Diastrophism is the movement and deformation of the Earth's crust. Forces acting on the crust can cause it to fold, fault, or fracture. Folding occurs when crust crumples upward or downward into anticlines and synclines. Faulting happens when unequal forces cause crust to break along normal, reverse, or strike-slip faults. The movement of tectonic plates explains diastrophism, with convergent boundaries generating compression and uplift, divergent producing tension and rifting, and transform causing shear. Plate tectonics theory developed in the 1960s and explains phenomena like earthquakes and volcanoes.

1. Diastrophism
Chapter 6

2. Diastrophism
• It pertains to any movement of the solid
part of the Earth.
• It is a process that results in deformation
of the Earth’s crust.
• The movement may be strong and sudden
that we feel the shaking of the Earth’s
surface, we call this earthquake.

3. Direction of Forces
• Upward forces cause the widespread
rising of the crust.
• Downward forces cause the widespread
sinking of the crust.
• Horizontal forces moving in the same
direction (compression) can cause
landmasses to crumple break and slip
against each other; horizontal forces that
move away from each other (tension).

4. Effects of Forces on the
Landmasses
• 1. Folding occurs when
a part of the crust
crumples, bends upward
and downward.
• TWO PARTS OF A FOLD
• 1. Crest or Anticline
• 2. Trough or Syncline

7. • 2. Faulting occurs when crust is fractured due to
unequal forces acting in opposite directions.
• Faults may be classified as
• 1. Normal
• 2. Reverse or Thrust
• 3. Strike-slip

8. • 1. Normal Faults occur when tensional forces pull the crust
apart.
• The forces move the crust vertically apart and are called
dip-slip fault since the displacement (slip) is along the tilt (dip) of
the fault line.

9. • 2. Reverse or Thrust faults are formed due to
strong compressional forces.
• This kind of fault is associated to transform faults.

10. • 3. Strike-slip or lateral faults occur when the blocks move
horizontally past each other.
• These kinds of fault is associated with plate boundaries and
are called transform faults.

11. 3. Trenching
• 3. Trenching –
occurs when large
masses of the rocks
in the crust slide and
slip against each
other due to great
forces coming from
different directions.

12. Causes of Diastrophism
• Theory of Isostasy –
• Isostasy can be explained as the balancing of forces
between the effects of gravity on the mass of a section of
earth and the resistance of that mass to sinking into the
mantle of the earth.
• The simplest analogy of isostasy is icebergs (this is
based on Archimedes’ Principal).
• This explains why the wearing down of mountains and
the filling up of the ocean basins have not resulted on a
leveled surface over the whole earth.
• As vertical adjustments take place, landmasses are
folded, buckled and thrusted.

13. The Contraction Theory
• Earth is shrinking
because it is cooling
and the great
pressure squeezes
parts of the earth into
a smaller volume.
• Gravity draws the
crust inward causing
it to buckle, bend and
trench.

14. Convection Theory
• According to this theory,
convection currents are
set in the crust and heat
comes from the
disintegration of
radioactive elements.
• As heat accumulates,
rocks become plastic and
moves upward causing the
surface of the earth to
bulge.

15. Continental Drift Theory
• Proposed by a German
meteorologist and
geophysicist, Alfred Wegener.
• Wegener hypothesized that
there was an original, gigantic
supercontinent 200 million
years ago, which he named
Pangaea, meaning "All-earth".
• Pangaea was a supercontinent
consisting of all of Earth's land
masses.
• Pangaea started to break up
into two smaller
supercontinents, called
Laurasia and Gondwanaland,
during the Jurassic period.

19. The Plants and Animals Match
• Fossil Evidence in Support of the
Theory
• Wegener noted that plant fossils of
late Paleozoic age found on several
different continents were quite
similar.
• He was intrigued by the
occurrences of plant and animal
fossils found on the matching
coastlines of South America and
Africa, which are now widely
separated by the Atlantic Ocean.
• He reasoned that it was physically
impossible for most of these
organisms to have traveled or have
been transported across the vast
ocean.
• The most compelling evidence that
the two continents were once
joined.

20. The Rocks Match
• Broad belts of rocks
in Africa and South
America are the same
type.
• These broad belts
then match when the
end of the continents
are joined.

21. The Shapes Match
• Sir Francis Bacon first noticed
this peculiarity in the 17th
century.
• The continents look as if they
were pieces of a giant jigsaw
puzzle that could fit together to
make one giant super-
continent.
• The bulge of Africa fits the
shape of the coast of North
America while Brazil fits along
the coast of Africa beneath the
bulge.

22. PLATE TECTONICS
• The theory of plate tectonics
(meaning "plate structure") was
developed in the 1960's.
• This theory explains the
movement of the Earth's plates
(which has since been
documented scientifically) and
also explains the cause of
earthquakes, volcanoes, oceanic
trenches, mountain range
formation, and many other
geologic phenomenon.
• The plates are moving at a speed
that has been estimated at 1 to 10
cm per year.
• Most of the Earth's seismic activity
(volcanoes and earthquakes)
occurs at the plate boundaries as
they interact.

28. Types of Plate Motion
• The ways that plates interact depend on
their relative motion and whether oceanic
or continental crust is at the edge of the
lithospheric plate.
• Plates move away from, toward, or slide
past each other.
• Geologists call these divergent,
convergent, and transform plate
boundaries.

29. • At a convergent plate boundary, lithospheric plates move
toward each other.
• The west margin of the South American continent, where
the oceanic Nazca Plate is pushed toward and beneath
the continental portion of the South American Plate, is an
example of a convergent plate boundary.

30. • At a divergent plate boundary lithospheric plates
move away from each other.
• The mid-Atlantic Ridge, a topographically high
area near the middle of the Atlantic Ocean, is an
example of a divergent plate boundary.

31. • At a transform plate boundary, plates slide past each
other.
• The San Andreas fault in California is an example of a
transform plate boundary, where the Pacific Plate slides
past the North American Plate.

34. • Relationship between plate tectonic setting
and structural style:
• Tectonic Setting
• Stress State
• Types of Structures
• Examples
• Divergent plates extension
• normal faults, roll over anticlines, tilted
blocks
• North Sea, Red Sea, Basin and
Range Convergent plates compression
• thrust faults, folds, faulted folds
• Andes, Zagros Mts (Iran), Canadian
Rockies Transform plate boundaries strike-
slip
• strike-slip faults, compressional and
extensional flower structures
• San Andreas fault, Alpine Fault (New
Zealand).