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This presentation discusses diastrophism. It explains the forces acting on the crust and what causes such movements.
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Presenter: Emmanuel C. Revilla BSEd-2U, Physical Sciences
Earth and Environmental ScienceProf. Tan Bicomong
DIASTROPHISM
Origin of DIASTROPHISM
• Greek diastrophē twisting, from diastrephein to distort, from dia- + strephein to twist.
• First Known Use: 1890
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What is Diastrophism?• Also called tectonism, is the large-scale deformation
of the earth’s crust by natural processes. • Is the movement of rock masses of the earth’s crust
that causes its deformation.• The movement may be strong and sudden that we feel
the shaking of the Earth’s surface, we call this earthquake.
What is Vulcanism?• It is composed of the effect produced by the movement of magma in the crust or by pouring it out on its surface.
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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).
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Stress and Strain(Stress is force acting on rock; strain is rock’s response to stress.)
Two types:• Compression (shortening) • Extension (stretching)
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• Effects of Forces on the Landmasses1. Folding occurs when a part of the crust crumples,
bends upward and downward. Compressional stress causes rocks to buckle
and fold.TWO PARTS OF A FOLD1. Crest or Anticline2. Trough or Syncline
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Folding - occurs when a part of the crust crumples, bends upward and downward.
TWO PARTS OF A FOLD• Crest or Anticline• Trough or Syncline
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• Effects of Forces on the Landmasses2. Faulting- occurs when crust is fractured due to
unequal forces acting in opposite directions. Rock is strained beyond ability to
remain intact; rock fractures; one side is displaced with respect to the other .• Fault plane: surface along which 2 sides move• Fault scarp: cliff formed along fault face
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Faults may be classified as:1. Normal2. Reverse or Thrust3. Strike-slip
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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.
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2. Reverse or Thrust faults are formed due to strong compressional forces.
Vertical movement along inclined fault plane such that one side rides up over the other.
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3. Overthrust Fault• Reverse fault with very low angle• More horizontal than vertical movement.
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4. Strike-slip or lateral faults occur when the blocks move horizontally past each other.
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• Effects of Forces on the Landmasses3. 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.
Why does the Earth’s crust move?
1. Convection theory- says that heat produced radioactive elements like uranium, thorium and an isotope of potassium in rocks in the earth’s interior starts convection currents. The crust expands and pushes rock forward. Frictional drag exerted by the circulation of convection currents cause crustal movements.
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Why does the Earth’s crust move?
2. Contraction theory- states that rocks on the outer crust wrinkle because the interior of the earth cools and contracts. Great pressure squeezes the earth into a smaller volume and extrudes molten rocks into surface.
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Why does the Earth’s crust move?
3. Theory of Isostacy- explains why the earth’s surface will never be levelled despite continuous erosion of continents and filling in of ocean basins. It is accepted to explain vertical and horizontal movements of the crust.
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• 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 levelled surface over the whole earth.• As vertical adjustments take place, landmasses are
folded, buckled and thrusted.
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Horizontal Movements
1. Continental Drift • 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.
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• Crust and upper mantle together slide as a unit above a weaker plastic zone- asthenosphere. Convection current may cause the movements; two lithospheric plates converge, one slides under the other.• Evidences in support of the theory:
The Plants and Animals MatchThe Rocks MatchThe Shapes Match
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Horizontal Movements
2. Plate Tectonics• The theory of plate tectonics (meaning "plate structure") was
developed in the 1960's. • States that the continents break-up, regroup into pieces and
form most of the ocean bottom features.• 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.
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• 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. • It says that the earth’s crust is made up of a few large thin
pieces that flow on top of the asthenosphere. Such flowing makes the plates move about and sometimes crash into each other.
Convection Currents- most widely accepted cause of the shifting of continents.
Subduction- the process in which one plate submerge under the other when they collide.
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Horizontal Movements
3. Sea-floor Spreading• States that sediments on the ocean floor are youngest near
the ridge, and become older outward and that the ages are symmetrical on opposing ridge sides. • New oceanic crust id formed at mid-oceanic ridges and
moves slowly to the trenches, where it is destroyed. • It explains the close fit between the opposite sides of the
Atlantic Ocean w/c looks like separated pieces of a single continent.
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