Introduction Flashcards
How do we know the plates move? (6)
- Bathymetry (mid ocean ridges vs deep sea trenches)
- Geomagnetism
- Radiometric dating
- Earthquake source locations
- GPS-derived plate velocities
- Geophysical imaging
What drives plate tectonics?
The release of the mantle’s gravitational potential energy, through convective overturn.
What feeds the mantle’s gravitational potential energy, which is released via plate tectonics? (2)
- Radioactive decay (internal heat production)
2. Cooling core (primordial heat being released)
What are the forces that act on the tectonic plates at the surface? (4)
- Ridge-push: rising magma pushes the oceanic lithosphere apart
- Slab-pull: cooler oceanic lithosphere becomes negatively buoyant and sinks into hotter mantle, pulls plate down.
- Suction force of overriding plate (force opposing slab-pull at subduction zone), varies laterally.
- Mantle flow force
What is the internal chemical structure of Earth?
Three layers:
- Crust (Quartz, Plagioclase); 0 - 40km
- Mantle (Olivine); 40 - 2850km
- Core (Fe, Ni); 2850 - 6370km
What is the thermo-mechanical internal structure of the Earth?
Five layers: Lithosphere 0 - 150km Asthenosphere/Upper Mantle 150 - 660km Lower Mantle 660 - 2850km Outer Core 2850 - 5150km Inner Core 5150 - 6370km
What is the “first motion”?
First reading received by a seismic receiver/ geophone.
What is an earthquake?
A sudden release of elastic energy stored in the lithosphere; released as seismic (elastic) waves.
Results from frictional sliding causing stress to accumulate until tectonic stress exceeds fault’s frictional strength.
Usually occurs at existing faults/fractures.
What area of the Earth’s surface does oceanic crust cover?
Three-fifths; 3 x 10^14 m^2
What area of the Earth’s surface is covered by continental crust?
Two-fifths; 2.0 x 10^14 m^2
What is the mean thickness of continental crust?
38km
What is the mean thickness of oceanic crust?
9km
What’s the maximum age of oceanic crust?
180Ma
What’s the mean age of continental crust?
2Ga
What’s the total surface area of Earth?
5.1 x 10^14 m^2
What’s the minimum thickness of continental crust (approx)?
20km
What’s the maximum thickness of continent crust found (approx)?
90km
What is the principle of Uniformitarianism?
That geological processes have occurred at constant rates throughout Earth’s history - what happened then is still happening now!
Who developed continental drift theory?
Alfred Wegener, in 1912
What is the lithosphere?
The cool, rigid outer shell of Earth, broken into tectonic plates.
What is the asthenosphere?
The upper mantle, a weak viscous substrate the lithospheric plates float on.
What were Steno’s Four Principles?
- Superposition
- Original Horizontality
- Lateral Continuity
- Cross-cutting relationships
Anderson’s Faulting Theory: What are the maximum, minimum and mean stresses of a NORMAL fault?
S1 (maximum): Sv
S2 (mean): Shmax
S3 (minimum): Shmin
What is the ‘ophiolite suite’ and what is its general stratigraphy?
The ophiolite suite is the general stratigraphy of oceanic crust and is represented by, from bottom to top:
- Upper mantle
- Layered peridotite
- Layered gabbros (intrusive basalt)
- Gabbro
- Sheeted dykes
- Pillow lavas
- Sediments
What are the major tectonic plates?
Pacific, Nazca, North American, South American, African, Eurasian, Antarctic, Arabian, Caribbean, Australian, Juan de Fuca, Indian, Phillipino, Cocos, Scotia… etc.
What are the two major SURFICIAL drivers of plate tectonics?
- Ridge push (upwelling magma)
- Slab-pull (cold sinking lithosphere)
What layers of the Earth do shear waves propagate through?
Crust, upper mantle (lith/asthenosphere), lower mantle (mesosphere), inner core. Outer core is liquid so no shear waves pass through.
What is the Moho discontinuity?
The crust mantle boundary (around 40km deep)
Why is there a drop in the velocity of P an S waves at the top of the upper mantle?
That’s where partial melting occurs (Decompression)
What occurs at the 410 and 660-km discontinuities?
Changes in olivine mineralogy
