Plate tectonics is the theory that Earth's outer shell is divided into several plates that glide over the mantle, the rocky inner layer above the core. The plates act like a hard and rigid shell compared to Earth's mantle. This strong outer layer is called the lithosphere.

1. Plate Tectonics

2. • Plate tectonics: Earth’s surface is divided into
a few large, thick plates that move slowly and
change in size
• Plate is a large, mobile slab of rock that is part
of Earth’s surface, bounded on four sides by
weak plane surfaces
• Plate consists of crust and upper part of the
mantle

3. -The Earth’s crust moves!!!!!
-The continents have not always been arranged
like they are today.
- The
Earth’s crust
is divided
into
segments
called
plates.

4. HISTORY OF PLATE
TECTONICS

5. History of Plate Tectonics
• The theory of plate tectonics has largely been
developed since 1967 but the history of ideas extend
back considerably longer.
• The theory of plate tectonics states that “the Earth’s
outermost layer is fragmented into a dozen of
large & small plates that are moving relative to
one another on top of the mobile Asthenosphere”.

6.  Before the advent of plate tectonics, however, some
people already believed that the present day
continents were the fragmented pieces of preexisting
larger landmasses (supercontinents).
 Plate tectonics is the relatively new scientific concept,
introduced in the 19th century.
 Plate tectonics theory has provided explanation to the
distribution of earthquakes & volcanic active zone
around the globe.

7. Abraham Ortelius(1527-1598)
 He was the first to note the similarity & suggest an
ancient separation in 1556. He suggested that the
Americas were “torn away from Europe & Africa
by earthquake & floods”.

8. Alexander Von Humbolt
• The German explorer
Humbolt also noted the
geometric& geological
similarities of the
opposing shores of the
Atlantic but also
suggested that the
Atlantic ocean was
formed by
Catastrophic Events.

9. Catastrophism vs. Uniformitarianism
Catastrophism Uniformitarianism
• A principle that states that
catastrophic events have
been important in Earth
history and modify the path
of slow change.
• The principle that states that
geological change occurs over
long periods of time.
• In addition, processes and
scientific laws operating today
also operated in the past and thus
past. Geological events can be
explained by forces observable
today.

10. Catastrophism:
Catastrophism is the theory that the Earth has
been affected in the past by sudden, short-lived,
violent events, possibly worldwide in scope.
This was in contrast to uniformitarians.
Uniformitarians:
Uniformitarians (sometimes described
as gradualism, in which slow incremental
changes, such as erosion, created all the Earth's
geological features. Uniformitarians held that
the present is the key to the past, and that all
things continued as they were from the
indefinite past.

11. James Hutton
 In the mid of 19th century
concept of “Catastrophism”
is replaced by that of
“Uniformitarianism” or
actualism as proposed by the
Scottish geologist James
Hutton in 1785.
 The Principle of uniformity is
commonly stated as:
“The present is Key to the
past”

12. • It means that slow processes going on at & beneath the
Earth’s surface today have been going on throughout
geological time & have shaped the surface record.
• However the geologic forces acting on the Earth today
are the same as those that have acted in the geologic
past.

13. CONTINENTAL DRIFT

14. Continental Drift & Alfred Wegner’s Theory
• In 1912, the German
meteorologist Alfred
Wegener (1880-1930),
first proposed the
theory of continental
drift, which state that
“parts of the Earth’s
crust slowly drift on
top of the mobile
asthenosphere”.

15.  Wegener hypothesized that all the continents were
assembled into supercontinents 225 Million years ago,
which he named “Pangaea”, meaning “All earth”.
 Pangaea was a supercontinent consisting of all of
Earth’s land masses.
 It existed from Permian to Jurassic periods.
 It began breaking up during the Jurassic period,
forming two supercontinents.

16. Laurasia
• It is the northern portion of supercontinents &
consists of North America, Europe & Asia.
• It is the southern portion of Supercontinent & include
South America, Antarctica, Africa, India &
Australia.
Gondwanaland

18. • These two supercontinents were separated by palaeo-
Thethys ocean.
• The ocean surrounding them was Panthalassa (literally
“all ocean”).

20. Alfred Supercontinents

22. Drawbacks of Alfred Wegener’s Theory
• Lack of plausible driving force was missing.
• Wegener suggested that continents drift
occurred in response to the centripetal force
experienced by the continents because of the
Earth’s rotation but it is not true.

23. Wegener’s theory vindication
• Although Wegener‘s continental
theory was rejected during his life
time due to lack of reasonable
mechanism for continental drift.
• Later on, the British geologist Arthur
Holmes championed the theory of
continental drift & proposed that
continents were moved by convection
current powered by the heat of
radioactive decay.

24.  However, after his death, new evidence from ocean
floor exploration and other studies rekindled interest in
Wagener's theory, ultimately leading to the
development of the theory of plate tectonics

25. EVIDENCES OF CONTINENTAL
DRIFT
• GEOMETRICAL FIT OF CONTINENTS
• Similarity of Rock Sequences and Mountain
Ranges
• Age provinces
• Igneous provinces
• Glacial Evidence
• Fossil Evidences
• Glossopteris flora

26. • Wegener devoted his life to doggedly pursuing
additional evidence to defend his theory.
• The evidence used by Wegener, du Toit, and others to
support the hypothesis of continental drift are as
follow;

27. 1)GEOMETRICAL FIT OF CONTINENTS
• Wegener, like some before him, was impressed by the close
resemblance between the coastlines of continents on opposite
sides of the Atlantic Ocean, particularly between South
America and Africa.
• The continents fit together like pieces of a giant jigsaw
puzzle.
• He cited these similarities as partial evidence
that the continents were at one time joined
together as a supercontinent that subsequently
split apart.

28.  Ancient “cratons” within continents match up when
they are brought together like a jigsaw puzzle.
 Craton is part of a continent that is stable and forms
the central mass of the continent.

29. • As his critics pointed out, though, the configuration
of coastlines result from erosional and depositional
processes and therefore is continually being
modified. So even if the continents had separated, as
Wegener proposed, it is not likely that the coastlines
would fit exactly.
• A more realistic approach is to fit the continents
together along the continental slope where erosion
would be minimal.

30. • In 1965 Sir Edward Bullard, an
English geophysicist, and two
associates showed that the best fit
between the continents occurs along
the continental slope at a depth of
about 2,000m.
• Since then, other reconstructions
using the latest ocean basin data have
confirmed the close fit between
continents when they are
reassembled to form Pangaea.

32. 2)Similarity of Rock Sequences and Mountain
Ranges
• If the continents were at one time joined, then the rocks
and mountain ranges of the same age in adjoining
locations on the opposite continents should closely match.
• Mountain Chains were continuous across the oceans.
• Example, the rocks in the Appalachian Mountain Belt, are
very similar to those found in British isles, Scandinavia
and Africa.
•

33. •The continuation of
Appalachian fold belt
of North America with
the Caledonian fold
belt of northern Europe
was noted.
•Similarly the
sedimentary deposits
associated with these
fold belts also
supported theory.

34. • The grain size & chemical composition of the
sediments can be used to determine the nature &
direction of the source.
• The source of the sediments in Caledonian fold belt
of northern Europe lies to the west in location now
occupied by Atlantic ocean, indicate that in past both
continents were side by side.

35. 3) Age provinces
• The correlation of
the patterns of
ages across the
southern Atlantic
is also noted.
Observed similar
rock units up to
Jurassic.

38. 4) Igneous provinces
• The igneous rocks
of similar age can
be traced b/w
various continents.
This consists of
both extrusive &
intrusive e.g. the
Mesozoic dolorites
spread through
Africa, Antarctica,
America.

39. 4) Glacial Evidence
• During the Late Paleozoic Era, massive glaciers
covered large continental areas of the Southern
Hemisphere. Evidence for this glaciation includes
layers of Till (sediments deposited by glaciers) and
Striations (scratch marks) in the bedrock beneath the
till.

40. • Fossil plants found in coals indicate that the Northern
Hemisphere had a tropical climate during the time that
the Southern Hemisphere was glaciated.
• All of the Gondwana continents except Antarctica are
currently located near the equator in subtropical to
tropical climates. Mapping of glacial striations in
bedrock in Australia, India, and South America
indicates that the glaciers moved from the areas of the
present-day oceans onto land. This would be highly
unlikely because large continental glaciers flow
outward from their central area of accumulation
toward the sea.

41. • Glacial deposits, including structures that indicate ice
flow, direction are located in ancient rocks as shown
in the figure below.

42. • If the continents did not move during the past, one
would have to explain how glaciers moved from the
oceans onto land and how large-scale continental
glaciers formed near the equator.
• But if the continents are reassembled as a single
landmass with South Africa located at the south pole,
the direction of movement of Late Paleozoic
continental glaciers makes sense.

45. 5) Fossil Evidences
• Some of the most compelling evidence for continental
drift comes from the fossil record.

46. a)Glossopteris flora
• Glossopteris, a tree-like
plant from the Permian
through the Triassic Period.
It had tongue-shaped leaves
and was about 12 ft (3.7 m)
tall. It was the dominant
plant of Gondwana.

47. Distribution of Glosspteris

48. b)Mesosaurus
• It is freshwater reptile
whose fossils are
found in Permian-
aged rocks in certain
regions of Brazil and
South Africa and no
where else in the
world.

49. • Because the physiology of freshwater and marine
animals is completely different, it is hard to imagine
how a freshwater reptile could have swum across the
Atlantic Ocean and found a freshwater environment
nearly identical to its former habitat.
• It is more logical to assume that Mesosaurus lived in
lakes in what are now adjacent areas of South
America and Africa, but were then united into a
single continent.

52. Plate Boundary
• Plate Boundary refers to the border between
two adjacent lithospheric plates, usually
classified by the relative motion taking place,
convergent, divergent, or transform.
• Plate boundaries can occur on landmasses
(continents) or in marine settings (oceans) or
both at the same time.

53. • Divergent
• Convergent
• Transform
Three types of Plate
Boundaries

54. Three types of Plate Boundaries

55. Divergent Plate Boundary
• Divergent plate boundaries are associated with
the following:
a. Tension or extension (pulling apart)
b. Normal faulting
c. Rifting (as in the mid-oceanic rift zone)
d. Creation of magma material inside the rift
zone

56. Divergent Boundary - Oceanic

57. Divergent Boundary - Continental

58. Divergent Boundary – Arabian and African Plates

60. Divergent Boundary –Iceland

61. • Spreading ridges
– As plates move apart new material is erupted
to fill the gap
Divergent Boundaries

62. Features/Landforms Associated with Divergent
Boundary
• Divergent zone: Oceanic, basaltic magma,
spreading center (Mid-Ocean Ridge). Also,
Continental: granitic, (East African Rift Zone)

63. Convergent Plate Boundary
• Convergent plate movement is associated with the
following:
a. Compression
b. Reverse faulting
c. Creation of a subduction zone
d. Mountain building processes
e. Collisions of plates:
– 1. Continent vs. oceanic
– 2. Oceanic vs. oceanic
– 3. Continent vs. continent

64. Convergent Boundary – Indian and Eurasian Plates

65. Collision Zones:
Continent vs. Oceanic
Oceanic vs. Oceanic
Continental vs.
Continental

66. Convergent Boundary – Oceanic & Continental

68. Andes Mountains,
South America

69. Convergent Boundary – Oceanic & Oceanic

70. Aleutian Islands, Alaska

71. • Forms mountains, e.g. European Alps, Himalayas
Continent-Continent Collision

73. Himalayas

74. Features/Landforms Associated with convergent
Boundary
1. Continent vs. Oceanic collision zone: subduction zone, deep
sea trench associated, volcanic arc, andesitic volcanic rock.
2. Oceanic vs. Oceanic collision zone: deep sea trench associated,
volcanic island arc, basaltic volcanic rock.
3. Continent vs. Continent collision zone: Granitic rocks,
mountain building processes, no volcanism, no magmatic
activities.

75. • Where plates slide past each other
Transform Boundaries
View of the San Andreas transform
fault

76. Transform Boundary – San Andreas Fault

77. Features/Landforms Associated with Transform
Boundary
• Transform boundaries are associated with the
following:
a. Horizontal grinding motion
b. Strike-slip faulting
c. Lateral offset of rock units