physical geology of taiwan by adjunct professor hao-tsu, chu department of geography national taiwan...

Physical Geology of

TaiwanBy Adjunct Professor Hao-Tsu,

ChuDepartment of Geography

National Taiwan University 　 Unless noted, the course materials are licensed under Creative Commons Attribution-NonCommercial-ShareAlike 2.5 Taiwan (CC BY-NC-SA 2.5)

http://creativecommons.org/licenses/by-nc-sa/2.5/tw/deed.en



Taiwan Geographical Environment & ResourcesTaiwan Geographical Environment & ResourcesPhysical Geology of TaiwanPhysical Geology of Taiwan

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 relati

ve motion to each other Plate tectonics is responsible for m

ost of Earth's geologic and topographical characteristics


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


Plate TectonicsProvide 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


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

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).

Image& text courtesy of Windows to the Universe


Two Types of Lithosphere

Oceanic lithosphere About 150 km thick It develops in the ocean

basins It mainly consisted of

mafic rocks rich in iron and magnesium

Density: 3.3g/cm3

Continental lithosphere 50-100 km thick It makes up about 70%

of the volume of Earth's crust

It comprised mostly of granitic rock

Density: 2.7g/cm3


A – Oceanic LithosphereB – Continental Lithosphere C – Mantle


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 Indo-Australian Plate may be

breaking apart into the Indian and Australian plates, which are shown

separately on this map.


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


3 Types of Plate Boundaries

Divergent boundariesThe 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 )

http://www.nature.nps.gov/geology/usgsnps/pltec/diverge.html


Divergent boundaries

1. Earth's surface layer is pulled apart and separate in the opposite directions

2. The cracks between the plates will fill in the liquid rock (magma) and then well up from the mantle to fill the gap.


Mid-Ocean Ridge The molten rock will be cooled and

produce anew oceanic crust. This continuous

processbuilds a chain of volcanoes and rift

valleyscalled a mid-ocean ridge


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.

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.


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


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.


Wiki mikenorton

Subduction Features


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.

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


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).


Unsolved Question on Driving Forces Ridge-push and trench-pull forces may be

influenced by decreasing forces

Wiki Surachit

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)


Hot SpotVolcanic regions presumed to be formed by underlying mantle that is hoteter compared with the mantleelsewhere. They may be on, near to, or far from tectonic plate boundaries. Those locations are called hot spots

Postulated "hot spots" around the world


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.

velocitytime

distance

(Age)


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.


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.)

Wiki Francesco Vitali


CopyrightsWork License Author/Source

Windows to the universehttp://www.windows2universe.org/earth/interior/earths_crust.html2011/08/02 visited

Wiki USGShttp://en.wikipedia.org/wiki/File:Oceanicoceanic_convergence_Fig21oceanocean.gif2011/08/02 visited

Wiki NASAhttp://commons.wikimedia.org/wiki/File:Subduktion_int.JPG2011/08/02 visited

Wiki USGShttp://commons.wikimedia.org/wiki/File:Plates_tect2_en.svg2011/08/02 visited

Wiki USGShttp://commons.wikimedia.org/wiki/File:Rift_Valley.JPG2011/08/02 visited

USGShttp://pubs.usgs.gov/gip/dynamic/Vigil.html2011/08/02 visited and revised

Wiki NASAhttp://commons.wikimedia.org/wiki/File:Ridge_render.jpg2011/08/02 visited



Wiki USGShttp://commons.wikimedia.org/wiki/File:World_Distribution_of_Mid-Oceanic_Ridges.gif2011/08/02 visited

Wiki NOAAhttp://commons.wikimedia.org/wiki/File:Earth_seafloor_crust_age_1996.gif2011/08/02 visited

Wiki mikenortonhttp://en.wikipedia.org/wiki/Accretionary_wedge2011/08/03 visited

USGShttp://earthquake.usgs.gov/learn/glossary/?term=accretionary%20wedge2011/08/02 visited

USGShttp://pubs.usgs.gov/gip/dynamic/understanding.html2011/08/02 visited

Wiki Surachithttp://commons.wikimedia.org/wiki/File:Oceanic_spreading.svg2011/08/02 visited and revised

Wiki Foulgerhttp://commons.wikimedia.org/wiki/File:CourtHotspots.png2011/08/06 visited



NASAhttp://rst.gsfc.nasa.gov/Sect2/Sect2_1a.html2011/08/06 visited

USGShttp://pubs.usgs.gov/gip/dynamic/San_Andreas.html2011/08/06 visited

physical geology of taiwan by adjunct professor hao-tsu, chu department of geography national taiwan...

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