Exsolution lamellae of baryte, Fe sulfides, Cu sulfides and Fe oxides were observed in apatite enclosed in garnet and omphacite and their intergranular spaces in ultrahigh-pressure eclogite in the Moldanubian Zone, Czech Republic. Micro-textural relations and compositional mapping of the apatite indicates a close relationship between the density of the exsolution lamellae and compositional domains that are rich in sulfur and iron. No relation between compositional domains and fluorine or chlorine content or any evidence of apatite metasomatisation was observed. On the basis of cathodoluminescence images, the compositional domains reflect sector zoning in apatite crystals by preferential uptake of elements due to differences in surface charge and morphology on the growth plane. It is concluded that the lamellae are products of exsolution in a closed system resulting from temperature decrease during metamorphism.

Marbles and interlayered coesite-bearing eclogites near the village ofSanqingge in the Sulu ultrahighpressure (UHP) terrane ofeastern China were studied to estimate their P-T evolution. Using garnet, omphacite and phengite as geothermobarometers, the coesite eclogites are calculated to have experienced P-T conditions of3.4 –3.7 GPa and ~600ºC (stage I), followed by decompression and a slight temperature decrease to 2.7–3.2 GPa and 520–560ºC respectively (stage II) and later to 2.6–2.8 GPa and ~500ºC (stage III). No water influx affected the eclogites until reaching amphibolite facies conditions of 0.5–1.3 Gpa and 595–685ºC (stage IV). As we interpret the occasional appearance ofcalcite with magnesite relics in the core as a reaction ofUHP dolomite and magnesite with Ca-rich fluids at stage IV to form CaCO3, the calculated pressure for stage I could be the maximum pressure experienced by these rocks. Thus, the crustal material ofthe Sanqingge quarry, originally sedimentary carbonates (now marbles) and interstratified basic tuffs (now eclogites), has been buried to a depth of ≥ 120 km at ~600ºC. This burial occurred in a subduction setting along a very low geotherm of 5–6ºC/km. The exhumation possibly occurred in the environment ofa subduction channel.

The Western Gneiss Region (WGR) of Norway consists largely of Proterozoic orthogneisses, but also contains paragneisses, peridotites, anorthosites, gabbros and coarse-grained intermediate-acid ‘rapakivi granites’. All of these lithologies enclose eclogites. Structural and isotopic data suggest that many of these rocks were juxtaposed by early Caledonian thrusting prior to eclogite formation at ca. 425 Ma.

Low-P protoliths can be demonstrated for many eclogites. Prograde metamorphism to eclogite facies is demonstrated by inclusion suites within garnet grains and zoning of eclogite minerals. The regional distribution of KD (gnt/cpx) and Xcpxjd shows a decrease in Tmax, and in the corresponding P, away from the present coastline. The lowest values (500 °C, 10 kbar) are found in the Sunnfjord area and the highest (∼ 800 °C) along the coast of Sunnmøre and Nordmøre.

Maximum pressures were reached at temperatures 100–200° < Tmax. This P-T-t path is consistent with the preservation of jadeite-rich cpx (and possible coesite) in the coastal regions. Earlier overestimates of Pmax, based on partitioning of Al between opx and gnt, resulted from combination of early low-T (low-Al) opx and T values derived from cpx/gnt equilibrated at Tmax. Despite pervasive later amphibolitization, high-P assemblages (phengite + kyanite, omphacite + quartz) are locally preserved within gneisses near the coast. The high-P metamorphism can be explained by westward subduction of the Baltic continental plate beneath the Greenland plate, during the Caledonian orogeny.

At least some of the Mg-Cr garnet peridotites of the WGR were derived from low-P protoliths (spinel ± chlorite peridotites, enclosing high-Al pyroxenites). While Sm-Nd mineral ages of most eclogites cluster around 425 Ma, garnet peridotites and their enclosed garnet pyroxenites give Proterozoic Sm-Nd mineral ages (1700–1000 Ma). The tectonic position of the Mg-Cr garnet peridotites, relative to the Caledonian high-pressure metamorphism, remains to be resolved.

Nyböite occurs as porphyroblasts in the Jianchang eclogite in the Donghai area, northeastern Jiangsu Province, eastern China. The Jianchang eclogite contains some inclusions of quartz after coesite in clinopyroxene, garnet and epidote. It has colourless to pale-violet pleochroism. A thin rim with violet pleochroism often develops around nyb6ite and is taramitic. It is further retrogressed by the symplectite which is mainly composed of hornblende, aegirine-augite and albite. Nyböite is associated with jadeitic pyroxene in the Jianchang eclogite, although other porphyroblastic amphiboles in other Donghai eclogites are barroisitic to katophoritic and are associated with omphacite.

Fe-Mg partitioning between garnet and clinopyroxene and the presence of coesite pseudomorphs indicate P-T conditions in the Jianchang eclogite of about 740 ± 60°C and more than 28 kbar. Similar P-T conditions were estimated for other porphyroblastic amphibole-bearing eclogites in the Donghai area. Nyböite can occur in the Na-Al-Fe-rich local bulk composition under the medium to high temperature and very high-pressure conditions. Retrograde rim amphibole is poorer in NaB, variable in Si content, and richer in NaA variable than the porphyroblastic amphibole in the Donghai area. This roughly implies a P-T path where P decreases without a large decrease of T.

We have investigated the chemical zoning of garnet in three texturally different eclogite types from the Leaota Massif, Romania, to test the various zonation patterns of Ca, Fe, Mg and Mn as indices of time-lines in porphyroblastic garnets. Mn zonation was found to mark various growth stages very well. It indicates in each of our three case studies a complex growth history dominated by multiple nucleation and coalescence, but also interrupted by partial resorption, as shown by morphological characteristics. Chemical variations of the main elements in garnet during prograde high-pressure metamorphism define time-lines other than those of Mn which decrease, highlighting the stages of porphyroblastic growth. In particular, the Ca/Mn, Mg/Mn and Mg/Fe ratios are useful in late growth stages, when low Mn contents and radial gradients do not allow a satisfactory resolution of Mn time-lines. These ratio-based time-lines further substantiate the potential of Mn time-lines in revealing non-concentric porphyroblastic growth. This is important in order to correctly relate garnet growth stages to stable mineral assemblages, a prerequisite for a reliable derivation of the metamorphic history of the host rock.

The Grenvillian granulite-facies complex on Holsnøy island, Bergen Arcs, W. Norway, has been metamorphosed at eclogite-facies conditions during the Caledonian orogeny (ca. 425 Ma). The granulite-eclogite facies transition takes place along shear zones and fluid pathways. Mineral thermobarometry indicates PT conditions of 800–900°C and 8–10 kbar for the Proterozoic granulite facies metamorphism and 700–800°C and 16–19 kbar for the eclogite-forming event. Quartz in the granulite facies complex contains CO2 fluid inclusions with less than 2.5 mole percent N2; the molar volumes are compatible with the PT conditions of the Proterozoic granulite metamorphism. Quartz in pegmatitic quartz + omphacite and quartz + phengite/paragonite veins coeval with shear-zone eclogites contain N2 ± CO2 fluid inclusions. Combined laser Raman microanalysis and microthermometry show that the least disturbed inclusions have XCO2 = 0.1–0.3, and molar volumes less than 40 cm3/mole, which may agree with the PT conditions during Caledonian high-pressure metamorphism. Younger, low-density N2 and N2-H2O fluid inclusions are the results of decrepitation and redistribution of early inclusions during the retrograde PT evolution of the eclogites.

The Rocky Beach Metamorphic Melange contains metre-scale phacoids of high-P low-T metamorphic rocks embedded in chlorite-actinolite schist. The phacoids include eclogite, glaucophane schist and omphacitite and provide evidence for four episodes of metamorphism with mineral assemblages: M1 = actinolite-glaucophane-titanite-apaite, M2 = almandine-omphacite-lawsonite ±quartz, M3 = phengite- glaucophane-K-feldspar-quartz, and M4 = chlorite-actinolite-calcite-quartz-titanite-white mica ± albite ± talc. M1-M3 occurred at a Neoproterozoic-Early Palaeozoic convergent plate boundary close to the eastern margin of Gondwana. Peak metamorphic conditions were attained during the static phase M2, with temperatures of ~560°C and pressures in excess of 1.8 GPa, equivalent to a depth of burial of at least 54 km.

Atoll garnet has been found in metabasites and quartz- and mica-rich rocks that have experienced low- to medium-temperature, high-pressure eclogite facies metamorphism in the Krušné Hory (Erzgebirge). They occur in several localities but are restricted to thin, texturally distinct zones, even on a thin-section scale. The mechanism of atoll garnet formation is documented by a series of micrographs and compositional maps and profiles of atoll garnet in combination with textural relations to other phases in the rocks. The core of full garnet or its relics in the atoll garnet have larger Ca and Fe, but smaller Mg contents, compared with the thin rim (ring). In addition to quartz, Na-Ca amphibole and phengite, the atoll cores are filled by a new garnet that has a composition similar to the outer rim. Formation of the atoll garnet is interpreted as resulting from fluid infiltration and element exchange between the garnet core and matrix, a process facilitated by a temperature increase during eclogite facies metamorphism. In addition to fluid access, the primary textures, mainly grain size, were also effective for the atoll garnet formation. Small grain fractions with thin rims were easily infiltrated by fluid, which used the short distance for element exchange between core and matrix. The core garnet was gradually dissolved and replaced by new garnet having the same crystallographic orientation as the rim or relics in the core.

Coesite has been found as an inclusion in garnet from the Mengzhong eclogite in Donghai county, northeastern Jiangsu province, eastern China. The host eclogite occurs closely associated with regionally developed gneiss and was formed under P-T conditions of about 810°C and more than 28 kbar.

Talc was identified as an equilibrium associate of omphacite, kyanite, zoisite, and garnet in some coesitebearing eclogites and as a retrograde phase in associated garnet peridotite from the Bixiling mafic-ultramafic complex in the Dabie ultrahigh-P metamorphic terrane, central China. Observed talc- and tremolite-bearing assemblages within the coexisting mafic and ultramafic rocks together with established phase relations for the simple system CaO-MgO-Al2O3-SiO2-H2O constrain the P-T path for retrograde metamorphism. This, together with reported talc occurrences from the Dora Maira massif, leads to the conclusion that UHP talc assemblages are confined to mafic and pelitic rocks of unusual chemistry, and are not stable at ultrahigh pressures in ultramafic rocks. Thus, talc cannot be an important H2O-bearing phase in deep mantle ultramafic rocks.

U–Pb zircon geochronology and trace element analysis was applied to eclogites and (ultra)high-pressure granulites that occur as volumetrically subordinate rock bodies within orthogneisses of the Orlica-Śnieżnik complex, Bohemian Massif. Under favourable circumstances such data may help to unravel protolith ages and yet-undetermined aspects of the metamorphic evolution, for example, the time span over which eclogite-facies conditions were attained. By means of ion-probe and laser ablation techniques, a comprehensive database was compiled for samples collected from prominent eclogite and granulite occurrences. The 206Pb/238U dates for zircons of all samples show a large variability, and no single age can be calculated. The protolith ages remain unresolved due to the lack of coherent age groups at the upper end of the zircon age spectra. The spread in apparent ages is interpreted to be mainly caused by variable and possibly multi-stage Pb-loss. Further complexities are added by metamorphic zircon growth and re-equilibration processes, the unknown relevance of inherited components and possible mixing of different aged domains during analysis. A reliable interpretation of igneous crystallization ages is not yet possible. Previous studies and the new data document the importance of a Carboniferous metamorphic event at c. 340 Ma. The geological significance of this age group is controversial. Such ages have previously either been related to peak (U)HP conditions, the waning stages of eclogite-facies metamorphism or the amphibolite-facies overprint. This study provides new arguments for this discussion because, in both rock types, metamorphic zircon is characterized by very low total REE abundances, flat HREE patterns and the absence of an Eu anomaly. These features strongly suggest contemporaneous crystallization of zircon and garnet and strengthen interpretations proposing that the Carboniferous ages document late-stage eclogite-facies metamorphism, and not amphibolite-facies overprinting.

The North-East Greenland eclogite province is divided into a western, central and eastern block by the sinistral Storstrømmen shear zone in the west and the dextral Germania Land deformation zone in the east. A family of steep, NNW-striking dextral mylonite zones in the Danmarkshavn area are geometrically and kinematically similar to the ductile Germania Land deformation zone, located 25 km to the east. Amphibolite facies deformation at Danmarkshavn is characterized by boudinage of eclogite bodies within quartzofeldspathic host gneisses, pegmatite emplacement into the boudin necks and subsequent deformation of pegmatites parallel to gneissosity, a widespread component of dextral shear within the gneisses, and localization of strain into 10–50 m thick dextral mylonite zones. The gneisses and concordant mylonite zones are cut by a swarm of weakly to undeformed, steeply dipping, E–W-striking pegmatitic dykes. Oscillatory-zoned zircon cores from two boudin neck pegmatites give weighted mean 206Pb/238U sensitive, high mass resolution ion microprobe (SHRIMP) ages of 376 ± 5 Ma and 343 ± 7 Ma. Cathodoluminescence images of these zircons reveal complex additional rims, with ages from ranging from c. 360 to 320 Ma. Oscillatory-zoned, prismatic zircons from two late, cross-cutting pegmatites yield weighted mean 206Pb/238U SHRIMP ages of 343 ± 5 Ma and 332 ± 3 Ma. Zircons from the boudin neck pegmatites record a prolonged growth history, marked by fluid influx, during amphibolite facies metamorphism beginning at c. 375 Ma. The cross-cutting pegmatites show that dextral deformation in the gneisses and ductile mylonite zones had stopped by c. 340 Ma. Ultrahigh-pressure metamorphism in the eastern block at 360 Ma requires that the Greenland Caledonides were in an overall contractional plate tectonic regime. This, combined with 20% steep amphibolite facies lineations in the eclogites, gneisses and mylonites suggests that dextral transpression may have been responsible for a first stage of eclogite exhumation between 370 and 340 Ma.

Peak and retrograde P–T conditions of Grenville-age eclogites from the Glenelg–Attadale Inlier of the northwest Highlands of Scotland are presented. Peak conditions are estimated as c. 20 kbar and 750–780°C, in broad agreement with previous work. The eclogites subsequently followed a steep decompression path to c. 13 kbar and 650–700°C during amphibolite facies retrogression. Peak eclogite facies metamorphism occurred > 1080 Ma and retrogression at c. 995 Ma, suggesting fairly sluggish uplift rates of < 0.3 km/Ma and cooling rates of < 1.25°C/Ma, when compared with other parts of the Grenville orogeny and/or modern orogens. However, current poor constraints on the timing of peak metamorphism mean that these rates cannot be used to interpret the geodynamic evolution of this part of the orogen. The P–T–t data, together with petrology and the field relationships between the basement rocks of the Glenelg–Attadale Inlier and the overlying Moine Supergroup, mean that it is difficult to support the currently held view that an unconformable relationship exists between the two. It is suggested that more data are required in order to re-interpret the Neoproterozic tectonic evolution of the northwest Highlands of Scotland.

By examining their rock sources and mode of manufacture, the author offers a new interpretation for the Neolithic polished axe blades found in the western Alpine region. The dominant examples were made from rock extracted on the Italian side of the Alps (eclogitic) and finished in workshops on the French side. These first appeared as large blades with symbolic status, as part of the Neolithic expansion in North Italy. By the middle Neolithic the blades were reduced in size, but enjoying their widest distribution, creating a cultural zone on the left bank of the Rhône, more than 200 km from their source. In the late Neolithic, although the zone of influence was still large, the eclogites in the Rhône Valley were giving way to more local rock sources and copper. The fluctuations in this supply are interpreted as reflecting the varied political relations of Alpine communities.

The Ballantrae complex has yielded its oldest yet determined age of 576 ± 32 Ma from an Sm–Nd internal isochron for a block ‘eclogite’ interpreted as being a component of the mélange-olistostrome unit at Knockormal. This unit is possibly older than the main ophiolitic part of the complex and the ‘eclogite’ block provides evidence for the existence of oceanic crust older than c. 575 Ma on the southern margin of the Laurentian shield.

An Sm–Nd internal isochron from a high-grade metapyroxenite in the metamorphic aureole beneath an obducted slab of mantle peridotite at Laigh Knocklaugh yields an age of 505 ± 11 Ma. This is interpreted as close to the age of metamorphism and is older than the K–Ar age of 478 ± 8 Ma determined for the amphibolites of the aureole which underlie the metapyroxenite. The metapyroxenite had a provenance deeper in the oceanic crust than the amphibolite and the former has been structurally detached and justaposed against the latter in this telescoped metamorphic sequence.

In this feasibility study, Sm/Nd and 143Nd/144Nd ratios have been determined on garnets and coexisting mineral and whole-rock phases from a selection of amphibolite facies rocks, granulite facies rocks and an eclogite. In two micaceous schists and an eclogite the distribution coefficient of the Sm/Nd ratio in garnet relative to other phases is in the range 2-3, i.e. comparable to values for phenocrysts in igneous rocks. In two granulite facies rocks the garnets have Sm/Nd distribution coefficients relative to other phases in the range 13-20 and have yielded precise ages.

Garnet from a granulite facies shear zone from the Limpopo belt in southern Africa, of Archaean age, has yielded concordant duplicate ages of 1974±14 Ma and 1988±14 Ma. These results have been interpreted as relating to the last tectonic event in the region, long after the main gneiss-forming event. Garnet from a granulite facies xenolith from a Carboniferous vent in the Midland Valley of Scotland has yielded an age of 356±10 Ma; this is related to the onset of basic magmatism in the region.