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41 Cards in this Set
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- Back
Rifting |
The process by which continental lithosphere undergoes extension. If thinning of crust is great, you will transition from rifting to spreading. |
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Delamination vs Pure shear model |
Delamination: Asymmetric model, single master fault that goes listric, creating a detachment fault and displaces and offsets the Moho. Pure shear: Symmetrical, stretching the crust, detachments trend towards each other. |
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Is the Basin and range (over 100% extension) the site of future spreading? |
No because the previous contraction shortened and thickened the crust. |
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What is the old school understanding of normal faults? What are low angle normal faults? |
That they always formed at dip angles of greater than 45. Detachment faults (younger on older, low grade on high grade) |
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What are grabens and horsts? |
Grabens are down dropped blocks, horsts are up thrown. |
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Rigid domino model (4) |
- No block internal strain - Faults and layers rotate simultaneously - Faults have the same total offset and dip - Faults and layers are planar |
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Rollover anticline |
On a listric fault, the hanging wall rolls over. |
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Antithetic fault Synthetic fault |
Dips into master fault Soles into master fault |
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If there is rotation of the hanging wall rocks... |
The fault is listric. |
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Normal faults usually have... |
Associated sedimentation. |
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What do low-angle normal faults accommodate? |
Extension. |
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Evidence against (2) and for low-angle faults (4) |
Against: 1) Rock mechanics, 2) scarcity of low-angle normal fault earthquakes For: 1) Least-work principle, 2) geologic reconstructions, 3) thermobarometric & paleomagnetic data, 4) seismic reflection profiles. |
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Rolling hinge model (3) |
- An initial listric normal fault - Extensional faulting drives isostatic rebound and abandonment of some faults - Uplift and erosion results in exposure of the metamorphic core |
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Inversion tectonics |
Normal faults become thrust faults |
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START HERE FOR QUIZ 6: Drivers of of contractional deformation (4): |
- Continent-continent collision - Collision of island arcs - Subduction of seafloor features - Rapid convergence between continental and subduction oceanic plates |
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Means of accommodating shortening: |
1) Volume loss: Dissolution of parts of the rock. 2) Pure Shear: Shorten in one direction -> thicken in other direction. 3) Buckling 4) Imbrication, thrusting |
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Thrust Sheet/Nappe |
Rock packages that make up the upper plate of a thrust fault. |
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Hinterland Foreland |
- The region in the center of an orogen - The marginal portion of orogen |
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Autochthonous vs Allochthonous |
- Rocks that are in place - Rocks that have been displaced |
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Klippe vs Fenster |
- An erosional outlier of a thrust sheet - An exposure of the footwall created by localized erosion of the thrust sheet |
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Flat vs Ramps |
- Parallel to bedding: HW flats, FW flats - Cuts across bedding (fault cut up-section) |
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Why do thrust faults have ramp-flat geometry? What does this mean? |
Thrust faults take advantage of preexisting planes of weakness. Instead of moving continually up an inclined fault plane, the fault cuts up-section in a stepwise manner. |
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Lateral Ramp |
Similar to a footwall ramp, but oriented such that it ramps up in the strike direction. |
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Blind thrusts |
Thrusts that don't make it to the surface.
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Cutoffs |
Both the hangingwall and footwall have cutoffs and have matching cut off angles. Cutoff lines mark the intersection of the thrust with the stratigraphic horizon it cuts. |
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Horse |
Thrust sheets tend to stack on each other as "horses". |
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Drag Fold |
Footwall rocks that are deformed into synclines.
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Fault trace |
Where a fault intersects the surface of the Earth. |
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Branch lines |
Where new faults are breaking off |
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What is a back thrust and how is it different? |
Regular thrust faults tend to propagate toward the foreland, when they propagate away from this, they are back thrusts. |
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Imbricate fan |
Where thrust faults daylight. (Several of them, looks like a fan) |
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Thin skinned (low-angle thrust faulting) |
Lots of basement involved. |
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Duplex |
A system of imbricate thrust faults that branch off from a floor thrust and curve upward to join a roof thrust at a branch line. |
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Basal Decollement |
Thrusts root into basal decollement, which is the main detachment surface at depth, usually at brittle-ductile transition. |
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Mechanics of Thrust Systems (3) |
1) Mechanical paradox of moving large thrust sheets 2) Thrust belt evolution: Critical Taper theory 3) Foreland basins |
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Two possible explanations for thrust belts moving uphill? |
1) Fluid pressure decreases the stress required to move a thrust belt 2) Thrust sheets do not move all at once, a wave of slip moves though a thrust sheet (like a caterpillar). |
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The wedge model of thrusting |
1) Material will not slide until wedge shaped. 2) Once a wedge forms, the mass can slide but only after it has attained its critical taper. |
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Critical taper |
Geometry function of the material strength and basal friction. Critical taper angle is controlled by the friction.
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Equilibrium |
Critical taper angle maintained |
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Sub-critical Super-critical |
- Growing the wedge - Need to thin out the wedge |
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Foreland basins |
A "hole" created by thrust belts because of loads that flex the lithosphere. |