DIASTROPHISM

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 impossible for mountains to be higher than 49, 000 feet (15,000 metres).

THEORIES EXPLAINING DIASTROPHI

SMHow does Diastrophism occur?

1.) Isostasy Theory state of

gravitational equilibrium between the Earth's lithosphere and asthenosphere

tectonic plates "float" at an elevation which depends on their thickness and density.

Simple Analogy:

Example:

North Greenland fjord cliffs

TRIVIA: The general

term 'isostasy' was coined in 1889 by the American geologist Clarence Edward Dutton.

2.) Contraction Theory

Earth 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 Earth's mantle pushes the plates

movement of a fluid, caused by differences in temperature

According to this theory:

The plate 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.

Fossils

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 Earth's outer

layer is fragmented into plates that are in constant motion.

Plate Boundaries and Their Motions

Divergent Convergen

t Transform/

Thrust

Major Earth Movements

Uplift Subsidence

TRIVIA:Do you know that?On every continent there is a city called 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 StressTensional StressShear Stress

STRESS AND STRAINStrain is a change in size, shape, or volume of a material.Response to stress

3 BASIC TYPES OF STRAIN

Elastic StrainPlastic StrainFracture Strain

NOTE :

Stress can happen with out strain, but strain cannot happen without stress.

2 Major Types of Structural Deformation

Fault Fold

Fault rocks break due to force

4 types: Normal Fault Reverse Fault Strike-Slip Fault Thrust Fault

Fold Rocks bend due to force

Types of Fold: Symmetrical Folds Assymetrical Folds Isoclinal Folds Overturned Folds Recumbant Folds Chevron Folds

REPORTED BY: CLARISSE P. CACAPIT

Syncline youngest rocks 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 Strain rocks

recover to their original shape.

Plastic or Ductile Strain

Rocks do not return to their original shape.

Fracture or Brittle Strain rocks

crack or break under the stress.