if you do not know geology please stay away this is a big part of my grade so i need someone who knows they stuff. i have powerpoints and him going over it for halp. Do 1,2,3,4,8
GOL 106 LAB 3
ROCK UNITS AND TIME ROCK UNITS
Group ________
Member Names
(1)_________________________________________________
(2)_________________________________________________
(3)_________________________________________________
Page
75
76
78
Figure
Question(s)
Fig. 8.5
All
All
All
Chapter 3
The Theory of Plate Tectonics
1
Unifying Theory
• A unifying theory is one
that helps
– explain a broad range of
diverse observations
– interpret many aspects
of a science on a grand
scale
– and relate many
seemingly unrelated
phenomena
• Plate tectonics is a unifying theory for geology.
2
Plate Tectonics
• Plate tectonics helps
to explain
– earthquakes
– volcanic eruptions
– formation of
mountains
– location of
continents
– location of ocean
basins
• Tectonic interactions
affect
– atmospheric and oceanic
circulation and climate
– geographic distribution,
evolution and extinction
of organisms
– distribution and
formation of resources
3
Early Ideas
about Continental Drift
• Edward Suess
• Austrian, late 1800s
– noted similarities between
the Late Paleozoic plant fossils
• Glossopteris flora
– and evidence for
glaciation in rock
sequences of
•
•
•
•
India
Australia
South Africa
South America
• He proposed the name
Gondwanaland
(or Gondwana)
– for a supercontinent
composed of these 4
continents
Alfred Wegener and the
Continental Drift Hypothesis
• German
meteorologist
• Credited with
hypothesis of
continental
drift
5
Alfred Wegener and the
Continental Drift Hypothesis
• He proposed that all
landmasses
– were originally united
into a supercontinent
named Pangaea
• He presented a series of maps
– showing the breakup of Pangaea
• He amassed a tremendous amount of geologic,
6
paleontologic, and climatologic evidence
Jigsaw-Puzzle Fit of Continents
• Continental Fit
7
Jigsaw-Puzzle Fit of Continents
• Matching mountain
ranges
• Matching glacial
evidence
8
Matching Fossils
9
Additional Support for
Continental Drift
• Alexander du Toit
(South African geologist, 1937)
– Proposed that a northern landmass, Laurasia, that
consisted of present-day
•
•
•
•
North America
Greenland
Europe
and Asia (except India).
Provided additional fossil evidence for Continental drift
10
The Perceived Problem with
Continental Drift
• Most geologists did not accept the idea of
moving continents because:
– There was no suitable mechanism to explain how
continents could move over Earth’s surface
• Interest in continental drift revived when
– new evidence from studies of Earth’s magnetic field
– and oceanographic research
– showed that the ocean basins were geologically
young features
11
Revival of Continental Drift Hypothesis
• Paleomagnetism is
–
–
–
–
a remnant magnetism
in ancient rocks
recording the direction
and the strength of
Earth’s magnetic field
– at the time of the rock’s
formation
• When magma cools
– below the Curie point temperature
– magnetic iron-bearing minerals align
– with Earth’s magnetic field
12
Polar Wandering
• In 1950s, research
revealed
– that paleomagnetism of
ancient rocks showed
orientations different
from the present
magnetic field
• Magnetic poles apparently
moved.
– The apparent movement was
called polar wandering.
– Different continents had
different paths.
• The best explanation
– is stationary poles
– and moving continents
13
Mapping Ocean Basins
• Ocean mapping
revealed
– a ridge system more than
65,000 km long, the
most extensive mountain
range in the world
Mid-Atlantic Ridge
• The Mid-Atlantic Ridge
– is the best known part of
the system
– and divides the Atlantic
Ocean basin in two
nearly equal parts
14
Seafloor Spreading
• Harry Hess, in 1962, proposed the theory of
seafloor spreading:
– Continents and oceanic crust move together
– Seafloor separates at oceanic ridges
• where new crust forms from upwelling and cooling
magma, and
• the new crust moves laterally away from the ridge
– The mechanism that drives seafloor spreading was
thermal convection cells in the mantle
• hot magma rises from mantle to form new crust
• cold crust subducts into the mantle at oceanic trenches,
where it is heated and recycled
15
Confirmation of Hess’s
Hypothesis
• Ocean research
revealed magnetic
anomalies on the sea
floor
• A magnetic anomaly is
a deviation from the
average strength of
Earth’s magnetic field
• The stripes are parallel and symmetrical with the
16
oceanic ridges
Age of Ocean Basins
17
Plate Tectonics
• Plate tectonic theory is based on a simple model of
Earth that the lithosphere is rigid and consists of oceanic
& continental crust with upper mantle
– it consists of variablesized slabs called
plates
– with plate regions
containing continental
crust
• up to 100 km thick
– and plate regions
containing oceanic
crust
• up to 10 km thick
18
Plate Map
19
Numbers represent average rates of relative movement in cm/yr
Atlantic Ocean Basin
North America
Europe
Atlantic
Ocean
basin
South America
Africa
20
An Example of Ancient Rifting
• What features in the rock record can geologists
use to recognize ancient rifting?
–
–
–
–
–
faults
dikes
sills
lava flows
thick sedimentary
sequences within rift
valleys
• Example:
– Triassic fault-block
basins in eastern US
21
Ancient Rifting
• These Triassic fault basins
– mark the zone of rifting
between North America and
Africa
sill
Palisades of Hudson
River
– They contain
thousands of meters
of continental
sediment
– and are riddled with
dikes and sills 22
Convergent Boundaries
• Older crust must be destroyed and recycled
– at convergent boundaries
– so that Earth’s surface area remains the same
• Where two plates collide,
– subduction occurs
• when an oceanic plate
• descends beneath the margin of another plate
– The subducting plate
• moves into the asthenosphere
• is heated
• and eventually incorporated into the mantle
23
Convergent Boundaries
• Convergent boundaries are characterized by
–
–
–
–
–
–
deformation
volcanism
mountain building
metamorphism
earthquake activity
valuable mineral deposits
• Convergent boundaries are of three types:
– oceanic-oceanic
– oceanic-continental
– continental-continental
24
Oceanic-Oceanic Boundary
• When two oceanic plates converge,
– one is subducted beneath the other along an oceanicoceanic plate boundary
– forming an oceanic trench and a subduction complex
• composed
of slices of
folded and
faulted
sediments
• and oceanic
lithosphere
scraped off
the
descending
plate
25
Volcanic Island Arc
• As the plate subducts into the mantle,
–
–
–
–
it is heated and partially melted
generating magma of andesitic composition
that rises to the surface
because it is less dense than the surrounding mantle
rocks
• At the surface
of the nonsubducting
plate,
– the magma
forms a
volcanic
island arc
26
Oceanic-Oceanic Plate Boundary
• A back-arc basin forms in some cases of fast
subduction.
– The lithosphere on the landward side of the island arc
– is stretched and thinned
• Example: Sea of Japan
27
Oceanic-Continental Boundary
• An oceanic-continental plate boundary
– occurs when a denser oceanic plate
– subducts under less dense continental lithosphere
• Magma generated by subduction
– rises into the continental crust to form large igneous
bodies
– or erupts to
form a
volcanic arc
of andesitic
volcanoes
– Example:
Pacific coast
of South
28
America
Oceanic-Continental Boundary
• Where the Nazca plate in the Pacific Ocean is
subducting under South America
– the Peru-Chile Trench marks subduction site
– and the Andes Mountains are the volcanic arc
Andes
Mountains
29
Continent-Continent Boundary
• Two approaching continents are initially
– separated by ocean floor that is being subducted
– under one of them, which, thus, has a volcanic arc
• When the 2 continents collide
– the continental lithosphere cannot subduct
• Its density is
too low,
– although
one
continent
may partly
slide under
the other
30
Continent-Continent Boundary
• When the 2 continents collide
– they weld together at a continent-continent plate
boundary, where an interior mountain belt forms
consisting of
• deformed
sedimentary
rocks
• igneous
intrusions
• metamorphic
rocks
• fragments of
oceanic crust
• Earthquakes
occur here
31
Continental-Continental Boundary
• Example: Himalayas in central Asia
–
–
–
–
Earth’s youngest and highest mountain system
resulted from collision between India and Asia
began 40 to 50 million years ago
and is still continuing
Himalayas
32
Recognizing Ancient
Convergent Boundaries
• How can former subduction zones
be recognized in the rock record?
– Andesitic magma erupted, forming island arc
volcanoes and continental volcanoes
– The subduction complex results in a zone of intensely
deformed rocks between the trench and the area of
igneous activity
– Sediments and submarine rocks are folded, faulted
and metamorphosed making a chaotic mixture of
rocks termed a mélange
– Slices of oceanic lithosphere may be accreted to the
continent edge and are called ophiolites
33
Ophiolite
• Ophiolites
consist of layers
– representing
parts of the
oceanic crust
and upper
mantle.
• The sediments include
– graywackes
– black shales
– cherts
• Ophiolites are
key to detecting
old subduction
zones
34
Transform Boundaries
• Transform plate boundary
– where plates slide laterally past each other
– roughly parallel to the direction of plate movement
• Movement results in
– zone of intensely shattered rock
– numerous shallow earthquakes
fracture
zone
• The majority of
transform faults
– connect two oceanic
ridge segments
– and are marked by
fracture zones
35
Transform Boundaries
• Example: San Andreas Fault,
California
– separates the Pacific plate
from the North American plate
– connects ridges in
• Gulf of California
• with the Juan de Fuca and
Pacific plates
– Many of the earthquakes in
California result from
movement along this fault
36
Hot Spots and Mantle Plumes
• Hot spots are locations where
– stationary columns of magma originating deep
within the mantle,
• called mantle plumes
– slowly rise to the surface
• Mantle plumes apparently remain stationary
• When plates move over them
– hot spots leave trails
• of extinct, progressively older volcanoes
• called aseismic ridges
• which record the movement of the plates
37
Hot Spots and Mantle Plumes
• Example: Emperor Seamount-Hawaiian
Island chain
Age increases
plate
movement
38
Plate Movement Measurements
• Hot spots
– determine the age of rocks and their distance from
a hot spot
– divide the distance by the age
– this gives the motion relative to the hot spot and
– the absolute motion of the plate
• Satellite-laser ranging
– bounce laser beams from a station on one plate off
a satellite, to a station on another plate
– measure the elapsed time after sufficient time has
passed to detect motion
– measure the elapsed time again
– use the difference in elapsed times to calculate the
39
rate of movement between the two plates
Plate Movement at Hot Spot
40
What Is the Driving Mechanism
of Plate Tectonics?
• Most geologists accept some type of convective
heat system
– as the basic cause
of plate motion
• In one possible
model,
– thermal convection
cells are restricted to
the asthenosphere
41
What Is the Driving Mechanism
of Plate Tectonics?
• In a second model, the entire mantle is
involved in thermal convection.
• In both models,
– spreading ridges mark
the rising limbs of
neighboring
convection cells
– trenches occur where
the convection cells
descend back into
Earth’s interior
42
What Is the Driving Mechanism
of Plate Tectonics?
• In addition to a thermal convection system,
– some geologists think that movement may be aided by
– “slab-pull”
• the slab is cold and
dense and pulls the
plate
– “ridge-push”
• rising magma pushes
the ridges up and
gravity pushes the
oceanic lithosphere
away from the ridge
and toward the
trench
43
How Are Plate Tectonics and
Mountain Building Related?
• An orogeny is an episode
– of intense rock deformation or mountain building
• It results from compressive forces
– related to plate movement
• During subduction,
– sedimentary and volcanic rocks are folded and
faulted along the plate margin
• Most orogenies occur along oceanic-continental
– or continental-continental plate boundaries
44
Terrane Tectonics
• Terranes differ from neighboring regions in their
–
–
–
–
fossil content,
stratigraphy,
structural trends,
and paleomagnetism
• They probably formed elsewhere
– were carried great distances as parts of other plates
until they collided with other terranes or continents
• Numerous terranes have been identified in
mountains of the North American Pacific coast
region
45
How Does Plate Tectonics Affect
the Distribution of Life?
• Present distribution of plants and animals
– is largely controlled by climate and geographic barriers
• Barriers create biotic provinces
– each province is a region characterized by a distinctive
assemblage of plants and animals
• Plate movements largely control barriers
– When continents break up, new provinces form
– When continents come together, fewer provinces result
– As continents move north or south they move across
temperature barriers
46
How Does Plate Tectonics Affect
the Distribution of Life?
• Physical barriers caused by
plate movements include
–
–
–
–
–
intraplate volcanoes
island arcs
mid-ocean ridges
mountain ranges
subduction zones
– Example: Isthmus
of Panama creates
a barrier to marine
organisms
Pacific
Caribbean
47
Plate Tectonics and the
Distribution of Natural Resources
• Plate movements influence the formation and
distribution of some natural resources such as
– petroleum
– mineral deposits
• Metal resources related to igneous and
associated hydrothermal activity include
– copper
– gold
– lead
– silver
– tin
– zinc
48
Plate Tectonics and the
Distribution of Natural Resources
• Magma generated by subduction can precipitate
and concentrate metallic ores
– Bingham Mine in Utah is a
– Example: copper
huge open-pit copper mine
deposits in western
Americas
49
Plate Tectonics and the
Distribution of Natural Resources
• Another place where hydrothermal activity
– can generate rich metal deposits is divergent plate
boundaries
• Example: island of Cyprus in the Mediterranean
– Copper concentrations there formed as a result of
precipitation adjacent to hydrothermal vents along a
divergent plate boundary
• Example: Red Sea
– copper, gold, iron, lead, silver ,and zinc deposits are
currently forming in the Red Sea, a divergent
boundary
50
QUESTIONS?
51
GOL 106 LAB 3
ROCK UNITS AND TIME ROCK UNITS
Group ________
Member Names
(1)_________________________________________________
(2)_________________________________________________
(3)_________________________________________________
Page
75
76
78
Figure
Question(s)
Fig. 8.5
All
All
All
Chapter 3
The Theory of Plate Tectonics
1
Unifying Theory
• A unifying theory is one
that helps
– explain a broad range of
diverse observations
– interpret many aspects
of a science on a grand
scale
– and relate many
seemingly unrelated
phenomena
• Plate tectonics is a unifying theory for geology.
2
Plate Tectonics
• Plate tectonics helps
to explain
– earthquakes
– volcanic eruptions
– formation of
mountains
– location of
continents
– location of ocean
basins
• Tectonic interactions
affect
– atmospheric and oceanic
circulation and climate
– geographic distribution,
evolution and extinction
of organisms
– distribution and
formation of resources
3
Early Ideas
about Continental Drift
• Edward Suess
• Austrian, late 1800s
– noted similarities between
the Late Paleozoic plant fossils
• Glossopteris flora
– and evidence for
glaciation in rock
sequences of
•
•
•
•
India
Australia
South Africa
South America
• He proposed the name
Gondwanaland
(or Gondwana)
– for a supercontinent
composed of these 4
continents
Alfred Wegener and the
Continental Drift Hypothesis
• German
meteorologist
• Credited with
hypothesis of
continental
drift
5
Alfred Wegener and the
Continental Drift Hypothesis
• He proposed that all
landmasses
– were originally united
into a supercontinent
named Pangaea
• He presented a series of maps
– showing the breakup of Pangaea
• He amassed a tremendous amount of geologic,
6
paleontologic, and climatologic evidence
Jigsaw-Puzzle Fit of Continents
• Continental Fit
7
Jigsaw-Puzzle Fit of Continents
• Matching mountain
ranges
• Matching glacial
evidence
8
Matching Fossils
9
Additional Support for
Continental Drift
• Alexander du Toit
(South African geologist, 1937)
– Proposed that a northern landmass, Laurasia, that
consisted of present-day
•
•
•
•
North America
Greenland
Europe
and Asia (except India).
Provided additional fossil evidence for Continental drift
10
The Perceived Problem with
Continental Drift
• Most geologists did not accept the idea of
moving continents because:
– There was no suitable mechanism to explain how
continents could move over Earth’s surface
• Interest in continental drift revived when
– new evidence from studies of Earth’s magnetic field
– and oceanographic research
– showed that the ocean basins were geologically
young features
11
Revival of Continental Drift Hypothesis
• Paleomagnetism is
–
–
–
–
a remnant magnetism
in ancient rocks
recording the direction
and the strength of
Earth’s magnetic field
– at the time of the rock’s
formation
• When magma cools
– below the Curie point temperature
– magnetic iron-bearing minerals align
– with Earth’s magnetic field
12
Polar Wandering
• In 1950s, research
revealed
– that paleomagnetism of
ancient rocks showed
orientations different
from the present
magnetic field
• Magnetic poles apparently
moved.
– The apparent movement was
called polar wandering.
– Different continents had
different paths.
• The best explanation
– is stationary poles
– and moving continents
13
Mapping Ocean Basins
• Ocean mapping
revealed
– a ridge system more than
65,000 km long, the
most extensive mountain
range in the world
Mid-Atlantic Ridge
• The Mid-Atlantic Ridge
– is the best known part of
the system
– and divides the Atlantic
Ocean basin in two
nearly equal parts
14
Seafloor Spreading
• Harry Hess, in 1962, proposed the theory of
seafloor spreading:
– Continents and oceanic crust move together
– Seafloor separates at oceanic ridges
• where new crust forms from upwelling and cooling
magma, and
• the new crust moves laterally away from the ridge
– The mechanism that drives seafloor spreading was
thermal convection cells in the mantle
• hot magma rises from mantle to form new crust
• cold crust subducts into the mantle at oceanic trenches,
where it is heated and recycled
15
Confirmation of Hess’s
Hypothesis
• Ocean research
revealed magnetic
anomalies on the sea
floor
• A magnetic anomaly is
a deviation from the
average strength of
Earth’s magnetic field
• The stripes are parallel and symmetrical with the
16
oceanic ridges
Age of Ocean Basins
17
Plate Tectonics
• Plate tectonic theory is based on a simple model of
Earth that the lithosphere is rigid and consists of oceanic
& continental crust with upper mantle
– it consists of variablesized slabs called
plates
– with plate regions
containing continental
crust
• up to 100 km thick
– and plate regions
containing oceanic
crust
• up to 10 km thick
18
Plate Map
19
Numbers represent average rates of relative movement in cm/yr
Atlantic Ocean Basin
North America
Europe
Atlantic
Ocean
basin
South America
Africa
20
An Example of Ancient Rifting
• What features in the rock record can geologists
use to recognize ancient rifting?
–
–
–
–
–
faults
dikes
sills
lava flows
thick sedimentary
sequences within rift
valleys
• Example:
– Triassic fault-block
basins in eastern US
21
Ancient Rifting
• These Triassic fault basins
– mark the zone of rifting
between North America and
Africa
sill
Palisades of Hudson
River
– They contain
thousands of meters
of continental
sediment
– and are riddled with
dikes and sills 22
Convergent Boundaries
• Older crust must be destroyed and recycled
– at convergent boundaries
– so that Earth’s surface area remains the same
• Where two plates collide,
– subduction occurs
• when an oceanic plate
• descends beneath the margin of another plate
– The subducting plate
• moves into the asthenosphere
• is heated
• and eventually incorporated into the mantle
23
Convergent Boundaries
• Convergent boundaries are characterized by
–
–
–
–
–
–
deformation
volcanism
mountain building
metamorphism
earthquake activity
valuable mineral deposits
• Convergent boundaries are of three types:
– oceanic-oceanic
– oceanic-continental
– continental-continental
24
Oceanic-Oceanic Boundary
• When two oceanic plates converge,
– one is subducted beneath the other along an oceanicoceanic plate boundary
– forming an oceanic trench and a subduction complex
• composed
of slices of
folded and
faulted
sediments
• and oceanic
lithosphere
scraped off
the
descending
plate
25
Volcanic Island Arc
• As the plate subducts into the mantle,
–
–
–
–
it is heated and partially melted
generating magma of andesitic composition
that rises to the surface
because it is less dense than the surrounding mantle
rocks
• At the surface
of the nonsubducting
plate,
– the magma
forms a
volcanic
island arc
26
Oceanic-Oceanic Plate Boundary
• A back-arc basin forms in some cases of fast
subduction.
– The lithosphere on the landward side of the island arc
– is stretched and thinned
• Example: Sea of Japan
27
Oceanic-Continental Boundary
• An oceanic-continental plate boundary
– occurs when a denser oceanic plate
– subducts under less dense continental lithosphere
• Magma generated by subduction
– rises into the continental crust to form large igneous
bodies
– or erupts to
form a
volcanic arc
of andesitic
volcanoes
– Example:
Pacific coast
of South
28
America
Oceanic-Continental Boundary
• Where the Nazca plate in the Pacific Ocean is
subducting under South America
– the Peru-Chile Trench marks subduction site
– and the Andes Mountains are the volcanic arc
Andes
Mountains
29
Continent-Continent Boundary
• Two approaching continents are initially
– separated by ocean floor that is being subducted
– under one of them, which, thus, has a volcanic arc
• When the 2 continents collide
– the continental lithosphere cannot subduct
• Its density is
too low,
– although
one
continent
may partly
slide under
the other
30
Continent-Continent Boundary
• When the 2 continents collide
– they weld together at a continent-continent plate
boundary, where an interior mountain belt forms
consisting of
• deformed
sedimentary
rocks
• igneous
intrusions
• metamorphic
rocks
• fragments of
oceanic crust
• Earthquakes
occur here
31
Continental-Continental Boundary
• Example: Himalayas in central Asia
–
–
–
–
Earth’s youngest and highest mountain system
resulted from collision between India and Asia
began 40 to 50 million years ago
and is still continuing
Himalayas
32
Recognizing Ancient
Convergent Boundaries
• How can former subduction zones
be recognized in the rock record?
– Andesitic magma erupted, forming island arc
volcanoes and continental volcanoes
– The subduction complex results in a zone of intensely
deformed rocks between the trench and the area of
igneous activity
– Sediments and submarine rocks are folded, faulted
and metamorphosed making a chaotic mixture of
rocks termed a mélange
– Slices of oceanic lithosphere may be accreted to the
continent edge and are called ophiolites
33
Ophiolite
• Ophiolites
consist of layers
– representing
parts of the
oceanic crust
and upper
mantle.
• The sediments include
– graywackes
– black shales
– cherts
• Ophiolites are
key to detecting
old subduction
zones
34
Transform Boundaries
• Transform plate boundary
– where plates slide laterally past each other
– roughly parallel to the direction of plate movement
• Movement results in
– zone of intensely shattered rock
– numerous shallow earthquakes
fracture
zone
• The majority of
transform faults
– connect two oceanic
ridge segments
– and are marked by
fracture zones
35
Transform Boundaries
• Example: San Andreas Fault,
California
– separates the Pacific plate
from the North American plate
– connects ridges in
• Gulf of California
• with the Juan de Fuca and
Pacific plates
– Many of the earthquakes in
California result from
movement along this fault
36
Hot Spots and Mantle Plumes
• Hot spots are locations where
– stationary columns of magma originating deep
within the mantle,
• called mantle plumes
– slowly rise to the surface
• Mantle plumes apparently remain stationary
• When plates move over them
– hot spots leave trails
• of extinct, progressively older volcanoes
• called aseismic ridges
• which record the movement of the plates
37
Hot Spots and Mantle Plumes
• Example: Emperor Seamount-Hawaiian
Island chain
Age increases
plate
movement
38
Plate Movement Measurements
• Hot spots
– determine the age of rocks and their distance from
a hot spot
– divide the distance by the age
– this gives the motion relative to the hot spot and
– the absolute motion of the plate
• Satellite-laser ranging
– bounce laser beams from a station on one plate off
a satellite, to a station on another plate
– measure the elapsed time after sufficient time has
passed to detect motion
– measure the elapsed time again
– use the difference in elapsed times to calculate the
39
rate of movement between the two plates
Plate Movement at Hot Spot
40
What Is the Driving Mechanism
of Plate Tectonics?
• Most geologists accept some type of convective
heat system
– as the basic cause
of plate motion
• In one possible
model,
– thermal convection
cells are restricted to
the asthenosphere
41
What Is the Driving Mechanism
of Plate Tectonics?
• In a second model, the entire mantle is
involved in thermal convection.
• In both models,
– spreading ridges mark
the rising limbs of
neighboring
convection cells
– trenches occur where
the convection cells
descend back into
Earth’s interior
42
What Is the Driving Mechanism
of Plate Tectonics?
• In addition to a thermal convection system,
– some geologists think that movement may be aided by
– “slab-pull”
• the slab is cold and
dense and pulls the
plate
– “ridge-push”
• rising magma pushes
the ridges up and
gravity pushes the
oceanic lithosphere
away from the ridge
and toward the
trench
43
How Are Plate Tectonics and
Mountain Building Related?
• An orogeny is an episode
– of intense rock deformation or mountain building
• It results from compressive forces
– related to plate movement
• During subduction,
– sedimentary and volcanic rocks are folded and
faulted along the plate margin
• Most orogenies occur along oceanic-continental
– or continental-continental plate boundaries
44
Terrane Tectonics
• Terranes differ from neighboring regions in their
–
–
–
–
fossil content,
stratigraphy,
structural trends,
and paleomagnetism
• They probably formed elsewhere
– were carried great distances as parts of other plates
until they collided with other terranes or continents
• Numerous terranes have been identified in
mountains of the North American Pacific coast
region
45
How Does Plate Tectonics Affect
the Distribution of Life?
• Present distribution of plants and animals
– is largely controlled by climate and geographic barriers
• Barriers create biotic provinces
– each province is a region characterized by a distinctive
assemblage of plants and animals
• Plate movements largely control barriers
– When continents break up, new provinces form
– When continents come together, fewer provinces result
– As continents move north or south they move across
temperature barriers
46
How Does Plate Tectonics Affect
the Distribution of Life?
• Physical barriers caused by
plate movements include
–
–
–
–
–
intraplate volcanoes
island arcs
mid-ocean ridges
mountain ranges
subduction zones
– Example: Isthmus
of Panama creates
a barrier to marine
organisms
Pacific
Caribbean
47
Plate Tectonics and the
Distribution of Natural Resources
• Plate movements influence the formation and
distribution of some natural resources such as
– petroleum
– mineral deposits
• Metal resources related to igneous and
associated hydrothermal activity include
– copper
– gold
– lead
– silver
– tin
– zinc
48
Plate Tectonics and the
Distribution of Natural Resources
• Magma generated by subduction can precipitate
and concentrate metallic ores
– Bingham Mine in Utah is a
– Example: copper
huge open-pit copper mine
deposits in western
Americas
49
Plate Tectonics and the
Distribution of Natural Resources
• Another place where hydrothermal activity
– can generate rich metal deposits is divergent plate
boundaries
• Example: island of Cyprus in the Mediterranean
– Copper concentrations there formed as a result of
precipitation adjacent to hydrothermal vents along a
divergent plate boundary
• Example: Red Sea
– copper, gold, iron, lead, silver ,and zinc deposits are
currently forming in the Red Sea, a divergent
boundary
50
QUESTIONS?
51
Chapter 4
Geologic Time:
Concepts and Principles
1
Grand Canyon
• When looking down into the Grand Canyon, we are
really looking at the early history of Earth
2
Grand Canyon
• More than 1 billion years of history are
preserved,
• like pages of a book,
– in the rock layers of the Grand Canyon
• Reading this rock book we learn that the area
underwent episodes of
– mountain building
– advancing and retreating shallow seas
• We know these things by
– applying the principles of relative dating to the rocks
– and recognizing that present-day processes have
operated throughout Earth history
3
What is time?
• We are obsessed with time, and organize our
lives around it.
• Most of us feel we don’t have enough of it.
• Our common time units are
–
–
–
–
–
–
–
Seconds
minutes
hours
days
weeks
months
years
• Ancient history involves
– hundreds of years
– thousands of years
• But geologic time involves
– millions of years
– even billions of years
4
4
Concept of Geologic Time
• Geologists use two different frames of reference
when discussing geologic time
– Relative dating involves placing geologic events
• in a sequential order as determined from their position in
the geologic record
– It does not tell us how long ago a particular event
occurred, only that one event preceded another
• For hundreds of years geologists
– have been using relative dating to establish a relative
geologic time scale
5
Relative Geologic Time Scale
• The relative
geologic time
scale has a
sequence of
–
–
–
–
–
eons
eras
periods
Epochs
Ages
6
Concept of Geologic Time
• The second frame of reference for geologic time
is absolute dating
– Absolute dating results in specific dates for rock
units or events
• expressed in years before the present
– It tells us how long ago a particular event occurred
• giving us numerical information about time
• Radiometric dating is the most common method
of obtaining absolute ages
– Such dates are calculated from the natural rates of
decay of various natural radioactive elements
present in trace amounts in some rocks
7
7
Geologic Time Scale
• The discovery of
radioactivity near the end
of the 19th century
allowed absolute ages to
be accurately applied to
the relative geologic time
scale
• The geologic time
scale is a dual scale
– A Relative Scale
– And an Absolute Scale
8
8
Relative-Dating Principles
• The fundamental geologic principles used in
relative dating are
1. Principle of superposition
– Nicolas Steno (1638-1686)
– In an undisturbed
succession of sedimentary
rock layers, the oldest layer
is at the bottom & the
youngest layer is at the top
• This method is used in determining the relative age
– of rock layers (strata) and the fossils they contain
9
9
Relative-Dating Principles
2. Principle of original
horizontality
– Nicolas Steno
– Sediment is deposited
• in essentially horizontal
layers
– Therefore, a sequence of
sedimentary rock layers
– that is steeply inclined
from horizontal
– must have been tilted
– after deposition and
lithification
10
Relative-Dating Principles
3. Principle of original lateral continuity
– Nicolas Steno’s third principle
– Sediment extends laterally in all direction until it thins
& pinches out or terminates against the edges of the
depositional basin
11
11
Relative-Dating Principles
4. Principle of Intrusion
– James Hutton (1726-1797)
– An igneous intrusion or a fault
must be younger than the rocks it
intrudes or displaces
12
Relative-Dating Principles
5. Principle of inclusion (components)
– Components/inclusions are older than the rock in
which they are found
components
13
13
Catastrophism
– Concept proposed by Georges Cuvier (1769-1832)
– dominated European geologic thinking
• The physical and biological history of Earth
– resulted from a series of sudden widespread
catastrophes which accounted for significant &
rapid changes in Earth & exterminated existing life
in the affected area
• Six major catastrophes occurred,
– corresponding to the six days of biblical creation
– The last one was the biblical deluge
14
14
Catastrophism
• This hypothesis was abandoned because
– it was not supported by field evidence
• Basalt was shown to be of igneous origin
• Volcanic rocks interbedded with sedimentary and
primitive rocks showed that igneous activity had
occurred throughout geologic time
• More than 6 catastrophes were needed to explain
field observations
• The principle of uniformitarianism became the
guiding philosophy of geology
15
Uniformitarianism
6. Principle of uniformitarianism
– Present-day processes have operated throughout
geologic time. ‘The present is the key to the past’
– Developed by James Hutton (1726-1797), advocated
by Charles Lyell (1797-1875)
• William Whewell coined the term
“uniformitarianism” in 1832
• Hutton applied the principle of uniformitarianism
– when interpreting rocks at Siccar Point, Scotland
• We now call what Hutton observed an
unconformity,
– but he properly interpreted its formation
16
16
Unconformity at Siccar Point
• Hutton explained that
– the tilted, lower rocks
– resulted from severe
upheavals that formed
mountains
– these were then worn
away
– and covered by
younger flat-lying
rocks
– the erosional surface represents a gap (hiatus) in the
rock record, called Unconformity
17
17
How Old is the Earth?
• Lord Kelvin (1824-1907)
– knew about high temperatures inside of deep mines and
reasoned that Earth was losing heat from its interior
• Assuming Earth was once molten, he used
– the melting temperature of rocks, the size of Earth, and
the rate of heat loss to calculate the age of Earth as
between 400 and 20 million years
• This age was too young for the geologic processes
envisioned by other geologists at that time, leading to a
crisis in geology
• Kelvin did not know about radioactivity
– as a heat source within the Earth
18
18
Absolute-Dating Methods
• The discovery of radioactivity
– destroyed Kelvin’s argument for the age of Earth
– and provided a clock to measure Earth’s age
• Radioactivity is the spontaneous decay
– of an element to a more stable isotope
• The heat from radioactivity
– helps explain why the Earth is still warm inside
• Radioactivity provides geologists
– with a powerful tool to measure absolute ages of
rocks and past geologic events
19
19
Atoms: A Review
• Understanding absolute dating requires
knowledge of atoms and isotopes
• All matter is made up of atoms
• The nucleus of an atom is composed of
– protons – particles with a positive electrical charge
– neutrons – electrically neutral particles
• with electrons – negatively charged particles –
outside the nucleus
• The number of protons (= the atomic number)
– helps determine the atom’s chemical properties
– and the element to which it belongs
20
Isotopes: A Review
• Atomic mass number
= number of protons + number of neutrons
• The different forms of an element’s atoms
– with varying numbers of neutrons are called isotopes
• Different isotopes of the same element
– have different atomic mass numbers but behave the
same chemically
• Most isotopes are stable,
– but some are unstable
• Geologists use decay rates of unstable isotopes
– to determine absolute ages of rocks
21
21
Radioactive Decay
• Radioactive decay is the process whereby
– an unstable
atomic
nucleus
spontaneously
transforms
into an atomic
nucleus of a
different
element
22
22
Radioactive Decay
• Three types of radioactive decay:
– In alpha decay, two protons and two neutrons
– (alpha particle) are emitted from the nucleus.
23
23
Radioactive Decay
– In beta decay, a neutron emits a fast moving
electron (beta particle) and becomes a proton.
– In electron capture decay, a proton captures an
electron and converts to a neutron.
24
24
Radioactive Decay
• Some isotopes undergo only one decay step
before they become stable.
– Examples:
• rubidium 87 decays to strontium 87 by a single beta
emission
• potassium 40 decays to argon 40 by a single electron
capture
• But other isotopes undergo several decay steps
– Examples:
• uranium 235 decays to lead 207 by 7 alpha steps and 6
beta steps
• uranium 238 decays to lead 206 by 8 alpha steps and 6
beta steps
25
Uranium 238 decay
26
Half-Lives
• The half-life of a radioactive isotope
– is the time it takes for one half of the atoms of the
original unstable parent isotope to decay to atoms
of a new more stable daughter isotope
• The half-life of a specific radioactive isotope
– is constant and can be precisely measured
27
27
Half-Lives
• The length of half-lives for different isotopes
– of different elements can vary from less than one
billionth of a second to 49 billion years!
• Radioactive decay
– is geometric, NOT linear,
– and produces a curved graph
28
28
Uniform Linear Change
• In this example
– of uniform
linear change,
water is
dripping into a
glass at a
constant rate
29
29
Geometric Radioactive Decay
– In radioactive
decay, during
each equal time
unit
• half-life
– the proportion
of parent atoms
decreases by 1/2
30
Determining Age
• By measuring the parent/daughter ratio
– and knowing the half-life of the parent
• which has been determined in the laboratory
– geologists can calculate the age of a sample
containing the radioactive element
• The parent/daughter ratio
– is usually determined by a mass spectrometer
• an instrument that measures the proportions of atoms
with different masses
31
31
Determining Age
• Example:
– If a rock has a parent/daughter ratio of 1:3
– or a ratio of (parent)/(parent + daughter) =
1:4 or 25%,
– and the half-live is 57 million years,
• how old is the rock?
– 25% means it is 2 halflives old.
– the rock is 57my x 2 =114
million years old.
32
32
What Materials Can Be Dated?
• Most radiometric dates are obtained
– from igneous rocks
• As magma cools and crystallizes,
– radioactive parent atoms separate from previously
formed daughter atoms
• Because they are the right size
– some radioactive parents are included in the crystal
structure of cooling minerals
33
33
What Materials Can Be Dated?
• The daughter atoms are different elements
– with different sizes and, therefore, do not generally
fit into the same minerals as the parents
• Geologists can use the crystals containing
– the parent atoms to date the time of crystallization
34
34
Igneous Crystallization
• Crystallization of magma separates parent atoms
– from previously formed daughters
• This resets the radiometric clock to zero.
• Then the parents gradually decay.
35
Sedimentary Rocks
• Generally, sedimentary rocks can NOT be
radiometrically dated
– The date obtained would correspond to the time of
crystallization of the mineral, when it formed in an
igneous or metamorphic rock,
– and NOT the time that it was deposited as a
sedimentary particle
• Exception: The mineral glauconite can be dated
– because it forms in certain marine environments as
a reaction with clay minerals during the formation
of the sedimentary rock
36
36
Dating Metamorphism
Dating the whole rock
yields a date of 700
million years = time of
crystallization.
a. A mineral has just
crystallized from magma.
b. As time passes, parent
atoms decay to daughters.
c. Metamorphism drives
the daughters out of the
mineral as it
recrystallizes.
d. Dating the mineral today
yields a date of 350
million years = time of
metamorphism, provided
the system remains closed
37
during that time.
37
Long-Lived Radioactive
Isotope Pairs Used in Dating
• The isotopes used in radiometric dating need to
be sufficiently long-lived so the amount of parent
material left is measurable
• Such isotopes include:
Parents
Daughters
Half-Life (years)
Uranium 238
Uranium 234
Thorium 232
Rubidium 87
Potassium 40
Lead 206
Lead 207
Lead 208
Strontium 87
Argon 40
4.5 billion
704 million
14 billion
48.8 billion
1.3 billion
Most of these
are useful for
dating older
rocks
38
38
Radiocarbon Dating Method
• Carbon is found in all forms of life
• It has 3 isotopes
– Carbon 12 and 13 are stable, but carbon 14 is not
– Carbon 14 has a half-life of 5730 years ± 30 years
– Carbon 14 dating uses the carbon 14/carbon 12 ratio
• of material that was once living
• The short half-life of carbon 14
– makes it suitable for dating material
– < 70,000 years old
• It is not useful for most rocks,
– but is useful for archaeology and young geologic
materials
39
Carbon 14
• Carbon 14 is constantly forming
– in the upper atmosphere
• When cosmic rays
– strike atoms of upper atmospheric
gases, splitting nuclei into protons
and neutrons
– When a neutron strikes a nitrogen
14 atom it may be absorbed by the
nucleus and eject a proton
changing it to carbon 14
40
Carbon 14
• The carbon 14 becomes
– part of the natural carbon cycle
– and becomes incorporated into
organisms
• While the organism lives
– it continues to take in carbon 14,
– but when it dies, the carbon 14
begins to decay without being
replenished
• Thus, carbon 14 dating
measures the time of death
41
Tree-Ring Dating Method
• The age of a tree can be determined
– by counting the annual growth rings in lower part
of the stem (trunk)
• The pattern of wide and narrow rings
– can be correlated from tree to tree
– a procedure called cross-dating
• The tree-ring time scale
– now extends back 14,000 years
42
42
Tree-Ring Dating Method
• In cross-dating, tree-ring patterns are used from
different trees, with overlapping life spans 4343
Geologic Time and Climate
Change
• With current debates concerning global warming
– it is extremely important to reconstruct part regimes
– as accurately as possible
• Geologists must have an accurate and precise geologic
calendar
– to model how Earth’s climate system
– has responded to past changes
44
44
Geologic Time and Climate
Change
• Geologists use stalagmites from caves
–
–
–
–
which are formed from calcium carbonate
and rise from a cave floor
Stalagmites record a layered history
with older layers in the center at its base
45
Geologic Time and Climate
Change
• Geologists can
radiometrically
date
– individual layers
of stalagmites
– with Uranium
234-Thorium 230
methods
46
46
Geologic Time and Climate
Change
• History of stalagmites
–
–
–
–
from Crevice Cave, Missouri
revealed a history of climatic and vegetation change
in the midcontinent US
75,000 and 25.000 years ago
• These changes correlated with vegetation and average
temperature fluctuations
– which were obtained from carbon 13 and oxygen 18 isotope
profiles
47
47
Geologic Time & Climate Change
48
Geologic Time & Climate Change
• Precise dating
techniques
– Uranium 234Thorium 230
• Allows
geologists to
model climate
systems from the
past
49
49
Geologic Time and Climate
Change
• By analyzing past environmental and climate
changes and their duration
– geologists hope to use data to predict, and possibly
modify regional climatic changes
50
QUESTIONS?
51
Chapter 2
Minerals
and
Rocks
1
Earth Materials – Minerals
• Some minerals,
– such as gold,
– have fascinated people for
thousands of years
– and have been supposed to have
mystical or curative powers
• Minerals have many essential
uses
– in industrial societies
• Minerals are the basic units
– that make up most of Earth’s
materials
2
Earth Materials – Rocks
• Rocks also have many uses:
– rocks crushed for aggregate in
cement and for roadbeds
– sawed and polished rocks for
tombstones, monuments, mantle
pieces and countertops
– Even the soils we depend on for
most of our food are formed by
alteration of rocks
3
Minerals
Minerals on
display
– at the
California
Academy of
Sciences in
San Francisco
4
Matter and Its Composition
• Matter
– anything that has mass and occupies space
– exists as solids, liquids, gases
– consists of elements and atoms
• Element
– a chemical substance
– composed of tiny particles called atoms
5
Atoms
• Atoms are the smallest
units of matter that retain the
characteristics of the element
• Atoms have
– a compact nucleus containing
• protons – particles with a positive
electrical charge
• neutrons – electrically neutral particles
– particles outside the nucleus
• electrons – negatively charged particles
6
Idealized Structure of an Atom
7
Atoms
• Atomic number
= the number of protons
• Atomic mass number
= number of protons + number of neutrons
• The number of neutrons in nucleus of an
element may vary
8
Isotopes
• Isotopes
– the different forms of an element’s atoms
– with varying numbers of neutrons
• Different isotopes of the same element
– have different atomic mass numbers
• Isotopes are important in radiometric dating
9
Carbon Isotopes
• Three isotopes of carbon (all with 6 protons)
– 6 neutrons = Carbon 12 (12C)
– 7 neutrons = Carbon 13 (13C)
– 8 neutrons = Carbon 14 (14C)
10
Electrons and Shells
• Electrons lie outside the nucleus
in one or more shells
• The outermost shells are involved
– in chemical bonding
– and contain up to 8 electrons
• Noble gas configuration of 8 electrons
• or 2 for helium or hydrogen
– have complete outer shells
– and are stable
• Other atoms attain
11
– a noble gas configuration
– through the process of bonding
Bonding and Compounds
• Bonding
– the process whereby atoms join to other
atoms
• Compound
– a substance resulting from the bonding
of two or more elements
• Oxygen gas (O2) is an molecule
• Ice (H2O) is a compound
– made up of hydrogen and oxygen atoms
• Most minerals are compounds
12
Ionic Bonding
• One way for atoms to attain the noble gas
configuration
– is by transferring electrons, producing ions
• Ion
– an atom that has gained or lost one or more
electrons
– and thus has a negative or positive charge
• Ionic bonding
– attraction between two ions of opposite charge
13
Covalent Bonding
• Another way for atoms
– to attain the noble gas configuration
– is by sharing electrons
• Covalent bonding
– results from
sharing of
electrons
shared electrons
14
Minerals
• Geological definition of a mineral:
–
–
–
–
–
naturally occurring
inorganically formed
solid substance
with defined chemical composition
and atoms arranged in specific 3dimensional frameworks
15
Minerals—The Building
Blocks of Rocks
• A mineral’s composition is shown by a
chemical formula
– a shorthand way of indicating how many atoms
of different kinds it contains
– Quartz molecules consist
Quartz: SiO2
of 1 silicon atom and 2
Ratio: 1: 2
oxygen atoms
– Orthoclase molecules
KAlSi3O8
consists of 1 potassium, 1
aluminum, 3 silicon, and 8
1: 1: 3: 8
oxygen atoms
16
Native Elements
• A few minerals
consist of only one
element.
• They are not
compounds.
• They are known as
native elements.
• Examples:
– Gold: Au
– Diamond: C
17
Diagnostic Mineral Properties
• Mineral properties are controlled by
– Chemical composition
– Crystalline structure
• Mineral properties are particularly useful
– for mineral identification and include:
•
•
•
•
•
•
color
streak
luster
crystal form
Magnetism
Reaction to HCl
•
•
•
•
•
•
cleavage
fracture
hardness
specific gravity
Taste
Smell
18
How Many Minerals
Are There?
•
•
•
•
More than 3500 minerals are known
Only about 2 dozen are particularly common
Many others are important resources
Mineral groups:
– minerals with the same negatively charged ion
or ion group
– belong to the same mineral group
• Most minerals in the crust
– belong to the group called silicates
19
Silicates
• Silicates are minerals containing
silica (Si and O)
– Silicon and Oxygen
• These minerals make up
almost 95% of Earth’s crust
– and account for about 1/3 of all
known minerals
• The basic building block of
silicates
– is the silicate tetrahedron
• which consists of one silicon atom
• surrounded by four oxygen atoms
20
Silicate Structures
– Single tetrahedron
– Ring structure
– Single chain
– Double chain
– Sheet structure
– Complex 3-D
structure
21
Types of Silicates
• Ferromagnesian silicates
– contain iron (Fe),
magnesium (Mg), or
both
Amphibole
• Nonferromagnesian
silicates
– do not contain iron or
magnesium
22
Other Mineral Groups
• Carbonates
– minerals with carbonate ion (CO3)-2
• calcite (CaCO3),
– constituent of limestone
• dolomite [CaMg(CO3)2],
– constituent of dolostone
Limestone
• Other mineral groups are
important
– but more as resources
– than as constituents of rocks
Dolostone
23
Rock-Forming Minerals
• Most rocks are solid aggregates
– of one or more minerals
• Hundreds of minerals occur in rocks,
– but only a few are common
– and called rock-forming minerals
• Most rock-forming minerals are silicates,
– but carbonates are also important
• Accessory minerals are present in small amounts
– and are ignored in classifying rocks
24
Rock Cycle
• The rock cycle is a pictorial representation
– of events leading to
– the origin, destruction, change and reformation
of rocks
• Rocks belong to 3 major groups
– igneous
– sedimentary
– metamorphic
• The rock cycle shows
– how these rock families are interrelated
– and can be derived from one another
25
Rock
Cycle
26
Igneous Rocks
• All igneous rocks
– cool and crystallize from magma,
solidify from lava, or consolidate
from pyroclastic materials
• Magma is molten material
– below the surface
• Lava is molten material on the
surface
• Pyroclastic materials
– are particles such as volcanic ash
27
Igneous Part of the Rock Cycle
Pyroclastic
material
Lava
28
Categories of Igneous Rocks
• Extrusive or volcanic rocks formed at the surface
from lava or pyroclastic materials
• Intrusive or plutonic rocks formed from
magma injected into the crust or formed in
place in the crust
– Plutons are intrusive bodies
29
Plutons
30
Igneous Rock Textures
• Texture is the size, shape, and arrangement of
crystals, grains, and other constituents of a rock
– It is controlled by the rate of cooling of magma or lava
31
Cooling-Rate Textures
• Phaneritic,
– with visible grains
• cooled slowly
• Aphanitic,
– with grains too small to see without magnification
• cooled quickly
• Porphyritic,
– with larger grains (phenocrysts) surrounded by a
finer-grained groundmass
• cooled slowly intrusively, then expelled onto the surface
• Glassy,
– with no grains
• cooled too quickly for minerals to grow
32
Igneous Rock Textures
• Other textures reveal further details
– of the formation of the rock
• Vesicular texture, with holes (vesicles),
– indicates the rock formed
– as water vapor and other gases
– became trapped during cooling of lava
• Pyroclastic or fragmental texture,
– containing fragments,
– formed by consolidation of volcanic ash
– or other pyroclastic material
• Pegmatitic texture,
− very large crystals forming at the end of
crystallization of magma
33
Igneous Rock Textures
Phaneritic
Aphanitic
Porphyritic
Pyroclastic
Glassy
34
Vesicular
Classifying Igneous Rocks
• Texture and composition are the criteria
– used to classify most igneous rocks
• Composition categories are based on mineral
composition
–
–
–
–
FELSIC, light colored, >65% silica
INTERMEDIATE, 53-65% silica
MAFIC, dark colored, 45-52% silica
ULTRAMAFIC,