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Earth's Structure, Plate Tectonics, and the Rock Cycle

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Title: Earth's Structure, Plate Tectonics, and the Rock Cycle


1
Our Hazardous EnvironmentGEOG 1110Dr. Thieme
  • Lecture 2
  • Earth's Structure, Plate Tectonics, and the Rock
    Cycle

2
Structure of Earth
Average density of the solid Earth 5.5 g/cm3
Rocks of continental crust average 2.5 to 3.0
g/cm3
Dense (Fe, Ni) core required by planetary motions
3
What Is Inside Earth?
Upper layer is crust two types continental
oceanic
Thickest layer mantle
Lowest layer iron-nickel core (molten outer
core solid inner core)
4
  • Relief and Tectonics
  • Ocean Basins are spreading away from mid-ocean
    ridges
  • Continental collisions build mountains and
    increase land surface elevation
  • ocean-ocean
  • ocean-continent
  • continent-continent

5
Earth's crust is divided into 7 major and 20
smaller plates
6
Plate boundaries are defined by areas of seismic
activity
7
Tectonic Cycle Earth's crust is constantly
being recycled as lithosphere is created at
spreading ridges, rides on aesthenosphere, and is
subducted into the mantle
8
  • Tectonic Cycle
  • New Ocean Crust is produced at spreading ridges
  • Different spreading rates along the ridge are
    accomodated by Transform Faults
  • Compressional Stress at Convergent Boundaries
    results in Folding and Faulting of Crustal Rocks
  • Earthquakes are responses to tectonic stresses

9
Divergence at Spreading Ridges
- most important area for creation of new crust -
sea floor spreading apart at gradual and constant
rate - ocean floor subducted at trenches, remains
geologically young
10
Ocean-Continent Convergence
- deep sea trenches on the ocean floor - denser
plate of oceanic crust is "subducted" beneath
continental crust - ocean floor remains
geologically young
11
Convergent Boundary - Oceanic-Oceanic
  • both plates are the same density
  • Aleutian, Mariana, and Tonga Islands in Pacific
  • Antilles in Caribbean

12
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13
Convergent Boundary - Continent-Continent
  • both plates are the same density
  • edges of colliding plates crumple into mountains
  • Himalayan Mountains in Nepal and India

14
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15
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16
divergent plate boundary
convergent plate boundary
transform faults/ triple junctions
17
Strike-slip (Transform) fault
Reverse (Thrust) fault
Normal fault
18
  • Transform Boundary
  • most transforms offset spreading ridges of
    oceanic crust
  • the San Andreas fault zone in California is a
    transform plate boundary
  • the Pacific plate is sliding horizontally to the
    northwest past a segment of the North American
    plate
  • transform plate motions result in the strongest
    shaking by earthquakes at the Earth's surface

19
Continental Transform Fault
20
San Andreas Transform Fault running across the
Carrizo Plain in California
21
Figure 1.18a
San Andreas Fault impounds drainage used by palm
trees
22
Figure 1.18b
Marsh in Pool impounded by San Andreas Fault
23
  • Rock Cycle
  • all types of rocks can be changed into other
    types by
  • time
  • heat
  • pressure
  • beginning the cycle with igneous rocks (high
    temperature) is arbitrary

24
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25
Igneous Rocks - crystallized from magma which
either intruded deep beneath the surface
("plutonic") or extruded to the surface
("volcanic") Sediment - particles and dissolved
substances which settle out of a liquid (oceans,
river floodplains, swamps), also windblown
(dunes) Sedimentary Rocks - sediment compacted
by weight of overlying layers, cemented by
percolating water, or chemically
precipitated. Metamorphic Rocks - Igneous rocks,
sediment, or sedimentary rocks altered by being
subjected to temperature or pressure conditions
above those at the Earth's surface.
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