Term
What is a geologic structure? 

Definition
A geologic structure is a geometric configuration of rocks 


Term

Definition
Shiny, flat cleavage planes along which a rock will easily break 


Term
What is a primary structure? 

Definition
An original structure that is formed at the same time as the rock 


Term
What is a secondary structure? 

Definition
A structure formed after the original rock has formed; usually the result of metamorphism 


Term
What are some primary structures? 

Definition
 Foliations: Bedding, igneous layering
 Lineations: current lineation, ripples 


Term
How is igneous layering and crossbedding defined? 

Definition
 Common in mafic rocks
 Usually defined by variations in feldspar/pyroxene ratios or grain/gradient size; modal layering 


Term
What are two criteria by which primary structures can be defined? 

Definition
Disharmonic folds and folds confined between flat layers; sediments are still soft when deformation occurs 


Term
What are four tectonic structures? 

Definition
 Foliation: slatey cleavage, schistosity, gneissosity (related to metamorphic grade)
 Lineation: mineral lineations, intersection lineations
 Folds: anticlines, synclines, recumbent folds
 Faults: cataclasites and mylonites 


Term
What two processes control the nature of planar tectonic fabrics? 

Definition
Metamorphic grade (temperature) and rock composition (mineralogy) 


Term
What is the difference between a recumbent fold and a reclined fold? 

Definition
 Recumbent fold: flatlying axial surface
 Reclined fold: plunges down the dip of its axial surface 


Term
What is the difference between strikeslip and dipslip faults? 

Definition
 Strikeslip faults: faulting is parallel to strike plane
 Dipslip faults: faulting is parallel to dip plane (ex. horst and graben structures) 


Term
What is the difference between cataclasites and mylonites? 

Definition
 Cataclasite: a cohesive and finegrained fault rock
 Mylonite: wellfoliated tectonic rock formed by intense plastic deformation; characterised by grain size reduction 


Term
What are three types of geological contacts? 

Definition
 Basecover relationships: unconformities
 Intrusive contacts
 Faulted contacts 


Term
What do geological maps show, and what must you be able to read from them? 

Definition
 Show the distribution of rocks and the orientation of structures in these rocks
 Allows rock identification, distribution, contact relations, structures and their orientations 


Term
What are the definitions of strike, dip, plunge, and pitch? 

Definition
 Strike: orientation (azimuth) of the line of intersection between a horizontal plane and the inclined plane of interest
 Dip: angle between a horizontal plane and the inclined plane of interest as measured in a vertical plane PERPENDICULAR to strike
 Plunge: angle between the inclined linear structure and a horizontal plane, as measured in a vertical plane oriented PARALLEL to strike
 Pitch (rake): the acute angle between a horizontal line and the inclined lineation measured within the plane on which the lineation lies 


Term

Definition
Surface expression of subsurface inclined foliation planes at different depths projected onto the map from the structural profile 


Term
How do you determine the thickness of bedding? 

Definition
 Must be measured PERPENDICULAR to bedding planes
 Draw a construction line perpendicular to the strike of the bed of interest
 Mark top/bottom of bed on this line
 Transpose this line onto a work sheet
 Use a protractor to extend the top/bottom of bed in profile, using the known dip angle
 Measure thickness using map scale 


Term
What is apparent dip and how is it measured? 

Definition
 Dip measured in any plane other than the vertical perpendicular plane to strike will give a value less than the true dip
 Draw a structural profile and strike lines for the foliation
 Draw a line oriented parallel to the plane of interest across the strike lines
 Transpose this line to a work sheet, and sketch in the map scale perpendicular to this
 Draw a profile for this line by plotting a sequence of points corresponding to the strike lines
 Connect the dots and measure the apparent dip 


Term
What are the differences between stereographic projections and orthographic projections? 

Definition
 Stereographic projections: do not preserve spatial relations; easier to perform but more difficult to visualise than orthographic projections; use equalangle and equalarea nets; planes project as curved lines; lines project as points
 Preserve spatial relationships; involve drawing crosssectional profiles at right angles to the strike of foliations; can involve drawing structural contours; can be used to determine thickness of beds, apparent dip of inclined foliations, orientation of intersection lineations 


Term
What are equal area and equal angle nets used for? 

Definition
 Equal area (Schmidt): used to determine the distribution of foliation and lineation measurements, and their statistical densities
 Equal angle (Wulff): used to solve geometrical problems 


Term

Definition
The transformation from an initial to a final geometry via distortion, rotation, volume change (dilation), and/or translation 


Term
What structures easily show signs of dilation? 

Definition
 Volume gain: extensional cracks filled with calcite
 Volume loss: stylolites 


Term
What two forms of deformation does strain produce? 

Definition
Distortion (change in shape) and dilation (change in size) 


Term
What happens to a structure that has undergone homogeneous deformation? 

Definition
 Straight lines remain straight and parallel lines remain parallel
 Circles become ellipses, spheres become ellipsoids 


Term

Definition
 A smooth closed curve which is symmetric about its centre
 Corresponds to the shape given when a plane intersects a cone 


Term
What are the foci of an ellipse? 

Definition
Two points on an ellipses major axis such that the sum of the distances from any point of the ellipse to those two points is constant and equal to the major diameter 


Term
What is a strain ellipse? 

Definition
Represents the distortion accommodated by a rock during homogeneous deformation 


Term
What is the difference between an incremental strain ellipse and a finite strain ellipse? 

Definition
 ISE: shows how an initial circle is affected by a tiny increment of deformation
 FSE: shows the total strain experienced by the rock; sum of all ISEs 


Term
What do the axes of the FSE and ISE indicate? 

Definition
If the axes are parallel, the strain is irrotational (coaxial). If not, the strain is rotational (noncoaxial). 


Term
What is the difference between pure and simple shear? What do they both have in common? 

Definition
 Simple shear: noncoaxial strain (rotational)
 Pure shear: coaxial strain (irrotational)
 Both refer to strain histories 


Term
What symbol is used to describe the degree of rotational strain? 

Definition
Wk = w/[(2(sx^2 + sy^2 +sz^2)]^2; where Wk is the kinematic vorticity number, w is the angular velocity vector, and s are principle strain rates parallel to incremental stretching axes 


Term

Definition
 Measures the relationship between internal rotation (vorticity) and how fast strain accumulates during deformation.
 Coaxial: Wk = 0
 Noncoaxial: Wk = 1
 Subsimple shear: 0 < Wk < 1
 Continuous spinning: Wk > 1 


Term
What is the difference between 1D, 2D, and 3D strain? 

Definition
 2D: no strain along intermediate strain axis (Y); lengthening along X is compensated by shortening along Z; changes in angles between lines that are initially perpendicular
 1D: changes in lengths of lines; extension, stretch, and quadratic elongation
 3D: change in lengths of axes X, Y, Z 

