Autumn, of the current year GLY 326 Structural Geology Lecture 30 Reverse Faults Autumn, of the current year

Dip-Slip Faults

Reverse faults: Compression Older strata on top of younger strata Thrusts (horses and wedges)

Reverse faults: In maps we mark them with a line with “teeth” indicating the hanging block.

So… where we can find compression? (shortening)

At the subduction zones!!!

Orogenesis (building mountains)…. thrust geometry (American Embassy in Santiago)

Thrust faults: Horses and Wedges A thrust fault is a reverse fault in which the dip of the fault plane is very low… (<30o)

Keystone Thrust, Nevada Paleozoic Jurassic (View to northwest)

HIMALAYAN FRONTAL THRUST Himalayan Frontal thrust- active thrust slicing up foreland basin Flat on ramp geometry here in poorly consolidated sediments

The McConnell thrust, Alberta. View to North The McConnell thrust, Alberta. ramp

Example: Lewis Thrust Fault

Example: Lewis Thrust Fault fenster klippe

hanging wall footwall

Lewis Thrust Fault (cont'd) Source: Breck P. Kent pre-Cambrian Limestone over Cretaceous Shales!!!

Flat-ramp geometry in the Chilean Andes.

New thrusts initiate & propagate in direction of foreland: new thrust develops “ahead” of old one Hinterland upper glide horizon lower glide horizon Foreland Incipient second thrust “piggy-backing” Incipient third thrust Hinterland and foreland: hanging and footwall in orogenesis

Some Rules For Thrust Faults Thrusts cut ‘UP’ stratigraphic section in transport direction (vergence)

continued forward propagation of thrusts produces duplex or imbricate fan: roof thrust Propagation ** * sole thrust horses DUPLEX: all the horses together.

Three views of thrust system “Wedge shape”

Duplex at Crows Nest Pass - Alberta (At any scale)

Thrust sheets + imbricate fans + duplexes + folds = thrust belt Fold & Thrust Belt

Lewis Thrust Fault (reconstructed)

To visit: http://www.see.leeds.ac.uk/structure/learnstructure/index.htm