ALBERT

Notes: A petrogenetic grid in the model system CaO–FeO–MgO–Al2O3–SiO2–H2O is presented, illustrating the phase relationships among the minerals grunerite, hornblende, garnet, clinopyroxene, chlorite, olivine, anorthite, zoisite and aluminosilicates, with quartz and H2O in excess. The grid was calculated with the computer software thermocalc, using an upgraded version of the internally consistent thermodynamic dataset HP98 and non-ideal mixing activity models for all solid solutions. From this grid, quantitative phase diagrams (P–T pseudosections) are derived and employed to infer a P–T path for grunerite–garnet-bearing amphibolites from the Endora Klippe, part of the Venetia Klippen Complex within the Central Zone of the Limpopo Belt. Agreement between calculated and observed mineral assemblages and garnet zonation indicates that this part of the Central Zone underwent a prograde temperature and pressure increase from c. 540 °C/4.5 kbar to 650 °C/6.5 kbar, followed by a post-peak metamorphic pressure decrease. The inferred P–T path supports a geotectonic model suggesting that the area surrounding the Venetia kimberlite pipes represents the amphibolite-facies roof zone of migmatitic gneisses and granulites that occur widely within the Central Zone. In addition, the P–T path conforms to an interpretation that the Proterozoic evolution of the Central Zone was controlled by horizontal tectonics, causing stacking and differential heating at c. 2.0 Ga.

Notes: A review and reinterpretation of previous experimental data on the deformation of partially melted crustal rocks reveals that the relationship of aggregate strength to melt fraction is non-linear, even if plotted on a linear ordinate and abscissa. At melt fractions, Φ 〈 0.07, the dependence of aggregate strength on Φ is significantly greater than at Φ 〉 0.07. This melt fraction (Φ = 0.07) marks the transition from a significant increase in the proportion of melt-bearing grain boundaries up to this point to a minor increase thereafter. Therefore, we suggest that it is the increase of melt-interconnectivity that causes the dramatic strength drop between the solidus and a melt fraction of 0.07. We term this drop the ‘melt connectivity transition’ (MCT). A second, less-pronounced strength drop occurs at higher melt fractions and corresponds to the breakdown of the solid (crystal) framework. This is the ‘solid-to-liquid transition’ (SLT), corresponding to the well known ‘rheologically critical melt percentage’. Although the strength drop at the SLT is about four orders of magnitude, the absolute value of this drop is small compared with the absolute strength of the unmelted aggregate, rendering the SLT invisible in a linear aggregate strength v. melt-fraction diagram. On the other hand, the more important MCT has been overlooked in previous work because experimental data usually are plotted in logarithmic strength v. melt-fraction diagrams, obscuring large strength drops at high absolute strength values. We propose that crustal-scale localization of deformation effectively coincides with the onset of melting, pre-empting attainment of the SLT in most geological settings. The SLT may be restricted to controlling flow localization within magmatic bodies, especially where melt accumulates.

Notes: Contact metamorphism caused by the Glenmore plug in Ardnamurchan, a magma conduit active for 1 month, resulted in partial melting, with melt now preserved as glass. The pristine nature of much of the aureole provides a natural laboratory in which to investigate the distribution of melt. A simple thermal model, based on the first appearance of melt on quartz–feldspar grain boundaries, the first appearance of quartz paramorphs after tridymite and a plausible magma intrusion temperature, provides a time-scale for melting. The onset of melting on quartz–feldspar grain boundaries was initially rapid, with an almost constant further increase in melt rim thickness at an average rate of 0.5–1.0 × 10−9 cm s−1. This rate was most probably controlled by the distribution of limited amounts of H2O on the grain boundaries and in the melt rims.The melt in the inner parts of the aureole formed an interconnected grain-boundary scale network, and there is evidence for only limited melt movement and segregation. Layer-parallel segregations and cross-cutting veins occur within 0.6 m of the contact, where the melt volume exceeded 40%. The coincidence of the first appearance of these signs of the segregation of melt in parts of the aureole that attained the temperature at which melting in the Qtz–Ab–Or system could occur, suggests that internally generated overpressure consequent to fluid-absent melting was instrumental in the onset of melt movement.

Notes: New eclogite localities and new 40Ar/39Ar ages within the Western Gneiss Region of Norway define three discrete ultrahigh-pressure (UHP) domains that are separated by distinctly lower pressure, eclogite facies rocks. The sizes of the UHP domains range from c. 2500 to 100 km2; if the UHP culminations are part of a continuous sheet at depth, the Western Gneiss Region UHP terrane has minimum dimensions of c. 165 × 50 × 5 km. 40Ar/39Ar mica and K-feldspar ages show that this outcrop pattern is the result of gentle regional-scale folding younger than 380 Ma, and possibly 335 Ma. The UHP and intervening high-pressure (HP) domains are composed of eclogite-bearing orthogneiss basement overlain by eclogite-bearing allochthons. The allochthons are dominated by garnet amphibolite and pelitic schist with minor quartzite, carbonate, calc-silicate, peridotite, and eclogite. Sm/Nd core and rim ages of 992 and 894 Ma from a 15-cm garnet indicate local preservation of Precambrian metamorphism within the allochthons. Metapelites within the allochthons indicate near-isothermal decompression following (U)HP metamorphism: they record upper amphibolite facies recrystallization at 12–17 kbar and c. 750 °C during exhumation from mantle depths, followed by a low-pressure sillimanite + cordierite overprint at c. 5 kbar and c. 750 °C. New 40Ar/39Ar hornblende ages of 402 Ma document that this decompression from eclogite-facies conditions at 410–405 Ma to mid-crustal depths occurred in a few million years. The short timescale and consistently high temperatures imply adiabatic exhumation of a UHP body with minimum dimensions of 20–30 km. 40Ar/39Ar muscovite ages of 397–380 Ma show that this extreme heat advection was followed by rapid cooling (c. 30 °C Myr−1), perhaps because of continued tectonic unroofing.

Notes: High-grade gneisses (amphibolite–granulite facies) of the Namche Barwa and Gyala Peri massifs, in the eastern Himalayan syntaxis, have been unroofed from metamorphic depths in the late Tertiary–Recent. Rapid exhumation (2–5 mm year−1) has resulted in a pronounced shallow conductive thermal anomaly beneath the massifs and the intervening Tsangpo gorge. The position of the 300 °C isotherm has been estimated from fluid inclusions using CO2–H2O immiscibility phase equilibria to be between 2.5 and 6.2 km depth below surface. Hence, the near-surface average thermal gradient exceeds 50 °C km−1 beneath valleys, although the thermal gradient is relatively lower beneath the high mountains. The original metamorphic fluid in the gneisses was 〉90% CO2. This fluid was displaced by incursion of brines from overlying marine sedimentary rocks that have since been largely removed by erosion. Brines can exceed 60 wt% dissolved salts, and include Ca, Na, K and Fe chlorides. These brines were remobilized during the earliest stages of uplift at 〉500 °C. During exhumation, incursion of abundant topography-driven surface waters resulted in widespread fracture-controlled hydrothermal activity and brine dilution down to the brittle–ductile transition. Boiling water was particularly common at shallow levels (〈2.5 km) beneath the Yarlung Tsangpo valley, and numerous hot springs occur at the surface in this valley. Dry steam is not a major feature of the hydrothermal system in the eastern syntaxis (in contrast to the western syntaxis at Nanga Parbat), but some dry steam fluids may have developed locally.

Notes: The Limousin ophiolite is located at the suture zone between two major thrust sheets in the western French Massif Central. This ophiolitic section comprises mantle-harzburgite, mantle-dunite, wehrlites, troctolites and layered gabbros. It has recorded a static metamorphic event transforming the gabbros into undeformed amphibolites and the magmatic ultramafites into serpentinites and/or pargasite-bearing chloritites. With various thermobarometric methods, it is possible to show that the different varieties of amphibole have registered low-P (c. 0.2 GPa) conditions with temperature ranging from high-T, late-magmatic conditions to greenschist–zeolite metamorphic facies. The abundance of undeformed metamorphic rocks (which is typical of the lower oceanic crust), the occurrence of Ca–Al (–Mg) metasomatism illustrated by the growth of Ca–Al silicates in veins or replacing the primary magmatic minerals, the P–T conditions of the metamorphism and the numerous similarities with oceanic crustal rocks from Ocean Drilling Program and worldwide ophiolites are the main arguments for an ocean-floor hydrothermal metamorphism in the vicinity of a palaeo-ridge. Among the West-European Variscan ophiolites, the Limousin ophiolites constitute an extremely rare occurrence that has not been involved in any HP (subduction-related) or MP (orogenic) metamorphism as observed in other ophiolite occurrences (i.e. France, Spain and Germany).

Notes: A structural, metamorphic and geochronological study of the Staré Město belt implies the existence of two distinct metamorphic events of similar peak P–T conditions (700–800 °C, 8–10 kbar) during the Cambro-Ordovician and the Carboniferous tectonometamorphic events. The hypothesis of two distinct periods of metamorphism was suggested on the basis of structural discordance between an undoubtedly Carboniferous granodiorite sill intrusion and earlier Cambro-Ordovician fabrics of a banded amphibolite complex. The analysis of crystal size distribution (CSD) shows high nucleation density (N0) and low average growth rate (Gt) for Carboniferous mylonitic metagabbros and mylonitic granodiorites. The parameter N0 decreases whereas the quantity Gt increases towards higher temperatures progressively approaching the values obtained from the Cambro-Ordovician banded amphibolite complex. The spatial distribution of amphibole and plagioclase shows intense mechanical mixing for lower-temperature mylonitic metagabbros. In high-temperature mylonites a strong aggregate distribution is developed. Cambro-Ordovician amphibolites unaffected by Carboniferous deformation show a regular to anticlustered spatial distribution resulting from heterogeneous nucleation of individual phases. This pattern, together with CSD, was subsequently modified by the grain growth and textural equilibration controlled by diffusive mass transfer during Carboniferous metamorphism. The differences between the observed textures of the amphibolites are interpreted to be a consequence of the different durations of the Carboniferous and Cambro-Ordovician thermal events.

Notes: Serpentinite mylonites from the Happo ultramafic complex show evidence of two stages of mylonitization at different temperature conditions. Peridotite mylonites exhibit two types of olivine – porphyroclasts and neoblasts – produced at the earlier stage. The olivine neoblasts have a stretching lineation with a fabric suggesting plastic deformation along (0 1 0) [0 0 1]. In addition to the olivine fabric, the stable association of olivine, orthopyroxene and tremolite in the peridotites that survived later serpentinization, and the Si and Na contents of tremolite, suggest that the earlier mylonitization took place at temperatures between 700 and 800 °C. Later mylonitization was associated with high-temperature serpentinization to form serpentinite mylonites. In contrast to a common type of serpentinite in orogenic belts, the serpentinite mylonites are cohesively foliated, rich in olivine and diopside, and poor in antigorite. The diopside has low Al, Cr and Na contents typical of a retrograde origin, and the olivine has a homogeneous composition except in areas subjected to contact metamorphism at a later stage. Modal composition and mineral chemistry suggest that the serpentinite mylonites were formed by a hydration reaction of tremolite and olivine to produce diopside and antigorite under stable conditions of olivine, at temperatures between 400 and 600 °C. Later-stage mylonitization has preferentially been superimposed on the earlier-stage mylonite zone with a common direction of foliation. The difference in temperature between the two mylonitization stages suggests that the shear zone was episodically active during the emplacement of the Happo complex. Conditions of relatively high temperature for serpentinization at a convergent plate boundary and high permeability caused by the early mylonitization favoured the formation of the serpentinite mylonites.

Notes: High-pressure kyanite-bearing felsic granulites in the Bashiwake area of the south Altyn Tagh (SAT) subduction–collision complex enclose mafic granulites and garnet peridotite-hosted sapphirine-bearing metabasites. The predominant felsic granulites are garnet + quartz + ternary feldspar (now perthite) rocks containing kyanite, plagioclase, biotite, rutile, spinel, corundum, and minor zircon and apatite. The quartz-bearing mafic granulites contain a peak pressure assemblage of garnet + clinopyroxene + ternary feldspar (now mesoperthite) + quartz + rutile. The sapphirine-bearing metabasites occur as mafic layers in garnet peridotite. Petrographical data suggest a peak assemblage of garnet + clinopyroxene + kyanite + rutile. Early kyanite is inferred from a symplectite of sapphirine + corundum + plagioclase ± spinel, interpreted to have formed during decompression. Garnet peridotite contains an assemblage of garnet + olivine + orthopyroxene + clinopyroxene. Thermobarometry indicates that all rock types experienced peak P–T conditions of 18.5–27.3 kbar and 870–1050 °C. A medium–high pressure granulite facies overprint (780–820 °C, 9.5–12 kbar) is defined by the formation of secondary clinopyroxene ± orthopyroxene + plagioclase at the expense of garnet and early clinopyroxene in the mafic granulites, as well as by growth of spinel and plagioclase at the expense of garnet and kyanite in the felsic granulite. SHRIMP II zircon U-Pb geochronology yields ages of 493 ± 7 Ma (mean of 11) from the felsic granulite, 497 ± 11 Ma (mean of 11) from sapphirine-bearing metabasite and 501 ± 16 Ma (mean of 10) from garnet peridotite. Rounded zircon morphology, cathodoluminescence (CL) sector zoning, and inclusions of peak metamorphic minerals indicate these ages reflect HP/HT metamorphism. Similar ages determined for eclogites from the western segment of the SAT suggest that the same continental subduction/collision event may be responsible for HP metamorphism in both areas.

Notes: A new quantitative approach to constraining mineral equilibria in sapphirine-bearing ultrahigh-temperature (UHT) granulites through the use of pseudosections and compatibility diagrams is presented, using a recently published thermodynamic model for sapphirine. The approach is illustrated with an example from an UHT locality in the Anápolis–Itauçu Complex, central Brazil, where modelling of mineral equilibria indicates peak metamorphic conditions of about 9 kbar and 1000 °C. The early formed, coarse-grained assemblage is garnet–orthopyroxene–sillimanite–quartz, which was subsequently modified following peak conditions. The retrograde pressure–temperature (P–T) path of this locality involves decompression across the FeO–MgO–Al2O3–SiO2 (FMAS) univariant reaction orthopyroxene + sillimanite = garnet + sapphirine + quartz, resulting in the growth of sapphirine–quartz, followed by cooling and recrossing of this reaction. The resulting microstructures are modelled using compatibility diagrams, and pseudosections calculated for specific grain boundaries considered as chemical domains. The sequence of microstructures preserved in the rocks constrains a two-stage isothermal decompression–isobaric cooling path. The stability of cordierite along the retrograde path is examined using a domainal approach and pseudosections for orthopyroxene–quartz and garnet–quartz grain boundaries. This analysis indicates that the presence or absence of cordierite may be explained by local variation in aH2O. This study has important implications for thermobarometric studies of UHT granulites, mainly through showing that traditional FMAS petrogenetic grids based on experiments alone may overestimate P–T conditions. Such grids are effectively constant aH2O sections in FMAS-H2O (FMASH), for which the corresponding aH2O is commonly higher than that experienced by UHT granulites. A corollary of this dependence of mineral equilibria on aH2O is that local variations in aH2O may explain the formation of cordierite without significant changes in P–T conditions, particularly without marked decompression.

Notes: The gabbroic/dioritic Pembroke Hornblende Granulite (PHG) of Milford Sound displays a geometrically simple mesoscopic network of sub-planar garnet reaction zones (GRZ) in which the meta-igneous hornblende granulite has been depleted of Na, Si, and H2O, and c. 25 vol.% almandine-rich garnet has formed. Some studies postulate the initial presence of melt along the centres of all GRZ, explaining the frequent absence of feldspathic veins by selective melt loss. A more parsimonious model is necessitated by structural evidence and, together with chemical data, suggests a relationship between mid-range metasomatic transport and anatexis. The Pembroke outcrops show a process of incipient melting of gabbro/diorite in an environment of relatively low aH2O in lithologies that have limited free quartz. A non-equilibrium steady state is proposed, in which a sodic dehydration fluid moves some distance via the GRZ network towards areas of partial melting. Only in these areas are Na and Si reconstituted as albite, with more garnet as byproduct, having avoided the need for melt percolation. The combined structural and chemical evidence directs a focus on mass transport in low-aH2O gabbroic environments. In subsequent events of shearing and complete transposition, both sets of garnet – the atypical GRZ residue and partial melt melanosomes – were inherited by the Milford Gneiss ‘facies’ of the PHG.

Notes: Hydration reactions are direct evidence of fluid–rock interaction during regional metamorphism. In this study, hydration reactions to produce retrograde actinolite in mafic schists are investigated to evaluate the controlling factors on the reaction progress. Mafic schists in the Sanbagawa belt contain amphibole coexisting with epidote, chlorite, plagioclase and quartz. Amphibole typically shows two types of compositional zoning from core to rim: barroisite → hornblende → actinolite in the high-grade zone, and winchite → actinolite in the low-grade zone. Both types indicate that amphibole grew during the exhumation stage of the metamorphic belt. Microstructures of amphibole zoning and mass-balance relations suggest that: (1) the actinolite-forming reactions proceeded at the expense of the preexisting amphibole; and (2) the breakdown reaction of hornblende consumed more H2O fluid than that of winchite, when one mole of preexisting amphibole was reacted. Reaction progress is indicated by the volume fraction of actinolite to total amphibole, Yact, with the following details: (1) reaction proceeded homogeneously in each mafic layer; (2) the extent of the hornblende breakdown reaction is commonly low (Yact 〈 0.5), but it increases drastically in the high-grade part of the garnet zone (Yact 〉 0.7); and (3) the extent of the winchite breakdown reaction is commonly high (Yact 〉 0.7). Many microcracks are observed within hornblende, and the extent of hornblende breakdown reaction is correlated with the size reduction of the hornblende core. Brittle fracturing of hornblende may have enhanced retrograde reaction progress by increasing of influx of H2O and the surface area of hornblende. In contrast to high-grade rocks, the winchite breakdown reaction is well advanced in the low-grade rocks, where reaction progress is not associated with brittle fracturing of winchite. The high extent of the reaction in the low-grade rocks may be due to small size of winchite before the reaction.

Notes: The combination of metamorphic petrology tools and in situ laser 40Ar/39Ar dating on phengite (linking time of growth, compositions and P–T conditions) enables us to identify a detailed P–T–d–t path for the still debated tectonometamorphic evolution of the Nevado-Filabride complex and infer new geodynamic-scale constraints. Our data show an isothermal decompression (at 550 °C) from 20 kbar for the Bédar-Macael unit and 14 kbar for the Calar Alto unit down to c. 3–4 kbar for both units at 2.8 mm year−1. At 22–18 Ma, this first part of the exhumation is followed by a final exhumation at 0.6 mm year−1 along a high-temperature low-pressure (HTLP) gradient of c. 60 °C km−1. The age of the peak of pressure is not precisely known but it is shown that it is around 30 Ma and possibly older, which is at variance with recent models suggesting a younger age for high-pressure (HP) metamorphism. Most of the exhumation is related to late-orogenic extension from c. 30 to 22–18 Ma. Thus the formation of the main ductile extensional shear zone, the Filabres Shear Zone (FSZ), occurred at 22–18 Ma and is clearly associated with a top-to-the-west shear sense once the FSZ is well localized. The transition from ductile to brittle then occurred at c. 14 Ma. The final exhumation, accommodated by brittle deformation, occurred from c. 14 to 9 Ma and was accompanied, from 12 to 8 Ma, by the formation of nearby extensional basins. The duration of the extensional process is c. 20 Myr which argues in favour of a progressive slab retreat from c. 30 to 9 Ma. The change in the shape of the P–T path at 22–18 Ma together with strain localization along the main top-to-the-west shear zone suggests that this date corresponds to a change in the direction of slab retreat from southwards to westwards.

Notes: Thermal zoning of the Highland Complex, Sri Lanka has been delineated using the Fe2+–Mg distribution coefficient between garnet and biotite from garnet–biotite gneiss samples collected with wide geographical distribution. In order to minimize the potential for retrograde Fe–Mg exchange and maximize the potential for retaining peak equilibrium KD (garnet–biotite) and temperature, garnet and biotite included within feldspar and quartz without other mineral inclusions have been selected. The calculated results indicate four distinct temperature contours with KD values varying from 1.84 to 6.38 and temperature varying from 996 to 591 °C. From the present results, it is possible to divide the Highland Complex into two major metamorphic zones: a high-temperature area in the central region and a low-temperature area in the south-western and north-eastern region. In conjunction with the metamorphic pressure variations estimated from the granulites of the Highland Complex in previous studies, it is shown that the high- and low-temperature areas are complemented by a high-pressure region towards the eastern side and a low-pressure region towards the western side of this complex. This thermal dome is interpreted to be an artifact of the different crustal levels exhumed following Pan-African metamorphism.

Notes: Monazite grains from Greater Himalayan Sequence gneisses, Langtang valley, Nepal, were chemically mapped and then dated in situ via Th–Pb ion-microprobe analysis. Correlation of ages and chemistry reveals at least five different generations of monazite, ranging from c. 9 to 〉300 Ma. Petrological models of monazite chemistry provide a link between these generations and the thermal evolution of these rocks, yielding an age for the melting of Greater Himalayan rocks within the Main Central Thrust sheet (c. 16 Ma), and for the timing of thrust sheet emplacement that are younger than commonly viewed. Chemical characterization of monazite is vital prior to chronological microanalysis, and many ages previously reported for monazite from the Greater Himalayan Sequence are interpretationally ambiguous.

Notes: This study presents calcite–graphite carbon isotope fractionations for 32 samples from marble in the northern Elzevir terrane of the Central Metasedimentary Belt, Grenville Province, southern Ontario, Canada. These results are compared with temperatures calculated by calcite–dolomite thermometry (15 samples), garnet–biotite thermometry (four samples) and garnet–hornblende thermometry (three samples). Δcal-gr values vary regularly across the area from 〉6.5‰ in the south to 4.0‰ in the north, which corresponds to temperatures of 525 °C in the south to 650 °C in the north. Previous empirical calibration of the calcite–graphite thermometer agrees very well with calcite–dolomite, garnet–biotite and garnet–hornblende thermometry, whereas, theoretical calibrations compare less well with the independent thermometry. Isograds in marble based on the reactions rutile + calcite + quartz =titanite and tremolite + calcite + quartz = diopside, span temperatures of 525–600 °C and are consistent with calculated temperature–X(CO2) relations. Results of this study compare favourably with large-scale regional isotherms, however, local variation is greater than that revealed by large-scale sampling strategies. It remains unclear whether the temperature–Δcal-gr relationship observed in natural materials below 650 °C represents equilibrium fractionations or not, but the regularity and consistency apparent in this study demonstrate its utility for thermometry in amphibolite facies marble.

Notes: Oxygen-isotope compositions of kyanite, andalusite, prismatic sillimanite and fibrolite from the Proterozoic terrane in the Truchas Mountains, New Mexico differ from one another, suggesting that these minerals did not grow in equilibrium at the Al2SiO5 (AS) polymorph-invariant point as previously suggested. Instead, oxygen-isotope temperature estimates indicate that growth of kyanite, andalusite and prismatic sillimanite occurred at c. 575, 615 and 640 °C respectively. Temperature estimates reported in this paper are interpreted as those of growth for the different AS polymorphs, which are not necessarily the same as peak metamorphic temperatures for this terrane. Two distinct temperature estimates of c. 580 °C and c. 700 °C are calculated for most fibrolite samples, with two samples yielding clear evidence of quartz-fibrolite oxygen-isotope disequilibrium. These data indicate that locally, and potentially regionally, oxygen-isotope disequilibrium between quartz and fibrolite may have resulted from rapid fibrolite nucleation. Pressures of mineral growth that were extrapolated from oxygen-isotope thermometry results and calculated using petrological constraints suggest that kyanite and one generation of fibrolite grew during M1 at 5 kbar, and that andalusite, prismatic sillimanite and a second generation of fibrolite grew during M2 at 3.5 kbar. M1 and M2 therefore represent two distinct metamorphic events that occurred at different crustal levels. The ability of the AS polymorphs to retain δ18O values of crystallization make these minerals ideal to model prograde-growth histories of mineral assemblages in metamorphic terranes and to understand more clearly the pressure–temperature histories of multiple metamorphic events.

Notes: The integration of information which can be gained from accessory [i.e. age (t)] and rock-forming minerals [i.e. temperature (T) and pressure (P)] requires a more profound understanding of the equilibration kinetics during metamorphic processes. This paper presents an approach comparing conventional P–T estimate from equilibrated assemblages of rock-forming minerals with temperature data derived from yttrium-garnet-monazite (YGM) and yttrium-garnet-xenotime (YGX) geothermometry. Such a comparison provides an initial indication on differences between equilibration of major and trace elements. Regarding this purpose, two migmatites, two polycyclic and one monocyclic gneiss from the Central Alps (Switzerland, northern Italy) were investigated. While the polycyclic samples exhibit trace-element equilibration between monazite and garnet grains assigned to the same metamorphic event, there are relics of monazite and garnet obviously surviving independent of their textural position. These observations suggest that surface processes dominate transport processes during equilibration of those samples. The monocyclic gneiss, on the contrary, displays rare isolated monazite with equilibration of all elements, despite comparably large transport distances. With a nearly linear crystal-size distribution of the garnet grain population, growth kinetics, related to the major elements, were likely surface-controlled in this sample. In contrast to these completely equilibrated examples, the migmatites indicate disequilibrium between garnet and monazite with a change in REE patterns on garnet transects. The cause for this disequilibrium may be related to a potential disequilibrium initiated by a changing bulk chemistry during melt segregation. While migmatite environments are expected to support high transport rates (i.e. high temperatures and melt presence), the evolution of equilibration in migmatites is additionaly related to change in chemistry. As a key finding, surface-controlled equilibration kinetics seem to dominate transport-controlled processes in the investigated samples. This may be decisive information towards the understanding of age data derived from monazite.

Notes: The presence of ternary feldspar in high-grade meta-igneous rocks, and the recognition of the thermometric significance of this mineral, has led recent researchers to postulate peak metamorphic temperatures in excess of 1000 °C. However, it needs to be established that such ternary feldspar is not in fact a survivor of the original high-temperature crystallization of the igneous protolith. After exsolution, the host and lamellae in the ternary feldspar grains may be stable throughout subsequent history as long as recrystallization does not occur. Such a history may involve rehydration and metamorphism, including H2O-saturated conditions, with the compositions and proportions of the host and lamellae being modified to reflect the P–T conditions experienced. In the case of the high-grade meta-igneous rocks from the Moldanubian of the Bohemian Massif, some samples that contain ternary feldspar preserve a substantial measure of their igneous heritage. Orthopyroxene-bearing granulites not only include types that are barely affected by the metamorphism, but also others that have undergone hydration of the igneous protolith prior to the development of a metamorphic overprint. A key to establishing the igneous origin of the ternary feldspar grains is their preservation in garnet that is either itself igneous, or of a relatively low-temperature metamorphic origin. Applying the logic to the other ternary feldspar-bearing meta-igneous rocks deprives the Moldanubian of its ultrahigh temperature (UHT) metamorphic status.

Notes: The effect of fluids on recrystallization behaviour is well known; however, the detailed microscale distribution of fluid in grain boundaries and the influence of fluid on grain boundary migration are still unresolved. In this study, in-situ deformation experiments in transmitted light microscopy were undertaken, as this allows continuous and direct observation of the whole range of processes involved in fluid-assisted grain boundary migration. A new see-through deformation apparatus was developed to enable the control of fluid pressure. Bischofite containing small amounts of aqueous fluid was deformed at temperatures between 50 and 90 °C, over a range of fluid pressure from 0.5 to 1 MPa, and strain rates of 5 × 10−6 to 1 × 10−4 s−1. The rates of grain boundary migration were measured at different temperatures and strain rates. Detailed observations during and after the deformation illustrate the evolution of migrating fluid-filled grain boundaries and show that the incorporation of fluids from inclusions as well as their pinch-off is dependent on the grain boundary velocity, the thickness of the grain boundary and the size and shape of the inclusions. Direct evidence is presented for the contraction of the grain boundary fluids into isolated inclusions after equilibrium conditions are attained.

Notes: A mid-ocean ridge basalt (MORB)-type eclogite from the Moldanubian domain in the Bohemian Massif retains evidence of its prograde path in the form of inclusions of hornblende, plagioclase, clinopyroxene, titanite, ilmenite and rutile preserved in zoned garnet. Prograde zoning involves a flat grossular core followed by a grossular spike and decrease at the rim, whereas Fe/(Fe + Mg) is also flat in the core and then decreases at the rim. In a pseudosection for H2O-saturated conditions, garnet with such a zoning grows along an isothermal burial path at c. 750 °C from 10 kbar in the assemblage plagioclase-hornblende-diopsidic clinopyroxene-quartz, then in hornblende-diopsidic clinopyroxene-quartz, and ends its growth at 17–18 kbar. From this point, there is no pseudosection-based information on further increase in pressure or temperature. Then, with garnet-clinopyroxene thermometry, the focus is on the dependence on, and the uncertainties stemming from the unknown Fe3+ content in clinopyroxene. Assuming no Fe3+ in the clinopyroxene gives a serious and unwarranted upward bias to calculated temperatures. A Fe3+-contributed uncertainty of ±40 °C combined with a calibration and other uncertainties gives a peak temperature of 760 ± 90 °C at 18 kbar, consistent with no further heating following burial to eclogite facies conditions. Further pseudosection modelling suggests that decompression to c. 12 kbar occurred essentially isothermally from the metamorphic peak under H2O-undersaturated conditions (c. 1.3 mol.% H2O) that allowed the preservation of the majority of garnet with symplectitic as well as relict clinopyroxene. The modelling also shows that a MORB-type eclogite decompressed to c. 8 kbar ends as an amphibolite if it is H2O saturated, but if it is H2O-undersaturated it contains assemblages with orthopyroxene. Increasing H2O undersaturation causes an earlier transition to SiO2 undersaturation on decompression, leading to the appearance of spinel-bearing assemblages. Granulite facies-looking overprints of eclogites may develop at amphibolite facies conditions.

Notes: A series of striking migmatitic structures occur in rectilinear networks through western Fiordland, New Zealand, involving, for the most part, narrow anorthositic dykes that cut hornblende-bearing orthogneiss. Adjacent to the dykes, host rocks show patchy, spatially restricted recrystallization and dehydration on a decimetre-scale to garnet granulite. Although there is general agreement that the migration of silicate melt has formed at least parts of the structures, there is disagreement on the role of silicate melt in dehydrating the host rock. A variety of causal processes have been inferred, including metasomatism due to the ingress of a carbonic, mantle-derived fluid; hornblende-breakdown leading to water release and limited partial melting of host rocks; and dehydration induced by volatile scavenging by a migrating silicate melt. Variability in dyke assemblage, together with the correlation between dehydration structures and host rock silica content, are inconsistent with macroscopic metasomatism, and best match open system behaviour involving volatile scavenging by a migrating trondhjemitic liquid.

Notes: Upper amphibolite facies felsic gneiss from Broken Hill records the metatexite to schlieren diatexite to massive diatexite transition in a single rock type over a scale of tens to hundreds of metres. The metatexites are characterized by centimetre-scale segregation of melt into leucosomes to form stromatic migmatite. The schlieren diatexites are characterized by the disaggregation of the rocks and the development of schlieren migmatite. The massive diatexites represent a higher degree of disaggregation, lack schlieren and contain plagioclase and K-feldspar phenocrysts. The transition from metatexite to schlieren diatexite and massive diatexite was heterogeneous with both disaggregation of the rock on a grain scale and disaggregation of the rock into centimetre- to metre-scale rafts. As melt contents increased, the proportion of material disaggregated on a grain scale increased. The high proportion of melt needed to form diatexites at upper amphibolite facies conditions was the result of an influx of hydrous fluid at temperatures just above the solidus of the diatexites. Nearby metapelitic rocks, with a slightly higher solidus temperature, undergoing subsolidus muscovite breakdown are the likely source of the fluid. Continued heating during and after the influx of fluid led to melt contents of up to c. 60 mol.% in the massive diatexite. The metatexite zone probably involved little added fluid. Continued deformation during cooling and melt crystallization resulted in the extensive development of schlieren and late-stage melt segregations and melt-rich shear bands in the schlieren diatexite zone. The rocks of the massive diatexite zone lack these late-stage segregations, consistent with the cessation of D2 deformation prior to them developing a crystal framework.

Notes: Cambrian orogenesis (550–490 Ma) in the Lambert Province of the southern Prince Charles Mountains resulted in three successive stages of deformation. The earliest of these deformations resulted in the development of a layer-parallel foliation (S1) that was folded into macro-scale recumbent folds (F2). Subsequent deformation buckled the rocks into long-wavelength (c. 20 km), SW- to NW-trending antiformal closures (F3) mostly separated from each other by west to SW trending, steeply dipping, high-strain zones. Metapelitic rocks from the region are divisible into two compositional types: a high-Al, -Fe and -K type and a high-Mg, -Ca and -Na type. In rocks of both composition, relic staurolite preceded the formation of upper amphibolite facies garnet + biotite + sillimanite ± muscovite mineral assemblages that record peak pressures and temperatures of c. 650–700 °C and 6–7 kbar. Subsequent decompression of c. 3 kbar is implied from texturally late plagioclase and a reduction in the modal abundance of garnet in the high-Al, -Fe and -K metapelites, and from texturally late cordierite in the more magnesium rocks. This clockwise P–T–t path, with prograde heating followed by rapid decompression, is: (i) equivalent to that recorded in the same-aged rocks at Prydz Bay located 600 km to the north, and (ii) similar to the modelled response of the crust to thickening following continent–continent collision. These results indicate that large areas of East Antarctica were thickened and rapidly exhumed, probably in response to collisional orogenesis during the Early Cambrian. This supports the inference that Early Cambrian orogenesis in the Prydz Bay–Prince Charles Mountains region of East Antarctica marks one of the fundamental lithospheric boundaries within Gondwana.

Notes: Interlayered 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.

Notes: The 3D shape, size and orientation data for white mica grains sampled along two transects of increasing metamorphic grade in the Otago Schist, New Zealand, reveal that metamorphic foliation, as defined by mica shape-preferred orientation (SPO), developed rapidly at sub-greenschist facies conditions early in the deformation history. The onset of penetrative strain metamorphism is marked by the rapid elimination of poorly oriented large clastic mica in favour of numerous new smaller grains of contrasting composition, higher aspect ratios and a strong preferred orientation. The metamorphic mica is blade shaped with long axes defining the linear aspect of the foliation and intermediate axes a partial girdle about the lineation. Once initiated, foliation progressively intensified by an increase in the aspect ratio, size and alignment of grains, although highest grade samples within the chlorite zone record a decrease in aspect ratio and reduction in SPO strength despite continued increase in grain size. These trends are interpreted in terms of progressive competitive anisotropic growth of blade-shaped grains so that the fastest growth directions and blade lengths tend to parallel the extension direction during deformation. The competitive nature of mica growth is indicated by the progressive increase in size and resultant decrease in number of metamorphic mica with increasing grade, from c. 1000 relatively small mica grains per square millimetre of thin section at lower grades, to c. 100 relatively large grains per square millimetre in higher grade samples. Reversal of SPO intensity and grain aspect ratio trends in higher grade samples may reflect a reduction in the strain rate or reduction in the deviatoric component of the stress field.

Notes: The assumption of oxygen isotope and major element equilibrium during prograde metamorphism was tested using staurolite-grade pelitic schists that have undergone sequential porphyroblast growth and multiple episodes of recrystallization of matrix minerals and foliation development. Textural relationships are used to infer a metamorphic history that involves garnet growth followed by staurolite growth, with each porphyroblast growth event followed by at least one period of recrystallization of matrix minerals. Conventional geothermobarometry using Qtz–Grt–Pl–Ms–Bt ± St equilibria yields peak P–T conditions of c. 625 °C at 9–11 kbar, consistent with KMnFMASH petrogenetic grid predictions for stability of the assemblage Grt + St + Bt. Qtz–Grt oxygen isotope fractionations yield apparent temperatures of c. 590 °C and Qtz–St fractionations yield an apparent temperature of c. 595 °C. Diffusional modelling indicates that quartz isotopic compositions were reset by c. 30 °C via retrograde isotopic diffusional exchange with micas. The isotopic temperatures appear to be in excellent agreement with one another, and suggest oxygen isotope equilibrium was attained between garnet and staurolite at c. 625 °C. However, the agreement of Qtz–Grt and Qtz–Str isotopic temperatures is not consistent with petrographic observations (garnet grew before staurolite) and petrogenetic grid constraints that predict that garnet grows over a temperature interval of c. 525–550 °C. Given that: (i) oxygen diffusion rates in staurolite and garnet are slow enough to render an individual porphyroblast effectively closed to exchange after it forms; and (ii) matrix minerals are able to exchange isotopes via recrystallization during each period of deformation; garnet and staurolite could not have simultaneously achieved oxygen isotope equilibrium with each other or with minerals in the recrystallized matrix. Thus, the Qtz–Grt fractionations, which yield apparent temperatures that are in apparent agreement with peak metamorphic temperature and apparent temperatures for Qtz–St fractionations, cannot be fractionations resulting from equilibrium isotopic exchange. Instead, they are apparent fractionations between porphyroblasts formed at different temperature and times in the prograde P–T–D path, and quartz that recrystallized and exchanged with micas and plagioclase during several phases of deformation.

Notes: Shape, size and orientation measurements of quartz grains sampled along two transects that cross zones of increasing metamorphic grade in the Otago Schist, New Zealand, reveal the role of quartz in the progressive development of metamorphic foliation. Sedimentary compaction and diagenesis contributed little to the formation of a shape-preferred orientation (SPO) within the analysed samples. Metamorphic foliation was initiated at sub-greenschist facies conditions as part of a composite S1-bedding structure parallel to the axial planes of tight to isoclinal F1 folds. An important component of this foliation is a pronounced quartz SPO that formed dominantly by the effect of dissolution–precipitation creep on detrital grains in association with F1 strain. With increasing grade, the following trends are evident from the SPO data: (i) a progressive increase in the aspect ratio of grains in sections parallel to lineation, and the development of blade-shaped grains; (ii) the early development of a strong shape preferred orientation so that blade lengths define the linear aspect of the foliation (lineation) and the intermediate axes of the blades define a partial girdle about the lineation; (iii) a slight thinning and reduction in volume of grains in the one transect; and (iv) an actual increase in thickness and volume in the survivor grains of the second transect. The highest-grade samples, within the chlorite zone of the greenschist facies, record segregation into quartz- and mica-rich layers. This segregation resulted largely from F2 crenulation and marks a key change in the distribution, deformation and SPO of the quartz grains. The contribution of quartz SPO to defining the foliation lessens as the previously discrete and aligned detrital quartz grains are replaced by aggregates and layers of dynamically recrystallized quartz grains of reduced aspect ratio and reduced alignment. Pressure solution now affects the margins of quartz-rich layers rather than individual grains. In higher-grade samples, therefore, the rock structure is characterized increasingly by segregation layering parallel to a foliation defined predominantly by mica SPO.

Notes: The Tres Arboles ductile fault zone in the Eastern Sierras Pampeanas, central Argentina, experienced multiple ductile deformation and faulting events that involved a variety of textural and reaction hardening and softening processes. Much of the fault zone is characterized by a (D2) ultramylonite, composed of fine-grained biotite + plagioclase, that lacks a well-defined preferred orientation. The D2 fabric consists of a strong network of intergrown and interlocking grains that show little textural evidence for dislocation or dissolution creep. These ultramylonites contain gneissic rock fragments and porphyroclasts of plagioclase, sillimanite and garnet inherited from the gneissic and migmatitic protolith (D1) of the hangingwall. The assemblage of garnet + sillimanite + biotite suggests that D1-related fabrics developed under upper amphibolite facies conditions, and the persistence of biotite + garnet + sillimanite + plagioclase suggests that the ultramylonite of D2 developed under middle amphibolite facies conditions. Greenschist facies, mylonitic shear bands (D3) locally overprint D2 ultramylonites. Fine-grained folia of muscovite + chlorite ± biotite truncate earlier biotite + plagioclase textures, and coarser-grained muscovite partially replaces relic sillimanite grains. Anorthite content of shear band (D3) plagioclase is c. An30, distinct from D1 and D2 plagioclase (c. An35). The anorthite content of D3 plagioclase is consistent with a pervasive grain boundary fluid that facilitated partial replacement of plagioclase by muscovite. Biotite is partially replaced by muscovite and/or chlorite, particularly in areas of inferred high strain. Quartz precipitated in porphyroclast pressure shadows and ribbons that help define the mylonitic fabric. All D3 reactions require the introduction of H+ and/or H2O, indicating an open system, and typically result in a volume decrease. Syntectonic D3 muscovite + quartz + chlorite preferentially grew in an orientation favourable for strain localization, which produced a strong textural softening. Strain localization occurred only where reactions progressed with the infiltration of aqueous fluids, on a scale of hundreds of micrometre. Local fracturing and microseismicity may have induced reactivation of the fault zone and the initial introduction of fluids. However, the predominant greenschist facies deformation (D3) along discrete shear bands was primarily a consequence of the localization of replacement reactions in a partially open system.

Notes: Metapelites, migmatites and granites from the c. 2 Ga Mahalapye Complex have been studied for determining the P–T–fluid influence on mineral assemblages and local equilibrium compositions in the rocks from the extreme southwestern part of the Central Zone of the Limpopo high-grade terrane in Botswana. It was found that fluid infiltration played a leading role in the formation of the rocks. This conclusion is based on both well-developed textures inferred to record metasomatic reactions, such as Bt ⇒ And + Qtz + (K2O) and Bt ± Qtz ⇒ Sil + Kfs + Ms ± Pl, and zonation of Ms | Bt + Qtz | And + Qtz and Grt | Crd | Pl | Kfs + Qtz reflecting a perfect mobility (Korzhinskii terminology) of some chemical components. The conclusion is also supported by the results of a fluid inclusion study. CO2 and H2O (〈inlineGraphic alt="inline image" href="urn:x-wiley:02634929:JMG579:JMG_579_mu1" location="equation/JMG_579_mu1.gif"/〉 = 0.6) are the major components of the fluid. The fluid has been trapped synchronously along the retrograde P–T path. The P–T path was derived using mineral thermobarometry and a combination of mineral thermometry and fluid inclusion density data. The Mahalapye Complex experienced low-pressure granulite facies metamorphism with a retrograde evolution from 770 °C and 5.5 kbar to 560 °C and 2 kbar, presumably at c. 2 Ga.

Notes: Quartzo-feldspathic veins emplaced within a migmatite terrane near Wilson Lake in the Grenville Province of central Labrador record a metamorphic event not evident in the host rocks. The discordant veins are undeformed and have undisturbed primary igneous/hydrothermal textures. Most of the veins contain euhedral kyanite, as well as aggregates of kyanite, K-feldspar, phlogopite and minor dumortierite which are likely pseudomorphs after primary phengite. The reconstructed phengite compositions range from 3.1 to 3.2 Si per 11 oxygen formula unit. The pseudomorph assemblage is interpreted as the product of phengite + quartz melting under H2O-undersaturated conditions, which brackets P–T conditions of formation to about 9–16 kbar and 775–875 °C. A parallel vein that is likely of the same generation contains the borosilicate phases, dumortierite, prismatine and grandidierite, but no kyanite. The borosilicate assemblages constrain the P–T conditions of vein crystallization to ≥10 kbar and c. 750–850 °C. Vein emplacement is constrained to T ≤ 875 °C at the same pressures, which is well within the kyanite zone.Because the host rocks and veins must have experienced the same P–T history following vein emplacement, the presence of unreacted sillimanite in the host migmatites implies insufficient time for host rock equilibration. Slow reaction rates because of anhydrous conditions are not a likely explanation given the abundance of biotite and hornblende in the host rocks. The ductility implied by the breakdown of a hydrous phase (phengite) and the production of an H2O-undersaturated melt in the veins contrasts with the apparently brittle behaviour of the host rocks. The absence of deformation since the time of vein emplacement, even at temperatures above 750 °C, suggests that the deep crust in this part of Labrador had a very short residence time under conditions of the kyanite zone. Rapid decompression from those conditions is consistent with quartz + phengite melting and accounts for the relatively brittle behaviour of the terrane as it was uplifted.

Notes: Regionally metamorphosed metapelites from Rogaland, SW Norway, contain zircon formed during the decompression reaction garnet + sillimanite + quartz → cordierite. The zircon, which occurs as inclusions in cordierite coronas around garnet, is texturally, chemically and isotopically distinct from older zircon in other textural settings in the matrix. A SHRIMP U–Pb age of 955 ± 8 Ma based on analyses in thin section on the decompression zircon from the cordierite coronas, therefore dates a point on the retrograde path, estimated from garnet–cordierite equilibria to be 5.6 kbar, 710 °C. This population was under-represented in conventional SHRIMP analyses of individual zircon in a mono-mineralic grain mount and, in the absence of a textural context, its significance unknown. The dominant age identified from SHRIMP analyses of the grain mount, in combination with analyses from matrix zircon in thin section, was 1035 ± 9 Ma. Based on the lack of consistent textural relationships with any specific minerals in thin section, as well as rare earth element chemistry, the 1035-Ma population is interpreted to represent zircon growth during incipient migmatization of the rocks at 6–8 kbar and c. 700 °C. This is consistent with previous estimates for the age of regional M1 metamorphism during the Sveconorwegian Orogeny. The most important outcome of this study is the successful analysis of zircon grains in a specific, well-constrained reaction texture. Not only does this allow a precise point on the regional P–T path to be dated, but it also emphasizes the possibility of zircon formation during the retrograde component of a typical metamorphic cycle.

Notes: The subduction and exhumation of accretionary prism metasedimentary rocks are accompanied by large-strain ductile deformations which may be recorded in microstructures. Porphyroblast microstructures have been a key to unravel the kinematics in such deformed belts. Shape-preferred orientation (SPO) of epidote and amphibole inclusions that define S-shaped trails in prograde cores of plagioclase porphyroblasts were analysed from the high-P/T Sambagawa metamorphic rocks. Inclusions are found to be elongate parallel to the [010] and [001] directions, respectively, and their long-axis orientations define an internal foliation Si (best-fit great circle) and lineation Li (maximum on the Si). S-shaped inclusion trails in the orthogonal sections do not exhibit the same geometries, but rather are grouped into two types, where the foliation intersection axes (FIAs) are nearly perpendicular and parallel to Li, respectively. These two types of S-shaped inclusion trails are seen in the sections inclined at low and high angles to the Li, respectively. However, the latter type commonly consists of composite trails, where the Si is first rotated about an FIA perpendicular to the Li (i.e. unique axis), and then about an FIA parallel to the Li. The S-shaped inclusion trails are interpreted to have formed by the successive overgrowth of matrix minerals and rotation of the plagioclase porphyroblast cores about a unique axis in non-coaxial deformation. The rotation of Si about an FIA nearly parallel to the Li is perhaps an apparent rotation, caused by the deflection of foliation around the growing prismatic plagioclase grain prior to inclusion into the porphyroblast. This study has for the first time documented the 3-D geometry of S-shaped inclusion trails in porphyroblasts from accretionary prism metasedimentary rocks and identified their origin, which helps to understand the flow kinematics in the deeper part of a subduction channel.

Notes: In the Orlica-Śnieżnik complex at the NE margin of the Bohemian Massif, high-pressure granulites occur as isolated lenses within partially migmatized orthogneisses. Sm–Nd (different grain-size fractions of garnet, clinopyroxene and/or whole rock) and U–Pb [isotope dilution-thermal ionization mass spectrometry (ID-TIMS) single grain and sensitive high-resolution ion microprobe (SHRIMP)] ages for granulites, collected in the surroundings of Červený Důl (Czech Republic) and at Stary Gierałtów (Poland), constrain the temporal evolution of these rocks during the Variscan orogeny. Most of the new ages cluster at c. 350–340 Ma and are consistent with results previously reported for similar occurrences throughout the Bohemian Massif. This interval is generally interpreted to constrain the time of high-pressure metamorphism. A more complex evolution is recorded for a mafic granulite from Stary Gierałtów and concerns the unknown duration of metamorphism (single, short-lived metamorphic cycle or different episodes that are significantly separated in time?). The central grain parts of zircon from this sample yielded a large spread in apparent 206Pb/238U SHRIMP ages (c. 462–322 Ma) with a distinct cluster at c. 365 Ma. This spread is interpreted to be indicative for variable Pb-loss that affected magmatic protolith zircon during high-grade metamorphism. The initiating mechanism and the time of Pb-loss has yet to be resolved. A connection to high-pressure metamorphism at c. 350–340 Ma is a reasonable explanation, but this relationship is far from straightforward. An alternative interpretation suggests that resetting is related to a high-temperature event (not necessarily in the granulite facies and/or at high pressures) around 370–360 Ma, that has previously gone unnoticed. This study indicates that caution is warranted in interpreting U–Pb zircon data of HT rocks, because isotopic rejuvenation may lead to erroneous conclusions.

Notes: The development of shear zones at mid-crustal levels in the Proterozoic Willyama Supergroup was synchronous with widespread fluid flow resulting in albitization and calcsilicate alteration. Monazite dating of shear zone fabrics reveal that they formed at 1582 ± 22 Ma, at the end of the Olarian D3 deformational event and immediately prior to the emplacement of regional S-type granites. Two stages of fluid flow are identified in the area: first an albitizing event which involved the addition of Na and loss of Si, K and Fe; and a second phase of calcsilicate alteration with additions of Ca, Fe, Mg and Si and removal of Na. Fluid fluxes calculated for albitization and calcsilicate alteration were 5.56 × 109 to 1.02 × 1010 mol m−2 and 2.57 × 108–5.20 × 109 mol m−2 respectively. These fluxes are consistent with estimates for fluid flow through mid-crustal shear zones in other terranes. The fluids associated with shearing and alteration are calculated to have δ18O and δD values ranging between +8 and +11‰, and −33 and −42‰, respectively, and ɛNd values between −2.24 and −8.11. Our results indicate that fluids were derived from metamorphic dehydration of the Willyama Supergroup metasediments. Fluid generation occurred during prograde metamorphism of deeper crustal rocks at or near peak pressure conditions. Shear zones acted as conduits for major crustal fluid flow to shallow levels where peak metamorphic conditions had been attained earlier leading to the apparent ‘retrograde’ fluid-flow event. Thus, the peak metamorphism conditions at upper and lower crustal levels were achieved at differing times, prior to regional granite formation, during the same orogenic cycle leading to the formation of retrograde mineral assemblages during shearing.

Notes: The thermodynamic properties of silicate minerals can be described as a linear combination of the fractional properties of their constituent polyhedra. In contrast, given the thermodynamic properties of these polyhedra, the thermodynamic properties of minerals can be estimated, where only the crystallography of the mineral needs to be known. Such estimates are especially powerful for hypothetical mineral end-members or for minerals where experimental determination of their thermodynamic properties is difficult. In this contribution the fractional enthalpy, entropy and molar volume for 35 polyhedra have been determined using weighted multiple linear regression analysis on a data set of published mineral thermodynamic properties. The large number of polyhedra determined, allows calculation of a much larger variety of phases than was previously possible and the larger set of minerals used provides more confident fractional properties. The OH-bearing minerals have been described by partial and total hydroxide coordinated components, which gives better results than previous models and precludes the need of a S–V term to improve estimates of entropy. However, the fractional thermodynamic properties only give adequate results for silicate minerals and double oxides, and should therefore not be used to estimate the properties of other minerals. The thermodynamic properties of ‘new’ minerals are calculated from a linear stoichiometric combination of their constituent polyhedra, resulting in estimates generally with associated uncertainty of 〈5%. The quality of such data appears to be of sufficient accuracy for thermodynamic modelling as shown for meta-bauxites from the Alps and the Aegean, where the effect of Zn on the P–T stability of staurolite can be both qualitatively and quantitatively reproduced.

Notes: Reaction progress exhibited by multivariant assemblages in micaceous limestones can provide an excellent record of metamorphic fluid flow. However, it is necessary to understand the sensitivity of these assemblages to bulk-composition parameters. Here, analysis of bulk composition on different scales and pseudosection construction are used to draw conclusions on relationships between bulk composition, fluid flow and reaction progress. Issues addressed include the effects of bulk composition on the mineralogical evolution of micaceous carbonates, the sensitivity of bulk composition to bulk-composition sampling methods, the magnitude of cross-layer fluid-composition gradients, the potential for metasomatism to drive reaction progress, and the relative timing of reaction in adjacent layers. Pseudosections successfully represent observed mineral assemblages, constrain the position of reactions in T–X(CO2) space, and allow assessment of the sensitivity of reaction position, inferred reaction progress and calculated fluid fluxes to uncertainties in bulk composition. The scale of bulk-composition sampling affects bulk compositions, calculated modes, predicted mineral assemblages and calculated fluid compositions. Larger samples record an average of different lithological subdomains, while point-count-derived bulk compositions are subject to uncertainties related to the small number of sample points. The optimum bulk composition for pseudosection purposes probably lies between measured bulk compositions. Results suggest that reaction progress in some extensively reacted layers was driven by infiltration of H2O-rich fluid which flowed or diffused parallel to layering, perpendicular to layering in response to fluid-composition gradients, and out of veins. Small variations in fluid composition across layering (ΔX(CO2) 〈 0.02) were maintained by internal buffering by the mineral assemblages. Internal buffering must also have driven samples up a sequence of narrow low-variance fields in T–X(CO2) space, and so reaction in adjacent layers must have close to simultaneous. Metasomatic effects on reaction progress are likely to have been small, so long as the porosity was low.

Notes: Metapelitic residual enclaves in the Neogene Volcanic Province of SE Spain are residues left after melt extraction. Glass (quenched melt) of granitic composition occurs as inclusions in most minerals and as intergranular pockets. The most common enclave types show one stage of garnet growth that is interpreted to have occurred at the same time as glass production. Some of these show a well-developed foliation outlined by fibrolite, biotite, graphite and glass, which wraps around elongate garnet crystals that have aspect ratios up to 10:1. Based on microstructures and chemistry, the garnet within these rocks shows clear core and mantle structure. The core has an average composition of Alm76–Prp08–Sps14–Grs03 and contains primary inclusions of biotite and melt, trapped during garnet growth. A thin (c. 100 μm), irregular mantle overgrows the garnet core, enclosing oriented fibrolite inclusions in strain caps, and biotite in strain shadows. In places, the overgrowths form skeletal elongated arms, which extend parallel to the foliation. The garnet mantle contains less Mn and higher XMg, but both core and mantle display flat Mn profiles, the contact being a sharp break. Ternary feldspar and Grt–Bt thermometry yield temperatures in the range 800–900 °C, with no systematic differences among the different microstructural domains of elliptical garnet. Based on the observed intracrystalline microstructures, the high amount of melt extraction in the rock by flattening component strain and the chemical zoning of garnet, the formation of elliptical garnet is modelled by a multistage sequence. This involves pressure solution and reprecipitation of the core, followed by post-kinematic, partly mimetic growth of the garnet mantle.

Notes: Thermal models for Barrovian metamorphism driven by doubling the thickness of the radiogenic crust typically meet difficulty in accounting for the observed peak metamorphic temperature conditions. This difficulty suggests that there is an additional component in the thermal budget of many collisional orogens. Theoretical and geological considerations suggest that viscous heating is a cumulative process that may explain the heat deficit in collision orogens. The results of 2D numerical modelling of continental collision involving subduction of the lithospheric mantle demonstrate that geologically plausible stresses and strain rates may result in orogen-scale viscous heat production of 0.1 to 〉1 μW m−3, which is comparable to or even exceeds bulk radiogenic heat production within the crust. Thermally induced buoyancy is responsible for crustal upwelling in large domes with metamorphic temperatures up to 200 °C higher than regional background temperatures. Heat is mostly generated within the uppermost mantle, because of large stresses in the highly viscous rocks deforming there. This thermal energy may be transferred to the overlying crust either in the form of enhanced heat flow, or through magmatism that brings heat into the crust advectively. The amplitude of orogenic heating varies with time, with both the amplitude and time-span depending strongly on the coupling between heat production, viscosity and collision strain rate. It is argued that geologically relevant figures are applicable to metamorphic domes such as the Lepontine Dome in the Central Alps. We conclude that deformation-generated viscous dissipation is an important heat source during collisional orogeny and that high metamorphic temperatures as in Barrovian type metamorphism are inherent to deforming crustal regions.

Notes: Metanorites from two eclogitized metagabbros of the Hercynian French Massif Central preserve coronitic textures of hornblende, garnet, quartz and/or kyanite produced at the expense of the primary magmatic assemblage orthopyroxene and plagioclase. Using a petrogenetic grid in the CFMASH system, two possible P–T evolutions for the origin of the coronas are evaluated. The sequence of reactions involving the formation of Hbl (–Ky) ± Grt and Qtz coronitic assemblages is consistent with an isobaric cooling at high pressure (c. 1–2 GPa) under hydrated conditions. However, this P–T path, inferred by using only petrographical observations, is inconsistent with the geochronological constraints: emplacement of the gabbro at 490 Ma and high-pressure metamorphism at 410 Ma. In order to reconcile petrographical observations with geochronological constraints, we propose a discontinuous two-stage evolution involving a change in water activity with time. (1) Emplacement and cooling of the norite at low pressure under anhydrous conditions, at 490 Ma. (2) During the Hercynian orogeny, the norite experienced an increase in pressure and temperature under fluid-present conditions. Adding water to the system implies a dramatic change in the petrogenetic grid topology, restricting the orthopyroxene–plagioclase assemblage only to high temperatures. Therefore, the breakdown of the unstable magmatic assemblage, through apparent retrograde reactions, occurred along the prograde P–T path which never crossed the equilibrium boundaries of these reactions.

Notes: Detailed petrographic analysis was performed on samples from five localities within the southern Adirondacks. Textures and zoning patterns in garnet from all samples provide evidence for dehydration melting of biotite. Zoning of grossular in garnet – providing a record of prograde growth – shows both increasing and decreasing trends in garnet from the same sample. However, Ca concentrations at the garnet rims of most samples are identical (grossular = 3.4%). These observations have been interpreted as evidence for the differential timing of garnet nucleation and growth. All Fe/(Fe + Mg) and some spessartine distributions are consistent between samples, displaying diffusive profiles established largely upon cooling. Only one sample, in which retrogression was minimal, contains garnet with flat Fe/(Fe + Mg) profiles. A general pelitic pseudosection constructed in the system MnNCKFMASH reveals a maximum for Ca in garnet where the plagioclase-out isopleth intersects the solidus (muscovite = 0). The pseudosection predicts bell-shaped core-to-rim profiles of grossular during anatexis, similar to those observed in the rocks. Garnet–biotite thermometry and GASP barometry indicate peak temperatures of at least 790 °C at about 7–9 kbar, similar to conditions determined for the central Adirondacks. Cooling rates determined from finite difference modelling of spessartine and Fe/(Fe + Mg) diffusional profiles indicate a multi-stage cooling history in which some period of rapid cooling (〉200 °C Myr−1) is required.

Notes: Oxide–sulphide–Fe–Mg–silicate and titanite–ilmenite textures as well as their mineral compositions have been studied in felsic and intermediate orthogneisses across an amphibolite (north) to granulite facies (south) traverse of lower Archean crust, Tamil Nadu, south India. Titanite is limited to the amphibolite facies terrane where it rims ilmenite or occurs as independent grains. Pyrite is widespread throughout the traverse increasing in abundance with increasing metamorphic grade. Pyrrhotite is confined to the high-grade granulites. Ilmenite is widespread throughout the traverse increasing in abundance with increasing metamorphic grade and occurring primarily as hemo-ilmenite in the high-grade granulite facies rocks. Magnetite is widespread throughout the traverse and is commonly associated with ilmenite. It decreases in abundance with increasing metamorphic grade. In the granulite facies zone, reaction rims of magnetite + quartz occur along Fe–Mg silicate grain boundaries. Magnetite also commonly rims or is associated with pyrite. Both types of reaction rims represent an oxidation effect resulting from the partial subsolidus reduction of the hematite component in ilmenite to magnetite. This is confirmed by the presence of composite three oxide grains consisting of hematite, magnetite and ilmenite. Magnetite and magnetite–pyrite micro-veins along silicate grain boundaries formed over a wide range of post-peak metamorphic temperatures and pressures ranging from high-grade SO2 to low-grade H2S-dominated conditions. Oxygen fugacities estimated from the orthopyroxene–magnetite–quartz, orthopyroxene–hematite–quartz, and magnetite–hematite buffers average 2.5 log units above QFM. It is proposed that the trends in mineral assemblages, textures and composition are the result of an external, infiltrating concentrated brine containing an oxidizing component such as CaSO4 during high-grade metamorphism later acted upon by prograde and retrograde mineral reactions that do not involve an externally derived fluid phase.

Notes: Silica-undersaturated, sapphirine-bearing granulites occur in a large number of localities worldwide. Such rocks have historically been under-utilized for estimating P–T evolution histories because of limited experimental work, and a consequent poor understanding of the topology and P–T location of silica-undersaturated mineral equilibria. Here, a calculated P–T projection for sapphirine-bearing, silica-undersaturated metapelitic rock compositions is constructed using THERMOCALC for the FeO-MgO-Al2O3-SiO2 (FMAS) and KFMASH (+K2O + H2O) chemical systems, allowing quantitative analysis of silica-undersaturated mineral assemblages. This study builds on that for KFMASH sapphirine + quartz equilibria [Kelsey et al. (2004) Journal of Metamorphic Geology, vol. 22, pp. 559–578]. FMAS equilibria are significantly displaced in P–T space from silicate melt-bearing KFMASH equilibria. The large number of univariant silica-undersaturated KFMASH equilibria result in a P–T projection that is topologically more complex than could be established on the basis of experiments and/or natural assemblages. Coexisting sapphirine and silicate melt (with or without corundum) occur down to c. 900 °C in KFMASH, some 100 °C lower than in silica-saturated compositions, and from pressures of c.≤1 to ≥12 kbar. Mineral compositions and composition ranges for the calculated phases are consistent with natural examples. Bulk silica has a significant effect on the stability of sapphirine-bearing assemblages at a given P–T, resulting in a wide variety of possible granulite facies assemblages in silica-undersaturated metapelites. Calculated pseudosections are able to reproduce many naturally occurring silica-undersaturated assemblages, either within a single assemblage field or as the product of a P–T trajectory crossing several fields. With an understanding of the importance of bulk composition on sapphirine stability and textural development, silica-undersaturated assemblages may be utilized in a quantitative manner in the detailed metamorphic investigation of high-grade terranes.

Notes: Several petrographic studies have linked accessory monazite growth in pelitic schist to metamorphic reactions involving major rock-forming minerals, but little attention has been paid to the control that bulk composition might have on these reactions. In this study we use chemographic projections and pseudosections to argue that discrepant monazite ages from the Mount Barren Group of the Albany–Fraser Orogen, Western Australia, reflect differing bulk compositions. A new Sensitive High-mass Resolution Ion Microprobe (SHRIMP) U–Pb monazite age of 1027 ± 8 Ma for pelitic schist from the Mount Barren Group contrasts markedly with previously published SHRIMP U–Pb monazite and xenotime ages of c. 1200 Ma for the same area. All dated samples experienced identical metamorphic conditions, but preserve different mineral assemblages due to variable bulk composition. Monazite grains dated at c. 1200 Ma are from relatively magnesian rocks dominated by biotite, kyanite and/or staurolite, whilst c. 1027 Ma grains are from a ferroan rock dominated by garnet and staurolite. The latter monazite population is likely to have grown when staurolite was produced at the expense of garnet and chlorite, but this reaction was not intersected by more magnesian compositions, which are instead dominated by monazite that grew during an earlier, greenschist facies metamorphic event. These results imply that monazite ages from pelitic schist can vary depending on the bulk composition of the host rock. Samples containing both garnet and staurolite are the most likely to yield monazite ages that approximate the timing of peak metamorphism in amphibolite facies terranes. Samples too magnesian to ever grow garnet, or too iron-rich to undergo garnet breakdown, are likely to yield older monazite, and the age difference can be significant in terranes with a polymetamorphic history.

Notes: Fan-shaped polycrystalline staurolite porphyroblasts, 3–4 cm in length and 0.5 cm in width, occur together with centimetre-sized euhedral prismatic staurolite porphyroblasts in pelitic schists of the Littleton Formation on the western overturned limb of the Bolton syncline in eastern Connecticut. The fans consist of intergrown planar splays of [001] elongated prisms, which are crudely radial from a single apex. The apical angles of the radial groupings range up to 70°. The orientations of the individual staurolite prisms are related by a rigid rotation about an axis perpendicular to the fan plane. The zone axes [001] always lie in the plane of the fan. Although the angle between the [100] zone axes of the individual prisms is uniform in each fan, it ranges from +30° to −30° in different fans. Internally, the fans display: (i) remnants of a passively captured Si foliation defined by disc-shaped quartz blebs (type 1 inclusions) and layers of very fine carbonaceous material and tabular ilmenite platelets; (ii) bent staurolite blades and undulose extinction along low-angle (010) subgrain boundaries near the apex of the fans; (iii) wedge-shaped dilatational zones containing equigranular inclusion-free quartz, mica and staurolite, and (iv) growth-related quartz inclusion trails roughly perpendicular to a crystal face (type 2 inclusions). The Si inclusion trails are typically perpendicular to the fan surface, radiate parallel to the blades, and show little to no curvature except at the very edge of the fans where they abruptly curve through nearly 90° into parallelism with an external Se foliation. Careful examination of the three-dimensional geometry of fans based on U-stage measurements, serial sections and two-circle optical goniometric measurements permits a detailed reconstruction of their sequential development. The origin of a fan involves limited intracrystalline deformation and brittle crack dilation, spalling, rotation, and growth of small marginal fragments and of new staurolite along wedge-shaped zones along the Si inclusion surfaces. Fans preferentially develop in porphyroblasts in which Si is subparallel to the 010 cleavage. These internal features reflect the rotation and deformation of a brittle porphyroblast relative to syn-growth shear stresses.

Notes: Detailed microtextural observations and bulk chemical analysis were undertaken on a garnet-pyroxenite nodule within retrograde eclogites from the NE Sulu ultrahigh-pressure metamorphic (UHPM) terrane. The results suggest that the protolith was a cumulate from a gabbroic body. The nodule consists primarily of coarse clinopyroxene grains with a very high content of the Ca-Tschermakite molecule. Microscopic observations and back-scattered electron images (BSE) demonstrate a complicated intergrowth of clinopyroxene, garnet and ilmenite, which represents the peak metamorphic assemblage. The primary clinopyroxene grains are armoured with a thin garnet corona up to 0.5 mm wide that forms an interconnected network. Within the clinopyroxene grains, four sets of garnet lamellae are distributed along crystallographic planes; locally, a vermicular intergrowth of garnet and diopside is developed. Besides the garnet, parallel arrays of ilmenite blebs are common within the clinopyroxene. Hydrous minerals such as amphibole, zoisite and titanite formed at later stages, and replaced diopside, garnet and ilmenite respectively. The P–T conditions determined for the formation of the garnet lamellae indicate that the garnet pyroxenite experienced UHP metamorphism at the same peak P–T condition as its host eclogite. The very high Ca-Tschermakite content (31–34 mol.%) of the primary clinopyroxene indicates crystallization at about 9–17 kbar and 1250–1450 °C, and together with the microtextural observations, suggests that the protolith of the garnet pyroxenite was a cumulate from a former gabbroic body, in which case, the host eclogite might represent the gabbroic body.

Notes: Thermodynamic calculations in petrology are generally performed at pressures and temperatures beyond the standard state conditions. Accurate prediction of mineral equilibria therefore requires knowledge of the heat capacity, thermal expansion and compressibility for the minerals involved. Unfortunately, such data are not always available. In this contribution we present a data set to estimate the heat capacity, thermal expansion and compressibility of mineral end-members from their constituent polyhedra, based on the premise that the thermodynamic properties of minerals can be described by a linear combination of the fractional properties of their constituents. As such, only the crystallography of the phase of interest needs to be known. This approach is especially powerful for hypothetical mineral end-members and for minerals, for which the experimental determination of their thermodynamic properties is difficult. The data set consists of the properties for 35 polyhedra in the system K–Na–Ca–Li–Be–Mg–Mn–Fe–Co–Ni–Zn–Al–Ti–Si–H, determined by multiple linear regression analysis on a data set of 111 published end-member thermodynamic properties. The large number of polyhedra determined allows calculation of a much larger variety of phases than was previously possible, and the choice of constituents together with the large number of thermodynamic input data results in estimates with associated uncertainty of generally 〈5%. The quality of the data appears to be sufficiently accurate for thermodynamic modelling as demonstrated by modelling the stability of margarite in the CASH system and the position of the talc–staurolite–chloritoid–pyrope absent invariant point in the KMASH system. In both cases, our results overlap within error with published equivalents.

Notes: The prograde pressure–temperature (P–T) path for the complexly polydeformed Proterozoic Broken Hill Block (Australia) has been reconstructed through detailed structural analysis in conjunction with calculation of compositionally specific P–T pseudosections of pelitic rock units within a high-temperature shear zone that formed early in the tectonic evolution of the terrane. Whilst the overall P–T path for the Broken Hill Block has been interpreted to be anticlockwise, the prograde portion of this path has been unresolved. Our results have constrained part of this prograde path, showing an early heating event (M1) at P–T conditions of at least c. 600 °C and c. 2.8–4.2 kbar, associated with an elevated geothermal gradient (c. 41–61 °C km−1). This event is interpreted to be the result of rifting at c. 1.69–1.67 Ga, or at c. 1.64–1.61 in the Broken Hill Block. Early rifting was followed by an episode of lithospheric thermal relaxation and burial, during which time sag-phase sediments of the upper Broken Hill stratigraphy (Paragon Group) were deposited. Following sedimentation, a second tectonothermal event (M2/D2) occurred. This event is associated with peak low-pressure granulite facies metamorphism (c. 1.6 Ga) and attained conditions of at least 740 °C at c. 5 kbar. A regionally pervasive, high-temperature fabric (S2) developed during the M2/D2 event, and deformation was accommodated along lithology-parallel, high-temperature shear zones. The larger-scale deformation regime (extensional or shortening) of this event remains unresolved. The M2/D2 event was terminated by intense crustal shortening during the Olarian Orogeny, during which time the first mappable folds within the Broken Hill Block developed.

Notes: A calibration is presented for an activity–composition model for amphiboles in the system Na2O–CaO–FeO–MgO–Al2O3–SiO2–H2O–O (NCFMASHO), formulated in terms of an independent set of six end-members: tremolite, tschermakite, pargasite, glaucophane, ferroactinolite and ferritschermakite. The model uses mixing-on-sites for the ideal-mixing activities, and for the activity coefficients, a macroscopic multicomponent van Laar model. This formulation involves 15 pairwise interaction energies and six asymmetry parameters. Calibration of the model is based on the geometrical constraints imposed by the size and shape of amphibole solvi inherent in a data set of 71 coexisting amphibole pairs from rocks, formed over 400–600 °C and 2–18 kbar. The model parameters are calibrated by combining these geometric constraints with qualitative consideration of parameter relationships, given that the data are insufficient to allow all the model parameters to be determined from a regression of the data. Use of coexisting amphiboles means that amphibole activity–composition relationships are calibrated independently of the thermodynamic properties of the end-members. For practical applications, in geothermobarometry and the calculation of phase diagrams, the amphibole activity–composition relationships are placed in the context of the stability of other minerals by evaluating the properties of the end-members in the independent set that are in internally consistent data sets. This has been performed using an extended natural data set for hornblende–garnet–plagioclase–quartz, giving the small adjustments necessary to the enthalpies of formation of tschermakite, pargasite and glaucophane for working with the Holland and Powell data set.

Notes: Integrated petrological and structural investigations of eclogites from the eclogite zone of the Voltri Massif (Ligurian Alps) have been used to reconstruct a complete Alpine P–T deformation path from burial by subduction to subsequent exhumation. The early metamorphic evolution of the eclogites has been unravelled by correlating garnet zonation trends with the chemical variations in inclusions found in the different garnet domains. Garnet in massive eclogites displays typical growth zoning, whereas garnet in foliated eclogites shows rim-ward resorption, likely related to re-equilibration during retrogressive evolution. Garnet inclusions are distinctly different from core to rim, consisting primarily of Ca-, Na/Ca-amphibole, epidote, paragonite and talc in garnet cores and of clinopyroxene ± talc in the outer garnet domains. Quantitative thermobarometry on the inclusion assemblages in the garnet cores defines an initial greenschist-to-amphibolite facies metamorphic stage (M1 stage) at c. 450–500 °C and 5–8 kbar. Coexistence of omphacite + talc + katophorite inclusion assemblage in the outer garnet domains indicate c. 550 °C and 20 kbar, conditions which were considered as minimum P–T estimates for the M2 eclogitic stage. The early phase of retrograde reactions is polyphase and equilibrated under epidote–blueschist facies (M3 stage), characterized by the development of composite reaction textures (garnet necklaces and fluid-assisted Na-amphibole-bearing symplectites) produced at the expense of the primary M2 garnet-clinopyroxene assemblage. The blueschist retrogression is contemporaneous with the development of a penetrative deformation (D3) that resulted in a non-coaxial fabric, with dominant top-to-the-N sense of shear during rock exhumation. All of that is overprinted by a texturally late amphibolite/greenschist facies assemblages (M4 & M5 stages), which are not associated with a penetrative structural fabric. The combined P–T deformation data are consistent with an overall counter-clockwise path, from the greenschist/amphibolite, through the eclogite, the blueschist to the greenschist facies. These new results provide insights into the dynamic evolution of the Tertiary oceanic subduction processes leading to the building up of the Alpine orogen and the mechanisms involved in the exhumation of its high-pressure roots.

Notes: The effective Young's moduli of co-continuous Al–Al2O3 composites over the 5–97 vol% Al2O3 composition range were experimentally measured and compared with theoretical composite modulus values predicted using the methods of Ravichandran, Tuchinskii, Hashin-Shtrikman, and the effective medium approximation (EMA). The influence of phase morphology and the modulus ratio (E1/E2) of the constituent phases on the resulting experimental and calculated Young's modulus is discussed. For two-phased co-continuous composites with a modulus ratio greater than 5, the EMA, with an appropriate microstructural shape factor, was the most consistent method for approximating the composite Young's modulus over the entire composition range.

Notes: Three different series of porous silicon nitride ceramics with volume fraction porosities in the range 0–0.5 were fabricated using different preparation routes: (i) partial sintering, (ii) the addition of fugitive inclusions, and (iii) partial hot pressing. The use of different sintering additives and firing conditions, depending on the preparation route, gives rise to different materials within a certain porosity range with variations in terms of microstructure and grain boundary phase. Mechanical properties, elastic moduli, and strength have been evaluated separately for each series of materials. Porosity dependences of Young's modulus, shear modulus, Poisson's ratio, and fracture strength have been assessed and a comparison of the different materials is made and discussed in relation to their microstructural features.

Notes: Monodisperse, spherical, and nonporous zirconia particles ranging from submicrons to microns for use as supports for capillary electrophoresis and chromatography were synthesized by the controlled hydrolysis of zirconium tetra-alkoxides in alcohol solutions in the presence of long-chain organic acids. Particle characteristics varied as a function of water concentration, the chain length of the organic acid, aging time, temperature, and extent of stirring. Changing these experimental parameters affected particle size, particle size distribution, and the degree of particle aggregation. Submicron particles were made by increasing the water concentration and decreasing aging time. Particle size increases as temperature during the aging period increases. Most importantly, large monodisperse particles (4 μm) could be made by extended stirring. In general, we found that particle size increases as the chain length of the organic acid increases. We also found that gentle rotation during the aging period prevented both particle settling and secondary nucleation. This allowed the production of large particles. BET nitrogen adsorption uptake measurements demonstrate that the particles could be sintered, without aggregating them, to remove virtually all internal porosity.

Notes: Fabrication of microstructures has been the subject of considerable attention in recent years. Techniques such as surface silicon micromachining and bulk silicon etch have emerged as practical methods for thin microstructures and processes such as LIGA (an acronym for the German words for lithography, electrodeposition, and molding) are being used to produce high aspect ratio structures from a limited set of electroformable metals and polymers. As microsystem technologies and application prospects continue to grow, it is of interest and much practical value to expand the material choices for LIGA-scale microstructures to ceramics and a broader class of metals. To this end, this paper investigates a new technique for the fabrication of high aspect ratio ceramic or metal microparts. This technique is based on capillary-driven microcasting and curing of an epoxy-based metallic or ceramic nanoparticulate slurry into a sacrificial plastic mold produced by microinjection molding. The cured preform is subsequently heated to remove the organic phase and to sinter the particulate ceramic or metallic phase. The fabrication process is discussed in the paper along with illustration of example microparts produced using the process. A theoretical model of the fluid flow during the microcasting process is developed and validated with experimental data from the fabrication of rectangular rib sections.

Notes: Compression molding of glass aspherical lenses has become a viable manufacturing process for precision optics. The widespread use of this process has been hampered by the lack of its fundamental understanding. This research is a part of the ongoing effort to understand some of the issues related to the process. Simple lens molding experiments were performed on a commercial precision lens molding machine. A finite element method (FEM) program was used to create a simple numerical model and analyze the molding process. Experimental results show that this process is capable of producing precision optical components. A comparison of the experimental results with the predicted results indicates that with a more sophisticated numerical model, it is possible to use FEM as a tool for process analysis.

Notes: A model and numerical framework is developed for piezoelectric materials. The model treats the piezoelectric and electrostrictive effects by incorporating orientation-dependent, single-crystal properties. The method is implemented in Object Oriented Finite Element program, a public domain finite element code, so it can be applied to arbitrary two-dimensional microstructures with crystallographic anisotropy. The model is validated against analytic solutions. Consistency of the method for known cases permits application of the technique to more complicated two-dimensional systems. The piezoelectric and electrostrictive response is determined for a few simple device geometries and provides insight for design and convergence criteria.

Notes: Molecular dynamic simulations of glasses belonging to the anorthite–diopside system have been performed in order to obtain an atomistic description of the material's structure. The structural parameters obtained by the simulations allow to confirm that the glass materials are characterized by a very similar short-range environment. The main differences have been observed in the intermediate-range order of the structure that describe the distribution and the packing of the tetrahedra constituting the three-dimensional networks. It is shown that the glass materials with composition close to the two extremes, corresponding to the pure glass anorthite or pure glass diopside, display the typical structural features of the tectosilicates and inosilicates subclass of minerals, respectively, to which anorthite and diopside crystals belong.

Notes: 3-D ordered macroporous sol–gel bioactive glass particles (3DOM-BG, pore size: 345 nm; molar composition: 75 SiO2–21 CaO–4 P2O5) were converted into nano-crystalline calcium-deficient carbonate apatite after soaking at 37°C in simulated body fluid. The as-formed, flake-like apatite transformed into a coral-like, highly crystalline hydroxyapatite with a minor tri-calcium phosphate phase after heating for 1 h at a temperature of 700°C. Fourier transform infrared results show the loss of carbonate and isolation of hydroxyl during heating. The heat treatment improved the apatite's resistance to dissolution in a buffer solution (pH=5).

Notes: Engineering tests and full-field strain measurements are used to assess the accuracy of predictions made by the Binary Model, a computational tool for textile composites. The test case is a carbon fiber/SiC matrix composite, in which the reinforcement is a three-dimensional angle-interlock weave. The test composites are thin, having been designed for heat exchanger applications. The thinness leads to strong variations in local strains and strong effects of tow waviness upon macroscopic elasticity. The model performs well in predicting both local variations in strain and macroscopic elasticity. The effect of averaging local strains over variable gauge lengths is explored. Strains averaged over an appropriate gauge length have recently been proposed as the preferred measures of strain for use in local failure criteria.

Notes: A temperature-induced gelation method has been developed for the preparation of sialon green bodies composed of Si3N4, AlN, Y2O3, and Al2O3. Using a polyester/polyamine condensation polymer as dispersant, stable suspension containing sialon, precursor powders could be prepared in methyl ethyl keton (MEK)/ethanol (E) solvent mixture with solids loading as high as 60 vol%. The solvency of the dispersant in MEK/E decreased dramatically on cooling. The sedimentation tests showed that the settling behavior changed from slow accumulation at ∼20°C to fast deposition of clusters at −15°C, because of the collapse of dispersant chains adsorbed at the surface of the particles. Steady shear viscosity and oscillatory measurements performed for 60 vol% suspensions as functions of temperature and added amounts of dispersant proved that suspensions were of low viscosity and high stability at room temperature, becoming predominantly very highly viscous and elastic as temperature decreased. The gelation mechanism was mainly based on the coiling up of dissolved dispersant molecules, inducing in situ gelation and the formation of a rigid network bridging the suspended particles. The green bodies showed negligible shrinkage during gelation, a small shrinkage during drying, homogeneous microstructures, narrow pore size distributions, and high relative density. It was possible to achieve dense α-sialon ceramics through pressureless sintering at 1750°C for 2 h.

Notes: Mechanical stress–strain behavior of LaCoO3, La0.8Ca0.2CoO3, and La0.7Ca0.3CoO3 was studied under compression at 25° and 300°C. A hysteresis in the stress–strain relationship due to reorientation of ferroelastic domains (deformation twins) was observed, and a remanent strain is measured after unloading. The cohersive stress, defined as the maximum in effective elastic compliance during first loading, increases with substitution of Ca for La and decreases with increasing temperature. Domain reorientation was confirmed by X-ray diffraction of surfaces parallel and perpendicular to the loading direction. LaCoO3 can be regarded as a soft ferroelastic material while the 30% Ca-substituted material is a hard ferroelastic. The hysteresis of the stress–strain relationship was clearly dependent on both composition and temperature.

Notes: Ceramic laminates exhibiting a threshold strength have been fabricated by dip-coating thick tape-cast Al2O3 layers into slurries containing mixtures of Al2O3 and either unstabilized zirconia (MZ-ZrO2) or mullite to produce thin compressive layers via both a molar volume change and a differential thermal contraction. Porosity was introduced into the thin compressive layers by adding rice starch to the dip-coating slurries, which decomposed during densification of the laminate. As the volume fraction of porosity is increased, the residual compressive stress (σC), as measured by piezospectroscopy, is reduced and approaches zero at approximately 0.65 volume fraction of porosity. The elastic modulus mismatch (E1/E2) between the thin and thick laminate layers accounted for approximately one-half of the threshold strength for volume fractions of porosity ≤0.30 (E1/E2〈0.4). Above 0.40 volume fraction of porosity, the strength significantly increased as did the scatter in strength values, and it was observed that the highly porous layers completely arrested crack extension; these materials no longer exhibited a threshold strength. For these laminates, failure occurred by the independent, sequential failure of one layer after another, followed by catastrophic failure due to delamination.

Notes: Single-phase silicon carbide (SiC) nanotubes were successfully synthesized by the reaction of carbon nanotubes with silicon powder at 1200°C for 100 h. X-ray diffraction patterns indicated that most of the carbon from the carbon nanotubes that were reacted with silicon at 1200°C for 100 h was transformed to SiC. Transmission electron microscopy observations revealed that both single-phase SiC nanotubes and C–SiC coaxial nanotubes, which are carbon nanotubes sheathed with a SiC layer, were synthesized after 100 h of reaction. The ratio of single-phase SiC nanotubes to C–SiC nanotubes increased with heat treatment at 600°C in air for 1 h because the remaining carbon was removed.

Notes: Long crack R-curve of a porous Si3N4 with aligned fibrous grains was investigated, using a chevron-notched beam technique. A crack was constrained to propagate normal to the grain alignment. The crack growth resistance of aligned porous Si3N4 was much larger compared with that of dense Si3N4 ceramics. Microstructure observations showed that pullouts of fibrous grains in aligned porous Si3N4 markedly increased during crack propagation relative to those of dense Si3N4, due to the existence of pores. The efficient grain pullouts in porous Si3N4 increased the bridging stress at the crack wake.

Notes: Hydroxyapatite (HA) is an interesting ceramic material for orthopedic applications, in particular for implant operations and bone regeneration, owing to its bioactivity and biocompatibility with the surrounding tissues. Even if different shaping processes can be used in order to obtain porous ceramic bodies with optimal final properties, the sponge impregnation method with aqueous HA dispersions is particularly suitable to achieve an appropriate macroporosity to bone regeneration. As for conventional slip or tape casting, the rheological behavior of HA suspensions must be properly fitted to process conditions and controlled through a satisfactory stabilization of the disperse phase, i.e., through an appropriate dispersant dosage and an accurate homogenization of dispersed powder. In the present work, HA powders with different crystallinity degree were used to prepare aqueous dispersions with different contents of solids and dispersant (ammonium polyacrylate). The specific surface area of HA powders is very high, and then special attention must be dedicated to the dispersant selection and the dispersion process since the rheology of HA suspensions is strongly influenced by the structural conditions of the disperse phase. Even small differences in dispersant concentration can lead to dramatic changes in the rheological properties also at relatively low values of solids volume concentration. Above a critical concentration, the viscosity drop associated with the apparently plastic behavior is confined within a very narrow stress range, a neat transition is observed in the linear viscoelastic properties, and the time-dependent effects induced by the shear history become quite important and crucial for the experimental characterization.

Notes: Pristine, Si-doped, and Si/Nd-codoped yttrium aluminum garnet (YAG) nanoparticles were synthesized by pyrolysis of complex compounds of aluminum and yttrium with triethanolamine. It was found that the coexistence of Si4+ and Nd3+ increased the solubility of both ions and promoted the formation of YAG phase. Single-phase, nanocrystalline Si/Nd:YAG powders were obtained at calcination temperatures as low as 920°C. The optical behavior of the Si/Nd:YAG nanopowders was similar to that of single-crystal Nd:YAG.

Notes: Alumina bilayers of different relative thicknesses and densities were produced with a strong interface using a modified gel-casting technique. Tolerance to surface damage is examined using biaxial flexure of disks damaged with a single Vickers indentation at various loads. The greatest surface flaw tolerance is seen in bilayers consisting of a thin porous layer on the tensile surface coupled to a thick dense layer. Here, the modulus mismatch causes redistribution of the applied stress, and fracture initiates at the internal porous-dense interface rather than at the surface from the introduced indentation flaw.

Notes: An extensive X-ray study of CeO2–Nd2O3 solid solutions was performed, and the densities of solid solutions containing various concentrations of NdO1.5 were measured using several techniques. Solid solutions containing 0–80 mol% NdO1.5 were synthesized by coprecipitation from Ce(NO3)3 and Nd(NO3)3 aqueous solutions, and the coprecipitated samples were sintered at 1400°C. A fluorite structure was observed for CeO2–NdO1.5 solid solutions with 0–40 mol% NdO1.5, which changed to a rare earth C-type structure at 45–75 mol% NdO1.5. The change in the lattice parameters of CeO2–NdO1.5 solid solutions, when plotted with respect to the NdO1.5 concentration, showed that the lattice parameters followed Vegard's law in both the fluorite and rare earth C-type regions. The maximum solubility limit for NdO1.5 in CeO2 solid solution was approximately 75 mol%. The relationship between the density and the Nd concentration indicated that the defect structure followed the anion vacancy model over the entire range (0–70 mol% NdO1.5) of solid solution.

Notes: Yttrium silicates are promising materials for improved oxidation and erosion protection for carbon fiber-reinforced composites. A two-layer coating system of low-pressure plasma-sprayed yttrium silicate on chemical vapor deposition-SiC-precoated C/C–SiC was tested under atmospheric re-entry conditions simulated within a plasma wind tunnel test facility. The thermal expansion behavior of Y2SiO5 and Y2Si2O7 was investigated. The chemical compatibility with and without increasing oxygen partial pressure at the interface of the two-layer system was calculated by the CALPHAD method. The calculations were compared with experimental results. Furthermore, a thermodynamic explanation is presented to understand and predict the observed coating failure mechanism, identified as blister formation.

Notes: The early stage of phase separation in aluminoborosilicate glass for liquid crystal display substrates was investigated using a scanning electron microscope (SEM) and small-angle X-ray scattering measurement device (SAXS). The phase-separated particles were detected with SAXS in samples in which no particle was observed with SEM. The particle diameter in an as-formed sample was 2 nm. The relationship between the diameter and heat-treatment time indicates that the phase separation proceeds by a diffusion-controlled process. Based on the results of Fourier-transform infrared spectroscopy, fast compositional change may occur in the early stage of phase separation.

Notes: Tin (Sn) substitution for titanium (Ti) was investigated in Ba6−3xNd8+2xTi18O54 (x=1/2, 2/3, and 3/4) ceramics. A small amount (z〈0.1) of Sn substitution resulted in Ba6−3xNd8+2x(Ti1−zSnz)18O54 solid solutions, and some secondary phases were observed with increasing Sn content. A small amount of Sn substitution improved the Qf value significantly, while, due to the formation of secondary phases, the Qf value degraded sharply for larger Sn content. The relative dielectric constant (ɛr) decreased with increasing Sn-content, while the temperature coefficient of resonant frequency (τf) generally decreased, although an obvious fluctuation was observed for x=3/4.

Notes: In this paper we report the synthesis of polygonal single-crystal aluminum borate microtubes by the direct calcination of alumina and boron nitride powders in air. The diameters of the obtained tubes vary between 1 and 15 μm; and the lengths are in the range of tens to hundreds of micrometers. The cross-sections of the microtubes are in the shapes of rectangular, hexagonal, and quasi-circle. A new solid–liquid–solid growth mechanism was proposed to account for the formation of microtubes instead of whiskers.

Notes: A modified Pechini method was used to prepare undoped and doped La0.67Ca0.33MnO3 (LCMO) with homogeneous compositions and uniform fine powders. The variations of the lattice parameters and cell volumes of doped LCMO are attributed to the effect of ionic size and the creation of the oxygen vacancy. The effect of Ba2+ on the magnetic and conduction properties of LCMO is mainly related to the enhancement of the Mn3+–O–Mn4+ bond angle. The occupation of Al ions in Mn sites and the creation of the oxygen vacancies lead to an increase of the resistivity and a decrease of Tc and Ms. The variable-range hopping model with p=1/4 and ρ0 independent of temperature was found to be the best fit for undoped and doped LCMO, shown in 〈link href="#f4"/〉. It is suggested that T0 is mainly the measure of the extent of the disorder. For Al3+-doped LCMO, the small-polaron mechanism was found to be dominant in the temperature range from 300 to 350 K, and the evaluated values of the activation energy are about 0.22 eV and independent of the Al concentration. Low-field magnetoresistance (LFMR) was found to be enhanced by Ba doping but diminished by Al doping. The segregation of Al ions to the grain-boundary region may play a significant role in the intent to form a one-slope field-dependent MR response. The mechanisms of MR response of doped LCMO were suggested. 〈figure xml:id="f4"〉4〈mediaResource alt="image" href="urn:x-wiley:00027820:JACE00610:JACE_00610_f4"/〉 Resistivity as a function of temperature showing that the best fit was the variable-range hopping model with p=1/4 and ρ0 independent of temperature for (a) La0.67(Ca1−xBax)0.33MnO3 in the temperature range from 300 to 430 K, (b) La0.67Ca0.33(Mn1−yAly)O3 in the temperature range from 260 K to Tc, and the small-polaron mechanism (ρ=CT exp (Ea/kT) for (c) La0.67Ca0.33(Mn1−yAly)O3, in the temperature range from 300 to 350 K.

Notes: Transparent glass ceramics containing CaF2 nano-crystals co-doped with Er–Yb were developed by heat treatment of glasses in the system SiO2–Al2O3–CaF2–LnF3 (Ln=Er, Yb). The crystal size of CaF2 increased with increasing heat-treatment temperature. Upconversion emission intensities at 660 and 540 nm increased dramatically with increasing heat-treatment temperature. The cathode luminescence mapping indicates that the visible Er-luminescence arises mainly from the precipitated CaF2 nano-crystals with a phonon energy lower than that of a silicate matrix. It is concluded that both Er and Yb were concentrated in the CaF2 nano-crystals, and the quantum efficiency of Er3+-luminescence and the energy transfer efficiency from Yb3+ were considerably improved after ceramization.

Notes: Titania microtube arrays were fabricated by replication of human hair. The microtube is nanoporous in its wall and has nanoporous platelets on its outer surface, which were derived from cuticle cells on hair surface. The wall thickness of titania microtubes could be controlled by adjusting the number of sol–gel cycles applied. The nanopores acted as an effective nanoreactor where Au nanoparticles were in situ synthesized. The microchannels, nanopores, and noble metal nanoparticles may provide a unique combination that would be attractive in such applications as catalysis, adsorption, and separation.

Notes: Tantalum(V) nitride, prepared by nitridation of nanosized Ta2O5 at 800°C for 8 h under ammonia flow, was thermally decomposed to cubic nanocrystalline TaN at a temperature of 1000°C for 3 h under argon atmosphere. The resulting powders have been characterized using X-ray diffraction (XRD) and transmission electron microscopy. XRD-pure cubic TaN nanoparticles with a diameter of 50–100 nm can be obtained by the process. The decomposition process was found to depend on the temperature. Mechanisms that account for the decomposition of Tantalum(V) nitride are discussed. The results indicate that the method can permit formation of cubic-phase Tantalum(III) nitride under ambient pressure and moderate temperatures.

Notes: E-glass fibers were coated with a 15CaO–15BaO–20SiO2–50TiO2 thin film by the sol–gel method. Mechanical and chemical tests were performed on coated and uncoated fibers in cement and cement extract solutions to investigate the interactions between cement and gel-glass film. The results show that the resistance of E-glass fibers to the alkali cement medium is enhanced by the 15CaO–15BaO–20SiO2–50TiO2 coating. The significant roles of TiO2, CaO, and BaO in the protection fibers from the alkaline attack of cement are described. Some evidence is presented that the alkali corrosion of the coated fibers results in the formation of a thick and compact Ti film that suppresses further corrosion reaction.

Notes: The sinterabilities of fine zirconia powders including 5 mass% Y2O3 were investigated, with emphasis on the effect of Al2O3 at the initial sintering stage. The shrinkage of powder compact was measured under constant rates of heating (CRH). The powder compact including a small amount of Al2O3 increased the densification rate with elevating temperature. The activation energies at the initial stage of sintering were determined by analyzing the densification curves. The activation energy of powder compact including Al2O3 was lower than that of a powder compact without Al2O3. The diffusion mechanisms at the initial sintering stage were determined using the new analytical equation applied for CRH techniques. This analysis exhibited that Al2O3 included in a powder compact changed the diffusion mechanism from grain boundary to volume diffusions (VD). Therefore, it is concluded that the effect of Al2O3 enhanced the densification rate because of decrease in the activation energy of VD at the initial sintering stage.

Notes: Crack-healing behavior of silicon carbide ceramics sintered with AlN and Sc2O3 has been studied as a function of heat-treatment temperature and applied stress. Results showed that heat treatment in air could significantly increase the indentation strength whether a stress is applied or not. After heat treatment with no applied stress at 1300°C for 1 h in air, the indentation strength of the specimen with an indentation crack of ∼100 μm (≈2c) recovered its strength fully at room temperature. In addition, a simple heat treatment at 1200°C for 5 h under an applied stress of 200 MPa in air resulted in a complete recovery of the unindented strength at the healing temperature. However, higher applied stress led to fracture of the specimens during heat treatment. The static fatigue limit of the specimens crack healed at 1200°C for 5 h under 200 MPa was ∼450 MPa at the healing temperature. The ratio of the static fatigue limit of the crack-healed specimen to the unindented strength was ∼80%.

Notes: Tetracalcium phosphate (TTCP) Ca4(PO4)2O is one of the major powder components of self-setting orthopedic and dental cements. Traditionally, TTCP powders are produced by a solid-state process by soaking Ca- and P-containing precursors between 1350° and 1500°C. Such procedures require expensive high-temperature furnaces and subsequent grinding of sintered particulates. Grinding not only introduces contamination but alters the structure of TTCP, thereby reducing its bioactivity. The present paper offers a lower temperature synthesis process for TTCP with several interesting features. First, the synthesis procedure used Ca(CH3COO)2·H2O and NH4H2PO4 as separate sources for Ca and P, respectively. Second, the reactants underwent multiple melting and decomposition stages, thus increasing the reactivity of the synthesis process. NH4H2PO4 melted at 190°C and engulfed the calcium acetate particles. The Ca-acetate component decomposed into CaCO3 at around 400°C while still surrounded by the molten phosphate liquid and an amorphous Ca-metaphosphate phase. Hydroxyapatite, Ca10(PO4)6(OH)2 (HA), and β-Ca3(PO4)2 crystallized upon heating the powder mixture to 700°C. Slightly above 1200°C, the TTCP phase was formed. This sequence of reactions led to a process temperature of 1230°C, the lowest temperature ever reported for the synthesis of TTCP. Third, the resulting powders required much less grinding, which itself is advantageous. Fourth, the resulting powders were in situ seeded with HA. HA-seeded TTCP powders were tested for their apatite-inducing ability by soaking them in synthetic body fluid at 37°C. TTCP powders of this study were readily covered with carbonated apatitic calcium phosphates within the first 72 h.

Notes: The effect of microstructure on the sliding-wear properties has been studied in two types of pressureless liquid-phase-sintered (LPS) SiC ceramics, one with coarse, in situ-grown elongated grains and the other with fine, equiaxed grains. Elongated-grain LPS SiC has been found to have dramatically improved sliding-wear properties over equiaxed-grain LPS SiC, which has been attributed to the interlocking network of elongated SiC grains. The introduction of an interlocking network of elongated grains represents a new guideline for the microstructural design of polycrystalline ceramics that are both sliding-wear resistant and toughened.

Notes: Microwave dielectric properties of polycrystalline Ca5Ta2TiO12 ceramics have been tailored using different glass additives. Several glasses such as B2O3, SiO2, B2O3–SiO2, ZnO–B2O3, Al2O3–SiO2, Al2O3–B2O3–SiO2, BaO–B2O3–SiO2, MgO–B2O3–SiO2, ZnO–B2O3–SiO2, PbO–B2O3–SiO2, and 2MgO–Al2O3–5SiO2 were added to calcined Ca5Ta2TiO12 powder in different weight percentages. Among these glasses, addition of 0.1 wt% of SiO2, Al2O3–SiO2, Al2O3–B2O3–SiO2, MgO–B2O3–SiO2, and 2MgO–Al2O3–5SiO2 improved the microwave dielectric properties. Fluxing of Ca5Ta2TiO12 with 0.1 wt% of 2MgO–Al2O3–5SiO2 glass has ɛr=39, Qu×f〉40 000 at 5 GHz and τf=+8 ppm/°C. Near-zero τf was obtained with the addition of glasses like Al2O3–SiO2, Al2O3–B2O3–SiO2, MgO–B2O3–SiO2, and 2MgO–Al2O3–5SiO2. Addition of all the glasses except BaO–B2O3–SiO2 reduced the τf of Ca5Ta2TiO12 ceramics. Two weight percent glass addition to Ca5Ta2TiO12 ceramics reduced their sintering temperature down to 1450°C from 1625°C and τf close to zero but deteriorated the ɛr and unloaded quality factor. The effects of glass content on the structure and microstructure of Ca5Ta2TiO12 ceramics were studied by X-ray diffraction and scanning electron microscopic techniques.

Notes: Neutron diffraction data of α-sialon and complementary phases were collected on the neutron powder diffraction (NPD) diffractometer installed in the NFL Studsvik, at a wavelength of 1.470 Å. Calculations were carried out by using the FullProf 2000 utilizing the crystal structure of the yttrium α-sialon phase. Selected profile and structure parameters were refined in the calculations. The calculated data showed that either La or Nd were also present in the α-sialon crystal structure in the presence of Y. The comparison of the present phases' weight contents, which were determined by the qualitative phase analysis between NPD and X-ray diffraction data, was carried out.

Notes: A series of [0.8Pb(Ni1/3Nb2/3)O3–0.2PbTiO3]/[(Ni0.2Cu0.2 Zn0.6)Fe2O4] (PNNT/NiCuZn) ferroelectric–ferromagnetic composites were prepared by the conventional solid-state route. The composites show good co-firing behaviors. X-ray diffraction and scanning electron microscope studies confirmed the coexistence of ferroelectric PNNT phase and ferromagnetic NiCuZn phase in the composites. No significant chemical interaction has occurred between PNNT phase and NiCuZn phase. All sintered samples exhibit typical magnetic hysteresis loops at room temperature. The saturation magnetization of composites rises linearly with the increase in NiCuZn content. Frequency dependence of initial permeability was also measured. With an increase in NiCuZn, the initial permeability increases and the cutoff frequency tends to decrease. The Maxwell–Garnett (MG) effective medium theory was used to model the magnetic properties of composites. Although the MG equation cannot give an accurate prediction for the initial permeability of composites because of the oversimplified assumption, it gives upper and lower limits for the initial permeability of compositions.

Notes: Bioresorbable and functionally graded apatites (fg-HAp) ceramics, which are characterized by gradations in crystallinity and the grain size of hydroxyapatite (HAp:Ca10(PO4)6(OH)2), were designed using bovine bone by the calcination and partial dissolution–precipitation method. The fg-HAp ceramics had macropores of 100–600 μm originated from spongy bone, and micropores of 10–160 nm. Fg-HAp ceramics loaded with recombinant human bone morphogenetic protein-2 (rhBMP-2/fg-HAp) were implanted into the subcutaneous tissue of rats. Eight weeks after the implantation, the surface and bulk degradations of the fg-HAp-containing body fluid occured, and small pieces of fg-HAp were incorporated into the induced bone and fatty marrow, suggesting that osteoinduction occurred in conjunction with bone remodeling. The rhBMP-2/fg-HAp ceramics developed could become a resorbable biomimetic material with fast bioresorption and osteoinduction characteristics.

Notes: A hydrothermally treated zirconia colloid was introduced during the precipitation of hydroxyapatite (HAP) to achieve an HAP–zirconia nanocomposite. High dispersion of zirconia was achieved at zirconia loadings below 8 wt%. Vickers hardness was optimized with a 1.5 wt% loading of zirconia. A low loading (1.5 wt%) of tetragonal zirconia was able to increase the bending strength of nanocrystalline HAP from 183 to 243 MPa. This HAP–zirconia nanocomposite was sintered to full density by 1000°C under an applied load of 50 MPa. The average grain sizes of HAP and zirconia were maintained at ≤100 nm. With the high strength and low loading of secondary phase, these HAP-based nanocomposites should be attractive for orthopedic and dental implant applications.

Notes: The effect of iron and iron/yttrium codoping on the densification and grain growth of ultra high-purity (99.995%) fine-grained alumina has been studied. The experiments were carried out under both oxidizing (flowing air) and reducing conditions (N2/H2 mixture, pO2∼5.1 × 10−14). For studies carried out in air, relative to undoped alumina, the addition of 1000 ppm Fe was found to reduce the densification rate by a factor of 5 and also retard the grain growth rate. This result, which was consistent with tensile creep data obtained in a separate study, was attributed to the retardation of grain-boundary diffusive processes by segregating Fe(III) ions. In contrast, under reducing conditions the 1000 ppm Fe- doped samples exhibited an increase in the densification rate of 2.5 orders of magnitude over that of the undoped samples. In the case of the codoped compositions (1000 ppm Fe/1000 ppm Y), for heat treatment in air, the densification behavior did not differ significantly from that of samples singly doped with Y (1000 ppm). However, under reducing conditions, the presence of the Fe2+ in the samples appeared to compensate for the retarding effect of the yttrium, such that the densification rate of the codoped samples was comparable with that of the undoped material. A mechanism based on compensating point defects is invoked to rationalize the more rapid kinetics under reducing conditions.

Notes: The phase composition, microstructure, and electrical resistivity of hot-pressed AlN ceramics with 0–4.8 wt% Sm2O3 additive were investigated. The phase composition was approximately consistent with that estimated from the Sm2O3–Al2O3 phase diagram using the amount of added Sm2O3 and oxygen content of the AlN raw material. When sintered at more than 1800°C, the AlN ceramics with 1.0–2.9 wt% Sm2O3 additive contained an Sm-β-alumina phase wetting the grain boundaries, and their electrical resistivity considerably decreased to 1010–1012Ω·cm. This resistivity decrease was caused by the continuity of the Sm-β-alumina phase with a resistivity lower than that of bulk AlN.