Stress

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Stress Strain
Structural geology Plate tectonics
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Stress Strain
Applied force deformation
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Increasing strain with increasing stress
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Rock deformation
Key factors Composition Temperature Stress
duration Stress rate
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Plate choctonics
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Joints (tectonic)
Brittle fracturing with little displacement
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Joints (igneous)
Contraction during cooling
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Faults
Brittle deformation with displacement
Extension 'normal' faults
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Faults
Compression 'reverse' faults
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Strike-slip faults
Lateral movement
San Andreas Fault, western USA
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Ductile (plastic) deformation

• Folding

King Oscar Fjord, Greenland
Mainly at depths gt10 km, and T gt300 C
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Low-grade strain

• Delabole butterflies, Cornwall

Tyne Wear Museums
University of Exeter
Fossil rich mudstone strained into slate
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High-grade strain
Gneiss, Aguanish, Quebec
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Mapping out the structures
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Old Lost Seas
The Theory of Plate Tectonics
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Earth Puzzles

• Fossil distributions
  Continental margins
• Volcanoes and earthquakes
  Compositions

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W is for Walcott
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W is for Wegener

• Continental drift
• Gondwanaland Pangaea
• near-universal and near-perpetual ridicule

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W is for Wilson

• Geophysicist
• Hotspots

• 'Proto-Atlantic
• Wilson Cycles

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Plate tectonics
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Earth interior
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Terms

• Crust (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

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How thick do you like your crust?
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Making the Earth move

• Mantle convection

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Seismology and the Moho
Andrija Mohorovicic, seismologist
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Seismology and the Moho
Base of brittle lithosphere at 1300 C
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Thin, young oceans
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Geomagneticoceans
Symmetric bands of magnetized minerals in ocean
crust
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Spreading ridges
Oceanic crust formed by extension Upwelling of
mafic magma
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Spreading ridges
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Convergence
Oceanic-continental (e.g. Andes)
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Convergence
Continental-continental (e.g. Himalayas)
Oceanic-oceanic (e.g. Japan)
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The full picture
Ocean birth to death Wilson Cycle
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Iapetus - the Old Lost Sea
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The Ordovician Atlantic
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Iapetus in Wales

• The Welsh Basin
• Palaeozoic marine mudstones
• (Many now slate)

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Iapetus in Scotland

• Glens and highlands

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Caledonian orogeny
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Old Lost Sea in Newfoundland

• An Iapetan slice of upper mantle

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W is for Williams

• Appalachians-Caledonides

Gros Morne National Park
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Avalonia
A micro-continent of the Iapetus Ocean
Colony of Avalon, Newfoundland
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Iapetus (1)
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Iapetus (2)
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Iapetus (3)
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The Iapetus of Man
Niarbyl Fault, nr Dalby, south-west Isle of Man
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The Iapetus of Man
NORTH AMERICA (Laurentia)
EUROPE (Avalonia)
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