Inuksuk - Nunavut, Canada
Geneviève Hsueh
TELLING TIME GEOLOGICALLY
GEOLOGIC TIME SCALE
Organizes all of Earth history into blocks of time
utilizing 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
Eons
Eras
Periods
Epochs
None last equal intervals of
time.
Based on events.
FOLDS, FAULTS & MOUNTAIN BELTS
Mountains and earthquakes illustrate the energy and
power 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.
FOLDS, FAULTS & MOUNTAIN BELTS
Mt. Everest
Long’s Peak, CO
FOLDS, FAULTS & MOUNTAIN BELTS
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.
FOLDS, FAULTS & MOUNTAIN BELTS
STRESSING AND STRAINING ROCKS
Rocks can be stressed in three ways.
1. TENSIONAL STRESS
Occurs at divergent plate boundaries.
Thins crust vertically and lengthens crust laterally.
FOLDS, FAULTS & MOUNTAIN BELTS
STRESSING AND STRAINING ROCKS
2. COMPRESSIONAL STRESS
Occurs at convergent plate boundaries.
Crumples rock, thickens rock vertically and
shortens rock laterally.
FOLDS, FAULTS & MOUNTAIN BELTS
STRESSING AND STRAINING ROCKS
3. SHEAR STRESS
Occurs at transform boundaries.
Rocks forced past each other in parallel, but
opposite directions.
FOLDS, FAULTS & MOUNTAIN BELTS
TYPES OF DEFORMATION
ELASTIC DEFORMATION
STRESS is applied, released and rock returns to
original 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 also
determine how rocks deform at the elastic limit.
FOLDS, FAULTS & MOUNTAIN BELTS
TYPES OF DEFORMATION
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.
FOLDS, FAULTS & MOUNTAIN BELTS
TYPES OF DEFORMATION
PLASTIC or DUCTILE DEFORMATION
Rocks subjected to stress at HIGH temperature and
HIGH pressure tend to BEND, resulting from
PLASTIC or DUCTILE DEFORMATION.
An irreversible change in shape and/or volume occurs
without 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.
FOLDS, FAULTS & MOUNTAIN BELTS
TYPES OF DEFORMATION
FOLDS, FAULTS & MOUNTAIN BELTS
FACTORS AFFECTING ROCK DEFORMATION
1. Heat
Weakens bonds within minerals.
2. Time
With enough time plastic deformation occurs.
Rapid stress causes breakage.
3. Composition
Mineralogy 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, FAULTS & MOUNTAIN BELTS
FOLDS
Rocks bend and flow when deformed plastically.
Produces FOLDS.
FOLDS are typically associated with compression.
FOLDS are found in metamorphic rocks and wet, clayrich sedimentary rocks and sediments at or near
the Earth’s surface.
FOLDS, FAULTS & MOUNTAIN BELTS
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 older
rocks are located at the center of the anticline.
FOLDS, FAULTS & MOUNTAIN BELTS
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.
FOLDS, FAULTS & MOUNTAIN BELTS
FOLD SYMMETRY
SYMMETRICAL FOLDS
To be symmetrical, the limbs of the fold must dip at
the same angle away from the fold axis.
FOLDS, FAULTS & MOUNTAIN BELTS
FOLD SYMMETRY
ASYMMETIRCAL FOLDS
To be asymmetrical, the limbs of the fold must dip at
the different angles away from the fold axis.
FOLDS, FAULTS & MOUNTAIN BELTS
FOLD SYMMETRY
If the limbs of a fold are rotated past vertical, an
OVERTURNED FOLD exists.
FOLDS, FAULTS & MOUNTAIN BELTS
FOLD SYMMETRY
If the axial plane tilts to near horizontal or horizontally,
a RECUMBENT FOLD exists.
FOLDS, FAULTS & MOUNTAIN BELTS
FOLD SYMMETRY
If the axis of the fold is tilted beyond horizontal, a
PLUNGING FOLD exists.
FOLDS, FAULTS & MOUNTAIN BELTS
DOMES AND BASINS
A DOME is a doubly plunging anticline.
FOLDS, FAULTS & MOUNTAIN BELTS
DOMES AND BASINS
A BASIN is a doubly plunging syncline.
FOLDS, FAULTS & MOUNTAIN BELTS
FAULTS
Rocks are brittle at low temperatures and low
lithostatic 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.
FOLDS, FAULTS & MOUNTAIN BELTS
FAULTS
JOINT
FAULT
FOLDS, FAULTS & MOUNTAIN BELTS
FAULTS
Rock masses or FAULT BLOCKS along either side of
the fracture have moved relative to each other.
Usually there is displacement of layers on either side of
the fault.
FOLDS, FAULTS & MOUNTAIN BELTS
FAULTS
Faults may look like lines on a rock surface, but
actually represent planes.
Called FAULT PLANE.
FOLDS, FAULTS & MOUNTAIN BELTS
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 and
you will know what type of stress produced it.
FOLDS, FAULTS & MOUNTAIN BELTS
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.
FOLDS, FAULTS & MOUNTAIN BELTS
TYPES OF FAULTS
STRIKE-SLIP FAULTS
The most famous strike-slip fault is the San Andreas.
FOLDS, FAULTS & MOUNTAIN BELTS
TYPES OF FAULTS
STRIKE-SLIP FAULTS
San 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.