Role Of Pressure Solution Research Articles

The Role of Pressure Solution in Diagenesis of Carbonate Deposits: Theory and Laboratory Simulation

Contemporary understandings of the physicochemical mechanism of diagenetic transformations in carbonate rocks have been reviewed. The transformations comprise the dissolution of stressed zones of the rocks with the formation of supersaturated solutions, mass transfer in the direction of the concentration gradient, and reprecipitation. Characteristic features of the mechanism, which make it possible to diagnose its effects on the results of petrographic observations and to simulate the process under laboratory conditions, have been discussed. Especial attention has been focused on applied aspects, which will stimulate further interdisciplinary studies performed at different scales.

Fault Permeability and Strength Evolution Related to Fracturing and Healing Episodic Processes (Years to Millennia): the Role of Pressure Solution

It is well known that fluids flow through faults and fractures but it is also demonstrated that fault zones act as impermeable barriers. Consequently, one must consider that faults are successively open and closed paths for fluids. On the human-activity time scale (years to millennia), studies of the seismic cycle offer the possibility of making a model of such evolution. According to this model, seismic (or hydraulic) fracturing opens fluid paths almost instantaneously through the faults with associated weakening and post-fracturing creep processes. Fault healing processes then progressively close such fluid paths, associated with fault strengthening and fluid pressure recovery. Such transient behaviors have major consequences in the studies of: the evolution of permeability along faults with application tooil-field reservoir exploitation and fluid and waste storage; the evolution of fluid fluxes along faults with application to mass balance and climate evolution on the scale of the earth; the timing of earthquakes and the probability of their occurrence. The aim is to understand and evaluate the kinetics of the processes and the specific characteristic times of the fracturing and healing cycles. Results from laboratory experiments and natural fault studies are presented that show how pressure solution processes can explain both creep and sealing processes and the way they are associated in nature. The various fault-healing processes are discussed with their various characteristics in times from weeks to millennia. It is shown how they can be integrated into creep and sealing laws. Laboratory experiments give the values of some parameters of the laws (kinetics, thermodynamic). Other parameters must always be evaluated from the study of natural structures (geometry of path transfer, pressure and temperature conditions, nature of minerals and fluids). Consequently, the duration of the fracturing and sealing cycle is related to some extent to the geological context of a faulted area. Finally, as the mechanisms of permeability and strength evolution interact and occur on various scales of time and space, they must be integrated into numerical models, which are briefly discussed.

Fault zone restrengthening and frictional healing: The role of pressure solution

Laboratory and field observations note the significant role of strength recovery (healing) on faults during interseismic periods and implicate pressure solution as a plausible mechanism. Plausible rates for pressure solution to activate, and the magnitudes of ultimate strength gain, are examined through slide‐hold‐slide experiments using simulated quartz gouge. Experiments are conducted on fine‐grained (110 μm) granular silica gouge, saturated with deionized water, confined under constant normal stress of 5 MPa and at modest temperatures of 20 and 65°C, and sheared at a maximum rate of 20 μm/s. Data at 20°C show a log linear relation between strength gain and the duration of holding periods, whereas the higher temperature observations indicate higher healing rates than the log linear dependencies; these are apparent for hold times greater than ∼1000 s. This behavior is attributed to the growth and welding of grain contact areas, mediated by pressure solution. The physical dependencies of this behavior are investigated through a mechanistic model incorporating the serial processes of grain contact dissolution, grain boundary diffusion, and precipitation at the rim of contacts. We use the model to predict strength gain for arbitrary conditions of mean stress, fluid pressure, and temperature. The strength gain predicted under the experimental conditions (σeff = 5 MPa and T = 65°C) underestimates experimental measurements for hold periods of less than ∼1000 s where other frictional mechanisms contribute to strength gain. Beyond this threshold, laboratory observations resemble the trend in the prediction by our mechanistic model, implicating that pressure solution is likely the dominant mechanism for strength gain. The model is applied to the long‐term prediction of healing behavior in quartzite fault zones. Predictions show that both rates and magnitudes of gain in contact area increase with an increase in applied stresses and temperatures and that fault healing aided by pressure solution should reach completion within recurrence interval durations ranging from <1 to ∼104 years, depending on applied stresses, temperatures, and reaction rates.

The role of solution in the formation of boudinage and transverse veins in carbonate rocks at Rheems, Pennsylvania

The interaction of pressure solution with extensional strain is the most important factor influencing boudinage and vein structures in a mesoscopically folded sequence of subgreenschist-grade carbonate rocks from the overturned limb of the Lebanon Valley fold nappe at Rheems, Pennsylvania. The formation of stylolites and slickolites in association with boudins and veins indicates that extreme bed-normal contraction is intimately connected with bed-parallel extension. A variety of boudin shapes in dolomitic beds, from rectilinear to pinch-and-swell and fish-mouth structures, are formed by a combination of cataclastic flow and heterogeneous pressure solution. Many veins record catastrophic failure and collapse of wallrock prior to or during crystallization of the vein-fill. At the earliest stage of boudinage, veins in boudin necks are straight and perpendicular to bedding. With continued extension, they adopt a bow-tie form in cross section as a result of inward flow of the surrounding matrix and pressure solution of the fragment corners and vein margins. With continued stylolitization and separation of boudins, bow-tie veins are converted into transverse veins of extraordinary dimension. Failure to recognize the role of pressure solution in the formation of boudinage structure may result in inaccurate estimates of extension, erroneous assumptions regarding volume change, and incorrect interpretations of the changes in stress regime with time.

The role of pressure solution and intermicrolithon-slip in the development of disjunctive cleavage domains: a study from Helvick Head in the Irish Variscides

The offset of sedimentary laminae, bedding surfaces, veins and other passive markers across disjunctive cleavage domains has commonly been attributed solely to pressure solution. A detailed study of disjunctive cleavage within siltstones and sandstones from Helvick Head, Co. Waterford, on the eastern margin of the Irish Variscides indicates that the cleavage domains were initially formed by pressure solution processes. However, the study also revealed features which cannot be explained by pressure solution alone. The cleavage domains represent planes of weakness within otherwise relatively homogeneous rock. During fold tightening they were rotated out of parallelism with the principal ( XY) plane of the finite strain ellipsoid, thus enabling shear movement between the microlithons. It is considered that this intermicrolithon-slip caused a rotation of the elongate quartz grains within the cleavage domains resulting in an asymmetry of their long axes with respect to the cleavage domain margin, grain microfracturing and occasionally slickensides on cleavage surfaces. Intermicrolithon-slip is unlikely to be a localized phenomenon but is probably widespread throughout the Irish Variscides and other orogenic belts.

Role of pressure solution and dissolution in geology

Role of pressure solution and dissolution in geology

Theoretical Models of Porosity Reduction by Pressure Solution for Well-Sorted Sandstones

ABSTRACT The reduction of due to pressure solution is analyzed for some theoretical models consisting of aggregates of spherical grains of uniform size. The analysis is carried out for all six of the stable regular packing arrangements suggested by Graton and Fraser (1935). For each regular packing arrangement, two limiting cases are considered, one with all of the dissolved material removed from the system and the other with all of the material locally precipitated. Even for the most compact packing arrangement and complete local precipitation, the amount of vertical shortening for total reduction is found to exceed 26 percent. A comparison of the amount of reduction due to solution and the additional reduction due to precipitation of the dissolved material as cemen indicates that for all cases, solution is more important in the early stages while cementation becomes more effective in the later stages. The exact relationship also varies according to the packing arrangement and its orientation with respect to the direction of compaction. Cases 1 and 6 show the maximum cementation-solution ratio while Case 3 shows the minimum ratio. The results obtained from studies of regular geometric arrays of spherical grains can be used to estimate the importance of pressure solution as compared to other porosity-reducing mechanisms in the diagenesis of well-sorted sandstones of uniform grain size. Any initial in the sandstone can be represented by combinations of different volume proportions of the various packing arrangements. By comparing the minus cement porosity in a sandstone with the volume of cement predicted by a theoretical model, the role of pressure solution and the minimum volume of cement that has entered or left the system can be estimated.

Discussion on pressure solution

The papers contained in Vol. 135, Part 1, represent a considerable advance in knowledge of the diagenesis of sandstones. The importance and nature of mineral reactions (e.g. replacement of feldspars, modification of clay minerals) and the role of pressure solution during diagenesis, are repeatedly discussed. However, on reading the terminal written discussions to these papers, one finds some misunderstanding about the exact meaning and nature of pressure solution. Our aim is to clarify this misunderstanding by examining the mechanism of pressure solution during the diagenesis and deformation of terrigenous sediments. In theoretical studies ( Rutter 1976 , de Boer 1977 ), pressure solution is defined as the transfer of material by diffusion through an intergranular pore fluid phase in response to stress gradients around grains. A stress gradient gives rise to a gradient in chemical potential, and diffusive transfer of material from the point of high stress to that of low stress occurs to dissipate this gradient. The distance of diffusion will be determined by (a) the scale on which the stress gradient is developed, and (b) the kinetics of intergranular diffusion ( Rutter 1976 ). Stress gradients may arise in sediments through (i) the generation of heterogeneous stresses at point contacts of detrital grains, leading to a variation in normal stress around a grain surface, and (ii) the formation of gradients in mean stress through a rock in relation to the regular development of sedimentary or tectonic structures (cusps, nodules, spaced cleavages, folds, etc.). A relation between the extent of pressure solution (as recorded