Global Tectonics: Plates and Plumes

Wegner saw the continents as a jigsaw puzzle that fit together into a prior single supercontinent, Pangea, surrounded by the sea Panthalassa

• core • mantle • crust

• Is where we live

• Continental and Oceanic crust

• 10-70km thick • Buoyant (less dense than oceanic) • Mostly old

• Thin (~7km) • Dense (sinks under continental crust • Young

The earth is divided into 12 major plates which are moved in various directions

It refers to the deformation of the crust as a consequence of plate interaction

rigid lithosphere

• The asthenosphere

The tectonic plates

Plates of lithosphere are moved around by the underlying hot mantle connection cells

• Strong lithospheric plates move atop the weaker, plastic asthenosphere • Deformation occurs at or near the edges of plates where they interact with other plates • The interiors of the plates are relatively undeformed

• Divergent • Convergent • Transform

• Show the creation of new oceanic lithosphere from the upwelling mafic magmas as well as a widening of the ocean basin Eg.) Iceland is an example of a mid-ocean ridge exposed above sea level - widening at the rate of ~4 mm/year

Three types: • Continent-oceanic crust collision • Ocean-ocean collision • Continent-continent collision

• Much of the western boundary of South America is this type of boundary. • Denser oceanic lithosphere flexes under the less dense, much older, continental crust. • When oceanic and continental plates converge, the oceanic plate must subduct beneath the continental plate because the density of thick continental crust is too low to permit it to sink into the asthenosphere

• When a convergent boundary forms between plates of oceanic lithosphere, the plate that is older, thicker, and denser subduct the less dense plate. • Several areas of the western Pacific typify this boundary, such as the area around Japan

They are formed when two oceanic plates collide. One runs over the other which causes it to sink into the mantle

When subduction brings two continents together limited subduction may occur, but the buoyancy of continental crus eventually stops the subduction. The contraction of crust in the collision zone doubles the thickness of continental crust and creates high mountains.

• Subduction • Rifting • Hotspots

• Form where narrow columns (plumes) of unusually hot mantle convectively rise from the core-mantle boundary • They leave tracks on moving plates.

are an upwelling of abnormally hot rock within earths mantle. They are stationary in the mantle and other data indicates that they move slowly, if at all