Unit 2. Internal energy and

landforms

TYPES OF BOUNDARIES AND LANDFORMS

Type of

boundary

Associated

landforms

Type of stress

on the rocks

Type of

deformations

Convergent

(destructive)

Ocean trenches,

mountain ranges,

island arcs

Compressional Rigid and fragile

rocks: reverse

faults, thrusts

Ductile rocks:

folds

Divergent

(constructive)

Ocean ridges,

continental rifts

Tensional Rigid and fragile

rocks: normal

faults

Transform

(passive)

Transform faults Shear Rigid and fragile

rocks: Transform

or tear faults

• It is the result of forces or stresses taking place in the

rocks. This result is always a change in the rocks shape,

size or relative position.

ROCK DEFORMATION

TYPES OF STRESS

• There are 3 types:

– Elastic: materials deform but return to their original

size and shape when the stress ends.

– Plastic o ductile: materials deform and do not return

to their original shape and size. It is a frequent

response of rocks in the crust and mantle where they

have surrounding conditions of high pressure and

high temperature.

– Fracture: materials break as a response to the

stress. It is a frequent response of rigid and fragile

rocks in the surface.

TYPES OF DEFORMATION

FACTORS THAT CONDITION THE TYPE OF ROCK

DEFORMATION

• Rock nature or composition. Example: clay and slate

are naturally ductile.

• Temperature

• Pressure

• Presence of fluids

• Stress length (duración del estrés)

Faults: they are fractures where the separated blocks of rock have displaced.

FRACTURE DEFORMATIONS: FAULTS (FALLAS).

PARTES DE UNA FALLA:

1. Bloque levantado. Upthrown block

2. Bloque hundido. Downthrown block

3. Plano de falla: superficie de fractura. Fault plane.

4. Salto de falla: longitud del desplazamiento entre los dos bloques.

Throw

1

4

3

2 5

¿What type of stresses have

generated these faults?

Classify these faults

A

B

C

A

B

C

TENSIONAL STRESS

(NORMAL FAULT)

COMPRESSIONAL STRESS

(REVERSE FAULT: FALLA

INVERSA)

SHEAR STRESS = ESFUERZO

DE CIZALLA

(TRANSFORM OR TEAR

FAULT = FALLA DE

DESGARRE)

Upthrown block = bloque levantado

Downthrown block = bloque hundido

Cabalgamiento

What type of stress is acting?

PLASTIC DEFORMATIONS:

FOLDS (PLIEGUES).

Compressional stress

ANTICLINE: fold that has the oldest materials in its core.

SYNCLINE: fold that has the newest materials in its core

CORE

CORE

OROGEN ORIGINS (=mountain ranges origin)

1) Subduction limits

2) Continental collision: Alpine-type orogens (continental – continental).

Few magmatism (subduction zone disappears) and a lot of metamorphism

(metamorphic rocks) and deformation (folds and normal faults at the end).

Presence of ophiolites (old ocean litosphere fragments) in the old boundary

between the two continents. Examples: Himalayas and Pyrenees.

3) Intermediate orogens (oceanic plate with orogens – continental). It is like

an Andean-type orogen but in the very edge of the continent an accretion

orogen is formed by the collision with terranes (island arcs that separate from

the oceanic litosphere). Example: The Rocky Mountains (North America).

4) Hot spots: Volcanic archipelagos. Fluid lava and less violent eruptions. Only

the island located above the hot spot is volcanically active. Examples: Canary

Islands or Hawaii archipelago.

• Island arcs (oceanic – oceanic). Volcanic. Viscous

magma and violent eruptions. Examples: Japan,

Indonesia.

• Andean-type orogens (oceanic – continental). Very

long mountain ranges which peaks are volcanos

(extinct or active). High risk of seismic and volcanic

activity. Abundant igneous rocks (from the

solidification of magma) and sedimentary rocks from

marine sediment (from the accretionary prism).

Example: Andes

The relief and landforms that contains are the result of the balance between the

internal geological processes, that construct them, and the external geological

processes, that model them.

HOW IS THE RELIEF MADE?

1) Internal geological processes (earthquakes, volcanos, mountain ranges,

etc.)

2) External geological processes (weathering, erosion, transport and

sedimentation)

AMPLIACIÓN

Indicar qué tipo de deformaciones, elástica,

plástica o por rotura, han sufrido las rocas

de las fotografías.

A

B

C

D

ESTRATOS

PLEGADOS

FRACTURAS

(diaclasas = joints)

Estrato 1

Estrato 3

Estrato 2

FRACTURA DEL TERRENO EN LA QUE UN BLOQUE

HA BAJADO RESPECTO A OTRO (FALLA)

What type of fault is it? Which is the downthrown block?

LÁMINAS DE ROCA PLEGADAS

Las rocas de la imagen son cuarcitas

plegadas.

¿Cómo se puede explicar que una roca

tan rígida se haya deformado plásticamente?