The Theory of Plate Tectonics - Boundaries, Stresses, and Faults

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Plates

• the Earth’s crust and upper mantle (Lithosphere) that are broken into sections.

section of the lithosphere → moves slowly over the asthenosphere

carries pieces of continental and oceanic crust

Theory of Plate Tectonics

• states that pieces of Earth’s lithosphere are in constant motion, driven by convection currents in the mantle.

slowly and in different directions

How do plates move?

Convection Currents

• in the mantle, the plates move slowly as the core heats the slowly-forming asthenosphere (the elastic/plastic-like part of the mantle).

Plate Boundaries

• edges of Earth’s plates meet at plate boundaries.

• extended deep into the lithosphere

Fault

• breaks in Earth’s crust where rocks have slipped past each other.

1. Divergent Boundaries

2. Convergent Boundaries

3. Transform Boundaries

The 3 Types of Boundaries:

Divergent Boundaries

• a plate boundary where two plates move away from each other

rifting

causes seafloor spreading

Tension

• the stress in divergent boundaries, wherein the rocks get thin in the middle as it is pulled apart

Normal Fault

• a break in Earth’s crust

• rock drops down as it breaks

• where the rock snaps from the stress of tension

Rift Valleys

• a geologic feature where sea-floor spreading occurs in the ocean

• mid-ocean ridges

• rift valleys

• fissure volcanoes

Features of Divergent Boundaries:

Compression

• the stress of convergent boundaries

• a plate boundary wherein two plates move towards each other

• (two plates that are colliding)

Convergent Boundaries

• places where plates crash (or crunch) together or subduct (one sinks under)

Type 1 of a Convergent Boundary

• ocean plate colliding with a less dense continental plate

Subduction Zone

• process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a convergent plate boundary.

Type 2 of a Convergent Boundary

• ocean plate colliding with another ocean plate

Trench

• the less dense plate slides under the more dense plate, creating a subduction zone

Type 3 of a Convergent Boundary

• a continental plate colliding with another continental plate

Collision Zones

• a place where folded and thrust faulted mountains form

• may form mountain ranges

Reverse Fault

• rock is forced upward as it is squeezed

Transform Boundaries

• a plate boundary where two plates move past each other in opposite direction

• may cause earthquakes, when the rock snaps from the pressure

Shearing

• the stress where rocks are pushed in two opposite directions (or sideways, but no rock is lost)

San Andreas Fault in California

• a famous fault at a transform boundary

Strike- Slip Fault

• where the rock is sheared from the stress of shearing

• rocks on each side of the fault slip past each other as they break

1. African Plate

2. Eurasian Plate

3. Indo-Australian Plate

4. North American Plate

5. Pacific Plate

6. South American Plate

7. Nazca Plate

The 7 Primary/Major Tectonic Plates