4.2 The Theory of Plate Tectonics Tectonics – ( Greek ) meaning “construction” Tectonics: The study of the formation of features in the earth’s crust Two types of crust: Oceanic crust Continental crust Open textbook to p. 72

Lithosphere & Asthenosphere Lithosphere – made up of the crust and the rigid upper mantle The lithosphere is broken into separate plates that ride on the denser asthenosphere. Asthenosphere – layer of plastic rock; a solid rock that slowly flows(like putty) when under pressure.

Plate Boundaries Divergent boundaries – where plates move away from each other

Plate Boundaries Convergent boundaries – where plates collide (3 types) 1. Ocean & Continent – forms a subduction zone; usually forms an ocean trench and mountains on land

Plate Boundaries Convergent boundaries – where plates collide 2. Two Continental plates – neither plate is subducted, so both are crumpled and uplifted

Plate Boundaries Convergent boundaries – where plates collide 3. Ocean & Ocean – forms deep ocean trench when one plate is subducted; subducted plate melts and forms volcanic chain (Island Arc)

Plate Boundaries Transform fault boundaries – forms where two plates are grinding past each other. Can you think of an example?

San Andreas Fault

Causes of Plate Motion Convection Currents – cycle of warm matter rising and cool matter sinking

Theory of Suspect Terranes 3 identifying characteristics: 1.Terrane contains rock and fossils that differ from the rocks and fossils of neighboring terranes. 2.There are major faults at the boundaries of a terrane. 3.The magnetic properties of a terrane do not match those of neighboring terranes See Figure 4-9 on p. 77 Continents are a patchwork of terranes, each with its own distinct geologic history.