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Structural Geology Exam 2
Structure
41
Geology
Undergraduate 3
10/26/2013

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Term
Normal Fault
Definition
HW moves down wrt FW
Accommodates horizontal crustal extension and vertical crustal thinning
Place younger rocks on older rocks
Term
Evidence for Listric shape at depth
Definition
1) Hanging blocks tilted toward fault
2) Roll over anticlines
3) Growth Faults
Term
Detachment Faults
Definition
Gently dipping portion of normal fault found at depth
Term
Why are there gently dipping faults?
Definition
1) Listric shape and erosion
2) Proffett's rule: Older listric faults cross-cut by younger listric faults, results in older faults rotating towards the HW, becoming more gently dipping
Term
Horst
Definition
Uplifted block; FW bound by 2 conjugate normal faults
Term
Graben
Definition
Downdropped region (HW) bound by 2 conjugate normal faults
Term
Half-Graben
Definition
Down-dropped region found by non-conjugate faults
Term
Why do normal faults form?
Definition
1) Horizontal extension (Continental rifting)
2) Response to flexure (hinge region of fold)
3) Collapse (volcanoes)
Term
What are Metamorphic Core Complexes and why are they important?
Definition
Long, gently dipping normal fault with a lot of slip (extension)
First recognized in Basin and Range Province
Term
Cataclasite
Definition
Very fine grained
Term
Mylonite
Definition
Rock formed as a result of ductile deformation, exposed due to normal faulting
Term
Tear Faults
Definition
Meso/macro scale
At a high angle to the main structures
Term
Transfer Faults
Definition
A "jumped" fault
Term
Transcurrent Faults
Definition
Largest type of strike-slip, cuts through crust
Term
Thrust Faults
Definition
HW moves up wrt FW
Places older rocks on younger rocks
Accommodates horizontal crustal shortening and vertical thinning
Term
Allochthon
Definition
Moved very far from its place of origin
Term
Autochthon
Definition
Thrust sheet that has not moved far from its place of origin
Term
Tip Line
Definition
Edge of fault
Term
Cut off angle
Definition
Angle that bedding makes with a fault
Term
Branch line
Definition
Where faults split/join
Term
Imbricate Fans
Definition
Series of listric faults that all dip in the same direction and overlap and join together
Term
How to find age of faults?
Definition
Younger faults form below and in front of older faults
Term
Duplexes
Definition
Made up of 2 or more horses
Contain root and floor faults
Term
Horse
Definition
A block of rock bound on all sides by faults
Term
Decollement
Definition
Bottom of the thrust - sole thrust
Term
Hinterland and Foreland
Definition
Material moves away from the Hinterland toward the Foreland
Fold-thrust belts
Fold hinge typically perpendicular to transport direction and parallel to thrusts
Term
Salients
Definition
Convex towards foreland, frontal ramps and/or more sediment to transport
Term
Recesses (Transverse zones)
Definition
Concave to foreland, lateral ramps and more or less sediment
Term
Fault-bend folds
Definition
Fault forms faster than motion of HW
Term
Fault propagation folds
Definition
HW starts moving and folding and formation of fault lags behind. Creates steep/overturned forelimb. May simply be deformation at fault tip.
Term
Windows
Definition
Erosion through the HW of a fault, FW surrounded by HW
Term
Klippes
Definition
Island of HW surrounded on all sides FW
Term
Forward (Normal) Thrusting
Definition
Younger thrust form below and in front of older thrusts
Term
Out of sequence thrusting
Definition
Younger thrusts form in HW of older thrusts
Term
Kinematic Analysis
Definition
Reconstruct and track motion history
Term
Rigid Deformation
Definition
Translation and rotation
Term
Non-rigid deformation
Definition
Distortion (shape change)
Dilation (size change)
Measured by strain!! Ratio of undeformed/deformed
Term
Homogenous
Definition
Straight lines remain straight
Parallel lines remain parallel
Ratios remain unchanged
Term
Angular shear strain
Definition
Measures angle between 2 initially perpendicular lines
Term
Pure Shear
Definition
Lines parallel to L1 and L3 don't rotate "coaxial"
Term
Simple Shear
Definition
Lines parallel to L1 and L3 rotate (non-coaxial)
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