环境地质学
Environmental Geology
主讲人,万新南 教授
Prof,Wan xinnan
地球内部过程
? Plate Tectonics
? Geologic Tectonics
? Earthquake
? Tsunamis海啸 and Coastal Flooding
地球内部过程
? Plate Tectonics
Several centuries ago,observers
looking at global maps noticed
the similarity in outline of the
eastern coast of South
America and the western coast
of Africa,In 1855,Antonio
Snider went so far as to
publish a sketch showing how
the two continents could fit
together,jigsaw-puzzle fashion
①, Such reconstruction gave
rise to the bold suggestion that
perhaps these continents had
once been part of the same
landmass,which had later
broken up.
地球内部过程
? Plate Tectonics
This concept of continental drift
had an especially vocal champion
in Alfred Wegener①,who began
to publish his ideas in 1912 and
continued to do so for more than
two decades,Several other
prominent scientists found the
idea plausible合理的, However,
most people scientists and
nonscientists alike,had difficulty
visualizing how something as
massive as a continent could
possible "drift” around on a solid
earth,or why it should do so②,
There were obvious physical
objections异议 to solid continents
plowing耕作 through solid ocean
basins,and no evidence of the
expected resultant damage in
crushed and shattered rock on
continents or sea floor③, The
majority of reputable scientists
either scoffed嘲笑 at the idea,or,
at best,politely ignored it.
地球内部过程
? Plate Tectonics
As it turns out其原因是,the
supporting evidence was simply
undiscovered or unrecognized at the
time,Beginning in the 1960s,data of
many different kinds began to
accumulate that indicated that the
continents have indeed moved,
Continental drift turned out产生 to be
just one aspect of a broader theory
known as plate tectonics,which has
evolved over the last two decades,
Tectonics is the study of large scale
movement and deformation of the
earth’s outer layers,Plate tectonics
relates such deformation to the
existence and movement of rigid刚性
,plates”over a weak or partly molten
layer in the earth’s upper mantle.
地球内部过程
? Plate Movements-Accumulating Evidence
The Topography of the Sea Floor,If South America and
Africa really have moved apart,one might expect to see some
evidence of this between them,some feature or features on the
sea floor to indicate the continents’ passage,A topographic map
of the floor of the Atlantic Ocean shows an obvious ridge running
north-south about halfway不彻底、中途 between those continents
大陆间近南北向的明显洋脊, This mid-ocean ridge might be the
seam缝 from which the two continents moved apart,Similar
ridges are found on the floors of other oceans,as seen in the
same figure,In other places,frequently along the margins of
continents,there are trenches沟堑 several kilometers deep, It
remained for scientists studying the ages and magnetic properties
of seafloor rocks,as described below,to demonstrate the
significance of the ocean ridges to plate tectonics,The trenches,
too,can be explained by plate tectonics.
地球内部过程
? Plate Movements-Accumulating Evidence
The Topography of the Sea Floor：
地球内部过程
? Plate Tectonics
Magnetism磁 in Rocks—General：
Most iron-bearing minerals are at least
weakly magnetic at surface temperatures,
Each magnetic mineral has a Curie居里
temperature,below which it remains
magnetic,but above which it loses its
magnetic properties,The Curie
temperature varies from mineral to
mineral,but it is always below the
mineral’s melting temperature,A hot
magma is therefore not magnetic,but as
it cools and solidifies,and ferromagnesian
铁镁矿物 silicates and other iron-bearing
minerals crystallize from it,those
magnetic minerals tend to line up in the
same direction,Like tiny compass
needles,they align themselves parallel to
the lines of force of the earth’s magnetic
field,which run north-south,and they
point to the magnetic north pole,They
retain their internal magnetic orientation
unless they are heated again,This is the
basis for the study of paleomagnetism,
“fossil magnetism” in rocks.
地球内部过程
? Plate Tectonics
Magnetic north,however,has not
always coincided with its present
position,In the early 1900s,
scientists investigating the direction
of magnetization of a sequence of
volcanic rocks in France discovered
some flows that appeared to be
magnetized in the opposite direction
from the rest,their magnetic minerals
pointed south instead of north,
Confirmation of this discovery in
many places around the world led to
the suggestion in the late 1920s that
the earth’s magnetic field had
“flipped翻动,” or reversed polarity;
that is,that the north and south poles
had switched转换 places,During the
time those surprising rocks had
crystallized,a compass needle would
have pointed to the magnetic south
pole,not north.
地球内部过程
? Plate Tectonics
The Topography of the Sea Floor,If
South America and Africa really have
moved apart,one might expect to see
some evidence of this between them,
some feature or features on the sea floor
to indicate the continents’ passage,A
topographic map of the floor of the
Atlantic Ocean shows an obvious ridge
running north-south about halfway不彻底、
中途 between those continents大陆间近南
北向的明显洋脊, This mid-ocean ridge
might be the seam缝 from which the two
continents moved apart,Similar ridges
are found on the floors of other oceans,
as seen in the same figure,In other
places,frequently along the margins of
continents,there are trenches沟堑
several kilometers deep, It remained for
scientists studying the ages and magnetic
properties of seafloor rocks,as described
below,to demonstrate the significance of
the ocean ridges to plate tectonics,The
trenches,too,can be explained by plate
tectonics.
地球内部过程
? Plate Tectonics
The Topography of the Sea Floor：
If South America and Africa really
have moved apart,one might expect
to see some evidence of this between
them,some feature or features on the
sea floor to indicate the continents’
passage,A topographic map of the
floor of the Atlantic Ocean shows an
obvious ridge running north-south
about halfway不彻底、中途 between
those continents大陆间近南北向的明显
洋脊, This mid-ocean ridge might be
the seam缝 from which the two
continents moved apart,Similar ridges
are found on the floors of other oceans,
as seen in the same figure,In other
places,frequently along the margins of
continents,there are trenches沟堑
several kilometers deep, It remained
for scientists studying the ages and
magnetic properties of seafloor rocks,
as described below,to demonstrate
the significance of the ocean ridges to
plate tectonics,The trenches,too,can
be explained by plate tectonics.
地球内部过程
? Plate Tectonics
The Topography of the Sea Floor：
地球内部过程
? Plate Tectonics
Magnetic north,however,has not
always coincided with its present
position,In the early 1900s,
scientists investigating the
direction of magnetization of a
sequence of volcanic rocks in
France discovered some flows
that appeared to be magnetized in
the opposite direction from the
rest,their magnetic minerals
pointed south instead of north,
Confirmation of this discovery in
many places around the world led
to the suggestion in the late 1920s
that the earth’s magnetic field had
“flipped翻动,” or reversed polarity;
that is,that the north and south
poles had switched转换 places,
During the time those surprising
rocks had crystallized,a compass
needle would have pointed to the
magnetic south pole,not north..
地球内部过程
Plate Tectonics
Paleomagnetism and Seafloor
Spreading,The ocean floor is made up
largely of basalt,a volcanic rock rich in
ferromagnesian minerals,During the 1950s,
the first large-scale surveys of the magnetic
properties of the sea floor produced an
entirely unexpected result,The floor of the
ocean was found to consist of alternating
“stripes” or bands of normally and reversely
magnetized rocks,symmetrically对称
arranged around the ocean ridges,At first,
this seemed so incredible that it was
assumed that the instruments or
measurements were faulty,However,other
studies consistently obtained the same
results,For several years,geoscientists
strove努力 to find a convincing explanation
for these startling observations.
地球内部过程
? Plate Tectonics
Then,in 1963,an elegant文雅的、上
流的 explanation was proposed by the
team of F.J,Vine and D.H,Matthews,
and independently by L,W,Morley,
The magnetic stripes could be
explained as a result of seafloor
spreading,the moving apart of
lithospheric岩石圈 plates at the ocean
ridges,If the oceanic lithosphere splits
and plates move apart,a rift裂缝 in the
lithosphere begins to open,But the
result is not a 50-kilometer-deep crack,
As rifting begins,the release of
pressure from above allows extensive
melting to occur,producing magma
that escapes from the asthenosphere
重软流圈, The magma rises,cools,
and solidifies to form new basaltic玄武
岩 rock,which becomes magnetized in
the prevailing direction of the earth’s
magnetic field,If the plates continue to
move apart,the new rock will also split
and part,making way for more magma
to form still younger rock,and so on.
地球内部过程
? Plate Tectonics
地球内部过程
? Plate Tectonics
地球内部过程
? Plate Tectonics
? If,during the course of seafloor
spreading,the polarity of the earth’s
magnetic field reverses,the rocks
formed after the reversal are polarized
oppositely from those formed before it
①, The ocean floor is a continuous
sequence of basalts formed over tens
or hundreds of millions of years,during
which time there have been dozens of
polarity reversals,The basalts of the
sea floor have acted as a sort of
magnetic tape recorder throughout
that time,preserving a record of
polarity reversals in the alternating
bands of normally and reversely
magnetized rocks,The process is
illustrated schematically in fig.3.8,
? 9-① 在海底扩张的过程中，如果地球磁
场极反转了，则反转后形成的岩石磁场
极再次反转。
地球内部过程
?Plate
Tectonics
? Types of Plate
Boundaries
地球内部过程
?Plate Tectonics
? Types of Plate Boundaries
? Divergent Plate Boundaries, At a divergent plate
boundary,such as a mid-ocean spreading ridge,
lithospheric plates move apart,the release of
pressure facilitates使容易 some melting in the
asthenosphere,magma wells up from the
asthenosphere,and new lithosphere is created (figure
3.15A),A great deal of volcanic activity thus occurs at
spreading ridges,In addition,the pulling-apart of the
plates of lithosphere results in earthquakes along
these ridge plate boundaries,
地球内部过程
? Plate Tectonics
? Types of Plate Boundaries
? ere,In the early stages of continental rifting volcanoes may erupt along the rift,or great flows of
basaltic lava may pour out through the fissures in the continent,If the rifting continues,a new
ocean basin will eventually form between the pieces of the continent,Geologists believe that this
is what is happening now in east Africa,The easternmost最东面 part of the continent is being rifted
apart from the rest and an ocean will one day separate the pieces,Lake Tanganyika,formed by this
rifting,shows its origins in the complementary补充 shapes of its east and west shores.
地球内部过程
? Plate Tectonics
? Types of Plate Boundaries
? As seawater circulates through the fresh,hot lithosphere at a spreading ridge,it is heated and reacts with
the rock,becoming metal-rich,As it gushes back out of the sea floor,cooling and reacting with cold
seawater,it may precipitate potentially valuable mineral deposits,Economically unprofitable不利 to mine
now,they may nevertheless prove useful resources for the future.
地球内部过程
?Plate Tectonics
Transform Boundaries,The actual structure of a spreading ridge
is more complex than a single,straight crack裂缝, A close look
at a mid-ocean spreading ridge reveals that it is not a
continuous rift thousands of kilometers long,Rather,ridge
consist of many short segments slightly offset from one another,
The offset area is a special kind of fault,or break in the
lithosphere,known as a transform fault (see figure 3.15A),The
opposite sides of a transform fault belong to two different plates,
and these are moving in opposite directions,As the plates
scrape擦刮 past each other,earthquakes occur along the
transform fault.
地球内部过程
?Plate Tectonics
The famous San Andreas Fault in California is an example of a
transform fault that slices a continent sitting along a spreading
ridge,The East Pacific Rise隆起,a seafloor spreading ridge off
the northwestern coast of North America,disappears under the
edge of the continent,to reappear farther south in the Gulf of
California,The San Andreas is the transform fault between
these segments of spreading ridge,Most of North America is
part of the North American Plate,The thin strip of California on
the west side of the San Andreas Fault,however,is moving
northwest with the Pacific plate,The stress resulting from the
shearing displacement across the fault leads to ongoing不间断的
earthquake activity.
地球内部过程
?Plate
Tectonics
Convergent Plate Boundaries,At a
convergent聚集、俯冲 plate
boundary,as the name indicates,
plates are moving toward each
other,Just what happens depends
on what sort of lithosphere is at the
leading edge of each plate (fig3.17),
continental lithosphere is relatively
low in density and is therefore
buoyant浮的 with respect to the
dense,iron-rich mantle,so it tends
to,float” on the asthenosphere岩流
圈, Oceanic lithosphere is more
similar in density to the underlying
asthenosphere,so it is more easily
forced down into the
asthenosphere as plates move
together.
地球内部过程
? Plate Tectonics
In a continent-continent collision,the two
landmasses come together,crumple,and
deform,One may partially override the other,
but the buoyancy 浮力 of continental
lithosphere ensures that neither sinks deep
into the mantle,and a very large thickness of
continent may result.大陆岩石圈的浮力保证了
两者都不会沉入地墁深处，只能导致大陆变厚
Earthquakes are frequent during active
collision as a consequence of the large
stresses involved in the process,The
extreme height of the Himalaya Mountains is
attributed to just this sort of continent－
continent collision,India was not always a
part of the Asian continent,Paleomagnetic
evidence indicates that it drifted northward
over tens of millions of years until it,ran
into” Asia,and the Himalayas were built up
in this collision,Earlier,the ancestral祖先的
Appalachian Mountains were built in the
same way,as Africa and North America
converged prior to the breakup of Pangaea泛
大陆、古陆, In fact,many major mountain
ranges worldwide represent sites of
sustained持续不变的 plate convergence in
the past.
地球内部过程
? Plate Tectonics
The subduction zones of the world balance the
seafloor equation,If new oceanic lithosphere is
constantly being created at spreading ridges,an
equal amount must be destroyed somewhere,or
the earth would simply keep getting bigger,This
excess额外 sea floor is consumed 消亡 in
subduction zones,The subducted plate is
heated by the hot asthenosphere,and,in time,
becomes hot enough to melt,Meanwhile,at the
spreading ridges,other melts rise,cool,and
crystallize to make new sea floor,So,in a sense,
the oceanic lithosphere is constantly being
recycled,which explains why few very ancient
seafloor rocks are known,Only rarely is a bit of
sea floor caught up in a continent during
convergence and preserved.在俯冲阶段大陆中
的洋底很难抓住老岩层并保存之 Most often,the
sea floor in a zone of convergence is subducted
and destroyed,The buoyant continents are not
so easily reworked更新 in this way; hence,very
old rocks may be preserved on them,Because
all continents are part of moving plates,sooner
or later they all are inevitably不可避免
transported传输 to a convergent boundary,as
leading oceanic lithosphere is consumed.
地球内部过程
? Plate Tectonics
Subduction zones are,geologically,very active
places,Sediments eroded from the continents
may accumulate in the trench沟壕 formed by the
down-going plate,and some of these sediments
may be carried down into the asthenosphere to
be melted along with the sinking lithosphere,
Volcanoes form where the melted material rises
up through the overlying plate to the surface,At
an ocean－ ocean convergence,the result is
commonly a line of volcanic islands,an island
arc (fig.3.17B),The great stresses involved in
convergence and subduction give rise to
numerous earthquakes,The bulk of mountain
building,and its associated volcanic and
earthquake activity,is related to subduction
zones,Parts of the world near or above modern
subduction zones,and therefore prone to both
volcanic and earthquake activity,include the
Andes region of South America,western Central
America,parts of the northwest United States
and Canada,the Aleutian Islands,China,Japan,
and much of the rim of the Pacific Ocean basin.
地球内部过程
? Plate Tectonics
? Stress and Strain in Geological Materials
? Lithosphere and Asthenosphere
? Locating Plate BounDarics
?
地球内部过程
? Plate Tectonics
? Plate Movements--Accumulating Evidence
? The Topography of the Sea Floor
? Magnetism in Rocks-- General
?
地球内部过程
? Plate Tectonics
? Types of Plate Boundaries
?
地球内部过程
? Plate Tectonics
? Paleomagnetism and Seafloor Spreading
? Age of the Ocean Floor
? Polar-Wander Curves
? Other Evidence
?
地球内部过程
? Part two3、板块漂移说
? 主要介绍地球表层的板块运动的发现、证
据；板块运动特征；板块运动的产物与影
响
? 4、地震
? 5、火山爆发
Environmental Geology
主讲人,万新南 教授
Prof,Wan xinnan
地球内部过程
? Plate Tectonics
? Geologic Tectonics
? Earthquake
? Tsunamis海啸 and Coastal Flooding
地球内部过程
? Plate Tectonics
Several centuries ago,observers
looking at global maps noticed
the similarity in outline of the
eastern coast of South
America and the western coast
of Africa,In 1855,Antonio
Snider went so far as to
publish a sketch showing how
the two continents could fit
together,jigsaw-puzzle fashion
①, Such reconstruction gave
rise to the bold suggestion that
perhaps these continents had
once been part of the same
landmass,which had later
broken up.
地球内部过程
? Plate Tectonics
This concept of continental drift
had an especially vocal champion
in Alfred Wegener①,who began
to publish his ideas in 1912 and
continued to do so for more than
two decades,Several other
prominent scientists found the
idea plausible合理的, However,
most people scientists and
nonscientists alike,had difficulty
visualizing how something as
massive as a continent could
possible "drift” around on a solid
earth,or why it should do so②,
There were obvious physical
objections异议 to solid continents
plowing耕作 through solid ocean
basins,and no evidence of the
expected resultant damage in
crushed and shattered rock on
continents or sea floor③, The
majority of reputable scientists
either scoffed嘲笑 at the idea,or,
at best,politely ignored it.
地球内部过程
? Plate Tectonics
As it turns out其原因是,the
supporting evidence was simply
undiscovered or unrecognized at the
time,Beginning in the 1960s,data of
many different kinds began to
accumulate that indicated that the
continents have indeed moved,
Continental drift turned out产生 to be
just one aspect of a broader theory
known as plate tectonics,which has
evolved over the last two decades,
Tectonics is the study of large scale
movement and deformation of the
earth’s outer layers,Plate tectonics
relates such deformation to the
existence and movement of rigid刚性
,plates”over a weak or partly molten
layer in the earth’s upper mantle.
地球内部过程
? Plate Movements-Accumulating Evidence
The Topography of the Sea Floor,If South America and
Africa really have moved apart,one might expect to see some
evidence of this between them,some feature or features on the
sea floor to indicate the continents’ passage,A topographic map
of the floor of the Atlantic Ocean shows an obvious ridge running
north-south about halfway不彻底、中途 between those continents
大陆间近南北向的明显洋脊, This mid-ocean ridge might be the
seam缝 from which the two continents moved apart,Similar
ridges are found on the floors of other oceans,as seen in the
same figure,In other places,frequently along the margins of
continents,there are trenches沟堑 several kilometers deep, It
remained for scientists studying the ages and magnetic properties
of seafloor rocks,as described below,to demonstrate the
significance of the ocean ridges to plate tectonics,The trenches,
too,can be explained by plate tectonics.
地球内部过程
? Plate Movements-Accumulating Evidence
The Topography of the Sea Floor：
地球内部过程
? Plate Tectonics
Magnetism磁 in Rocks—General：
Most iron-bearing minerals are at least
weakly magnetic at surface temperatures,
Each magnetic mineral has a Curie居里
temperature,below which it remains
magnetic,but above which it loses its
magnetic properties,The Curie
temperature varies from mineral to
mineral,but it is always below the
mineral’s melting temperature,A hot
magma is therefore not magnetic,but as
it cools and solidifies,and ferromagnesian
铁镁矿物 silicates and other iron-bearing
minerals crystallize from it,those
magnetic minerals tend to line up in the
same direction,Like tiny compass
needles,they align themselves parallel to
the lines of force of the earth’s magnetic
field,which run north-south,and they
point to the magnetic north pole,They
retain their internal magnetic orientation
unless they are heated again,This is the
basis for the study of paleomagnetism,
“fossil magnetism” in rocks.
地球内部过程
? Plate Tectonics
Magnetic north,however,has not
always coincided with its present
position,In the early 1900s,
scientists investigating the direction
of magnetization of a sequence of
volcanic rocks in France discovered
some flows that appeared to be
magnetized in the opposite direction
from the rest,their magnetic minerals
pointed south instead of north,
Confirmation of this discovery in
many places around the world led to
the suggestion in the late 1920s that
the earth’s magnetic field had
“flipped翻动,” or reversed polarity;
that is,that the north and south poles
had switched转换 places,During the
time those surprising rocks had
crystallized,a compass needle would
have pointed to the magnetic south
pole,not north.
地球内部过程
? Plate Tectonics
The Topography of the Sea Floor,If
South America and Africa really have
moved apart,one might expect to see
some evidence of this between them,
some feature or features on the sea floor
to indicate the continents’ passage,A
topographic map of the floor of the
Atlantic Ocean shows an obvious ridge
running north-south about halfway不彻底、
中途 between those continents大陆间近南
北向的明显洋脊, This mid-ocean ridge
might be the seam缝 from which the two
continents moved apart,Similar ridges
are found on the floors of other oceans,
as seen in the same figure,In other
places,frequently along the margins of
continents,there are trenches沟堑
several kilometers deep, It remained for
scientists studying the ages and magnetic
properties of seafloor rocks,as described
below,to demonstrate the significance of
the ocean ridges to plate tectonics,The
trenches,too,can be explained by plate
tectonics.
地球内部过程
? Plate Tectonics
The Topography of the Sea Floor：
If South America and Africa really
have moved apart,one might expect
to see some evidence of this between
them,some feature or features on the
sea floor to indicate the continents’
passage,A topographic map of the
floor of the Atlantic Ocean shows an
obvious ridge running north-south
about halfway不彻底、中途 between
those continents大陆间近南北向的明显
洋脊, This mid-ocean ridge might be
the seam缝 from which the two
continents moved apart,Similar ridges
are found on the floors of other oceans,
as seen in the same figure,In other
places,frequently along the margins of
continents,there are trenches沟堑
several kilometers deep, It remained
for scientists studying the ages and
magnetic properties of seafloor rocks,
as described below,to demonstrate
the significance of the ocean ridges to
plate tectonics,The trenches,too,can
be explained by plate tectonics.
地球内部过程
? Plate Tectonics
The Topography of the Sea Floor：
地球内部过程
? Plate Tectonics
Magnetic north,however,has not
always coincided with its present
position,In the early 1900s,
scientists investigating the
direction of magnetization of a
sequence of volcanic rocks in
France discovered some flows
that appeared to be magnetized in
the opposite direction from the
rest,their magnetic minerals
pointed south instead of north,
Confirmation of this discovery in
many places around the world led
to the suggestion in the late 1920s
that the earth’s magnetic field had
“flipped翻动,” or reversed polarity;
that is,that the north and south
poles had switched转换 places,
During the time those surprising
rocks had crystallized,a compass
needle would have pointed to the
magnetic south pole,not north..
地球内部过程
Plate Tectonics
Paleomagnetism and Seafloor
Spreading,The ocean floor is made up
largely of basalt,a volcanic rock rich in
ferromagnesian minerals,During the 1950s,
the first large-scale surveys of the magnetic
properties of the sea floor produced an
entirely unexpected result,The floor of the
ocean was found to consist of alternating
“stripes” or bands of normally and reversely
magnetized rocks,symmetrically对称
arranged around the ocean ridges,At first,
this seemed so incredible that it was
assumed that the instruments or
measurements were faulty,However,other
studies consistently obtained the same
results,For several years,geoscientists
strove努力 to find a convincing explanation
for these startling observations.
地球内部过程
? Plate Tectonics
Then,in 1963,an elegant文雅的、上
流的 explanation was proposed by the
team of F.J,Vine and D.H,Matthews,
and independently by L,W,Morley,
The magnetic stripes could be
explained as a result of seafloor
spreading,the moving apart of
lithospheric岩石圈 plates at the ocean
ridges,If the oceanic lithosphere splits
and plates move apart,a rift裂缝 in the
lithosphere begins to open,But the
result is not a 50-kilometer-deep crack,
As rifting begins,the release of
pressure from above allows extensive
melting to occur,producing magma
that escapes from the asthenosphere
重软流圈, The magma rises,cools,
and solidifies to form new basaltic玄武
岩 rock,which becomes magnetized in
the prevailing direction of the earth’s
magnetic field,If the plates continue to
move apart,the new rock will also split
and part,making way for more magma
to form still younger rock,and so on.
地球内部过程
? Plate Tectonics
地球内部过程
? Plate Tectonics
地球内部过程
? Plate Tectonics
? If,during the course of seafloor
spreading,the polarity of the earth’s
magnetic field reverses,the rocks
formed after the reversal are polarized
oppositely from those formed before it
①, The ocean floor is a continuous
sequence of basalts formed over tens
or hundreds of millions of years,during
which time there have been dozens of
polarity reversals,The basalts of the
sea floor have acted as a sort of
magnetic tape recorder throughout
that time,preserving a record of
polarity reversals in the alternating
bands of normally and reversely
magnetized rocks,The process is
illustrated schematically in fig.3.8,
? 9-① 在海底扩张的过程中，如果地球磁
场极反转了，则反转后形成的岩石磁场
极再次反转。
地球内部过程
?Plate
Tectonics
? Types of Plate
Boundaries
地球内部过程
?Plate Tectonics
? Types of Plate Boundaries
? Divergent Plate Boundaries, At a divergent plate
boundary,such as a mid-ocean spreading ridge,
lithospheric plates move apart,the release of
pressure facilitates使容易 some melting in the
asthenosphere,magma wells up from the
asthenosphere,and new lithosphere is created (figure
3.15A),A great deal of volcanic activity thus occurs at
spreading ridges,In addition,the pulling-apart of the
plates of lithosphere results in earthquakes along
these ridge plate boundaries,
地球内部过程
? Plate Tectonics
? Types of Plate Boundaries
? ere,In the early stages of continental rifting volcanoes may erupt along the rift,or great flows of
basaltic lava may pour out through the fissures in the continent,If the rifting continues,a new
ocean basin will eventually form between the pieces of the continent,Geologists believe that this
is what is happening now in east Africa,The easternmost最东面 part of the continent is being rifted
apart from the rest and an ocean will one day separate the pieces,Lake Tanganyika,formed by this
rifting,shows its origins in the complementary补充 shapes of its east and west shores.
地球内部过程
? Plate Tectonics
? Types of Plate Boundaries
? As seawater circulates through the fresh,hot lithosphere at a spreading ridge,it is heated and reacts with
the rock,becoming metal-rich,As it gushes back out of the sea floor,cooling and reacting with cold
seawater,it may precipitate potentially valuable mineral deposits,Economically unprofitable不利 to mine
now,they may nevertheless prove useful resources for the future.
地球内部过程
?Plate Tectonics
Transform Boundaries,The actual structure of a spreading ridge
is more complex than a single,straight crack裂缝, A close look
at a mid-ocean spreading ridge reveals that it is not a
continuous rift thousands of kilometers long,Rather,ridge
consist of many short segments slightly offset from one another,
The offset area is a special kind of fault,or break in the
lithosphere,known as a transform fault (see figure 3.15A),The
opposite sides of a transform fault belong to two different plates,
and these are moving in opposite directions,As the plates
scrape擦刮 past each other,earthquakes occur along the
transform fault.
地球内部过程
?Plate Tectonics
The famous San Andreas Fault in California is an example of a
transform fault that slices a continent sitting along a spreading
ridge,The East Pacific Rise隆起,a seafloor spreading ridge off
the northwestern coast of North America,disappears under the
edge of the continent,to reappear farther south in the Gulf of
California,The San Andreas is the transform fault between
these segments of spreading ridge,Most of North America is
part of the North American Plate,The thin strip of California on
the west side of the San Andreas Fault,however,is moving
northwest with the Pacific plate,The stress resulting from the
shearing displacement across the fault leads to ongoing不间断的
earthquake activity.
地球内部过程
?Plate
Tectonics
Convergent Plate Boundaries,At a
convergent聚集、俯冲 plate
boundary,as the name indicates,
plates are moving toward each
other,Just what happens depends
on what sort of lithosphere is at the
leading edge of each plate (fig3.17),
continental lithosphere is relatively
low in density and is therefore
buoyant浮的 with respect to the
dense,iron-rich mantle,so it tends
to,float” on the asthenosphere岩流
圈, Oceanic lithosphere is more
similar in density to the underlying
asthenosphere,so it is more easily
forced down into the
asthenosphere as plates move
together.
地球内部过程
? Plate Tectonics
In a continent-continent collision,the two
landmasses come together,crumple,and
deform,One may partially override the other,
but the buoyancy 浮力 of continental
lithosphere ensures that neither sinks deep
into the mantle,and a very large thickness of
continent may result.大陆岩石圈的浮力保证了
两者都不会沉入地墁深处，只能导致大陆变厚
Earthquakes are frequent during active
collision as a consequence of the large
stresses involved in the process,The
extreme height of the Himalaya Mountains is
attributed to just this sort of continent－
continent collision,India was not always a
part of the Asian continent,Paleomagnetic
evidence indicates that it drifted northward
over tens of millions of years until it,ran
into” Asia,and the Himalayas were built up
in this collision,Earlier,the ancestral祖先的
Appalachian Mountains were built in the
same way,as Africa and North America
converged prior to the breakup of Pangaea泛
大陆、古陆, In fact,many major mountain
ranges worldwide represent sites of
sustained持续不变的 plate convergence in
the past.
地球内部过程
? Plate Tectonics
The subduction zones of the world balance the
seafloor equation,If new oceanic lithosphere is
constantly being created at spreading ridges,an
equal amount must be destroyed somewhere,or
the earth would simply keep getting bigger,This
excess额外 sea floor is consumed 消亡 in
subduction zones,The subducted plate is
heated by the hot asthenosphere,and,in time,
becomes hot enough to melt,Meanwhile,at the
spreading ridges,other melts rise,cool,and
crystallize to make new sea floor,So,in a sense,
the oceanic lithosphere is constantly being
recycled,which explains why few very ancient
seafloor rocks are known,Only rarely is a bit of
sea floor caught up in a continent during
convergence and preserved.在俯冲阶段大陆中
的洋底很难抓住老岩层并保存之 Most often,the
sea floor in a zone of convergence is subducted
and destroyed,The buoyant continents are not
so easily reworked更新 in this way; hence,very
old rocks may be preserved on them,Because
all continents are part of moving plates,sooner
or later they all are inevitably不可避免
transported传输 to a convergent boundary,as
leading oceanic lithosphere is consumed.
地球内部过程
? Plate Tectonics
Subduction zones are,geologically,very active
places,Sediments eroded from the continents
may accumulate in the trench沟壕 formed by the
down-going plate,and some of these sediments
may be carried down into the asthenosphere to
be melted along with the sinking lithosphere,
Volcanoes form where the melted material rises
up through the overlying plate to the surface,At
an ocean－ ocean convergence,the result is
commonly a line of volcanic islands,an island
arc (fig.3.17B),The great stresses involved in
convergence and subduction give rise to
numerous earthquakes,The bulk of mountain
building,and its associated volcanic and
earthquake activity,is related to subduction
zones,Parts of the world near or above modern
subduction zones,and therefore prone to both
volcanic and earthquake activity,include the
Andes region of South America,western Central
America,parts of the northwest United States
and Canada,the Aleutian Islands,China,Japan,
and much of the rim of the Pacific Ocean basin.
地球内部过程
? Plate Tectonics
? Stress and Strain in Geological Materials
? Lithosphere and Asthenosphere
? Locating Plate BounDarics
?
地球内部过程
? Plate Tectonics
? Plate Movements--Accumulating Evidence
? The Topography of the Sea Floor
? Magnetism in Rocks-- General
?
地球内部过程
? Plate Tectonics
? Types of Plate Boundaries
?
地球内部过程
? Plate Tectonics
? Paleomagnetism and Seafloor Spreading
? Age of the Ocean Floor
? Polar-Wander Curves
? Other Evidence
?
地球内部过程
? Part two3、板块漂移说
? 主要介绍地球表层的板块运动的发现、证
据；板块运动特征；板块运动的产物与影
响
? 4、地震
? 5、火山爆发
