Institute of Geology

Presentation BY:“Azhar Mahmood”

Topic:

Study of deform rocks, Folds And Its Types

1: What do deform rock look like ?2:How do rock deform?3:How do we know …. Why some rocks break and other flows ?

4:How are resources related to geological structures?

5:How do gelogical structure relate to stress,strain and strenght?

•Why study of deform rocks??

• Describe the orientation of rock tilted or dipping bed .• Describe folded rocks • Limbs: The two dipping side of the folds is called limb.• Hing line: Where the dipping limbs join.• Plunging fold: When the hing line plungs downward into the ground.Anticline: Limbs dip away from hing line.Syncline: Limbs dip in towards hing line.

What do deform rock look like ?

Particular rocks deform depend upon …

1:Its temperature amd depth2:The amount ,rate and direction of the stress

3:And the quantity of water in the rock

•How do roks deform?

• Some rocks are strong and other are not• Some behave britly while other behave plastically• With increasing deapth,temprature and confining pressure

decreases brittle fracture and increase plastic flow• Fault and joints are thus expected near the surface,while plastic

flow should occur at deapth • Some few weak material flow under less extreme conditions

such as rock salt and glassier ice

•How do we know …. Why some rocks break and other flows ?

• Oil gas and ground water all move through pores and all three have different densities that came them to stratify.The lighter oil and gas will tend to migrate upward and leak out to the surfaces,If no layer stop them from doing so .• Metal rich mineral resources commonly form along

joints and faults where warm fluid with hig concentration of metal ions flow and cool to precipate these metallic minerals

•How are resouces realted to geological structures?

•How do geological structres relate to stress,strain and strength?

Deformation by tension results in the lengthening of the land scape such as in the basin And the deformation by compression can fold or fracturebut results in a shorting of land scape

•Stress :

•The force that act on the rock unit to change its shape and its volume •And stress causes strain and deformation

•STRAIN

Change in shape or size of an object in response to an applied stress.

= Deformation

Three Types of Strain

Elastic

Ductile (Plastic)

Brittle (Rupture)

•Elastic Deformation

a temporary change in shape or size that is recovered when the

applied stress is removed.

•Ductile (Plastic) Deformation

• A permanent change in shape or size that is not recovered when

the stress is removed.

• i.e. it flows or bends

•Brittle Deformation

(rupture)• the loss of cohesion of a body under the influence of deforming

stress.

• i.e. “it breaks”

•Objectives of deformation• Observe and describe the deformation visible at earth

surface • Understand the relationship between deformation and

the foces that drive it • Learn the causes and effects of eath quakes • Understand the relationship between earth resources

and the rock deformation

Types of Fold

o Fold: folds are bending of rocks due to different forces

Hormonic folding is where the number and positions of folds in successive surfaces broadly match.

Harmonic Fold

Disharmonic Folds

Folding where the number and positions of folds is successive surfaces does not broadly match.

Anticline & Syncline

. The word anticline is from Greek meaning “opposite or inclined” ,the older rock are in the center(core)and the limbs dip away from each other.

--------------------------The word is from the Greek meaning “together inclined” ,The younger rock are in the center(core)the limbs dip toward each other

Symmetrical Fold

A symmetrical fold is one in which the axial surface essentially vertical. The term up write is also used or symmetrical fold is one that no limb is steeper than the other.

Asymmetrical Fold

If one limb of the fold is steeper than the other it is called asymmetrical fold.

Monocline Fold

A simple fold with only dipping limb is called a monocline

Recumbent Fold

A recumbent fold is one in which

the axial plane is horizantal or axial

plane is sub horizantal. These folds are present

when the deformation is

intense and one fold lie on the top of next fold, so that axial plane becomes sub horizantal or

horizantal

Isoclinal Fold

In isoclinal fold, from the Greek meaning “Equally inclined” refer to folds in which the two limbs dip at equal angle in the same direction.

Box Fold

A box fold is one in which the crust is broad and flat; two hinges are present , one either side of the flat crust.

Shevron Fold

A shevron fold is one in which the hinges are sharp and angular.

Infered fold

Folds larger than an outcrop are based on inference. More over, the part of the fold that was above the present surface of the earth has been removed by erosion.

Drag Fold

Drag folds form when a competent(Strong) bed slides passed and incompetent(weak) bed. such minner folds may formed on the limbs of larger folds because of the slipping of beds passed each other, or they may develop beneath over thurst blocks, The axial planes of the drag folds are not perpendicular to the bedding of the competent strata, but are inclined at an angle.

Fan Fold

A fan fold is one , in which both limbs are overturned. In the anticlinal fan fold , the two limbs dip towards each other; in the synclinal fan fold the two limbs dip away from each other.

Field Identification

Direct observation of fold in Field

The easiest and most satisfactory method is to observe folds, but this can be done in comparatively few regions. Folds may be deduced from other data, and are relatively minner features associated with much larger folds. Where ever small folds are observed in single out crop it is desirable to record their attitude. To do this one must measure the attitude of hinges and attitude of the axial planes. The pattern shown by minner folds in plane should also be recorded as it is of great use, in conjunction with the plunge of fold s in deducing larger structures. In larger folds that can not be observed in a single out crop or in series of closely adjacent outcrop, the attitude of axial plane and the hinges can not be measured directly, nevertheless the same principles apply and geologist should always think a fold 3 dimension.

Thank You