OBJECTIVES: At the end of the presentation, you should be able to know about the following: • Definition of Diastrophism • Theories explaining Diastrophism • Stress and Strain • Faults and Folds
Defining DIASTROPHISM:Tectonismdeformation of Earth’s crust by natural processes (movements)leads to the formation of continents and ocean basins, mountain systems, plateaus, rift valleys, and other features.
TRIVIA:Do you know that?Due to Earth’s gravity it is impossiblefor mountains to be higher than49, 000 feet (15,000 metres).
How does Diastrophism occur?
1.) Isostasy Theory state of gravitational equilibrium between the Earths lithosphere and asthenosphere tectonic plates "float" at an elevation which depends on their thickness and density.
Example:North Greenland fjord cliffs
TRIVIA: Thegeneral term isostasy was coined in 1889 by the American geologist Clarence Edward Dutton.
2.) Contraction TheoryEarth is SHRINKING.Gravity draws the crust inward causing it to bend, buckle and trench.
Shrinking resulted in a reduction in the Earth’s diameter while the circumference remained unchanged due to folding and buckling of the crust
3.) Convection Current Theory convection within the Earths mantle pushes the plates movement of a fluid, caused by differences in temperature
According to this theory: Theplate is the cooled surface layer of a convection current in upper mantle.
4.) Continental Drift Theory Continents were joined in a super-continent, called Pangaea (all lands). Over a vast period of time, the continents drifted apart to their current locations.
Some Evidences: The jigsaw fit of the outline of the continental margins.
Numerous geological similarities between South America and Africa.
TRIVIA: Continental Drift theory was first presented by Alfred Wegener who died two days after his 50th birthday.
5.) Expansion Theory Earth is physically expanding in diameter, mass, or both.
6.) Plate Tectonics Theory Earths outer layer is fragmented into plates that are in constant motion.
Plate Boundaries and Their Motions Divergent Convergent Transform/ Thrust
Major Earth Movements Uplift Subsidence
TRIVIA:Do you knowthat?On everycontinentthere is a citycalled Rome.
STRESS AND STRAIN3 main concepts about stress and strain:rocks deform,stress causes strain and strain results in structures,different physical conditions create different structures
STRESS is a Force acting on some areas
3 BASIC TYPES OF STRESS Compressional Stress Tensional Stress Shear Stress
STRESS AND STRAIN Strain is a change in size, shape, or volume of a material. Response to stress
3 BASIC TYPES OF STRAINElastic StrainPlastic StrainFracture Strain
NOTE : Stresscan happen with out strain, but strain cannot happen without stress.
2 Major Types ofStructural Deformation Fault Fold
Fault rocksbreak due to force 4 types:Normal FaultReverse FaultStrike-Slip FaultThrust Fault
Fold Rocks bend due to forceTypes of Fold: Symmetrical Folds Assymetrical Folds Isoclinal Folds Overturned Folds Recumbant Folds Chevron Folds
REPORTED BY:CLARISSE P. CACAPIT
Syncline youngestrocks occur in the core of a fold Caused by compressional stress U-shaped
Anticline oldest rocks occur in the core of a fold Caused by compressional stress A-shaped
Compressional Stress two plates move together or one moves and applies a force on another one that is not moving.
Tensional Stress one part of a plate moves away from another part of a plate.
Shear Stress two plates slide past one another
Elastic Strainrocks recover to their original shape.
Plastic or Ductile Strain Rocks do not return to their original shape.
Fracture or Brittle Strainrocks crack or break under the stress.