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Plate Tectonics > Introduction > Flashcards

Introduction Flashcards

1
Q

How do we know the plates move? (6)

A
  1. Bathymetry (mid ocean ridges vs deep sea trenches)
  2. Geomagnetism
  3. Radiometric dating
  4. Earthquake source locations
  5. GPS-derived plate velocities
  6. Geophysical imaging
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2
Q

What drives plate tectonics?

A

The release of the mantle’s gravitational potential energy, through convective overturn.

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3
Q

What feeds the mantle’s gravitational potential energy, which is released via plate tectonics? (2)

A
  1. Radioactive decay (internal heat production)

2. Cooling core (primordial heat being released)

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4
Q

What are the forces that act on the tectonic plates at the surface? (4)

A
  1. Ridge-push: rising magma pushes the oceanic lithosphere apart
  2. Slab-pull: cooler oceanic lithosphere becomes negatively buoyant and sinks into hotter mantle, pulls plate down.
  3. Suction force of overriding plate (force opposing slab-pull at subduction zone), varies laterally.
  4. Mantle flow force
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5
Q

What is the internal chemical structure of Earth?

A

Three layers:

  • Crust (Quartz, Plagioclase); 0 - 40km
  • Mantle (Olivine); 40 - 2850km
  • Core (Fe, Ni); 2850 - 6370km
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6
Q

What is the thermo-mechanical internal structure of the Earth?

A 
Five layers:
Lithosphere 0 - 150km
Asthenosphere/Upper Mantle 150 - 660km
Lower Mantle 660 - 2850km
Outer Core 2850 - 5150km
Inner Core 5150 - 6370km
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7
Q

What is the “first motion”?

A

First reading received by a seismic receiver/ geophone.

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8
Q

What is an earthquake?

A

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.

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9
Q

What area of the Earth’s surface does oceanic crust cover?

A

Three-fifths; 3 x 10^14 m^2

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10
Q

What area of the Earth’s surface is covered by continental crust?

A

Two-fifths; 2.0 x 10^14 m^2

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11
Q

What is the mean thickness of continental crust?

A

38km

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12
Q

What is the mean thickness of oceanic crust?

A

9km

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13
Q

What’s the maximum age of oceanic crust?

A

180Ma

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14
Q

What’s the mean age of continental crust?

A

2Ga

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15
Q

What’s the total surface area of Earth?

A

5.1 x 10^14 m^2

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16
Q

What’s the minimum thickness of continental crust (approx)?

A

20km

17
Q

What’s the maximum thickness of continent crust found (approx)?

A

90km

18
Q

What is the principle of Uniformitarianism?

A

That geological processes have occurred at constant rates throughout Earth’s history - what happened then is still happening now!

19
Q

Who developed continental drift theory?

A

Alfred Wegener, in 1912

20
Q

What is the lithosphere?

A

The cool, rigid outer shell of Earth, broken into tectonic plates.

21
Q

What is the asthenosphere?

A

The upper mantle, a weak viscous substrate the lithospheric plates float on.

22
Q

What were Steno’s Four Principles?

A
  1. Superposition
  2. Original Horizontality
  3. Lateral Continuity
  4. Cross-cutting relationships
23
Q

Anderson’s Faulting Theory: What are the maximum, minimum and mean stresses of a NORMAL fault?

A

S1 (maximum): Sv
S2 (mean): Shmax
S3 (minimum): Shmin

24
Q

What is the ‘ophiolite suite’ and what is its general stratigraphy?

A

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
25
Q

What are the major tectonic plates?

A

Pacific, Nazca, North American, South American, African, Eurasian, Antarctic, Arabian, Caribbean, Australian, Juan de Fuca, Indian, Phillipino, Cocos, Scotia… etc.

26
Q

What are the two major SURFICIAL drivers of plate tectonics?

A
  • Ridge push (upwelling magma)

- Slab-pull (cold sinking lithosphere)

27
Q

What layers of the Earth do shear waves propagate through?

A

Crust, upper mantle (lith/asthenosphere), lower mantle (mesosphere), inner core. Outer core is liquid so no shear waves pass through.

28
Q

What is the Moho discontinuity?

A

The crust mantle boundary (around 40km deep)

29
Q

Why is there a drop in the velocity of P an S waves at the top of the upper mantle?

A

That’s where partial melting occurs (Decompression)

30
Q

What occurs at the 410 and 660-km discontinuities?

A

Changes in olivine mineralogy

Plate Tectonics (10 decks)

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