Download Sevier Orogenic Belt in Nevada and Utah

SevierOrogenicBeltinNevadaandUtah
RichardLeeArmstrong
GEOL730
EmmaMcConville
MotivationandPurpose
Motivation:
Purpose:
DeterminewhethertheSevier
orogenywasproducedbyasingle
seriesofthrustingeventsand
brackettheageoftheSevier
orogeny
TocharacterizetheSevierthrusts
inNevadaandUtahandconstrain
thetimingoftheSevierorogeny
usingstratigraphy
Background
• GeologicSettingandStratigraphicHistory
• AntlerOrogeny(LateDevonian):
• Carbonate(miogeosyncline)andsiliceousassemblages
(eugeosyncline)
• WesternandcentralNevadaeugeosynclineassemblages
havebeenthrustedoverthemiogeosyncline
assemblages
• SoutheasternNevadaandwesternUtahmiogeosyncline
assemblageshavebeenthrustedoverthinshelffacies
• North-centralUtahsubsidenceoftheOquirrh basin(alot
ofsedimentdeposition)
• East-centralNevadaArcturusbasinfilledwiththick
limestone
• UpperPermiandeposits(ParkCityGroup)area
widespreadblanketofrelativelyuniformthickness
andlithologyovertheentireregion,includingthe
AntlerorogenicbeltandColoradoPlateaushelf
• MiddleTriassic,marinewaterswithdrewfrom
easternGreatBasin
Methods
• Pre-NormalFaultingPaleogeology- SevierOrogenic
Belt
• RemovedtheeffectsofnormalfaultingandTertiary
sedimentation,thebroadfeaturesofpre-Tertiary
structuresarevisible
• Possibletoreconstructpaleo-strikesanddipsbyrotating
theoldestTertiarydeposits(commonlyignimbrites)backto
horizontalanddeterminetheeffectofthesamerotation
ontheolderrock
• Figureonrightshowstheunitswhichoverliethe
uniformityusedforthereconstruction
• Inallareastheunconformitypostdatesthemain
Mesozoicdeformationanditpredatesmajor
normalfaulting
• Pre-NormalFaultingPaleogeology- SevierOrogenic
Belt
• Blackdots(n=900)representlocationswherethereis
informationonrocksthatunderlaytheunconformity
• Pre-NormalFaultingPaleogeology- SevierOrogenicBelt
• Structuraltrendsaregenerallynorthtonortheast
• Eastsideofmapisabroad,virtuallyundeformed,forelandbasin
filledbyCretaceousdeposits
• Olderonyoungerrocks
• MostoftheSevierthrustingrepresentsanearlierstageofdeformation
thanthefolding
Displacement
• Onmajorthrustsaminimumtotaldisplacementof25miles
• Displacementisapproximatelyequaltothethicknessofthecrustandcannot
bemerelytheclimaxofdeformationinatightfold
~25mitotal
Gass Peak,Glendale,
Muddy Mountain,
Mormon Mountain
Frisco,Mineral
Range,Pavant,
CanyonRange
Nebo,Charleston,
Strawberry,PoleCanyon
(~5mi),Sheeprock
thrusts, andOquirrh
basinandthrust
Willard,Paris,
Woodruff (~30
mi)
Displacement
Thrust
Displacement
ReferenceandEvidence
Idaho-Wyoming belt
75mi
RubyandHubbert, 1959(structural
considerations)
WillardandCharleston thrusts
40mi
Crittenden, 1961(displacement ofisopachs)
Charlestonthrust
20 mi(minimum)
?(eastward displacement oftheTintic
QuartziteoverJurassicstrata)
Mount Nebofolding andthrusting
12mi
Hintze,1960
Sheeprock-Pole Canyonthrust
5mi
Author (estimated, crosssection)
NeedlesRange(couldbe
considered partofSevierbelt)
8-10mi
Hintze,1960
Muddy Mountain andGlendale
thrust
20mi(minimum)
Longwell, 1961(explainobservable structural
relationships)
Conclusions:
1)Totalshortening of40milesacrosstheSevierbeltisaminimum value,60milesisadequatetoaccommodate
comfortablyanyof theestimates
2)IntheNebo-Charlestonsectormuchoftheshortening istakenupbythefoldandthrustswestofthemajor
thrust, makingdisplacementintheregion less(10-20miles)
3) Sevierisstructurallycontinuous from NevadatoIdaho,500miles
StratigraphicEvidenceConcerningAgeof
DeformationinSevierOrogenicBelt
• Evidence:
• CommencementofSevierbelt:LatePermianisopachsshowasouthwesttrendingarchinsouthwesternUtahandadjacentNevadathatcoincideswith
thebeltofMesozoicthrusting.Brill’smap(1963)showsthatthisarchaffected
thedistributionofLeonardianstrata,butnotthedistributionofWolfcampian
strata
• Jurassictime,thehinterlandoftheSevierbeltbecameasourceofclastic
sediment.InthesouthernWasatchMountains,UpperJurassicandlowermost
Cretaceousconglomeratesoccurconformablyonbothuppersndlowerplates
ofthemajorthrustoftheSeiverbelt,suggestingupliftanddeformation
• Summary:evidenceforapre-CretaceousSevierarchissuggestivebutnot
conclusive
RockyMountainGeosyncline
TheSevierorogenic beltistheonlypossible
sourceforthelargequantityofcarbonate
andquartziteclastsderived fromlower
PaleozoicandEocambrianrocksof the
Cordillerangeosyncline.
RockyMountainGeosyncline
Invertedstratigraphyof
thelowerPaleozoic
clasts
ConclusionsaboutSevierOrogeny
• Orientedprimarilynorthtonortheast
• Continuousbelt500mifromsouthernNevadato
Idaho(500mi)
• Producedbyoneextensiveevent
• FaintevidencesuggestsSevierbeganinthelate
PermianandpeakedinthelateJurassicand
Cretaceous
• Majorthrustingceasedbeforetheendofthe
Montanatime(lateCretaceous)
• TotalvolumeofCretaceoussedimenterodedfrom
belt25,000ftthickX100mileswide(estimated
fromisopachsofWeimerandHaun,1960)
• Shorteningcorrespondstoapproximately50miles