Exam 1 Flashcards
Exam 1
Strike and Dip using (180, 60)
180/60 W
Strike Definition
Azimuth of an imaginary line that lies in the plane of a surface and is everywhere at the same elevation.
Dip Definition
Steepest angle of inclination in the plane, always orthogonal
Rake Definition
Orientation of a line that lies in a plane
Plunge Definition
Vertical inclination, measured as an angle downward from the horizontal
Pole Definition
Orientation of a line drawn at right angles to the plane
Trend Definition
Horizontal direction of the strike, direction of plunge
Anticline
Oldest rocks towards the interior
Syncline
Youngest rocks near the center
Antiform
Upward closing, limbs dip away from the hinge
Synform
Downward closing, limbs dip towards the hinge
Stereonet
Spherical projection. Not for location data, for orientation data.
Beta plot
Strike and dip
Pi plot
Poles for strike and dip
Interlimb Angle
It is the angle subtended by the tangents at two adjacent inflection points, which may reflect the intensity of compression.
Class 1 Fold
Thinner hinge and thicker limbs, inner < outer.
Class 2 Fold
Thicker hinge, thinner limbs. Inner = outer.
Class 3 Fold
Thickest hinge, thinnest limbs. Inner > outer.
Buckling
Response to compression in direction parallel to layering. Strong contrast in material properties between layers. Competent layer in weak matrix is shortened parallel to the length of the layer.
Chevron
Lower temperature, compressional. A structural feature characterized by repeated well behaved folded beds with straight limbs and sharp hinges. Well developed, these folds develop repeated set of v-shaped beds. 120, symmetric.
Kink
Tabular fold-zones resulting from the operation of a shear couple and commonly occur as conjugate sets, usually developing late in the structural history of orogenic systems. 60, asymmetric.
Shear
Layering does not contribute to compression of the fold, structure is from shear folding. Typically class 2 and parasitic folding.
Bending
Externally applied load, monoclinic.
Unconformity
Put simply, an unconformity is a break in time in an otherwise continuous rock record
Disconformity
a break in a sedimentary sequence which does not involve a difference of inclination between the strata on each side of the break.
Nonconformity
Nonconformities are unconformities that separate igneous or metamorphic rocks from overlying sedimentary rock
Hinge
The hinge of an anticline refers to the location where the curvature is greatest, also called the crest
Crest point
Highest point of antiform
Crest line
A line on a folded layer which is common to and links the highest points on that layer.
Trough Point
Lowest point on a synform
Trough line
The line occupying the lowest part of the fold
Plunging Fold
A fold that is tilted downwards in space, parallel to the fold hinge plane.
Overturned
has the axial plane inclined to such an extent that the strata on one limb are overturned
Basin and Dome
Domes and basins are structures with approximately circular or slightly elongate, closed outcrop patterns. Domes are convex upward; basins are concave upward.
Disharmonic
A fold which exhibits sharp changes in its geometric properties (i.e. wavelength, symmetry, and shape) when compared with other folds in adjacent layers.
Harmonic
A fold which maintains its geometric form, integral wavelength, and symmetry throughout a sequence of layers.
Parasitic
Typical structures in geological multilayer folds; they are characterized by a small wavelength and are situated within folds with larger wavelength.
Category: Gentle
Interlimb Angle: 180-170
Category: Open
Interlimb Angle: 170-90
Category: Tight
Interlimb Angle: 90-10
Category: Isoclinal
Interlimb Angle: 10-0
Category: Fan
Interlimb Angle: <0
Subhorizontal
Hinge Line Plunge: 0-10
Gently Plunging
Hinge Line Plunge: 10-30
Moderately Plunging
Hinge Line Plunge: 30-60
Steeply Plunging
Hinge Line Plunge: 60-80
Subvertical
Hinge Line Plunge: 80-90
Upright
Axial Surface Dip: 90-80
Steeply Inclined
Axial Surface Dip: 80-60
Moderately Inclined
Axial Surface Dip: 60-30
Gently Inclined
Axial Surface Dip: 30-10
Recumbant
Axial Surface Dip: 10-0 A recumbent fold has an essentially horizontal axial plane.
Axial Surface
The imaginary surface bisecting the limbs of the fold.
Hinge Line
Where limbs of the folds meet.
Cylindrical Fold
Can be traced by a single line with a consistent trend-plunge
Non-cylindrical
The hinge lines, inflection lines, trough lines and crest lines may be curved and irregular.
