GEOL 1303 EXAM 2

Weathering

The physical breakdown and chemical alteration of rock at the earths surface

Mass Wasting

The transfer of rock and soul downslope under the influence of gravity

Erosion

The physical removal of material by mobile agents such as water wind or ice

Mechanical Weathering

Physical forces break rocks into smaller pieces without altering rocks mineral composition

Chemical Weathering

Chemical transformation of rock into one or more new compounds

Rates of weather are controlled by….

Mineral Composition, Climate, Particle size

Beds

Graded bedding

Cross bedding

Ripple Bedding

Mudcracks

Depositions environments

Places where sediments accumulate

Metamorphism

The solid-state change in composition and/or texture of a rock due to high temperatures

Agents of metamorphism

Heat, Pressure, Fluids

Contact metamorphism

Changes caused by the high temperature of an intruding magma, which can “bake” the surrounding rock. The baked zone is called the metamorphic areole

Regional metamorphism

Changes caused by the high temperatures and deviatoric stresses associated with mountain building

Hydrothermal metamorphism

Changes caused by the interaction with hot, ion rich fluids

Confining stress

Equal forces acting on all sides of an object

Stress

Force per unit area

Differential stress

Unequal forces acting on an object. Deformation is caused by differential stress

Shield volcano

-gentle sides

-produced by divergent plate boundaries

-can be huge

-long duration of activity

Cinder cone

Formed mainly of basaltic pyroclastic material

-steep sides

-produced by divergent plate boundaries

-relatively small

-short lived

Viscosity is mainly controlled by…

• composition

• Dissolved gasses

• Temperature

Pressure

• high pressure = ductile deformation

• Low pressure = brittle deformation

The wetter and hotter the climate the greater role of…

Chemical weathering

The colder and dryer the climate the greater the role of…

Mechanical weathering

Chemical sedimentary rocks

• Limestone

• Chert

• Coal

• Evaporites

Metamorphic facies

An assemblage of minerals in a metamorphic rock indicative of a range of pressure and temperature conditions experienced during metamorphism

Temperature

• High temperature: ductile deformation

• Low temp: brittle deformation

Strain rate

• high strain rate: brittle deformation

• Low strain rate: ductile deformation

Viscosity

A measure of a magmas resistance to flow

Low viscosity

Magma flows easily

High viscosity

Magma doesn’t flow easily

Composite Volcano (stratovolcqnoes)

• mainly alternating pyroclastic deposits and andesitic lava flows

• Usually produced by convergent plate boundaries

• Relatively large

• Eruptions often highly explosive

Lava dome

A steel sided dome of highly viscous congealed lava

Calderas

Large circular depressions

Joints

Fractures are produced by these tectonic stresses

Principle of Superposition

In an unreformed sequence of layered rocks the oldest rocks are at the bottom and the youngest are at the top

Principle of original horizontality

Stratified rocks are assumed to have been originally horizontal

any deviation from horizontality would then be the result of post deposition deformation

Principle of cross cutting relationships

Younger features cut across older features