构造地质学双语joints.docx
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构造地质学双语joints.docx
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构造地质学双语joints
公司内部档案编码:
[OPPTR-OPPT28-OPPTL98-OPPNN08]
构造地质学双语joints
Chapter4Joint
Keywords
Beddingjoints
Strikejoints
Dipjoints
Obliquejoints
Fractures
Diagonaljoint
层节理
走向节理
倾向节理
斜向节理
破裂
斜节理
Jointsets
Jointsystem
Systematicjoints:
Non-systematicjoints
Plumosestructure
节理组
节理系
系统节理
非系统节理
羽饰构造
Shearjoint
Tensionjoint
en-echelon
Longitudinaljoints
Transversejoints
剪节理
张节理
雁列(脉,节理)
纵节理
横节理
Hackle
plumeaxis
tensiongashes
Regionaljoint
Stylolites
羽脉
羽轴
张裂脉
区域性节理
缝合线
Fracturesaresurfacesalongwhichrocksormineralshavebroken.Joints,beoneofthemostcommonlyfoundpervasivemesoscopicstructure,arethefractureswithoutapparentdisplacementinrocks.Thesediscontinuitieswillbeencounteredinmanyengineeringtasksinvolvingnationalandlocalneeds.Cracksinrockscarrygroundwaterfarmoreefficientlythanthebulkrockwithitsrelativelylowpermeability.Incontrasttherecoveryofgeothermalenergyrequirescracksinhotrocksothatheatfluidspumpedalongthecrackscanactasthemediumwithwhichheatedwateristransportedtothesurface.Therecoveryofpetroleumisbestaccomplishedwhenwellscutafracturednetworkcontaininglargeamountsofpetroleum.Theproperty,orientationanddistributionofjointsarecloselyrelatedtothefolds,faultsandregionalstructures.So,thestudiesofjointsareveryhelpfultoanalyzethegeologicalstructure.
1.Classificationofjoints
Theclassificationofjointsisbasedontwomainfactors:
(1)thegeometricalrelationshipwithotherrelatedstructures.
(2)Mechanismsofthejoint’sforming.
Jointsarerelativelybelongingtosmall-scalestructures.Theorientationsofjointsoftenhavegeometricalrelationshipwithotherstructures.
(1)A:
Therelationshipbetweenjointsstrikeandsenseofassociatedstrata.
Strikejoints.Strikeofthejointisparalleltothestrikedirectionofbed.
Dipjoints.Thestrikeofthejointisperpendiculartothestrikeofbed.
Obliquejoints.Thestrikeofthejointisobliquetothestrikeofbed.
Beddingjoints.Jointplaneisparalleltothebeddingplanes.
B:
Therelationshipbetweenjointandfoldaxis
Longitudinaljoints:
Strikeofthejointisparalleltothefoldaxes.
Transversejoints:
Strikeofthejointisperpendiculartofoldaxes.
Diagonaljoint:
Strikeofthejointisaobliquetofoldaxes.
(2)Accordingtothemechanismofjoints
Shearjoint.Incompression,jointsdevelopintheconjugatesheardirections(theorientationofsymmetricfractureplanes)makingtheloweranglewiththemajorprincipalstressdirection.Shearjointsareoftengrooved,striated,polishedorslickensidedbyevensmallamountsofsheardisplacement.
Conjugateshearfracturesmaybeusedtomapmaximumprincipalstressinthevicinityofafaultzone.
Shearjoint
Tensilejoint
Intension,jointsdevelopbystretchingnormaltothetensilestressdirectionwhichisusuallytheminorprincipalstress.Tensionjointsarerough(unlesssubsequentlyweathered).Incoarsegrainedrockssuchsurfacesmaybeveryrough.Tensionaljointincludecolumnarjointsinbasalts,dykesandsills,tensiongashes,calciteandquartzfilledveins.Extensionjointsarenotonelongdiscontinuitybutratherseveraljointsthatformend-to-endinajointzone.
(3)Jointsetsandjointsystems
Jointsets:
manyadjacentjointswithsimilargeometryandorientation.Systematicjoints:
roughlyplanar,sub-parallelorientations,regularspacing.Non-systematicjoints:
curvedandirregularingeometry,usuallyterminateagainstsystematicjoints.
Jointsystem:
madeupoftwoormoresetsofjoints,maybepersistentoverlargeregions.Thegeometryofjointsystemsaredescribedwiththefollowingmeasurementsandobservations:
orientation,scaleandshape,spacingandaperture,intersectionsandterminations,spatialpatterns.
3.Surfacemorphology
Somejointsurfacesdisplaybeautifulsurfaceornamentation,thatisplumestructure.Plumosestructureconsistsofanumberofmorphologicalcomponents:
plumeaxis,hackles,andfringezone.Curvedhacklemarksradiateoutwardfromthepoint(origin)wherethejointoriginated.Thesestructuresindicatethepropagationdirectionofthejoint.Thefringeofajointmaybemarkedbycloselyspaceden-echelonjointsobliquetothemainjointface.
3.Enechelonveins
Veinsarefracturefilledwithaprecipitate,commonlyquartzorcalcite,rarelymud.Enechelonveiniskindofveinwhichcanbefoundinmanyrocks,especiallyincarbonaterocks.Enechelonareparallelorsubparallel,closely-spaced,overlappingorstep-likeminorstructuralfeaturesinrock,suchasfaultsandtensionfractures,thatareobliquetotheoverallstructuraltrend
Sigmoidaltensiongashes,generallyS-orZ-shaped,formalongzonesofductileshear.Thistypeofextensionalfractureisusuallymineral-filledandformenechelonarraysalongtheshearzone.EnEchelontensionfractures(gashes)mayindicatethedirectionofdisplacementbytwofeatures:
1)Sigmoidalprofilesoffractures,and2)offsetdirectionofvein-filledfractures"
Thesigmoidalprofilesoffracturesarecross-sectionalviewsthataidindeterminingthedirectionofrotation.TheprofilesresembleanS-shapedfeaturewiththetipspointinginthedirectionofrotation,eitherclockwiseorcounter-clockwise.
Thegashfracturesformasextensionalfracturesthatareperpendiculartotheminimumcompressivestress,sigma3(seediagram).Thefracturesmayberotatedbyductiledeformationeitherduringorafterformation.Asgashfracturesdevelopatdifferenttimesofductileshearingtheyshowdifferentamountsofrotation.Sincesigma3isnormaltotheunrotatedportionofthegashfracture,eitherthetipsofthesigmoidalfractureorthenewlyformedfracturestellsthestressorientation.Theyoungestfracturesmaynotshowanyorverylittlerotation.(seediagram).
4.Stylolites
Stylolitesareirregularsurfacesthatcommonlyappearasdark,jaggedlinesonexposedsurfacesofcarbonaterock.Theiroriginisusuallyattributedtosolutionthatoccursafterthehostrockwasformed.Thedarklayersareinsolubleresidues.Stylolitesoftencrossthewholerock,cuttinggrains,matrixandcementstylolitesbelongtopressuresolutionstructuresformedatstrainlocalisationsiteswithinrocks,andcanbeusedtoindicatethestressdirection.
4.RelationshipsBetweenJointsandOtherStructures
Columnarjoints:
polygonalfracturesformedduringcoolingoflavaflowsandshallowintrusions.Duetotensilestressessetupasigneousrockcontractsduringcooling.
Sheet(orexfoliation)joints:
curvedjointsthataresub-paralleltothetopography.Earthsurfacesiserodedandrelievesverticalstressbutlateralstressisnotreducedproportionally.Thereforeverticalstressbecomesminimumprincipalstressandjointsformperpendiculartolandsurface.Shrinkageofcoolingplutons(largehomogenousigneousmasses)mayalsoproducesheetingjointsorexfoliation.
Jointsassociatedwithfolds:
Severalsetsofjointsmaydevelopinresponsetofolding.Conjugateshearjointsobliquetothefoldaxisaredevelpoedbycompression.Tensionjointscandevelopduetobending,particularlyinthevicinityofthefoldhinge.Jointsparalleltothestrikeofthefoldaxisarecalledstrikejoints;thoseparalleltothelimbdipareknownasdipjoints.Suchjointsaregenerallytensilefractures.
Jointsassociatedwithfaults:
highstresslevelsinthehangingwallandfootwallofafaultcanresultintheformationofconjugateshearjoints,withonesetparalleltothefaultplaneandtheothersetatanobliqueangleofabout65?
.
Jointsinplutonicrocks:
severaljointsetsarecommonlyobservedinplutons.Suchjointsarethoughttoberelatedtostressessetupduringcoolingoftherockmasswithinaregionalstressfield.
Regionaljointsets:
remarkablyconsistentsetsofjointsareobservedattheregionalscale,particularlyinweaklydeformedsedimentary"platformsequences".Suchjointsareusuallytectonicjoints:
thatisextensionaljointsformedduetohorizontaltectoniccompressionunderconditionsofelevatedporefluidpressure.
withJointsandVeinsintheField
Studywayofjointsvarieswithdifferentpurposes,butingeneral,allofthestudiesonjointsarebasedonthemeasurement,observation,andstatistics.
(1)Localities.Theobservationlocalitiesshouldhavethefollowingfeatures:
Wellexposedoutcrops
Clearlyobservablestructure
Beddingswithtableorientation
Clearrelationshipofjointsetsandjointsystems.
(2)Contentsofobservation
Geologicalbackgroundobservation.Includingtheorientationandrocktypesofbeddings,thefeaturesoffaultandfolding.
Classificationofjoints,jointsetsandjointsystems.Describingtheintersectionandterminationofdifferentjointsets.
Timing:
Youngerjointscommonlyterminateintoolder,existingjoints.Becausefracturestopsatfreesurfaceofthepreexistingjointandcannotpropagateacrossit.Also,jointstendtobecomeparallelormorecommonlyperpendiculartothefreesurfacebecausethefreesurfacecannotsupportshearstress.
Measurementofjointdensity.Thejointdensitycanbemeasuredbyjointnumbersinunitlengthortotalunitlengthsinunitarea.
Observationofjointsurface.Specialattentionshouldbepaidtostriation,plumestructureandothersmallscalestructures.
Whetherthejointhasbeenfilledwithminerals.Thedistributionandscaleofveins.
(3)Records
Usingspeciallydesignedtablestorecordstheresultofmeasurementandobservation.
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- 构造 地质学 双语 joints