Pressure Solution (PS)

1. Pressure Solution (PS)

2. PS: Volatile-assisted diffusion, a.k.a. solution-mass-transfer, a.k.a. pressure solution • Like Coble-creep (but only in presence of water), diffusion of matter occurs along grain boundaries, fractures and other discontinuities • “solubility” of material probably affected by elastic or plastic deformation at high stress grain boundaries • May not involve true “solution,” since a true fluid may not be present on grain boundaries at high normal stress • Little evidence of T or grain size sensitivity Source: John Platt course notes

3. Image from Greg Davis’ structure resources DVD

4. Stylolites: seams of insoluble material left behind at localized sites of pressure solution Image from Greg Davis’ structure resources DVD

5. At higher T, crenulation cleavage develops in slates & schists by pressure solution Image from Greg Davis’ structure resources DVD

6. Why we know PS is important • Dominant mechanism for low-T deformation cleavage, folds, fibers, veins... • Arguably main mechanism of Internal deformation of thrust belts (minor faults and unfaulted material)

7. Issues • Kinetics/flow laws • Low activation energy prohibits extrapolations from high T-fast strain rate experiments • Multiple potential rate-limiting factors (e.g. diffusion, advection, reaction kinetics) • Major uncertainties on associated stresses, strain rates and thus viscosity. • Temperature range (above ~100°C for qtz, room temperature for calcite –Platt notes)

8. Renard et al (2000) • Theoretical treatment • PS in gouge (much faster than along stylolites), works at recurrence interval rates • Fluids play key role in viscous relaxation of upper crust after EQ • PS may be important mechanism of post-seismic creep (gouge zones)

9. Results of some PS-related papers and work

10. Andreani et al, 2005 Identify PS mechanism in serpentinite gouge zones

11. Hsuëhshan Range, Taiwan • 50% shortening by P. soln. T = ~200-~300°, strain rates 2.5*10-15 /s - 4*10-14 /s, viscosity < 2.5*1020 Pa s - 5.6*1022 Pa s

12. Accretionary complexes show volume losses of 30-40% by p.s. at low stresses and temperatures of 200-400°C 1 1e.g. Ring et al, 2001; Schwarz and Stockhert, 1996

13. Gratier & Gamond (1990) • Goal: explain seismic & aseismic slip (by PS) on the same fault Fig. 1 mass transfer required along and at ends of faults Note Molnar 1983 citation: elastic strains always<1%

14. Gratier & Gamond (1990) cont. • Sometimes displacement entirely by mass transfer • Estimate size of closed system (for small faults) • In one location ~100 m scale of infiltration along a fault

15. Gratier & Gamond (1990) cont. • Crack seal mechanism aseismic • aseismic and seismic creep may alternate along same fault

16. Gratier & Gamond (1990) cont. • Fiber length/Asperity length ~.4 interpreted as dissolved portion of asperity... assume PS is limited by asperity length then make some

17. Gratier & Gamond (1990) cont. • Energy for faulting and PS might be compared (if we knew the energy needed for PS)

18. Gratier & Gamond (1990) cont. • Alpine crust viscosity: • Strain rate of ~10^-14 • Order of magnitude of stress guessed • Viscosity 10^19 -10^21 ± “1 or 2 orders of magnitude uncertainty” • Compare with laboratory estimate of 10^17 by same authors • 10^17 (salt) to 10^21 (lithospheric mantle)... Major uncertainty.

19. Meyer et al, 20061 • Press ms and qtz together at 2.5 atm in surface forces apparatus in presence of fluid at 25°C. • A strain rate of 10-5 is obtained for fine sand = viscosity of ~1010 Pa s! (like rhyolite lava) 1Experimental investigation of the dissolution of quartz by a muscovite mica surface: Implications for pressure solution, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, B08202, doi:10.1029/2005JB004010, 2006

24. Conclusion • pressure solution is a major player in low temperature crustal deformation but is poorly understood