Hamilton's Finale

Fault

Fault

A discontinuity along which there is visible offset by shear displacement

Why would a fault stop at the boundary between rock layers?

Softer, more plastic rock

Rock was deposited after the formation of the fault

Rake

Angle along the plane between the strike direction and a lineation (or fault slip). Measured clockwise

Separation

Apparent offset of a feature across a fault along its trace

Slip

Absolute offset of a feature or amount of motion along a fault

Heave

Horizontal component of separation

Throw

Vertical component of separation

Scarps

Offsets/steps in land surface coinciding with locations of faults and formed by recent fault movements

Fault-Line Scarps

Offsets/steps in land surface coinciding with fault trace and formed by differential weathering of juxtaposed units

Slickensides

Smoothed, sometimes highly polished, surfaces created by fault grinding

Slickenlines

Striations or lineations that indicate the direction of movement

Slickenfibers

Slip-fibers or crystal fibers. Crystal growth that looks similar to a slickenside that indicates the direction of movement

Describe fault rocks as depth increases

Upper few km: incohesive rocks, often starts with breccia then grinds to gouge. Rapid movement may produce gouge and/or pseudotachylyte

Greater depth: produce more cohesive breccias and cataclasites

Below 10-15 km: plastic behavior dominates over the long term

Pseudotachtylyte

Type of rock formed by frictional melting during earthquakes

Riedel Shears

En-echelon segments that accommodate bulk displacement at an angle to the larger displacements

Synthetic Shears

R-Shears. Lie closer to the main trend and have the same sense of slip as the main fault

Antithetic Shears

R’-Shears. Conjugate to the synthetic segments and have the opposite sense of displacement

Pull-Apart Basin

Region in the releasing bend of a fault where the earth sinks down due to tension

Dilational Jog

Pull-apart or releasing bend produced by the transtension mode of deformation

Antidilational Jog

Restraining bend produced by the transcompressive mode of deformation

Fault Drag

The bending of beds near a fault away from the direction of movement

Reverse Drag

The bending of beds near a fault towards the direction of movement

Fault Slipping

Faults slip more closer to the point of origin of the slip

Antithetic Faults

Faults that dip towards the main fault

Synthetic Faults

Faults that dip with the main fault

Duplex

An isolated, fault-bound block

Graben

A region bounded by faults and displaced downwards. V-shaped

Horst

A region bounded by faults and displaced upwards. A-shaped

Flower Structures

Restraining and releasing beds can form clusters of oblique thrust or normal faults. These faults link together to form a series of isolated, fault-bound blocks

Positive Flower Structure

Found at the restraining bend where there is uplift

Negative Flower Structure

Found at the releasing bend where there is downwarping

Allochtonous

Rock far out of place due to thrusting

Autochthonous

Rock not displaced but in contact with allochthonous rocks

Klippe

An isolated exposure of allochthonous rock

Nappe

A large exposure of allochthonous rock

Window

A gap cutting through allochthonous rock into the autochthon below

Thin-Skinned

Basement rock is not involved

Thick-Skinned

Basement rock is involved

Thrust Wedges

Form horses along ramps

Back Thrusts

Wedges that go the opposite direction of the main trust

High Basal Friction

Shallower thrusts, thicker piles

Low Basal Friction

Steeper thrusts, thinner piles, more backthrusts

Anticline

A fold that is convex in the direction of the youngest beds

Syncline

A fold that is convex in the direction of the oldest

Antiform

Convex up

Synform

Concave up

Recumbent Folds

Folds lying on their sides

Isoclinal

Folds where the limbs are more or less equally inclined (almost parallel)

Monoclines

Regional scale step-like folds where otherwise horizontal or very shallowly dipping strata to bend abruptly to steeper inclinations within narrow zones

Fold Geometries

Kink Band, Concentric, Similar, Cuspate, Circular, Elliptical, Chevron, Box

Cylindrical Fold

Hinge line is straight

Fold Tightness

Gentle (170), Open (90), Tight (10), Isoclinal (0)

Concentric Folds

Folds where layer thickness does not change along the fold. Strain is accommodated by flexural slip

Similar Folds

Folds where layer geometry is nearly the same from one layer to the next. Hinges are thickened and limbs are thinned

Class 1 Dip Isogon

Dip isogons converge toward the inner arc, which is tighter than the outer arc

Class 2 Dip Isogon

Dip isogons parallel the axial trace. E.g. similar folds

Class 3 Dip Isogon

Dip isogons diverge toward the inner arc, which is more open than the outer arc

Buckling

Strain accommodated by internal flow of the layer as well as slip along the layer boundaries. Resulting folds have dominant wavelength

Boudinage

A series of elongated parallel sections formed by the fracturing of a sedimentary rock stratum during folding

Parasitic Folds

Smaller folds that form within a larger fold