The Theory of Plate Tectonics Plate Tectonics The

The Theory of Plate Tectonics

Plate Tectonics • The Earth’s lithosphere is divided into plates that move on top of the asthenosphere. Lithosphere Asthenosphere When the water moves beneath the raft, the raft moves with it. When the asthenosphere moves, the lithosphere moves with it… Earth’s Major Plates

Types of Plate Boundaries • • When two plates meet, they form a boundary. There are three types of boundaries 1. Convergent 2. Divergent 3. Transform

Convergent Boundaries • Two plates push together Oceanic crust sinks, Continental crust rises!! • • Term to know: SUBDUCTION means the crust is SINKING! Three types of convergent boundaries: 1. Ocean/Ocean = TRENCH 2. Ocean/Continental = TRENCH 3. Continental/Continental = MOUNTAINS

Convergent Collision #1 (Oceanic/Oceanic) Both oceanic plates SINK (subduction!) and form a TRENCH. Magma rises and forms and island arc of volcanoes. Subd uctio n Zon e

Convergent Collision #2 (Oceanic/Continental) • The oceanic plate sinks (subduction!) below the continent and the continental plate slides over the top of the oceanic plate. Forms a TRENCH. Subduction Zone

Convergent Collision #3 (Continental/Continental) • Both continental plates collide and rise up forming MOUNTAINS. (Ex. Himilayas)

Divergent Boundaries • Two plates pull apart causing a rift valley in the middle. Rift Valley • Sea-floor spreading is created by a divergent boundary. Mid Ocean Ridge

Transform Boundaries • Plates slide past each other in a side to side motion. (Ex. San Andreas Fault) This fence used to line up!! San Andreas Fault

WHY do the plates move? …CONVECTION CURRENTS in the mantle…Hot rock (less dense) rises to the surface, cools (more dense), and sinks back to the mantle. COOL ROCK SINKS HOT ROCK RISES

Convection Currents