How tectonics works

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How tectonics works
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Plates forces

• Tectonic forces applied at edges and transmitted
  through whole plate
• Internal forces from gravitational potential
  energy
• Generally isostatic
• Tractions on top bottom small (air and
  asthenosphere are weak)

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Plates properties

• Approximately rigid
• Hence deform elastically until brittle yield
  strength
• Heat flow by diffusion
• Continental and oceanic lithosphere differ

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Continental lithosphere properties

• low density (chemical cause)
• Heterogeneous
• May have multiple weak and strong layers
• May be very old

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Oceanic lithosphere properties

• Density increases with cooling
• Homogeneous
• Approximate as single elastic sheet
• Recycled by lithospheric convection

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Plates feedbacks
thickness
Differentiation by partial melt
temperature
stiffness
age
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Plates dynamics
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Ridges and rifts forces

• Doming and downhill sliding (ridge push)
• Far-field pull
• Resistance from plate strength

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Ridges and rifts properties

• Normal faults dike injection
• Formation of new lithosphere
• High temperature and heat flow
• Low density
• Low stiffness
• Thin lithosphere

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Ridges and rifts feedbacks
Lithospheric thinning
Faulting
Strength in tension
melting
Induced mantle convection
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Ridges and rifts dynamics

• Active vs. passive rifting
• New lithosphere formed (no mass conservation)
• Advection of mass away from boundary
• Change in properties with time (distance/velocity
  )
• Gravity helps faulting

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Trenches and collisions forces

• Slab negative buoyancy (slab pull)
• Far-field push?
• Resistance from basal drag
• Resistance from mantle
• Resistance to bending

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Trenches and collisions properties

• Low T slab
• High density slab
• High stiffness slab
• Brittle failure to great depth
• Friction at interface
• Accretionary wedge/lubrication

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Trenches and collisions
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Trenches and collisions feedbacks
Lithospheric thickening
Plate shortening (mass loss)
Faulting
Slab foundering
Rayleigh-Taylor instability
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Trenches and collisions dynamics

• Active vs. free subduction
• Lithosphere lost (no mass conservation)
• Advection of mass toward boundary
• Differentiation of crust
• Gravity hinders faulting
• Induced mantle flows

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Transforms forces

• Far-field applied forces
• Resisted by fault friction
• Resisted by drag

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Transforms properties

• Same material always in fault zone
• Evolution of fault segments
• Evolution of fault friction

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Transforms feedbacks
rotation
friction
strain rate
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Transforms dynamics

• Passive pulling
• Localization
• Gravity does not contribute