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