Transcript Slide 1

Announcements
Field trip during lab today/tomorrow
Field trip this Saturday to Collosal Cave area
7:30 AM at loading dock. We will map some really
cool stuff! Please review map symbols and bring
stereonets. We may return after sunset.
There will be a "What is it" quiz next lecture- review
fault rocks and kinematic indicators!
Nov. 13 - Draft #1 of fault paper due!
Outline for Today
1. More about geometry and kinematics of thrust
systems
2. Forced folds
the architecture of many fold-thrust belts
"thin-skinned" deformation
development of duplexes
map pattern of a duplex
lateral ramps
compartmental faulting and tear faults
footwall rocks are
commonly
deformed into
synclines
Footwall syncline in the Canadian Cordillera
Footwall syncline in the Canadian Cordillera
also, triangle zones
also, triangle zones
The observation
that faults do not
continue around
the entire Earth
suggests that
they must
terminate
Generally, a
gradual decrease
in slip toward
fault termination
Younger and structurally deeper faults
lead to rotation of older faults
Summary
Thrust systems:
1. Accommodate significant crustal shortening
2. Basal detachment/decollement; decoupling within the crust
3. Faults have ramp and flat geometries
4. Thrusts place older/higher grade rocks over younger/lower grade rocks
5. Faults cut up-section
6. Faults generally propagate (get younger) toward the foreland
7. Younger and structurally deeper faults rotate older faults to steeper
angles
1. breached
anticline
What is it?
2. fault
tips/
terminati
ons
4. klippe
5. window
6. lateral
ramp
7. blind
thrust
8. branch
lines
Fold and thrust belts!
Mt Kidd
Forced folds (D&R 413-423)
Free folds: fold profiles are based entirely on physicalmechanical properties of the layers
Forced folds: geometry related to movement over fault
ramps- "they just go along for the ride, and some of the
beds happen to fined themselves in awkward places and
are required to stretch or bend"
2-main types of forced folds:
fault-bend folds
fault-propagation folds
Fault-bend folds
Fault-propagation
folds
monoclines as "drape" folds
"thick-skinned" basement-involved shortening
Colorado Plateau
monoclines may
be related to
thick-skinned
deformation
Major issues
• “mechanical paradox” of thrusting - why such
thin sheets (e.g. 100 km long/2-3 km thick) can
remain intact during faulting?
• What happened to the missing basement?
• Why are almost all faults dipping one way when
rock mechanics predict equal chance for both?
Next lecture:
(1) thrust belt mechanics (p. 336-339)
(2) Discuss fault project