The thermodynamic properties of 154 mineral end-members, 13 silicate liquid end-members and 22 aqueous fluid species are presented in a revised and updated data set. The use of a temperature-dependent thermal expansion and bulk modulus, and the use of high-pressure equations of state for solids and fluids, allows calculation of mineral–fluid equilibria to 100 kbar pressure or higher. A pressure-dependent Landau model for order–disorder permits extension of disordering transitions to high pressures, and, in particular, allows the alpha–beta quartz transition to be handled more satisfactorily. Several melt end-members have been included to enable calculation of simple phase equilibria and as a first stage in developing melt mixing models in NCKFMASH. The simple aqueous species density model has been extended to enable speciation calculations and mineral solubility determination involving minerals and aqueous species at high temperatures and pressures. The data set has also been improved by incorporation of many new phase equilibrium constraints, calorimetric studies and new measurements of molar volume, thermal expansion and compressibility. This has led to a significant improvement in the level of agreement with the available experimental phase equilibria, and to greater flexibility in calculation of complex mineral equilibria. It is also shown that there is very good agreement between the data set and the most recent available calorimetric data.

An internally consistent thermodynamic data set for phases of petrological interest

Calculation of the thermodynamic and transport properties of aqueous species at high pressures and temperatures: Standard partial molal properties of organic species

Constraints on melting and magma production in the crust

A companion paper (England & Thompson, 1984a) investigates the pressure-temperature—time (PTt) paths followed by rocks undergoing burial metamorphism in continental thickening events. This paper discusses problems involved in inferring such paths from the petrological data available in metamorphic rocks and—once such paths are determined—how they may be interpreted in terms of the thermal budgets of metamorphism. Each of the principal facies series (glaucophane-jadeite, andalusite-sillimanite and kyanite-sillimanite) may be encountered by rocks involved in the thickening and erosion of continental crust in a regime of average continental heat flow. The inference of a minimum thermal budget required for a given metamorphism depends strongly on a knowledge of the PTt paths followed by rocks during the metamorphism. Discrimination between possible thermal regimes is greatly enhanced if portions of PTt paths, rather than single PT points, are available, and additional constraint is possible if these paths are supplemented by geochronological, structural and heat flow data. 1. I N T R O D U C T I O N One of the standard inverse problems of metamorphic petrology is to infer the thermal regime operating during a metamorphic episode from the mineral assemblages and compositions in rocks that reach the surface after the episode is finished. In fact, orogenic processes are sufficiently complicated, and petrological data sufficiently limited that no formal inverse is ever attempted; interpretation usually depends on the calculation of pressure-temperature— time {PTt) paths for model tectonic settings and on using these with metamorphic petrological data to give estimates of thermal regimes operating during metamorphism. The previous paper (England & Thompson, 1984a, hereafter called Part I) outlined some of the model pressure-temperature-time (PTt) paths that would be followed by rocks under a variety of conditions resulting from crustal thickening, and addressed the question of what class of information is recoverable from PT data obtained from metamorphic rocks. A major conclusion of Part I is that we expect the overall thermal development of a regional metamorphic terrain to depend on relatively few large scale parameters and, consequently, that if it is possible to extract information from mineral assemblages about regional PTt paths, we should be able to make estimates of the magnitudes of the parameters controlling the regional metamorphic budget—notably the total heat supply to the orogenic belt, the lengthscales of thickening, the length and time scales of erosion and the extent of magmatic involvement in the metamorphic episode. Smaller scale phenomena (intrusions, transposition of isograds by folding or faulting, etc.) will affect observations made in the field, but cannot be uniquely interpreted in terms of larger scale phenomena. I Journal of Petrology. Vol. 25. Part 4. pp. 929-955. I984| 930 A. B. THOMPSON AND P. C. ENGLAND In this paper we discuss the problems of relating petrological PT points or, more usefully, portions of PTt paths to regional thermal regimes. In principle such data, particularly in conjunction with heat flow, isotopic and structural studies, can provide valuable information on the tectonic setting and thermal budget of metamorphism. Unfortunately, it is often not possible to gather all the information necessary for a unique interpretation of a given terrain; nonetheless PTt data may be used to place constraints on metamorphic processes, and we hope that the considerations presented here will help in the interpretation of such data. 2. PT POINTS AND PTt PATHS Many of the inferences of conditions during the evolution of orogenic belts that have been made using PT data from metamorphic rocks are based on relatively simple conceptual models of the metamorphic environment and, while these models serve a useful purpose, it is important to recognize their limitations as well as their merits. In this section we consider how these conceptual models need modification in view of the nature of the PTt paths that are followed by rocks undergoing regional metamorphism. For consistency, most of the paths discussed here are taken from section 5 of Part I, but many of the arguments may readily be applied (with the appropriate adjustments) to other forms of PTt paths. The first set of problems encountered in inferring thermal and tectonic regimes from metamorphic data are concerned with deciding where on a PTt path the points that make up a PT array are recorded, and the rest of this section is largely concerned with them. We consider how the kinds of PTt paths calculated in Part I influence PT data recorded in mineral assemblages on the surface, through their effects on reaction kinetics, chemical diffusion and through the control exerted by fluids on the mineral assemblages preserved. In particular, we emphasize the means whereby information may be gained on parts of PT paths, rather than on discrete PT points. 2.1. Geotherms, facies series and PT paths The material of these papers concerns the perturbing and relaxation of temperatures in continental lithosphere, and the PT conditions experienced by rocks moving relative to these evolving geotherms. As the word geotherm is used in at least two distinct senses in the petrological literature it is worth including definitions here to avoid possible ambiguities. A geotherm is simply the relation between temperature and depth within the earth at any one time; this relation may be a steady state one or a transient one, but in either case its FIG. 1. Metamorphic mineral assemblages at the erosion surface in (a) are assigned through experimentally calibrated mineral reactions to metamorphic fades series (6) and fades (c). The equilibrium data in (b) are shown as examples only; the sources are given by Thompson & Thompson (1976, fig. 13) and by Thompson & Tracy (1979, fig. 2) and transferred to this figure using a crustal density of 2-8 Mg m~. The equilibria include two versions of the relative stability of Al2SiOj polymorphs (from Holdaway, 1971 and Richardson el a/., 1969; where andalusite = AND; kyanite = KYA; sillimanite = SIL), and the breakdown of albite (ALB) to jadeite (JAD) plus quartz (QTZ). The dehydration reactions produdng almost pure H2O (vapor = V) are experimentally investigated in the presence of excess water (onp x 1). Other abbreviations: muscovite (MUS), analdme (ANL), pyrophyllite (PYP), potash-feldspar (KSP). Mineral assemblages assigned to mineral facies (c) at the erosion surface in (a) are shown with normal type to distinguish them from facies representing present day conditions in the underlying crust, shown by italic type. The P-T locations of metamorphic facies (c) and facies series (6) are based upon correlation with experimental studies of many more mineral equilibria than shown here (for example see Fyfe el a/., 1978, fig. 6.8). Because of the transitional nature of mineral assemblages in the field and the displacement of calibrated reactions through crystalline solution in natural minerals, the P-T boundaries of facies and fades series are approximate and gradational. One common practice is the assigning of mineral assemblages at the erosion surface (solid points in (a)) to a steady-state geotherm, shown by the heavy curves in (6) and (c). The dashed lines crossing the geotherm in (c) represent schematic PTt paths experienced by rocks during exhumation (see Part I). •1 3 JO m C C C jo m I H m m C m m H X P R E S S U R E , kb < p » 2 .8 g c m \" 3 ) ? * * * PR ES SU R E , kb ( p -2 .8 g c m \" 3 ) 932 A. B. THOMPSON AND P. C. ENGLAND reference level is the earth's surface. A transient geotherm may be the result of transient heat sources, of motions due to erosion, overthrusting, rifting etc., or of thermal relaxation from a previously perturbed regime; all three of these cases occur during the evolution of the systems discussed in this paper. Individual PT points obtained from mineral assemblages are often interpreted in terms of geothermal gradients (Fig. 1); it should be clear from Part I that while an individual PT point may have been set on a geotherm, its relation to the heat source distribution giving rise to that geotherm is usually unclear. The problem becomes worse if an array of PT points from one terrain is to be interpreted; such arrays have been referred to, misleadingly, as 'metamorphic geotherms' (e.g. England & Richardson, 1977). In fact these arrays bear no relation to any one geotherm that existed during metamorphism, because they consist of a set of PT conditions inferred from assemblages that were preserved at different times and different places during metamorphism (e.g. England & Richardson, 1977, fig. 1; section 3.1 below). We prefer the designation 'piezothertnic array' (Richardson & England, 1979) for the set of peak metamorphic conditions experienced in a thickened pile, or 'PT array' for a suite of metamorphic conditions preserved in a metamorphic terrain. Certain rock types and minerals are often regarded as characteristic of distinct pressure (/>) and temperature (T) regimes, and the indications these give of changing metamorphic grade on a regional scale lie behind the facies series concept of Miyashiro (1961). The three principal facies series, glaucophane-jadeite (Gla—Jad), kyanite—sillimanite (Kya-Sil) and andalusite-sillimanite (And—Sil) are taken to be representative of, respectively, high P— low T, intermediate T and P, and high T-low P metamorphism. In addition, several workers (e.g. Heitanen, 1967) specify intermediate facies series (see Fig. 1). In principle this approach acknowledges only that the rocks involved have passed through some region of PT space that is characterized by the stability fields of the diagnostic minerals, although the facies series concept, in its application, is often used to infer a tectonic setting for the metamorphism. We shall refer in this paper to facies, but we 

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Pressure—Temperature—Time Paths of Regional Metamorphism II. Their Inference and Interpretation using Mineral Assemblages in Metamorphic Rocks

Determination of the homogenization temperatures and densities of supercritical fluids in the system NaClKClCaCl2H2O using synthetic fluid inclusions

Calculations show that H2O and CO2 produced during devolatilization of an average pelite will occupy ∼12 vol. % of the rock at 500°C and 5 kb. Because the tensional strength of well foliated rock at metamorphic conditions is vanishingly small, such a volume of fluid having any vertical extent will fracture the rock and escape upward owing to its lower density.

Volatile production and transport in regional metamorphism

Hydration state, charge and chemical stoichiometry, and Gibbs free energy of aqueous species.A hydrothermal apparatus, capable of obtaining the necessary solubility data in fluid mixtures, is described. Stoichiometry of the dominant aqueous silica species of Si(OH) 4 . 2H 2 O in the supercritical region of H 2 O. Prediction of silica concentrations in CO 2 -H 2 O mixtures in the system CaO-MgO-SiO 2 -HCl-CO 2 -H 2 O at 2 kbar and 450 degrees C.--Modified journal abstract.

The extraction-quench technique for determination of the thermodynamic properties of solute complexes; application to quartz solubility in fluid mixtures

Unit-Cell Parameters of the Microcline-Low Albite and the Sanidine-High Albite Solid Solution Series

Stability of scapolite in the system Ab-An-NaCl-CaCO3 at 4 kb and 750°C

The partitioning of cations between coexisting single- and multi-site phases with application to the assemblages: orthopyroxene-clinopyroxene and orthopyroxene-olivine

Philip M. Orville

Papers

Volatile production and transport in regional metamorphism

The extraction-quench technique for determination of the thermodynamic properties of solute complexes; application to quartz solubility in fluid mixtures

Unit-Cell Parameters of the Microcline-Low Albite and the Sanidine-High Albite Solid Solution Series

Stability of scapolite in the system Ab-An-NaCl-CaCO3 at 4 kb and 750°C

The partitioning of cations between coexisting single- and multi-site phases with application to the assemblages: orthopyroxene-clinopyroxene and orthopyroxene-olivine