26 October 2004GLG310 Structural Geology. 26 October 2004GLG310 Structural Geology Shear Zones Have a look at Davis and Reynolds, Chapter 9.

Shear Zones

• Have a look at Davis and Reynolds, Chapter 9

Shear Zones

Shear Zones

Shear zones

• Brittle or ductile– Brittle shear zone = fault zone

• Tabular or sheet like, planar or curviplanar zone composed of rocks that are more highly strained than the rocks adjacent to the fault zone

• Quartz starts to flow rather than fracture at about 300C

Semi-brittle shear zones

2004 Parkfield EarthquakeRamón Arrowsmith

& special guest Matt Fouch

Earthquake of the Month: Special Seminar

Brittle-ductile s.z.

Sense of shear

S-C fabric: S surface = schistosity, C surface = shear surfaces

Sense of shear

Sense of shear: Ductile shear zone

Pure vs. Simple shear

Pure vs. Simple shear

Analysis of shear strain

Continuous or discontinuous strain

Transpression or Transtension

Can have both pure and simple shear along a shear

zone

-R+AVelocities relative to stable North America