The Story of Plate TectonicsNovember 12, 2013

Last Week We Learned• Continental Drift• Why plate tectonics

move – convection cells (like a lava lamp)

• Think back to density

Convection Cells in the Mantle• Lithosphere: the solid outer

layer of the Earth that consists of the crust and the rigid (unable to bend) upper part of the mantle

• Asthenosphere: the solid, plastic layer of the mantle beneath the lithosphere; made of mantle rock that flows very slowly and allows tectonic plates to move on top of it

• Play movie at 3:57

Page 5 of ESRT

There are four types of plate boundaries: There are four types of plate boundaries:

1. 1. Divergent boundaries Divergent boundaries -- where new crust is generated as -- where new crust is generated as the plates pull away from each other. the plates pull away from each other.

2. 2. Convergent boundaries Convergent boundaries -- where crust is destroyed as one -- where crust is destroyed as one plate dives under plate dives under another. another. 3. 3. Transform boundaries Transform boundaries -- where crust is neither produced -- where crust is neither produced nor destroyed as the plates slide horizontally past each othernor destroyed as the plates slide horizontally past each other.

4. 4. Plate boundary zones Plate boundary zones -- broad belts in which boundaries -- broad belts in which boundaries are not well defined and the effects of plate interaction are are not well defined and the effects of plate interaction are unclearunclear

Divergent Plate Divergent Plate BoundariesBoundaries

• The Mid-Atlantic The Mid-Atlantic Ridge, which Ridge, which splits nearly the splits nearly the entire Atlantic entire Atlantic Ocean north to Ocean north to south, is probably south, is probably the best-known the best-known and most-studied and most-studied example of a example of a divergent-plate divergent-plate boundary.boundary.

Convergent Plate Convergent Plate BoundariesBoundaries

3 Types of Convergent Boundaries3 Types of Convergent Boundaries

Ocean to ContinentOcean to ContinentOcean to OceanOcean to Ocean

Continent to ContinentContinent to Continent

• The The convergence of convergence of the Nazca and the Nazca and South South American American Plates has Plates has deformed and deformed and pushed up pushed up limestone limestone strata to form strata to form towering peaks towering peaks of the Andesof the Andes

• The 6,000-The 6,000-km-plus km-plus journey of journey of the India the India landmass landmass (Indian (Indian Plate) Plate) before its before its collision collision with Asia with Asia (Eurasian (Eurasian Plate) Plate) about 40 to about 40 to 50 million 50 million years agoyears ago

Transform BoundariesTransform Boundaries

• The Blanco, The Blanco, Mendocino, Mendocino, Murray, and Murray, and Molokai Molokai fracture fracture zones are zones are some of the some of the many many fracture fracture zones zones (transform (transform faults) that faults) that scar the scar the ocean floor ocean floor and offset and offset ridgesridges

• The San Andreas fault The San Andreas fault zone, which is about zone, which is about 1,300 km long and in 1,300 km long and in places tens of places tens of kilometers wide, slices kilometers wide, slices through two thirds of through two thirds of the length of the length of California. Along it, California. Along it, the Pacific Plate has the Pacific Plate has been grinding been grinding horizontally past the horizontally past the North American Plate North American Plate for 10 million years, at for 10 million years, at an average rate of an average rate of about 5 cm/yrabout 5 cm/yr

HotspotsHotspots

Regions of earthquake and volcanic Regions of earthquake and volcanic activity which do not occur along activity which do not occur along

plate boundariesplate boundaries

• The vast majority of earthquakes and volcanic eruptions The vast majority of earthquakes and volcanic eruptions occur near plate boundaries, but there are some occur near plate boundaries, but there are some exceptionsexceptions

• Map of part of the Pacific basin showing the volcanic trail Map of part of the Pacific basin showing the volcanic trail of the Hawaiian hotspot-- 6,000-km-long Hawaiian Ridge-of the Hawaiian hotspot-- 6,000-km-long Hawaiian Ridge-Emperor Seamounts chainEmperor Seamounts chain