Download Note on Plate tectonics

Plate Tectonics Ch 8
I. Plate Tectonics - study of the movement of
the plates of the Earth’s surface
A. Lithosphere - crust & upper mantle
broken into plates that can move

ocean plates are made of Basalt

continent plates are made of Granite
http://www.brainpop.com/science/earth/platetectonics/index.asp
B. Asthenosphere
-layer below the lithosphere;
-part of the mantle that has partially
melted rock enabling plates to slide
over each other
II. Evidence for Plate Tectonics
1.
Similarities in the shapes of the continents,
they look like puzzle pieces
2.
Fossil remains of Mesosaurus are only
found in Brazil, South America & in South
Africa
3.
Specific rocks coincide on Africa & South
America where they seem to fit
Fossils of Pangaea
A. Alfred Wegener

Proposed theory of continental drift

Noted the evidence for continental drift
which eventually developed into the
theory of plate tectonics
III. Plate boundaries
•Areas where plates come together or
move apart
• Belts where earthquakes& volcanoes
occur
•Largest belt is called the Pacific Ring
of Fire
Ring of Fire
3 Types of Plate Boundaries
1.
Converging Plate Boundaries – come
together
2.
Diverging Plate Boundaries – move apart
3.
Transform Plate Boundaries - sliding
http://www.pbs.org/wnet/savageearth/animations/hellscrust/index.html
A. Converging Boundaries
(coming together)


a. Collision
b. Subduction
1. Collision - two continental plates
coming together forming a mountain chain
(C-C)
a.
Himalayas - formed
from India & Eurasia
crashing together
b. Ural Mountains - formed 300 million yrs.
ago by a collision between Europe & Asia
c. Southern Appalachians -formed by a
collision between North America & Africa
2. Subduction


Oceanic plate being pushed beneath another
oceanic plate or a continental plate; (O-O or OC)
a. O-O subduction results in a trench & island
arc
Subduction Ex.
Ex. #1. Pacific Plate under the Philippine
Plate: forms the Mariana Trench &
Mariana Islands
 #2 Pacific Plate under the Eurasian
Plate: forms the Aleutian Trench &
Aleutian Islands

b. O-C subduction
Results in trench & coastal, continental
mountains
 Ex. #1Nazca Plate under the South
American Plate: forms Peru-Chile Trench
& the Andes Mountains

O-C Subduction



#2 Juan de Fuca Plate under the North
American Plate
Forms Cascadian Trench, Mt. St. Helens & the
Cascade Mountain Range
http://bcove.me/s3bmueq3
Mt. St. Helens
Land Sat Photos Before & After
What is left of the trees
@ Mt. St. Helens
Remains of tress floating on Spirit
Lake on the slopes of Mt. St. Helens
B. Diverging Boundaries (moving apart)


youngest rock is on the rift zone
Rock is older the further away it is from the
rift in the plates
Examples of Divergent Plate Boundaries
http://geology.wr.usgs.gov/docs/parks/animate/A49.gif
1. Mid Atlantic
Ridge - N.
American
& Eurasian
Plates are
parting; Iceland
2. East Pacific Rise
- Pacific & Nazca
Plates are parting
C. Sliding Boundaries (transform)
1.
N. American & Pacific Plates: forming the San
Andreas Fault in CA
IV. Craton - continent core; oldest & most
altered rock of continent
3 Sources of Material Added to the Continents
-
Sediments deposited by rivers
Volcanic Rock added during eruptions
Terrane- Deep sea sediments at O-C plate
boundaries ocean sediments scraped off &
left behind to become part of the continent
at subduction zones
V. Harry Hess Princeton University
Theory of Sea Floor Spreading
 Hot, less-dense material in the mantle is forced
upward to the surface at a mid-ocean ridge
 The sea floor is carried away from the ridge as
the new material flows sideways out of the rift
 The new sea floor cools, becomes more
dense than the layer below it & sinks a bit to
form a trench
Evidence for Sea Floor Spreading
1.
Age Evidence - rocks at the mid-ocean
ridges are younger than the rocks further
from the rift
2.
Magnetic Clues - in iron bearing basalt rock
of ocean floors; sea floor rocks show many
magnetic reversals; magnetic alignment of
rocks flip flops back & forth parallel to the
mid-ocean ridges
http://geology.wr.usgs.gov/docs/parks/animate/A47.gif
Sea Floor Spreading
VI Causes of Plate Tectonics
A.
Convection Currents - the cycle of heat
rising, cooling & sinking
B.
Differences in rock density; more dense
rock sinks (ocean floor)