Download Plate tectonics

Plate tectonics
1. Intro-important concepts
2. Kinematics-plane view & on a sphere
3. Extensional tectonics
4. Compressional tectonics
5. Transform boundaries
Today’s lecture:
1. Earth Structure
2. What is lithosphere, asthenosphere?
3. Describe the fundamental observations that led to PT
4. Continents in motion
5.The oceanic crust and lithosphere
6.Transform faults
7. Convergent margins, subduction and collision
8. Making it all work.
Chondrites- bulk Earth
Iron meteorites=core-like
Heat engine- very efficient
Earth differentiation- primarily by magmatism
Mantle convectionMostly solid state
Melting shallow by
adiabatic
decompression
Lithosphere- the
cold
lid at the top
Earth
Io
Convection hypotheses: two layers vs one layer
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Gravity highs (continents) and lows (oceans)
Earthquales and magmatism- highly localized
atcontinental margins and within oceans
Oceanic lithosphere- different from continental:
Basaltic crust, relatively thin (5-7 km), leads to
topographic lows
Mid-ocean ridges, transform faults
Young------- Old
CRUST REPLACEMENT Growth rate of 2 - 4 cm
per year and a length of 60,000 km means that new
crust is created at a rate of Crust - (2-4 cm per year) x
60,000 km = (2-3x10**[-5] km) x 60,000 km = 1.2-1.8
square kilometers per year How long does it take to
replace all of the oceanic crust? The total surface area
of the Earth is Area = 4 x pi x R**2 = 4 x pi x (6,400
km)**2 ===>
Area = 5.1x10**8 square km. The oceans cover 55 %
of the Earth's crust and so the time required to
replace all of the oceanic crust is time = 0.55 x 5.1 x
10**8 sq km / 1.2-1.8 sq km per year ===> time =
160,000,000-240,000,000 years
That is, the entire oceanic crust of the
Earth is replaced every few hundred
million years.
Is this prediction correct?
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Spreading at mid-ocean ridges must be
compensated by subduction. In addition,there are
transform faults in the oceans.
Transform faults accommodate obliqueness of
spreading-that is spreading is perpendicular to the
ridge axis and any curvature is taken up by
transforms.
Oceanic transform faults are similar to
lithospheric-scale strike-slip fault on continents,
such as the San Andreas. There is a major
difference- key to understanding plate tectonics.
Paleogeography
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Convergent margins- what happens there?
There are two types- subduction and collision
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Continents carry the record of convergent
margin events of the past
Continents also break- to form new oceans
IMPORTANT CONCEPTS:
Lithosphere-asthenosphere, mantle
convection
Oceanic lithosphere, Mid-ocean ridges
Transform faults, magnetic
anomalies,magmatism
Paleogeography,, convergent marginssubduction and collision,
How
does the
future
look
like?
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