Tectonics Flashcards
Which planets have a mantle (i.e. not a solid core) in the solar system?
The Earth, Venus (but no plate tectonics, so just hotspot volcanism), Mars (one plate formed from several)
What, a priori, is evidence of plate tectonics?
Parts of the earth’s surface are contracting whilst other bits are extending
What is Global Hypsometry used for?
To show the distribution of the world’s topography by surface area
What is significant about global hypsometry?
A bimodal distribution due to continental and oceanic crust differences;
continental crust is thicker and less dense than oceanic crust, which is older
How does paleomagnetism work?
As the seafloor spreads and cools to <100 degrees, the magnetic minerals in the magma align themselves to the magnetic pole
Why is continental rifting significant?
Forms new oceanic crust over time
Why is seafloor spreading significant?
Effusive volcanism releases CO2, a major flux in the geological carbon cycle
Why is plate subduction important?
- Ensures that the world does not expand
- Sight of earthquakes and volcanism
What are the 2 main sources of internal heat?
1) Primordial (latent) heat from planetary accretion
2) Heat in core due to long- and short-lived radioactivity (major), (Francis, P. and Oppenheimer, C., Volcanoes, 2nd ed., 2004, Oxford UP)
Why is studying hotspots important?
- Allows plate velocity to be determined
- Allows plate direction to be determined
What methods are there of studying the interior of the Earth?
- Chemically with rocks
- Seismic shadows
What is the lithosphere?
All of the crust and upper part of mantle (asthenosphere being plastic part of mantle)
Which plate type (continental vs oceanic) is more rigid? Why is this significant?
Oceanic more rigid, so seismicity is less diffused at margins involving oceanic plates
Is the mantle liquid?
No, it is solid. It can still flow though, just as glaciers flow. Pitch used as a metaphor in Holmes’ Principles of physical geology 4th ed
How do we know the mantle flows?
Isostatic rebound in the Holocene
How do we know convection is driving mantle flow?
Rayleigh number strongly favours mantle convection (Ra is > 10^6) (Kearey, et al., 2009)
What are the two categories of forces acting on plates?
1) Edge force mechanisms: Ridge push and slab pull
2) Mantle drag mechanisms (driven by convection)
(Kearey, et al., 2009)
Name 3 key types of faults
1) Normal faults (extension forces)
2) Reverse faults (compression forces)
3) strike-slip faults (conservative boundaries)
By what process does the mantle flow?
Creep formation as crystal structures deform (Oppenheimer and Francis, 2004)
What is believed to cause excessive effusive eruptions and continental flood basalts (CFBs)?
Plumes rising from the core under thermal instability (lower density etc) can adhere to one another, propagating the rise of magma
What are trench forces?
- Edge forces at subduction cells driven by localised convection cells (from heated material, esp. water, above subducting plate) in the mantle wedge (also Conrad and Lithgow-Bertelloni, 2002)
- “Sucks” in the subducting plate
Open University, 2019
What is the main role of plate tectonics?
To transfer heat away from the core (Kump et al., 2014)
What is the main role of mantle convection?
To transfer heat from the core to the lithosphere (Kump et al., 2014)
How is heat transferred from the core?
- Convection occurs as the solid mantle heats, expands and rises due to positive buoyancy induced by a lower density, before being replaced by cooler material
- Warmer mantle material reaches the moho discontinuity at the base of the lithosphere
- Heat is transferred by conduction through the lithosphere to the surface
- Mantle material cools and descends back towards the core
(Kump, et al., 2014)