Plate Tectonics

Not a form of Dubstep

I. Plate Tectonics – Relatively new theory (1929) explaining movements of earth’s lithosphere. Helps explain the following.

Alfred Wegener-circa 1931

A. Locations of volcanoes, faults, earthquakes and mountains.B. Origin of most landforms and ocean floor features.

C. How continents and ocean floor formed and why they are different.

D. Continuing changes of Earth’s surface.

E. Distribution of past and present life on earth.

II. Evidence supporting continental drift.A. Accurate maps began to suggest the continents “fit” together like a puzzle.- Rock sequences match along Corresponding coastlines.

B. Measuring the Age of the ocean floor Confirmed that the seafloor was spreading.-Newer near Oceanic ridges and becoming older as one moves away (from ridges).-Heat flow also DECREASES as one moves away from the oceanic ridges

C. Fossils Provide evidence as well.1. Tell us relative age of seafloor.2. Show similar organisms on once joined coasts.3. Provide hints about past climates.

D. Continental drift was confirmed by the location of magnetic poles through geologic time.

1. Magnetite – Contained in nearly all igneous rock. Is naturally magnetic.

-So, while still magma (liquid), magnetite aligns with polar magnetism.

2. Studying alignment of Magnetite around globe indicated poles have “wandered” through time.

a. However, the wandering curve observed on Eurasia and America were slightly different.

-There can be only one pole at a time-So the crust had to have moved (continental

drift)

E. Seafloor magnetic pattern1. Magnetic fields are symmetrical and parallel to the oceanic ridges. 2. Every new “stripe” of seafloor created at the Oceanic ridge, has a unique magnetism. So we get banding.

III. Revisit Continental and Ocean crust.A. Isostasy – explains why continent floats and ocean floor sinks.

- While much more complicated it is basically the principal of bouyancy.

B. Continental Crust – 1. Thick2. Sedimentary rock…Granite (mostly)3. Less dense.4. Floats like a marshmallow.

C. Oceanic crust.1. Thin2. Dense3. Made of igneous rock (basalt from volcanic ridge)4. Sinks like brick.

D. Remember the Lithosphere? - Physical, outermost division of the earth layers.-**Contains mostly Crust, but also a little bit of Mantle (from the chemical divisions).

IV. ProcessesA. Convection cells – The Engines for movement of Earth’s plates.

1. Caused by heating and cooling Mantle.

2. Fueled by Radioactivity in the mantle.

3. Hot mantle rises at ridges (eg. Mid-Atlantic ridge..a plate boundary.), cools as it moves away from ridge and sinks at Trenches (a different kind of boundary like Mariana trench).

B. Hotspots. – caused by huge plumes of hot magma within the mantle.1. The crust moves over these and eruptions through time leave trailsa. Hawaiian islands are an example.

b. Yellowstone national park is another.

2. Some found under continental masses.3. Most often associated with Oceanic Ridges.

V. Plate Boundaries. A. Three types of movement at plate boundaries (Divergent, Convergent, Transform)

1. Divergent plate boundariesa. An example is the crest of the mid-

ocean ridge.b. this is where new crust is being formed and the plates are moving apart.

c. A rift valley is formed at continental divergent boundaries. The Red Sea is an example.

2. Convergent Plate boundariesa. Deep sea trenches and mountain ranges are examples of features found at convergent boundaries (eg. Himalayan mts. Or Mariana Trench) Rocky Mountain Link (Nat. Geo)

Age of the seafloor and plate convergence directions in the epicentral area of the 2004 Sumatra–Andaman earthquake.

Kanamori H Phil. Trans. R. Soc. A 2006;364:1927-1945

©2006 by The Royal Society

b. At Oceanic-oceanic convergent plate boundaries Volcanic Island Arcs often form.

c. At Oceanic-Continental convergent boundaries, Andesitic volcanoes often form.

THE ENDNo…Wait……ask me about Moment Magnitude.

And The Red Sea