Download principles of STRUCTURAL GEOLOGY and TECTONICS

GEOLOGICTIME
Lab14
principlesof
STRUCTURALGEOLOGY
andTECTONICS
AlessandroGrippo,Ph.D
StructuralGeologyandTectonics
•  Branchesofgeologythatdealwiththe
reconstruc;onofmovementsthathaveoccurred
over;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,ascausedforinstanceby
earthquakes(StructuralGeology)
•  micro-andsubmicroscopicscale:deforma;oninrocksand
minerals(StructuralGeology)
CompressionandTension
Shear
Howdowestudy
Lithosphere’sdeformaHon?
•  Qualita;veandquan;ta;veanalysis
–  con;nuummechanics
–  laboratorydeforma;ontes;ng
–  mathema;calmodels
–  studyofgeophysicaldata
•  seismic,gravity,magne;c
–  satelliteimages,airborneandspacebornedata
–  petrologyandgeochemistry
–  sedimentology,stra;graphy,paleontology
LithosphericdeformaHons
originateStructures
•  Aforce(stress)causesadeforma;on(strain)
–  elas;cdeforma;on
–  briOledeforma;on
•  joints
•  faults
–  duc;ledeforma;on
•  folds
ElasHc,BriLle,andDucHleDeformaHon
ANtudes:strikeanddip
•  Inordertounderstandhowtectonic
deforma;onoccursweneedtounderstand
theorienta;onofstructuresinspace
•  Thissystemisbasedonthestrikeandthedip
ofasurface(itsaQtude)
•  Mostlyusedforgeologicmapping,strikeand
dipareusefulinunderstandingstructures
TopographicMapvs.GeologicMap
•  TheSTRIKEisalinethatcomesfromthe
intersec;onofaninclinedplane(a;ltedlayer,
forinstance)withanimaginaryhorizontal
surface
•  Itsdirec;oncanbemeasuredinthefieldwith
acompass
•  TheDIPisissimplytheangleofmaximum
inclina;onofoursurface(layer)
•  Thedipisalwaysat90°fromthestrike
•  Thedippointsinthedirec;onofthe;lt
StrikeandDipsymbols
•  AQtudeisrepresented
byaT-shapedsymbol
–  thelongarmoftheT
representsthestrike
–  theshortarmoftheT
representsthedip
–  anumberisassociatedwith
thesymbol,indica;ngthe
angleofdip
Ver;callayers:dipis90°
Duluth,Minnesota
©AlessandroGrippo
•  A:the“normal”symbolforstrikeanddip:alayer;ltedby
10°towardsENE
•  B:ver;callayers
•  C:horizontallayers
FOLDS
Domesand
Basins
FRACTURES,orJOINTS
•  Fracturesare
surfacesalongwhich
rocksorminerals
havebroken
•  Fracturesgenerate
twofreesurfaces
wherenoneexisted
before
•  Systema;cJoints
–  planar,parallelto
eachother,
regularlyspaced
JointSets
•  Otherkindsofjoints
Exfolia;onJoints
ColumnarJoints
HalfDome,YosemiteNa;onalPark,California
Devil’sTowerNa;onalPark,Wyoming
FAULTS
•  Faults:fracturesalong
whichmo;onoccurs
•  Centuries-oldmining
terminologyused
–  Footwall
•  Blockbelowthefaultplane
•  Minerwouldstandhere
–  Hangingwall
•  Blockabovethefaultplane
•  Hangalanternhere
Faulttypes
•  Faulttypes
–  Dis;nguishedby
direc;onofrock
displacement
•  Normaldip-slip
•  Reversedip-slip
•  Strike-slip
•  Dip-slipfaults”
–  Ver;calmo;on
–  NormalFaults
•  thehangingwallmovesdownwardwithrespecttothe
footwall(causedbyextension)
–  ReverseFault
•  thehangingwallmovesupwardwithrespecttothe
footwall(causedbycompression)
•  Normal(dip-slip)Fault
–  Hangingwallmovesdownrela;vetofootwall
•  Reverse(dip-slip)Fault
–  Hangingwallmovesuprela;vetofootwall
ThrustFaults
•  Transform(Strike-slip)Fault
–  Crustmovesinhorizontaldirec;on
•  Someac;vefaultsdonotextendtothesurface
–  BlindFaults
StructuralGeologyandTectonics
theend