Presentation on theme: "Inuksuk - Nunavut, Canada Geneviève Hsueh TELLING TIME GEOLOGICALLY GEOLOGIC TIME SCALE Organizes all of Earth history into blocks of time utilizing."— Presentation transcript:
Inuksuk - Nunavut, Canada
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 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 H 2 O 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, clay- rich 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 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.