Taiwan Geographical Environment and Resources
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Transcript Taiwan Geographical Environment and Resources
Physical Geology of
Taiwan
By Adjunct Professor Hao-Tsu, Chu
Department of Geography
National Taiwan University
Unless noted, the course materials are licensed
under Creative Commons AttributionNonCommercial-ShareAlike 2.5 Taiwan (CC
BY-NC-SA 2.5)
Plate Tectonics
Definition:
How the Earth's surface is built of plates
Key Principles:
The entire outer surface of Earth is
divided into rocky plates
The plates are consistently in relative
motion to each other
Plate tectonics is responsible for most
of Earth's geologic and topographical
characteristics
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Plate Tectonics
The initiator
Continental drift theory by Alfred Lothar Wegener in 1912
Four major scientific advancement form the
plate tectonics theory
Demonstration of the ruggedness and youth of the ocean
floor around 1950
Seafloor-spreading hypothesis near 1960
Confirmation of repeated reversals of the Earth magnetic
field in the geologic in 1967
Precise documentation that the world's earthquake and
volcanic activity is concentrated along oceanic trenches and
submarine mountain ranges
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Plate Tectonics
Provide a unified mechanism to explain
Continental drift
Evolution and extinction of organisms
The frequencies and distribution of earthquakes and
volcano eruptions
The formation and location of ocean basins and
continents
Mountain building processes and mountain chain
locations
Distribution and formation of natural resources
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Lithosphere
The plate tectonics are segments of the lithosphere.
The lithosphere is the outer rigid part of the earth,
including the crusts and upper mantle
It floats on the asthenosphere, which is the outer
plastically deforming region of Earth's mantle
The lithosphere is not totally rigid, but slightly elastic
Image& text courtesy of Windows to the Universe
This image shows a cross section
through the earth’s crust and upper
mantle showing lithosphere plates
(made of the crust layer and the top
part of the mantle) moving over the
asthenosphere (upper mantle).
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Two Types of Lithosphere
Oceanic lithosphere
Continental lithosphere
About 150 km thick
50-100 km thick
It develops in the ocean It makes up about 70%
basins
of the volume of Earth's
crust
It mainly consisted of
mafic rocks rich in iron It comprised mostly of
and magnesium
granitic rock
Density: 3.3g/cm3
Density: 2.7g/cm3
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A – Oceanic Lithosphere
B – Continental Lithosphere
C – Mantle
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Plate Boundaries
Earth's crust is fractured into about 20
lithospheric plates. The place where two plates
encounter is called plate boundary
Earth is dynamic and plates are kept moving very
slowly relative to each other
All plates move at between 2cm ~ 10cm per year
Lithosphere exists as separate and
distinct tectonic plates, which float on
the fluid-like (visco-elastic solid)
asthenosphere. The relative fluidity of
the asthenosphere allows the tectonic
plates to undergo motion in different
directions. This map shows 15 of the
largest plates. Note that the IndoAustralian Plate may be breaking
apart into the Indian and Australian
plates, which are shown separately
on this map.
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Plate Boundaries
It is associated with
earthquakes and volcano
eruptions
The earthquakes of the
interior area of all plates
are much less frequent
than ones on the plate
boundaries.
East African Rift: An
active continental rift
zone marked by a series
of faults caused by
volcanic action in eastern
Africa
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3 Types of Plate Boundaries
Divergent boundaries
The plates move away from each other
(i.e.the Red Sea http://www.nature.nps.gov/geology/usgsnps/pltec/diverge.html)
Convergent boundaries
The plate move toward another
(i.e. Mariana Trench)
Transform boundaries
The plates slide horizontally past each other
(i.e. New Zealand's Alpine Fault )
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Divergent boundaries
1.
2.
Earth's surface layer is pulled apart
and separate in the opposite
directions
The cracks between the plates will
fill in the liquid rock (magma) and
then well up from the mantle to fill
the gap.
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Mid-Ocean Ridge
The molten rock will be cooled and produce a
new oceanic crust. This continuous process
builds a chain of volcanoes and rift valleys
called a mid-ocean ridge
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Mid-Ocean Ridges
The mid-ocean ridge wraps around the globe for more than 65,000 km like
the seam of a baseball, with an average depth to the ridge crest of 2500 m.
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Text courtesy of Haymon et al., NOAA-OE, WHOI.
Convergent Boundaries
When one plate is denser than the
other; the denser lithosphere does
inevitably move under the less denser.
This process is called subduction
Since the oceanic lithosphere may get
subducted, generally the age of the
ocean basins is quite young, while the
older crust locates away from a ridge.
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Subduction Features
Three key features are associated with
subduction zones:
Deep oceanic trenches
Volcanic arc parallel to the zones
Oceanic arcs (or Volcanic island arcs)
Continental arcs
Eearthquakes
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Age of Oceanic Crust
In this graph, the ocean
crustal age is shown by
different colors. Red
means the crust has been
newly created on the
geologic time scale; and
the blue represnets the
ones formed million years
ago.
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Subduction
Features
Wiki mikenorton
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Convergent Boundaries
Accretionary wedge
(Accretionary prism)
Sediments, the top layer
of material on a tectonic
plate, that accumulate
and deform where
oceanic and continental
plates collide. These
sediments are scraped
off the top of the
downgoing oceanic
crustal plate and are
added to the edge of the
continental plate.
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Image and text courtesy of USGS
Plate Collision
Collisions may happen between
Two continental plates
A continental plate and an island arc
The collision
between the Indian
and Eurasian plates
has pushed up the
Himalayas and the
Tibetan Plateau
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Plate Driving Forces
Possible driving forces for plate tectonics
(coutesy of USGS)
Bottom lithosphere tractions by convection currents.
Trench pull (covered earlier).
Ridge push (sliding off a high, crust in compression).
Trench suck (rollback).
Global expanding or contracting forces.
Membrane forces on spinning ellipsoid (e.g. variants
of polar fleeing forces).
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Unsolved Question on Driving Forces
Ridge-push and trench-pull forces may be
influenced by decreasing forces
Conceptual drawing of
assumed convection cells in
the mantle (see text). Below
a depth of about 700 km,
the descending slab begins
to soften and flow, losing its
form. Below: Sketch
showing convection cells
commonly seen in boiling
water or soup. This analogy,
however, does not take into
account the huge
differences in the size and
the flow rates of these cells.
(Courtesy USGS)
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Wiki Surachit
Hot Spot
Volcanic regions presumed to be formed by underlying
mantle that is hoteter compared with the mantle
elsewhere. They may be on, near to, or far from tectonic
plate boundaries. Those locations are called hot spots
Postulated "hot
spots" around
the world
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Plate Velocities
Plate velocities are determined by the following
hypotheses:
Hotspot reference frame
Hotspots are fixed to one location
Most hotspot chains are linear. If you know the age
of two hotspots and their in-between distance, you
will know the velocity of the plates when they are
formed.
distance
time
(Age)
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velocity
Transform Boundaries
It is a fault caused by tectonic plates sliding
by each other, usually not smoothly, and
often the reason of powerful earthquakes.
They do not have obvious topographical
feautures as divergent/convergent plates.
Examples of some
types of faults
(transform
boundaries). Part
of them are the
active producers of
earthequakes
globally.
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Aerial view of the
San Andreas fault
slicing through the
Carrizo Plain in the
Temblor Range east
of the city of San
Luis Obispo.
(Photograph by
Robert E. Wallace,
USGS.)
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Wiki Francesco Vitali
Copyrights
Work
License
Author/Source
Windows to the universe
http://www.windows2universe.org/earth/interior/earths_crust.html
2011/08/02 visited
Wiki USGS
http://en.wikipedia.org/wiki/File:Oceanicoceanic_convergence_Fig21oceanocean.gif
2011/08/02 visited
Wiki NASA
http://commons.wikimedia.org/wiki/File:Subduktion_int.JPG
2011/08/02 visited
Wiki USGS
http://commons.wikimedia.org/wiki/File:Plates_tect2_en.svg
2011/08/02 visited
Wiki USGS
http://commons.wikimedia.org/wiki/File:Rift_Valley.JPG
2011/08/02 visited
USGS
http://pubs.usgs.gov/gip/dynamic/Vigil.html
2011/08/02 visited and revised
Wiki NASA
http://commons.wikimedia.org/wiki/File:Ridge_render.jpg
2011/08/02 visited
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Wiki USGS
http://commons.wikimedia.org/wiki/File:World_Distribution_of_Mid-Oceanic_Ridges.gif
2011/08/02 visited
Wiki NOAA
http://commons.wikimedia.org/wiki/File:Earth_seafloor_crust_age_1996.gif
2011/08/02 visited
Wiki mikenorton
http://en.wikipedia.org/wiki/Accretionary_wedge
2011/08/03 visited
USGS
http://earthquake.usgs.gov/learn/glossary/?term=accretionary%20wedge
2011/08/02 visited
USGS
http://pubs.usgs.gov/gip/dynamic/understanding.html
2011/08/02 visited
Wiki Surachit
http://commons.wikimedia.org/wiki/File:Oceanic_spreading.svg
2011/08/02 visited and revised
Wiki Foulger
http://commons.wikimedia.org/wiki/File:CourtHotspots.png
2011/08/06 visited
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NASA
http://rst.gsfc.nasa.gov/Sect2/Sect2_1a.html
2011/08/06 visited
USGS
http://pubs.usgs.gov/gip/dynamic/San_Andreas.html
2011/08/06 visited
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