Kinetics of pressure solution at halite‐silica interfaces and intergranular clay films

Abstract

of pressure solution at halite-silica interfaces and intergranular clay films" (1995). by diffusion through an intergranular film with a very high diffusion coefficient (• 10 -5-10 -7 cm2/s). The data further suggest that the diffusion coefficient and/or thickness of this film increases with decreasing normal stresses, at least for normal stresses less than about 4 MPa. As no island-channel boundary structures were observed, we propose that this film consists of a continuous layer of strongly adsorbed (i.e., structured) water that is maintained between the halite and silica lenses during deformation. Convergence rates in similar experiments conducted at a constant load of 0.11 N but at 8.3 ø, 50.2 ø, and 90.2øC were approximately constant at a given normal stress and contact spot size. The cause of this temperature insensitivity is unknown but might result from changes in interphase boundary structure or thickness with increasing temperature that are sufficient to offset the expected thermal activation. An experiment was also conducted in which a halite lens was pressed against a fused silica fiat coated with an 0.8-/•m-thick film of Na-montmorillonite in brine. This clay film produced an approximately fivefold increase in convergence rates over those observed in a halite/ silica experiment conducted without clay at the same load and temperature. The strong sensitivity of IPS rates both to contact spot radius and to the presence of second phases along grain boundaries suggests that fine-grained, clay-rich fault gouges and multiphase granular aggregates should be particularly susceptible to pressure solution creep in the middle to upper crust.

Precipitation sealing and diagenesis: 2. Theoretical analysis

“…This puzzling experimental observation does not agree with many other experimental findings of a rate that varies strongly with temperature [e.g. Rimstidt and Barnes, 1980], although temperature independence has been experimentally observed under pressure solution conditions [Hickman and Evans, 1995]. Another possible explanation may be that temperature independence is caused by abundance of fines created during crushing, with high free energy.…”

Experimental calcite dissolution under stress: Evolution of grain contact microstructure during pressure solution creep

“…[8] A single indenter setup was specifically designed to study dissolution of calcite under stress, the method is similar to the one used by Hickman and Evans [1995]. First, Iceland spar calcite crystals were cleaved and polished to start each experiment with a flat crystallographic surface.…”

Slip behavior of simulated gouge‐bearing faults under conditions favoring pressure solution

“…For example, both pressure solution and neck growth have been proposed to lead to fault healing and strength recovery in periods of interseismic quiescence [Angevine et al, 1982; Hickman and Evans, 1995], either by cementing grain contacts (by neck growth) or by gouge compaction and contact area increase (pressure solution). This type of effect has been observed in so-called slide-hold-slide experiments on fine-grained quartz gouge under hydrothermal conditions [Fredrich and Evans, 1992;Karner et al, 1997].…”

“…Generally, crustal strength is modeled using a frictional fault-sliding law for the upper, brittle part of the crust, plus power law creep equations describing plastic flow at deeper crustal levels [Goetze and contacts in response to gradients in local radius of curvature of the solid-liquid interface [Hickman andEvans, 1992, 1995]. Although solution transfer processes are widely recognized to be important in controlling fault rheology [Chester, 1995;Hickman et al, 1995], views are contradictory regarding their mechanical effect.…”