Abstract: The Devonian Udachnaya-East pipe (Siberia) presents a rare example of exceptionally fresh kimberlite rocks, containing a rich assemblage of alkali carbonate, chloride and sulphate minerals in its groundmass. Accordingly, bulk groundmass compositions have unusually high concentrations of sodium and chlorine (up to 6 wt.% each), while water contents are very low. High Na2O and low H2O are inconsistent with currently accepted model kimberlite magma compositions; and high Na and Cl contents in the Udachnaya-East pipe have been ignored by the geoscience community, because of possibility of contamination from sedimentary crustal rocks. New textural evidence suggests that the chloride and alkali carbonate minerals in this kimberlite are co-magmatic with perovskite. Radiogenic isotope ratios for the perovskite (87Sr/86Sr ~0.7031, eNd +5, eHf +5.3, obtained by solution-mode and laser-ablation methods) are very primitive and provide no support for a crustal contaminant. The new perovskite data confirm previously published Sr-Nd-Pb isotopic evidence for the chlorides and alkali carbonates themselves, but are considered more reliable because of possible open system behaviour and analytical problems with unstable halide and carbonate minerals. Similar isotope ratios (87Sr/86Sr=0.70292, eNd=+5, eHf=+6.5) are recorded in a clinopyroxene macrocryst, which contains chlorides and alkali carbonates within melt inclusions, implying a similarly primitive isotopic signature for the host kimberlite. We infer that assimilation of evaporitic sediments is unlikely and that abundant chlorine and sodium in the kimberlite originated in the upper mantle. Our results and published experimental data on mantle chloride melts and presence of a chloride component in diamond-hosted fluid inclusions suggest a previously unrecognised role for mantle-derived halide melts in the genesis, composition and rheological properties of kimberlite primary melts.

Abstract: Copper K-edge X-ray absorption spectra were recorded from natural polyphase brine fluid inclusions in miarolitic quartz from the Omsukchan Granite, Russia, as a function of temperature up to 700 °C. The inclusions studied represent two distinct fluids, which contain either 0.02 or 0.94 wt.% Cu homogeneously distributed in solution at temperatures above salt dissolution (350�550 °C). X-ray absorption near edge structure (XANES) spectra of the solution phase in the Cu-poor inclusions exhibit an intense edge feature near 8983 eV that is characteristic of the linear [CuCl2]� complex. This spectrum was obtained at all temperatures between 200 and 700 °C and from around 15 inclusions. Extended X-ray absorption fine structure (EXAFS) spectra recorded at 550 °C were modelled to give a Cu�Cl bond length of 2.11(2) �, also consistent with [CuCl2]�. XANES spectra of the Cu-rich inclusions appear similar to that of [CuCl2]� but are shifted to higher energy. This spectrum was obtained between 350 and 700 °C and from all three inclusions studied. EXAFS recorded at 700 °C gave a Cu-ligand bond length of 2.19(1) �. This complex is yet to be identified. The results for the Cu-poor inclusions indicate that [CuCl2]� is stable at magmatic temperatures, extending the known range of this complex by 200 °C. This is the first time that Cu speciation has been determined at these temperatures and provides an example of how inclusions can be used as sample cells for the spectroscopic study of fluids at extreme conditions.

Abstract: Platinum-group element (Os, Ir, Ru, Pt and Pd) abundances and Re�Os isotopic composition of fifteen peridotites (eleven spinel lherzolites and four spinel harzburgites) from the Mamonia complex, Cyprus, were determined as well as major and trace element compositions of bulk-rocks and minerals. Spinel lherzolites show excellent correlation between parameters indicating the degree of melting � e.g. Fo content in olivine, Cr# (Cr/(Cr+Al)) of Cr-spinel, Al and Yb concentrations in clinopyroxene. The degree of partial melting, calculated using Cr-spinel compositions, range from 1% to 9%. The PGE contents in spinel lherzolites show correlation with each other and with the spinel compositions, and thus can be related to the partial melting of the mantle source. The PGE abundances of the mantle source are estimated using the least depleted spinel lherzolite samples: Os 3.6±0.5, Ir 3.4±0.5, Ru 6.5±0.9, Pt 6.1±0.2, Pd 3.9±0.2 (in ppb). Spinel harzburgites, despite a good correlation between the whole rock major element abundances and mineral compositions (e.g., Yb in clinopyroxene and Cr# of spinel), indicate no relationship between the Fo content of olivine and the Cr# of spinel. Hence, the harzburgites cannot be the residuum of simple partial melting, but have a more complex origin (e.g. melt percolation). Pt/Ir ratios increase in the harzburgites as Pt increases. Similar behavior of Pt and Pd is observed in abyssal and SCLM harzburgites, and explained by sulfide precipitation during melt percolation. Rhenium concentrations in most Mamonia peridotites are significantly higher than in the primitive mantle and does not show correlations with PGE. Indeed Re concentrations tend to increase with the Cr# of spinel. Thus its distribution is not governed by partial melting and we suggest that Re addition to the peridotites of Mamonia occurred during serpentinization. The Re�Os model ages of peridotites form three age clusters at 250 Ma, 600�800 Ma and >1000 Ma. The youngest age is consistent with the age of magmatic rocks in the Mamonia Complex, whereas the �oldest� peridotites may belong to remnants of the subcontinental mantle.

Abstract: Melt inclusions were studied in chrome diopside from the Inagli deposit of gemstones in the Inagli massif of alkaline ultrabasic rocks of potassic affinity in the northwestern Aldan shield, Yakutia, Russia. The chrome diopside is highly transparent and has an intense green color. Its Cr2O3 content varies from 0.13 to 0.75 wt %. Primary and primary�secondary polyphase inclusions in chrome diopside are dominated by crystal phases (80�90 vol %) and contain aqueous solution and a gas phase. Using electron microprobe analysis and Raman spectroscopy, the following crystalline phases were identified. Silicate minerals are represented by potassium feldspar, pectolite [NaCa2Si3O8(OH)], and phlogopite. The most abundant minerals in the majority of inclusions are sulfates: glaserite (aphthitalite) [K3Na(SO4)2], glauberite [Na2Ca(SO4)2], aluminum sulfate, anhydrite (CaSO4), gypsum (CaSO4 *2H2O), barite (BaSO4), bloedite [Na2Mg(SO4)2 *4H2O], thenardite (Na2SO4), polyhalite [K2Ca2Mg(SO4)4 *2H2O], arcanite (K2SO4), and celestite (SrSO4). In addition, apatite was detected in some inclusions. Chlorides are probably present among small crystalline phases, because some analyses of aggregates of silicate and sulfate minerals showed up to 0.19�10.3 wt % Cl. Hydrogen was identified in the gas phase of polyphase inclusions by Raman spectroscopy. The composition of melt from which the chrome diopside crystallized was calculated on the basis of the investigation of silicate melt inclusions. This melt contains 53.5 wt % SiO2, considerable amounts of CaO (16.3 wt %), K2O (7.9 wt %), Na2O (3.5 wt %), and SO3 (1.4 wt %) and moderate amounts of Al2O3 (7.5 wt %), MgO (5.8 wt %), FeO (1.1 wt %), and H2O (0.75 wt %). The content of Cr2O3 in the melt was 0.13 wt %. Many inclusions were homogenized at 770-850 oC, when all of the crystals and the gas phase were dissolved. The material of inclusions heated up to the homogenization temperature became heterogeneous even during very fast quenching (two seconds) producing numerous small crystals. This fact implies that most of the inclusions contained a salt (rather than silicate) melt of sulfate-dominated composition. Such inclusions were formed from salt globules (with a density of about 2.5 g/cm3) occurring as an emulsion in the denser (2.6 g/cm3) silicate melt from which the chrome diopside crystallized.

Abstract: Olivine is the principal mineral of kimberlite magmas, and is the main contributor to the ultramafic composition of kimberlite rocks. Olivine is partly or completely altered in common kimberlites, and thus unavailable for studies of origin and evolution of kimberlite magmas. The masking effects of alteration, common in kimberlites worldwide, are overcome in this study of exceptionally fresh diamondiferous kimberlites of the Udachnaya-East pipe from the Daldyn-Alakit province, Yakutia, northern Siberia. The serpentine-free kimberlites contain large amount of olivine (~ 50 vol%) in a chloride-carbonate groundmass. Olivine is represented by two populations (olivine-I and groundmass olivine-II) differing in morphology, colour and grain size, and trapped mineral and melt inclusions. The large fragmental olivine-I is compositionally variable in terms of major (Fo85-94) and trace element concentrations, including H2O content (10-136 ppm). Multiple sources of olivine-I, such as convecting and lithospheric mantle, are suggested. The groundmass olivine-II is recognised by smaller grain sizes and perfect crystallographic shapes that indicate crystallisation during magma ascent and emplacement. However, a simple crystallisation history for olivine-II is complicated by complex zoning in terms of Fo values and trace element contents. The cores of olivine-II are compositionally similar to olivine-I, which suggests a genetic link between these two types of olivine. Olivine-I and olivine�II have oxygen isotope values (+5.6 ± 0.1 � VSMOW, 1 std. dev.) that are indistinguishable from one another, but higher than values (+5.18 ± 0.28 �) in �typical� mantle olivine. These elevated values most likely reflect equilibrium with the Udachnaya carbonate melt at low temperatures and 18O - enriched mantle source. The volumetrically significant rims of olivine-II have constant Fo values (89.0 ± 0.2 mol%), but variable trace element compositions. Uniform Fo compositions of the rims imply absence of fractionation of the melt�s Fe2+/Mg, which can be possible in the carbonatite melt � olivine system. The kimberlite melt is argued to have originated in the mantle as a chloride-carbonate liquid, devoid of �ultramafic� or �basaltic� aluminosilicate components, but became olivine-laden and olivine-saturated by scavenging olivine crystals from the pathway rocks and dissolving them en route to the surface. During emplacement the kimberlite magma changed progressively towards an original alkali-rich chloride-carbonate melt by extensively crystallising groundmass olivine and gravitational separation of solids in the pipe.

Abstract: It has long been proposed that MORB and OIB have constant supra-primitive mantle (PM) Nb/U values identical to each other. This fact together with complementary sub-PM values for the continental crust (CC), are taken as fundamental evidence, linking the mantle sources of MORB and OIB to the formation of the CC. Given that plate subduction at convergent margins is the major known process that dramatically fractionates Nb from U, and consequently that subducted oceanic slabs are the main primary carriers of supra-PM Nb/U, a constant supra-PM Nb/U in MORB mantle implies that the mixing of subducted oceanic crust is essentially finished or the newly recycled oceanic crust has Nb/U close to that of the mantle. The similarity between Nb and U as well as the constancy of Nb/U in MORB are revisited here based on MORB glass data obtained using laser ablation ICP-MS. The result shows that Nb/U is not correlated with Nb/Hf, supporting that Nb and U are similarly incompatible. Further investigation shows that Nb is not perfectly identical to, but is faintly more incompatible than U as indicated by the good correlation between log(U) and log(Nb) with a slope of 0.954, very close to 1. Nonetheless, the similarity between Nb and U is high enough, such that the average Nb/U value of MORB glasses should be very close to that of the MORB mantle. By contrast, the difference between Ce and Pb is more obvious. Ce is more incompatible than Pb with a slope of 1.13 in a log(Pb) versus log(Ce) diagram. Therefore, the Ce/Pb of MORB should be a little bit higher than that of the mantle source. The Nb/U value is not as uniform as expected for the similar incompatibility in studied MORB glasses, but varies by a factor of ~2, suggesting that MORB mantle source is not yet homogenized in term of Nb/U. This indicates that the mixing back of subducted oceanic crust is still an ongoing process, i.e., subducted oceanic crust is recycling back after staying in the lower mantle for billions of years

Abstract: Melt inclusions within forsterite-rich olivine crystals in two mixed magmas from the Indonesia�Australia collision zone provide information on the primary melts formed within this tectonic environment. Although whole rock Sr, Nd and Pb isotope data show a strong influence of subducted continental material, the melt inclusion major and trace element compositions are only subtly different from typical subduction-related magmas. The presence of low-Ca olivine crystals with inclusions of aluminous spinel in one sample can be explained by localised reactions during influx of hot basaltic magma in a partially crystallised magma chamber. The mineralogy of the samples is similar to that of other mixed arc magmas. Major and trace element data for reheated melt inclusions show subtle distinctions compared to non-collisional magmas in terms of CaO/Al2O3, Th/Nb and Sr/Y ratios, reflecting partial melting processes during slab to wedge transfer of subducted continental material. Magmas influenced by the subduction of continental material are therefore very similar to normal subduction-related magmas, apart from their radiogenic isotope signature. Magmas with crustal isotope ratios and highly unusual (e.g. peraluminous) geochemical compositions must therefore be formed by other processes, such as upper crustal contamination.

Abstract: Chloride-bearing clasts from the Udachnaya-East pipe kimberlites, Yakutia, Russia, contain abundant to accessory rasvumite, KFe2S3, and djerfisherite, K6Na0-1(Fe,Ni,Cu)(24)S26Cl, which have been previously described in the groundmass of the host kimberlite. Rasvumite occurs in chloride-"nyerereite" and carbonate clasts, where it forms prismatic crystals (up to 5 mm) or is associated with djerfisherite in a rim around pyrrhotite. Djerfisherite is the omnipresent sulfide in all types of chloride-containing clasts, in which it rims pyrrhotite and forms individual xenomorphic to subhedral grains and, more rarely, octahedral crystals at the contact with host kimberlite. In chloride clasts and the host kimberlites, the following sequence of crystallization was found: pyrrhotite - rasvumite - djerfisherite, reflecting an increase in the activity of Cl in the evolved melt. The composition of rasvumite from the Udachnaya-East pipe is close to ideal KFe2S3, with low abundances of Rb, Cs and Na (< 0.9, < 0.2 and <0.15 wt.%, respectively). Analyses of the rasvumite by the LA-ICP-MS technique indicates the presence of T1 (95-480), Ba (110-215), Pb (25-190), Te (up to 60), Se (20-135) and Co (25-100 ppm). These data also indicate compositional differences between unaltered rasvumite and its oxidized rim; the levels of Na, Mg, V, Mn, Ni, As, Sr, Sb and W increase by an order of magnitude. Unlike djerfisherite in the kimberlite groundmass, that in the chloride clasts is generally characterized by higher amounts of Fe and lower amounts of Cu, with low contents of Rb (< 2000 ppm), Cs (< 100 ppm), and Tl (< 330 ppm). Sulfides of potassium in chloride-bearing clasts are considered to be primary phases crystallized from an evolved kimberlitic melt.

Abstract: Plate tectonic processes introduce basaltic crust ( as eclogite) into the peridotitic mantle. The proportions of these two sources in mantle melts are poorly understood. Silica-rich melts formed from eclogite react with peridotite, converting it to olivine-free pyroxenite. Partial melts of this hybrid pyroxenite are higher in nickel and silicon but poorer in manganese, calcium, and magnesium than melts of peridotite. Olivine phenocrysts' compositions record these differences and were used to quantify the contributions of pyroxenite-derived melts in mid-ocean ridge basalts ( 10 to 30%), ocean island and continental basalts ( many > 60%), and komatiites ( 20 to 30%). These results imply involvement of 2 to 20% ( up to 28%) of recycled crust in mantle melting.

Abstract: The origin of compositional heterogeneities among the magmas parental to mid-ocean ridge basalts (MORB) was investigated using a single rock piece of the olivine-phyric basalt from 43 degrees N, Mid-Atlantic Ridge (AII D11-177). The exceptional feature of this sample is presence of very primitive olivine crystals (90-91 mol% Fo) that are significantly variable in terms of CaO (0.15-0.35 wt%). A population of low-Ca olivine (0.15-0.25 wt% CaO) is also notably distinct from high-Ca olivine population in AII D11-177, and primitive MORB olivine in general, in having unusual assemblage of trapped mineral and glass inclusions. Mineral inclusions are represented by high-magnesian (Mg# 90.7-91.1 mol%) orthopyroxene and Cr-spinel, distinctly enriched in TiO2 (up to 5 wt%, c.f. < 1 wt% in common MORB spinel). Glass inclusions associated with orthopyroxene and high-Ti Cr-spinel have andesitic compositions (53-58 wt% SiO2). Compared to the pillow-rim glass and "normal" MORB inclusions, the Si-rich glass inclusions in low-Ca olivine have strongly reduced Ca and elevated concentrations of Ti, Na, K, P, Cl, and highly incompatible trace elements. Strong variability is recorded among glass inclusions within a single olivine phenocrysts. We argue that the observed compositional anomalies are mineralogically controlled, and thus may arise from the interaction between hot MORB magmas and crystal cumulates in the oceanic crust or magma chamber.

Abstract: This study examines melt inclusions containing bubbles of aqueous fluid (L, V, and L + V), occurring in rhyolites from the Okataina Volcanic Centre, New Zealand, and the Rio Blanco Cu-Mo deposit, Chile. We demonstrate that these aqueous fluids coexisted with silicate melts (magmas) and represent either post-trapping exsolution (in the case of Okataina), or co-trapping of phases already coexisting in the magma (in the case of Rio Blanco). Microthermometry proves that some of the bubbles are a single-phase aqueous liquid, and all are shown by PIXE analysis to be metal rich saline solutions. As such, these aqueous fluids provide the closest approximation to direct testing of the proposition that cooling magmas exsolve metal-rich aqueous fluid. In the case of pre-trapping exsolution at Rio Blanco we show that some inclusions record and preserve magmatic emulsions (melt + aqueous fluid) that are the first stage in the evolution of hydrothermal fluids. We demonstrate that heating experiments on volatilerich melt inclusions can produce in-situ exsolution of hypersaline metal-rich aqueous fluid bubbles, potentially permitting magmachamber processes to be experimentally modelled.

Abstract: Chlorine in the Earth is highly depleted relative to carbonaceous chondrites and solar abundances(1). Knowledge of the Cl concentrations and distribution on Earth is essential for understanding the origin of these depletions. Large differences in the stable chlorine isotope ratios of meteoritic, mantle and crustal materials have been used as evidence for distinct reservoirs in the solar nebula(2) and to calculate the relative proportions of Cl in the mantle and crust(3). Here we report that large isotopic differences do not exist, and that carbonaceous chondrites, mantle and crust all have the same Cl-37/Cl-35 ratios. We have further analysed crustal sediments from the early Archaean era to the Recent epoch and find no systematic isotopic variations with age, demonstrating that the mantle and crust have always had the same delta Cl-37 value. The similarity of mantle, crust and carbonaceous chondrites establishes that there were no nebular reservoirs with distinct isotopic compositions, no isotopic fractionation during differentiation of the Earth and no late (post-core formation) Cl-bearing volatile additions to the crustal veneer with a unique isotopic composition.

Abstract: Djerfisherite, an unusual potassium- and chlorine-bearing sulphide K6Na(Fe,Ni,Cu)(24)S26Cl, is found in remarkably fresh rocks of the Udachnaya-East kimberlite pipe, including several varieties of kimberlite and a kimberlite-hosted phlogopite-spinel lherzolite xenolith. In both kimberlite breccia and monticellite kimberlite djerfisherite is a common groundmass mineral. Djerfisherite is also present as a daughter phase in olivine-hosted inclusions of trapped carbonate-chloride melt and sulphide melt. The mineral is present as irregular or rounded grains (up to 80-100 mu m) in association with magnetite and pyrrhotite in the kimberlite groundmass, and together with carbonates, Na-K-chlorides, silicates, magnetite, sulphates and Fe-Ni-sulphides in melt inclusions. Djerfisherite in the lherzolite xenolith is mainly interstitial (up to 100 mu m) and commonly rims primary mantle sulphides that show clear signs of replacement. Broad compositional variations in Fe, Ni and Cu are common in djerfisherite from different occurrences of the Udachnaya-East pipe. Textural relations, heating stage experiments with melt inclusions and compositional data, suggest a late magmatic origin of djerfisherite in the Udachnaya-East kimberlite groundmass, at shallow depths and at T <= 800 degrees C. In contrast, djerfisherite in the lherzolite xenolith appears to be a product of direct precipitation from evolved kimberlite magma infiltrating into lithospheric xenoliths or reactions of evolved kimberlite fluids/melts with primary minerals in xenoliths.

Abstract: The volcanic hazard potential of Mount Etna volcano is currently nourished by long-lasting, powerful eruptions of basaltic magmas coupled with increased seismicity and ground deformation, and the world's largest discharge of volcanic gases. The current evolutionary cycle of Mount Etna activity is consistent with subduction-related chemical modifications of the mantle source. Arrival of a new mantle-derived magma batch beneath the volcano has been hypothesized, but is still elusive among the erupted products. Here we demonstrate petrological and geochemical affinities between the magmas supplying modern eruptions and high-Mg, fall-stratified (FS) basalts ejected violently similar to 4 k.y. ago. The FS primitive magmas (similar to 13 wt% MgO) are characteristically volatile enriched (at least 3.8 wt% H2O and 3300 ppm CO2), and bear a trace element signature of a garnet-bearing, metasomatized source (high Gd/Yb, K/La, U/Nb, Pb/Ce, Ca/Al). They started crystallizing olivine (Fo(91)), clinopyroxene (Mg# 92.5), and Cr spinel deep in the plumbing system (> 5 kbar), contributing to the cumulate piles at depth and to differentiated alkaline basalt and trachybasalt magmas in the shallow conduit. Continuous influx of mantle-derived, volatile-rich magmas, such as those that supplied the FS fallout, provides a good explanation for major compositional and eruptive features of Mount Etna.

Abstract: Submarine volcanic glasses from the eastern Manus Basin of Papua New Guinea, ranging from basalt to rhyodacite, clarify the geochemical behavior of Cl in arc-type magmas. For the Manus samples, Cl is well correlated with non-volatile highly incompatible trace elements, suggesting it was not highly volatile and discounting significant seawater contamination. The Cl partition coefficient is close to but slightly lower than that of Nb and K2O, a behavior similar to that in mid-ocean ridge basalts (MORB) and ocean island basalts (OIB). The similar incompatibilities of Cl and Nb imply that the Cl/Nb values of the eastern Manus Basin glasses reflect their magma source. For glasses from other west Pacific back-arc basins, Cl/Nb, Ba/Nb, and U/Nb increase towards the subduction trench, indicating increased contribution of a component enriched in Cl, Ba, and U, likely from subduction-released slab fluids. It is estimate that similar to 80% of the Cl in the Manus arc-type glasses was added directly from subducted slab-derived fluids. We have also modeled Cl behavior during magma evolution in general. Our results show that the behavior of Cl in magma is strongly influenced by pressure, initial H2O content, and the degree of magmatic fractionation. At early stages of magmatic evolution, for magmas with initial H2O content of < 4.0 wt%, Cl is highly incompatible under all pressures. By contrast, for more evolved magmas at moderately high pressure and high H2O contents, considerable amounts of Cl can be extracted from the magma once H2O saturation is reached. Accordingly, Cl is usually highly incompatible in MORB and OIB because of their low H2O contents and relatively low degrees of fractional crystallization. The behavior of Cl in arc magmas is more complicated, ranging from highly incompatible to compatible depending on H2O content and depth of magma chambers. The behavior of Cl in the eastern Manus Basin magmas is consistent with low H2O contents (1.1-1.7 wt%) and evolution at low pressures (< 0.1 GPa). Modeling results also indicate that Cl will behave differently in intrusive rocks compared to volcanic rocks because of the different pressures involved. This may have a strong influence on the mechanisms of ore genesis in these two tectonic settings.

Abstract: The oxygen fugacity (f)(O2) of the Earth's mantle is one of the fundamental variables in mantle petrology. Through ferric-ferrous iron and carbon-hydrogen-oxygen equilibria, (f)(O2) influences the pressure-temperature positions of mantle solidi and compositions of small-degree mantle melts(1-3). Among other parameters, (f)(O2) affects the water storage capacity and rheology of the mantle(4,5). The uppermost mantle, as represented by samples and partial melts, is sufficiently oxidized to sustain volatiles, such as H2O and CO2, as well as carbonatitic melts(6,7), but it is not known whether the shallow mantle is representative of the entire upper mantle. Using high-pressure experiments, we show here that large parts of the asthenosphere are likely to be metal-saturated. We found that pyroxene and garnet synthesized at >7 GPa in equilibrium with metallic Fe can incorporate sufficient ferric iron that the mantle at >250 km depth is so reduced that an (Fe,Ni)-metal phase may be stable. Our results indicate that the oxidized nature of the upper mantle can no longer be regarded as being representative for the Earth's upper mantle as a whole and instead that oxidation is a shallow phenomenon restricted to an upper veneer only about 250 km in thickness.

Abstract: The compositions of parental magmas forming kimberlitic rocks remain largely unknown because of masking effects of syneruptive contamination and degassing, and post-magmatic alteration. Among most affected elements are volatiles (H2O and CO2) and alkalies (Na and K). This study attempts to overcome the problems related to the alteration of kimberlites by detailed petrographic and chemical analyses of exceptionally fresh, and thus essentially anhydrous (< 0.5 wt.% H2O), kimberlite samples from the Udachnaya-East pipe (Daldyn-Alakit region, Siberia). The groundmass of these kimberlites contains abundant carbonate (calcite, shortite, zemkorite) and chloride (halite, sylvite) minerals, cementing olivine phenocrysts, and forming round segregations ("nodules"). The nodules, belonging to the chloride and chloride-carbonate types, show no evidence of thermometamorphic effects on the contacts with the host kimberlite. The chloride-carbonate nodules demonstrate liquid immiscibility textures that are remarkably similar to those observed in the olivine-hosted chloride-carbonate melt inclusions at similar to 600 degrees C. The similarity of oxygen and carbon isotope values of carbonates from the groundmass and nodules (delta O-18 12.5 to 13.9 parts per thousand VSMOW; delta C-13 -3.7 to -2.7 parts per thousand VPDB) points to their common origin at similar temperatures. We argue for crystallisation of the chloride-carbonate nodules from residual kimberlite melts, pooled after exhaustion of the silicate melt component. The enrichment of the residual melt in alkali carbonate and chloride is partly reflected in the bulk groundmass compositions (10-11 wt.% CO2, 2.3-3.2 wt.% Cl, 2.6-3.7 wt.% Na, and 1.6-2.0 wt.% K). We propose that this enrichment is inherited from the kimberlite parental magma, and it can be responsible for the kimberlite low liquidus temperatures, low viscosities, and rapid emplacement.

Abstract: Three distinct phases of basaltic volcanism (Older Series, 7.8-5.4 Ma; Intermediate Series, 3.5-1.9 Ma; Younger Series, 0.7-0.03 Ma), related to the Deccan-Reunion mantle-plume, occurred over a time span of nearly 8 million years on the island of Mauritius, Indian Ocean. Bulk rock compositions of 52 analyzed samples (including samples from 32 recent borehole sections), as well as the compositions of olivine and spinel phenocrysts, reveal significant temporal variations in the composition of the Mauritius magmas. Two distinct compositional groups are identified based on their major and trace element compositions. The Group 1 basalts comprise the Younger Series, Intermediate Series and the earlier products of the Older Series rocks, and have higher MgO (7.6-13.6 wt.%) and lower K2O (0.2-0.5 wt.%) and La/Sm (2.1-3.5) compared to Group 2 basalts (MgO 6.2-9.2 wt.%; K2O 1.0-1.5 wt.%; La/Sm 3.6-4.1), which exclusively encompass the later differentiation products erupted during the end of the Older Series volcanism, denoted as Older Differentiated (OD) Series. Petrographic and mineralogic studies further confirm the presence of two distinct groups. Relatively primitive olivine compositions (Fo: 87-80) in Group 1 rocks are characterized by increasing CaO (0.2 to 0.3 wt.%) with decreasing Fo content, whereas in Group 2 rocks olivine (Fo: 86-80) show decreasing CaO (0.4 to 0.3 wt.%) with decreasing Fo content. Olivine-hosted spinel inclusions also show strong compositional differences between groups 1 and 2. Unusually Al-rich spinels (compared to that usually found in plume derived magma) and the positive Sr anomalies in Group I rocks suggest assimilation of crustal gabbros by the plume magmas. We propose a laterally heterogeneous plume and the contributions from variable plume components to account for the compositional differences observed in the two Mauritian lava groups. The early-Shield building Older Series lavas (oldest Group 1 lavas), characterized with a relatively less enriched trace element abundances, most likely derive from extensive melting of a depleted peridotite matrix in the core of the plume. Melting of this already depleted source produced the later Intermediate and Younger Series eruptions. Towards the late-shield stage, melts presumably derive from the enriched pyroxenite/eclogite components in the outer part of the plume.

Abstract: High-calcium, nepheline-normative ankaramitic basalts (MgO>10 wt.%, CaO/Al2O3>1) from Rinjam volcano, Lombok (Sunda arc, Indonesia) contain phenocrysts of clinopyroxene and olivine (Fo(85-92)) with inclusions of spinel (Cr# 58-77) and crystallised melt. Olivine crystals have variable but on average low NiO (0.10-0.23 wt.%) and high CaO (0.22-0.35 wt.%) contents for their forsterite number. The CaO content of Fo(89-91) olivine is negatively correlated with the Al2O3 content of enclosed spinel (9-15 wt.%) and positively correlated with the CaO/Al2O3 ratios of melt inclusions (0.9-1.5). Major and trace element patterns of melt inclusions are similar to that of the host rock, indicating that the magma could have formed by accumulation of small batches of melt, with compositions similar to the melt inclusions. The liquidus temperature of the magma was similar to 1275 degrees C, and its oxygen fugacity <= FMQ + 2.5. Correlations between KO, Zr, Th and LREE in the melt inclusions are interpreted to reflect variable degrees of melting of the source; correlations between Al2O3, Na2O, Y and HREE are influenced by variations in the mineralogy of the source. The melts probably formed from a water-poor, clinopyroxene-rich mantle source.

Abstract: Kimberlites, the deepest terrestrial magmas and the principal source of diamonds, must have low viscosity and high buoyancy, which govern their exceptionally fast transport from mantle depths to the surface. Appreciation of the rheological properties of kimberlite magmas relies on research into their temperatures and compositions. Understanding of the alkali and volatile element budget is central to these studies, but is hampered by contaminated and altered compositions of kimberlites worldwide. Kimberlites of the diamondiferous Udachnaya-East pipe (Siberia) are exceptionally fresh, with low H2O (<0.5 wt%), but high CO2 (up to 14 wt%), Cl (up to 6 wt%), and alkalies ( up to 6 wt% Na2O and 2.0 wt% K2O). After crystallization of olivine the kimberlite melt evolved towards essentially carbonate-chloride compositions. The groundmass assemblage and compositions of the Udachnaya-East kimberlite resemble modern halogen-rich natrocarbonatite lavas from the Oldoinyo Lengai volcano. Rheological measurements on the Oldoinyo Lengai lavas can be used to constrain properties of the kimberlite magma.

Abstract: The chemical composition of basaltic magma erupted at the Earth's surface is the end product of a complex series of processes, beginning with partial melting and melt extraction from a mantle source and ending with fractional crystallization and crustal assimilation at lower pressures. It has been proposed that studying inclusions of melt trapped in early crystallizing phenocrysts such as Mg-rich olivine and chromite may help petrologists to see beyond the later-stage processes and back to the origin of the partial melts in the mantle(1,2). Melt inclusion suites often span a much greater compositional range than associated erupted lavas, and a significant minority of inclusions carry distinct compositions that have been claimed to sample melts from earlier stages of melt production, preserving separate contributions from mantle heterogeneities(1-4). This hypothesis is underpinned by the assumption that melt inclusions, once trapped, remain chemically isolated from the external magma for all elements except those that are compatible in the host minerals(1,2). Here we show that the fluxes of rare-earth elements through olivine and chromite by lattice diffusion are sufficiently rapid at magmatic temperatures to reequilibrate completely the rare-earth-element patterns of trapped melt inclusions in times that are short compared to those estimated for the production and ascent of mantle-derived magma(5,6) or for magma residence in the crust(7). Phenocryst-hosted melt inclusions with anomalous trace-element signatures must therefore form shortly before magma eruption and cooling. We conclude that the assumption of chemical isolation of incompatible elements in olivine- and chromite-hosted melt inclusions(1,2) is not valid, and we call for re-evaluation of the popular interpretation that anomalous melt inclusions represent preserved samples of unmodified mantle melts.

Abstract: Group-I kimberlites are the crystallization products of low-degree partial melts derived from the convective mantle [1, 2]. Since kimberlites are the main economic source of diamonds, the evolution of primary kimberlite melts is of great importance for deciphering mantle compositions, melting conditions, and diamond genesis. Most kimberlites consist of a brecciated mixture of olivine phenocrysts and xenogenic mantle and crustal material embedded in a fine- or coarse-grained groundmass, which is dominated by serpentine, calcite, and, occasionally, dolomite [3-5]. Thus, the evolutionary trend of kimberlite magmas is controlled by Mg silicates (high contents of MgO and SiO2) and carbonates (high contents of CaO and CO2). However, this trend can be intensely affected by interactions during ascent, the assimilation of mantle and crustal xenoliths, and the syn- and postmagmatic alteration of most kimberlite rocks. Almost all studied kimberlites around the world, even aphanitic [6, 7] or "uncontaminated" or "fresh" ones, were variably affected by these processes [7-10]. In the studying kimberlites, special attention was given to one aspect of the evolution of kimberlite magmas in mantle and crustal conditions: the entrapment of country rocks and interaction with them [3, 11]. Nodules in kimberlites (peridotites, eclogites, metamorphic and sedimentary rocks, as well as diamondiferous rocks) are usually used to estimate physicochemical and structural conditions in the subcontinental lithosphere, the properties of kimberlite magma, and the crystallization conditions of diamonds. It is convenient to study these processes in the Udachnaya kimberlite pipe in Yakutia because of a large number, diversity, and remarkable freshness of its nodules [11, 12]. Our study was focused on a new (carbonate-chloride) type of nodules recently found in kimberlites at deep levels (>350 km) of the open-pit mine at the Udachnaya-Vostochnaya pipes. Host kimberlites are also unique in chemical and mineral composition. The groundmass is predominantly olivine-carbonate-chloride in composition and shows almost no evidence of replacement [13, 14]. The presence of such nodules in unaltered kimberlites seems not to be coincidental and provides new insight into the evolution of kimberlite magmas.

Abstract: A method is proposed for determining the water concentration in silicate melt inclusions (MI) by confocal rnicro-Raman spectroscopy, Without exposing the inclusions for measurements (a prerequisite of all previous methods). The latter is important for extremely water-rich MI (e.g., those in evolved granites and pegmatites), which would loose H2O on exposure. Furthermore, this technique permits determination of the water concentration in it single MI. We use a comparative technique, determining the total water content of a sample against a reference glass of known water content. Because this process is non-destructive it does not preclude the subsequent use of other analytical techniques

Abstract: Metal evolution in a composite granitic pluton was tracked by analyzing melt inclusions in 11 quartz samples from 7 zones at the Timbarra gold deposit, Australia. We present the first quantitative microanalyses of gold (Au) in granitic silicate melt inclusions using laser ablation inductively coupled plasma mass-spectrometry and show how Au and other metals become enriched during fractional crystallization in a granite intrusion. Au was enriched during fractionation from a monzogranite to a highly fractionated alkali-feldspar granite. Similar enrichment behavior for other metals implies that no gold-enriched precursor melt is required and fractional crystallization can enrich the Au concentration to economic levels. The low content of accessory oxides and sulfides, the absence of early Cl-bearing fluids, the volatile content in the melt, and a prolonged crystallization constitute important factors for extensive metal enrichment during crystal fractionation. These characteristics play a crucial role in felsic, highly fractionated plutons and their associated deposits such as intrusion-related Au deposits. The gold enrichment during fractionation also implies that Au is directly sourced from the granites.

Abstract: Unravelling the origin of different components contributing to subduction-related magmas is a prerequisite to understanding the sources and processes involved in their origins. Mafic, high-Ca subduction-related magmas from geographically-diverse areas (Indonesia, Solomon Islands, Kamchatka, Valu Fa Ridge) contain two populations of olivine crystals, of which only the high-Ca population (CaO = 0.3-0.5 wt.%) crystallized from the melt that dominantly contributed to the whole rock composition. Forsterite-rich (Fo90-94), low-Ca (CaO < 0.15 wt.%), high-Ni (NiO > 0.3 wt.%) olivine crystals, which constitute 16-37 vol.% of total olivine population, are generally interpreted as mantle or lithospheric xenocrysts. However, in these samples, the olivine shape and chemical zoning, the composition of included minerals (orthopyroxene, clinoenstatite and Cr-spinel) and presence of melt inclusions, are indications that these crystals are phenocrysts from a mafic magma with high silica and low calcium contents. The coexistence of contrasting magmas (mafic high-Ca silica-poor versus low-Ca silica-rich) within a number of arc systems and their mixing may not be a rare event, and should be taken into account when developing models of arc petrogenesis.

Abstract: Mineral and melt inclusions in olivines from the most Mg-rich magma from the southern West Sulawesi Volcanic Province indicate that two distinct melts contributed to its petrogenesis. The contribution that dominates the whole-rock composition comes from a liquid with high CaO (up to 16 wt %) and low Al2O3 contents (CaO/Al2O3 up to 1), in equilibrium with spinel, olivine (Fo85-91; CaO 0.35-0.5 wt %; NiO 0.2-0.30 wt %) and clinopyroxene. The other component is richer in SiO2 (>50 wt %) and Al2O3 (19-21 wt %), but contains significantly less CaO (<4 wt %); it is in equilibrium with Cr-rich spinel with a low TiO2 content, olivine with low CaO and high NiO content (Fo90-94; CaO 0.05-0.20 wt %; NiO 0.35-0.5 wt %), and orthopyroxene. Both the high- and low-CaO melts are potassium-rich (>3 wt % K2O). The high-CaO melt has a normalized trace element pattern that is typical for subduction-related volcanic rocks, with negative Ta-Nb and Ti anomalies, positive K, Pb and Sr anomalies, and a relatively flat heavy rare earth element (HREE) pattern. The low-CaO melt shows Y and HREE depletion (Gdn/Ybn 41), but its trace element pattern resembles that of the whole-rock and high-CaO melt in other respects, suggesting only small distinctions in source areas between the two components. We propose that the depth of melting and the dominance of H2O- or CO2-bearing fluids were the main controls on generating these contrasting magmas in a syn-collisional environment. The composition of the low-CaO magma does not have any obvious rock equivalent, and it is possible that this type of magma does not easily reach the Earth's surface without the assistance of a water-poor carrier magma.

Abstract: The data obtained on melt and fluid inclusions in minerals of granites, metasomatic rocks, and veins with tin ore mineralization at the Industrial'noe deposit in the southern part of the Omsukchan trough, northeastern Russia, indicate that the melt from which the quartz of the granites crystallized contained globules of salt melts. Silicate melt inclusions were used to determine the principal parameters of the magmatic melts that formed the granites, which had temperatures at 760-1020oC, were under pressures of 0.3-3.6 kbar, and had densities of 2.11-2.60 g/cm 3 and water concentrations of 1.7-7.0 wt %. The results obtained on the fluid inclusions testify that the parameters of the mineral-forming fluids broadly varied and corresponded to temperatures at 920- 275oC , pressures 0.1-3.1 kbar, densities of 0.70-1.90 g/cm3 , and salinities of 4.0-75.0 wt % equiv. NaCl. Electron microprobe analyses of the glasses of twelve homogenized inclusions show concentrations of major components typical of an acid magmatic melt (wt %, average): 73.2% SiO2 , 15.3% Al2O3 , 1.3% FeO, 0.6% CaO, 3.1% Na2O , and 4.5% K2O at elevated concentrations of Cl (up to 0.51 wt %, average 0.31 wt %). The concentrations and distribution of some elements (Cl, K, Ca, Mn, Fe, Cu, Zn, Pb, As, Br, Rb, Sr, and Sn) in polyphase salt globules in quartz from both the granites and a mineralized miarolitic cavity in granite were assayed by micro-PIXE (proton-induced X-ray emission). Analyses of eight salt globules in quartz from the granites point to high concentrations (average, wt %) of Cl (27.5), Fe (9.7), Cu (7.2), Mn (1.1), Zn (0.66), Pb (0.37) and (average, ppm) As (2020), Rb (1850), Sr (1090), and Br (990). The salt globules in the miarolitic quartz are rich in (average of 29 globules, wt %) Cl (25.0), Fe (5.4), Mn (1.0), Zn (0.50), Pb (0.24) and (ppm) Rb (810), Sn (540), and Br (470). The synthesis of all data obtained on melt and fluid inclusions in minerals from the Industrial'noe deposit suggest that the genesis of the tin ore mineralization was related to the crystallization of acid magmatic melts.

Abstract: Major element and sulfur concentrations have been determined in experimentally heated olivine-hosted melt inclusions from a suite of Apollo 12 picritic basalts (samples 12009, 12075, 12020, 12018, 12040, 12035). These lunar basalts are likely to be genetically related by olivine accumulation (Walker et al. 1976a, b). Our results show that major element compositions of melt inclusions from samples 12009, 12075, and 12020 follow model crystallization trends from a parental liquid similar in composition to whole rock sample 12009, thereby partially confirming the olivine accumulation hypothesis. In contrast, the compositions of melt inclusions from samples 12018, 12040, and 12035 fall away from model crystallization trends, suggesting that these samples crystallized from melts coin positionally distinct from the 12009 parent liquid and therefore may not be strictly cogenetic with other members of the Apollo 12 picritic basalt suite. Sulfur concentrations in melt inclusions hosted in early crystallized olivine (17075) are consistent with a primary magmatic composition of 1050 ppm S, or about a factor of 2 greater than whole rock compositions with 400-600 ppm S. The Apollo 12 picritic basalt parental magma apparently experienced outgassing and loss of S during transport and eruption on the lunar surface. Even with the higher estimates of primary magmatic sulfur concentrations provided by the melt inclusions, the Apollo 12 picritic basalt magmas would have been undersaturated in sulfide in their mantle source regions and capable of transporting chalcophile elements from the lunar mantle to the surface. Therefore, the measured low concentration of chalcophile elements (e.g., Cu, Au, PGEs) in these lavas must be a primary feature of the lunar mantle and is not related to residual sulfide remaining in the mantle during melting. We estimate the sulfur concentration of the Apollo 12 mare basalt source regions to be similar to 75 ppm, which is significantly lower than that of the terrestrial mantle.

Abstract: Foid-bearing syenite cognate xenoliths represent fragments of the upper peripheral parts of the K-phonolitic portions of the 79 AD magma chamber, wrenched during the explosive eruption. Abundant multiphase fluid inclusions are hosted within K-feldspar and coexist with rare silicate melt inclusions. This gives evidence to the exsolution of a magmatic volatile-rich phase from the peripheral parts of the silicate magma chamber. The characterization of daughter mineral assemblage of these fluid inclusions, by SEM-EDS and Raman spectroscopy, indicates two ubiquitous main components: Na-K chlorides (halite + sylvite) and Na-Ca carbonates (calcite plus/minus nahcolite). Microthermometric experiments indicate nearly magmatic trapping temperatures (760 degrees C to 830 degrees C) of the homogeneous chloride-carbonate liquid. Cooling of such liquid produces two immiscible melt phases (chlorides and carbonates) at 455-435 degrees C. This suggests that a hypersaline-carbonate fluid, exsolved from the silicate magma, can further experience another unmixing event that would occur in essentially 'post-magmatic' environment.

Abstract: The kimberlite rocks of the Udachnaya-East pipe (Siberia) are uniquely fresh and contain very high abundances of primary volatiles (Cl, CO2, S). Alkali elements and chlorine are extremely abundant in the reconstructed kimberlite melt compositions, and this enrichment is very important for our understanding of deep-mantle melting and melt transport. Here we present new isotopic data that confirm a mantle origin for these kimberlitic chlorides and carbonates, and constrain the kimberlite emplacement age as ca. 347 Ma. The initial Nd and Ph isotope ratios in a large salt aggregate, in a CI-S-enriched water leachate of the groundmass, and in the silicate fraction of the groundmass are very similar (epsilon(Nd) = +3 to +4, Pb-206/Pb-204 = 18.6, Pb-207/Pb-204 = 15.53), implying a comagmatic origin of the chlorides and carbonates and the silicates. Combined Sr, Nd, and Ph isotope data are used to rule out any significant contributions to the kimberlite chlorine budget from crustal sources, such as the Cambrian evaporite sequences of the Siberian platform. Our data support the interpretation that exsolved Na-K chloride and Na-K-Ca carbonate formed directly from original uncontaminated kimberlite magma. High Cl abundances in kimberlites suggest the presence of a Cl-rich reservoir in the deep sublithospheric mantle

Abstract: Alaskan-type platinum-bearing plutons and potassium-enriched mafic to ultramafic volcanic rocks are temporally and spatially associated within the Late Cretaceous-Paleocene Achalvayam-Valaginskii intra-oceanic palaeo-arc system, allochthonousy present in the Kogak Highland and Kamchatka Peninsula (Far East Russia). The compositions of the parental magmas to the Alaskan-type complexes are estimated using the Galmoenan platonic complex as an example. This complex, composed of dunites, pyroxenites and minor gabbros, is the largest (~ 20 km3) in the system and the best studied owing to associated platinum placer deposits. The compositions of the principal mineral phases in the Galmoenan intrusive rocks [olivine (Fo(79-92)), clinopyroxene (1-3.5 wt % Al2O3, 0.1-0.5 wt % TiO2), and Cr-spinel (5-15 wt % Al2O3 and 0.3-0.7 wt % TiO2)] are typical of liquidus assemblages in primitive island-arc magmas in intra-oceanic settings, and closely resemble the mineral compositions in the Achaivayam-Valaginskii ultramafic volcanic rocks. The temporal and spatial association of intrusive and extrusive units, and the similarity of their mineral compositions, suggest that both suites were formed from similar parental magmas. ne composition of the parental magma for the Galmoenan platonic rocks is estimated using previously reported data for the Achaivayam-Valaginskii ultramafic volcanic rocks and phenocryst-hosted melt inclusions. Quantitative simulation of crystallization of the parental magma in the Galmoenan magma chamber shows that the compositions of the cumulate units are best modelled by fractional cryallization with periodic magma replenishment. The model calculations reproduce well the observed mineral assemblages and the trace element abundances in clinopyroxene. Based upon the estimated composition of the parental magmas and their mantle source, we consider that fluxing of a highly refractory mantle wedge (similar to the source of boninites) by chlorine-rich aqueous fluids is primarily responsible for both high degrees of partial melting and the geochemical characteristics of the magmas, including their enrichment in platinum-group elements.

Abstract: In most porphryr, systems the obscuring effects of hydrothermal processes and subsequent alteration, along with limited exposure of source rocks, preclude a detailed understanding of how and where metals and volatiles were derived. However, in this study we examine melt inclusions which have escaped alteration and that sampled all of the phases coexisting in the magma, in late- and postmineral rhyolitic units from the Rio Blanco Cu-Mo deposit, Chile. These inclusions demonstrate the existence of a volatile-rich melt, the exsolution from it of an aqueous volatile-rich phase, initially as melt + vapor bubble emulsions, and the disruption of these emulsions into melt and primary magmatic fluids. Trapping of these emulsions may explain the occurrence of melt inclusions containing widely, varying proportions of melt and aqueous fluid found at Rio Blanco. We demonstrate the sequestering of metals into the exsolved volatile phases and the derivation from these of possible ore-forming hydrothermal fluids, with particular reference to the implications for metal transport. Melt inclusions show differences between adjacent comagmatic intrusions that may be directly related to the extent of mineralization of the respective bodies. In one of the Rio Blanco postmineral rhyolite bodies melt inclusions show exsolution of the volatile-rich phase but only minor evidence of trapping of a metal-rich vapor. In contrast, inclusions from an adjacent late mineral rhyolite body show similar volatile phase exsolution but also provide evidence of ponding of metal-rich hydrothermal fluids during the final stages of cooling.

Abstract: Studies of melt inclusions trapped in magmatic phenocrysts can provide a new perspective on several key outstanding problems in the understanding of the genesis of orthomagmatic ore deposits, particularly with respect to the concentration of metals in parental magmas. The published data shows a mismatch between low and high abundances of Cu (and Ag) in unheated and remelted melt inclusions, respectively. This experimental study investigates the possibility that quartz-hosted rhyolitic melt inclusions may change their composition during laboratory heating under different conditions. Exceptional volatility of Cu and Ag and inert behavior of other metals (Zn, Pb, Mo, Sn, W) and lithophile trace elements at high temperature (850oC) is demonstrated. Heating experiments with melt inclusions require specific conditions that should take the high volatility of Cu and Ag into account. The open system behavior of Cu and Ag can also affect the composition of melt inclusions within the time frame between trapping and eruption

Abstract: A relationship between convergent margin magmas and copper gold ore mineralization has long been recognized(1-6). The nature of the genetic link is controversial, particularly whether the link is due to high-oxygen-fugacity (f(O2)) melts and fluids released from subducted slabs(5-7) or to brine exsolution during magmatic evolution4. For submarine, subduction-related volcanic glasses from the eastern Manus basin, Papua New Guinea, we here report abrupt decreases in gold and copper abundances, coupled with a switch in the behaviour of titanium and iron from concentration increases to decreases as SiO2 rises. We propose that the abrupt depletion in gold and copper results from concurrent sulphur reduction as a result of f(O 2) buffering, causing enhanced formation of copper-gold hydrosulphide complexes that become scavenged from crystallizing melts into cogenetic magmatic aqueous fluids. This process is particularly efficient in oxidized arc magmas with substantial sulphate. We infer that subsequent migration and cooling of exsolved aqueous fluids create links between copper-gold mineralization and arc magmatism in the Manus basin(8,9), and at convergent margins in general(1-6).

Abstract: At the Bajo de la Alumbrera porphyry Cu-Au deposit, NW Argentina, several key textural elements preserve evidence for volatile separation. Interconnected miarolitic cavities, while being studied extensively in granites, have now been recognized in intrusions related to porphyry Cu mineralization. Pods of saccharoidal quartz are connected by narrow, anastomosing zones of graphic quartz-alkali feldspar intergrowths and ragged biotite (with lesser apatite and magnetite). Their connectivity can be as much as 15 cm; however, more commonly, the interconnected miarolitic cavities are approximately 1 to 2 rum across and 5 cm or less, long. Features such comb-quartz layered textures and magmatic-hydrothermal veins (P veins), combined with aqueous fluid phase equilibria from fluid inclusions, better constrain physical models of exsolution. We interpret these textures in the context of vapour phase formation, coalescence and accumulation in an evolving silicic magma. Recognition of textures, such as the interconnected miarolitic cavities reported here, may provide a simple exploration tool for porphyry Cu deposits, helping explorers to recognize evidence for a potentially fertile intrusions.

Abstract: Rhenium and other trace element data were obtained in situ by laser ablation ICP-MS analysis of submarine-erupted volcanic glasses and olivine-hosted melt inclusions from the Valu Fa Ridge, the south tip of the Lau Basin, in the southwestern Pacific Ocean. The chemistry of the Lau Basin basaltic glasses changes systematically from compositions similar to MORB in the Lau Spreading Centers, to more arc-like compositions in the Valu Fa Ridge, providing geochemical profiles both along the Lau Spreading Centers (ridges) and across the Valu Fa Ridge. The east seamount samples of the Valu Fa Ridge have diagnostic trace element ratios (Ba/Nb, Nb/U, Ce/Pb) close to global arc averages, with high Ba/La, indicating addition of considerable amounts of subduction-released fluids. In contrast, samples from the west seamount and the Lau Spreading Centers show a smaller influence from subduction fluids. The variable degrees of subduction influences apparent in the chemistry of these suites provide an ideal means to explore the mechanisms of Re enrichment in undegassed arc magmas. All of the analyzed arc melts have significantly higher Re concentrations than previously published, largely subaerially erupted samples, confirming that high Re is a characteristic of undegassed arc magmas. The east seamount samples are characterized by higher Re and lower Yb/Re than the more MORB-like Lau Spreading Center lavas. The lack of correlation between Yb/Re and Fo of host olivine suggests that low Yb/Re is not due to magmatic differentiation. When the Lau Basin sample suite is plotted together with MORB data, Yb/Re is positively correlated with Ce/Pb and Nb/U, and negatively correlated with Ba/Nb, indicating that Re is much more mobile than Yb during dehydration of subducted slabs. Thus, Re enrichment in arc magmas is likely due to addition of Re via fluids released from subducted slabs; the recognition of high Re in arcs favors arguments for a slab origin of radiogenic Os-187/Os-188 components in arc rocks.

Abstract: Kimberlite magmas, as the deepest probe into Earth's mantle (>150 km), can supply unique information about volatile components (hydrogen, carbon, chlorine, sulfur) in mantle-derived melts and fluids. All known kimberlite rocks are not suitable for studies of mantle volatiles because of their pervasive postmagmatic alteration; however, this study discusses an exceptionally fresh group I kimberlites (<0.5 wt% H2O) from the Udachnaya-East diamondiferous pipe in Siberia. Kimberlite groundmass, in addition to euhedral olivine and calcite, is extremely enriched (at least 8 wt%) in water-soluble alkali chlorides, alkali carbonates, and sulfates (ratio 5:3:1), and often shows immiscibility textures. A primary magmatic origin of alkali chlorides and alkali carbonates is confirmed by the study of strontium isotopes in the water- and dilute acid-leachates of the groundmass (Sr-87/Sr-86 = 0.7069 and 0.7050) that contrast with much more radiogenic isotope composition of the Cambrian platform sedimentary rocks and the Udachnaya-East mine-site brines. Melt inclusions in groundmass olivine, composed of halite, sylvite, alkali-Ca carbonates, phlogopite, olivine, and CO2 fluid, were used to determine the composition and evolution of the kimberlite melt prior to emplacement. Melt inclusions show immiscibility between chloride and carbonate liquids at <600oC in heating stage experiments. The chloride and carbonate enrichment in the kimberlite parental magma suggests the presence of a powerful agent for chemical modifications (metasomatism) in the mantle and crust.

Abstract: Exsolution (unmixing) of the volatile element-rich phases from cooling and crystallising silicate magmas is critical for element transport from the Earth's interior into the atmosphere, hydrosphere, crustal hydrothermal systems, and the formation of orthomagmatic ore deposits. Unmixing is an inherently fugitive phenomenon and melt inclusions (droplets of melt trapped by minerals) provide robust evidence of this process. In this study, melt inclusions in phenocrystic and miarolitic quartz were studied to better understand immiscibility in the final stages of cooling of, and volatile exsolution from, granitic magmas, using the tin-bearing Omsukchan Granite (NE Russia) as an example.Primary magmatic inclusions in quartz phenocrysts demonstrate the coexistence of silicate melt and magma-derived Cl-rich fluids (brine and vapour), and emulsions of these, during crystallisation of the granite magma. Microthermometric experiments, in conjunction with PIXE and other analytical techniques, disclose extreme heterogeneity in the composition of the non-silicate phases, even in fluid globules within the same silicate melt inclusion. We suggest that the observed variability is a consequence of strong chemical heterogeneity in the residual silicate-melt/brine/vapour system on a local scale, owing to crystallisation, immiscibility and failure of individual phases to re-equilibrate. The possible evolution of non-silicate volatile magmatic phases into more typical "hydrothermal" chloride solutions was examined using inclusions in quartz from associated miarolitic cavities.

Abstract: The Baffin Island picrites are highly magnesian (less than or equal to22 wt% MgO) olivine tholeiites, erupted through felsic continental crust. Plots of most major and minor element oxides against MgO for the lavas define very tight trends consistent with modi. cation of melts parental to the erupted suite by olivine fractionation or accumulation. However, melt inclusions trapped in primitive olivine phenocrysts in these lavas have much more diverse compositions. After correction for post-entrapment modi. cation, the inclusions are systematically slightly lower in Al2O3, and significantly higher in SiO2, K2O and P2O5 than the lavas' fractionation trends. CaO, Na2O and TiO2 contents lie within the lavas' fractionation trends. Similarly, most inclusions are higher in Sr/Nd, K/Nb, Rb/Ba, Rb/Sr, U/Nb and Ba/Th than the lavas. These characteristics resulted from up to approximate to 15% contamination of evolving picritic-basaltic liquids by locally-derived, broadly granitic partial melts of the quartz + feldspar-rich crust through which the picrites erupted. Contamination was minor in the bulk lavas (< 1%), suggesting that the inclusions' compositions partly reflect a link between wall rock reaction and precipitation of liquidus olivine. Rapid crystallisation of liquidus olivine from the picrites, along with melting of felsic crustal wall rocks of magma chambers or conduits, were likely during emplacement of hot picritic magmas into cooler felsic crust. Inclusion compositions may thus reflect mixing trends or may be constrained to phase boundaries between olivine and a phase being resorbed, for example, an olivine-plagioclase cotectic. The extent of contamination was probably a complex function of diffusion rates of components in the magmas, and phenocryst growth rates and proximity to wall rock. These results bear on the common observation that melt inclusions' compositions are frequently more heterogeneous than those of the lavas that host them.

Abstract: The eastern coast of King Island in southeastern Australia exposes a thick, well-preserved sequence of latest Neoproterozoic volcanic, and related shallow intrusive rocks. These rocks are associated with shallow marine carbonates and siltstones and pass up into massive conglomerates representing a marine flooding event and unconformity, during continental break-up and subsequent volcanic passive margin formation. Unusual differentiated sills (Grimes Intrusive suite) with extreme internal variation (wehrlite to andesite compositions) intrude deformed Proterozoic metasediments of the Rodinian basement. A thin, basal tholeiitic basaltic volcanic unit (City of Melbourne Volcanics) is less contaminated than the underlying sills, and preceded eruption of a thick sequence of highly depleted picritic pillows, sub-aerial flows and hyaloclastites (Shower Droplet Volcanics). The picrite sequence is overlain by thick tholeiitic basalts and reworked volcanogenic conglomerates (Bold Head Formation) that show a strong compositional similarity to enriched mid ocean ridge basalts. Both the picrites and the upper tholeiitic basalts are not crustally contaminated and have an Nd-Sm isochron age of 579 +/- 16 Ma with initial epsilonNd of +4.2. The lithostratigraphy and range of compositions represented are analogous to early magmatism associated with continental break-up and volcanic passive margin formation, including voluminous Seaward Dipping Reflector Sequences, in the Mesozoic North Atlantic volcanic margins.

Abstract: Variations in the Os-187/Os-188 isotopic signature of mantle and mantle-derived rocks have been thought to provide a powerful chemical tracer of deep Earth structure. Many studies have inferred from such data that a long-lived, high-rhenium component exists in the deep mantle (Re-187 is the parent isotope decaying to Os-187, with a half-life of similar to42 billion years), and that this reservoir probably consists of subducted oceanic crust(1-3). The interpretation of these isotopic signatures is, however, dependent on accurate estimates of rhenium and osmium concentrations in all of the main geochemical reservoirs, and the crust has generally been considered to be a minor contributor to such global budgets. In contrast, we here present observations of high rhenium concentrations and low Yb/Re ratios in arc-type melt inclusions. These results indicate strong enrichment of rhenium in undegassed arc rocks, and consequently the continental crust, which results in a crustal estimate of ~2p.p.b. rhenium, as compared to previous estimates of 0.4-0.2p.p.b. (refs 4, 5). Previous determinations of rhenium in arc materials, which were largely measured on subaerially erupted samples, are likely to be in error owing to rhenium loss during degassing. High mantle-to-crust rhenium fluxes, as observed here, require a revaluation of geochemical models based on the Re-187-Os-187 decay system(1-3).

Abstract: At a porphyry copper-gold deposit in Bajo de la Alumbrera, Argentina, silicate melt inclusions coexist with hypersaline liquid- and vapor-rich inclusions in the earliest magmatic-hydrothermal quartz veins. Copper concentrations of the hypersaline liquid and vapor inclusions reached maxima of 10.0 weight % (wt %) and 4.5 wt %, respectively. These unusually copper-rich inclusions are considered to be the most primitive ore fluid found thus far. Their preservation with coexisting melt allows for the direct quantification of important oreforming processes, including determination of bulk partition coefficients of metals from magma into ore-forming magmatic volatile phases.

Abstract: Olivine-hosted melt inclusions in tholeiitic picrites from five Hawaiian volcanoes (Koolau, Mauna Loa, Kilauea, Loihi, and Hualalai) have major and trace element compositions that illustrate the magmatic characteristics of ocean island volcanoes and the nature of mantle plumes. The geochemistry of these melt inclusions reflects the well known geochemical features that distinguish Hawaiian shield volcanoes, but with considerably greater diversity than whole rock compositions, providing a higher resolution of the magmatic processes contributing to Hawaiian plume magamatism. Naturally quenched inclusions from Kilauea, Mauna Loa, and Hualalai have been modified by crystallization of olivine on the walls of the inclusion and diffusive interaction with the host crystal. In contrast, melt inclusions in two Loihi picrites have not been affected by re-equilibration with their host olivines, reflecting a relatively brief interval between crystallization of the olivines and eruption of these lavas. Corrected major element compositions of experimentally melted inclusions from two Koolau picritic tholeiites are similar to those of erupted lavas from this volcano and document the presence of Koolau melts with at least 14% MgO. Trace element characteristics of melt inclusions from Mauna Loa, Kilauea, and Loihi can be produced by melting of a moderately depleted, garnet lherzolite source. The extent of melting generally increases from Loihi < Kilauea < Mauna Loa, although rare inclusions from Mauna Loa also indicate contributions of relatively small degree (2-4%) melts to these lavas. Extent of melting and isotopically defined source components appear to be linked in the melting regime, with the Mauna Loa component being sampled preferentially at larger degrees of melting. Melt inclusions with trace element characteristics indicating a recycled basaltic eclogite source were not found at Mauna Loa or any of the other volcanoes. Compositions of the Koolau inclusions do require a unique source component, however, possibly reflecting contributions from ancient lithosphere, either within the plume or entrained in the upper mantle.

Abstract: Slamet Volcano, in Central Java, Indonesia, is an active calc-alkaline stratovolcano composed largely of basalts and basaltic andesites. The phenocryst mineralogy of the most magnesian basalts (MgO > 7 wt%) has been studied in detail to investigate the nature of early magmatic processes in a large arc volcano. On the basis of stratigraphy, mineralogy, petrography and geochemistry, the studied basalts are subdivided in two groups; Old Slamet (OS) and New Slamet (NS). Olivine in the OS basalts is within the range Fo(92-65) and shows a homogenous composition distribution, with a significant proportion of crystal cores near equilibrium with whole-rock compositions. However, distinct high- and low-Ni sub-populations may be distinguished at any given Fo content (e.g. 0.25-0.10% and 0.32-0.27 wt% NiO for the low- and high-NiO sub-populations respectively at Fo(85)). Chromian spinel inclusions within the high-NiO olivines have higher Cr# (75-80) and Fe2+/Fe3+ ratio (2.6-3.2) and lower TiO2 (0.23-0.44 wt%) contents than those within low-NiO olivines (Cr# 58-77, Fe2+/Fe3+ 1.3-2.5 and TiO2 0.73-0.91 wt%). Plagioclase and pyroxene phenocrysts display dominantly oscillatory zoning, with cores close to equilibrium with whole-rock compositions. Olivine in the NS basalts is within the range Fo(90-61) and shows a discontinuous distribution of composition including two principal peaks: the first is similar toFo(78-90), close to expected equilibrium compositions; the second is similar toFo(62-70), clearly too Fe-rich to be in equilibrium with whole-rock compositions and composed mainly of reversely zoned crystals. In terms of NiO content, a single (low-Ni) sub-population is observed. Chromian spinel inclusions with high Cr# and Fe2+/Fe3+ ratio and low TiO2 are not observed within the olivines of these basalts. Plagioclase and pyroxene phenocrysts are typically reversely zoned and display ubiquitous disequilibrium textures. The cores of these crystals are not in equilibrium with host basalt compositions. The mineralogy of these basalts indicates that the OS basalts resulted from mixing between two parental magmas produced from contrasted sources, probably a relatively depleted and H2O-poor harzburgite and a less depleted and more hydrated harzburgite to lherzolite. Subsequent evolution occurred in a magmatic system in which variations in volatile contents and/or temperature played a more important role than magma mixing. The NS basalts were produced from the less depleted source only, but magmas interacted extensively with remnants of earlier crystal mush/magma batches. Open-system processes operated early in the life of all these magmas, and influenced their geochemistry. Magma mixing was ubiquitous process and together with fractional crystallisation controlled the evolution of the basaltic magmas of Slamet Volcano.

Abstract: The composition of primary magmas and their mantle sources can be successfully inferred from the study of melt inclusions trapped in spinel phenocrysts. This is particularly true in the case of severely altered rocks, in which spinel and spinel-hosted melt inclusions usually retain primary magmatic information. We report the results of the study of melt inclusions in high-Cr (Cr# 90-95), primitive (Mg# 65-78) spinel in the Palaeocene low-Ca boninites from Cape Vogel, Papua New Guinea. Melt inclusions are represented by the aggregate of skeletal olivine crystals in the residual glass. Raster beam electron Microprobe analyses of melt inclusions demonstrated that they are broadly similar in composition to primitive orthopyroxene and to the most primitive boninites in this area, having (in wt.%): very high MgO (18-30), SiO2 (53-61) and very low TiO2 (0.04-0.19), Al2O(3) (3-9), CaO (2-4), Na2O (<0.9), K2O (0.05-0.15) and CaO/Al2O3 (0.4-0.6). H2O abundances in melt inclusions, analysed by an ion probe, are very high (1-2 wt.%), and they could have been even higher (similar to3.5 wt.%) if the melts lost H2O before crystallisation. Trace elements in melt inclusions, analysed by laser ablation ICPMS, have exceptional depletion in HREE (<1 PM) and significant enrichment in LREE over HREE (La/Yb 5-12), and Ph (Ce/Pb 2-12) and Zr (Zr-N/Sm-N 2-3.4) over REE. The compositions of melt inclusions correlate well with the compositions of host spinel showing the fractionation path of initial ultramafic melt. Cape Vogel primary melts could have originated from melting of extremely refractory hot (> 1500 oC) harzburgitic mantle fluxed by subduction-related, H2O-bearing enriched components. Trace element composition of these enriched components is estimated from melt inclusion compositions by mass balance calculations.

Abstract: Magma-derived fluids are important in geologic processes (e.g., metal sequestration and ore deposition) but are intrinsically transient. Samples of magmatic fluids represented by fluid inclusions in a single zoned quartz crystal from a miarolitic cavity within a porphyritic leucogranite hosting the Industrialnoe tin deposit, northeastern Russia, were studied by using modern in situ analytical methods (laser Raman spectroscopy, proton-induced X-ray emission). The fluid inclusions are either dominated by vapor or by complex multiphase brines. The inclusions within a given trapping plane have similar phase relationships; however, there are significant variations between inclusions in different healed fractures. Phase and chemical compositions of individual brine inclusions demonstrate significant compositional heterogeneity (in terms of absolute element concentrations and ratios) of high-temperature magmatic fluids accumulated in the miarolitic cavity. This finding suggests that fluids leaving a crystallizing magma may have variable initial compositions that are subsequently modified by reactions with the rocks while the fluid is in transit to a miarolitic cavity, as well as by processes in the cavity, such as mixing, crystallization, and boiling. The inferred chemical diversity and fractionation of granite-derived fluids at near-magmatic conditions imply that fluids entering a cooler hydrothermal system are extremely complex and their metallogenic signature may differ from that of related ore deposits.

Abstract: Hypotheses for the formation of many types of hydrothermal ore deposits often involve the direct contribution of magma-related fluids (e.g., Cu-Mo-Au porphyries) or their superimposition on barren hydrothermal cells (e.g., volcanic-hosted massive sulfide deposits). However, the chemical and phase compositions of such fluids remain largely unknown. We report preliminary results of a comprehensive study of fluid bubbles trapped inside glassy melt inclusions in primitive olivine phenocrysts and pillow-rim glasses from basaltic magmas from different tectonic environments, including mid-ocean ridges (Macquarie Island, SW Pacific and Mid-Atlantic Ridge 43°N Fracture Zone), ocean islands (Hawaii) and a variety of modern and ancient backarc-island arc settings (eastern Manus Basin, Okinawa and Vanuatu Troughs, Troodos, New Caledonia and Hunter Ridge-Hunter Fracture Zone). Fluid bubbles from all localities, studied using electron microscopy with EDS and laser Raman spectroscopy, are composed of CO2-(± H2O ± sulfur)-bearing vapor and contain significant amounts of amorphous (Na-K-Ca-Fe alumino-silicates and dissorded carbon) and crystalline phases. The crystals are represented mainly by carbonates (magnesite, calcite, ankerite, dolomite, siderite, nahcolite and rhodochrosite), sulfates (anhydrite, gypsum, barite and anglesite), and sulfides (pyrite, arsenopyrite, chalcopyrite and marcasite), though other minerals (brukite, apatite, halite, clinoenstatite, kalsilite, nepheline, amphibole and mica) may occur as well. We argue that chemical components (e.g., C, H, S, Cl, Si, Al, Na, K, Fe, Mn, Cr, Ca, Mg, Ba, Pb and Cu) that later formed precipitates in fluid bubbles were originally dissolved in the magmatic fluid, and were not supplied by host glasses or phenocrysts after entrapment. Magma-related fluid rich in dissolved metals and other non-volatile elements may be a potential precursor to ore-forming solutions.

Abstract: The effects of source composition and source evolution during progressive partial melting on the chemistry of mantle-derived mid-ocean ridge basalt (MORB) melts were tested using a comprehensive geochemical and Sr-Nd-Pb isotopic dataset for fresh, magnesian basaltic glasses from the Miocene Macquarie Island ophiolite, SW Pacific. These glasses: (1) exhibit clear parent-daughter relationships; (2) allow simple reconstruction of primary melt compositions; (3) show exceptional compositional diversity (e.g. K2O/TiO2 0.09-0.9; La/Yb 1.5-22; Pb-206/Pb-204 18.70-19.52); (4) preserve changes in major element and isotope compositions, which are correlated with the degree of trace element enrichment (e.g. La/Sm). Conventional models for MORB genesis invoke melting of mantle that is heterogeneous on a small scale, followed by binary mixing of variably lithophile element-enriched melt batches. This type of model fails to explain the compositions of the Macquarie Island glasses, principally because incompatible element ratios (e.g. Nb/U, Sr/Nd) and Pb isotope ratios vary non-systematically with the degree of enrichment. We propose that individual melt batches are produced from instantaneous 'parental' mantle parageneses, which change continuously as melting and melt extraction proceeds. This concept of a 'dynamic source' combines the models of small-scale mantle heterogeneities and fractional melting. A dynamic source is an assemblage of locally equilibrated mantle solids and a related melt fraction. Common MORB magmas that integrate the characteristics of numerous melt batches therefore tend to conceal the chemical and isotopic identity of a dynamic source. This study shows that isotope ratios of poorly mixed MORB melts are a complex function of the dynamic source evolution, and that the range in isotope ratios within a single MORB suite does not necessarily require mixing of diverse components.

Abstract: Compositions of ~2500 spinel-olivine pairs and 400 melt inclusion-spinel pairs have been analysed from 36 igneous suites from oceanic, arc and intraplate tectonic settings. Our data confirm that Cr-spinel mg-number is largely controlled by melt composition, but also influenced by octahedral site substitutions, and rate of cooling. Lavas quenched in submarine environments tend to have higher mg-number at a given cr-number than slowly cooled subaerial lavas and peridotites. Unlike mg-number, Cr-spinel Al2O3 and TiO2 contents show good correlations with melt composition, with only limited post-entrapment modifications. Out data suggest that increased activity of Al2O3 decreases the partitioning of TiO2 into spinels. The Al2O3 content of Cr-spinel is a useful guide to the degree of partial melting of mantle peridotites; however, this same relationship is obscured in volcanic rocks. Al2O3 contents of volcanic Cr-spinels are mostly determined by melt composition rather than mantle source composition. The data also suggest that most spinels from residual mantle peridotites can be readily differentiated from those hosted in volcanic rocks. Mantle peridotite spinel tend to have lower TiO2 and higher Fe2+/Fe3+ ratios than spinel from volcanic rocks. The spinel compositions in our database can be subdivided on the basis of tectonic setting and mode of occurrence using an Al2O3 vs TiO2 diagram. A total of seven fields can be distinguished with varying degrees of overlap. This diagram can then be used to determine the tectonic setting of spinel from altered mafic igneous rocks such as serpentinites or meta-basalts, or detrital spinel in sandstones.

Abstract: Dredged glass from the southern Mid-Atlantic Ridge near the Bouvet Triple Junction has unique major element, trace element, and isotopic composition, distinct from typical mid-ocean ridge basalts, It is a high-Mg (Mg# 67.8), high-Ni (NiO 290 ppm) andesite depleted in highly incompatible and heavy rare-earth elements with an isotopic signature of ancient continental lithosphere (i.e., low (206)Pb/(204)Pb and Nd-143/Nd-144 and high Sr-87/Sr-86 and delta O-18). The origin of this glass is attributed to melting of a Precambrian garnet-bearing, mafic lithology, possibly related to lower crustal blocks stranded in the upper mantle during breakup of Gondwana and opening of the Atlantic. This composition can be used to explain anomalous geochemical features of oceanic rocks in the Southern Hemisphere.

Abstract: The large range of chemical variation within intimately associated highly magnesian volcanic rocks in the Palaeoproterozoic Central Lapland Greenstone Belt prompted the construction of a new classification scheme for MgO-rich volcanic rocks, based on an [Al2O3] vs [TiO2] diagram where the axes are the Al2O3 and TiO2 contents (in mole proportions) of the rocks projected from the olivine composition. This diagram places the Lapland rocks in the fields of Ti-enriched komatiites and picrites. Komatiitic rocks are depleted in both light and heavy rare earth elements (LREE and HREE) relative to middle REE (MREE) and possess relatively high TiO2 even in the most LREE-depleted varieties, whereas picritic rocks approach geochemically Hawaiian picrites. Seven clinopyroxene and whole-rock pairs analysed for Sm Nd isotopes yield an average age of 2056 +/- 25 Ma for the komatiites. Uncontaminated komatiites and picrites have similar positive epsilon (Nd) values (+4) indicating generation from a mantle source with a long-term depletion in LREE and relative to MREE. Geochemical characteristics of the komatiite-picrite association, including REE and Nb/Y Zr/Y systematics, indicate chemical heterogeneities in the source region, which seem to have been created by complex depletion and enrichment processes shortly before or elated to a dynamic melting process. The high MgO contents of the rocks coupled with chemical similarity between the Lapland and Hawaiian picrites supports a mantle plume model for their genesis. Nevertheless, the geotectonic evolution appears to have proceeded without significant regional uplift shortly before volcanism.

Abstract: The eastern Manus Basin is an actively forming backarc extensional zone behind the New Britain Island are, which hosts a number of submarine volcanic edifices and hydrothermal fields. Isotopic and trace element geochemical characteristics of the edifices are comparable with those of the adjacent subaerial New Britain are, and differ significantly from those of MORE-like lavas on and near the Manus Spreading Ridge in the central part of the basin. Fractional crystallisation dominates magma evolution from primitive basalts to andesites, dacites and rhyodacites in the eastern Manus Basin, but several lineages with differing trace element enrichment have been delineated. Melt inclusions within olivine phenocrysts (Fo(82-92)) Of two representative east Manus basalts, respectively, with modest (0.2 wt%) and high (0.8 wt%) potassium contents, host ubiquitous CO2-bearing vapour bubbles, denoting presence of an immiscible fluid phase at early stages of crystallisation. Bubbles often carry precipitate phases whose abundance is broadly proportional to the bubble size reaching a maximum in fluid bubbles with little or no melt. Among the precipitates, detected by laser Raman spectroscopy and EDS-scanning electron microscopy, carbonates are common and include magnesite, calcite, ankerite, rhodochrosite and nahcolite (NaHCO3). Gypsum, anhydrite, barite, anglesite, pyrite, and chalcopyrite have also been found. Some amorphous precipitates recrystallise after bubbles are opened to Na-Ca carbonates, halite and Na-K-Ca alumine-silicates. Copper abundances decrease from basalt to dacite across the eastern Manus fractionation spectrum, whereas Pb behaves as an incompatible element, increasing to highest values in the dacites. Zinc abundance reaches maximum concentrations in andesite, and decreases during further fractionation. Loss of Cu especially from the fractionating magmas, in the absence of immiscible sulphide liquid, strongly implies metal partitioning into CO2-H2O fluid, which is degassed significantly during magma fractionation. Hydrothermal fluids in the PACMANUS system may carry a direct contribution of the magmatic metal-bearing fluid, exsolved from the crystallising are-like magmas at this immature backarc basin, and are able to transport and concentrate major amounts of ore metals, particularly Cu.

Abstract: Taiwan is an active mountain belt formed by oblique collision between the Luzon are and the Asian continent. Regardless of the ongoing collision in central and southern Taiwan, a post-collisional extension regime has developed since the Plio-Pleistocene in the northern part of this orogen, and led to generation of the Northern Taiwan Volcanic Zone. Emplaced at similar to0.2 Ma in the southwest of the Volcanic Zone, lavas from the Tsaolingshan volcano are highly magnesian (MgO approximate to 15 wt.%) and potassic (K2O approximate to 5 wt.%, K2O/Na2O approximate to 1.6-3.0). Whereas these basic rocks (SiO2 approximate to 48 wt.%) have relatively low Al2O3 approximate to 12 wt.%, total Fe2O3 approximate to 7.5 wt.% and CaO approximate to 7.2 wt.%, they are extremely enriched in large ion lithophile elements (LILE, e.g. Cs, Rb, Ba, Th and U). The Rb and Cs abundances, > 1000 and 120 ppm, respectively, are among the highest known from terrestrial rocks. In addition, these rocks are enriched in light rare earth elements (LREE), depleted in high Field strength elements (HFSE), and display a positive Pb spike in the primitive mantle-normalized variation diagram. Their REE distribution patterns mark with slight Eu negative anomalies (Eu/Eu * approximate to 0.90 - 0.84), and Sr and Nd isotope ratios are uniform (Sr-87/Sr-86 approximate to 0.70540-0.70551; Nd-143/(144) Nd approximate to 0.51268-0.51259). Olivine, the major phenocryst phase, shows high Fo contents (90.4 +/- 1.8; 1 sigma deviation), which are in agreement with the whole rock Mg-values (83 - 80). Spinel inclusions in olivine are characterized by high Cr/Cr+Al ratios (0.94-0.82) and have compositions similar to those from boninites that originate from highly refractory peridotites. Such petrochemical characteristics are comparable to the Group I ultrapotassic rocks defined by Foley et al. [Earth-Sci. Rev. 24 (1987) 81], such as orogenic lamproites from central Italy, Span and Tibet, We therefore suggest that the Tsaolingshan lavas resulted from a phlogopite-bearing harzburgitic source in the lithospheric mantle that underwent a recent metasomatism by the nearby Ryukyu subduction zone processes. The lavas exhibit unique incompatible trace element ratios, with Rb/Cs approximate to 8, Ba/Rb approximate to 1, Ce/Pb approximate to 2, Th/U approximate to 1 and Nb/ U approximate to 0.8, which are significantly lower than the continental crust values and those of most mantle-derived magmas. Nonmagmatic enrichment in the mantle source is therefore required. Based on published experimental data, two subduction-related metasomatic components, i.e., slab-released hydrous fluid and subducted sediment, are proposed, and the former is considered to be more pervasive for causing the extraordinary trace element ratios observed. Our observations lend support to the notion that dehydration from subducting slabs at convergent margins, as a continuing process through geologic time, can account for the fractionation of these elemental pairs between the Earth's crust and mantle

Abstract: The 5.2 to 3.9 Ma late porphyries at Rio Blanco are spatially associated with hydrothermal tourmaline-cemented breccias and a significant Cu-Mo deposit. Magmatic inclusions in quartz from these rocks are used to better Understand late-stage magmatic processes, particularly those involving melt-melt and melt-fluid immiscibility. Inclusions are represented by glass of common rhyolitic composition (hereafter, type 1), crystallized volatile-rich felsic melt (type 2) H2O- and salt-rich fluids, and microphenocrysts. Coexistence of types 1 and 2 material, within the same growth plane. and within a single inclusion, suggests that crystallizing rhyolitic magma separated into two silicate melts (volatile-poor and volatile-rich). The volatile-rich silicate melt had a prolonged evolution, extending below the solidus of volatile-poor silicate melt, with a progressive reduction of the silicate/volatile ratio, and ultimately to highly saline fluids. The latter may have been the source of hydrothermal fluids that had the potential to transport metals. The occurrence of immiscibility in the Rio Blanco rhyolites may be in some ways comparable to that in volatile-rich pegmatites and strongly suggests that this process may be common in other se normal felsic magmas and important in the origin of mineralized porphyries

Abstract: Foid-bearing syenites and endoskarn xenoliths of the A.D. 472 Vesuvius eruption represent the magma chamber-carbonate wall-rock interface. Melt inclusions hosted in crystals from these rocks offer a rare opportunity to depict the formation and the composition of metasomatic skarn-forming fluids at the peripheral part of a growing K-alkaline magma chamber disrupted by an explosive eruption. Four principal types of melt inclusions represent highly differentiated phonolite (type 1), hydrosaline melt (type 3), unmixed silicate-salt melts (type 2), and a complex chloride-carbonate melt with minor sulfates (type 4). The high-temperature (700-800oC) magmatic-derived hydrosaline melt is considered to be the main metasomatic agent for the skarn-forming reactions. The interaction between this melt (fluid) and carbonate wall rocks produces a Na-K-Ca carbonate-chloride melt that shows immiscibility between carbonate and chloride constituents at ~700oC in 1 atm experiments. This unmixing can be viewed as a possible mechanism for the origin of carbonatites associated with intrusion-related skarn systems.

Abstract: Part of the Mesoproterozoic (1.6 Ga) Gawler Range Volcanics in South Australia is composed of mingled feldspar- quartz- phyric dacite, rhyodacite and rhyolite lavas. Field relationships suggest that dacite erupted first, locally grading into rhyodacite, followed by mingled dacite and rhyolite or rhyodacite and rhyolite, and finally in some areas rhyolite, and imply that the three lithofacies co-existed in a compositionally stratified magma chamber. Data on the bulk rock, groundmass and melt inclusion compositions suggest that post-eruption alteration has had very little effect on the original rock compositions. Melt inclusions in quartz from rhyolite and rhyodacite-dacite, respectively, belong to two compositional populations. Inclusions in the rhyolitic quartz have less evolved compositions with lower SiO2 (72-76.4wt%) and higher Al2O3 (13.2-15.6wt%) and Na2O (2.5-4.2wt%) abundances. In contrast, melt inclusions in quartz from the rhyodacite-dacite are more "evolved" (i.e., 75.5-78.3 wt% SiO2, 11.2-12.7 wt% Al2O3 and 1.7-2.2 wt% Na2O). The two melt populations define a single compositional trend towards groundmass compositions, which are essentially similar in all three lithofacies (77.8-80.5 wt% SiO2, 9.9-11.1 wt% Al2O3 and 2.2-2.4 wt% Na2O). This trend is consistent with the derivation of the groundmass melt from a single precursor melt of rhyolitic composition by means of crystallisation of dominant plagioclase, K-feldspar and minor quartz. Plagioclase-enriched dacite-rhyodacite magma comprises a mixture of the residual melt and plagioclase phenocrysts that accumulated in the upper part of the magma chamber and erupted first. Similar residual melt containing quartz and K-feldspar phenocrysts was present deeper in the magma chamber and erupted later to form quartz-, K-feldspar-phyric rhyolite.

Abstract: Macquarie Island is an exposure above sea-level of part of the crest of the Macquarie Ridge. The ridge marks the Australia-Pacific plate boundary south of New Zealand, where the plate boundary has evolved progressively since Eocene times from an oceanic spreading system into a system of long transform faults linked by short spreading segments, and currently into a right-lateral strike-slip plate boundary. The rocks of Macquarie Island were formed during spreading at this plate boundary in Miocene times, and include intrusive rocks (mantle and cumulate peridotites, gabbros, sheeted dolerite dyke complexes), volcanic rocks (N- to E-MORB pillow lavas, picrites, breccias, hyaloclastites), and associated sediments. A set of Macquarie Island basaltic glasses has been analysed by electron microprobe for major elements, S, Cl and F; by Fourier transform infrared spectroscopy for H2O; by laser ablation-inductively coupled plasma mass spectrometry for trace elements; and by secondary ion mass spectrometry for Sr, Nd and Pb isotopes. An outstanding compositional feature of the data set (47.4-51.1 wt % SiO2, 5.65-8.75 wt % MgO) is the broad range of K2O (0.1-1.8 wt %) and the strong positive covariation of K2O with other incompatible minor and trace elements (e.g TiO2 0.97-2.1%; Na2O 2.4-4.3%; P2O5 0.08-0.7%; H2O 0.25-1.5%; La 4.3-46.6 ppm). The extent of enrichment in incompatible elements in glasses correlates positively with isotopic rations of Sr (Sr-87/Sr-86 = 0.70255-0.70275) and Pb (Pb-206/Pb-204 = 18.951-19.493; Pb-207/Pb-204 = 15.528-15.589; Pb-208/Pb-204 = 38.523-38.979), and negatively with Nd (Nd-143/Nd-144 = 0.51310-0.51304). Macquarie Island basaltic glasses are divided into two compositional groups according to their mg-number-K2O relationships. Near-primitive basaltic glasses (Group I) have the highest mg-number (63-69), and high Al2O3 and CaO contents at a given K2O content, and carry microphenocrysts of primitive olivine (Fo(86-89.5)). Their bulk compositions are used to calculate primary melt compositions in equilibrium with the most magnesian Macquarie Island olivines (Fo(90.5)). Fractionated, Group II, basaltic glasses are saturated with olivine + plagioclase +/- clinopyroxene, and have lower mg-number (57-67), and relatively low Al2O3 and CaO contents. Group I glasses define a seriate variation within the compositional spectrum of MORB, and extend the compositional range from N-MORB compositions to enriched compositions that represent a new primitive enriched MORB end-member. Compared with N-MORB, this new end-member is characterized by relatively low contents of MgO, FeO, SiO2 and CaO, coupled with high contents of Al2O3, TiO2, Na2O, P2O5, K2O and incompatible trace elements, and has the most radiogenic Sr and Pb regional isotope composition. These unusual melt compositions could have been generated by low-degree partial melting of an enriched mantle peridotite source, and were erupted without significant mixing with common N-MORB magmas. The mantle in the Macquarie Island region must have been enriched and heterogeneous on a very fine scale.We suggest that the mantle enrichment implicated in this study is more likely to be a regional signature that is shared by the Balleny Islands magmatism than directly related to the hypothetical Balleny plume itself.

Abstract: Detrital spinel is a widespread heavy mineral in sandstones from the Maastrichtian-Middle Eocene sedimentary basins in the SE Alps. Chemistry of detrital spinels from the Claut/Clauzetto and Julian Basins (N Italy and NW Slovenia) is used to constrain petrological and geochemical affinities and tectonic provenance of the source rocks. In addition, we have analysed melt inclusion compositions in the detrital volcanic spinels to better constrain the nature of their parental magmas. This is the first study of melt inclusions in detrital spinels. Two principal compositional groups of detrital spinels are recognised based on their TiO2 and Fe2+/Fe3+; one derived from peridotites, the other from basaltic volcanics. Peridotitic spinels are more abundant and have TiO2 < 0.2 wt% and high Cr/Cr + Al(40-90), characteristic of suprasubduction zone harzburgites. Significant chemical variations among volcanic spinels (TiO2 up to 3 wt%, Al2O3 12-44 wt%) suggest multiple sources, with geochemically distinct characteristics, including MORE-type and backarc basin basalts, subduction-related magmas and tholeiites produced during early continental rifting. Compositions of homogenised melt inclusions in spinels with TiO2 > 0.2 better distinguish the differences between the compositions of their host spinels and help to further clarify the geodynamic provenance of extrusive source rocks. Several compositional groups of melt inclusions have been recognised and represent diverse magmatism of marginal basins, including MORB- and subduction-related geochemical types, as well as magmas characteristic of early continental rifting. These results, combined with the data on regional ophiolitic complexes and tectonic reconstructions favour the Internal Dinarides of Yugoslavia as a possible source area for the SE Alps sediments.

Abstract: Immiscible phases derived from degassing silicate magmas are considered to be precursors of metal-bearing hydrothermal fluids in porphyry deposits. The development of melt-inclusion techniques provides a window into this critical period of porphyry formation, when the cooling, decompression, and crystallization of silicate melts result in the formation of immiscible phases. The record of magmatic to hydrothermal evolution is presented using inclusions in clinopyroxene phenocrysts from the syenitic Balut dike, one of the host-rock lithologies for mineralization at the Dinkidi Cu-Au porphyry deposit, Philippines. Primary inclusions include silicate glass, multiphase aggregates comprising salts, silicates, sulfates, carbonates, sulfides and oxides, and highly saline aqueous fluids. Various analyses, including in situ laser ablation inductively coupled plasma-mass spectrometry of the multiphase inclusions, determined elevated concentrations of Cl, S, As, Tl, K, Na, and a number of metals, including those that form ore-grade deposits (e.g., Cu) and those that do not (e.g., Mo, Pb, Zn, and W) at the Dinkidi porphyry deposit. Silicate melt and multiphase salt-rich inclusions in clinopyroxene are interpreted as having originally formed as immiscible phases at magmatic temperatures.

Abstract: The Banska Stiavnica Au-Ag base metals epithermal deposit is hosted within a Neogene-age volcanic caldera in central Slovakia. The caldera comprises a central granodiorite stock that has been capped by comagmatic andesite and rhyolite extrusions. The intrusive felsic rocks possess a close spatial and temporal relationship with the mineralization and associated hydrothermal alteration. To investigate the possible genetic link between magmatic and hydrothermal activity paragenetically constrained melt and fluid inclusions in magmatic quartz and vein minerals were studied, using microthermometric techniques. Primary melt inclusions in magmatic quartz from the granodiorite vary in composition from essentially silicate H2O- and Cl-rich melt with low-salinity fluid (8.3-9.6 wt % NaCl equiv) to high-density hypersaline brines (similar to 80 wt % NaCl equiv). Salinities of secondary fluid inclusions in magmatic quartz systematically decrease along the NaCl saturation curve toward lower temperatures and salinities equivalent to those determined for primary fluid inclusions in sphalerite and vein minerals (quartz, barite, fluorite) within the deposit (<400 degrees C, <12 wt % NaCl equiv). This systematic evolution in measured and calculated characteristics (temperature, pressure, salinity, and density) of the studied fluid inclusions indicates that exsolved magmatic brines and aqueous chloride solutions were the primitive precursors to the hydrothermal ore-forming fluids that produced epithermal mineralization upon mixing with meteoric waters in the near-surface environment.

Abstract: Siliceous, aluminous and alkali-rich glasses, commonly found in patches and veins in spinel peridotite xenoliths, have been attributed to a number of different origins. These include low-degree primary melts of the mantle, exotic metasomatic melts influxing into the lithosphere, or breakdown of amphibole, and other phases during high-temperature transport of the xenoliths to the surface in their host magmas. We present new laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of trace element abundances in glasses, and in metasomatically introduced phases (clinopyroxene, amphibole, phlogopite, apatite) from a suite of spinel wehrlite, Iherzolite and harzburgite xenoliths from southeastern Australia. The majority of glass compositions are best explained by melting of amphibole (usually complete, as amphibole is now absent from most samples) with varying but significant contributions from partial melting of clinopyroxene. However, some glasses require additional components derived from partial or complete modal melting of phlogopite, or apatite. The data confirm our earlier model, that the glass present in patches in these samples derives from high-temperature, transport-related breakdown of a metasomatic phase assemblage (amphibole + clinopyroxene + phlogopite + apatite) present in the xenoliths prior to their entrainment in the host magmas

Abstract: Olivine-hosted homogenized melt inclusions in a primitive basalt AII32-12-7 from 43oN Mid-Atlantic Ridge have magnesian basalt compositions (10-12 wt% MgO) with high CaO (13.2-15.2 wt%), relatively low Al2O3 (12.8-15.5 wt%), and form a linear array that ranges to extremely high CaO/Al2O3 values (0.8-1.2). These melt compositions are unusual for MORB, as is the observed phenocryst assemblage, which comprises primitive olivine (Fo(87-92) with up to 0.45 wt% CaO), Cr-diopside (Mg# 90-92), and Cr-rich spinel (Cr# 50-70) and directly reflects these melt compositions. The melt compositional array extends from peridotite-saturated compositions formed near 1 GPa to lie well within the clinopyroxene phase volume, or possibly along a clinopyroxene + olivine phase boundary. We interpret the array as either the product of melt-wallrock reaction between a I GPa MORB melt and a clinopyroxene-rich lithology (wehrlite or clinopyroxenite), or of mixing between melt fractions derived separately from these distinct lithologies (i.e. peridotite and clinopyroxenite/wehrlite). Derivation of the melt array from a conventional mantle peridotite source, possibly involving fractional melting near or beyond the point of clinopyroxene exhaustion, is inconsistent with the melt compositions and the trend of the array. Trace element abundance patterns in the melt inclusions range from depleted to highly enriched (e.g. La-n/Yb-n 0.6-7.0), and indicate the generation of compositionally diverse melt fractions via fractional melting processes and/or melting of geochemically distinct source heterogeneities. Most melt inclusions, and the pillow-rim glass, are enriched in the more incompatible trace elements, and have high Nb and Ta contents relative to other highly incompatible elements. These characteristics and the Pb isotopic composition of the pillow-rim glass (Pb-206/Pb-204 = 19.654) indicate the presence of a HIMU mantle source component that can be linked to lateral dispersion of a geochemical signal commonly attributed to the Azores mantle plume.

Abstract: Compositions of spinel and grassy melt inclusions in primitive olivine (FO89.3-91) from basalt AII32 D11-177 at 43°N, Mid-Atlantic Ridge fall into two principal groups. The dominant (similar to 90%) Group-I spinel and melt inclusions have typical MORB compositions. In contrast, Group-II. Cr-spinels are strongly enriched in TiO2 (2.6-4.1 wt%), and Group-II melt inclusions show significant enrichment in SiO2 (54.6-58.4 wt%), TiO2, Na2O and K2O, whereas their CaO contents (9.3-11.1 wt%) are unusually low. Group-II melts are also remarkable in crystallizing high-Mg orthopyroxene (Mg# 91). These mineral associations and melt compositions are unusual for MORB, and are interpreted to result from interaction between MORB-like melts and harzburgitic peridotite at low pressure.

Abstract: New mineralogical and geochemical data from a suite of glass +/- apatite +/- amphibole +/- phlogopite +/- carbonate-bearing spinel wehrlite, lherzolite and harzburgite xenoliths from the Newer Volcanics, southeastern Australia, are consistent with metasomatic interactions between harzburgitic or refractory lherzolitic lithosphere, and penetrative sodic dolomitic carbonatite melts. Metasomatism occurred when ascending dolomitic carbonatites crossed the reaction enstatite + dolomite = forsterite + diopside + CO2 at similar to 1.5-2.0 GPa, resulting in partial to complete replacement of primary orthopyroxene by sodic clinopyroxene, together with crystallization of apatite, amphibole and phlogopite, and release of CO2-rich fluid. In the sample suite examined, the minimum amount of carbonatite melt may be estimated on the assumption that metasomatism occurred in a closed system, and that the precursor lithology was clinopyroxene-poor harzburgite. The derivative wehrlite compositions require 6-12% carbonatite addition, the lherzolites require similar to 8% or less, and the harzburgites require minimal addition of carbonatite. However, metasomatism probably also involved an open system component, during which by partitioning relationships with the reacting carbonatite, resulting in loss from the metasomatized volume of a fugitive, siliceous, aluminous, alkali- and LILE-enriched silicate melt

Abstract: Mantle-derived xenoliths from western Victoria, Australia, contain glass in patches and veinlets, and as secondary inclusions within xenolith minerals. Glass patches are commonly associated with primary clinopyroxene, spinel and in some cases relict pargasitic amphibole, phlogopite, apatite or calcitic carbonate. The patches and veins are filled with secondary microphenocrysts of olivine, clinopyroxene and spinel. The siliceous, aluminous, alkali-rich glasses display ranges in major element compositions which are similar to those of glasses in mantle xenoliths worldwide. Textures and compositions of glass and associated phases in the Victorian xenolith suite argue strongly against origins involving equilibrium partial melting of spinel peridotite, or migration of exotic metasomatic melts.Metasomatism of the southeastern Australian lithosphere is expressed by formation of amphibole, phlogopite, and apatite, and increased abundances of clinopyroxene at the expense of orthopyroxene, in Iherzolite or harzburgite. Partial or complete melting of this metasomatic assemblage occurred immediately prior to, or during, entrainment of the xenolith in the host magmas, and locally produced disequilibrium liquids, now preserved as glass. Melting in the xenoliths was caused by the thermal and decompressional effects of transport in the host magma, or by thermal and metasomatic effects in the lithosphere associated with adjacent intrusion of magmas. Large inter-xenolithic variation in glass compositions was caused by variations in the nature and proportions of the precursor metasomatic assemblage, by reaction of the melts with primary orthopyroxene in the Iherzolites and harzburgites, and by rapid, disequilibrium crystallization from the melts of an assemblage of olivine, clinopyroxene and spinel in ail samples.

Abstract: We present a detailed mineralogical, petrological and melt inclusion study of unusually fresh, primitive olivine + clinopyroxene phyric Lower Pillow Lavas (LPL) found near Analiondas village in the northeastern part of the Troodos ophiolite (Cyprus). Olivine phenocrysts in these primitive LPL show a wide compositional range (Fo(82-92)) and have higher CaO contents than those from the Upper Pillow Lavas (UPL). Cr-spinel inclusions in olivine are significantly less Cr-rich (Cr/Cr + Al = 28-67 mol%) compared to those from the UPL (Cr# = 70-80). These features reflect differences in melt compositions between primitive LPL and the UPL, namely higher CaO and Al2O3 and lower FeO* compared to the UPL at a given MgO. LPL parental melts (in equilibrium with Fo(92)) had similar to 10.5 wt% MgO and crystallization temperatures similar to 1210 degrees C, which are significantly lower than those previously published for the UPL (14-15 wt% MgO and similar to 1300 degrees C for Fo(92)). The fractionation path of LPL parental melts is also different from that of the UPL. It is characterized initially by olivine + clinopyroxene cotectic crystallization joined by plagioclase at similar to 9 wt% MgO, whereas UPL parental melts experienced a substantial interval of olivine-only crystallization. Primitive LPL melts were formed from a mantle source which was more fertile than that of tholeiites from well-developed intra-oceanicarcs, but broadly similar in its fertility to that of Mid-Ocean Ridge Basalt (MORB) and Back Are Basin Basalts (BABE). The higher degrees of melting during formation of the LPL primary melts compared to average MORE were caused by the presence of subduction-related components (H2O). Our new data on the LPL coupled with existing data for the UPL support the existing idea that the LPL and UPL primary melts originated from distinct mantle sources, which cannot be related by progressive source depletion. Temperature differences between these sources (similar to 150 degrees C), their position in the mantle (similar to 10 kbar for the colder LPL source vs 15-18 kbar for the UPL source), and temporal succession of Troodos volcanism, all cannot be reconciled in the framework of existing models of mantle wedge processes, thermal structure and evolution, if a single mantle source is invoked. Possible tectonic settings for the origin of the Troodos ophiolite (forearc regions of intra-oceanic island are, propagation of backarc spreading into are lithosphere) are discussed.

Abstract: Phenocryst assemblages, and mineral and melt inclusion compositions of magmas erupted at near-axis seamounts on either side of Valu Fa Ridge provide a hitherto unprecedented insight into the complexity of magma generation in this back-are basin tectonic setting, Two fundamentally different primitive primary melt compositions are identified based on melt inclusion compositions, olivine phenocryst chemistry, and the early co-crystallisation of either magnesian clinopyroxene (Mg# to 93) or magnesian orthopyroxene (Mg# to 93.5) with magnesian olivine (to Fo(94)) and Cr-rich spinel (Cr# = 0.78-0.87). One magma type is a H2O-rich (similar to 2.5 wt%), high-CaO (similar to 14 wt%), low-Al2O3 (similar to 8 wt%) magnesian basalt, variants of which occur in both the eastern and western seamounts, The other is a low-Ca boninite-like magma that only occurs as a component of the western seamount magmas.Large and systematic variations in incompatible trace-element compositions of melt inclusions trapped in primitive olivine phenocrysts, reflect an integration of diverse but geochemically related melt fractions to produce the magmas at each seamount. Trace-element systematics require the variable addition of a LILE-, Pb-, and Cl-rich component to the mantle wedge source with increased influence toward the Tofua are. This component, as invoked in most models of are magma genesis, is likely to be a supercritical aqueous fluid released by dehydrating subducting ocean crust beneath the volcanic are front.We propose that southward propagation of the back-are basin spreading center mantle provided heat necessary to generate both magmatic suites by decompression melting of refractory hydrated sub-are lithosphere, probably veined by clinopyroxene-rich dykes in the case of the high-CaO magma series, These near-ridge seamount lavas are very similar to those drilled at ODP Site 839 in the Lau Basin, and we suggest that the Site 839 basalts, as well as other Lau Basin seamount are-like magmas, were produced from sub-are lithosphere during southward propagation of the Eastern Lau Spreading Center similar to 2-3 Ma.

Abstract: Melt inclusions trapped in Cr-spinel in mid-ocean ridge picrites (FAMOUS area, Atlantic Ocean) were studied using a heating stage and analyzed with both electron and ion microprobes. This new technique can provide information on the most primitive magma compositions, olivine-spinel- melt compositional relationships, crystallization temperature and geochemical diversity of parental melts. The study of melt inclusions in spinel can be applied to different high-Mg suites to show the effects of shallow level fractionation, mixing and contamination that usually affect the composition of volcanic rocks and glasses.

Abstract: Data on the mineralogy and petrology of primitive ancient and prehistoric basaltic magmas of Mt Etna (Sicily) are scarce. A systematic study of the mineralogy and magmatic inclusions in olivine phenocrysts from the most Mg-rich tholeiitic (Aci Castello, Aci Trezza and Adrano), transitional (Paterno) and alkaline (Mt. Maletto, Mt. Spagnolo and Timpa di Acireale) basalts has been undertaken, using the electron microprobe and heating/freezing stages.The maximum Fo content in olivine increases from 86 mol.% in tholeiites, to 88 mol.% in transitional basalt and up to 89-90.5 mol.% in alkaline basalts. The relationship between Fo of the most primitive olivine from alkaline samples and the Cr# of coexisting spinel indicates that their parental melts were near primary. Clinopyroxene Mg# values (maximum and range) correspond closely to those of olivine, suggesting their early co-crystallization. Orthopyroxene (Mg# 86 mol.%) has been found as inclusions in the most magnesian olivine in tholeiitic lavas only.Crystallization temperatures determined from melt inclusion studies revealed no contrast between samples of different affinity, and range from 1240 degrees to 1100 oC. The pressure of crystallization is believed to be higher than 2 kbar (up to 6 kbar), as indicated by the density of primary CO2 inclusions in olivine, and indirectly, by the early clinopyroxene crystallization.Melt inclusions in olivine from tholeiitic lavas form a continuous trend from Q-normative, low potassium and low phosphorus (0.2 wt%) to Si-undersaturated, Ne-normative compositions, enriched in K2O and P2O5 (similar to 1.6 wt%). The range in melt inclusion compositions cannot be accounted for by crystal fractionation and was probably generated during partial melting.The melts reconstructed from melt inclusions in olivine phenocrysts from a Mt. Maletto alkaline lava define a compositional trend consistent with early clinopyroxene + olivine fractionation. The melt equilibrated with the most primitive olivine (Fo(90.5)), clinopyroxene (Mg# 92) and Cr-spinel (Cr# 80) is considered to be a near-primary melt (Mg# 71-74 mol.%; CaO/Al2O3 ~ 1.3), formed by the melting of a clinopyroxene-rich source. The likelihood of a single magma parental to both the tholeiitic and alkaline suites is confidently ruled out.Comparison of characteristic features of the magmatism of Mt. Etna and adjacent areas (Mt. Iblei and the Aeolian are) testifies to progressive depletion of a mantle source by continuous magma extraction, and its heterogeneous chemical and modal modification.

Abstract: Al-rich spinels (100Cr/(Cr + Al) < 5, Al2O3 > 50 wt%) are common in alpine peridotites, both terrestrial and lunar mafic and ultramafic cumulates, and in certain metamorphic rocks, but they are apparently rare in terrestrial volcanic rocks. Here we describe the occurrence of Al-rich spinel inclusions in olivine phenocrysts in island are volcanic rocks from five new localities: Bukit Mapas (Sumatra) and eastern Ball in the Sunda are, and Epi, Merelava, and Ambrym islands in the Vanuatu are. More commonly, relatively Cr-rich spinels also occur as inclusions in the same olivine phenocrysts, and it appears that the Cr-poor aluminous spinels must be in disequilibrium with the host basaltic melts. In the rocks studied, Al-rich spinels also coexist with trapped silicate glasses and highly aluminous clinopyroxene in melt inclusions in olivine. This paragenesis suggests an origin involving contamination by localised Al-rich melt pockets as opposed to a xenocrystic origin. Two mechanisms to produce this high-Al melt in basaltic magma chambers are suggested: (1) localized high-Al melt production by complete breakdown of assimilated lower crustal gabbroic rocks. In this model the high-Al melt may crystallise Al-rich spinels which are subsequently trapped as solid inclusions by phenocryst phases of the host basaltic melt or may be trapped as melt inclusions in which Al-rich spinels and Al-rich clinopyroxene crystallise as daughter phases, and (2) incongruent breakdown of amphibole in amphibole-rich cumulates in sub-are, or sub-GIB volcano magma chambers. The latter reaction produces a melt with similar to 20-22% of Al2O3, aluminous clinopyroxene, Al-rich spinel and olivine. Mixing between these amphibole breakdown products and host basaltic melt may occur throughout the evolution of a magmatic system, but particularly during recharge with hot magnesian basalt batches. Aluminous spinels and aluminous clinopyroxene produced during amphibole breakdown, or perhaps crystallised from aluminous melt produced in the same reaction, are incorporated into the magma during recharge, and subsequently trapped, together with the coexisting Cr-spinels, by crystallising olivine and clinopyroxene.

Abstract: The origin, evolution and primary melt compositions of late Cretaceous high-K ultramafic volcanics and associated basalts of Eastern Kamchatka are discussed an the basis of a study of the mineralogy and geochemistry of the rocks and magmatic inclusions in phenocrysts. The exceptionally primitive composition of the phenocryst assemblage [olivine-Fo(88-95), Cr-spinel-Cr/(Cr + Al) up to 85] provides direct evidence of the mantle origin of primary melts, which were highly magnesian compositions (MgO 19-24 wt%). The rocks and melts are characterized by strong high field strength element (HFSE) depletion in comparison with rare earth elements, and high and variable levels of enrichment in large ion lithophile elements (LILE), P, K and H2O (0.6-1.2 wt% in picritic to basaltic melts). epsilon(Nd) values lie in a narrow range (+10.7 to +9.1), typical of N-MORB (mid-ocean ridge basalt), but Sr-87/Sr-86 (0.70316-0.70358) is slightly displaced from the mantle array. High-K ultramafic melts from Kamchatka are considered as a new magma type within the island-are magmatic spectrum; basaltic members of the suite resemble are shoshonites. The primary melts were produced under high-pressure (30-50 kbar) and high-temperature (1500-1700 oC) conditions by partial melting of a refractory peridotitic mantle.

Abstract: The origin and the relationships between the high potassic (HKS) and potassic (KS) suites of the Roman Comagmatic Province and the nature of their primary magmas have been intensively debated over the past 35 years. We have addressed these problems by a study of mineralogy (olivine Fo(92-87), Cr-spinel and diopside) and melt inclusions in olivine phenocrysts from a scoria sample of Montefiascone (Vulsini area). This rock is considered as one of the most primitive (MgO = 13.5 wt%, NiO = 340 ppm; Cr = 1275 ppm) in the northern part of the Roman Comagmatic Province. The compositions of both the olivine and their melt inclusions are controlled by two main processes. In the case of the olivine Fo < 90.5, fractional crystallization (olivine + diopside + minor spinel) was the principal mechanism of the magma evolution. The olivine (Fo(92-90.5)) and the Cr-spinel (Cr# = 100. Cr/(Cr + Al) = 63-73) represent a near-primary liquidus assemblage and indicate the mantle origin of their parental magmas. The compositions of melt inclusions in these olivine phenocrysts correspond to those of poorly fractionated H2O-rich (similar to 1 wt%) primary melts (MgO = 8.4-9.7 wt%, FeOtotal = 6-7.5 wt%). They evidence a wide compositional range (in wt%: SiO2 = 46.5-50, K2O = 5.3-2.8, P2O5 = 0.4-0.2, S = 0.26-0.12; Cl = 0.05-0.03, and CaO/Al2O3 = 0.8-1.15), with negative correlations between SiO2 and K2O, Al2O3 and CaO, as well as positive correlations between K2O, and P2O5, S, Cl, with nearly constant ratios between these elements. These results are discussed in terms of segregation of various mantle-derived melts. The high and constant Mg# [100. Mg/(Mg + Fe2+)] 73-75 of studied melts and their variable Si, K, P, Ca, Al, S contents could be explained by the melting of a refractory lithospheric mantle source, heterogeneously enriched in phlogopite and clinopyroxene (veined mantle source).

Abstract: At its southernmost end, the main spreading centre of the North Fiji Basin is propagating into arc crust of the poorly-known Hunter Ridge. We define nine magmatic groups from major element glass chemistry and olivine and spinel compositions in samples dredged from twenty six sites in this area by the ''R/V Academician A. Nesmeyanov'' in 1990. These include groups of boninites, island arc tholeiites (IAT), mid-ocean ridge basalts (MORB), enriched mid-ocean ridge basalts (E-MORB), olivine porphyritic andesites and basaltic andesite and Na-rhyolites. Primitive lavas containing highly forsteritic olivine phenocrysts are common in all the groups, except for the rhyolites.We report over 100 glass analyses for dredged rocks from this region, and about 300 olivine-spinel pairs for representatives of all the magmatic groups identified, except the Na-rhyolites.The MORB in this region are probably produced at the propagating spreading centre in the southern part of the North Fiji Basin. Juxtaposition of shallow, hot MORB-source diapirs supplying the MORB in this area, and the sub-arc damp, refractory upper mantle beneath the Hunter Ridge, provides suitable petrogenetic conditions to produce a range of magma types, from island arc tholeiites through to high-Ca boninites. The latter were recovered in eleven dredges.The E-MORB lavas recovered from the extreme southern margin of the North Fiji Basin are shown to be essentially identical to those dredged from adjacent older South Fiji Basin crust. It is hypothesized that the former were either scraped off the South Fiji Basin crust during an episode of oblique subduction that may have generated the Hunter Ridge during the last 5 Myr, or alternatively, that slices of the South Fiji Basin crust were trapped and incorporated into the North Fiji Basin as the subduction zones fronting the Vanuatu arc stepped or propagated southward.

Abstract: The study of fluid (FI) and melt inclusions (MI) can be a powerful tool for understanding melt generation, crystallization, mixing histories of magmas and the conditions of magma evolution during their ascent to the surface. FI and MI data from the alkali syenite xenoliths of different subvolcanic igneous systems in the Neapolitan volcanic area (Vesuvius, Campi Flegrei, Ponza and Ventotene) in Italy provide valuable information on the nature of fluid and melt phases trapped during the late evolutionary stages of these alkaline magmatic systems. They also document liquid immiscibility at pre-eruptive magma conditions and furnish evidence that high salinity fluids (brines) exsolve directly from magma in the upper part of chambers at the magmatic/hydrothermal transition and play critical roles in ore metal transport. Magma chamber margins are of particular significance because FI and MI may record the various evolutionary processes during the crystallization of the magmatic system. The complex daughter crystal assemblages seen in the silicate melt + CO2 + H2O and silicate melt, hypersaline or S-rich aqueous inclusions found in xenoliths of some samples record high solute contents in the fluid(s) during entrapment and provide direct evidence of the magmatic source of these metals. The latter inclusions could be of considerable interest for the interpretation of ore genesis, because FI and MI demonstrate a linkage of these systems with low sulfidation epithermal deposits and some porphyry systems. In addition, FI and MI data are used to address the problem of frequent ground movements (bradyseism) in the Campi Flegrei, interpreted as representing a modern analog behaving physically like a porphyry system.

Abstract: mmiscibility (unmixing of melts and fluids) should be almost inevitable at some point in the evolution of most mantle and crustal magmas during cooling and crystallization. Formation of two immiscible phases "results in a major geochemical fractionation all chemical species present, the elements (and their isotopes), and their various compounds, become distributed between these two phases... the compositional divergence between the two phases is... extreme" (Roedder 2003). The variations in compositions of melts undergoing immiscibility, and physical parameters of their evolution in the plutonic environments, mean that each intrusion should be expected to show differences in the processes of exsolution and compositions of exsolving phases. One of the immiscible phases is universally volatile-rich, and this has important consequences for further magma evolution and geological processes related to it. More specifically, volatile-rich phases generally have significant density and viscosity contrasts with parental silicate magmas, and thus rapid separation of the newly exsolved phases is expected. Further, the exsolution of volatile-rich phases exerts major controls on the chemistry of a magmatic system, particularly on metal partitioning between immiscible melts and fluids, so the volatile phase is highly efficient at sequestering the metals (e.g., Candela 1989; Candela & Piccoli 1995; Williams et al. 1995; Heinrich et al. 1999; Webster 2004). Magmatic immiscibility and the related formation of volatile-rich melts and fluids are prerequisites for the origin of mineralized hydrothermal solutions that may transport metals to a suitable depositional site. Immiscible separation, however, is not restricted to magmas that form mineralized rocks. The fugitive nature of magmatic immiscibility involves problems in unraveling physical and chemical characteristics of this fundamental process. If separation of immiscible phases was efficient, the residual magma should be significantly depleted in incompatible volatiles and metals relative to the parental magma, and reconstructing the original metal and volatile content is extremely difficult. One rapidly developing approach to this problem is the use of melt and fluid inclusions trapped and preserved in magmatic minerals (e.g., Roedder 1992; De Vivo & Frezzotti 1994; Bodnar 1995; Lowenstern 1995; Student & Bodnar 1999; Frezzotti 2001; Kamenetsky et al. 2003; Lowenstern 2003 and references therein). Such inclusions provide the closest approximation to samples of continuously evolving (and thus ephemeral) melts and magmatic fluids. Many studies of magmatic inclusions have made possible the recognition of several types of magmatic immiscibility (e.g., between silicate melts, sulfide melts, aqueous and carbonic liquids and vapors, hydrosaline liquids and various combinations of these). For brevity, in this work only those examples from plutonic systems, of which the author has first-hand experience, will be presented and discussed in detail.

Abstract: Immiscible phase separation during the cooling and crystallisation of magmas is an inherently fugitive phenomenon and melt inclusions may provide the only remaining evidence of this process. We detail those features of such inclusions that can both prove the existence of immiscible phase separation, and constrain the compositional signature of the process. To do so requires the combination of traditional methods (petrographic examination, microthermometry, etc.) with state of the art microbeam analytical techniques (laser Raman spectroscopy and proton-induced X-ray emission). Examples of inclusions in phenocrysts from barren and mineralised rocks are provided to illustrate the approach and validate the interpretations.