plate tectonics the earth’s crust is in motion. relating plate tectonics to the rock cycle and...
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http://earthsci.terc.edu/content/investigations/es0602/es0602page01.cfm?chapter_no=investigation
4 Main Layers of the Earth Crust – Made up of two types: Oceanic and
Continental. Contains mostly Silicon, Oxygen, and Aluminum
Mantle – Divided into upper and lower mantle; mostly Iron and magnesium
Outer Core – Liquid, mostly Iron and Nickel
Inner Core – Solid, Mostly Iron and Nickel
Comparison of Earth’s Two Types of Crust
Oceanic
Continental
Thinner and more dense
Made up mostly of mafic (basaltic) igneous rocks basalt and gabbro
Thicker and less dense Made up mostly of the
felsic (granitic) igneous rocks granite and rhyolite
Theories Prior to Plate Tectonics
Continental Drift Proposed by Alfred Wegener
Says that the continents have moved horizontally to their present location
Evidence for Continental Drift
Continents fit together
Fossils
Continents fit like a puzzle
Wegener called this large landmass Pangaea
Fossils of similar animals such as mesosaurus and plants like glossopteris were found on different continents.
(See fig. 2, p.273)
Evidence for Continental Drift (continued)
Climate
Rock Type and Structure
Warm-weather fossils found in the Arctic
Evidence of glaciers found in present-day warm areas.
Same rock types and structures on different continents (example: Eastern U.S. and Western Europe
Theories Prior to Plate Tectonics (continued)• Seafloor Spreading• Proposed by Harry Hess .
• The theory states that hot, less dense material in the mantle is forced upward to the surface at the mid - ocean ridges.
Seafloor Spreading (continued)• As magma is forced upward at mid-ocean
ridges, it flows in opposite directions away from the ridge.
• As it moves away from the ridge, the magma cools, solidifies, gets thinner and becomes ______ dense.
• Becoming more dense than the asthenosphere below it, the oceanic crust sinks downward at convergent boundaries, forming trenches
Evidence for Seafloor Spreading• Age of the
Seafloor
• Oceanic crust is younger than continental crust
• Oceanic crust is 160-180 million years old while continental crust is almost 4 billion years old.
• Rocks are younger at the mid-ocean ridges and get increasingly older away from the ridge on both sides
Evidence for Seafloor Spreading (continued)
• Magnetic Clues • Iron minerals in basaltic rocks align with the Earth’s magnetic field.
• The magnetic field has reversed several times.
• The reversal creates an alternating pattern of normal and reversed polarity that is the same on both sides of the ridge (see fig.7, p.278).
Theory of Plate Tectonics• (Unifying theory that explains many
complex Earth systems);
• This theory helps explain continental _______, seafloor ________, AND provides a cause (mechanism) for these movements of the crust.
• The cause was what was lacking in the previous theories.
Theory of Plate Tectonics (cont.)
• The theory of plate tectonics states that the Earth’s continental and oceanic crust is broken up into sections. These sections are called tectonic or lithospheric plates, and they move over the surface the Earth.
• The larger plates and their boundaries can be seen in figure 9 on page 281.
Layers Related to Plate Tectonics
• Lithosphere
• Asthenosphere
• Consists of the crust and rigid upper mantle
• Broken into large pieces called tectonic plates.
• Plastic-like part of the upper mantle.
• Is beneath the lithosphere
Tectonic Plate Boundaries
• 3 Types of Boundaries
• Divergent – plates move away from each other
• Convergent – plates move toward each other
• Transform – plates slide past each other horizontally
As the tectonic (lithospheric) plates move along and above the asthenosphere, the plates meet at three types of boundaries:
Divergent Boundaries
• The tectonic plates are moving away from each other
• Characteristics of a divergent boundary are:
- Shallow-focus Earthquakes - Volcanoes since molten material
of the mantle is so close to the
surface.• Examples of divergent boundaries are
the Mid-Atlantic _______ and the East-African rift valley.
A plume of hot magma rises from deep within the mantle pushing up the crust and causing pressure forcing the
continent to break and separate.
Lava flows and earthquakes would be seen.
As the rift valley expands two continental plates have been constructed from the original one. The
molten rock continues to push the crust apart creating new crust as it does.
Convergent Boundaries
1) Oceanic-to-Continental2) Oceanic-to-Oceanic3) Continental-to-
Continental
• Plates move directly towards each other• There are three types of convergent boundaries:
Oceanic-to-Continental Convergent Boundaries• The more dense _______ crust
subducts under the less dense ___________ crust.
• Characteristics include: - Trench at subduction zone - Volcanoes - Shallow- and deep-focus
earthquakes
• An example is the ______ mountains on the west coast of South America
http://www.pbs.org/wnet/savageearth/animations/
Oceanic-to-Oceanic Convergent Boundaries
An older, cooler, and _____ dense oceanic plate subducts under another oceanic plate
Characteristics include: - Volcanic island arcs - Earthquakes and volcanoes - Ocean or sea on both sides of the boundary
Examples of this type of boundary are Japan and the Aleutian Islands in Alaska
Continental-to-Continental Convergent Boundary
This occurs when less –dense continental-crust plates collide.
Being less dense, these plates can only move upward during collision.
Characteristics include: - Tall mountains - Earthquakes (Shallow- and medium-focus) - Absence of __________ since there is no subduction.
The Himalaya mountains where _____ and ____ collided are an example.
Transform Plate Boundaries At this boundary, the tectonic plates slide past
each other with little or no vertical movement or subduction.
Characteristics of a transform boundary: - Shallow-focus Earthquakes - An Absence of volcanoes since there is no subduction.
An example of a transform boundary is the ___ _______ fault in California
Other Characteristics Related to Plate Tectonics
Volcanoes and Earthquakes are concentrated along plate boundaries
An example is the “ring of ____” around the Pacific Ocean
(See figures 2 on page 301 and 5 on page 333)
Other Characteristics of the Plate Tectonics Theory
(continued)• An EXCEPTION to earthquakes and
volcanoes being along plate boundaries is the occurrence of hot spots.
• These occur where the mantle material is very close to the surface in isolated areas within a plate (See fig.8 on p.335)
• An example of a hot spot is ________
What Causes the Plates to Move?
• The cause of tectonic (lithospheric) plate movement is __________ currents in the plastic-like mantle, or the _____________
• There are different models made to explain these __________ currents
(See figure 12 on page 285)
http://www.geocities.com/Athens/Agora/3006/geogpb/tectonicprocessesreview.htm
Comprehensive Review
http://www.harlan.k12.ky.us/ges/7th%20online%20tests/ch._14_plate_tectonics.htm
http://www.glencoe.com/sec/science/lep_science/earth_science/tutor/quizzes/test11.html
(Also see links on volcano power point presentation)
Va. Tectonic landforms linkhttp://filebox.vt.edu/users/shamner/EPortfolio/Lessonplans/PlateTectonics/Day%205.pdf