announcements cottonwood exercise and homework are due on thursday the project for those who missed...
TRANSCRIPT
Announcements
Cottonwood exercise and homework are due on Thursday
The project for those who missed the field trip is now available online- deadline for that is Tuesday March 25, in class (no extensions!,
zero credit after deadline)
Cottonwood trip- a few thoughts
Changes in dips? How can you explain them?
Definitely a fault; what kind?
Need to think about cross- section
Strike-slip fault systems(D&R: 357-371)
1. Tectonic settings and significance
2. Geometries
3. Active strike-slip faults-
4. mineralization + petroleum
At the scale of plate tectonics, transform (strike-slip) plate boundaries are subordinate to convergent and divergent plate margins- but they play a critical role
oceanic (ridge-ridge) transform faults, revisited
Continental strike-slip faults- the San Andreas
How deep should earthquakes be within an active strike-slip fault?
Down to the brittle-ductile transition
The Alpine fault in New Zealand transfers slip
between two subduction zones (trench-trench
transform)
The North Anatolian fault-rupture near Izmitlast September.
Major active continental strike-slip faults in Asia
tectonic extrusion or escape hypothesis
Strike-slip faults can transfer slip between different thrust or extensional systems
Strain can be partitioned into different styles of fault systems-
Strain partitioning in oblique convergent margin settings
Fault traces are rarely straight- they can curve, branch, or be arranged en echelon.
This leads to a wide variety of strike-slip related deformation
Transtension in releasing bends may lead to development of sag ponds and pull-apart basins
Restraining bends and transpressional deformation- folds and thrusts
The San Andreas bend near Los Angeles:thrusting related to strike-slip faulting
Many strike-slip fault systems are characterized by faults that converge downward and form flower structures
compressional setting: "positive" or "palm tree" flower structure
extensional setting: "negative" or "tulip" flower structure
Some flower structures look like duplexes turned on their side- strike-slip duplexes
Riedel shears- especially common in strike-slip fault systems
R: synthetic Riedel shearR': antithetic Riedel shearP: synthetic shear, subordinate to R and R' or absent
summary ofstrike-slip-relateddeformation
What is important about strike-slip faults and why do we care?
1. Many active strike-slip faults are associated with high slip rates, major earthquakes, and lithospheric plate boundaries
2. Oil and mineral exploration.
Significance of strike-slip fault systems for oil
Many Archean and Phanerozoic mineral deposits (especially gold) are associated with zones of strike-slip deformation
Important terminology/conceptsridge-ridge and trench-trench transform faults
concept of continental extrusion or escape
strike-slip faults as transfer faults
strain partitioning
oblique convergence
releasing vs. restraining bend
transpression vs. transtension
sag ponds and pull-apart basins
flower structures
strike-slip duplexes
right-stepping vs. left-stepping fault arrays
folds in strike-slip zones
Riedel shears