Inuksuk - Nunavut, Canada Geneviève Hsueh TELLING TIME GEOLOGICALLY GEOLOGIC TIME SCALE Organizes...

Inuksuk - Nunavut, Canada

Geneviève Hsueh

TELLING TIME GEOLOGICALLY

GEOLOGIC TIME SCALE

Organizes all of Earth history into blocks of timeutilizing significant geologic events.

Preliminary subdivisions were done in the 18th and 19th centuries using relative dating techniques.

20th century allowed determination of numerical ages.Used all the numerical dating techniques to do this.

TELLING TIME GEOLOGICALLY

GEOLOGIC TIME SCALE

Subdivisions of Time

EonsEras

PeriodsEpochs

None last equal intervals oftime.

Based on events.

FOLDS, FAULTS & MOUNTAIN BELTS

Mountains and earthquakes illustrate the energy andpower of plate tectonics.

Produces large mountain ranges such as the Rockies,Alps, Himalaya and Appalachians.

We also observe rocks that have been bent or folded.Focus on the geologic processes that deform the

Earth’s crust = STRUCTURAL GEOLOGY.


Mt. Everest

Long’s Peak, CO


STRESSING AND STRAINING ROCKS

Plate movement applies powerful forces to rocks.Converging, diverging and sliding rocks subject their

margins to powerful stresses.STRESS is the force applied to a rock.If rocks are stressed enough, they will DEFORM.DEFORMATION alters the shape and/or volume of

the rocks.This change is called STRAIN.


STRESSING AND STRAINING ROCKSRocks can be stressed in three ways.1. TENSIONAL STRESS

Occurs at divergent plate boundaries.Thins crust vertically and lengthens crust laterally.


STRESSING AND STRAINING ROCKS2. COMPRESSIONAL STRESS

Occurs at convergent plate boundaries.Crumples rock, thickens rock vertically and shortens rock laterally.

FOLDS, FAULTS & MOUNTAIN BELTSFOLDS, FAULTS & MOUNTAIN BELTS

STRESSING AND STRAINING ROCKS

3. SHEAR STRESSOccurs at transform boundaries.Rocks forced past each other in parallel, but opposite directions.


TYPES OF DEFORMATION

ELASTIC DEFORMATION

STRESS is applied, released and rock returns tooriginal shape and volume.

Material is not DEFORMED.If stressed to a point where the material doesn’t resume

original shape and volume, the rock is deformed.Point at which this occurs is the ELASTIC LIMIT.

Pressure and temperature when stress is applied alsodetermine how rocks deform at the elastic limit.



ELASTIC DEFORMATION

Rocks subjected to stress at LOW temperature and LOW pressure tend to BREAK.

Causes the bonds between atoms to break.

Breaking in rocks is called BRITTLE FAILURE.



PLASTIC or DUCTILE DEFORMATION

Rocks subjected to stress at HIGH temperature and HIGH pressure tend to BEND, resulting fromPLASTIC or DUCTILE DEFORMATION.

An irreversible change in shape and/or volume occurswithout the rock breaking.

Rocks go beyond the elastic limit.Atoms move about and adjust without the bonds

breaking.Atoms move from areas of high stress to those with

low stress.


FACTORS AFFECTING ROCK DEFORMATION

1. HeatWeakens bonds within minerals.

2. TimeWith enough time plastic deformation occurs.Rapid stress causes breakage.

3. CompositionMineralogy of rocks affect how rocks respond to

stress (calcite, mica weak; garnet, qtz strong).Water is another compositional factor.

Increased H2O content > plastic deformation


FOLDS

Rocks bend and flow when deformed plastically.Produces FOLDS.FOLDS are typically associated with compression.FOLDS are found in metamorphic rocks and wet, clay-

rich sedimentary rocks and sediments at or nearthe Earth’s surface.


ANTICLINES AND SYNCLINES

An ANTICLINE is an inverted bowl-shaped structure formed when sedimentary rock layers are folded to produce an arch or elongated dome. The stratigraphically olderrocks are located at the center of the anticline.


ANTICLINES AND SYNCLINES

A SYNCLINE is a trough- or bowl-shaped fold in which the youngest rock forms the core and the limbs dip toward the axis.


FOLD SYMMETRY

SYMMETRICAL FOLDS To be symmetrical, the limbs of the fold must dip at

the same angle away from the fold axis.


FOLD SYMMETRY

ASYMMETIRCAL FOLDSTo be asymmetrical, the limbs of the fold must dip at

the different angles away from the fold axis.


FOLD SYMMETRY

If the limbs of a fold are rotated past vertical, anOVERTURNED FOLD exists.


FOLD SYMMETRYIf the axial plane tilts to near horizontal or horizontally,

a RECUMBENT FOLD exists.


FOLD SYMMETRYIf the axis of the fold is tilted beyond horizontal, a

PLUNGING FOLD exists.


DOMES AND BASINSA DOME is a doubly plunging anticline.


DOMES AND BASINSA BASIN is a doubly plunging syncline.


FAULTS

Rocks are brittle at low temperatures and lowlithostatic pressures.

Some stresses from tectonic forces break rocks.Brittle failure is observed in rocks as FRACTURES.Rocks with fractures along which there is no movement

are called JOINTS.Fractures along which movement has occurred are

called FAULTS.


FAULTS

JOINT FAULT


FAULTS

Rock masses or FAULT BLOCKS along either side ofthe fracture have moved relative to each other.

Usually there is displacement of layers on either side of the fault.


FAULTS

Faults may look like lines on a rock surface, butactually represent planes.Called FAULT PLANE.


TYPES OF FAULTS

All faults result from motion between adjacent blocks.Either or both blocks SLIP, relative to their original

position.Each type of stress (compression, tension and shear)

will produce a unique type of fault.

Determine what type of fault you are observing andyou will know what type of stress produced it.


TYPES OF FAULTS

STRIKE-SLIP FAULTS

Produced by horizontal slip of adjacent blocks.Movement is parallel to the fault plane.Produced by horizontal shear stresses.Occur at transform plate boundaries.


TYPES OF FAULTS

STRIKE-SLIP FAULTS

The most famous strike-slip fault is the San Andreas.


TYPES OF FAULTS

STRIKE-SLIP FAULTSSan Andreas Fault in 1906 earthquake moved 7 m in

several seconds.Parts creep along daily with little movement and little

damage.Others move less often, but with large displacement.Surface expression may produce long linear features,

ridges or depressions.

Inuksuk - Nunavut, Canada Geneviève Hsueh TELLING TIME GEOLOGICALLY GEOLOGIC TIME SCALE Organizes...

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