REE Abundances Research Articles

Occurrence of lamproitic dykes at the northern Margin of the Indravati Basin, Bastar Craton, Central India

Occurrence of two lamproitic dykes intruding the basement granite near Khadka village at the northern margin of the Indravati Basin, Bastar craton is reported. Combined field, microscopy, XRD, EPMA and whole-rock geochemical investigations reveal that these lamproites were subjected to high degree of hydrothermal alteration as well as possible metamorphism. However, relicts of their original textures are well-preserved thereby providing important clues as to the nature of the protolith. Quartz, carbonate, chlorite and phlogopite constitute the bulk mineralogy whereas spinel, apatite and iron oxides are the accessory phases. Chemical composition of the groundmass spinels are strikingly similar to those from the lamproites. The Khadka lamproite dykes display high abundances of compatible elements such as Ni (238-396 ppm), Cr (484-892 ppm), and V (160-200 ppm) as well as high-field strength elements such as Zr (719-2057 ppm) and Nb (92-126 ppm) that resemble those in lamproites. Khadka lamproites also have high whole-rock REE abundances (ΣREE up to 1260 ppm) and display fractionated chondrite-normalized REE patterns (La/Yb= 113-237) which together with their average compatible and incompatible trace elemental ratios (e.g. Nb/Zr, Nb/La, Ba/Rb) are strikingly similar to those of the Mesoproterozoic Krishna lamproites of the Eastern Dharwar craton. Available field evidences suggest the Khadka lamproites to be of at least Palaeoproterzoic age (1.88 Ga) which makes them some of the oldest such rocks as yet documented from the Indian shield.

REE, Mn, Fe, Mg and C, O Isotopic Geochemistry of Calcites from Furong Tin Deposit, South China: Evidence for the Genesis of the Hydrothermal Ore‐forming Fluids

AbstractThe Furong tin deposit in the central Nanling region, South China, consists of three main types of mineralization ores, i.e. skarn‐, altered granite‐ and greisen‐type ores, hosted in Carboniferous and Permian strata and Mesozoic granitic intrusions. Calcite is the dominant gangue mineral intergrown with ore bodies in the orefield. We have carried out REE, Mn, Fe, and Mg geochemical and C, and O isotopic studies on calcites to constrain the source and evolution of the ore‐forming fluids. The calcites from the Furong deposit exhibit middle negative Eu anomaly (Eu/Eu*= 0.311–0.921), except for one which has an Eu/Eu* of 1.10, with the total REE content of 5.49–133 ppm. The results show that the calcites are characterized by two types of REE distribution patterns: a LREE‐enriched pattern and a flat REE pattern. The LREE‐enriched pattern of calcites accompanying greisen‐type ore and skarn‐type ore are similar to those of Qitianling granite. The REE, Mn, Fe, and Mg abundances of calcites exhibit a decreasing tendency from granite rock mass to wall rock, i.e. these abundances of calcites associated with altered granite‐type and greisen‐type ores are higher than those associated with skarn‐type ores. The calcites from primary ores in the Furong deposit show large variation in carbon and oxygen isotopic compositions. The δ13C and δ18O of calcites are −0.4 to −12.7‰ and 2.8 to 16.4‰, respectively, and mainly fall within the range between mantle or magmatic carbon and marine carbonate. The calcites from greisen and altered granite ores in the Furong deposit display a negative correlation in the diagram of δ13C versus δ18O, probably owing to the CO2‐degassing of the ore‐forming fluids. From the intrusion to wall‐rock, the calcites display an increasing tendency with respect to δ13C values. This implies that the carbon isotopic compositions of the ore‐bearing fluids have progressively changed from domination by magmatic carbon to sedimentary carbonate carbon. In combination with other geological and geochemical data, we suggest that the ore‐forming fluids represent magmatic origin. We believe that the fluids exsolved from fractionation of the granitic magma, accompanying magmatism of the Qitianling granite complex, were involved in the mineralization of the Furong tin polymetallic deposit.

Magnesian anorthositic granulites in lunar meteorites Allan Hills A81005 and Dhofar 309: Geochemistry and global significance

Abstract– Fragments of magnesian anorthositic granulite are found in the lunar highlands meteorites Allan Hills (ALH) A81005 and Dhofar (Dho) 309. Five analyzed clasts of meteoritic magnesian anorthositic granulite have Mg′ [molar Mg/(Mg + Fe)] = 81–87; FeO ≈ 5% wt; Al2O3 ≈ 22% wt; rare earth elements abundances ≈ 0.5–2 × CI (except Eu ≈ 10 × CI); and low Ni and Co in a non‐chondritic ratio. The clasts have nearly identical chemical compositions, even though their host meteorites formed at different places on the Moon. These magnesian anorthositic granulites are distinct from other highlands materials in their unique combination of mineral proportions, Mg′, REE abundances and patterns, Ti/Sm ratio, and Sc/Sm ratio. Their Mg′ is too high for a close relationship to ferroan anorthosites, or to have formed as flotation cumulates from the lunar magma ocean. Compositions of these magnesian anorthositic granulites cannot be modeled as mixtures of, or fractionates from, known lunar rocks. However, compositions of lunar highlands meteorites can be represented as mixtures of magnesian anorthositic granulite, ferroan anorthosite, mare basalt, and KREEP. Meteoritic magnesian anorthositic granulite is a good candidate for the magnesian highlands component inferred from Apollo highland impactites: magnesian, feldspathic, and REE‐poor. Bulk compositions of meteorite magnesian anorthositic granulites are comparable to those inferred for parts of the lunar farside (the Feldspathic Highlands Terrane): ∼4.5 wt% FeO; ∼28 wt% Al2O3; and Th <1 ppm. Thus, magnesian anorthositic granulite may be a widespread and abundant component of the lunar highlands.

METAMORPHIC-HYDROTHERMAL REE MINERALS IN THE BACUCH MAGNETITE DEPOSIT, WESTERN CARPATHIANS, SLOVAKIA: (Sr,S)-RICH MONAZITE-(Ce) AND Nd-DOMINANT HINGGANITE

Accessory REE minerals occur in a small metamorphic magnetite ore deposit at Bacuch, Veporic Superunit, central Slovakia. We distinguish two populations of monazite. Monazite I forms subhedral to euhedral crystals associated with magnetite. It contains ≤12 wt.% ThO2, ≤2.7% UO2, ≤0.85% SO3, with low Ca and Sr contents. Compared to the common monazite-(Ce) I, monazite-(Nd) I (≤26.1% Nd2O3) occasionally occurs with an atomic ratio Nd:Ce up to 1.17. Monazite II is present as irregular aggregates with hingganite in younger hydrothermal quartz – albite – chlorite veinlets, or as rim zones on monazite I. Monazite II is depleted in Th and U and has an unusually high content of S (≤11.3% SO3, 0.31 apfu S) and Sr (≤8.7% SrO, 0.18 apfu Sr). This composition indicates a (Ca,Sr)S(REE,Y)−1P−1 substitution as a dominant mechanism of Sr and S entry into the monazite structure. Some monazite II crystals display an elevated Eu content (≤1.2% Eu2O3). Xenotime-(Y) forms subhedral crystals, in association with monazite-(Ce) I, magnetite, pyrite transformed to goethite (?) and quartz. Gadolinite-group minerals at Bacuch are represented by hingganite with an atomic value of X □/ X (□ + Fe) in the range 0.51–0.72. Neodymium is locally the most abundant REE (17.8–18.7% Nd, ~0.56 apfu ), and an Nd-dominant member of the gadolinite group was identified. The composition of hingganite-(Y) was also determined. The principal mechanism of substitution in hingganite is Fe2+O2□−1(OH)−2. Primary monazite I and xenotime are most likely products of regional metamorphism, together with magnetite mineralization. On the contrary, Sr- and S-rich monazite II and hingganite originated during a younger (Alpine) metamorphic-hydrothermal overprint in a fluid-rich regime.

Chemical composition of whole-rocks samples and volcanic glasses of the Miocene Tamateyama and Sekibutsu Tuffs in the area surrounding the Nara Basin

We used XRF and INAA methods to analyze the chemical composition of whole-rock and volcanic glass samples from the Tamateyama and Sekibutsu Tuffs in the area surrounding the Nara Basin. Both tuffs have rhyolitic compositions with SiO2=73.6-75.0 wt.%, similar to that of the Muro Pyroclastic Flow Deposits (Muro PFD). The REE patterns of the tuffs are characterized by light REE enrichment, a pronounced negative Eu anomaly, and relatively constant chondrite-normalized middle to heavy REE abundances. These features are similar to those of S-type felsic rocks of the Outer Zone of southwest Japan. Our new petrochemical data provide additional constraints on correlations of the Tamateyama Tuff, Sekibutsu Tuff, and Muro PFD, and indicate that these units were derived from a large felsic igneous body in the Outer Zone of the Kii Peninsula.

The Jugsaipatna Anorthosite Complex, Eastern Ghats Belt, India: Magmatic lineage and petrogenetic implications

The Jugsaipatna Anorthosite Complex (JAC) in the Eastern Ghats Mobile Belt (India) comprises a central anorthosite – leuconorite – troctolitic norite core mantled by a rim of high-Al gabbronorite (HAG). Small dykes of ferrodiorite occur in the core region of the JAC. A lensoidal body of eucritic gabbronorite occurs in contact with leuconorite and outer gabbronorite rim. Baring ferrodiorites, the mafic members such as HAG, troctolitic norite and eucritic gabbronorite are not known in other anorthosite complexes of this high grade belt. The HAG is characterised by high Al 2O 3 content (17 wt.%), enriched ΣREE and LREE, absence of ‘Eu-anomaly’ and negative Sr anomaly and is, therefore inferred to be the source melt for the JAC suite of rocks. The eucritic gabbronorite comprising An-rich plagioclase and high-Al pyroxenes has a komatiitic affinity with high Cr–Ni contents and primitive REE patterns. Troctolitic norite, leuconorite and anorthosite are interpreted to be cumulate rocks fractionated from the HAG. The ferrodiorite with enriched Fe, Ti, P, Zr and REE abundances and a prominent ‘negative Eu’ anomaly corresponds to the residual melt of the plagioclase (+pyroxene) dominated fractionates that comprise anorthosite-leuconorite.

Antarctic lunar meteorites Yamato-793169, Asuka-881757, MIL 05035, and MET 01210 (YAMM): Launch pairing and possible cryptomare origin

The Antarctic lunar meteorite Meteorite Hills (MET) 01210 is a polymict regolith breccia, dominantly composed of mare basalt components. One relatively large (2.7 × 4.7 mm) basalt clast in MET 01210 (MET basalt) shows remarkable mineralogical similarities to the lunar-meteorite crystalline mare basalts Yamato (Y)-793169, Asuka (A)-881757, and Miller Range (MIL) 05035. All four basalts have similar rock texture, mineral assemblage, mineral composition, pyroxene crystallization trend, and pyroxene exsolution lamellae. The estimated TiO 2 contents (∼2.0 wt%) of the MET basalt and MIL 05035 are close to the bulk-rock TiO 2 contents of Y-793169 and A-881757. These similarities suggest that Y-793169, A-881757, MIL 05035, and the MET basalt came from the same basalt flow, which we designate the YAMM basalt. The source-basalt pairing of the YAMM is also supported by their similar REE abundances, crystallization ages (approx. 3.8–3.9 Ga), and isotopic compositions (low U/Pb, low Rb/Sr, and high Sm/Nd). The pyroxene exsolution lamellae, which are unusually coarse (up to a few microns) by mare standards, imply a relatively slow cooling in an unusually thick lava and/or subsequent annealing within a cryptomare. Reported noble gas and CRE data with close launch ages (∼1 Ma) and ejection depths (deeper than several meters) among the four meteorites further indicate their simultaneous ejection from the moon. Despite the marginally close terrestrial ages, pairing in the conventional Earth-entry sense seems unlikely because of the remote recovery sites among the YAMM meteorites. The high abundance (68%) of mare components in MET 01210 estimated from a two-component mixing model calculation could have resulted from either lateral mixing at a mare-highland boundary or vertical mixing in a cryptomare. The proportion of mare materials in MET 01210 is greater than in Apollo core samples at the mare-highland boundary. The burial depth (>several meters deep) inferred from the lack of surface irradiation of MET 01210 exceeds the typical mare regolith thickness (a few meters). Thus, the source of the YAMM meteorites is likely a terrain of locally high mare-highland mixing within a cryptomare. We searched for a possible source crater of the YAMM meteorites within the well-defined cryptomare, based on the multiple constraints obtained from this study and published data. An unnamed 1.4 km-diameter crater (53°W, 44.5°S) on the floor of the Schickard crater is the most suitable source for the YAMM meteorites. The 238U/ 204Pb ( μ) value of the YAMM basalts is extremely low, relative to those of the Apollo mare basalts, but comparable to those of the Luna 24 very low-Ti basalts. The low- μ source indicates a derivation from a less differentiated mantle with a lack of KREEP components. Although the chemical sources of materials and heat source of melting might be independent, the heat source that generated the source magma of the YAMM and Luna 24 basalts may not be related to KREEP, unlike the case of the Apollo basalts. The distinct chemical and isotopic compositions of mantle sources between the Apollo basalts and the YAMM/Lunar 24 basalts imply differences in mantle composition and thermal evolution between the Procellarum KREEP Terrane (PKT) and non-PKT regions of the nearside.

Zircon geochronology and trace element characteristics of eclogites and granulites from the Orlica-Śnieżnik complex, Bohemian Massif

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

Steric hindrance and the enhanced stability of light rare-earth elements in hydrothermal fluids

A series of X-ray absorption spectroscopy (XAS) experiments were made to determine the structure and stability of aqueous REE (La, Nd, Gd, and Yb) chloride complexes to 500 °C and 520 MPa. The REE3+ ions exhibit inner-sphere chloroaqua complexation with a steady increase of chloride coordination with increasing temperature in the 150 to 500 °C range. Furthermore, the degree of chloride coordination of REE3+ inner-sphere chloroaqua complexes decreases significantly from light to heavy REE. These results indicate that steric hindrance drives the reduction of chloride coordination of REE3+ inner-sphere chloroaqua complexes from light to heavy REE. This results in greater stability and preferential transport of light REE3+ over heavy REE3+ ions in saline hydrothermal fluids. Accordingly, the preferential mobility of light REE directly influences the relative abundance of REE in rocks and minerals and thus needs to be considered in geochemical modeling of petrogenetic and ore-forming processes affected by chloride-bearing hydrothermal fluids.

MINERALOGY AND GEOCHEMISTRY OF KIMBERLITES NK-2 AND KK-6, NARAYANPET KIMBERLITE FIELD, EASTERN DHARWAR CRATON, SOUTHERN INDIA: EVIDENCE FOR A TRANSITIONAL KIMBERLITE SIGNATURE

We have carried out a mineralogical and geochemical study on two previously uncharacterized kimberlites of coherent facies, NK–2 and KK–6, from the Narayanpet kimberlite field (NKF), Eastern Dharwar craton (EDC), southern India. Both these kimberlites have a distinct inequigranular texture resulting from two generations of variously sized olivine macrocrysts and groundmass microphenocrysts. Other groundmass phases include clinopyroxene (diopside), serpentine, phlogopite, calcite, spinel, perovskite and apatite. Electron-microprobe analyses of various groundmass minerals support their kimberlitic affinity. Primitive Mg-numbers, Ni and Cr contents and high enrichment in incompatible trace elements are hallmarks of these kimberlites. From major- and trace-element geochemistry, crustal contamination seems to be minimal. The LILE and HFSE display excellent correlations amongst themselves and also with each other, thereby implying limited effects of post-emplacement hydrothermal alteration. Ratios of highly mobile and immobile incompatible trace elements ( e.g. , La, Ce, Nb, Ba, Pb and Th) strongly resemble those of transitional kimberlites of southern Africa and are confined to the arrays of mixing lines between Group-I and Group-II kimberlites. The REE abundances of NK–2 and KK–6 kimberlites suggest variable degrees of partial melting. Petrogenetic modeling depicts them to be products of a greater degree of melting. A mixed Group-I and Group-II “southern African” kimberlite source is inferred for the generation of NK–2 and KK–6 magmas, as well as for several other EDC kimberlites. This can explain several overlapping petrological and geochemical characters of Group-I and Group-II kimberlites displayed by the kimberlites of southern India. Lower whole-rock Ti and Fe contents in the NK–2 and KK–6, compared to those in other non-diamondiferous kimberlites from the NKF, suggests that they are promising diamond prospects; we recommend their bulk processing.

Crustal origin of zircon in a garnet peridotite: a study of U-Pb SHRIMP dating, mineral inclusions and REE geochemistry (Erzgebirge, Bohemian Massif)

Garnet peridotites provide insight into geochemical processes within the upper mantle, which can be recorded in the mineral zircon. We separated zircon from a garnet peridotite of the Erzgebirge (Zoblitz), Bohemian Massif, and dated it by means of U-Pb with SHRIMP, determined its trace and REE geochemistry and investigated its inclusions. Two types of zircon were distinguished: (a) Inclusion-free zircon with weak cathodoluminescence (CL) emission. For some of these zircons oscillatory zoning or, partly, sector zoning could be observed indicating precipitation from a melt or fluid. These zircons are characterised by high HREE contents and a strong negative Eu anomaly. The latter feature indicates that they formed within the stability field of plagioclase. SHRIMP results reveal a 206 Pb/ 238 U age of 332.1 ± 4.8 Ma (error at 95 % c.l.). This age is younger than the one ascribed to the metamorphic peak by previous studies ( ca. 341 Ma) and similar to ages suggested for exhumation stages ( ca. 332–330 Ma). (b) Inclusion-bearing, very U-rich zircons with no, or very weak, CL emission. The inclusions (a few μm large) are quartz, albite, K-feldspar and felsic melt. These zircons have high trace- and REE contents and are especially rich in LREE. Their chondrite-normalized REE pattern is flat. They formed later in the exhumation path than the inclusion-free zircons. Zircons of this type did not yield a reliable SHRIMP age because of their very high U contents. Garnet shows a REE pattern typical for this mineral. MREE-HREE partitioning between zircon and garnet reveals that the two minerals were far from equilibrium. This applies for both zircon types. The whole-rock chemistry displays absolute REE abundances slightly higher than the chondritic values (except for La and Ce) and enrichment in LREE. Our results show that zircon in the garnet peridotite formed during exhumation, within the stability field of plagioclase (presence of albite inclusions or negative Eu anomaly) during two distinct stages by infiltration of two types of fluid/melt with different chemistry (very different trace and REE composition of the two zircon types), far from equilibrium with the (U)H P mineral garnet ( D MREE-HREE zrc/grt ≫ 1). These fluids/melts probably originated from the immediately adjacent felsic gneisses. It is likely that two pulses of influx of a highly differentiated melt (very U-rich zircons, presence of albite) occurred and led to precipitation of zircon: the first at higher- T (no mineral inclusions in zircon) and the second at lower T , closer to the solidus (felsic inclusions in zircon).

Secular evolution of the lithospheric mantle beneath the eastern North China craton: evidence from peridotitic xenoliths from Late Cretaceous mafic rocks in the Jiaodong region, east-central China

The Mesozoic lithospheric mantle beneath the North China craton remains poorly constrained relative to its Palaeozoic and Cenozoic counterparts due to a lack of mantle xenoliths in volcanic rocks. Available data show that the Mesozoic lithospheric mantle was distinctive in terms of its major, trace element, and isotopic compositions. The recent discovery of mantle peridotitic xenoliths in Late Cretaceous mafic rocks in the Jiaodong region provides an opportunity to further quantify the nature and secular evolution of the Mesozoic lithospheric mantle beneath the region. These peridotitic xenoliths are all spinel-facies nodules and two groups, high-Mg# and low-Mg# types, can be distinguished based on textural and mineralogical features. High-Mg# peridotites have inequigranular textures, high Mg# (up to 92.2) in olivines, and high Cr# (up to 55) in spinels. Clinopyroxenes in the high-Mg# peridotites are generally LREE-enriched ((La/Yb)N>1) with variable REE concentrations, and have enriched Sr–Nd isotopic compositions (87Sr/86Sr = 0.7046–0.7087; 143Nd/144Nd = 0.5121–0.5126). We suggest that the high-Mg# peridotites are fragments of the Archaean and/or Proterozoic lithospheric mantle that underwent extensive interaction with both carbonatitic and silicate melts prior to or during Mesozoic time. The low-Mg# peridotites are equigranular, are typified by low Mg# ( < 90) in olivines, and by low Cr# ( < 12) in spinels. Clinopyroxenes from low-Mg# peridotites have low REE abundances (ΣREE = 12 ppm), LREE-depleted REE patterns ((La/Yb)N < 1), and depleted Sr–Nd isotopic features, in contrast to the high-Mg# peridotites. These geochemical characteristics suggest that the low-Mg# peridotites represent samples from the newly accreted lithospheric mantle. Combined with the data of mantle xenoliths from the Junan and Daxizhuang areas, a highly heterogeneous, secular evolution of the lithosphere is inferred for the region in Late Cretaceous time.

How We Could Know the REE Abundance Pattern of Magma Source

How We Could Know the REE Abundance Pattern of Magma Source

Mg and Fe-rich carbonate–silicate high-density fluids in cuboid diamonds from the Internationalnaya kimberlite pipe (Yakutia)

Microinclusions in 44 cuboid diamonds from the Internationalnaya kimberlite pipe (Yakutia) show wide compositional variations. In comparison with the available worldwide database most microinclusions in diamonds from Internationalnaya define a continuous range of compositions from carbonatitic to hydrous-silicic high-density fluids (HDFs). The hydrous-silicic compositional range is reported here for the first time in Yakutian diamond-forming fluids. The hydrous-silicic end-members are rich in water, SiO 2, Al 2O 3, K 2O and P 2O 5. Carbonatitic end-members are rich in carbonate, CaO, MgO, Na 2O and FeO. Microinclusions in diamonds from Internationalnaya show a range from magnesian to extremely iron-rich compositions. There are two compositional arrays of microinclusions: (i) carbonate-rich with SiO 2 < 10 wt.% where FeO decreases without any correlation with sulfur, water, carbonate or chlorine and (ii) carbonatitic to hydrous-silicic where FeO generally decreases as SiO 2 contents increase. The trace-element patterns of the microinclusions are generally similar to those of kimberlites and carbonatites, but there are significant differences in the major elements. The relative abundance of K in the microinclusions is significantly higher. The microinclusions have smooth patterns for the LILE, normalized to a primitive mantle composition. HFSE patterns in the microinclusions show some depletion in Ti, Zr and Hf relative to Ta, Nb and Mo. Primitive mantle normalized REE patterns reveal low abundances of the heavy REE and high concentrations of light REE. The La/Dy ratio of microinclusions varies widely, decreasing from carbonatitic to hydrous-silicic compositions. A general correlation of δ 13C of diamonds with the relative abundance of carbonates in the microinclusions suggests that carbon isotope compositions are related to the evolution of the parental media. The carbonate–silicate range of high-density fluids observed in diamonds from Internationalnaya may be explained by fractional crystallization of mantle fluids/melts, or mixing between liquids with different compositions.

Rare Earth Elements in Manganese Nodules from the Central Pacific Ocean

Abstract Manganese nodules in areas CP and CC of the central Pacific are rich in REE. Comparatively speaking, the REE contents of nodules in area CP are hihger than those in area CC; and the REE contents of nodules from seamounts are higher than those of nodules from sea-floor plains and hills. Within the nodules, the REE show a zonal distribution. The REE distribution patterns of the nodules are similar to those of the sediments and have a mirror image relationship with those of the sea water. Trivalent REE were not obviously differentiated when they entered into the nodules from the sea water. A major factor causing the difference of REE abundances between nodules and sediments is the redox conditions. The redox intensity of the ocean floor of the Pacific is controlled mainly by Antarctic Bottom Water (AABW). The iron-bearing facies in the nodules is the main carrier of REE.

Rare Earth Elements in Manganese Nodules from the Central Pacific Ocean

Abstract Manganese nodules in areas CP and CC of the central Pacific are rich in REE. Comparatively speaking, the REE contents of nodules in area CP are hihger than those in area CC; and the REE contents of nodules from seamounts are higher than those of nodules from sea-floor plains and hills. Within the nodules, the REE show a zonal distribution. The REE distribution patterns of the nodules are similar to those of the sediments and have a mirror image relationship with those of the sea water. Trivalent REE were not obviously differentiated when they entered into the nodules from the sea water. A major factor causing the difference of REE abundances between nodules and sediments is the redox conditions. The redox intensity of the ocean floor of the Pacific is controlled mainly by Antarctic Bottom Water (AABW). The iron-bearing facies in the nodules is the main carrier of REE.

Trace element constraints on mid-crustal partial melting processes – A garnet ionprobe study from polyphase migmatites (Damara orogen, Namibia)

ABSTRACTTrace element abundances in garnet from a polyphase migmatite were measured by secondary ion mass spectrometry (SIMS) in order to identify some of the effective variables on the trace element distribution between garnet and melanosome or leucosome. In general, garnet is zoned with respect to REE, in which garnet cores are enriched by a factor of 2–3 relative to the rims. For an inclusion-rich garnet from the melanosome, equilibrium distribution following a simple Rayleigh fractionation is responsible for the decreasing concentrations in REE from core to rim. Inclusion-poor garnet from the same melanosome located in the vicinity of the leucosomes shows distinct enrichment and depletion patterns for REE from core to rim. These features suggest disequilibrium between garnet and the host rock which, in this case, could have been an in-situ derived melt. This would probably indicate a period of open-system behaviour at a time when the garnet, originally nucleated in the metamorphic environment reacted with the melt. In addition, non-gradual variation in trace element abundances between core and rim may suggest variable garnet growth rates. Inclusion-free garnet from the leucosome, interpreted to have crystallised in the presence of a melt, has a small core with high REE abundances and a broad rim with lower REE abundances. Here, crystal-liquid diffusion-controlled partitioning is a likely process to explain the trace element variation.

Geochemistry of hematitite and itabirite, Quadrilátero Ferrífero, Brazil

Twenty-one samples of hematitite and twelve samples of itabirite were collected from different deposits of the Quadrilátero Ferrífero (QF) area and were analyzed for trace and rare earth elements. The purpose of the study is to understand the element distribution in the QF in comparison with other iron formations (IF) around the world. Trace element contents are relatively low with considerable variability, being lower than the contents in the Algoma IF, Anamikie IF, Maru IF in Nigeria and Orissa IF in India. REE's abundance is relatively low, but higher than REE's of Hamersley IF of Western Australia, Surgur belt in India and lower than Kuruman IF in South Africa. Chondrite normalized patterns show slight degrees of fractionation for LREE to HREE and slightly positive Eu anomalies coupled with positive values of (La/Yb)CN and (La/Sm)CN ratios.

Petrogenesis of augite-bearing ureilites Hughes 009 and FRO 90054/93008 inferred from melt inclusions in olivine, augite and orthopyroxene

Melt inclusions in ureilites occur only in the small augite- and orthopyroxene-bearing subgroups. Previously [Goodrich C.A., Fioretti A.M., Tribaudino M. and Molin G. (2001) Primary trapped melt inclusions in olivine in the olivine–augite–orthopyroxene ureilite Hughes 009. Geochim. Cosmochim. Acta 65, 621–652] we described melt inclusions in olivine in the olivine–augite–orthopyroxene ureilite Hughes 009 (Hughes). FRO 90054/93008 (FRO) is a near-twin of Hughes, and has abundant melt inclusions in all three primary silicates. We use these inclusions to reconstruct the major, minor and rare earth element composition of the Hughes/FRO parent magma and evaluate models for the petrogenesis of augite-bearing ureilites. Hughes and FRO consist of 23–47 vol % olivine (Fo 87.3 and 87.6, respectively), 7–52 vol % augite ( mg 89.2, Wo 37.0 and mg 88.8, Wo 38.0, respectively), and 12–56 vol % orthopyroxene ( mg 88.3, Wo 4.9 and mg 88.0, Wo 4.8, respectively). They have coarse-grained (⩽3 mm), highly-equilibrated textures, with poikilitic relationships indicating the crystallization sequence olivine → augite → orthopyroxene. FRO is more shocked than Hughes, experienced greater secondary reduction, and is more weathered. The two meteorites are probably derived from the same lithologic unit. Melt inclusions in olivine consist of glass ± daughter cpx ± metal–sulfide–phosphide spherules ± chromite, and have completely reequilibrated Fe/Mg with their hosts. We follow the method of Goodrich et al. (2001) for reconstructing the composition of the primary trapped liquid they represent (olPTL), but correct an error in our treatment of the effects of reequilibration. Inclusions in augite consist of glass, which shows only partial reequilibration of Fe/Mg. The composition of the primary trapped liquid they represent (augPTL) is reconstructed by reverse fractional crystallization of wall augite from the most ferroan glass. Inclusions in orthopyroxene consist of glass + 30–50 vol % daughter cpx. The cpx shows complete, but the glass only partial, reequilibration of Fe/Mg. A range of possible compositions for the primary trapped liquid they represent (opxPTL) is calculated by modal recombination of glass and cpx, followed by addition of wall orthopyroxene and adjustment of Fe/Mg for equilibrium with the primary orthopyroxene. Only a small subset of these compositions is plausible on the basis of being orthopyroxene-saturated. Results indicate that olPTL, assumed to represent the parent magma of these rocks, was saturated only with olivine and in equilibrium with Fo ∼ 83. AugPTL and opxPTL are very similar in composition; both are close to augite + orthopyroxene co-saturation and in equilibrium with Fo 87/8. We suggest that olPTL was reduced to Fo 87/8 due to smelting during ascent, and show that this produces a composition very similar to that of augPTL and opxPTL. REE data for each of the three primary silicates and the least evolved melt inclusions in olivine are used to calculate REE abundances in the Hughes/FRO parent magma. All four methods yield very similar results, indicating a REE pattern that is strongly LREE-depleted (Sm/La = 3.3–3.7), with a small negative Eu anomaly (Eu/Eu* = 0.82) and slight HREE-depletion (Gd/Lu = 1.4–1.6). The Hughes/FRO parent magma provides a robust constraint on models for the petrogenesis of augite-bearing ureilites. Its major, minor and rare earth element composition suggests derivation through mixing and/or assimilation processes, rather than as a primary melt on the ureilite parent body.

Rare earth elements in thermal water from the Sob-1 well, Murska Sobota, NE Slovenia

Thermal water produced from the Sob-1 well is a water mixture contributed from several stratified aquifers that belong to two hydrogeological subsystems termed Middle- and Upper Subsystem. The subsystems’ thermal waters differ appreciably in the REE and Y signatures; ΣREE + Y averages to about 10 and 0.2 ppb for the Middle- and Upper-subsystem, respectively. As the Sob-1 well experiences pressure cycling, the inflow from the subsystems’ aquifers is not constant but cycles as well causing the cycling of chemical composition of abstracted thermal water mixture, including REEs and Y. PAAS normalized cycling REE and Y distribution for thermal water mixture from the Sob-1 well indicates that the abundance of REEs and Y is mainly controlled by solubility of their carbonate and bicarbonate species, and therefore by availability of free and dissolved carbon dioxide in the aquifer.