Faults fold and deformation

Hanging wall or headwall moves down in relationship to the foot wall in a normal fault.

Normal Fault

Result from compressional forces where rocks are pushed upward.

Reverse Fault

Factor of how rock material behaves

Temperature and Confining pressure

Folds can:

Occur together

Plunging folds dip between

10° to 80°

Complex fold situations

upright meaning that their axial planes are vertical and both sides dip at the same angle.

Strike and dip

used to describe the orientation of rock layers

Factors influencing mass wasting

vegetation cover

What factors influence mass wasting part 3

water content

Compressive

Creates folds, reverse & thrust faults

Tensional

Creates normal faults

Shear

Creates strike-slip faults and oblique

Most famous Strike-Slip fault

The San Andreas

what factors influence mass wasting part 2

Weathering and climate

Folded rock layers

When compressed, rock layers deform into folds because the rocks have entered plastic strain or deformation.

Recumbent Folds

When deformation is so extreme that axial planes of folds have become horizontal, this creates a special overturned fold called a recumbent fold.

all faults caused by

compression

mass wasting more common in

loose or poorly consolidated material than in bedrock because it breaks apart more easily

ConfiningPressure

lower confining pressure allows materials to be brittle and fracture sooner.

in humid areas, weathering is deeper and produces tens of meters of unconsolidated material which leads to increased

mass wasting

faults

a fracture along which rocks on opposite sides of the fracture have moved parallel with the fracture surface

How do we figure out Strike

a long line oriented parallel to the compass direction of the rock layer

How do we figure out Dip

a short tick mark is placed in the center of the line on the side to which the inclined layer

oldest in the middle

anticline

water content in mass wasting

may increase the weight of a slope to induce failure reduces the amount of friction between particles clay particle are platy and slide easily past one another

Geologic Structure Joints:

often associated with folding events.

Dynamic Forces

plate boundaries cause fracturing, folding, metamorphism, and igneous activity.

All rock layers dip towards the axis in

plunging synclines

Plunging fold

refers to how a fold looks when they appear to dive or underneath adjacent rocks.

Monocline

represents a simple bend or flexure in otherwise horizontal or uniformly dipping rock layers.

Syncline

represents an downward arched fold with the youngest rock layers in its core.

Anticline

represents an upward fold with the oldest rock layers in its core.

Faults Cause:

rock layers to break, bend, fold, etc.

What can extreme stress and pressure cause

rocks to shear along a plane of weakness creating a fault.

Fracture:

Irreversible strain causing rock to break or faults to form.

How rock folds are formed

1. type of stress applied to rock 2. temperature of rock 3. pressure under which the rock is deformed 4. type of rock being deformed

Vertical folds dip between

81° to 90°

Youngest rockas at the folds center

Basin

are inclined meaning they have different angles on either side of the fold.

Complex folds

Why are joints different:

Do not have any significant offset or rock layers either vertically or horizontally

Oldest rocks at the folds center

Dome

Unlike an anticline, all the folded rock layers dip outward from a central point as opposed from a line in an anticline

Domes

Parallel lines are NOT

Faults

On a large scale these features are known as rift valleys.

Graben Fault

Produced when tensional stresses result in the subsidence of a block of rock

Graben Fault

What is the new fault

Graben Fault

Grand monocline

Grand canyon

Produced by the development of two reverse faults causing a major block of rock to be pushed upward.

Horst Fault

new fault

Horst Fault

More ways that deformation causes rocks to change their shape

Joints, folds, domes, basins

What are the three groups of folds

Monocline, Anticline, Syncline

Result of tensional forces (pulling apart of rocks).

Normal Fault

The hanging wall or head wall moves down in relation to the foot wall

Normal Fault

Major Groups of faults

Normal ► Reverse ► Thrust ► Strike-Slip► Oblique-Slip

Both walls move outward and pull apart.

Oblique-slip fault

Caused by a combination of shearing and tension of compressional forces.

Oblique-slip fault

Combination of upward and downward movement of the headwall and footwall.

Oblique-slip fault

Vertical movement roughly matches horizontal movement along fault plane.

Oblique-slip fault

All rock layers dip away from the fold axis in

Plunging anticlines

Headwall moves up in relationship to the footwall in a reverse fault due to compression.

Reverse Fault

The headwall has moved upward in relation to the foot wall.

Reverse Fault

Geologic Structures Domes:

Rock layers dip away from the center with the rocks getting older from the outside in

Geologic structures:Basins

Rock layers dip towards the center with the youngest rocks at the fold's center.

Ductile Deformation

Strain is irreversible causing folds to form.

Fault blocks move side ways from one another instead of up or down.

Strike-Slip faults

All movement is in the direction of the fault plane's strike.

Strike-slip faults

Caused by right lateral or left lateral depending on the apparent direction of offset.

Strike-slip faults

Formed by shearing forces.

Strike-slip faults

Relative motion of fault is along a horizontal plane not a vertical plane.

Strike-slip faults

Complex Folds:

Symmetrical, Asymmetrical, isoclinal, overturned, recumbent, chevron

Looks like the head wall thrusts over the foot wall.

Thrust fault

less than or equal to 45 degrees.

Thrust fault

Why do geologist measure the orientation of rock layers

To describe the type of folding that has occurred

What is a rock deformation?

defined as a change in the shape or volume of rocks and is caused by: Dynamic Forces

Geologic Structures Joints:

distinctively different from faults

When a rock is subjected to increasing stress:

either deforms or breaks

Geologic Structures Joints:

fractures with no displacement of rock.

Geologic Structure Joints:

generally planar fracture formed in a rock as a result of stress applied to the rock.

Headwall

is above the fault plane.

Headwall moving upward

is always compression

Footwall moving upward

is always tension

Orientation of rock layers: Dip

is the angle between a horizontal plane & the inclined plane and is measured perpendicular to the direction of strike

Dip

is the angle that the bed makes with horizontal, measured in the vertical plane, in the direction perpendicular to the strike.

Orientation of rock layers: strike

is the compass direction of any horizontal line formed on the rock plane

Stress

is the force applied to a body of rock or crust.

Strike

is the orientation of the line of intersection between the horizontal plane and the rock bed.

Strain

is the resulting deformation that occurs to the rock.

Footwall

lies below the fault plane.

Overturned folds

limbs dip in the same direction, That means one side has been rotated 90 degrees from its original position and it is now upside-down.

Fold center

syncline

Forms a downward bending arch

syncline

youngest layer is in the core of the fold

syncline

Temperature

temperatures stretch the bonds of mineral molecules causing them to be more ductile.

Normal Faults Caused by

tension

Differenital Stress

tension, compression, Shearing

How are faults formed

tensional or compressive or shearing stress.

What does Strike measure

the "direction" of the rock in relationship to north

mass wasting

the downslope movement of material under the direct influence of gravity varies by geologic factors

Factors influencing mass wasting

the steepest angle that a slop can maintain without failure is the angle of repose

What does Dip measure

the steepness or angle of the rock layer .