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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