Earth History
GEOL 2110
Theory of Plate Tectonics
Part 2:
Elements of Plate Tectonics
Major Concepts
• Plate Tectonic theory posits that the earth outer layer
(lithosphere) is composed of rigid plates that are moving
relative to each other; Plates are composed of either thin
oceanic crust or thick continental crust overlying upper
mantle
• Plate boundaries that are diverging are where new oceanic
crust is being created as the mantle upwells, decompresses
and partially melts.
• Plate boundaries that are converging involve one oceanic
crust plate subducting beneath another or a continental
edge. This triggers earthquakes and explosive volcanism
resulting from partial melting of a hydrated mantle wedge
• Orogenesis occurs when continental crust encounters
continental crust
Plate Tectonic Theory
The Earth’s outer shell (lithosphere) is composed of rigid plates that
are moving relative to one another.
Internal Structure of the Earth
Compositional Layers
Physical
Layers
Plate Tectonics Drives Two Stages Crust-making
A. Mantle partially melts to make ocean crust
B. Ocean crust partially melts to make continental crust
What Moves the Plates?
Mantle Push
Ridge Slide
Slab
Pull
Types of Plate Boundaries
Divergent Plate Boundaries
Mid-ocean Ridges
Where Stage 1 Crust is Made
Basalt
Rock Type of the Ocean Crust
Remember:
Melting the mantle makes
mafic magma!! Always
Pillow Lavas
Hydrothermal Alteration of Ocean Crust
Preparing it for Stage 2 Melting
“Black Smokers”metal-rich hydrothermal waters
venting into the ocean floor
Continental
Rifting :
The creation
of new ocean
basins
Continental Rifting
and
The Break-up
of Pangea
Age of the Atlantic Ocean Crust
Recording the Break-up
Beginning the Break-up
225 Ma
Youthful Oceanic Crust
Convergent
Boundaries
Making 2nd Stage Crust
Ancient
Continental
Crust
Convergent Boundaries
Where the Action Is!!
Ocean - Ocean
Earthquakes
OceanContinent
Volcanoes
Continent - Continent
Consequences of Convergence
Explosive Volcanism
Mt. St. Helens
May 18, 1980
Consequences of Convergence
Mountain Building
and
Rock Deformation
Consequences of Convergence
Earthquakes
Banda Ache, Dec. 26, 2004
OROGENESIS
The Culmination
of Convergence
Ancient Orogens
Looking into the Roots of
Mountain Belts
Jay Cooke
St. Cloud
Penokean Orogen
Transform
Fault Plate
Boundaries
The San
Andreas Fault
San Francisco Earthquake
April 18, 1906 Mag 7.8
Mantle
Plumes/
Hotspots
Mantle
Hotspots in
the Oceans
Sites of overthickened crust
and the
formation of
ocean islands
and plateaus
Famous Hotspots
Yellowstone
Hawaii
Iceland
Sedimentary Basins and Plate Tectonics
Evolution of Sedimentation during
Arc-Continent Collision
The Grand Unifying Theory of the Earth
FRIDAY
Midterm Exam 1
Chapters 1 to 7