Plate Tectonics Monroe August 31, 2012. Alfred Wegener, father of continental drift.

Plate Tectonics

Monroe

August 31, 2012

Alfred Wegener, father of continental drift

Wegener thought that the continents were once connected.


Continents fit into each other



Landforms, like mountains




Fossils of continents meshed in key areas





Climate evidence

a. Coal fields in Antarctica

b. Glacial till in India





Climate evidence

People did not go along with theory, because they could not figure out what force would be strong enough to move a continent.

Continents would crack if pushed through ocean

Gravity would not make them go “downhill”

Spin of the Earth was not fast enough





People did not go along with theory, because they could not figure out what force would be strong enough to move a continent.

Continents would crack if pushed through ocean

Gravity would not make them go “downhill”

Spin of the Earth was not fast enough

Wegener died on expedition to Greenland

Probably died by falling into a crevice

When digging in Greenland, when you are are deep as you are going to go, one yells “I’ve found Wegener”.

Theory widely accepted in early 1960’s

www.vulkaner.no/v/vulkinfo/ tomtech/etomtech.html

Location of major plates on Earth

http://pubs.usgs.gov/publications/graphics/Fig2-5globes.gif

The breakup of Pangaea, the last of the supercontinents

www.astro.umn.edu/~john/ Ast1001/earth/Earth.html

oak.cats.ohiou.edu/.../ Diversification.htm

www.ucmp.berkeley.edu/ tectonics/quakecenters.html

http://www.classzone.com/books/earth_science/terc/content/visualizations/es0806/es0806page01.cfm?chapter_no=visualization

Location of earthquakes along plate boundaries.

Location of the mid-ocean ridges, where the Earth is coming apart.

http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm

http://education.sdsc.edu/optiputer/flash/hotSpots.htm

http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm

This is a transform fault.

Location “A” is moving to the right in relation to location “B”

A

B

Plates can also slide past each other (transform). This is a divergent fault area, moving away from each other.

This is a transform fault area, moving past each other without destruction.

When plates converge, one of three things can happen.

1. A continental plate (granite) can collide with oceanic plate (basalt), and the more dense goes under (subducts).

2160??

During the Cascadia Megathrust event, the Earth “broke” along a fault about 600 miles long, and “moved” about 60 feet.

2160??

During the Cascadia Megathrust event, the Earth “broke” along a fault about 600 miles long, and “moved” about 60 feet.

2160??

The last large earthquake here was a (flippin’) 8.7 to 9.2!!!! This was based on carbon dating of the debris that was caused, and then buried, by the resulting tsunami. It happened near sunset on Tuesday, the 26th of January of the year 1700.

People got really excited, for a while.


1. A continental plate (granite) can collide with continental plate (granite), and it crumples (mountains), like the Himalayas.


1. An oceanic plate (basalt) can collide with an oceanic plate (basalt), and it make an island arc (Japan) or the Alaskan islands. Note, on the next slide, how the islands form along the “face” of the subducting plate.

Note: along the entire leading edge of the subducting oceanic plate, there are islands. They are in an arc, hence ISLAND ARC.

Same deal. There will chains of islands along the facing edge of a subducting oceanic plate, if it goes under another oceanic plate.

1. The ocean comes apart at ridges. Most of these are in the middle of oceans.

2. “Slab Pull” means that gravity is pulling the leading edge of the plate into the Earth, and the rest of the plate is coming afterwards. Kind of like a table cloth sliding along a table, if too much is hanging over the edge.

1. We know that the plates come apart here (called Sea Floor Spreading), because of magnetic anomalies.http://www.uwsp.edu/geo/faculty/ritter/glossary/s_u/sea_flr_spread.html

http://www.uwsp.edu/geo/faculty/ritter/glossary/s_u/sea_flr_spread.html

Both of these pictures are subducting plates, but the top one is a oceanic under continental (which makes mountains), and the bottom one is

Oceanic under oceanic, which makes islands.

The farther inland one goes, the deeper the earthquakes are, because the subducting plate is deeper down. The focus points where the rocks will lock up, and then break during quakes, will be deeper.

Break it down (Old School Style)

Plates come together at PLATE BOUNDARIES

CONVERGENT (Where they come together)

a. Continent to continent (mountains like Himalayas)

b. Ocean to Ocean (Island arcs like Japan, with TRENCH)

c. Continent to Ocean (Rockies and Andes, with TRENCH and MOUNTAINS)

DIVERGENT (Where they come apart)

a. RIDGE (small hump where lava comes up)

b. RIFT (where the canyon is between plates)

c. SEA FLOOR SPREADING (where Ridges and Rifts are)

d. NEWEST (land is born here)

TRANSVERSE (Where they slide past each other)

a. L.A. and San Francisco

b. Crooked sidewalks

All of this is energy driven

a. Convection currents

b. Heat from birth of Earth, gravitational pressure, radioactive decay

Plate Tectonics Monroe August 31, 2012. Alfred Wegener, father of continental drift.

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