Exam 1 Chapters 1-3 Flashcards
How do we examine deformation?
Through geometric, kinematic, and dynamic analysis
What is geometric analysis?
Examine deformation through shape, orientation, and size
What is kinematic deformation?
Examines deformation through the description of motion and displacement
What is dynamic analysis?
Examines deformation through the study of forces causing deformation (separates observations from interpretations)
What does a tectonic plate consist of
the crust and the upper mantle (lithosphere)
Crust thickness
7-70km
Mantle thickness
~2900km
Core thickness
2900-6370km
3 compositonal layers of the earth
crust, mantle, core
5 rheological layers of the earth
lithosphere, asthenosphere, lower mantle, outer core, inner core
What are transformations?
describe how original locations, orientations, shapes and/or sizes of volumes of rock or material points within volumes of rock become changed
what are the four kinds of transformations?
translation, rotation, dilation, and distortion
Rotation
a rotation of material points about some common axis
translation
all points in a body move the same distance along parallel paths
dilation
a change in size without a change in shape
distortion
a change in shape of a body of rock
rigid body deformation
each point within the body of rock maintains the same location related to the other points
- translation and rotation
non-rigid body deformation
the spacing of points within the body of rock change with respect to one another
- dilation and distortion
strain
results from non-rigid body deformation through change in size or shape
- results from change in spatial arrangement
Primary structures
develop during the formation of a rock body
examples of primary structures
cross bedding, ripple marks, graded bedding, ropy texture in basalt
secondary structures
develop in rocks after their formation
mohorovic discontinuity
the boundary between the earths crust and the mantle
angular shear
measure of the change in angles between lines
clockwise rotation
negative
counterclockwise rotation
positive
strain ellipse
distortion acuminated by a geologic body as a result of deformation
what are S1 and S3
the principal axes of the finite strain ellipse
S1
the long axis of the finite strain ellipse and the direction of maximum finite stretch
S3
the short axis of the finite strain ellipse and the direction of minimum finite stretch
plane strain
- the strain is two dimensional
- neither stretching or shortening in direction perpendicular to the plane that contains the directions of maximum and minimum finite stretch
end case of coaxial deformation
pure shear
coaxial deformation
lines that at the very first instant of deformation were aligned parallel to the direction of the long and short axes of strain (s1 and s3) will remain mutually perpendicular and parallel to the the long and short axes of the strain ellipse throughout the deformation
pure shear
extension of the material will be balanced by the shortening
non coaxial deformation
all particles move parallel to the direction of shearing but the directions of greatest stretch (s1) and least stretch (s3) continuously change, oblique to the direction of shearing
what is used to portray how a circle would be affected by very small increments of deformation
instantaneous strain ellipse
in coaxial deformation how is (s1.) related to (s1) and (s3.) to (s3)
they are parallel
in non coaxial deformation how are (s1.) and (s1) related and (s3.) and (s3)
S1 is successively rotated out of parallelism with (s1.) same with (s3.) and (s3)
how does normal stress act on the surface
perpendicular
how does shear stress act on the surface
parallel
9 stresses
3 are normal
6 are shear
