Diffusion metasomatism and mineral reaction zones; general principles and application to feldspar alteration

Weare, John H.; Stephens, John; Eügster, Hans P.

doi:10.2475/ajs.276.7.767

Cited by 49 publications

(16 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The irreversible thermodynamics of the interrelationships of chemical reaction and diffusion have been successfully described for systems close to equilibrium through a phenomenological treatment by, among others, de Groot & Mazur (1962), Katchalsky & Curran (1965), and Prigogine (1967). More recent work by Fisher (1973Fisher ( ,1977, Weare et al (1976), and Foster (1977,1981) has illustrated the value of the phenomenological approach in the description of geological processes. The great strength of the phenomenological treatment in the description of diffusion related processes lies in the effective bridging of the gap between chemical and physical driving forces by relating the affinities of reaction (A = -En,/*, (n x and /i f are, respectively, the number of moles and the chemical potential of component i)) to spatial derivatives (= V/ij) for nearequilibrium systems which are dominated by continuous processes.…”

Section: Reaction Behaviour In the Metaquartz Dioritementioning

confidence: 99%

The Effects of Disequilibrium and Deformation on the Mineralogical Evolution of Quartz Diorite During Metamorphism in the Eclogite Facies

Koons

Rubie

Fruch-Green

1987

Journal of Petrology

107

104

View full text Add to dashboard Cite

In the Sesia Zone, Western Alps, a large volume of orthogneiss formed as a result of eclogite fades metamorphism and deformation of quartz diorite during early Alpine underthrusting and subduction. Rare lenses of undeformed metaquartz diorite, preserved within the orthogneiss, represent an early stage in the evolution of this latter rock type. The metamorphic and microstructural evolution of the orthogneiss in the eclogite fades has been reconstructed from studies of gradational contacts between undeformed and strongly deformed rocks.High pressure transformations of the original igneous plagioclase + biotite + quartz assemblage to jadeitic pyroxene (Jd 0 . 95 _ 0 . 83 ) + zoisite + quartz + garnet + 2 muscovites developed prior to deformation. Slow intergranular diffusion resulted in a state of disequilibrium between small textural domains in the metaquartz diorite. The compositions of the phases of the undeformed metaquartz diorite do not reflect the bulk rock composition, but were controlled by their position relative to reactant phases. The jadeitic pyroxenes, for example, formed in localized domains which originally consisted of sodic plagioclase whereas omphacite was the equilibrium pyroxene for the bulk rock composition.Mineralogical changes which occurred during subsequent deformation of the metaquartz diorite are interpreted as resulting from a progressive enlargement of equilibrium domains and the partial equilibration of mineral compositions to the bulk rock composition rather than from changes in pressure and temperature. Initially during high-strain deformation, fine-grained aggregates of jadeitic pyroxene + quartz + zoisite (originally pseudomorphing plagioclase) are inferred to have deformed by a mechanism of grain boundary sliding accommodated by diffusive mass transfer. Muscovite and garnet compositions homogenized during the deformation but due to slow intracrystalline diffusion, pyroxene compositions (Jd o . 9J _ 0 . go ) remained metastable. The coarsening of pyroxene eventually terminated deformation by grain boundary sliding and this mineral subsequently deformed by intracrystalline plastidty. This latter process was accompanied by and perhaps catalysed a change in pyroxene composition from metastable jadeite towards omphacite by a reaction involving the resorption of garnet and the nucleation and growth of paragonite. The resulting orthogneiss consists of quartz -I-omphadte + garnet + phengite + paragonite + zoisite. The rock is characterized by a broad range of pyroxene compositions (Jd o . 8 _ O5 ) due to the incomplete equilibration of this mineral to the bulk rock composition and a lack of Fe-Mg exchange equilibrium between pyroxene and garnet. However, in contrast to the undeformed metaquartz diorite, there are no obvious textural indications of disequilibrium between phases in the orthogneiss.

show abstract

Section: Reaction Behaviour In the Metaquartz Dioritementioning

confidence: 99%

The Effects of Disequilibrium and Deformation on the Mineralogical Evolution of Quartz Diorite During Metamorphism in the Eclogite Facies

Koons

Rubie

Fruch-Green

1987

Journal of Petrology

107

104

View full text Add to dashboard Cite

show abstract

“…The study of water-rock interaction began by focusing on geochemical interactions in the absence of transport processes, although a few notable exceptions exist (Thompson 1959;Weare et al 1976). Moreover, these analyses began by adopting a primarily thermodynamic approach, with the implicit or explicit assumption of equilibrium between the fluid and rock.…”

Section: Introductionmentioning

confidence: 99%

Fluid-Rock Interaction: A Reactive Transport Approach

Steefel

Maher

2009

Reviews in Mineralogy and Geochemistry

212

189

View full text Add to dashboard Cite

“…1 illustrates the basic kinetic processes relevant to metamorphic fluid reactions. Many earlier papers focused on the description of transport control during metamorphic reactions, in particular diffusion control (Fisher and Elliott, 1974;Joesten, 1974Joesten, , 1977Joesten, , 1983Fisher, 1975Fisher, , 1978Frantz andMao, 1975, 1976;Weare et al, 1976). The description of diffusion was amenable to treatment by the theory of irreversible thermodynamics.…”

Section: Kinetics Of Metamorphic Fluid-rock Reactionsmentioning

confidence: 99%

Metamorphic reaction rate laws and development of isograds

Lasaga

1986

Mineral. mag.

113

View full text Add to dashboard Cite

A n S T R A C T. New data on the kinetics of dehydration o f muscovite+quartz suggest the necessity for a careful treatment of both surface kinetics and diffusion processes in metamorphic reactions. A new model is proposed that illustrates the relative role of diffusion and surface reactions in the overall metamorphic process. The rate law for the reaction at mineral surfaces derived from the experimental data is shown to be probably non-linear and similar to rate laws derived from Monte Carlo calculations. The experimental rate data is then used in a heat flow calculation to model the evolution of the muscovite isograd in the field. The position of the isograd, the temperature oversteps above equilibrium, and the width of 'reaction zones' are then analysed as a function of intrusion size and kinetic parameters.KEYWORDS: metamorphic reactions, surface kinetics, diffusion, rate laws. THE fOCUS of metamorphic petrology today is shifting from a static mode based on the thermodynamics of mineral assemblages to a dynamic mode aimed at the quantification of the processes that produced the metamorphism. As a result, the non-equilibrium aspects and the kinetics of metamorphic processes are being increasingly studied. The proper role of equilibrium versus kinetics in describing metamorphism is still being debated today. As petrologists initially tackled the complexities of the texture and mineralogy of metamorphic rocks, many of which could not coexist according to an equilibrium model, the concept of local equilibrium (Thompson, 1959;Helgeson, 1968; Fisher and Elliott, 1974) was born. In this fashion, equilibrium was maintained at least on a local scale, which meant essentially for surfaces of mineral grains in physical contact with each other. Isotope studies (Lattanzi et al., 1980; Rumble et al., 1982;Rumble and Spear, 1983;Tracy et al., 1983) have investigated the length scale of equilibrium and found many cases where it was only a few centimetres.Closer inspection of the chemical composition of minerals has unearthed a wide variety of zoning profiles which preserve, albeit encoded by the ~) Copyright the Mineralogical Societykinetics, the details of the metamorphic history. The ubiquitous zoning found in several metamorphic minerals has led to recent papers on their kinetic significance (Lasaga et al., 1977;Lasaga, 1983;Ozawa, 1984;Smith and Ehrenberg, 1984;Wilson andSmith and Wilson, 1985; Docka et al. (in press).More recently, the kinetic study has been extended to the generation, motion and characterization of metamorphic fluids. Within the assumption of local equilibrium, it was logical to assume that the local mineral assemblage would control or buffer the composition of the fluid phase during dehydration/hydration and decarbonation/ carbonation reactions and that the kinetics were fast enough to be ignored. This control, however, can only be achieved by the continuous and concurrent dissolution and growth of one or several minerals. As Greenwood (1975) has shown, the amount of fluid involved during evolution...

show abstract

Diffusion metasomatism and mineral reaction zones; general principles and application to feldspar alteration

Cited by 49 publications

References 0 publications

The Effects of Disequilibrium and Deformation on the Mineralogical Evolution of Quartz Diorite During Metamorphism in the Eclogite Facies

The Effects of Disequilibrium and Deformation on the Mineralogical Evolution of Quartz Diorite During Metamorphism in the Eclogite Facies

Fluid-Rock Interaction: A Reactive Transport Approach

Metamorphic reaction rate laws and development of isograds

Contact Info

Product

Resources

About