Stress & Strain

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Stress & Strain. Structural geology & Plate tectonics. Stress & Strain. Applied force & deformation. Increasing strain with increasing stress. Rock deformation. Key factors: Composition Temperature Stress duration Stress rate. Plate choctonics. Joints (tectonic). - PowerPoint PPT Presentation

Transcript of Stress & Strain

  • Stress & StrainStructural geology & Plate tectonics

  • Stress & StrainApplied force & deformation

  • Increasing strain with increasing stress

  • Rock deformationKey factors:CompositionTemperatureStress durationStress rate

  • Plate choctonics

  • Joints (tectonic)Brittle fracturing with little displacement

  • Joints (igneous)Contraction during cooling

  • FaultsBrittle deformation with displacementExtension = 'normal' faults

  • FaultsCompression = 'reverse' faults

  • Strike-slip faultsSan Andreas Fault, western USALateral movement

  • Ductile (plastic) deformation= Folding

    Mainly at depths >10 km, and T >300 CKing Oscar Fjord, Greenland

  • Low-grade strainDelabole butterflies, Cornwall

    Fossil rich mudstone strained into slateTyne & Wear MuseumsUniversity of Exeter

  • High-grade strainGneiss, Aguanish, Quebec

  • Mapping out the structures

  • The Theory of Plate TectonicsOld Lost Seas

  • Earth Puzzles* Fossil distributions * Continental margins* Volcanoes and earthquakes * Compositions

  • W is for Walcott

  • W is for Wegener* Continental drift* Gondwanaland & Pangaea

    = near-universal and near-perpetual ridicule

  • W is for WilsonGeophysicistHotspots'Proto-AtlanticWilson Cycles

  • Plate tectonics

  • Earth interior

  • TermsCrust (chemical) = mafic-felsic rocks overlying ultramafic mantle(0-70 km thick)

    Lithosphere (mechanical) = brittle upper layers (crust + upper mantle)(0-300 km thick)

    Aesthenosphere (mechanical) = ductile part of upper mantle

  • How thick do you like your crust?

  • Making the Earth moveMantle convection

  • Seismology and the MohoAndrija Mohorovicic, seismologist

  • Seismology and the MohoBase of brittle lithosphere at ~1300 C

  • Thin, young oceans

  • GeomagneticoceansSymmetric bands of magnetized minerals in ocean crust

  • Spreading ridgesOceanic crust formed by extension;Upwelling of mafic magma

  • Spreading ridges

  • ConvergenceOceanic-continental (e.g. Andes)

  • ConvergenceOceanic-oceanic (e.g. Japan)Continental-continental (e.g. Himalayas)

  • The full pictureOcean birth to death = Wilson Cycle

  • Iapetus - the Old Lost Sea

  • The Ordovician Atlantic

  • Iapetus in WalesThe Welsh Basin

    Palaeozoic marine mudstones(Many now slate)

  • Iapetus in ScotlandGlens and highlands

  • Caledonian orogeny

  • Old Lost Sea in NewfoundlandAn Iapetan slice of upper mantle

  • W is for WilliamsAppalachians-CaledonidesGros Morne National Park

  • AvaloniaA micro-continent of the Iapetus OceanColony of Avalon, Newfoundland

  • Iapetus (1)

  • Iapetus (2)

  • Iapetus (3)

  • The Iapetus of ManNiarbyl Fault, nr Dalby, south-west Isle of Man

  • The Iapetus of ManNORTH AMERICA(Laurentia)EUROPE(Avalonia)

  • Next week