòu)造次生構(gòu)造侵位碎屑頂積層ForesetBottomsetRippleMarksMudcrackRake(pitch)前積層底積層波痕泥裂（側(cè)伏角）Section1IntruductiontoStructuralgeologyStructuralgeologyisthebranchofgeologythatdealswiththeform,arrangement,andinternalstructureoftherocks,andesp.withthedescription,representation,andanalysisofstructures,chieflyonamoderatetosmallscale,withintheEarth'scrust,particularlythosestructurescreatedasaresultofdeformation.Suchdeformationsmaybecausedbytectonicmovements,mass(gravity)movement,meteoriteimpact,andahostofothermechanisms.Thesubjectissimilartotectonics,butthelatterisgenerallyusedforthosestructuresthatforminresponsetostressesgenerateddirectlybyplateinteractions(e.g.,convergence,collision,rifting).Structuralgeologyisthestudyofthegeometry,kinematics,anddynamicsofrockstructures.Geometricanalysisisthedescriptiveorqualitativeportionofstructuralgeology.Thisportionofstructuralgeologyisasthenameimplies:Astudyofthesize,shape,andorientationofstructures.Thisisthemaincontentcoveredinthiscourse.Astudyofthemotioncausingthegeometrieswithinrocksiscalledkinematics.Orinotherwords,thekinematicsisthedescriptionofthepaththatrockstookduringdeformation.Dynamicsisthestudyoftheforceswhichcausedthedeformationsstudiedduringkinematicanalysis.Inthecaseofstructuralgeologydynamicsincludesthestudyofhowrocksreacttostress.Inthisclass,wewillemphasizethebasisofstructuralgeology—GeometryorGeometricAnalysis—andwillspendlittletimeonmovements(kinematics)andforces(dynamics)thatcausethedeformation.Structuralgeologyisthestudyofrockdeformation.Itisveryusefulforhumanactivitiesandeconomicalproduction.TheimportanceofStructuralgeologycanbesummarizedasthefollowingfourprimaryreasons:Rockdeformationiscommonintherockrecord.Thereforedecipheringthegeologicevolutionofanarearequiresatleastabasicunderstandingofstructuralgeology.Thedistributionandsizeofmanyexploitableresources,suchasoil,gas,minerals,andgroundwater,areoftenatleastinpartcontrolledbystructures.Activestructuresposehazardstosocietyintheformofearthquakesandearthquakerelatedhazards.Manygeologicalengineeringapplications,suchaswastedisposal,orlargeconstructionprojects,aredevelopedindeformedrocks.Section2PrimarystructureofsedimentaryrocksGeologicStructures,beingdefinableshapeorfabricinarock,canbeclassifiedintwotypes:Primarystructuresarethoseproducedduringtheformationofrocks.Secondarystructuresarethoseformedafterhostrockisformd,suchasafault,fold,orjointproducedbytectonicmovementAnyprimaryrockstructurescanbesubsequentlymodifiedbysecondarystructuresresultingfromdeformationoftheoriginalrockbody.Amajorgoalofgeometric(ordescriptive)structuralanalysisistoseparateprimaryvssecondarystructureandinferlargerscalegeometryfromasetofoutcropscaleobservations.Differentrocktypeshavedifferentprimarystructures.Forthesedimentaryrocks,primarystructuresarethoseformedlithologicstratification,beddings.Forsedimentaryrocksbeddingisespeciallyuseful.Sedimentarylayersarecommonlylaiddownhorizontallywithbeddinglevel,planarandcontinuousintheoriginalundeformedstate.Soifwefindbedsthatarestronglyinclined,foldedandcutandoffsetweareabletorecognisedeformationandbegintoanalyseit.Primarystructureinigneousrockisthoseoriginatedcontemporaneouslywiththeformationoremplacementoftherock,butbeforeitsfinalconsolidation.Forexample,thecompositionalbandingdevelopedduringsolidificationofmagma,whichislayeringdefinedbyalternationsofdifferentmineralsduetothevariationincrystallizationconditions.Ingeneraltheprimarystructureinigneousrocksarelessusefulsimplybecausewecanbelesscertainabouttheoriginalorganisationandscaleofthefeatures.Relativelyspeaking,metamorphicrocksshowrarelytheprimarystructurebecausemetamorphicrocksthemselvesoriginateaseithersedimentaryorigneousrocks.BeddinganditsrecognizationBedding,asthebasicreferencesurfaceforthestrucuturealanalysis,isthemostfundementalprimarystructureinsedimentaryrocks.Thedeformationofrocksaredisplayedmainlybythebedding,so,thefiststepofthestrucuturealstudyistorecognizethebedding.Depositonalbeddingcanberecogniziedbythevariationofitscompositon,textureandcolour.variationofcompostion:variationofcompositonisveryimportantcriteriontoshowthebedding.variationoftexture.Inmostcases,detritalsedimentaryrocksconsistoflayerswithdifferentgrainsizesandshapes.Studingcarfullythevariationingrainsizeandshapecanfindoutthebeddings.variationofcolourbeddingplanestructures:theprimarybeddingplanesturctures,suchasripplemarks,rain-dropimpressions,andmudcracks,canalsobeusedasindicatorstorecognizebedding.StratigraphicfacingandstratigraphicfacingindicatorsStratigraphicfacingistheyongingdirection.Alotofprimarystructuresareusefulasway-upcriteria.(1)Crossbeds:Aresurfaceswithinathicker,masterbedthatareobliquetothebeddinginthemasterbed.DefinedbysubtlepartingorconcentrationofgrainsFormwhengrainsmovefromthewindwardorupstreamsideofaduneripple,towardtheleewardordownstreamside.Crossbedsoftenconsistoftopset,foresetandbottomsed.Topset:thin,usuallyconcaveupward,laminationsparalleltotheuppermasterbedding.Foreset:inclined,curved,laminationsorbedsdepositedparalleltotheslipface?Bottomset:thinlaminationsparalleltothebottommasterbedding

Theforesetbedsareinclinedatanangletothemainplanesofstratification.Theyoftenformhigherforesetanglesattheupperbeddingcomparedtothetangentialanglesbelow.Thisfeaturescanbeusedforfacing.Gradedbeds:Progressivefiningofclastgrainsize,fromthebasetothetopofabed;formasaconsequenceofdepositionbyturbiditycurrents.Thesystematicvariationofgrainsizecanindicatewhichwayisup.RippleMarks:Ridgesandvalleysonthesurfaceofabed,formedduetocurrentflow.Ripplemarkshavemanykinds,ofwhich,theoscillationripplemarksareoftenusedasfacingindicator,wherecrestsarepointedtotopandtroughsarecurvedMudcracks:Mudcracksareshrinkagecracksformedindepositsofdryingclayorsilt.TheyoftenhaveaV-shapeincrosssection.Individualcrackstaperdownward.So,bycarefulstudyoftheshapeofcracks,wecandecidewhichwayisup.Section4:GeologicmapGeologicmapsareamongthebestsourcesofinformationforpreliminarysitelocationanddesign.Thus,engineersneedtobecomefamiliarwiththeconstructionanduseofthesemaps.Elementsofageologicmapincluderocktypes,relativeagesoftherocks,geologiccontactsbetweendifferentrockunits,geologicstructures(e.g.,faults),andmaybetopographiccontours.Geologicalmapisconstructedonthecontourmap.Contouringisatechniqueofdepictingthe3-dimensionalsurfacetopographyin2-dimensionsonpaper.Thisisdonebyplottingonmappointshavingsamealtitudevaluesandjoiningsuchpointstomakesmoothcurvedlines.Thelinesarecalledcontoursandthevalueofaltituderepresentedbythecontouristhecontourvalue.Usuallyadjacentcontourlinesaredrawnatregularintervalsofaltitudevalues.Somecharacteristicsofcontourmapare:iLEs---23Tl七Ti1|II7._一一---||I200,IIwillshowcircularorellipticalcontours.fortheinnercirclesorellipses.pses.willshowcircularorellipticalcontours.fortheinnercirclesorellipses.pses.ElevatedregionshavehighercontourvaluesDepressionshavelowercontourvaluesfortheinnercirclesorelliRivervalleysusuallyshowV-shapedcontours.Regionswithunislopearerepresentedbyparallellineswithconstantseparationofcontours.Steepslopesare-inferredbycloselyjspacedcontourscomparedtogentleslopes.Geologicalformationsaremappedontocontourmapsbyshadingtheareawhereaformationiseitherexposedorliesbelowsoilcover.Importantconclusionsregardingunderlyingstructurecanbedrawnbystudyingsuchmaps--Whenbed/formationpatchesfollowthecontours,thebedsarehorizontal.Whenbedoutcropcutsacrossthecontoursandisboundedbystraightlines,thebedsarevertical.Inbetweentheaboveextremecases,whentheformationboundariesarecurvedandtheyintersectthecontours,thebedsareinclined.Mostoftheoriginallyhorizontalbeddingbecomesinclinedduetothedeformation.Theoutcroppatternorgeologiccontactofobliquebeddingoftenhascertainregularity.Theoutcroponthemap(theintersectionofgeologicalcontactandthetopography)showsaVshape,thisiscalledV’srule(V字型法則).Essentially,ifarocklayerdipsintoaslope,itwillappearto"V"upstreamonatopographicmap;conversely,ifitdipsinthesamedirection(andsteeperthan)theslope,itwillappearto"V"downstream.ThebasicruletellsusthattheV-formofanoutcropinavalleypointsinthedirectionofdip.Exceptionstothisrulearefew:horizontalbeddingandminordipsinavalleydownwardsdirectionunderananglesmallerthanthatofthevalleyitself.Herearesomeexamples:A:Theformationishorizontal,thereforetheformationcontacts,ie,thelinesonthemapwherethetopandbottomsurfacesoftheformationintersectthetopography,areparalleltothecontourlines.B:Theformationisvertical,thereforetheformationcontactstransectthemapasstraightlines.C:TheVpointsupthevalley,thereforetheformationdipsbeneaththevalleyinanup-valleydirection.Theformationdipssteeply,muchmoresteeplythanthestreamgradient,sothe"V”patternisshalloworblunt.D:TheVpointsupthevalley,thereforetheformationdipsbeneaththevalleyinanup-valleydirection.Theformationdipsgently,muchmoregentlythanthestreamgradient,sothe"V”patternisexaggerated.E:TheVpointsdownthevalleyatananglewhichissteeperthanthestreamgradient.Hint:planarsurface,nonplanarsurface,outcroppattern,inamapview,Conversely,gostraightacrossthetopography,visualize,illustrations,apex,exception,idest,transectLabi:GeologicMapWhatisaGeologicMap?Geologicmapsarenotlikeothermaps.Geologicmaps,likeallmaps,aredesignedtoshowwherethingsare.But,whereasthemapsweknowbestshowthedistributionofroadsorriversorcountyboundaries,ageologicmapshowsthedistributionofgeologicfeatures,includingdifferentkindsofrocksandfaults.Ageologicmapisusuallyprintedontopofaregularmap(calledabasemap)tohelpyoulocateyourselfonthemap.Thebasemapisprintedwithlightcolors,soitdoesn'tinterferewithseeingthegeologicfeaturesonthemap.Thegeologyisrepresentedbycolors,lines,andspecialsymbolsuniquetogeologicmaps.Understandingthesefeatureswillallowyoutounderstandmuchofthegeologyshowninalmostanystandardgeologicmap.ColoredAreasThemoststrikingfeaturesofgeologicmapsareitscolors.Eachcolorrepresentsadifferentgeologicunit.Ageologicunitisavolumeofacertainkindofrockofagivenagerange.Soasandstoneofoneagemightbecoloredbrightorange,whileasandstoneofadifferentagemightbecoloredpalebrown.Manygeologicunitsaregivennamesthatrelatetowheretheircharacteristicsarebestdisplayed,orwheretheywerefirststudied.Forexample,the周店sandstonewasfirstdescribedin周店Valley,HubeiProvince.Somegeologicunitshavenotyetbeennamed,sothoseareidentifiedwithtermsrelatedtothekindofrockintheunitlike'Sandstoneandshale,''Unnamedsandstone',or'Undividedshale'.Butallunits,namedandunnamed,haveacoloronthegeologicmap,andtheareaofagivencoloristheareawherethatgeologicunitistheoneatthesurface(usuallythesoilontopoftherocksisdisregarded).Geologicunitsarenamedanddefinedbythegeologistswhomadethegeologicmap,basedontheirobservationsofthekindsofrocksandtheirinvestigationsoftheageoftherocks.Asmoreinformationisgathered,perhapsbyothergeologists,newgeologicunitsmightbedefined.Thesedisagreementscanbeabasisforscientificprogress,andillustratetheneedforcontinuingtoinvestigatethegeologyofanarea.Hint:geologicalunit,LetterSymbolsInadditiontocolor,eachgeologicunitisassignedasetofletterstosymbolizeitonthemap.Usuallythesymbolisthecombinationofaninitialcapitalletterfollowedbyoneormoresmallletters.Thecapitalletterrepresentstheageofthegeologicunit.GeologistshavedividedthehistoryoftheEarthintoEons(thelargestdivision),Eras,Periods,andEpochs,mostlybasedonthefossilsfoundinrocks.ThemostcommondivisionoftimeusedinlettersymbolsongeologicmapsisthePeriod.Occasionallytheageofarockunitwillspanmorethanoneperiod,iftheperiodofmanyyearsrequiredtocreateabodyofrockhappenstofallonbothsidesofatimeboundary.Inthatcasebothcapitallettersareused.Forexample,QTwouldindicatethattherockunitbegantoforminTertiarytimeandwascompletedinQuaternarytime.Thefewgeologicunitsformedanunknownamountoftimeagohavelettersymbolswithnocapitalletters.Thesmalllettersindicateeitherthenameoftheunit,ifithasone,orthetypeofrock,iftheunithasnoname.SoKbtwouldbethesymbolfortheBantouFormation(板頭組)(formedintheCretaceousPeriod),whilegbwouldbethesymbolforgabbro(adark-coloredigneousrock)ofunknownage.Hint:Symbolize:Dothedotsonaladybugsymbolizeit'sage?Thenumberofspotsidentifiesthetypeofladybug.Asladybugsage,thecolorofthespotsfade.LinesonthemapContactLinesTheplacewheretwodifferentgeologicunitsarefoundnexttoeachotheriscalledacontact,andthatisrepresentedbydifferentkindsoflinesonthegeologicmap.Thetwomaintypesofcontactsshownonmostgeologicmapsaredepositionalcontactsandfaults.Allgeologicunitsareformedover,under,orbesideothergeologicunits.Forexample,lavafromavolcanoflowsoverthelandscape,andwhenthelavahardensintorock,theplacewherethelava-rock錯(cuò)restsontherocksunderneathisadepositionalcontact.Wheretheoriginaldepositionalcontactbetweengeologicunitsispreserved,itisshownonthegeologicmapasathinline.FaultHowever,ingeologicallyactiveareasliketheHimalayas,geologicunitstendtobebrokenupandmovedalongfaults(itisfaultmovementsthatcauseearthquakes!).Whendifferentgeologicunitshavebeenmovednexttooneanotheraftertheywereformed,thecontactisafaultcontact,whichisshownonthemapbyathickline.Faultscancutthroughasinglegeologicunit.Thesefaultsareshownwiththesamethicklineonthemap,buthavethesamegeologicunitonbothsides.Remember,justbecausethemapshowsafaultdoesn'tmeanthatfaultisstillactiveandislikelytocauseanearthquake.Rockscanpreserverecordsoffaultsthathavebeeninactiveformanymillionsofyears.Butknowingwherethefaultsareisthefirststeptowardfindingtheonesthatcanmove.SpecialgeologicmapsofthefaultsknowntobestillmovingareconstantlybeingupgradedhereattheChinaGeologicalSurvey,aswellasbyProvincialgeologicalsurveysanduniversityresearchers.FoldsAnotherkindoflineshownonmostgeologicmapsisafoldaxis.Inadditiontobeingmovedbyfaults,geologicunitscanalsobebentandwarpedbythesameforcesintoroundedwavelikeshapescalledfolds.Alinethatfollowsthecrestortroughofthefoldiscalledthefoldaxis.Thisismarkedonageologicmapwithalinealittlethickerthanadepositionalcontact,butthinnerthanafaultSolid,dashed,ordottedlinesAllthicknessesoflinesarealsomodifiedbybeingsolid,dashed,ordotted.Oftencontactsareobscuredbysoil,vegetation,orhumanconstruction.Thoseplaceswherethelineispreciselylocateditisshownassolid,butwhereitisuncertainitisdashed.Theshorterthedash,themoreuncertainthelocation.Adottedlineisthemostuncertainofall,becauseitiscoveredbyageologicunit,sonoamountofsearchingatthesurfacecouldeverlocateit.Thelinesonthemapmayalsobemodifiedbyothersymbolsontheline(triangles,smalltickmarks,arrows,andmore)whichgivemoreinformationabouttheline.Forexample,faultswithtrianglesonthemshowthatthesidewiththetriangleshasbeenthrustupandoverthesidewithoutthetriangles(thatkindoffaultiscalledareversefaultorathrustfault).AllthedifferentsymbolsonthelinesareexplainedinthemapkeyMapKeyAllgeologicmapscomewithatablecalledamapkey.Inthemapkey,allthecolorsandsymbolsareshownandexplained.Themapkeyusuallystartswithalistshowingthecolorandlettersymbolofeverygeologicunit,startingwiththeyoungestormostrecentlyformedunits(intheexamplemapthosearetheman-madedeposits),alongwiththenameoftheunit(ifithasone)andashortdescriptionofthekindsofrock