Flashcards in Ch8 Deck (28):
What are Geologic Structures?
Structural Geology is the study of how rock bodies become deformed
-AND the study of the characteristics of mountain building processes, faults, folding, and shearing processes known as deformation.
a general term refers to the changes in the shape or position of a rock body in response to differential stress
used to describe the forces that deform rocks
often associated with convergent plate boundaries.
associated with divergent plate boundaries.
associated with transform boundaries
Types of Deformation
recoverable. When stress increases gradually, rocks initially respond by deforming elastically
rocks fracture of break when the strength of the rock is supposed (low temp, low pressure)
type of solids flow that produces a change in the shape of an object w/out fracturing. (high temp, high pressure)
the compass direction of the line produced by the intersection of an inclined rock layer or fault with a horizontal plane at the surface
the angle of inclination of the surface of the rock unit or fault from the horizontal plane. Dip includes both an angle of inclination and a direction towards which the rock is inclined
relative motion of rock units is primarily vertical
-normal faults: hanging wall moves down relative to hanging wall
-reverse fault: hanging wall moves up relative to the foot wall
dominent relative motion of rock units is horizontal; can be described as right-lateral fault or left-lateral fault
Geological structures: Fold
an imaginary plane that divides the fold as equally as possible into two halves
-two halves are called LIMBS
are tilted by tectonic forces that cause their hinge lines to slope downward.
-Downward folds, or concave folds
-youngest rock in the middle of the fold
Upward Folds or Convex Folds
Oldest rocks in the middle
The bearing (compass direction) measured in the direction that the axis is inclined downward
The angle between the fold axis and the horizontal. The outcrop pattern of an eroded plunging anticline “points” in the direction it is plunging. The opposite is true of a plunging syncline
Main Types of Fold
Overturned Folds(Fold that is titled so that one limb is upside down.)
Large, somewhat circular structures formed when strata are warped upward Oldest strata at the center of the dome.
Large somewhat circular structures formed when strata are warped downward Youngest strata at the center of the basin
a two dimensional representation of the location and attitudes of rock formations and contacts. Shows topography of the surface with contour lines.
Geologic Cross Sections
a drawing of a vertical slice through the Earth – a two dimensional cut-‐away view.
a combination of the geologic map and two cross sections – shows the relationship of what we see on the Earth’s surface and what is taking place below the Earth’s surface.