Announcements Cottonwood exercise and homework are due on Thursday The project for those who missed...

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