Title: How tectonics works
1How tectonics works
2Plates 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)
3Plates properties
- Approximately rigid
- Hence deform elastically until brittle yield
strength - Heat flow by diffusion
- Continental and oceanic lithosphere differ
4Continental lithosphere properties
- low density (chemical cause)
- Heterogeneous
- May have multiple weak and strong layers
- May be very old
5Oceanic lithosphere properties
- Density increases with cooling
- Homogeneous
- Approximate as single elastic sheet
- Recycled by lithospheric convection
6Plates feedbacks
thickness
Differentiation by partial melt
temperature
stiffness
age
7Plates dynamics
8Ridges and rifts forces
- Doming and downhill sliding (ridge push)
- Far-field pull
- Resistance from plate strength
9Ridges and rifts properties
- Normal faults dike injection
- Formation of new lithosphere
- High temperature and heat flow
- Low density
- Low stiffness
- Thin lithosphere
10Ridges and rifts feedbacks
Lithospheric thinning
Faulting
Strength in tension
melting
Induced mantle convection
11Ridges 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
12Trenches and collisions forces
- Slab negative buoyancy (slab pull)
- Far-field push?
- Resistance from basal drag
- Resistance from mantle
- Resistance to bending
13Trenches and collisions properties
- Low T slab
- High density slab
- High stiffness slab
- Brittle failure to great depth
- Friction at interface
- Accretionary wedge/lubrication
14Trenches and collisions
15Trenches and collisions feedbacks
Lithospheric thickening
Plate shortening (mass loss)
Faulting
Slab foundering
Rayleigh-Taylor instability
16Trenches 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
17Transforms forces
- Far-field applied forces
- Resisted by fault friction
- Resisted by drag
18Transforms properties
- Same material always in fault zone
- Evolution of fault segments
- Evolution of fault friction
19Transforms feedbacks
rotation
friction
strain rate
20Transforms dynamics
- Passive pulling
- Localization
- Gravity does not contribute