4.2 The Theory of Plate Tectonics

4.2 The Theory of Plate TectonicsTectonics – (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 & AsthenosphereLithosphere – 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 BoundariesDivergent boundaries –

where plates move away from each other

Plate BoundariesConvergent boundaries – where plates collide (3 types)

1. Ocean & Continent – forms a subduction zone; usually forms an ocean trench and mountains on land

Plate BoundariesConvergent boundaries – where plates collide

2. Two Continental plates – neither plate is subducted, so both are crumpled and

uplifted

Plate BoundariesConvergent 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 water rising and cool water sinking

Suspect terranesTheory of suspect terranes - Continents are patchwork of terranes, each with

its own distinct geologic history.

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

Suspect terranes