Pressure Solution (PS)

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

Image from Greg Davis’ structure resources DVD

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

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

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)

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 )

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)

Results of some PS-related papers and work

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

Hsuëhshan Range, Taiwan 50% shortening by P. soln. T = ~200-~300°, strain rates 2.5* /s - 4* /s, viscosity < 2.5*10 20 Pa s - 5.6*10 22 Pa s

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

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%

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

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

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

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

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.

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

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