The Theory The Theory of Plate Tectonicsof Plate Tectonics

Plate TectonicsPlate Tectonics The inner structure of the The inner structure of the

Earth has different layers:Earth has different layers:is made of two layersis made of two layers•Core (Inner and outer)Core (Inner and outer)•MantleMantle•Crust (Oceanic and Crust (Oceanic and Continental)Continental)

The Earth’s interiorThe Earth’s interior

7000 C

4000 C

1000 C

The Lithosphere (crust and The Lithosphere (crust and outer mantle) floats on the outer mantle) floats on the Asthenosphere (fluid Asthenosphere (fluid layer). layer).

The Lithosphere is broken The Lithosphere is broken up into tectonic plates.up into tectonic plates.

The PlatesThe Plates

* Hover over for names

The plates move in relation The plates move in relation to each other and form to each other and form three different types of three different types of plate boundaries:plate boundaries:•ConvergentConvergent•DivergentDivergent•TransformTransform

How does it work?Plates move due to convection currents in the Astenosphere. The inner fluids become hotter than the outer ones. Hot fluids are less dense than cold ones, so they ascend while the colder ones descend. This makes what we call convection currents.

mantle convectionmantle convectionHeat transfer from the core to the Heat transfer from the core to the mantle produces slow convectionmantle produces slow convection

of the mantle materialof the mantle material

(in the order of centimetres per year)(in the order of centimetres per year)

Mantle convection produces lateral Mantle convection produces lateral forces at the boundary between the forces at the boundary between the

mantle and the crustmantle and the crust

Lateral forces at the crust-Lateral forces at the crust-mantle boundary push the mantle boundary push the crust around – in different crust around – in different

directions – and this leads to directions – and this leads to the motion of the plates. the motion of the plates.

The plates are moving at The plates are moving at rates of cm/yearrates of cm/year

Kinds of Plate Kinds of Plate BoundariesBoundaries

ConvergentConvergentOccurs when plates collide. There Occurs when plates collide. There are three types.are three types.

DivergentDivergentOccur when two plates Occur when two plates are moving apart and are moving apart and new crust is created new crust is created by magma pushing up by magma pushing up from the Earth’s from the Earth’s mantle. mantle.

DivergentDivergent Divergent boundaries create Divergent boundaries create

the the mid-ocean ridgesmid-ocean ridges, where , where the ocean floor is created. This the ocean floor is created. This process is called process is called Sea-floor Sea-floor spreadingspreading. As a consequence, . As a consequence, the older rocks of the ocean the older rocks of the ocean floor are always closer to the floor are always closer to the continents.continents.

Hydrothermal ventsHydrothermal vents In mid-ocean ridges, there In mid-ocean ridges, there

are fractures that allow the are fractures that allow the sea water to seep down and sea water to seep down and get heated by the mantle. get heated by the mantle. The hot water then forces its The hot water then forces its way back up through the way back up through the crust and emerges in crust and emerges in hydrothermal vents, or deep-hydrothermal vents, or deep-sea hot springs. sea hot springs.

Hydrothermal ventsHydrothermal vents The hot water coming from The hot water coming from

the mantle has sulfide the mantle has sulfide minerals dissolved, that will minerals dissolved, that will precipitate when the water precipitate when the water emerges from the vent and emerges from the vent and cools. These minerals form cools. These minerals form deposits, like the chimney-deposits, like the chimney-like like black smokersblack smokers..

TransformTransformOccur where plates grind past each Occur where plates grind past each

other. As a consequence, other. As a consequence, earthquakes occur frequently in earthquakes occur frequently in these areas.these areas.

Transform boundaryTransform boundary

Hot SpotsHot Spots Hot spots are places where a Hot spots are places where a

plume of hot magma rises plume of hot magma rises from the mantle and forces its from the mantle and forces its way through the Lithosphere way through the Lithosphere to form volcanoes. As the to form volcanoes. As the plate moves, new volcanoes plate moves, new volcanoes are created. One example are are created. One example are the Hawaiian Islands. the Hawaiian Islands.