Transcript Document

PLATE TECTONICS:
PLATE BOUNDARIES
LAYERS OF THE EARTH
1. Crust (brown/tan)
2. Mantle (light &
dark orange)
3. Core (yellow &
white)
LAYERS OF THE EARTH
Lithosphere
{
Crust and
upper mantle make up
the LITHOSPHERE
 rigid plates (OCEANIC &
CONTINENTAL plates)
Beneath the lithosphere is the
ASTHENOSPHERE
 plastic” mantle
(flows, moves the plates)
 higher temperature & pressure
 low temperature &
pressure
PLATE TECTONICS
the surface of the Earth is made of
rigid plates

Size and position of plates can change over
time

PLATE BOUNDARIES Edges of plates, where
two plates “float” side-by-side, is where
geologic activity takes place

Plates movement is from convection currents
deep in the mantle
EARTH’S MAJOR PLATES:
Pacific, N. American, S. American, African, Eurasian, Indian, Antarctic
CONVECTION CURRENTS
MOVE THE PLATES
CONVECTION CURRENTS
MOVE THE PLATES
This continual movement (called convection currents)
causes the crust to move in plate tectonics.
CONVECTION CURRENTS
MOVE THE PLATES
 Material in the
mantle is heated by
the radioactive core
 it floats to the
surface next to the
crust
 as it cools, it moves
back down towards
the core
7c Movement of matter among reservoirs is driven
by Earth’s internal and external sources of energy
PLATE BOUNDARIES

Divergent boundaries
 plates move apart

Convergent boundaries
 plates move together

Transform boundaries
 plates slide past

DIVERGENT BOUNDARIES
Make new crust
When two plates move apart and magma
surfaces forming NEW crust (usually oceanic)
• continental rift zones (landmass
splits into two or more segments)
• mid-ocean ridges
(sea-floor is elevated)
DIVERGENT BOUNDARIES
Make new crust
Rift valley
continent-continent
DIVERGENT BOUNDARIES
Make new crust: Sea Floor Spreading

Youngest rocks form at ridge

Older rocks are further from
ridge

Oldest rocks are located at
subduction zones
DIVERGENT BOUNDARIES
Make new crust: Sea Floor Spreading
Every ~20,000 years the polarity of the Earth changes.
This is change is reflected in the rocks, whose
polarity is fixed once the magma is cooled.

As magma rises and cools, iron
and magnesium minerals align
themselves to the Earth’s
magnetic field

“Magnetic Stripes” are formed

The Earth’s magnetic field
reverses polarity

Magnetic stripes are mirrored on
each side of the mid-ocean ridge
CONVERGENT BOUNDARIES
plates colliding

Destroys old crust and forms new
mountains

Three types of convergent boundaries
CONVERGENT BOUNDARIES
plates colliding
Continent-continent convergence:
Folded mountains
Ex
Himalayas
Eurasian/Indian plates
CONVERGENT BOUNDARIES
plates colliding: Subduction Zones

Subduction Zones: where ocean plates slide under another plate

Creates magma which moves upward, pushing up the land above it.

Magma/lava solidifies into intrusive/extrusive igneous rock

Heat from the magma can change the rock around it. Rock that
recrystallizes without melting becomes metamorphic rock..
Denser oceanic
plates always
subduct beneath
less dense
continental plates
CONVERGENT BOUNDARIES
plates colliding
Ocean-continent convergence:
Trench &
Coastal Volcanoes
Andes Mountains
Nazca & S.American plates
CONVERGENT BOUNDARIES
plates colliding
Ocean-ocean convergence:
Trench &
Island arc
TRANSFORM BOUNDARIES
When two plates slide past each other

no tearing or crushing - no
damage occurs to the
lithosphere

Faults –San Andreas Fault

Cause most earthquake
damage
Summary of Plate Movements
Convection currents