Mountain Building

FOLDS FAULTS

• Orogenesis: Processes that produces a

mountain belt.

• Deformation: all changes in the original

shape and/or size of a rock body.

Rock Deformation

Stress is the force

per unit area acting

on a solid.

Strain: The change

in shape or volume

of a body of rock as

a result of stress.

Factors effecting rock deformation

1. Temperature and Pressure

- Ductile deformation - produces a change in the

size and shape of an object without fracturing

the object.

- Brittle deformation - fracturing of an object

once its strength is exceeded.

2. Rock Type

• Mineral composition and texture of a rock also

greatly affect how it will deform.

3. Time

• Forces that are unable to deform rock when first

applied may cause rock to flow if the force is

maintained over a long period of time.

Rock Deformation Stresses The three types of stresses

Tensional

Compressional

Shear

Divergent boundaries

Convergent boundaries

Transform boundaries

FOLDS

1. Anticlines are

most commonly

formed by the

upfolding, or

arching, of rock

layers.

2. Synclines

are linear

downfolds in

sedimentary

strata.

FOLDS

3. Monoclines are large step-like folds in otherwise horizontal

sedimentary strata.

Four Types of Faults

1. Normal faults - hanging wall block

moves down relative to the footwall

block.

2. Reverse faults - hanging wall block

moves up relative to the footwall block.

3. Thrust faults - reverse faults with dips

less than 45o.

4. Strike-slip faults - movement is horizontal

and parallel to the trend, or strike, of the

fault surface.

NORMAL FAULT

Types of Faults and Stress

• Normal Fault: hanging wall moves down;

TENSION.

• Reverse Fault: hanging wall moves

up;COMPRESIONAL.

• Thrust Fault: Reverse faults that dip

greater then 45*; COMPRESIONAL.

• Strike Slip Fault: movement is horizontal

to strike of the fault; STRIKE—SLIP.

Joints

• Joints are

fractures along

which no

appreciable

movement has

occurred.

Types of Mountains

1- Folded Mountains - Mountains

that are formed primarily by folding

Mountains are classified by the dominant processes

that have formed them.

2- Fault-block mountains are

formed as large blocks of

crust are uplifted and tilted

along normal faults.

3 - Grabens are formed by

the downward displacement

of fault-bounded blocks. 4 - Horsts are elongated, uplifted

blocks of crust bounded by faults.

Types of Mountains

• Uplifted

mountains - circular or elongated

structures formed by

uplifting of the

underlying basement

rock.

Domes and Basins -

upwarping produces

a circular or elongated

structure

Mountain Formation Most mountain building occurs at convergent plate boundaries.

Colliding plates provide the compressional forces that fold,

fault, and metamorphose the thick layers of sediments

deposited at the edges of landmasses.

Ocean-Ocean Convergence

produces volcanic mountains.

Ocean-Continental Convergence

produce volcanic mountains and folded mountains.

Continental-Continental Convergence

collision between the continental

fragments will result and form folded mountains.

Divergent boundary

fault-block type mountains

Mountain Building by

Continental Accretion

Continental

Accretion -

process that

occurs when

crustal fragments

collide with and

stay connected to

a continental plate

Terranes - any

crustal

fragments that

have a geologic

history distinct

from that of the

adjoining

fragments.

Mountain Formation Not all mountains are formed by plate

boundaries. Some are formed by hot spots

or regional extension or stretching.

Isostatic Adjustment •Isostasy is the concept that Earth’s crust is floating in

gravitational balance upon the material of the mantle.