Effect Of Fluid Composition Research Articles

The effect of fluid composition on the behavior of well cemented, quartz-rich sandstone during faulting

Previous studies [O'Kane, A., Onasch, C.M., Farver, J., 2007. The role of fluids in low-temperature, fault-related deformation of quartz arenite. Journal of Structural Geology 29, 819--836; Cook, J., Dunne, W.M., Onasch, C.M., 2006. Development of a dilatant damage zone along a thrust relay in a low-porosity quartz arenite, Journal of Structural Geology 28, 776–792] found that quartz arenite within two fault zones in the Appalachian foreland thrust belt displays very different structural styles and histories despite deforming at similar pressures and temperatures during the Alleghanian orogeny. A comparison of the grain-scale deformation and fluid histories using transmitted and cathodoluminescence microscopy and fluid inclusion microthermometry, shows that fluid composition was a controlling factor for causing these differences. The Cove fault zone deformed in the presence of aqueous fluids, first a CaCl 2 brine and then an iron-rich fluid. The precipitation of quartz cement from the brine kept pace with brittle deformation, maintaining overall rock cohesion in the fault zone. The introduction of iron-rich fluids caused a switch from precipitation to dissolution of quartz, along with precipitation of goethite. In a damage zone along a backthrust in the Cave Mountain anticline, early deformation occurred in the presence of an aqueous fluid from which quartz was precipitated. The latest deformation, however, occurred in the presence of a methane-rich fluid, which inhibited the precipitation of quartz cement producing porous breccias and open fractures despite deformation at 6 km depth. Fluid composition not only affected cementation in the fault zones, but also the selection of grain-scale deformation mechanisms. Therefore, it is a controlling factor in determining the behavior and strength of these fault zones.

The effect of fluid composition on the mechanism of the aragonite to calcite transition

AbstractExperiments were performed to investigate the transformation of natural aragonite crystals to calcite by reaction with aqueous solutions of calcium carbonate at hydrothermal conditions for different periods of time. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and Laser ablation inductively coupled mass spectrometry (LA-ICP-MS) were used to characterize the reaction product. The results indicate that the replacement of aragonite by calcite follows an interface-coupled dissolution-precipitation mechanism.

Effects of fluid composition and temperature on the salt film formation potential

Elevated activating-ion concentrations in solution favor anionic activation of the metal and lead to the salt film formation potential becoming less noble. Addition of inhibiting ions makes the potential more noble in the series sulfate, nitrate, and hydroxyl on account of changes in the strength of the Fe-[A−] bonds in the surface complex.

Lattice Boltzmann simulations of phase separation in chemically reactive binary fluids

We use a lattice Boltzmann method to study pattern formation in chemically reactive binary fluids in the regime where hydrodynamic effects are important. The coupled equations solved by the method are a Cahn-Hilliard equation, modified by the inclusion of a reactive source term, and the Navier-Stokes equations for conservation of mass and momentum. The coupling is twofold, resulting from the advection of the order parameter by the velocity field and the effect of fluid composition on pressure. We study the evolution of the system following a critical quench for a linear and for a quadratic reaction source term. Comparison is made between the high and low viscosity regimes to identify the influence of hydrodynamic flows. In both cases hydrodynamics is found to influence the pathways available for domain growth and the eventual steady states.

Layering and double-diffusion style convection in Europa's ocean

We assess the effects of fluid composition and depth-dependent hydrostatic pressure on dynamics in a europan ocean primarily composed of aqueous Na 2SO 4 and MgSO 4, for both a saturated and a dilute ocean. We observe a salinity- and pressure-dependent check on buoyancy in putative upwellings, which could act as a mechanism for storing heat in the ocean's base. Uptake of salt to a warmed parcel of water from the seafloor environment causes upwellings to lose buoyancy before reaching the base of the overlying ice, implying a tendency toward ocean stratification. We make an analogy to double-diffusive convecting systems observed in the Red Sea and elsewhere in Earth's waters. Using currently understood parameterizations for onset and stability, we estimate a range of temperatures and salinities for which double-diffusive convection may occur in Europa's ocean. In the Red Sea, boundary layers separating convecting zones have been observed to move upward as the lower layer acquires heat and salt. We examine the possibility of stratification and double-diffusive convection as mechanisms for heat storage in Europa's ocean, and possible correlation with recently inferred changes in ice surface alteration style over the last 30–80 Myr.

Preferential embrittlement of graphitic schists during extensional unroofing in the Alps: the effect of fluid composition on rheology in low‐permeability rocks

AbstractInterlayered graphitic and non‐graphitic schists from the Tauern Window, Eastern Alps, record contrasting mechanical behaviour during extensional exhumation. Graphitic schists contain mesoscale extension fractures, pervasive microcracks in garnet, and abundant secondary fluid inclusion planes; all three types of structures are oriented perpendicular to the stretching lineation. Crack spacings in garnet from graphitic samples are tightly clustered around a mean of 180 μm. Non‐graphitic schists have fewer and more randomly oriented microcracks and fluid inclusion planes and maintained strain compatibility via crystal plasticity. The presence or absence of graphite appears to have exerted a fundamental control on rheology during unroofing. Calculations for a model graphitic rock at 500 °C and fO2 = 10−24 MPa show that the equilibrium metamorphic fluid evolves from XCO2 = 0.07 to 0.38 during decompression from 700 to 400 MPa, in agreement with microcrack fluid inclusion data that show a change from XCO2 < 0.1 to 0.45 in graphitic samples over the same pressure interval. This compositional shift results in >60% expansion of the pore fluid during decompression. H2O‐rich fluid in non‐graphitic rocks expands <15% over the same pressure interval. The greater pore fluid expansion in low‐permeability graphitic horizons likely promoted tensile failure during unroofing. These results suggest that microcracking should be an inevitable consequence of decompression in many graphitic schists, whereas rocks that lack graphite are less likely to undergo microcracking. Microseismicity is predicted to be more common in graphitic than non‐graphitic rocks during unroofing of mountain belts.

Unusual transition in quartzite dislocation creep regimes and crystal slip systems in the aureole of the Eureka Valley–Joshua Flat–Beer Creek pluton, California: a case for anhydrous conditions created by decarbonation reactions

Microstructures and quartz c-axis fabrics were analyzed in five quartzite samples collected across the eastern aureole of the Eureka Valley–Joshua Flat–Beer Creek composite pluton. Temperatures of deformation are estimated to be 740±50 °C based on a modified c-axis opening angle thermometer of Kruhl (J. Metamorph. Geol. 16 (1998) 142). In quartzite layers located closest (140 m) to the pluton-wall rock contact, flattened detrital grains are plastically deformed and partially recrystallized. The dominant recrystallization process is subgrain rotation (dislocation creep regime 2 of Hirth and Tullis (J. Struct. Geol. 14 (1992) 145)), although grain boundary migration (dislocation creep regime 3) is also evident. Complete recrystallization occurs in quartzite layers located at a distance of ∼240 m from the contact, and coincides with recrystallization taking place dominantly through grain boundary migration (regime 3). Within the quartzites, strain is calculated to be lowest in the layers closest to the pluton margin based on the aspect ratios of flattened detrital grains. The c-axis fabrics indicate that 〈 a〉 slip operated within the quartzites closest to the pluton-wall rock contact and that with distance from the contact the operative slip systems gradually switch to prism [ c] slip. The spatial inversion in microstructures and slip systems (apparent “high temperature” deformation and recrystallization further from the pluton-contact and apparent “low temperature” deformation and recrystallization closer to the pluton-contact) coincides with a change in minor phase mineral content of quartzite samples and also in composition of the surrounding rock units. Marble and calc-silicate assemblages dominate close to the pluton-wall rock contact, whereas mixed quartzite and pelite assemblages are dominant further from the contact. We suggest that a thick marble unit located between the pluton and the quartzite layers acted as a barrier to fluids emanating from the pluton. Decarbonation reactions in marble layers interbedded with the inner aureole quartzites and calc-silicate assemblages in the inner aureole quartzites may have produced high X CO 2 (water absent) fluids during deformation. The presence of high X CO 2 fluid is inferred from the prograde assemblage of quartz+calcite (and not wollastonite)+diopside±K-feldspar in the inner aureole quartzites. We suggest that it was these “dry” conditions that suppressed prism [ c] slip and regime 3 recrystallization in the inner aureole and resulted in 〈 a〉 slip and regime 2 recrystallization, which would normally be associated with lower deformation temperatures. In contrast, the prograde assemblage in the pelite-dominated outer part of the aureole is biotite+K-feldspar. These “wet” pelitic assemblages indicate fluids dominated by water in the outer part of the aureole and promoted prism [ c] slip and regime 3 recrystallization. Because other variables could also have caused the spatial inversion of c-axis fabrics and recrystallization mechanisms, we briefly review those variables known to cause a transition in slip systems and dislocation creep regimes in quartz. Our conclusions are based on a small number of samples, and therefore, the unusual development of crystal fabrics and microstructures in the aureole to the EJB pluton suggests that further study is needed on the effect of fluid composition on crystal slip system activity and recrystallization mechanisms in naturally deformed rocks.

Effects of Fluid Composition on Mist Composition

In a reported study, mists of selected synthetic metalworking fluids were generated in laboratory experiments by two processes, nebulization (atomization) and air sparging (bubbling). Short-chain fatty acid species were determined by in situ trimethylsilyl derivatization. Comparison of relative amounts of the short-chain acids collected from mists generated by nebulization with those generated by sparging showed that the sparged mists had significantly higher amounts of neodecanoic, nonanoic, and dodecanedioic acids. Comparison of the amounts of acids collected by the resin cartridges to amounts found on the filters showed that significant losses of octanoic and isononanoic acids occurred over 8 hours of collection and that only dodecanedioic acid was not lost from the filter over a 22-hour sampling period. In another reported metalworking mist study, contaminants of metalworking fluids, e.g., tramp oils, were shown in laboratory experiments to increase the misting potential of water-based metalworking fluids. Significantly, tramp oil contamination caused less misting in synthetic fluids than soluble and semi-synthetic fluids.

Garnet composition as a petrogenetic indicator: An example from a marble -- calc-silicate granulite interface at Kondapalle, Eastern Ghats Belt, India

TheP-T-fluid histories of aluminous garnet+clinopyroxene-bearing calc-silicate granulites are commonly constrained through interpretation of sequential reaction textures based on activity-corrected petrogenetic grids for model systems, for example the widely used CAS(CO2-H2O) topologies. Application of these topologies to calc-silicates of diverse bulk composition is limited by the fact that the role of clinopyroxene and hence of garnet composition in the garnet-forming reactions is ignored or not adequately considered. In this contribution the complexities that arise from the involvement of clinopyroxene in the garnet-forming reactions are critically evaluated. As an example, the paragenetic relations and compositional features of clinopyroxene and coronitic garnet across paired scapolite- and wollastonite-dominated reaction zones (scp+cpx±qtz,cal,qtz — wo+cal+cpx±scp) developed between marble layers (cal±cpx,wo,scp) and their host calc-silicate granulite (cpx+pl±qtz,scp) at an exposure in the high-grade Eastern Ghats Belt (India) are examined. The microtextural features and systematic changes of modal and phase compositions across the profile indicate that clinopyroxene, scapolite, plagioclase, quartz and calcite as well as wollastonite participated in the garnet-forming reactions. Using the sub-assemblage qtz+cal+cpx+scp+grt+v in the system CaO-FeO-Al2O3-SiO2-CO2 it is demonstrated that at the ambient P-T-Xfluid conditions, the reaction coefficients of the participating phases are uniquely defined by the garnet composition. As a result, the P-T slope of a garnet-forming reaction changes with the garnet composition, with sharp changes at “singular points” across which one or more phases change their sides with respect to garnet in a given reaction. To consider the consequences of these complexities on the reaction topology of calc-silicate granulites, a new petrogenetic grid for the system CaO-FeO-Al2O3-SiO2-CO2 involving clinopyroxene has been constructed. The effects of fluid composition (CO2-H2O-O2), fluid pressure (Pfluid

Fluid ionic composition influences hydraulic conductance of xylem conduits

The direct effect of fluid composition on xylem hydraulic conductance is investigated in excised stem segments of chrysanthemum (Dendranthema× grandiflorum Tzvelev cv. Cassa) plants. Dynamic changes in hydraulic conductance are accurately measured at 30 s intervals before and after modifications of the composition of the standard fluid (deionized water). It is investigated whether osmotic properties of the flowing solution influence overall hydraulic conductance by affecting the hydraulic conductance of vessel‐to‐vessel pit membranes, as has previously been suggested. Various iso‐osmotic salt solutions (20 mOsm kg−1) of different composition raised the hydraulic conductance of 20 cm long stem segments approximately 5–8% compared to deionized water. In contrast, carbohydrate solutions with similar osmotic strength and pH did not cause any change in hydraulic conductance. KCl solutions that greatly differed in osmotic strength all increased hydraulic conductance, but the response was not correlated with the osmotic strength of the solution. Increasing the number of vessels that were open from one cut end to the other by shortening the stem segments greatly increased the hydraulic conductance response. Changing from deionized water to a salt solution caused an immediate increase in hydraulic conductance, while a shift back to deionized water resulted in a slow decline. This decline lasted longer when the salt solution contained divalent cations compared to monovalent cations. It is concluded that the presence of cations and not the osmotic strength in the flowing solution influenced the hydraulic conductance. The phenomenon is not caused by the vessel‐to‐vessel pit membranes, which in fact suppressed the effect, due to their large contribution to the overall resistance to water flow.

Fluid ionic composition influences hydraulic conductance of xylem conduits.

The direct effect of fluid composition on xylem hydraulic conductance is investigated in excised stem segments of chrysanthemum (Dendranthema x grandiflorum Tzvelev cv. Cassa) plants. Dynamic changes in hydraulic conductance are accurately measured at 30 s intervals before and after modifications of the composition of the standard fluid (deionized water). It is investigated whether osmotic properties of the flowing solution influence overall hydraulic conductance by affecting the hydraulic conductance of vessel-to-vessel pit membranes, as has previously been suggested. Various iso-osmotic salt solutions (20 mOsm kg-1) of different composition raised the hydraulic conductance of 20 cm long stem segments approximately 5-8% compared to deionized water. In contrast, carbohydrate solutions with similar osmotic strength and pH did not cause any change in hydraulic conductance. KCl solutions that greatly differed in osmotic strength all increased hydraulic conductance, but the response was not correlated with the osmotic strength of the solution. Increasing the number of vessels that were open from one cut end to the other by shortening the stem segments greatly increased the hydraulic conductance response. Changing from deionized water to a salt solution caused an immediate increase in hydraulic conductance, while a shift back to deionized water resulted in a slow decline. This decline lasted longer when the salt solution contained divalent cations compared to monovalent cations. It is concluded that the presence of cations and not the osmotic strength in the flowing solution influenced the hydraulic conductance. The phenomenon is not caused by the vessel-to-vessel pit membranes, which in fact suppressed the effect, due to their large contribution to the overall resistance to water flow.

Application of Two-phase Deviation Factor to Material Balance Calculations For Gas-condensate Reservoirs

Abstract Material balance calculations for gas-condensate reservoirs with reservoir pressures below the dew-point pressure require the use of two-phase deviation factor to account for the phase behaviour effects of a gas-condensate fluid. Recently, an empirical correlation for the two-phase deviation factor has also been presented in the literature. In this study, a phase behaviour package based on the Redlich-Kwong equation of state as modified by Zudkevitch and Joffe has been used to investigate some of the issues in connection with the application of two-phase deviation factor to material balance calculations for gas-condensate reservoirs. This study shows that the two-phase deviation factor does not necessarily increase in the two-phase region as the pressure increases, whereas the empirical correlation shows that the twophase deviation factor always increases with pressure. A study has also been carried out to quantify the errors in estimating the initial gas-in-place due to input data errors, fluid composition effects, computation methodology for deviation factor, and the use of improper deviation factor. Introduction For a normally-pressured, volumetric, dry gas reservoir, the relevant material balance equation is(1): Equation 1 (available in full paper) Equation (1) is also suitable for material balance analysis of pressure-cumulative production data with all data collected at reservoir pressures above dew-point pressure for a volumetric, gas-condensate reservoir. However, material balance analysis for pressure-production data below dew-point pressure can be carried out in combination with the pressure-production data above dewpoint pressure, if two-phase deviation factor (z2ph) replaces gas deviation factor (zv) in Equation (1) for all data below dew-point pressure(2,3). The variable, z2ph, is expressed by the following equation: Equation 2 (available in full paper) As stated in References (2) and (3), two-phase deviation factor can be computed using constant-composition expansion (CCE) calculations for typical reservoir engineering applications. Obviously, z2ph = zv for pressures above dew-point pressure because liquid phase does not exist (i.e., L = 0) above dew-point pressure. References (2) and (3), among others(4), have suggested that the Redlich-Kwong equation of state as modified by Zudkevitch and Joffe(5,6) (referred to as ZJRK EOS in this paper) is adequate for computations of phase behaviour aspects of typical gas-condensate reservoirs. Details of the ZJRK EOS used in this study appear in Reference (7). Recently, Rayes et al.(8), have presented an empirical correlation for the two-phase deviation factor for gas-condensate fluids. The correlation expresses two-phase deviation factor as a function of pseudo-reduced pressure and pseudo-reduced temperature. They developed their correlation based on 67 constant volume depletion studies with C7+ >4%. They concluded that their correlation yields an average error of 3.66% in predicting two-phase deviation factor. Rayes et al.,(8) also recommended that for C7+< 4% and for a well stream specific gravity < 0.911, the singlephase gas deviation factor can be used for the material balance calculations. In this study, the results from the Rayes et al.(8), correlation are compared with the results from the ZJRK EOS. Ambastha and van Kruysdijk(9) studied the effects of input data error on material balance analysis for volumetric, gas and gascondensate reservoirs.

Interfacial structure analysis for the prediction of morphology of crystals and implications for the design of tailor-made additives

In order to analyze the influence of fluid on the growth morphology of crystals, a so-called interfacial analysis has been developed within the framework of inhomogeneous cell models. In this analysis, the effects of fluid composition (including solute, solvent, impurities, etc.) and concentration on the growth and morphology of crystals are explicitly taken into account. One of the key steps in this analysis is to identify the effective growth units in different crystallographic orientations and to calculate their concentrations. This involves a conformation analysis and calculation of the entropy barrier using a statistic thermodynamic approach. This technique has been applied with great success to predict morphologies of a variety of crystals growing from solutions, which cannot be predicted correctly using the conventional PBC analysis. An example of paraffin crystals grown from solutions is given. Based on similar principles, implications for the design of tailor-made additives are proposed.

Diffusion of chlorine in fluid-bearing quartzite: effects of fluid composition and total porosity : J. M. Brenan, Contributions to Mineralogy & Petrology, 115(2), 1993, pp 215–224

Diffusion of chlorine in fluid-bearing quartzite: effects of fluid composition and total porosity : J. M. Brenan, Contributions to Mineralogy & Petrology, 115(2), 1993, pp 215–224

Fluid composition effects on silica gel aging

Abstract The effect of aging conditions on the pore structure development in porous hydrogel and xerogel silica spheres has been monitored by following changes in pore radius, pore volume and surface area during autoclave experiments carried out in water. The pore structure development on aging spherical silica gel bodies is primarily influenced by temperature, pH and the silica to water ratio which affects the rate of silica transport. The more rapid aging of the colloidal silica observed in xerogels when compared in the hydrogels is probably due to an increase in (de)polymerization rate, catalyzed by ionized tertiary silanol groups. Both the high pH and high [NaCl] increase the concentration of ionized and sodium-complexed surface silanol groups, [Si s O − Na + ]. High pH strongly increases the repulsion between negative charged silica particles and increases the transport rate of silica. The high [NaCl] reduces the transport rate of silica and shields the negative charge on the surface. The pore radius and pore volume of hydrogel spheres are increased with pH, whereas they remain constant with increasing [NaCl].

Diffusion of chlorine in fluid-bearing quartzite: effects of fluid composition and total porosity

To assess further the role of pore fluids in enhancing mass transport in deep-seated rocks, bulk diffusion coefficients (D-values) for chlorine have been measured at 1.0 GPa and 1000°C in texturally-equilibrated quartzites containing varying amounts (0.3–2.8 vol%) of H2O or a CO2−H2O mixture (X CO2=0.4). Experiments were used to monitor transport predominantly through the fluid phase by employing a chemical tracer dissolved in the fluid (chlorine) that is virtually insoluble in the rock matrix (quartzite) but is somewhat soluble in a small fraction of dispersed indicator minerals (fluorapatite). For diffusion in H2O-bearing quartzite, experiments with ≥ 1 vol.% fluid exhibit a continuous decrease in D-values with decreasing porosity whereas an abrupt drop in the diffusion coefficient is indicated by the experiments with 0.3 vol.% fluid. At a given total porosity, diffusion coefficients obtained from quartzites containing the CO2−H2O fluid range from ∼80x to > 3000x lower than those from H2O-bearing experiments. Bulk transport measurements were correlated with textural observations and the observed reduction in bulk D-values for quartzites containing the CO2−H2O fluid reflects the overall isolated nature of porosity in such samples. The drop in the bulk D-value for quartzites with 0.3 vol.% H2O probably arises from the elimination of interconnected porosity owing to the presence of a sufficient number of dry grain edges. Textural observations, combined with transport measurements, are consistent with the pore structure predicted by dihedral angle measurements. However, due to anisotropy in the interfacial energy of quartz, long-range fluid connectivity is dramatically reduced in quartzites with low H2O contents, despite a median dihedral angle of less than (but near) 60°. Observed variations in chlorine D-values in samples with connected and non-connected porosity are found to be consistent with previous bulk property measurements on texturally-equilibrated, fluid-bearing rocks. Results of this study, combined with prior bulk diffusion measurements for oxygen, provides a general assessment of the effect of small amounts of fluid on the enhancement of mass transport in quartzose lithologies over a range of crustal P and T. At conditions of textural equilibrium, it is expected that the fluid phase provides little or no contribution to the long-range diffusive flux of solutes in quartz-rich rocks containing small amounts of H2O or CO2−H2O mixtures.

Rutile solubility and mobility in supercritical aqueous fluids

Experimental and thermodynamic data and the apparent immobility of Ti under metamorphic conditions suggest that rutile is very insoluble in aqueous fluids at upper crustal conditions. New solubility measurements at 1.0–2.93 GPa and 800–1200°C show, however, that under certain pressure and temperature conditions rutile is quite soluble in H2O. Solubilities were estimated from the measured weight loss of a single crystal equilibrated with a known mass of fluid in a piston cylinder apparatus. Measured solubilities in H2O range from 0.15 wt% (wt loss crystal/wt fluid) at 2.93 GPa and 1000°C to 1.9% at 1.0 GPa and 1100°C. Solubility increases with increasing temperature and with decreasing pressure in a manner given by the following fit to the experimental data: $$\log _{10} m_{Ti} = - 7049/T - (0.589* P)/T + 5.14$$ wherem Ti is the molality of Ti in the fluid,T is in degress Kelvin andP is in MPa. The effect of fluid composition on rutile solubility was also examined at 1.0 GPa and 1000°C for H2O-CO2, 1m NaCl, and 1m HF fluids. Kesults suggest that solubility depends on the mole fraction of H2O in the fluid but is independent of ionic strength and fluid pH. This behavior implies that Ti dissolves as the neutrally-charged hydrolysis product Ti(OH)4. The free energy of this species was calculated for each set of experimental conditions. TheP-T dependence of rutile solubility suggests that aqueous fluids derived from subducted oceanic lithosphere would dissolve rutile or other Ti-rich minerals from the deepest portion of the mantle wedge and precipitate them at higher levels. Subsequent melting of the base of the mantle wedge would form HFSE-depleted IAB.

Partitioning of trace elements between olivine and aqueous fluids at high P-T conditions: implications for the effect of fluid composition on trace-element transport

In order to investigate the effect of fluid composition on trace-element transport at high pressure and temperature, olivine/fluid partition coefficients ( D) were measured in experiments involving aqueous carbonate-, chlorine- and NaOH- bearing fluids at 1.0 GPa and 1000°C. Radiotracers of Ce, Gd, Yb, Ba, Sr, Cs, and Na were used to monitor trace-element levels. D values were calculated by mass balance using the trace-element contents of acid-washed olivines from run-products combined with whole-sample abundances. A single reversal experiment in which pre-doped olivine was annealed in tracer-free water yielded results consistent with forward experiments involving olivine + H 2O. This result suggests crystal/fluid equilibrium was approached over the 5-day durations used for all experiments. Partition coefficients were found to vary with fluid chemistry and, with the exception of the D's for Na, olivine/fluid values are markedly lower than those determined for olivine/H 2O. Interelement ratios in the fluid also vary with fluid chemistry as exemplified by enhanced partitioning of Ce relative to Gd into Na, K or Cs carbonate-bearing compositions. Consideration of the trace-element exchange equilibria between olivine and fluid suggests that variation in the activity coefficient for aqueous trace-element and charge-balancing cations is likely to account for the interfluid variation in D values. Na partitioning is interpreted to be coupled to the formation of Na Al complexes as has been suggested in previous studies. These data indicate that, although trace elements do not partition strongly into H 2O coexisting with olivine, the addition of dissolved salts dramatically changes this result. Such variation in D values for different fluid chemistries suggests that fluid composition, in addition to residual mineralogy, may affect both absolute trace-element abundances and interelement fractionation in high P-T aqueous fluids.

Effect of varying fluid composition on mass and energy transport in the Earth's crust

The ability of fluids flowing through a given volume of crustal rock to affect mass and energy transfer is controlled by the physical and chemical nature of the fluid. Most numerical simulations of fluid‐flow and fluid‐rock interaction approximate the mass and energy transfer characteristics of crustal fluids using the physical, thermodynamic and transport properties of H2O. Results of fluid inclusion studies indicate that H2O is, in fact, the dominant component of fluids from most shallow to intermediate depth crustal environments, with other components usually present in varying amounts. In many crustal environments, properties of the fluids are adequately represented by those of the system H2O‐CO2‐NaCl.In the pure H2O system, mass and energy transport properties reach extrema and become very sensitive to small variations in temperature or pressure in a restricted region of P‐T space near the critical point. This “critical region” migrates to higher and lower temperatures as NaCl or CO2, respectively, are added to water, and mass and energy transport properties become less sensitive to temperature or pressure variations when either NaCl or CO2 are added to water.The effect of fluid composition on mass transfer is illustrated by the system SiO2‐H2O‐NaCl. The SiO2‐H2O sub‐system is characterized by a solubility maximum, or region of retrograde solubility, at temperatures and pressures slightly above the critical point of water. Addition of NaCl increases the solubility of silica and shifts the quartz solubility maximum to higher temperatures and pressures relative to pure H2O.

Metamorphic studies: research in progress

Report of a meeting of the Metamorphic Studies Group held at Burlington House, on 5 March, 1986. The meeting was organized by K. H. Brodie. A Metamorphic Studies Group meeting on Metamorphic studies: research in progress and the fifth Annual General Meeting of the Group were held on 5 March 1986. Fifteen papers were presented, including four from overseas speakers. For the first time this year the talks included one invited overseas speaker, Professor W. L. Griffin from the Mineralogisk-Geologisk Museum in Oslo, who presented a review of high pressure metamorphism in Western Norway. The morning session was chaired by Stephen Daly, and concentrated on the topical theme of the role of fluids in metamorphism. B. Yardley started the session with a joint paper with S. Bottrell considering the important effects that fluid immiscibility may have in natural metamorphism, particularly at low grades. In particular, in a two-phase system the relative permeability may become very low for a phase of low proportions. This may have the effect concentrating, for example, NaCl in the fluid phase. K. W. Burton then considered the effects of fluid composition on surface energy, using metamorphic sector zoning as an example. Increasing surface energy increases the overstepping of an equilibrium boundary, leading to fewer nuclei which will tend to grow relatively large. In the garnets investigated, inclusions, were found to be rich in CO 2 , H 2 O (plus N +Ar), and it was suggested that quartz intergrowths commonly develop as a result of low