Geo C.O.5

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235 Terms

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Plate Tectonics

A unifying theory that states that the earth is composed of lithospheric crustal plates that move slowly, change size and interact with each other

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Plate Boundaries

Plates move away, toward, or past each other through intense geologic activity

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1. Pacific
2. North American
3. Eurasian
4. African
5. Antarctic
6. Indo- Australian
7. South American

Seven Largest tectonic plates (Descending Order)

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Alfred Wegener

German meteorologist, presented the first comprehensive and detailed theory of continental drift.

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glossopteris (plant), Lystrosaurus and Cynognathus animals) fossils

found on all five continents

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Mesosaurus (reptile)

found in Brazil and South Africa Only

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Pangaea

Supercontinent

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Laurasia

Northern Supercontinent (North America and Asia- excluding India)

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Gondwanaland

Southern supercontinent (South America, Africa, India, Antarctica, and Australia)

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Late Paleozoic

Glaciation patterns were evident on the southern continents

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Late Paleozoic

Coal beds deposited in the northern continents from swampy, probably warm environments

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Paleoclimate Belts

suggest polar wandering as potential evidence for continental drift.

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Polar Wandering

the apparent movement of the poles

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1. The continents remained motionless, and the poles moved (polar wandering)
2. The poles did not move, and the continents moved
3. Both occurred

Evidence

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Skepticism about Continental Drift

Land Bridges
Winds or Ocean currents
Polar Wandering
Mechanism

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Land Bridges

could explain the distribution of land-dwelling reptiles on scattered continents.

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Winds or Ocean currents

could explain distribution of fossil plants on separate continents.

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Polar Wandering

could be explained by moving poles rather than moving continents

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Mechanism

Wegner’s proposed mechanism was not accepted by most geologist in the northern hemisphere

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Curie Point

The mineral magnetite becomes magnetized in cooling lava once its temperature drops below the _____.

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mineral magnetic

Uses _____ properties to determine direction and distance to the magnetic pole when rocks formed.

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Steeper dip angle

_____ indicate rockets formed closer to the magnetic poles

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increasing

Rocks with _____ age point to pole locations increasingly far from present magnetic pole positions.

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The Revival of Continental Drift

  • The mineral magnetite becomes magnetized in cooling lava once its temperature drops below the Curie Point.

  • Uses mineral magnetic properties to determine direction and distance to the magnetic pole when rocks formed.

  • Steeper dip angle indicate rockets formed closer to the magnetic poles

  • Rocks with increasing age point to pole locations increasingly far from present magnetic pole positions.

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Evidence from Paleomagnetism

  • Apparent polar wander curves for different continents suggest real movement relative to one another.

  • Permian rocks in every continent show a different pole position which seems highly unlikely.

  • By reconstructing their locations to form Pangae, the polar wandering paths are nearly identical, indicating that the continents were once joined together.

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relative

Apparent polar wander curves for different continents suggest real movement _____ to one another.

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Permian rocks

in every continent show a different pole position which seems highly unlikely.

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identical

By reconstructing their locations to form Pangae, the polar wandering paths are nearly _____, indicating that the continents were once joined together.

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Fitting of Continents

Redefined the edge of each continent as the middle of the continental slope greatly improved the fit.

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Fitting of Continents

Isotopic ages, glacial striations, rock types, structure, and sequence match.

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History of Continental Positions

Paleomagnetic data indicate the direction and rate of movement

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History of Continental Positions

Pangaea split apart 200 millions years ago but the continents have been in motion for much longer (2 to 4 billion years)

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Geologic Evidence for Continental Drift

  • Fitting of Continents

  • History of Continental Positions

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Seafloor Spreading

Takes place at divergent plate boundaries.

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Seafloor Spreading

The concept that the _____ like a conveyor belt away from the crest of the midoceanic ridge.

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Seafloor Spreading

Proposed in 1962 by Harry Hess

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Hess’s Driving Force

Deep Mantle Convection

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Deep Mantle Convection

Circulation pattern driven by rising of hot material (hot mantle rock) and/or the sinking of cold material (oceanic crust)

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The Mid-Oceanic Ridge

Hot mantle rocks rie beneath

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The Mid-Oceanic Ridge

Decompression melting occurs

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The Mid-Oceanic Ridge

Circulation pattern diverges moving rock away from the ridge

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Oceanic Trenches

Rocks have cooled and become denser

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Oceanic Trenches

Crust sinks beneath a continent or island arc back into the mantle.

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Age of the Sea Floor

<200 million years

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Divergent Boundaries

plates move apart.

<p>plates move apart.</p>
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Convergent Boundaries

plates move together

<p>plates move together</p>
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Transform Boundaries

plates slide past one another

<p>plates slide past one another</p>
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Marine magnetic anomalies

refer to alternating positive and negative magnetic patterns, forming stripe-like features that run parallel to the mid-oceanic ridges.

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The Vine- Matthews Hypothesis

  • New basaltic magma continually extrudes at the ridge crest and cools to record the earth’s magnetism including magnetic field reversals.

  • Matches pattern of reversals seen in continental rocks allow us to measure the rate of movement and to predict the age of the sea floor

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New basaltic magma

continually extrudes at the ridge crest and cools to record the earth’s magnetism including magnetic field reversals.

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reversals

Matches pattern of _____ seen in continental rocks allow us to measure the rate of movement and to predict the age of the sea floor

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Rates of Motion and Seafloor Age

Examining the magnetic polarity of the seafloor, scientist can deduce its age

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Measuring the Rate of Motion

  • Compared to known magnetic reversals from lava flows on land.

  • Rate of plate motion – equals the distance from ridge divided by age of rocks.

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Rate of plate motion

equals distance from ridge divided by age of rocks.

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Predicting Seafloor Age

  • Seafloor age increases with distance from mid-oceanic ridge.

  • The symmetric age pattern reflects plate motion away from the ridge.

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increases

Seafloor age _____ with distance from mid-oceanic ridge.

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symmetric

The _____ age pattern reflects plate motion away from the ridge.

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Fracture Zones

Zones that marks left within plate interiors because of transform faults displacing segments of mid-ocean ridges

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Transform Faults

Occur at the edges of spreading segments.

<p>Occur at the edges of spreading segments.</p>
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Measuring Plate Motion Directly

Are most accurately measured using satellite-based methods. The three frequently employed space-based techniques are very long baseline interferometry (VLBI), satellite laser ranging (SLR), and the Global Positioning System (GPS)

<p>Are most accurately measured using satellite-based methods. The three frequently employed space-based techniques are very long baseline interferometry (VLBI), satellite laser ranging (SLR), and the Global Positioning System (GPS)</p>
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Divergent Plate Boundaries

  • Drift Apart

  • Often associated with frequent earthquakes, magma ascends from the earth’s mantle to the surface. It cools and solidifies, forming a fresh oceanic crust

<ul><li><p>Drift Apart</p></li><li><p>Often associated with frequent earthquakes, magma ascends from the earth’s mantle to the surface. It cools and solidifies, forming a fresh oceanic crust</p></li></ul>
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Transform Plate Boundaries

  • Slides horizontally past one another

  • Transforms may connect:

    • two offset segments of mid-oceanic ridge and a trench. Two trenches

    • Transform offsets of mid-oceanic ridges allow series of straight-line segments to approximate curved boundaries required by spheroidal earth.

<ul><li><p>Slides horizontally past one another</p></li><li><p>Transforms may connect:  </p><ul><li><p>two offset segments of mid-oceanic ridge and a trench. Two trenches </p></li><li><p>Transform offsets of mid-oceanic ridges allow series of straight-line segments to approximate curved boundaries required by spheroidal earth.</p></li></ul></li></ul>
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Convergent Plate Boundaries

  • Two tectonic plates collide.

  • Collision can lead to the edges of one or both plates crumpling upward, forming mountain ranges.

  • One of the plates may bend downward and create a deep seafloor trench

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Ocean-ocean

marked by ocean trench, benioff zone, volcanic island arc

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Ocean-continent

ocean trench, benioff zone, volcanic arc and mountain belt

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Continent- continent

mountain belts and thrust faults

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Plate boundaries

can move over time

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Mid-oceanic ridge crests

can migrate toward or away from subduction zones or abruptly jump to new positions.

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Convergent boundaries

can migrate if subduction angle steepens, or an overlying plate has a trench ward motion of its own.

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Transform boundaries

can shift as slivers of plate shear off.

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Plates

can change size over time.

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The North American plate is increasing in size

  • A new seafloor is being added on the trailing edge as the Atlantic Sea floor spreads.

  • Most of the plate is not being subducted.

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The Nazca Plate is getting smaller.

  • Leading edge is being subducted under South America.

  • Trailing edge is adding sea floor but at a slower rate.

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Leading edge

is being subducted under South America.

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Trailing edge

is adding sea floor but at a slower rate.

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The Attractiveness of Plate Tectonics

  • Explains distribution and composition of volcanoes, earthquakes, and mountain belts.

  • Explains the major features of the sea floor.

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The Cause of Plate Motions

Convection currents in the mantle involve the heating and upward movement of materials to the surface, while cooler liquids sink.

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heating and cooler

Convection currents in the mantle involve the _____ and upward movement of materials to the surface, while _____ liquids sink.

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Any proposed mechanism must explain why:

  • Mid-oceanic ridges are hot and elevated, while trenches are cold and deep.

  • Ridge crests have tensional cracks.

  • The leading edges of some plates are subducting sea floor, while others are continents (which cannot subduct).

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Mid-oceanic ridges

_____ are hot and elevated, while trenches are cold and deep

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tensional cracks

Ridge crests have _____.

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The leading edges

of some plates are subducting sea floor, while others are continents (which cannot subduct).

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Mantle Convection

May be the cause or an effect of circulation set up by the ridge-push and/ or slab-pull.

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Ridge Push

as new plate moves away from the divergent boundary it cools and thickens and subsides.

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Slab Pull

cold lithosphere sinking at a steep angle through the hot mantle should pull the surface part of the plate away from the ridge crest.

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Trench Suction

if subducting plates fall into the mantle at angles steeper than their dip then trenches, and the overlying plates are pulled horizontally seaward toward the subducting plate.

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Mantle Plume

  • narrow columns of hot mantle rock that rise through the mantle.

  • Large ______ may spread out and tear apart the overlying plate forming a Hot Spot at the Earth’s surface(examples include Hawaii, Yellowstone, and Iceland)

    • Flood basalt eruptions.

    • Drifting apart of continental land masses.

    • New divergent boundaries may form.

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Hot Spot Volcanism

a location on Earth either over a mantle plume or beneath the rocky outer layer, known as the crust, where magma is hotter than the surrounding magma.

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Mantle plume hot spots in the interior of a plate produce volcanic chains.

  • Orientation of the volcanic chain shows direction of plate motion over time.

  • The age of volcanic rocks can be used to determine the rate of plate movement.

  • Hawaiian Islands are a good example

<ul><li><p>Orientation of the volcanic chain shows direction of plate motion over time.</p></li><li><p>The age of volcanic rocks can be used to determine the rate of plate movement. </p></li><li><p>Hawaiian Islands are a good example</p></li></ul>
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How is Earth’s Interior Studied?

  • the structure of the Earth's interior, scientists depend on seismic waves, which are shock waves generated by earthquakes and explosions, travelling through the planet and across its surface.

  • The deep interior of the Earth must be studied indirectly.

  • Direct access only to crustal rocks and small upper mantle fragments brought up by volcanic eruptions or slapped onto continents by subducting oceanic plates.

  • The deepest drill hole reached about 12 km but did not reach the mantle

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indirectly

The deep interior of the Earth must be studied _____.

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crustal rocks & small upper mantle fragments

Direct access only to _____ and _____ brought up by volcanic eruptions or slapped onto continents by subducting oceanic plates.

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mantle

The deepest drill hole reached about 12 km but did not reach the _____.

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Geophysics

Branch of geology that studies the interior of the earth.

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Seismic waves

provide evidence that the Earth's interior is composed of several concentric layers

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Layers of the earth

a thin outer crust,followed by a mantle, a liquid outer core, and a solid inner core.

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P-waves (Primary)

the fastest

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S-waves (Secondary

arrive after the P-waves

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Seismic Reflection

the return of some waves to the surface after bouncing off a rock layer boundary Sharp boundary between two materials of different densities will reflect seismic waves

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Seismic Refraction

Bending of seismic waves as they pass from one material to another having different seismic wave velocities