flood basalts or large igneous provinces … basalts.pdf · flood basalts or large igneous...
TRANSCRIPT
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FLOODBASALTSorLARGEIGNEOUSPROVINCES(LIP)(ArmageddonVolcanoes?)
Civilizationlivesbygeologicalconsent,subjecttochangewithoutnotice.WillDurant,1946
Therearebothcontinental(yellow)andoceanic(orange)floodbasaltprovincesTheyarecharacterizedby: Hugevolumes Thickpilesofflows Relativelyshortduration(16Ma) ClosesthistoricaleruptionistheLaki eruption,Iceland(1783)
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SiberianFloodBasalts
FaroeIslands NorthAtlanticFloodBasalts
Greenland NorthAtlanticFloodBasalts
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EasternGreenland NorthAtlanticFloodBasalts
HowaretheyFormed?
Meteorite or Comet impact.
Melting the head of mantle plumes.
De-lamination of the lithosphere.
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ThePlumeModel
ManyFloodBasaltsareassociatedwithcontinentalbreakupandtheformationofvolcaniccontinentalmargins
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TheDeccanFloodbasaltsandReunionhotspottail
WherearethefloodbasaltsassociatedwiththeHawaiiantail?
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TheColumbiaRiverBasalts
Ginko overGrandeRondeBasaltsinPalouseCanyon
Vastpilesofthick(20 100m)lavaflows,someofwhichareupto600kminlength.
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Stratigraphy,AgeandVolumeoftheColumbiaRiverBasaltsTotalVolume=174,400Km3
Over90%eruptedwithin
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Typicalcolumnarjointinginaflow
Pillowbasaltsandpalagonite atthebaseofaflow
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ComparisonofRozawithothernormalflows
1. Kupainaha Flows,Kilauea 0.5km3 in5.6yrs =25m3/sec
2. MaunaLoa,1859 0.27km3 in10months=4m3/sec
3. Laki 1783,Iceland 14.7km3 in9months=709m3/sec
4. Roza Flow(CRB) 1300km3 in6 14yrs 2600 8100m3/sec
EstimatesofthetimetakentoeruptColumbiaRiverBasaltflows
Swansonsuggeststhe1300km3 Roza flowwasemplacedin7days! HoandCashmanestimatethe500kmlongGinko flowwasalsoemplacedin7days. Reidel estimatesmonthsforthePomonaflow. Selfetal.(basedonworkofMartin)estimate6 14yearsfortheRoza flow.
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GrowthoftheRoza flow(1300km3 )in6to14years
ComparisonofthestructureoftheRoza flowunitwithexamplesfromIcelandandKilauea
VF=VesiclefeaturesJH=Jointingfeatures
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Inflationmodelforthegrowthoffloodbasaltflows(Selfetal.,1997)
AreFloodBasaltsResponsibleforMassExtinctions?IstheMantleaSerialKiller?WhatistheKillMechanism?
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TheGeologicalTimeScale(BreaksbetweenPeriodsandEpochsbasedonmajor
changesinfaunaandflora(extinctions))
Amazingcorrelationbetweenthetimeofmajorextinctionsandtheagesoffloodbasalts.Onlyone knownimpactevent(Chicxulub)atendofCretaceous.
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Correlations,althoughsuggestive,arenot proofTimingisCritical
Problems Needtoknowpreciseageanddurationofextinctions. Needtoknowpreciselywhenandforhowlongfloodbasaltswereerupted.
Dating EarlyK/Ar datingindicatederuptionsover4050Myr. Modern40Ar/39Ardatingnarrowsthisdowntounder2
Myr for80 90%oftheeruptiveevent. NewPb datingofzirconnarrowsthisdownfurtherto
lessthan1Myr.
ExampleofrefiningagesofKarrooFloodBasalts,S.Africa
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EXAMPLE SIBERIANTRAPS
TheendofPermianextinction(90%ofallmarinespeciesandlargestlossoffloralandfaunaldiversityinearthshistory)occurredabout250Myr ago.
EarlyK/Ar datingoftheSiberianTrapsgaveagesfrom235 220Myr.
Conclusion noconnection. Subsequent40Ar/39ArdatingincreasedandrefinedtheagesfortheTrapsto250+/ 1.6Myr.
SmokingGun! New(2013)veryprecisezircondatingshowsthefollowing:1) AgeofendofPermianextinction(Meishan,China)between
251.94and251.88Myr (inotherwordstheextinctionoccurredinlessthan100thousandyears!).
2) Thebeginningoftheeruptionoccurredat252.28Myr (thatis,before theextinctionevent).
CauseandEffect!
TheLakiEruption,Iceland(17831784)
Duration 9months(June February) Volume 14.7km3 Nodirectfatalitiesbutseveralfarms
destroyed 50percentofcattledied 75percentsheep 24percentofentireIcelandpopulation
diedofstarvationandillness
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EffectsonEuropeandNorthAmerica
Dropinwintertemperatureof1 3oC Volcanichaze(VOG)blanketedmuchof
EuropeandnorthernN.America. 40%highermortalityratethanexpectedin
Englandinbothsummerandwinter.
TotalSO2 fromeruption=122MtTotalSO2 inplume=99Mt(81%)TotalSO2 fromflows=23Mt(19%)
EstimatedsulfurreleasefromtheLaki eruption
Amegatonne(Mt)=1millionmetrictons(1000x106 kg)
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ReleaseofSulfurandothergasesduringtheeruptionoftheentireRosaflows(1300km3 )
SO2 HCl HFOriginalamountinMagma(Mt) 13795 1065 4840Amountreleasedlocallybylava(Mt) 2808 307 333Amountreleasedfromvents(Mt) 9617 397 1442Totalamountreleased(Mt) 12425 704 1774
Comparewith122MtofSO2 releasedfromtheLakieruption
PossibleKillMechanisms
VolcanicwinterduetoSO2 gasinvolcanicplumes. GlobalwarmingduetoreleaseofvolcanicCO2. Acidrain(fromSO2,HCl,HF)involcanicplumes. Acidificationandanoxicconditionsoftheoceans(fromSO2,
HCl,HF)involcanicplumes. OzonedestructionduetoreleaseofHCl andHFgases Releaseofmethane(greenhousegas)duetoeruptionof
submarinefloodbasalts MassivereleaseofCO2 (globalwarming)duetocontact
metamorphismofunderlyingcarbonateandcoalsediments. Anoxicconditionsintheoceansduetocontact
metamorphismandassimilationofsaltbeds.
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Twostagedegassingoffloodbasalts:ExamplefromDeccanBasalts(Selfetal.199XXXXX)
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