EESA06H3 Lecture Notes - Lecture 6: Kuchinoerabu-Jima

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EESA06Lecture6TheDeathofOceans
WhyIsThisImportant?
● IndiacollideswithAsiaafter25MaclosingtheTethysOceanandcreatingthe
MediterraneanSeaduringtheAlpineHimalayanOrogeny
● Thischangesglobalclimatesandresultsiniceagesofthelastfewmillionyears
● PacificRimofFire:involveswidespreadsubductionandmeltofPacificoceancrust
belowsurroundingcontinents
● Subductioncreatesnewcontinentalcrustresultingingrowthofcontinentsthrough
geologictimeandcreatesnaturalhazardsaroundthepacificrim,andtheireffectson
cities
Question:WhyDoOceansUltimatelyClose?
● Stage1:EastAfricanRift
○ Continentundergoesextension
○ Thecrustisthinnedandariftvalleyforms
● Stage2:RedSea
○ Continenttearsintwo
○ Continentedgesarefaultedanduplifted
○ Basalteruptionsformoceaniccrust
● Stage3:AtlanticOcean
○ Continentalsedimentsblanketthesubsidising“passive”marginstoform
continentalshelves
○ Theoceanwidens
○ Amidoceanridgedevelops,asintheAtlanticOcean
Answer
● Outermarginsofoceanplatearedenseandthick
● Themarginsofoceanplatebecometooheavy
● Theybegintosubductbackintothemantle,creatingasubductionzone
● Thisconsumestheoceanfloorcrustfasterthanwhichitisbeingproducedatthe
midoceanridge
● Thispullsthecontinenttowardstheclosingoceanandeventuallyclosestheocean
WidespreadOceanClosure
● Rodiniawastheresultofaworldwideoceanclosure1billionyearsago
● NewcrustwasaddedtoeasternNorthAmerica(muchofOntario)
● AmazoniaisnorthernSouthAmerica
● AmazoniahastheexactsamerocksthatwerefoundinOntario
TheLifeCycleofOceans
● PangeaisaCshapedsupercontinent
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