Presentation on theme: "Announcements Cottonwood exercise and homework are due on Thursday The project for those who missed the field trip is now available online- deadline for."— Presentation 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: ) 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
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 Izmit last 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 shear R': antithetic Riedel shear P: synthetic shear, subordinate to R and R' or absent
summary of strike-slip-related deformation
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/concepts ridge-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