structural geology (fault)(2)

                                                                   FAULT

It is a plane of weakness developed in rock bodies due to tensional forces along which relative movement of the beds or lava flow takes place is called fault.

·        Fractures are passive consequence of the tectonic forces without any movement of beds or lava flows is called Fracture.

·        Parts of Fault

1.     The plane along which movement has taken place is called Fault plane

2.     Strike of Fault – It is direction of line form by the intersection of fault plane with horizontal

3.     Dip of Fault – It is angle made by fault plane with Horizontal

4.     Hade of Fault – It is angle made by fault plane with vertical

5.     Throw of Fault – The vertical displacement of beds is called throw of the fault

6.     Heave of Fault – It is Horizontal displacement of beds is called Heave of fault

7.     Up throw side – side which is thrown upward

8.     Down throw side- side which is thrown downward

9.     Hanging wall – The block above the                                                                            Foot wall – The block below the fault plane.

ABCD = fault plane

FW = foot wall

HW = Hanging wall

AC = fault plane

D = Dip of fault

AO = Throw of fault

OC = Heave of fault

Q = Hade of fault

Types of faults

A)  Based on Attitude of fault plane

a   Vertical fault – if fault plane is vertical

bInclined fault – if fault plane is oblique

     Strike fault – if fault plane is parallel to strike of beds

d    Dip fault – if fault plane is parallel to dip of beds

B)    

C)   Based on Angle Fault Plane

a    High angle fault

    Low angle fault

D)  Based on apparent movement

a   Normal Fault

It is inclined fault

Fault plane is steep

Due to tensional forces.

HW has gone as compared F.W.

Dip a fault plane is in the same

 direction as down throw side

  Reverse Fault

It is Inclined fault

Fault plane is gently dipping

Due to strong lateral compressive forces

HW has gone up as compared to F.W.

Dip of fault plane is an opposite

direction that of the down throw of fault

E)   Based on Gravity

a    Horst or Ridge fault

·        Two parallel fault

·        Central block thrown up

·        Topographic elevation (Ridge)

b)  Graben or Trough fault (Rift valley)

·        Central block goes down

·        Topographic depression

·        Formation of Rift valley

       

Based on fault pattern

a)     Parallel fault – A series of fault having same dip & strike

b)    Step fault – step like appearance

c)     Radial fault – Radiating Pattern

d)    Peripheral fault – curved fault

e)     Over thrust fault – due to strong lateral compressive forces acting on one direction

Structural Geology (1)Folds

FOLDS

Folds are the undulations in the rocks.  They are best displayed in stratified formation.

Folds May originate in many ways

1.     Horizontal Compression

2.     Horizontal Couple

3.     Convection Currents

4.     Intrusion of viscous magma

5.     Differential compaction of sediments.

6.     Chemical changes

7.     Contemporaneous deformation

8.     Ice push

Parts of the Folds –

1.     Limbs – Sides of the  fold

2.     Core – Central part of the fold

3.     Crest – Highest point of the fold

4.     Trough – Lowest point of the fold

5.     Crestal Line – The line passing through highest point of fold

6.     Trough line – The line passing through lowest pt. of fold

7.     Crestal plane – The plane passing through crest lines

8.     Trough planes- The plane passing through trough lines

9.     Amplitudes – The maxi displacement of beds in one direction

10.Wavelength – Distance between two successive crest or two successive          

11.Axis of fold – It is the line on a folded bedding plane along which the  

12. direction of dip changes is called axis of fold or Hinge line or Axial line

13.Axial plane- It is the plane containing axes of all  bedding plane.

Types of Folds

01-                                                                   Anticline Fold –

·        Convex upward

·        Limbs dip away from each other

·        Older beds occurs at core

02-                                                                   Syncline Fold –

·         Concave upward

·        Limbs dip towards each other

·        Younger beds occurs at core

03-                                                                   Isoclinals Fold-

·        Due to strong lateral compressive

·        forces acting from one side

·        Both limb dips in the same direction

 

04-                                                                   Symmetrical fold

·        Axial plane is vertical

·        Limbs dip in opposite dir

·        The amt of dip is same

·        Distance of limb from axial plane is equal.

05-                                                                   Asymmetrical Fold

·        Axial plane is inclined

·        Limbs dip in opposite dir with different amt of dip

·        One limb is steeper than the other

·        Distance of the limb from axial plane is not same.

06-                                                                   Recumbent Fold-

·        Axial plane is horizontal

·        One of the limb is turned through 180^o approx.

·        Both limbs Horizontal

·        The beds in over turned limb are much thicker than normal limb

·        Many sec. fold in normal are called digitations

The curve linear portion joining the normal limb to overturned limb is called  arch bent.

07-                                                                   Chevron Fold

·        Hinges are sharp & angular

08-                                                                   Box Fold

·        Crest and trough are b road & f lat

09-                                                                   Mono cline Fold

·         

·        Beds are relatively that but appear to haven been bent locally to exhibit higher dip localized change in their attitude.

                                                                                                                                               

10-                                                                   Fan fold – Both Limbs are over turned\

11-                                                                   Closed or tight fold – Thin at crest or trough

structural geology

Structural Geology

             It deals with large scale features of rock masses such as their size, shape and their attitude in space.

Outcrop – Portions of the rock formation which are exposed at the surface (Exposure)

Outlier – It is an outcrop of younger bed surrounding on all sides by older beds.

          E.g. Isolated hill (because of erosion)                                               

Inliers – It is an outcrop of older beds surrounding on all sides of younger beds.(valley)

Bedding Plane – 1) Two Successive beds are separated from each other by plane surface which                                                        . is called a bedding plane

2) Beds are two type a) Horizontal bed (If attitude is not disturbed no strike and dip) b) Inclined bed (If attitude is distributed due to uplift).

Dip – The angle that a bed makes with the horizontal is called its dip or amount of Dip. And the direction in which its dips is called dip direction

The max angle of Dip is true dip of beds.   If  dip seen in any other direction  is called apparent dip.Apparent dip is always less than true dip

Amt. of dip of any beds can be found out by direct. Measurement  in the field by means of clinometers (If suitable exposure is available).

Strike –    If a horizontal.  line  is drawn on inclined bedding plane it will run in direction at right angle to the dip direction is called strike.

Conformable bed – When deposition goes on uninterruptedly at a site a sequence beds will be formed all of which will have same strike and dip are called conformable beds and series of beds are called conformable series of beds.

The Vertical distance between the top and bottom of a bed is called its vertical thickness. And perpendicular distance between the two  its   is True thickness.

A bed will have a definite thickness only when it is bounded by two bedding plane.