Transcript Plate Tectonics notes

Plate Tectonics
Earth’s Interior
• A. The Composition and
Structure of the Earth
– Most information scientist
have gathered about the
interior of the Earth come
from instruments, rock
samples and earthquake
data.
– The Earth is divided into
three layers: crust, mantle
and core.
•
Earth’s Interior cont.
1. The Crust
a. The outermost layer of
the Earth./
Lithosphere [land
layer or rock sphere]
divided into tectonic
plates.
b. Ranging from 5 to
100km thick (actually
the thinnest layer of
the Earth).
c. Layer we live on.
•
Earth’s Interior cont.
d. Two types of crust
1. Continental crust
(composition similar to
granite)
*Oxygen, sodium,
Potassium,
aluminum, & silicon
*Average thickness of
30km (5 to 100km)
2. Oceanic Crust –
(composition similar to
basalt)
* iron, magnesium, and calcium
* Average thickness of between
5 to 8km
* Denser than continental crust
•
Earth’s Interior cont.
2. The Mantle
a. The layer of the Earth
between the crust and
the core.
b. Contains most of the
Earth’s mass.
c. Composition: iron &
magnesium
d. Moho is the boundary
between the crust and
the mantle.
*Plasticity – when a solid
has the ability to flow. (the
higher temperatures in the
mantle allow the solid rock
to flow and change shape.
•
Earth’s Interior cont.
3. The Core
a. Inner most layer of the
Earth.
b. Mostly made of iron,
(may explain the magnetic
field that surrounds the
Earth.) nickel and possibly
sulfur and oxygen.
c. Made of two parts
1. Inner Core – solid,
inner most layer.
*temperature reaches
5000C
•
Earth’s Interior cont.
2. Outer Core- surrounds the
inner core.
* molten/ liquid
* temperature range 2000
C to 5000 C
– The speed of seismic
waves (earthquake waves)
help to determine the
density and thickness of
the Earth’s layers.
•
The third layer of the earth is underneath the
mantle, known as the liquid outer core. At about
1,300 miles thick, it is almost entirely made of iron,
nickel, and oxygen. The heat is so intense that the
metals are molten, and the layer flows very slowly,
generating energy that produces the magnetic field
of the earth.
Earth’s Interior cont.
B. Tectonic Plates
– Tectonic Plates are
pieces of the lithosphere
that move on top of the
mantle. (Pieces of a
puzzle)
– 10 Major Tectonic Plates
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Pacific Plate
North American Plate
Cocos Plate
Nazca Plate
South American Plate
African Plate
Eurasian Plate
Indian Plate
Australian Plate
Antarctic Plate
•
Restless Continents
A. Earth’s Changing
Surface: Evidence of
Crust Movement
1. Distorted Layers
2. Sedimentary rocks in
high places.
3. Fossils
4. Thick rock layers
5. Geosynclines: shallow
basin where the Earth’s
crust sinks as sediments
build up.
Restless Continents cont.
B. Earth’s Drifting Continents
1. Pangaea – “all Earth”
the Earth believed to be
one giant land mass that
broke up into large
pieces, which have drifted
apart.
2. Theory of Continental Drift –
theory of Pangaea
* proposed by Alfred
Wegener (early 1900’s)
•
Restless Continents cont.
3. Evidence
a. Fossils – fossils of the same
plant and animal species found
on both sides of the Atlantic
Ocean
b. Rocks – glacial deposits
c. Continental Boundaries form
somewhat of a puzzle.
C. Sea- Floor Spreading
* New evidence for drift
1. Sea-floor spreading is the
process where new oceanic
lithosphere is created as older
material is pulled away.
•
Sea-Floor Spreading
Restless Continents cont.
2. As tectonic plates move
away from each other the
sea floor spreads, and
magma fills the gap.
3. Mid-ocean ridge – places
where sea-floor spreading
takes place. (underwater
mountain chains that run
through the Earth’s ocean
basins, ex. Mid-Atlantic
Ridge)
4. Older crust is farthest from
mid-ocean ridge closest to
continents.
•
A vast chain of mountains that runs along the centers of Earth's
oceans
Restless Continents cont.
5. Evidence of sea-floor
spreading is Magnetic
Reversals
a. when the Earth’s magnetic
poles change place.
b. reversals recorded in the
ocean floor – molten rock at
the mid-ocean ridged contain
tiny grains of magnetic
minerals, these minerals act
like compasses. They align
with the magnetic field of the
Earth, creating a band of
stone recording the ocean.
When the Earth’s magnetic
field reverses, a new band of
stone is started. This time the
magnetic mineral grains point
in the opposite direction.
•
Magnetic Reversals: Magnetic reversals
usually occur a few times every million
years, but when superplumes activity
occurs magnetic reversals stop
for the millions of years they are active.
Notice the below left chart: During the
Cretaceous no magnetic reversals occured.
This is some of the evidence
that superplumes are active. The image to
the right shows a scientist's view of how
magnetic reversals look when in the
process of switching.
Above: Supercomputer models of Earth's magnetic field. On the left is a
normal dipolar magnetic field, typical of the long years between polarity
reversals. On the right is the sort of complicated magnetic field Earth has
during the upheaval of a reversal
The Theory of Plate Tectonics
• The theory that the Earth’s
lithosphere is divided into tectonic
plates that move. A theory
devised to explain both
continental drift and sea-floor
spreading.
A. Tectonic Plate Boundaries –
the Earth’s plates move at
different speeds and
directions.
1. Convergent Boundarywhen two tectonic plates push
together, where they meet is
the boundary
•
A boundary where crustal
plates collide with each other
Continental-continental
The Theory of Plate Tectonics cont.
a. continental/ continental
•
b. continental/ oceanic
c. oceanic/ oceanic
Oceanic - continental
Oceanic-oceanic
The Theory of Plate Tectonics cont.
2. Divergent Boundary –
when two tectonic plates
move away from each
other
a. mid-ocean ridges
b. can occur on
continents too
c. earthquakes occur
The Theory of Plate Tectonics cont.
3. Transform Boundary – when
tectonic plates slide past each
other
example: San Andreas Fault
(Pacific plate and the North
American plate slide past each
other)
San Andreas Fault
San Andreas Fault
The Theory of Plate Tectonics cont.
B. Three Possible Causes of
Plate Motion
1. Ridge Push- an oceanic
plate slides under continental
lithosphere
2. Convection – hot material
from deep inside the Earth
rises while cooler material near
the surface sinks.
3. Slab Pull – the denser
oceanic lithosphere plate sinks
and pulls the rest of the
tectonic plate with it.
The Theory of Plate Tectonics cont.
C. Tracking Plate Motion
1. Plate move at different rates
depending on type of plate,
shape of plate, and
interactions with the plates
around it.
2. Measurement can be done
at surface level, example: San
Andreas Fault
3. The Global Positioning
System (GPS): measures the
rate of plate movements by
continuously sending radio
signals via satellites
GPS receiver
Deforming the Earth’s Crust
• Earth’s crust changes due to
stress is called deformation.
A. Three Types of Stress (or
forces) that change the Earth’s
Crust
1. Compression- force push
together, or squeeze.
* occurs at convergent
boundaries
ex. Rocky Mountains & The
Cascade Range formed this
way.
Deforming the Earth’s Crust cont.
2. Tension – push or pull away
from each other along a single
line of motion
* occurs at divergent
boundaries
* example: ground splits in an
Earthquake
3. Shear – pull in opposite
directions
Deforming the Earth’s Crust cont.
B. Folding – occurs when rock
layers for due to bends in the
Earth’s crust.
1. anticline- upward fold
2. syncline – downward fold
Syncline fold
3. monocline – both ends of
the fold are still horizontal
Anticline fold
Monocline fold
Deforming the Earth’s Crust cont.
C. Faulting- a fracture or break in
the surface
1. There are two sides to a
fault (fracture or break)
a. hanging wall – part that is
above the fault
b. footwall – part below the
fault
2. Three Types of Faults
a. Normal Fault –
*hanging wall moves
down relative to footwall
*when rocks pulled apart
due to tension
normal fault
Deforming the Earth’s Crust cont.
b. Reverse Fault –
*hanging wall move up in
relation to footwall
*when rocks are pushed
together by compression
c. Lateral Fault / Strike Slip–
* Movement horizontal to
the right or left
Deforming the Earth’s Crust cont.
D. Land forms and Mountain
Building
1. Folded Mountains – form
when rock layers squeeze
together and are pushed
upward. ex/. Appalachian
Mountains
2. Fault-block Mountains –
form when normal faults cause
large blocks of the Earth’s
crust to drop relative to other
blocks.
ex. Tetons (in Wyoming)
3. Volcanic Mountains –
formed when molten rock
erupts. Ex. Mt. Hood