Transcript Lecture3_ptectonics2

Plate tectonics
TYPES OF PLATE
BOUNDARIES
1. Convergent
2. Divergent
3. Transform
TYPES OF PLATE BOUNDARIES
1. Convergent
2. Divergent
3. Transform
PLATE BOUNDARIES
Divergent
 Plates move apart and
new crust is formed

 Heat from below rises
 Under ridges, underlying
rock melts, comes to
surface and creates new
crust
 Mid-ocean ridges are long
chains of volcanoes
 Locations of shallow
earthquakes
PLATE BOUNDARIES
Divergent
Sea-floor spreading
(i.e. Atlantic ocean) at
Mid-Ocean Ridges
PLATE BOUNDARIES
Divergent
On Continents:
Continental rifting
(i.e. African and
Arabian plates to
form Red Sea)
Animation 1.
sea floor spreading
PLATE BOUNDARIES
Divergent
On Continents:
Continental rifting
(i.e. African and
Arabian plates to
form Red Sea)
PLATE BOUNDARIES
Divergent
On Continents:
Continental rifting
(i.e. African and
Arabian plates to
form Red Sea)
PLATE BOUNDARIES
Divergent
Age of Ocean floor
increases away
from divergent
boundary
PLATE BOUNDARIES
Transform
Plates move past each
other (i.e. San Andreas
fault)
Ocean floor transform
faults
Evidence
shallow earthquakes
no volcanoes
Geodetic rates across faults
PLATE BOUNDARIES
PLATE BOUNDARIES
Transform
Plates move past each
other (i.e. San
Andreas fault)
-shallow earthquakes
-no volcanoes
PLATE BOUNDARIES
Convergent
Plates move toward
each other
-shallow,
intermediate and
deep earthquakes
For example off the coast of Washington
PLATE BOUNDARIES
Convergent
a. Ocean & Continent
(Juan de Fuca & N
America)
Ocean crust more dense
compared to continental
crust dives under
continents
Deep trenches created
where the plates dive
under continents
Large earthquakes
Volcanoes over the
subducting slab on the
overriding plate
Pacific-North America
plate boundary
1) Convergent boundary in
PNW
2) Divergent boundary
between Juan de Fuca &
Pacific plates
3) Transform boundary in
California
4) Divergent boundary
between Baja California
and mainland Mexico
PLATE BOUNDARIES
Convergent
b. Ocean & Ocean (off
the coast of the
Aleutian Islands in
Alaska)
-denser plate subducts
-deep trench
-volcanoes created on
overlying plate =
island arcs
PLATE BOUNDARIES
Convergent
b. Ocean & Ocean (off
the coast of the
Aleutian Islands in
Alaska)
-denser plate subducts
-deep trench
-volcanoes created on
overlying plate =
island arcs
PLATE BOUNDARIES
Convergent
c. Continent &
Continent—
Thick and low density so
neither subducts
Collide into each other
and create mountains
Indian Plate collides into
Eurasian Plate =
Himalayas,
PLATE BOUNDARIES
Convergent
c. Continent &
Continent—
-Both quite thick and low
density so neither
subducts
-They colide into each
other and create
mountains
TYPES OF PLATE BOUNDARIES
3 plate boundaries
Divergent
Transform
Convergent
continent-ocean
ocean-ocean
continent-continent
Need name, date and class.
Neat handwriting
Question of the week:
Name the three types of
plate boundaries.
The interior of the Earth
The Earth’s crust
The crust is relatively
light & brittle.
Most earthquakes
occur within the crust.
The interior of the Earth
Continental crust
1) Composed of mostly
granitic rocks (high Si
rocks)
2) These rocks are rich in
quartz & feldspar
3) Continental rocks are
relatively light & buoyant.
The interior of the Earth
Oceanic crust
1) Composed of mostly
basaltic rocks
2) These rocks are rich
in feldspar & pyroxene
3) Oceanic rocks are
heavier and less buoyant
than crustal rocks.
The interior of the Earth
Mantle
1) Located beneath the crust
2) Dense silicate rocks
3) More iron, magnesium, and
calcium than the crust
1) Hotter and denser because
temperature and pressure
inside the Earth increase with
depth
2) Solid on and strong on shorttime scales
3) Convecting on long timescales
The interior of the Earth
Earth’s core
The Earth's core consists of
two parts:
1) 2,200 km-thick liquid
outer core and
2) 1,250 km-thick solid inner
core.
As the Earth rotates, the
liquid outer core spins,
creating the Earth's
magnetic field.
Summary
Compositional layering
Core: high density, iron and
nickel.
Mantle: medium density (3.3
g/cm3, iron and magnesium plus
silicon and oxygen-based rocks
Crust: a) denser oceanic crust
(3.0 g/cm3
b) less dense continental
crust (2.7 g/cm3)
Contains silicon and
oxygen-based rocks
Physical layering
Defined by physical properties
or rheology.
The increase in temperature
and pressure with depth affects
the material physical properties
The mechanical behavior of
earth material may behave
like:
1) brittle solid or
2) deform like putty or
3) melt to become a liquid.
Physical layering
1. Inner Core (core)
radius 1216 km
solid
2. Outer Core (core)
2270 km
liquid
3. Lower Mantle (mantle)
2240 km
rigid layer
4. Asthenosphere (upper
mantle)
660 km
soft, weak layer (silly putty)
top is actually slightly melted,
Asthenosphere is mechanically
detached from the lithosphere
Physical layering
5. Lithosphere
Crust and uppermost mantle
~100 km thick, ranges from a
few km up to ~400 km
Thicker under continents
Thinner under oceans, very thin
at mid-ocean ridges
Rigid layer, not connected below
so can move.