1 / 17

High T Deformation Mechanisms involved in Localization

High T Deformation Mechanisms involved in Localization. Ge 277, 2011, Steve Kidder. Outline. Dislocation Creep Diffusion Creep Grain Boundary Sliding Other.

aimee
Download Presentation

High T Deformation Mechanisms involved in Localization

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. High T Deformation Mechanisms involved in Localization Ge277, 2011, Steve Kidder

  2. Outline • Dislocation Creep • Diffusion Creep • Grain Boundary Sliding • Other Caviat: These mechanisms and constituitive relationships have generally been developed for monomineralic aggregates, while most crust contains multiple minerals Salinas shear zone, Kidder & Ducea (2006)

  3. 1. Dislocation Creep involves dislocations... (Translation of a stressed edge dislocation)

  4. TEM image of tangled dislocations in quartz • (FOV ~ 1 µm?) Typical density 2.6x109 cm/cm^3

  5. Dislocation Creep • Grain size evolves to a constant (generally smaller) size proportional to differential stress • Viscosity not grain size sensitive • Lattice Preferred Orientation can reduce viscosity (e.g. by 10x in qtz; Muto, 2011) Stress exponent varies A includes water fugacity term

  6. Undeformed Black Hills Sandstone (BHQ), cross polars Cross polarized light. Color reflects grain orientation ~50 microns

  7. BHQ (fast strain rate, 10^-4 /s), note strong lattice distortion, tiny rxl grains ~50 microns

  8. Recrystallized Grain Size proportional to Differential stress Empirical relationship observed in materials deformed in dislocation creep regime: σd = kdm d = recrystallized grain diameter m (= ~-1) and k experimentally determined Stipp and Tullis, 2003

  9. 2. Diffusion Creep (incl. pressure soln.) Deformation by migration of point defects, most commonly along grain boundaries

  10. Pressure solution (diffusion flow) in sandstone…

  11. Pressure Solution: cleavage (~ horizontal) cutting lithological layering ~1 mm

  12. Diffusion Creep • Strongly grain size sensitive • Grain size not reduced

  13. 3. Grain Boundary Sliding assisted Disl. Creep Precigout et al. 2007

  14. 3. Grain Boundary Sliding assisted Dislocation Creep • Both reduces grain size, and grain size weakening • Documented (so far) only in Olivine & Ice

  15. Comparison • Disl. creep: • Diff. creep: • GBS Disl. creep:

  16. GBS assisted Disl. Creep helps explain localization • 1D numerical experiments indicate a 2 order of mag. increase in strain rate associated with localization Precigout& Gueydan. 2009 Classical view

  17. Other microscale mechanisms involved in typical shear crustal zones • Microcracking • Metamorphic changes • Grain boundary sliding • Partial melting (all can assist in localization) Salinas shear zone, Kidder & Ducea (2006) Veins/cracks at ~700-800 °C Veins/cracks at 500-550 °C, W. Gneiss, Norway

More Related