Deformation

Created by

Mia Tabitha

Cards (57)

what are the two scales in which deformation takes place on?
spatial and temporal
how does deformation vary in spatial scale?
from atomic scale in single crystals to regional scale in mountain belts
how does deformation vary in temporal scales?
from seconds to minutes during seismic episodes to millions of years for mountain building
what are the two broad types of forces which operate on geologic structures?
faults and folds
what are faults?
tensional tectonic forces pull rocks apart from the central fracture, causing them to fail and fracture
what is it called when displacement occurs during faulting?
a fault system
what are folds?
what were originally horizontal rocks are pushed together by compressional forces
what kind of force is involved in faulting?
tensional
what kind of force is involved in folds?
compressional
what are the three sources of information about deformation processes?
field observations, laboratory experiments and satellite information which can be coupled with numerical computer simulations
what are the four types of stress?
compression, tension, normal and shear
what are the two types of compression stress?
uniform and differential
what is compression stress?
acts to shorten an object
what is uniform stress?
stress is uniform in all directions and the principle stress axis are the same throughout
what is differential stress?
stress is not uniform in all directions, greater stress is coming from the sides than above and below or vice versa. the principle stress axis is not the same throughout
what do three perpendicular stress axes result in?
2 sheet planes along which there is a maximum tendency for failure
what is tension stress?
acts to lengthen an object - earths material is being pulled apart, meaning it fractures
what is normal stress?
the stress is acting perpendicular to the surface - neither compression or tension occurs
what is shear stress?
the pressure acts parallel to the surface - the two blocks are sliding side by side
which four factors will influence how minerals, rocks and sediments respond differently to applied stress?
temperature, confining pressure, mineral / rock type, strain rate
what type of rock tends to behave as brittle material and is thus susceptible to faults?
igneous and metamorphic rock
what type of rock tends to behave softer and more ductile and is therefore susceptible to folds?
sedimentary rocks
what is the strain rate?
the rate of deformation - how fast we are trying to deform the substance
what rate of deformation results in more faulting?
rapid
what rate of deformation results in more folding?
slow
what does a rapid rate of deformation result in?
brittle failure and faulting
what does a slow rate of deformation result in?
plastic deformation and folding
what is strain?
a dimensionless measure of the extent of deformation
why is strain dimensionless?
it has no physical units - we refer to it as a percentage, decimal or fraction
what does plastic deformation resulting in folding produce?
folded dykes
what does brittle deformation resulting in fracturing create?
faults in sedimentary rocks
what is the dip of strata?
a measure of the maximum angular deviation of an inclined plane from the horizontal
what is the strike of strata?
the direction of a line formed by the intersection of a horizontal plane with an inclined plane
which range are rocks in when folds are formed?
plastic range
which range are rocks in when faults are formed?
brittle range
what is the classification of folds based on?
their geometry, the symmetry of the fold and the orientation of the fold in relation to the fold axis
what are monocline folds?
open, gentle folds, step like, form when differential compaction occurs over underlying features
what are anticline folds?
'N shaped' upward arched folds
what are syncline folds?
'U shaped' downward arched folds
which two types of deformation are we thinking of when we discuss mountain building?
anticline and syncline folding