This document provides information about plate tectonics and the dynamics of the Earth. It discusses key topics such as continental drift, Earth's layered structure, types of plate boundaries including convergent, divergent and transform boundaries, seafloor spreading, plate motions, and forces driving plate tectonics. The objectives are to understand concepts like continental drift, Earth's structure, plate margins, seafloor spreading, how plates move on the surface of the sphere, and driving forces. Diagrams and figures are included to illustrate these topics.
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More Related Content
Lecture 2-The Dynamic Earth.pdf
1. Where is Earth in the
Universe??
What is the earth
made out off???
2. 2. The Dynamics of Earth
Sub-Unit
2. The Dynamics of Earth:
Continental drift
Earth’s structure
Types of Plate Margins
Seafloor spreading
Plate motion on the surface of the sphere
Forces driving plate tectonic motions
3. 2. The Dynamics of Earth
Objectives
Know what is a continental drift
and the factors causing it
Identify different layers that
made up the spherical earth
Identify different types of Plate
Margins
Understand Seafloor spreading
Know how plates are moving on
the surface of the sphere
Categories forces driving plate
tectonic motions
4. • Is a dynamic planet, endlessly changing both internally
And externally
Processes of transforming the
surface of earth
1. endogenic processes (i.e., of
internal origin)- by volcanism
and tectonism, metamorphism ,
earthquakes , crustal warping ,
folding and faulting .
The Earth
5. 2. Exogenic processes (i.e., of external origin) -
such as weathering, erosion, transportation,
deposition, denudation.
• Also, Earth surface is deformed by geological
processes at rates that are extremely slow in
human terms, cm per year
weathering, erosion, transportation
deposition
Pacific Plate - North American Plate –
5cm/year
Mt William
Wara Simbu
Purari
6. Hypotheses to explain the underlying mechanisms causing
dynamics of earth
Hypothesis of a Contracting Earth (late nineteenth)
- shrinking cause mountains like wrinkles
• Propose Southern landmass combine
into one great continent in Palaeozoic
times called Gondwanaland.
(Africa, Antarctica, Arabia, Australia,
India and South America).
In the late nineteenth century - Austrian
geologist Eduard Suess
• In 1912 - German meteorologist Alfred
Wegener proposed the idea of Super
Continent called Pangea (Greek: All
the Earth)
Formation of Nappe structures in the Alps
7. • Alexander Du Toit, a South African
geologist, (1937) proposed that “northern
continents” are all combine as Laurasia.
(North America (including Greenland),
Europe and most of Asia)
Laurasia and Gondwanaland split apart
in the Early Mesozoic
Super Continent of Pangae Land is
supported by the proposed Laurasia
and Gondwanaland
The hypothesis of Displacement was
Born!
8. 1.2.2 Continental drift
Continental Drift was proposed by “Displacement hypothesis”
• crustal blocks having
continental dimensions
are making large-scale
horizontal displacement
continental drift,
• The displacements take
place slowly over long time
intervals.
Wegener’s reconstruction of Pangaea
9. Computer-assisted reconstructions
Pangaea Reconstruction
The traces of opposite continental
margins were matched by an iterative
procedure
They digitized the continental
outlines
• approximately 50 km
intervals for different depth
• (900 m) depth was used for
matching
10. Geographical and Magnetic Poles
Earth magnetic field
(Geomagnetic Field)
• points vertically
downward in the North
Pole
• Points vertically upward
in the South Pole
• Forms earths
magnetosphere
• Can change polarity over
time
• caused by electric
currents in the liquid
outer core
Palaeomagnetism and continental drift
11. Palaeomagnetism and continental drift
Palaeomagnetism - study of the past record of the direction and
intensity of Earth's magnetic (geomagnetic field) field in rocks by
oxides of iron (magnetite, hematite, maghemite) when they form.
• Magnetic Pole Changes with
respect to time
12. (a) In hot lava flows, thermal
energy exceeds atomic magnetic
exchange energy and the magnetic
moments (movements) are
randomized.
(b) When the lava cools,
magnetic moment aligns parallel
to the ambient geomagnetic field.
(c) When magnetic particles are
eroded from a source rock and are
deposited as a sediment, the
particles may align with the
geomagnetic field to give rise to a
depositional remanent
magnetization (DRM).
How rocks acquire a remanent magnetization?
13. Virtual geomagnetic pole (VGP)
position –calculation of the
position of the magnetic pole at the
time in which rocks get magnetised
• By connecting mean VGP
positions of different ages
for sites on the same
continent apparent polar
wander path is obtain
Conclude that poles are not
moving but continents are!!
Apparent polar wander (APW) -The
appearance that the pole has shifted
with time
• retrace the relative motion of
continents,
• formation and break-up of
supercontinents
14. Earth structure
Early in the twentieth
century it became evident
from the study of seismic
waves
• interior of the Earth has a
radially layered structure
• boundaries are marked by
abrupt changes in
seismic velocity or
velocity gradient
• Each layer is
characterized by
composition, pressure
and temperature in the
layer
• Four main layers are the
crust, mantle and the
outer and inner cores
15. • S waves cannot pass through
fluid while P waves can
• shadow zone -angular
distances of 104 to 140 degrees
from a given earthquake that
does not receive any direct P
waves
• Only refracted P waves arrive
at position opposite the
epicentre
How seismic is used to determination of the properties of
the Four Layer
P and S Waves
16. Depths of the most
important seismic
discontinuities
giving boundaries
of layer
Inner Core
Solid;
Radius of Earth
1. Crust
2. Upper Mantle
• Lithosphere
• Asthenosphere
3. Lower Mental
• Mesosphere
4. Outer Core
5. Inner Core
17. Lithospheric plates
• Lithosphere- crust and uppermost
mantle are rigid, forming a hard
outer shell
• Asthenosphere- weaker layer may
be able to flow over long periods of
time like a viscous liquid or plastic
solid,
• The convection current in the
mental causes relative motions of
the overlying lithospheric plates
• when strongly stressed, fracture
happens causing earthquake.
Ridge
Lithosphere
Asthenosphere
Trench
Trench Ridge
This action
• resulted in the plate movements
• Seismic zones of the earth
Earthquakes – is a violent release of elastic
energy due to sudden displacement on a
fault plane
18. Seismic Belts:
(a) the circum-Pacific “ring of fire”;
(b) a sinuous belt running from the Azores through North Africa and the
Alpine–Dinaride–Himalayan mountain chain as far as S.E. Asia; and
(c) the world-circling system of oceanic ridges and rises.
Seismic Zones of the Earth
19. Tectonic plates
Tectonic plates - fragmented slabs of
lithosphere that visible trough
boundaries called tectonic plate
boundaries.
• Sizes range: 1000 - 10,000 sq. km
(e.g., the Pacific plate and Philippines
plate)
• Movement – mm-cm/year
• Twelve major plates - (Antarctica,
Africa, Eurasia, India, Australia,
Arabia, Philippines, North America,
South America, Pacific, Nazca, and
Cocos) and several minor plates (e.g.,
Scotia, Caribbean, Juan de Fuca).
The seismic zones subdivide the lithosphere laterally into tectonic plates
21. 2. Divergent - two tectonic
plates move away from
each other
Three types of plate boundary (Margins)
3. Transform - Two plates
sliding past each other
1. Convergent - two plates
come together,
Constructive plate margins.
Destructive plate margin
Conservative plate margin,
22. There are 3 types of Convergent Boundaries…
Type 1: Oceanic plate-Continental plate collision
• oceanic is more dense and sub duct beneath continental plate
• Hot more buoyant material rises
• Magmatic arc formation
Subduction: The process by which oceanic crust sinks beneath a
deep-ocean trench and back into the mantle at a convergent plate
boundary.
24. Type 2: Ocean plate - Ocean plate collision
The less dense plate slides under the more dense plate
creating a subduction zone called a TRENCH
Oldest will subduct
25. Type 3: Continental plate - Continental plate collision
Neither subduct due to buoyancy of crusts
A place where folded and thrust faulted mountains
form.
26. • May form Mountain Ranges.
These are Folded Mountains, like the Himalayas
28. Two plates move apart
Run through ocean basins
Divergent Plate Boundaries
29. Mid-oceanic ridges,
transform faults and rift
valleys, and the formation of
the ocean floor are
characteristics associated
with divergent plate
boundaries.
Magma
30. Transform Plate Boundary
Plate 1
Plate 2
Transform Plate Boundary -two plates slide past one another
The fracture zone that forms a transform plate boundary is known as
a transform fault
32. Sea-Floor Spreading
The process
by which
molten
material
adds new
oceanic
crust to
the ocean
floor
In 1961 R. Dietz term this process
“sea-floor spreading” for the ridge process
33. Seafloor spreading formed Mid-Ocean Ridge
Mid-Ocean Ridge:
The undersea mountain
chain where new ocean
floor is produced;
Cause of divergent plate
boundary
Mid-Ocean Ridge
35. What evidence did scientists find for sea-
floor spreading in the 1960s?
Evidence from molten material
Evidence from magnetic stripes
Evidence from drilling samples
36. The Vine–Matthews–Morley hypothesis
“When hot lava solidifies and its temperature cools below the Curie
temperature of its magnetic minerals, the basalt becomes strongly
magnetized in the direction of the Earth’s magnetic field at that
time.”
Evidence of Magnetic strip
37. Along an active spreading ridge:
• basalt form symmetrically on opposite sides of the spreading center,
• each carrying the magnetic imprint of the field in which it formed.
• Sea-floor spreading can persist for many millions of years at an
oceanic ridge.
• changes in polarity of different time
-ve
+ve
38. Evidence From Drilling Samples
When scientists sampled the rocks, they found that the
further away from the ridge the rocks were older
The younger rocks were always in the center of the ridges
39. Rates of sea-floor spreading
• the opposite sides are moving away from the ridge at
equal speeds
• increasing slowly at a mean rate of 17mm /yr
40. Computation of
half-rates of sea-
floor spreading at
different spreading
centers by
measuring the
distances to
anomalies with
known
radiometric ages
Total spreading rate is
twice the half-spreading
rate
41. 2. Constructive plate margin-
two tectonic plates move away
from each other
Plate Margins
3. Conservative plate margin -
Two plates sliding past each
other
1. Destructive plate margin -
two plates come together
Eg. Divergent boundaries
Eg. Convergent boundaries
Eg. Transform boundaries
42. Hotspots
refer to a long-lasting center of surface volcanism and locally high
heat flow rooted in the mantle below the lithosphere
• more common in
the ocean basins
• hot, rising plume
• forming a volcanic island
• Seamount
The motion of the plate
transports the island away
from the hotspot and the
volcanism becomes extinct
43. Example
• radiometric dating of basalt samples from islands and
seamounts along the Hawaiian Ridge portion of the
Hawaiian–Emperor chain
44. Plate motion on the surface of a sphere
Earth's surface is a sphere
• Made up of Earth's tectonic plates
• Plates move continuously with respect to
each other,
Mathematically speaking, the most
general way to describe the motion
of rigid plate on a sphere is through
rotation about a fixed pole
This is known as Euler geometrical
theorem
45. This is described in the Euler
geometrical theorem, which
shows that every displacement
of a plate from one position to
another on the Earth's surface
can be regarded as a simple
rotation of that plate about a
suitably chosen axis, known as
an Euler pole or pole of
rotation, which passes through
the centre of the Earth.
b
A
Euler
pole or
pole of
rotation
47. Forces driving plate tectonic motions
There are forces acting on lithospheric plates that causing the
movement of plates
• Forces can be driving and resistive
Upper mantle convection forces
• mantle drag force (𝑭𝑫𝑭) – caused by flow of material beneath a plate on
the base of the plate. If convection is fast compare to plate movement. The
plate is dragged. Opposite is true.
• Continental drag force (𝑭𝑪𝑫) – caused by greater weight of the plate
48. • ridge push force (𝑭𝑹𝑷) – gravitational sliding towards trenches
Force at spreading ridges
Forces at transform faults
• transform force (𝑭𝑻𝑭) - frictional resistance in the contact
zone
49. • slab pull force (𝑭𝑺𝑷) – downward pull force of the mantle to
the subducting slab
• slab resistance force (𝑭𝑺𝑹) – resistance
the slab experience as it tries to move
further down into mantle
Forces at subduction zones
Forces at Subduction Zone
50. Forces at Plate collisions
• “trench suction” (𝑭𝑺𝑼) – force caused by pull force on the lower plate
that pulls the upper plate towards the trench.
• collision resistance force (𝑭𝑪𝑹) – opposite motion of
colliding plates cause resistance
51. Forces at hotspots
• hotspot force (𝐹𝐻𝑆) – caused by transfer of mantle
material to the lithosphere
52. Driving Forces are:
• slab pull,
• slab suction,
• ridge push and
• trench pull force on the upper plate
In Conclusion
Resistive Forces are:
• slab resistance,
• collision resistance, and
• transform fault forces.