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Geology 1330 > Plate Tectonics > Flashcards

Plate Tectonics Flashcards

1
Q

Eduard Suess

A

Late nineteenth century.

– Postulated that southern continents were once part of a giant continent called Gondwanaland

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2
Q

Alfred Wegener

A 
Early twentieth century.
– Fitted together separate continents to form giant
supercontinent of Pangaea.
– First proposed his
continental drift hypothesis
in 1915
– Published The Origin of
Continents and Oceans
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3
Q

Continental drift hypothesis

A 
– Supercontinent called
Pangaea broke apart and
the “pieces” drifted to their
present positions to become
modern continents
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4
Q

The Great Debate

A

• Strong opposition to the continental drift
hypothesis from the scientific community
• Hypothesis lacked a viable mechanism for
moving continents:
–Wegener incorrectly suggested that
continents broke through the ocean crust,
much like ice breakers cut through ice
• Wegener’s hypothesis was correct in principle,
but contained incorrect details
• A few scientists considered Wegener’s ideas
plausible and continued the search for more
evidence

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5
Q

Evidence that supported the Continental Drift

A 
–Fit of the continents
–Fossil evidence
– Rock type and structural similarities
–Paleoclimatic evidence
–Paleomagnetism
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6
Q

Fossil Evidence for Continental Drift

A 
A. L. Du Toit (early twentieth
century) identified ancient
fossils on widely separated
continents:
• Some fossils from different
continents were remarkably
similar to one another
• Wondered how similar
animals could have crossed
entire oceans
• Concluded that the now
separated continents have at
one time been joined
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7
Q

Paleoclimatic Evidence

A 
• Glacial deposits found in
South America, Africa,
India and Australia:
– Some in places where the
climate is now tropical
• Grooves in bedrock at these
locations may have been
carved by ancient glaciers
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8
Q

What type of ancient rocks and fossils do not match the climate at their present location? What is this an example of and what does it suggest?

A 
• Coal in Antarctica
• Reef-building corals in
frozen Greenland
• Glacial deposits in Sahara
Desert
Example of Paleoclimate Evidence for Continental Drift. Suggests that continents were at one time at different latitudes and "drifted" to present positions.
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9
Q

What is paleomagnetism?

A

Study of the magnetic properties of ancient rocks. This provides further evidence
that continents drifted over time.

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10
Q

When and how was the magnetic field discovered.

A

discovered by the Chinese in the 13th century by floating a lodestone on a piece of wood – it pointed north.

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11
Q

Compass directions define two components of magnetism:

A

– Declination: Horizontal swing

– Inclination: Tilt of magnetization

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12
Q

Declination

A

Compass direction points to the magnetic north pole

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13
Q

Inclination

A

Magnetic inclination is the
angle a compass needle
makes with Earth’s surface and is a function of latitude

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14
Q

What can magnetic materials in volcanic rocks record?

A

The direction of Earth’s magnetic field at the time the lava flow crystallized.

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15
Q

Assembling continents to their former positions does what to the Polar Wandering Paths?

A

Aligns them

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16
Q

Magnetic polarity reversals throughout Earth history are recorded as?

A

Magnetic stripes in oceanic crust.

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17
Q

Presently magnetic lines of force travel from?

A

The south to north magnetic poles

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18
Q

What happens to the oceanic crust during normal and reverse magnetism?

A

During normal magnetism, the oceanic crust acquires normal polarity and during reverse magnetism the oceanic crust acquires reversed polarity.
The crust can split apart in opposite directions, forming stripes on either side of a mid-ocean ridge.

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19
Q

Youngest oceanic lithosphere occurs along?

A

Mid-ocean ridges. Oceanic lithosphere is progressively older away from these ridges.

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20
Q

How does the thickness of sediments change with distance from a ridge crest.

A

The thickness increases.

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21
Q

Oldest oceanic lithosphere occurs along where?

A

The edge of the ocean basin adjacent to a subduction zone and/or continental margin.

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22
Q

Stages in the formation of an ocean basin

A
  • Hot upwelling mantle material impinges on the base of continental lithosphere.
  • There is a continental rift (splitting of the continental lithosphere)
  • Linear sea develops between the now separated continents
  • Linear sea evolves into a mature ocean basin, with a mid-ocean ridge at the origin of the rift and passive continental margins.
    e. g. gulf coast and east coast of North America
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23
Q

What are deep-sea fans?

A

Deposits of sediments in deep water that have been carried offshore by currents.

24
Q

Divergent plate boundary

A
  • constructive

- two plates move apart from one another

25
Q

Convergent plate boundary

A
  • destructive

- two plates collide with one possibly subducting beneath the other.

26
Q

Subduction

A

The sideways and downward movement of the edged of a plate of the earth’s crust into the mantle beneath another plate.

27
Q

Transform plate boundary

A
  • lithosphere is conserved

- two plates slide laterally past one another

28
Q

Mantle convection cells sink at?

A

Convergent plate boundaries

29
Q

Convection cell

A

a self-contained convection zone in a fluid in which upward motion of warmer fluid in the center is balanced by downward motion of cooler fluid at the periphery.

30
Q

Parts of a subduction zone

A
  • Trench
  • Accretionary wedge of prism
  • Forearc Basin
  • Volcanic Arc
31
Q

Trench

A

Deep depression on seafloor where oceanic plate bends downward

32
Q

Forearc Basin

A

Where volcanic material and sediment accumulate in subduction zone

33
Q

Accretionary wedge/prism

A

Leading edge of overriding plate in subduction zone where sediment and pieces of oceanic crust scraped off of down-going plate accumulate.

34
Q

Volcanic arc

A

Formed when the subducted plate reaches a depth hot enough to melt it and the mantle and magma rises to erupt at the surface.

35
Q

The three type of convergent plate boundaries

A
  • Ocean-ocean convergence
  • Ocean-continent convergence
  • Continent-continent convergence
36
Q

Ocean-ocean convergence

A

Oceanic lithosphere subducts beneath another oceanic plate; characterized by linear chain of volcanoes called island arcs

37
Q

Ocean-continent convergence

A

Oceanic lithosphere subducts beneath continental lithosphere; causes continental volcanic arc

38
Q

Continent-continent convergence

A

Two continental plates collide; causes mountain ranges like the Himalayas

39
Q

collage (collage tectonics)

A

an assemblage of micro-continents, arcs, and other crustal fragments accreted along the edge of a continent adjacent to a subduction zone.

40
Q

Driving forces of plate tectonics

A
  • Slab pull
  • Ridge push
  • Whole-mantle convection
  • Layer-cake convection
41
Q

Slab pull

A

Results from the sinking of a cold, dense slab of oceanic lithosphere and is the major driving force of plate motion; major driving force of plate motion

42
Q

Ridge push

A

a gravity driven force that results from the elevated position of the ridge

43
Q

Convection in the mantle enhances plate motion when?

A

When the velocity of the asthenosphere exceeds that of the overlying plate.

44
Q

Whole-Mantle Model

A

Sinking slabs of cold oceanic lithosphere are the downward limbs of convection cells, while rising mantle plumes carry how material from the core-mantle boundary toward the surface.

45
Q

Layer-Cake Convection Model

A

Has two largely disconnected layers. A dynamic upper layer driven by descending slabs of cold oceanic lithosphere and a sluggish lower layer that carries heat upward without appreciably mixing with the layer above.

46
Q

Bathymetry

A

“submarine topography,” or the depths and shapes of underwater terrain.

47
Q

Feature of seafloor bathymetry

A
  • Deep trenches
  • Immense fracture zones
  • Countless submerged volcanoes
  • Enormous submarine mountain ranges (mid-ocean ridges)
48
Q

Mid-ocean ridges extend the length of?

A

Entire ocean basins; can be hundred or thousand of kilometers long.

49
Q

Sites of numerous submarine hot springs where heated seawater is discharged

A

Mid-ocean ridge

50
Q

Ophiolites

A

Slices of oceanic crust found on land

51
Q

Pillow basalts

A

result of the rapid cooling of hot, fluid magma that comes into contact with water

52
Q

Sheeted Dyke Complex

A

consists of swarms of basaltic dykes, the feeder channels for the overlying pillow basalts

53
Q

Gabbros

A

usually banded or layered resulting from the crystallization in the magma chamber at the base of the crust

54
Q

Convection cells spread apart at?

A

Mid-ocean ridges, carrying plates in opposite directions

55
Q

Transform faults do what to mid-ocean ridges?

A

These faults break the mid-ocean ridges into segments causing an offset(s) along the ridge.

56
Q

Mantle plume

A
  • Long-lived structures
  • Some originate at the core-mantle boundary
  • Hot plumes relatively buoyant and rise towards the surface
57
Q

Rising plumes of mantle material create?

A

Hot spots in the overlying crust; volcanoes can form over them

Geology 1330 (3 decks)

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