Plate Tectonics
Earth Science
Geology 007
What phenomena result from the
peculiar structure of the Earth?
Plate Tectonics
• Movement of plates of the Earth’s
lithosphere on the underlying asthenosphere.
• Driven by heat flow in the Earth’s mantle
(pushes up) and gravity (pulls down).
• Interaction of plates at plate boundaries
responsible for most of Earth’s large-scale
geological features.
• Continents are produced by plate tectonics.
Oceanic crust ρ = 3.0 g/cc
Lithosphere
Continent
ρ
= 2.7
g/cc
Rigid mantle ρ = 3.3 g/cc ρ = 3.3
g/cc
Asthenosphere mantle
ρ = 3.25 g/cc
Continental crust is less dense and thicker than
oceanic crust.
DEM - Earth
DEM - Venus
DEM - Mars
Venus and Mars do not have continents - their entire crust is
composed of the same rock found on the Earth’s ocean basins.
Rock in the Earth’s
mantle flows via
convection, driven by
the interior heat.
Ocean floor crust is derived from magma from the
asthenosphere.
Where does continental crust come from?
The
asthenosphere
is melting above
the subducting
ocean plate due
to the release
of water from
the plate.
Origin of
Continental
Crust
Melting Melting of
of dry rock mixed
mantle with water
rock
Silica
Temperature
3.01
Seafloor
2.77
2.65
Density
Continents
Galapagos Islands
Andes Mountains
Galapagos Islands
Andes Mountains
Shield Volcano and
Aa basalt lava flow
Fernandina, Galápagos
Physical Geology - Rock Cycle and Isostasy
Pumice (silica) ashfall
Otavalo, Ecuador
Physical Geology - Rock Cycle and Isostasy
What causes
oceanic
lithosphere to
subduct?
Graph of Age vs. Depth of Ocean Floor
Mid-Ocean
Ridge
Trench
Why might the ocean floor sink as it gets older?
Oceanic crust ρ = 3.0 g/cc
Rigid mantle ρ = 3.3 g/cc
Lithosphere
Continent
ρ = 2.7 g/cc
Asthenosphere mantle
ρ = 3.25 g/cc
Mid-ocean ridge
time
Trench
Oceanic crust ρ = 3.0 g/cc
lithosphere
Rigid mantle
ρ = 3.3 g/cc
Asthenosphere mantle
ρ = 3.25 g/cc
Mid-ocean ridge
time
Trench
Oceanic crust ρ = 3.0 g/cc
Rigid mantle
ρ = 3.3 g/cc
Asthenosphere mantle
ρ = 3.25 g/cc
age = 0 my
ρlithosphere = 3.0 g/cc x 1.0 + 3.3 g/cc x 0 = 3.0
ρlithosphere < ρasthenosphere
Mid-ocean ridge
time
Trench
Oceanic crust ρ = 3.0 g/cc
Rigid mantle
ρ = 3.3 g/cc
Asthenosphere mantle
ρ = 3.25 g/cc
age = 10 my
ρlithosphere = 3.0 g/cc x .4 + 3.3 g/cc x .6 = 3.18
ρlithosphere = ρasthenosphere
Mid-ocean ridge
time
Trench
Oceanic crust ρ = 3.0 g/cc
Rigid mantle ρ = 3.3 g/cc
Asthenosphere mantle
ρ = 3.25 g/cc
subduction
age = 100 my
ρlithosphere = 3.0 g/cc x .06 + 3.3 g/cc x .94 = 3.28
ρlithosphere > ρasthenosphere