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This is Planet Earth /
Earth Story
Lecture 5
PLATE TECTONICS II
Drifting Continents, Oceans That
Open And Close, Mountains
and Basins
Alfred Wegener’s evidence for
Continental Drift
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Continental fit
Correlation of rocks
and climate
Crustal structure
Distribution of fossil
plants and animals
Direct measurements
of changing distance
between the
continents
Best to use continental margins rather
than coastlines
Arthur Holmes (1931) – Sub-crustal convection causes continental and
oceanic crust to move together
Exploration of the Ocean Floor –
Oceanic Ridges
Oceanic ridges (shown in red) wind their way between the continents
Sea Floor Spreading
Trench
Oceanic ridge
Magnetic stripes on the sea
floor
Continental Drift + Sea Floor Spreading
= PLATE TECTONICS
(Tuzo Wilson, 1965)
Oceanic Ridge
(Constructive Boundary)
The Mid-Atlantic Ridge
The ridge was central
in the breakup of
Pangaea that began
some 180 million
years ago.
Subduction Zones
(Destructive Boundary)
Ocean-Continent
Destructive/ Convergent
Boundary (e.g. West coast
of South America –
subduction of Nazca Plate )
Ocean-Ocean Destructive/
Convergent Boundary
(e.g. Japan)
The Pacific ‘Ring of Fire’
The Island arcs
and oceanic
trenches the
encircle the
whole of the
Pacific plate are
referred to as
the ‘Ring of
Fire’
Collisional Boundary
Leads to formation of a mountain / orogenic belt
The Himalayas - example of a collisional boundary
The Himalayas and the Tibetan
Plateau
The collision between
the Indian and Eurasian
plates has pushed up
the Himalayas and the
Tibetan Plateau. The
cross-sections show the
meeting of these two
plates before and after
their collision. The
reference points (small
squares) show the
amount of uplift of an
imaginary point in the
Earth's crust during this
mountain-building
process.
Conservative Boundary
Transform faults are also referred to as STRIKE-SLIP or WRENCH faults
Conservative / Transform Boundary Examples
San Andreas fault
J. Tuzo Wilson is credited with the concept of
transform faults. He proposed that these large
faults or fracture zones connect two spreading
centres or occur on land
Summary of Plate Boundaries
Hawaiian Islands
Hots Spots
Convection in the Asthenosphere
Thermal convection in fluids was first described by Lord Rayleigh
Plate Tectonic Driving Mechanisms
Ridge Push
Slab Pull
Convection
Currents  Mantle Drag
Present day relative movements
of plates
Recommended Reading
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Press, F. and Siever, R. 2000.
Understanding Earth (3rd Edition).
Freeman (ISBN 0-71674-117-2).
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Chapter 20
Skinner, B.J., Porter, S.C. and Park, J.
2004. Dynamic Earth: An Introduction
to Physical Geology (5 th Edition). Wiley
(ISBN 0-471-45157-6).
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Chapter 2