Lab 14 principles of STRUCTURAL GEOLOGY and...
Transcript of Lab 14 principles of STRUCTURAL GEOLOGY and...
StructuralGeologyandTectonics
• Branchesofgeologythatdealwiththereconstruc;onofmovementsthathaveoccurredover;meinEarth’sLithosphere
• fromLa;n(struere)andGreek(tektos)=tobuild
• movementsinclude– simplemo;on– bending– breaking
StructuralGeologyandTectonics
• Ifweknow– underwhatcondi;onsmo;onoccurs– howdeforma;onsareoriginated
• Thenwe– getinforma;onforreconstruc;ngEarth’sHistory
• bigscale:platemo;on(Tectonics)• medium-sizescale:mountainbuilding(Tectonics)• smallscale:localdeforma;on,ascausedforinstancebyearthquakes(StructuralGeology)
• micro-andsubmicroscopicscale:deforma;oninrocksandminerals(StructuralGeology)
HowdowestudyLithosphere’sdeformaHon?
• Qualita;veandquan;ta;veanalysis– con;nuummechanics– laboratorydeforma;ontes;ng– mathema;calmodels– studyofgeophysicaldata
• seismic,gravity,magne;c
– satelliteimages,airborneandspacebornedata– petrologyandgeochemistry– sedimentology,stra;graphy,paleontology
LithosphericdeformaHonsoriginateStructures
• Aforce(stress)causesadeforma;on(strain)– elas;cdeforma;on
– briOledeforma;on• joints• faults
– duc;ledeforma;on• folds
ANtudes:strikeanddip
• Inordertounderstandhowtectonicdeforma;onoccursweneedtounderstandtheorienta;onofstructuresinspace
• Thissystemisbasedonthestrikeandthedipofasurface(itsaQtude)
• Mostlyusedforgeologicmapping,strikeanddipareusefulinunderstandingstructures
• TheSTRIKEisalinethatcomesfromtheintersec;onofaninclinedplane(a;ltedlayer,forinstance)withanimaginaryhorizontalsurface
• Itsdirec;oncanbemeasuredinthefieldwithacompass
• TheDIPisissimplytheangleofmaximuminclina;onofoursurface(layer)
• Thedipisalwaysat90°fromthestrike
• Thedippointsinthedirec;onofthe;lt
StrikeandDipsymbols
• AQtudeisrepresentedbyaT-shapedsymbol
– thelongarmoftheTrepresentsthestrike
– theshortarmoftheTrepresentsthedip
– anumberisassociatedwiththesymbol,indica;ngtheangleofdip
• A:the“normal”symbolforstrikeanddip:alayer;ltedby10°towardsENE
• B:ver;callayers
• C:horizontallayers
FRACTURES,orJOINTS
• Fracturesaresurfacesalongwhichrocksormineralshavebroken
• Fracturesgeneratetwofreesurfaceswherenoneexistedbefore
• Otherkindsofjoints
Exfolia;onJoints
HalfDome,YosemiteNa;onalPark,California
ColumnarJoints
Devil’sTowerNa;onalPark,Wyoming
FAULTS
• Faults:fracturesalongwhichmo;onoccurs
• Centuries-oldminingterminologyused– Footwall
• Blockbelowthefaultplane• Minerwouldstandhere
– Hangingwall• Blockabovethefaultplane• Hangalanternhere
Faulttypes
• Faulttypes– Dis;nguishedbydirec;onofrockdisplacement
• Normaldip-slip• Reversedip-slip
• Strike-slip
• Dip-slipfaults”– Ver;calmo;on
– NormalFaults• thehangingwallmovesdownwardwithrespecttothefootwall(causedbyextension)
– ReverseFault• thehangingwallmovesupwardwithrespecttothefootwall(causedbycompression)