Earth Science Geology unit

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Earth ScienceGeology unit

• Plate tectonics and Volcanism

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vocabulary

• 1. Continental drift
• 2. Mid-ocean ridge
• 3. Sea-floor spreading
• 4. Lithosphere
• 5. Asthenosphere
• 6. Paleomagnetism
• 7. Plate tectonics
• 8. Divergent boundary
• 9. Convergent boundary
• 10. Transform boundary
• 11. mantle Convection from page 252
• 12. Rift
• 13. Pangaea

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Plate tectonics

• The study of the formation and movements of the
  rigid lithospheric plates that cover the Earths
  surface

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What is Continental Drift?

• Wegeners theory that the continents were
  drifting apart because of the evidence of shape,
  fossils, and rock similarities.
• Visual concept chapter 10

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What are the five kinds of evidence initially
used to propose continental drift? The fit of
the coastlines, fossil evidence, rock type,
structural similarities and paleoclimates
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Shape of the Land

• Why is the fit of the continents better now than
  when proposed by Wegener?
• We now know that the edges of the continental
  shelves mark the edges of the continent and not
  the coastline. A computer fit of these edges show
  a remarkable fit for North America and Europe and
  between South America and Africa.

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Fossil Evidence
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• What fossil evidence was used by Wegner to
  support continental drift?
• For example,
• the same reptiles, lystrosaurus and mesosaurus,
  are found in Africa and South America

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• Opponents thought "land bridges" were the answer.
  
• Wegner also noted that since animals in places
  like Australia and New Zealand had evolved in
  isolation, they had a radically different
  population of animals and plants.
• Note A dinosaur was recently found in early
  Jurassic sediments only 400 miles from the
  present south pole.
• It's name is cryolophosaurus
• it was a carnosaur and was about 20 ft. long

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• The same plants, for, example a seed fern called
  glossopteris is also found on these two
  continents plus Antarctica, India, etc. These
  areas now have widely different climates.
  Reptiles from before 200 m.y. are found in
  Antarctica..

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Rock type and structural similarities

• In order for a jigsaw puzzle to make sense, the
  colors and textures of adjacent pieces have to
  match. Rocks in northwestern Africa match those
  of eastern Brazil.

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• The Appalachian mountains match mountains in
  northern Europe

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What was the main reason for the rejection of
Wegener's theory?
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No energy or mechanism for movement

• but Wegner's hypothesis was that tidal forces of
  the moon were responsible.
• Geologists didn't like the other idea of
  continents plowing through the ocean basins

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How do the plates move?
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• Plates move on the plastic asthenosphere with the
  ocean plates being thinner (50- 100 km) compared
  to the continental plates (100-150 km).

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Asthenosphere
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Convection Currentsvisual concept cause ch10
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What is normal polarity for the earth's magnetic
field?

• The same polarity as we have today, with the
  positive pole of the compass pointing north. and
  having a downward declination for North America.

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• Where is the earth's magnetic north pole, i.e.
  where lines of force are vertical.?

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• It's 11 degrees from the geographic pole--in
  northern Canada

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Magnetic latitude
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What is the magnetic declination?

• It is the angle between true north and magnetic
  north, measured in a horizontal plane.Its given
  to you at the bottom of every topographic map. It
  gives the direction to the magnetic pole.

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Magnetic Pole reversals

• Evidence in the rocks shows that the earths
  magnetic poles have reversed several times in the
  earths history.
• This shows that at spreading boundaries new
  crustal material is forming

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• What is reversed polarity for the earth's
  magnetic field?

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• In this case, the compass points south towards
  the south magnetic pole. The declination would be
  upward if we are measuring from the northern
  hemisphere.

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• What is the average length of time for magnetic
  reversals to take place?

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Recent Geomagnetic Reversals.

• There have been about 171 reversals in the last
  76 million years. This is about 2 reversals in 1
  million years or about 500,000 years per
  reversal.
• Visual concept 3 ch10 magnetic reversals

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Geomagnetic Reversals
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• Explain why there are parallel magnetic stripes
  on the floor of the Atlantic Ocean.

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• At present volcanic rocks cooling on the
  mid-ocean ridges are being magnetized normally.
• Assuming a spreading rate of 2 cm/year, rocks
  that were magnetized over 700,000 ago are about 2
  x 700,000 cm from the center or
• 14 x 100 cm.
• There are 100 cm in a kilometer, so 14 x 105/ 105
  14 km or about 8.5 miles.
• So 8.5 km away (on either side) the rocks have
  reverse magnetism.

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• Detailed mapping of the oceans showed a global
  oceanic ridge system.
• The Mid-Atlantic Ridge had a central rift valley
  showing it was a area of tension (pulling apart).
  
• In addition the ridges had high heat flow and
  universal volcanism. They are made entirely of
  basaltic lava flows that cooled rapidly.

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• These stripes of positive and negative
  magnetization parallel the mid-ocean ridges and
  continue all the way to the borders of the ocean.
• As mentioned else ware, it can be shown by
  palemagnetic or radioactive dating, etc, that the
  oldest oceanic crust is Jurassic in Age.

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Sea-Floor Spreading

• Harry Hess in early 1960's , proposed the concept
  of "sea-floor spreading". a. ocean ridges
  located above upwelling convection cells in the
  mantle.b. many volcanoes and layers of basalt
  generated here.c. tension pulls material apart
  and it is carried away on conveyor belt.d.
  conveyor belt goes on to trenches where oceanic
  crust descends into the mantle.
• Visual concept ch10 2

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Plate Tectonics

• The upper part of the earth (lithosphere)
  consists of about 20 rigid plates.

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• Most of them are composed of a continent and
  surrounding ocean basin which move together.
• A few plates (Nazca, Pacific) are almost
  completely oceanic.

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• Plates move on the plastic asthenosphere with the
  ocean plates being thinner (50- 100 km) compared
  to the continental plates (100-150 km).

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• Remember that the plate boundaries are well
  defined by the distribution of earthquake
  epicenters.

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• Most volcanoes and fold mountains occur on these
  boundaries.
• Plates have moved significant distances through
  Geologic Time

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Types of Boundaries

• Diverging plates move apart
• Spreading centers Mid ocean ridges
• Rift valleys and fracture zones are also at
  diverging boundaries.

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Diverging Boundaries
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Mid-Atlantic Ridge
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Sliding Plate Boundaries

• Transform Boundaries A fault boundary with
  vertical fault plane and plates moving laterally.
  
• Sliding plate boundaries are where two plates
  slide past each other.
• San Andreas fault in California is an example.
• North American and Pacific plates are sliding
  past each other.

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• The San Andreas forms from the Pacific ridge
  (where the plate boundary is a spreading center)
  and starts in the Gulf between Baja and mainland
  Mexico . It continues NW through California, and
  just north of San Francisco becomes part of the
  Juan de Fuca ridge.
• The San Andreas is a right-lateral transform
  fault.

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• The Dead Sea area and whole eastern border of
  Israel is also a (left-lateral) transform fault.
• This extension or "pulling apart" has caused the
  surface of the Dead "Sea" to be about 1200 feet
  below sea level.

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San Andreas CA
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Collision Boundaries

• Two plates coming together.
• They may fuse together

Continent to continent
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Ocean and Continent Converging
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Types Subduction Boundaries

• One plate goes beneath another
• Oceanic is denser!
• Continental is less dense!
• Deep earthquakes occur here

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Plate Boundaries

• The location of Earthquakes and volcanoes
• Pacific ring of fire is a plate boundary

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Continental growth

• Materials that produce continental growth
• Deep sea sediments
• Volcanic rocks
• River deposited sediments

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Hot Spots

• String of volcanoes in the middle of a
  lithospheric plate
• Hawaiian Islands are an example
• These hot spots are probably the effects of
  mantle plumes--a hot mass which migrates up from
  the mantle-core boundary.
• Other hot spots in the Pacific are shown by the
  other chains of islands.
• Other large hot spots, for example, are under
  Iceland and Yellowstone National Park.

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Confirmation Satellite Laser Ranging shows that
Hawaii is moving NW at about 8.5 cm./year.
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Cratons

• The oldest and most altered rock of a continent.
• The Canadian shield is North Americas craton.

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Thin-Skinned Thrusting

• Passing of one plate over another in a flat area
  resulting in the formation of mountain ranges
  like the Appalachians

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Terranes

• Large blocks of lithosphere that have been moved
  and attached to a continent.
• They retain the polarity and fossils from their
  original source.

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• Which of the following factors is most important
  when determining the type of collision that forms
  when two lithospheric plates collide?
• A. the density of each plate
• B. the size of each plate
• C. the paleomagnetism of the rock
• D. the length of the boundary

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A. the density of each plate
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• At locations where sea-floor occurs, rock is
  moved away from a mid-ocean ridge. What replaces
  the rock as it moves away?
• F. molten rock
• G. older rock
• H. continental crust
• I. compacted sediment

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I. compacted sediment
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• Which of the following was a weakness of
  Wegeners proposal of continental drift when he
  first proposed the hypothesis?
• A. an absence of fossil evidence
• B. unsupported climatic evidence
• C. unrelated continent features
• D. a lack of proven mechanisms

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D. a lack of proven mechanisms
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What is the name for the process by which the
Earths crust breaks apart?
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rifting
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6. What is the name for the layer of plastic
rock directly below the lithosphere?
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Asthenosphere
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• Read the passage below. Then, answer questions
  79.
• The Himalaya Mountains
• The Himalaya Mountains are a range of mountains
  that is 2,400 km long and that arcs across
  Pakistan, India, Tibet, Nepal, Sikkim, and
  Bhutan. The Himalaya Mountains are the highest
  mountains on Earth. Nine mountains in the chain,
  including Mount Everest, the tallest above-water
  mountain on Earth, rise to heights of more than
  8,000 m above sea-level. Mount Everest stands
  8,850 m tall.

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• The formation of the Himalaya Mountains began
  about 80 million years ago. A tectonic plate
  carrying the Indian subcontinent collided with
  the Eurasian plate. The Indian plate was denser
  than the Eurasian plate. This difference in
  density caused the uplifting of the Eurasian
  plate and the subsequent formation of the
  Himalaya Mountains. This process continues today.
  The Indian plate continues to push under the
  Eurasian plate. New measurements show that Mount
  Everest is moving to the northeast by as much as
  10 cm per year.

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• According to the passage, what geologic process
  formed the Himalaya Mountains?
• A. divergence
• B. continental drift
• C. strike-slip faulting
• D. convergence

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D. convergence
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• Which of the following statements is a fact
  according to the passage?
• F. The nine tallest mountains on Earth are
  located in the Himalaya Mountains.
• G. The Himalaya Mountains are the longest
  mountain chain on Earth.
• H. The Himalaya Mountains are located within
  six countries.
• I. The Himalaya Mountains had completely formed
  by 80 million years ago.

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• H. The Himalaya Mountains are located within six
  countries.

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• Which plate is being subducted along the fault
  that formed the Himalaya Mountains?
• A. The Indian plate is being subducted.
• B. The Eurasian plate is being subducted.
• C. Both plates are being equally subducted.
• D. Neither plate is being subducted.

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• D. Neither plate is being subducted.

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10. What type of boundary is found between the
South American plate and the African Plate? A.
convergent B. divergent C. transform D.
subduction
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• B. divergent

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• 11. What type of boundary is found between the
  South American plate and the African plate? What
  surface features are most often at boundaries of
  this type?

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• Answers should include the boundary between the
  South American plate and the African plate is a
  divergent boundary most divergent boundaries are
  located on the ocean floor and produce mid-ocean
  ridges and underwater mountain ranges

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• What type of crustal interaction is indicated by
  the letter E?
• F. continental rifting
• G. sea-floor spreading
• H. divergence
• I. subduction

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I. subduction
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• 13. Describe how a transform boundary differs
  from the boundaries shown by letters D and E in
  terms of plate movement and magmatic activity.

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• Answer unlike the plates at a convergent
  boundary, shown by letter E, or divergent
  boundary, shown by letter D, plates at a
  transform boundary move past one another, not
  into or away from one another
• transform boundaries produce a number of
  earthquakes, but they do not produce magma or
  cause mountain formation

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End of Chapter 13
Show visual concepts chapter 10
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Chapter 14

• Review

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Felsic Magmaaka marshmallow fluff

• Lots of silica
• Thick
• Light colored
• Slow moving
• Lots of gases trapped in felsic lava
• Associated with explosive eruptions

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Mafic Magmaaka maple syrup

• Low silica
• Thin
• Dark
• Fast moving
• Gases escape easily
• Smooth lava flow eruptions

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Tephra

• Ash
• Lapilli
• Blocks
• Bombs
• Solid fragments from eruptions

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Rift Eruptions

• Smooth lava flows
• On land
• On sea floor
• Shield cones
• Volcanic plateaus
• Columnar jointing

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Subduction boundaries

• Explosive eruptions
• Cinder cone formations tall thin
• Island chains
• Young mountains

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Famous Eruptions

• Most occurred at Subduction zones
• Vesuvius
• Krakatau
• Crater lake

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Volcanoes in space

• Moon
• Mars
• Jupiters moon Io

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Magma

• Cooled under ground forms plutons
• Examples
• Dikes
• Sills
• Laccoliths
• Volcanic necks
• Batholiths
• stocks

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!!!!!!!!!!!!!STUDY!!!!!!!!!!!!
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