The carbonatites at Loe Shilman, near Khyber in NW Pakistan, fenitize their country rocks to form a metasomatic zone c.100 m wide of alternate dark blue (mafic) and pale grey (felsic) banded fenites which grade into unfenitized bedded slates and phyllites. The Na-amphiboles in the banded fenites form a complete solid solution series between magnesio-arfvedsonite and magnesio-riebeckite which coexist with varying proportions of aegirine, albite, and K-feldspar, with or without phlogopite or biotite.

The amphiboles show a gradual decrease in Na2O, K2O, Mg ratio [100Mg/(Mg + FeT + Mn)] and iron oxidation ratio, and an increase in total iron away from the carbonatite contact. The pleochroism correlates with the chemistry and distance from the carbonatite contact.

The Mg ratio decreases from 74 to 35 away from the carbonatite contact. The iron oxidation ratio [100Fe3+/ (Fe3+ + Fe2+)] decreases in the magnesio-arfvedsonite for the first 30 metres from the carbonatite contact, and then increases in the magnesio-riebeckite from 40 to 60 metres from the carbonatite contact. K relative to Na decreases away from the contact in the amphibole, and the decrease in K causes an increase in vacancy in the A site. The main variation in the chemistry in this solid solution series is due to (K,Na)A+(Mg,Fe2+)c ⇌ □ + (Fe3+)c substitution.

The application of ion microprobe analysis to REE determination is discussed, with special reference to REE-bearing accessory minerals (e.g. allanite, monazite, apatite, xenotime, sphene). The main analytical problems are shown to be (a) interferences in the mass spectrum caused by molecular ions, and (b) matrix effects, i.e. variations in ion yield with sample composition. Interference suppression using either high mass resolution or secondary-ion energy discrimination is fairly effective, but entails a significant sacrifice in peak intensity. In the absence of a viable model for predicting matrix effects, it is proposed that empirical standardization should be used. Often better absolute accuracy can be obtained by combining ion microprobe and electron microprobe data for REE present in sufficiently high concentrations. Detection limits for REE are in the part per million region at present, with spatial resolution typically around 10 μm, but there is considerable scope for improvement. Better standards and improved understanding of matrix effects should also lead to greater accuracy in quantitative analysis.

The 2 km × 5 m Newmains Dyke in the Scottish Southern Uplands consists mainly of primitive (mg number > 70), at least partly mantle-derived lamprophyre (vogesite spessartite, SiO2 50–60%), with hornblende-pyroxene-rich cumulates (SiO2 < 50%) and small amounts of quartz syenitic to granite residua (60–73% SiO2). The lamprophyres and cumulates yield an Rb-Sr whole-rock isochron age of 395±9 Ma (MSWD 2.0), and (87Sr/86Sr)i 0.70514±5—identical values to the nearby Criffell granitic pluton. After some 65% hornblende + clinopyroxene fractionation of parent lamprophyre magma, a volatile phase separated and metasomatically enriched the country rock greywackes in K, Ba, and Rb. The remaining quartz syenitic liquids became contaminated by 87Sr from these greywackes, which have a mean (87Sr/86Sr)395 value of 0.70789±114. Further fractionation of the contaminated syenitic liquids gave the granitic rocks, which have (87Sr/86Sr)395 values of 0.7056–64. The dyke appears to demonstrate in situ some of the hidden processes previously invoked to explain the evolution of the Criffell pluton itself.

New data on the kinetics of dehydration of 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.

It is shown here that dyke rocks of type localities for ‘soda-minettes’ are not minettes (= lamprophyres dominated by phlogopite and K-rich feldspar). It has long been suggested that ‘soda-minette’ also be applied to otherwise normal minettes from elsewhere that carry modally variable amounts of groundmass aegirine and/or, more commonly, arfvedsonitic to riebeckitic amphibole. Despite the presence of sodic pyriboles, these rocks are poorer in Na2O then minettes lacking these phases. ‘Soda-minette’ is thus misleading and self-contradictory to the many petrologists to whom ‘soda-’ legitimately connotes that the rock in question either has K/Na < 1 and/or is rich in albitic feldspar. To eliminate this ambiguity it is recommended, with the approval of twenty-six other petrologists, that ‘soda-minette’ no longer be used as a rock name. As minettes with Na-pyribole(s) are markedly K-rich and most are both ultrapotassic and peralkaline, independent of the modal abundance of the Na-pyrobile, it is suggested that one of these three chemical characteristics be utilized adjectivally in naming these minettes.

A number of geochemical plots are suggested by means of which metamorphosed quartzofeldspathic sedimentary rocks (meta-sandstones, meta-arkoses, quartzites, etc.) can be distinguished from their metamorphosed igneous mineralogical analogues (metarhyolite, meta-granite, etc.). These plots are applied to an enigmatic, partly mylonitized, quartzofeldspathic series, the Delaney Dome Formation, which is involved in a major thrust zone. The formation is shown to be igneous and is probably a meta-rhyolite. The plots proposed should have general application in identifying the precursors of both high-grade and low-grade quartzofeldspathic rocks of unknown origin.

Veins of tourmalinite were formed by wallrock alteration adjacent to steep fractures in bleached, indurated Skiddaw Group metasedimentary rocks around Crummock Water, north-west Lake District. The vein rock is a fine-grained granoblastic mosaic of tourmaline, quartz, and minor rutile in which bedding is preserved. Brecciation, in which tourmalinite fragments are set in a coarser quartz-tourmaline matrix, is present in some veins. Networks of cross-cutting quartz veinlets with tourmaline, chlorite, and muscovite are very common. The tourmaline is intermediate schorl dravite and mostly brown in plane polarized light, though prisms in breccia matrix and veinlets have blue, low-Ti cores and brown rims. Comparison of tourmalinite and host-rock analyses indicates almost complete loss during tourmalinization of K, Rb, Li, Ba, As, and La, plus depletion in Ce, Y, Na, Sr, P, and Mn. The elements Si, B, Mo, and erratically, minor F, W, and Sn were introduced. Cu, Pb, Zn, and Ca show both gains and losses probably due to initial depletion and subsequent local enrichment. Reduction in Al, Zr, and Ti concentrations relates to dilution by introduced silica. The tourmalinite veins were formed by the action of hydrothermal fluids derived from the concealed late-Caledonian granitic intrusion responsible for the thermal metamorphism of the country rocks.

Spinel lherzolite xenoliths from two localities in the Massif Central are undepleted in Al2O3, CaO, and Na2O. One suite from Tarreyres, is K2O depleted and amphibole-bearing whereas the other, from Monistrol d'Allier some 18 km away, is amphibole-free and has a higher mean K2O content of 0.035 wt.%. We present bulk major and minor element abundances in a harzburgite and a lherzolite from each locality and microprobe analyses of their constituent phases. Amphibole-bearing lherzolite and its pyroxenes are light-rare earth element (LREE) depleted, whereas amphibole-free lherzolite and its pyroxenes are LREE enriched. Both harzburgites and their pyroxenes are LREE enriched and one rock contains LREE enriched glass. The harzburgites are like harzburgite xenoliths from elsewhere but each lherzolite represents a previously unrecognized type of mantle in terms of the mineralogy and REE content. The implication for basalt genesis are briefly discussed.

A proportion of the heat added to a body of rock during prograde metamorphism will be absorbed in the chemical work of metamorphic recrystallization. When and where heat is so absorbed will affect the exact thermal histories of the rocks, and hence the metamorphic textures. This paper reports the results of modelling of the inter-relations between reaction progress and thermal histories in a rock column. The results suggest that volumes of rock undergoing reaction at any moment act as heat sinks and absorb heat from the surrounding rock, that reaction generally takes place close to the temperature at which nucleation took place, and that steady heating of a rock pile can give rise to a reaction history in which spurts of reaction are separated by ‘quiet’, non-reactive intervals.

A picrite dyke with an olivine-bearing chilled margin and an olivine-rich centre has been used to test for the presence of a boundary layer around rapidly grown olivine crystals and for any variations in the olivine/melt partition coefficient for uranium as a result of probably different crystal growth rates. The technique of fission-track mapping is shown to be suitable for this kind of study despite the very low uranium concentrations in the olivines. A boundary layer appears to be present around some olivine crystals but it is not a consistent feature. Uranium partition between olivine and melt was not affected by different crystal growth rates, as revealed by different crystal morphologies.

Transmission electron microscopy and analytical electron microscopy have been used to study the breakdown reaction of muscovite during pyrometa-morphism. The transformation has been shown to be topotactic in nature, with the orientations of the product biotite and alkali feldspar being strongly controlled by the precursor phase. Microprobe investigations indicate that the reaction is probably isochemical with no detectable interaction with adjacent phases. Chemical analyses of the products carried out by AEM have enabled a possible balanced reaction to be calculated. It is proposed that the spatial distribution of the product minerals can be interpreted in terms of diffusion of species from one domain in the crystal to another over distances of 5 to 10 µm as a result of chemical potential gradients which develop during the reaction. The reaction probably occurred under conditions of declining temperature between 900 and 750 °C over a period of 4–5 days. This time period was insufficient to enable the reaction to reach completion as indicated by the presence of relics of muscovite coexisting with K-feldspar, corundum, biotite, hercynite, and mullite.

Ratios between elements Mg, Fe, Co, Cr, Ni, V, and Sc are consistently different in mafic rocks of the upper critical zone, and those above the Bastard unit. Within the 300 m section above the Merensky Reef, 87Sr/86Sr ratios increase from c.0.7063 to c.0.7087, irrespective of rock type. Decoupling of Mg/(Mg + Fe2+) ratios and the Ca contents of plagioclase, and wide variations in the proportions of anorthosite within the Bastard, Merensky, and Merensky Footwall units, are inconsistent with anorthosite formation by simple fractional crystallization of magma batches of limited volume. Conversely, significant differences in Sr-isotope ratios show that these anorthosites could not have shared a common parental liquid. These data are used to develop a model whereby (a) the 300 m column above the critical zone represents the mixing of liquids of isotopically and geochemically discrete upper critical and main zone lineages, (b) mafic layers of the Bastard, Merensky, and Merensky Footwall units crystallized from discrete injections of primitive, mafic liquid while (c) the leucocratic upper parts of these units crystallized during progressive hybridization of liquid residua, which remained after significant separation of mafic phases, with a supernatant column representing the liquid residua of earlier cycles, and (d) the buoyancy of plagioclase, and enlargement of the primary phase volume of plagioclase consequent upon an increase in An/Ab ratio of hybrid liquids, were significant factors in the generation of anorthositic layers.

Amphibolites from the Grampian Moines of Scotland contain clinopyroxene-plagioclase symplectites and plagioclase-hornblende coronas around garnet. The clinopyroxene-plagioclase symplectites are interpreted as former omphacites. It is inferred that an eclogitic garne-tomphacite-quartz assemblage once existed, but has since undergone partial reaction to an amphibolite facies hornblende-plagioclase assemblage. An early high-pressure metamorphic event occurred in parts of the Moine.

The free energies of formation of the minerals libethenite, Cu2PO4OH, pseudomalachite, Cu5(PO4)2(OH)4, cornetite, Cu3PO4(OH)3, tarbuttite, Zn2PO4OH, spencerite, Zn2PO4OH · 1.5H2O, and scholzite, CaZn2(PO4)2 · 2H2O, have been determined at 298.2 K using solution techniques. The values of ΔfG° (298.2 K) for the above minerals are, respectively, −1228.8±3.0, −2840.3±4.2, −1600.9±5.9, −1632.1±4.0, −1982.4±3.1, and −3556.7±7.6 kJ mol−1. These results, together with others from the literature concerning hopeite, Zn3(PO4)2·4H2O, hydroxyapatite, Ca5(PO4)3(OH), and the synthetic salt Cu3(PO4)2 · 2H2O have been used to construct a model for the formation of suites of Zn(II) and Cu(II) phosphate minerals found in the oxidation zone of base metal orebodies. The distributions and modes of occurrence of many natural assemblages of these minerals are readily explained by the model. Particular attention has been focused on deposits at Broken Hill, Zambia, and Saginaw Hill, Arizona, USA.

The problems of characterizing inter-granular regions and of estimating rates of intergranular diffusion in metamorphic rocks are discussed. Inter-granular regions can be anhydrous, hydrated but under-saturated with H2O, or saturated with H2O, but only in the latter case can a free aqueous fluid phase be present. Estimates of intergranular diffusion coefficients (DIGR) at 550°C derived from a variety of published experimental work, vary from ∼ 10−8 m2 s−1 for diffusion of species through an intergranular fluid film to ⩽ 4 × 10−24 m2 s−1 for diffusion of SiO2 or O in anhydrous grain boundaries in quartzite. Estimates of DIGR for hydrated grain boundaries vary from ∼ 10−13 m2 s−1 to ∼ 10−21 m2 s−1; the concentration of H2O in the grain boundaries and the identity of the diffusing species (generally unknown) may be important controlling factors, and there exists the possibility of a spectrum of values between these two extremes.

Using available kinetic data it is shown that a free aqueous fluid could never have been present in parts of the basement terrane of the Sesia Zone (Western Alps) during uplift from the eclogite facies, except possibly late in the cooling history. The breakdown of sodic pyroxene + quartz occurred in response to the localized infiltration of catalytic aqueous fluid, possibly over a time interval as short as 6–6000 a, and possibly under conditions remote from equilibrium. H2O-present conditions during a dehydration reaction in metapelites of the Adula nappe (central Alps) could also have been of short duration. These examples are consistent with a model in which basement rocks at deep crustal levels are dry for long periods of time and in which the development of equilibrium mineral assemblages and microstructures generally occurs over relatively short periods of time under transitory fluid-present conditions (caused by devolatilization and/or infiltration).

Despite poor exposures and lack of ‘stratigraphic’ control, there is consistent mineralogical and textural evidence that the Insch Upper Zone (UZ) represents a cumulate sequence developed from a single episode of progressive fractionation. This sequence has been subdivided on the basis of the phase layering, with cumulus plagioclase, pyroxenes and Fe-Ti oxides providing continuity from the Middle Zone (although the pyroxenes appear to be temporarily restricted to inter-cumulus status in the lower part of the UZ succession). The reappearance of cumulus olivine after its absence throughout the Middle Zone, marks the base of the UZ, and it is later joined by cumulus apatite, and then by alkali feldspar and zircon. Higher in the succession cumulus orthopyroxene, followed by olivine and Fe Ti oxide, eventually disappear. There is pronounced cryptic variation of the principal cumulus minerals (olivine Fo47−6, orthopyroxene En58−24, clinopyroxene Mg#63−6, plagio-clase An60−39 and the cumulus alkali feldspar is distinctly Ba-rich when it first appears. Comparison with the later fractionation stages of other layered intrusions shows broad similarities to the Bushveld and Skaergaard intrusions and closer similarities to the Fongen-Hyllingen body, which, like Insch, is a Caledonian synorogenic intrusion. The behaviour of the Insch pyroxenes, which show smoothly progressive Fe-enrichment despite their temporary absence as cumulus phases early in the UZ, together with the apparent range in cumulus plagioclase compositions in each sample, are taken to indicate that the cumulus mineral assemblages have been to some extent modified by re-equilibration with trapped inter-cumulus magma.

The origin in rocks of the common iron sulphides, pyrrhotine, Fe1-xS and pyrite, FeS2 and their behaviour during geochemical processes is best considered using the simplified redox reaction: 2FeS ⇌ FeS2 + Fe2+ + 2e−.

Thus pyrrhotine is more reduced than pyrite and is the stable iron sulphide formed from magmas except where relatively high oxygen fugacities result from falling pressure or hydrothermal alteration. Pyrite, on the other hand, is the stable iron sulphide in even the most reduced sedimentary rocks where it usually forms during diagenesis through bacteriogenic reduction of sulphate; it is stable throughout the pressure/temperature range endured by normal sedimentary rocks. Pyrrhotine after pyrite or sulphate in metasediments of regional metamorphic origin results mainly from progressive reduction on metamorphism due to the presence of graphite-buffered fluids. Pyrrhotine and/or pyrite may be precipitated from hydrothermal solutions on epigenetic or syngenetic mineralization but pyrrhotine will only be preserved if protected from oxidation to pyrite or to more oxidized species. Exhalative pyrrhotine appears to have been more common in Precambrian times and/or in depositional environments destined to become regionally metamorphosed. FeS can be considered to be the soluble iron sulphide, rather than FeS2, in reduced aqueous systems although pyrite may precipitate from solution as a result of redox reactions. The relatively soluble nature of FeS explains the observed mobility of iron sulphides in all rock types.