Thermal expansion data up to 920° C by powder X-ray diffraction methods are presented for four noseans, five haüynes, and one sodalite. The rate of thermal expansion is at first high and increases with temperature; this is interpreted as due to the untwisting of the partially collapsed framework. Above a certain temperature (which depends on the mineral and its composition) the rate of thermal expansion is much lower and is linear with temperature; this corresponds to the rate of thermal expansion of the more fully expanded framework. Sodalite does not show this second stage below 920° C. The thermal expansion behaviour of other framework silicates is interpreted in analogy to that of the sodalite group.

The heat outputs of higher burn up spent fuels (SF) create problems for disposal in mined repositories, including needs for reduced container loadings and extended pre-disposal cooling. An alternative that is less temperature sensitive is deep borehole disposal (DBD) which offers safety, cost, security and other potential benefits and could be implemented relatively quickly using currently available deep-drilling technology. We have modified our previously proposed version of DBD to be more appropriate for higher burn-up fuels by using smaller (0.36 m diameter) stainless steel containers, a smaller (0.56 m diameter) borehole, and different support matrices. We present the results of new heat-flow modelling for DBD of UO2 and MOX SF with burn ups of 55 and 65 GWd/t showing how temperatures evolve, especially on the outer surface of the containers. Consequences for the performance of the support matrices and the disposal concept are discussed. The thermal modelling indicates DBD is a viable option for higher burn-up SF and could be a practical disposal route for many combinations of fuel types, burn ups, ages and container loadings. Further, the results suggest that DBD of complete fuel assemblies, a desirable option, would be feasible and require much shorter pre-disposal cooling than necessary for disposal in mined repositories.

Most unroofing mechanisms invoked for the exhumation of blueschist-plus-eclogite terranes, including corner-flow and extensional collapse of the orogenic wedge, predict steep unroofing paths for the deeply-buried rocks and are applicable only to unroofing from depths within the crust. Many high-P and ultrahigh-P rocks of continental affinity are derived from greater depths than this. Their lack of warming during unroofing, together with indications that they may rest directly on less deeply buried equivalents, are suggestive of shallow unroofing paths similar to those for the subduction-channel model. They are interpreted to have been emplaced by the upward extrusion of coherent slices of continental crust, bounded below by thrust faults and above by normal faults, with unroofing paths essentially reversing the original burial paths.

Where continental crust has been subducted into the mantle, upward extrusion is probably driven largely by buoyancy forces, although examples of upward extrusion without subduction into the mantle indicate that buoyancy forces may not be essential. Two features in addition to buoyancy may promote upward extrusion. Slab breakoff may reduce the pull from the descending slab, and subduction-zone geometry may change as a continental margin is dragged into the subduction zone. Both features may promote the extrusion of continental crust at precisely the time at which it has been partially subducted.

A close spatial relationship between a lateral ramp and a lobate zone of extruded high-P rocks in the Mesoproterozoic Grenvillian orogen indicates that lateral ramps may be important in localizing extrusion. Lateral ramps disturb the two-dimensional flow, with channelling of material into the region of the lateral ramp as it is extruded. Many exhumed ultrahigh-P terrains are associated with jogs in the trends of orogenic fronts that may reflect the presence of lateral ramps at depth. Ultrahigh-P rocks may be expected to be concentrated at such jogs, and may record the channelling in their deformation history.

The Rhenohercynian thrust- and fold-belt of Central Europe hosts a syn- to post-kinematic Variscan vein mineralisation, which is restricted to the Rhenish Massif, Germany. It is formed during four major stages and siderite is the principal ore mineral of the 'main stage'. The latter can be traced throughout the massif, but is mainly developed in the Siegerland district as synkinematic lodes which are hosted by low-grade metamorphic pelites of Lower Devonian age.

Fluid inclusion studies prove large-scale homogeneous ore forming fluids of low salinity (≤5 wt.% NaCI equiv.) and Na(-K > -Fe ≫ Mg)-C1 composition, which are CO2 undersaturated (XCO2 = 0.003-0.1). Siderite precipitation at 220−≤320°C and 0.7-1.4 kbar can be deduced by microthermometry, chlorite themometry, REE fractionation and experimental data. Thereby the maximum formation temperature comes close to or even exceeds the peak metamorphic temperature. From Mn contents and δ13C-δ18O variation of siderite a trend is apparent in which formation temperatures gradually decrease from S.E. to N.W. across the belt. This trend correlates with decreasing degree of host-rock deformation and decreasing metamorphic grade. Fluid composition as well as stable isotopes and REE fractionation of siderite point to ore-forming solutions, which were generated and equilibrated at depth during prograde metamorphism.

Structural characteristics of the lodes, age determinations, and P-T estimations prove fluid ascent and siderite precipitation during and/or immediately after peak metamorphism predating the postkinematic magmatism of the Rhenohercynian belt. Main(-siderite)-stage mineralisation of the Rhenish Massif is classified as metamorphogeneous.

The Lovozero alkaline massif is the largest of the world's layered peralkaline intrusions (∼650 km2). We describe the evolution of clinopyroxene from the liquidus to the late residual stage throughout the whole vertical section (2.5 km thick) of the Lovozero Complex. Microprobe data (∼990 analyses) of the clinopyroxenes define a relatively continuous trend from diopside containing 15–20% hedenbergite and 10–12% aegirine components, to pure aegirine. The main substitutions during the evolution of the Lovozero pyroxenes are (Na,Fe3+,Ti) for (Ca,Mg,Fe2+). The composition of the pyroxene changes systematically upwards through the intrusion with an increase in Na, Fe3+ and Ti and decrease in Ca and Mg.

The compositional evolution of the Lovozero pyroxene reflects primary fractionation processes in the alkaline magma that differentiated in situ from the bottom to the top of the magma chamber as a result of magmatic convection, coupled with the sedimentation of minerals with different settling velocities.

The temperature interval of pyroxene crystallization is very wide and probably extends from 970 to 450°C. The redox conditions of pyroxene crystallization in the Lovozero intrusion were relatively low, approximating the QFM buffer.

Synthetic Eu-anorthite of the alkali feldspar structure type has been refined to Rw = 4.7% using 3-D counter diffractometer data and full-matrix least-squares methods. The chemical composition of the feldspar is Eu0.92Al1.76Si2.24O8, based on both occupancy refinement of the Eu atom site and estimation of the Al/Si distribution calculated from the mean T-O bond length. The unit cell parameters are a = 8.373(1), b = 12.959(1), c = 7.124(1) Å, and β = 115.51(1)° and the symmetry is enhanced to C2/m. Mean bond lengths are T(1)-O = 1.677 Å, T(2)-O = 1.668 Å, and Eu-O = 2.721 Å. The average Al/Si distribution over the T(1) and T(2) sites calculated from the mean T-O bond length is in fairly good agreement with an estimate of the Al content from the bond strength calculation; the Al partition is calculated as t1 = 0.47 and t2 = 0.41 respectively. Summing the bond strengths of these Eu and partially disordered Al/Si cations approximates to electrostatic neutrality for the anion content of the feldspar structure, indicating that this synthetic Eu feldspar can be non-stoichiometric, signifying vacancies on the alkali cation site.

Plagioclase and melilite generally show a positive Eu anomaly. A fair insight into the driving force of this anomaly can be afforded by the crystallo-chemical affinities of Eu2+ and Eu3+ cations to the crystal structures of their host minerals; (1) ioinic radius, (2) electrostatic charge balance and (3) tolerance for non-stoichiometry of the crystal structure.

A plot of seventy-five new analyses of members of the helvine group and fifty-seven analyses from the literature indicates complete miscibility between the Fe and Zn members (danalite and helvine) and between the Fe and Mn members (danalite and genthelvite). The new analyses include essentially pure helvine and genthelvite (for both of which X-ray data are presented) and the nearest approach to pure danalite (86 at. % Fe). Two new localities for genthelvite, the rarest member, are reported.

The arsenopalladinite concentrates from Itabira, Minas Gerais, Brazil, have been found to contain three arsenide-antimonides of palladium, namely arsenopalladinite, atheneïte, and isomertieite. The second and third of these are new minerals.

Arsenopalladinite, redefined, is Pd5(As,Sb)2 and triclinic with a 7·399, b 14·063, c 7·352 Å, α 92° 03′, β 118° 57′, γ 95° 54′. Z = 6. Dmeas = 10·4, Dcalc = 10sd46. In reflected light arsenopalladinite is white with a yellowish creamy hue. The mineral shows complex polysynthetic twinning and is strongly anisotropic. Reflectance measurements at 470, 546, 589, and 650 nm respectively gave: in air, 46·67–48·86, 49·97–52·90, 52·82–54·96, and 55·61–57·72 in oil, 32·30–35·07, 37·12–39·40, 38·97–41·32, and 40·28–43·07. VHN100 379–449, av. 407.

Atheneïte, (Pd, Hg)3As, is hexagonal, space group P6/mmm and cell dimensions a 6·798, c 3·483 Å. The strongest lines of the powder pattern are 2·423 vvs (111) , 2·246 vs (201), 1·371 s (212), 1·302 s (302), 1·259 s (321). Z =2. Dcalc = 10·16. In reflected light atheneïte is white with a faint bluish tint compared to arsenopalladinite. Anisotropy distinct. Untwinned. Reflectivities for the two grains examined are: in air, 470 nm 47·51–54·75, 47·43–51·18; 546 nm 50·79–58·01, 51·36–54·36; 589 nm 53·13–61·01, 53·24–55·86; 650 nm 55·94–63·13, 54·76–56·77; in oil, 470 nm 30·03–43·67, 33·46–37·31; 546 nm 33·42–47·75, 37·64–41·07; 589 nm 35·80–49·04, 39·40–42·24; 650 nm 38·25–50·49, 41·07–42·85. VHN100 419–442, av. 431.

Isomertieite, (Pd,Cu)5(Sb,As)2, is cubic, space group Fd3m, a 12·283 Å. The strongest lines of the powder pattern are 2·356 vs (333, 511), 2·167 vvs (440), 0·8599 s (10.10.2, 14.2.2), 0·8206 s (12.8.4), 0·7996 s (10.10.6, 14.6.2), 0·7881 s (999, 1.11.1, 13·7·5, 15·3·3), 0·7801 s (12.10.2, 14.6.4). Z = 16. Dcalc = 10·33. In reflected light isomertieite is a pale yellow colour. One grain was isotropic, three others displayed weak anisotropy. Untwinned. Reflectance measurements at 470, 546, 589, and 650 nm gave respectively: in air, 44·74–46·46, 52·23–53·25, 55·05-57·49, 56·97–62·03; in oil, 31·04–31·40, 38·42–38·90, 40·80–42·16, and 42·91–45·63. VHN100 587–597, av. 592.

Quantitative colour values are also given, and the chemical and optical properties are compared with the related mineral, stibiopalladinite.

Gem minerals at Lava Plains, northeast Queensland, offer further insights into mantle-crustal gemformation under young basalt fields. Combined mineralogy, U-Pb age determination, oxygen isotope and petrological data on megacrysts and meta-aluminosilicate xenoliths establish a geochemical evolution in sapphire, zircon formation between 5 to 2 Ma. Sapphire megacrysts with magmatic signatures (Fe/Mg ∼100–1000, Ga/Mg 3–18) grew with ∼3 Ma micro-zircons of both mantle (δ18O 4.5–5.6%) and crustal (δ18O 9.5–10.1‰) affinities. Zircon megacrysts (3±1 Ma) show mantle and crustal characteristics, but most grew at crustal temperatures (600–800°C). Xenolith studies suggest hydrous silicate melts and fluids initiated from amphibolized mantle infiltrated into kyanite+sapphire granulitic crust (800°C, 0.7 GPa). This metasomatized the sapphire (Fe/Mg ∼50–120, Ga/Mg ∼3–11), left relict metastable sillimanite-corundum-quartz and produced minerals enriched in high field strength, large ion lithophile and rare earth elements. The gem suite suggests a syenitic parentage before its basaltic transport. Geographical trace-element typing of the sapphire megacrysts against other eastern Australian sapphires suggests a phonolitic involvement.

In reviewing the distribution of fluorine in igneous rocks it is clear that F abundance is related to alkalinity and to some extent to volatile contents. Two important F-bearing series are recognized: (1) the alkali basalt—ultrapotassic rocks in which F increases with increasing K2O and decreasing SiO2 contents; and (2) the alkali basalt—phonolite—rhyolite series with F showing positive correlation with both total alkalis and SiO2. Detailed studies of series (1) show that F abundance in ultrapotassic magmas (lamproite, kamafugite, lamprophyre) occurs in descending order in the sequence phlogopite>apatite>amphibole>glass. Fluorine contents in the same minerals from fresh and altered mantle xenoliths may be several orders of magnitude less than those in the host kamafugite. For many lamproites, F contents correlate with higher mg# suggesting that F is highest in the more primitive magmas.

Experiments at mantle conditions (20 kbar, 900–1400°C) on simplified F-bearing mineral systems containing phlogopite, apatite, K-richterite, and melt show that F is generally a compatible element. Additionally, low F abundance in minerals from mantle xenoliths suggests that F may not be available in mantle source regions and hence is unlikely to partition into the melt phase on partial melting. Melting experiments on the compositions of F-free and F-bearing model phlogopite harzburgite indicate that even small variations in F content produce melts similar in composition to those of lamproite.

Phase relations in the system PbS-PbSe-PbTe were investigated in the temperature range between 1150 and 300°C. There is a complete solid solution series along the join PbS-PbSe, whereas miscibility gaps exist below ∼ 350°C and 805°C along joins PbSe-PbTe and PbS-PbTe, respectively. Both gaps extend into the ternary system, and the range of the gap between PbS and PbTe reduces in size with temperature as well as Se-content.

By using the subregular model of mixing (Ganguly and Saxena, 1987), mixing energetics and activity composition relations of PbX were derived. The temperature-dependence of the interaction parameters was calculated to be 5057.6 − 1.7T, 9605.2 − 4.4T, 3933.2 − 3.1T (T < 500°C), 6410.3 − 6.35T (T < 500°C) 1649 − 0.26T, 1594.6 − 0.2T, and 12906.3 − 17.3T for WWSte, WTeS, WSeTe, WTeSe, WSSe, WSeS, and WSSeTe, respectively. A critical temperature along the join PbS-PbSe at ∼ 100°C was obtained from interaction parameter calculation, which suggests the separation of the PbS-PbSe series.

Correlation of solid-solution ranges established in this study with natural occurrences was made.

Morimotoite, Ca3TiFe2+Si3O12, has been found in contaminated rocks which are considered to be a kind of endoskarn at Fuka, Bitchu-Cho, Okayama Prefecture, Japan. Morimotoite is derived from andradite, , by the substitution Ti + Fe2+ = 2Fe3+. It is associated with calcite, vesuvianite, grossular, wollastonite, hematite, prehnite, fluorapatite, perovskite, zircon, baddeleyite and calzirtite. It is cubic with space group Ia3d. The unit cell dimension a is 12.162(3) Å. Its refractive index n is 1.995(2) and the density 3.75(2) g cm−3 (meas.), 3.80 g cm−3 (calc.). The Mohs' hardness is 7.5. Calculation of the analytical data on the basis of twelve oxygen atoms and eight cations shows that this mineral has a simplified chemical formula Ca3(Ti,Fe2+Fe3+)2(Si,Fe3+)3O12 where Ti > Fe2+ > 0.5. Morimotoite was synthesized at low oxygen fugacities, 650 and 700°C and 1 kbar total pressure.

This paper examines the effects of shear stress on the structural parameters that define the ‘crystallinity’ of graphite. The results show that highly crystalline graphite samples ground for up to 120 min do not undergo detectable changes in the three-dimensional arrangement of carbon layers but crystallite sizes (Lc and La) decrease consistently with increasing grinding time. Grinding also involves particle-size diminution that results in lower temperatures for the beginning of combustion and exothermic maxima in the differential thermal analysis curves. These changes in the structural and thermal characteristics of graphite upon grinding must be taken into account when such data are used for geothermometric estimations.

Tectonic shear stress also induces reduction of the particle size and the Lc and La values of highly crystalline graphite. Thus, the temperature of formation of graphite according to structural as well as thermal data is underestimated by up to 100°C in samples that underwent the most intense shear stress. Therefore, application of graphite geothermometry to fluid-deposited veins where graphite is the only mineral found should take into consideration the effect of tectonic shearing, or the estimated temperatures must be considered as minimum temperatures of formation only.

Electron microprobe and textural data are used to deduce a crystallization history for plagioclase in the Grand Manan Island (Canada) diabase sheet. The plagioclase crystals consist of a prominent core (An79-67) surrounded by a distinctly more calcic zone (An82-76), which grades into a normally zoned mantle (An73-40). This zoning pattern is interpreted as reflecting the elevation of a dry diabase magma from at least 10 to 20 km to near surface conditions.

Two new minerals shchurovskyite, ideally K2CaCu6O2(AsO4)4, and dmisokolovite, ideally K3Cu5AlO2(AsO4)4, are found in sublimates of the Arsenatnaya fumarole at the Second scoriacone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka Peninsula, Russia. They are associated with one another and with johillerite, bradaczekite, tilasite, melanarsite, tenorite, hematite, aphthitalite, langbeinite, orthoclase, etc. Shchurovskyiteoccurs as coarse tabular or prismatic crystals up to 0.15 mm in size or anhedral grains forming parallel aggregates and crusts up to 1.5 cm × 2 cm across. Dmisokolovite forms tabular, prismatic or dipyramidal crystals up to 0.2 mm in size, commonly combined in clusters or crusts up to0.7 cm × 1.5 cm across. Both minerals are transparent with a vitreous lustre. They are brittle, with Mohs' hardness ≈3. Shchurovskyite is olive-green or olive drab. Dmisokolovite is bright emerald-green to light green. Dcalc = 4.28 (shchurovskyite) and 4.26 (dmisokolovite)g cm–3. Both are optically biaxial; shchurovskyite: (+), α = 1.795(5), β = 1.800(5), γ = 1.810(6), 2Vmeas = 70(15)°; dmisokolovite: (–), α = 1.758(7), β = 1.782(7), γ = 1.805(8), 2Vmeas = 85(5)°. The Ramanspectra are given. Chemical data (wt.%, electron-microprobe; first value is for shchurovskyite, second for dmisokolovite): Na2O 0.00, 0.83; K2O 8.85, 10.71; Rb2O 0.11, 0.00; MgO 0.00, 0.35; CaO 4.94, 0.21; CuO 43.19, 38.67; ZnO 0.42, 0.20; Al2O30.04, 4.68; Fe2O3 0.00, 0.36; P2O5 0.59, 0.78; V2O5 0.01, 0.04; As2O5 40.72, 43.01; SO3 0.35, 0.00; total 99.22, 99.84. The empirical formulae, based on 18 O a.p.f.u., are shchurovskyite: K2.05Rb0.01Ca0.96Cu5.92Zn0.06Al0.01P0.09S0.05As3.86O18;dmisokolovite: Na0.28K2.36Mg0.09Ca0.04Cu5.04Zn0.04 Al0.95Fe0.053+P0.11As3.88O18. The strongest reflections of X-ray powder patterns [d,Å(I)(hkl)]are shchurovskyite: 8.61(100)(200, 001), 5.400(32)(110), 2.974(32)(312, 510), 2.842(47)(003, 020), 2.757(63) (601, 511), 2.373(36)(512, 420) and 2.297(31)(421, 222, 313); dmisokolovite: 8.34(95)(002), 5.433(84)(110), 2.921(66)(510, 314), 2.853(58)(511, 020) and 2.733(100)(006, 512, 602). Shchurovskyiteis monoclinic, C2, a = 17.2856(9), b = 5.6705(4), c = 8.5734(6) Å, β = 92.953(6)°, V = 839.24(9) Å3 and Z = 2. Dmisokolovite is monoclinic, C2/c, a = 17.0848(12), b = 5.7188(4), c =16.5332(12) Å, β = 91.716(6)°, V = 1614.7(2) Å3 and Z = 4. Their crystal structures [single-crystal X-ray diffraction data, R = 0.0746 (shchurovskyite) and 0.1345 (dmisokolovite: model)] are closely related in the topology of the main buildingunits. They are based on a quasi-framework consisting of AsO4 tetrahedra and polyhedra centred by Cu in shchurovskyite or by Cu and Al in dmisokolovite. K and Ca are located in channels of the quasi-framework. The minerals are named in honour of outstanding Russian geologists andmineralogists Grigory Efimovich Shchurovsky (1803–1884) and Dmitry Ivanovich Sokolov (1788–1852).

The dehydration of pure and waste gypsums has been examined using in situ synchrotron angledispersive X-ray diffraction. Pure gypsum was studied under a number of defined environments; various industrial waste gypsums were also studied under a common standard environment. It is found that the dehydration of gypsum to anhydrite proceeds via the hemihydrate and γ-anhydrite phases and the interplay and behaviour of these phases has been determined by full structural ‘Rietveld’ refinement. In the study of the pure gypsum system, the hemihydrate structure is shown to be preserved as water is lost. A ‘zero-water hemihydrate’ is observed before refinement in the higher symmetry γ-anhydrite cell is possible. The waste gypsum materials studied showed significant differences in the temperatures at which key transformation events occurred; these observations raise implications concerning the re-use of by-product gypsum materials. Finally, high temperature data are re-examined in the search for a variation of the anhydrite structure.

In the deep geological disposal of nuclear waste in crystalline rock, erosion of the bentonite buffer may occur during periods of glaciation. Previous researchers have examined the mechanism and rates of extrusion and erosion for purified montmorillonite samples in smooth planar fractures. In this paper, we investigate the influence of using MX-80 material (as delivered, i.e. including accessory minerals) and a naturally varying aperture on bentonite erosion. A bespoke fracture flow cell was constructed for this purpose and flow through conducted with deionized water. Throughout the experiment, gravimetric analysis was undertaken on the effluent and the swelling pressure of the bentonite monitored. Quantitative image analysis of the extrusion process was also undertaken. When the swelling pressure data were analysed, alongside both the oscillations in erosion rate and the area of the accessory-mineral ring, a two-stage mechanism governing the erosion process became apparent. Once an accessory-mineral ring had formed at the edge of the extruded material, further increases in swelling pressure resulted in a breach in the accessory-mineral ring, triggering an erosive period during which, the mineral ring was supplemented with additional minerals. The cycle repeated until the ring was sufficiently strong that it remained intact. This observed process results in erosion rates one order of magnitude less than those currently used in long-term safetycase calculations.

Uranyl-silicates are widespread minerals in oxidised parts of various uranium deposits, and they frequently contain associations of the polymorphic forms of uranophane. In several recent works devoted to the study of uranium deposits as natural analogues of high-level nuclear waste repository (HLNWR), uranophane is frequently mentioned but without determination of the exact polymorphic species. The existence of two polymorphs presenting different stabilities has to be taken into account when considering the long-term behaviour of these minerals and the use of thermodynamic models for predicting the radionuclide migration in HLNWR. We present here new crystallographic data on betauranophane, and preliminary results of synthesis experiments of uranyl silicates. XRD patterns and calculated parameters of beta-uranophane from a Mexican U-deposit are presented. Synthesis experiments succeeded in crystallising uranophane (alpha form) at different pH, Si-, Ca- and Na activities, but beta-uranophane was never obtained. The controlling physico-chemical parameters responsible for the occurrence of these two polymorphic forms are still unknown.

Major element, trace element, and REE data for metasedimentary granulites and their retrogressed derivatives formed from Archaean parent-rocks at two localities in the Lewisian complex of north-west Scotland are presented.

The metasedimentary rocks are enclosed in and intruded by metatonalites and related calc-alkaline rocks and have been highly deformed and metamorphosed along with these rocks. They are geochemically distinct from this meta-igneous suite and range from highly aluminous to highly siliceous types. Comparisons of major and trace element data with those for unmetamorphosed Archaean and post-Archaean sediments suggest that they are derived from a detrital shale-greywacke assemblage, which may have included a volcaniclastic component. High ΣREE and ΣLREE suggest that the source-rocks included fractionated felsic igneous rocks.

Evidence that depletion in the large ion lithophile elements K, Rb, Th accompanied high-pressure granulite metamorphism supports the view, based on data derived from the associated meta-igneous rocks, that depletion was effected by active fluids rather than by abstraction of a partial melt and suggests that removal of K and Th began only when a considerable reduction of Rb had taken place.

A study of low-grade metamorphism in late Silurian to early Carboniferous rocks in the North Hill End Synclinorium and adjacent anticlinoria has been made by the determination of illite crystallinity and bo values of K-white mica in eighty slates and phyllites. Illite crystallinity values vary from 0.40 Δ°2θ on the Molong Anticlinorium to 0.12 Δ°2θ within the axis of the synclinorium, suggesting anchizonal to epizonal metamorphic conditions. This is in agreement with previous observations on Ca-Al-hydrosilicate assemblages which indicated a change from prehnite-pumpellyite facies in the anticlinoria adjacent to the synclinorium to middle greenschist facies in the axis. Local variations in crystallinity are attributed to variation in ak+ in fluids migrating along cleavage zones.

The mean bo value obtained from the pelites is 9.017 Å (σn = 0.008; n = 80) which is in close agreement with that obtained from part of the adjacent Capertee Anticlinorium ( = 9.019 Å; σn = 0.007; n = 52). However, ‘t’ tests indicate that two bo populations are present in the synclinorium ( = 9.019 and 9.022 Å), with the lower values concentrated in the southern portion of this structure. The two populations are considered to be the result of slightly different metamorphic conditions prevailing during the deformation of the rocks in the synclinorium. A higher geothermal gradient affecting rocks giving the lower bo values is attributed to the presence of granitoids at shallower depths than elsewhere in the synclinorium.