Experimental modeling of the origin of the Moon’s metallic core at partial melting

Geochemical criteria of the Moon’s composition as deficient in Fe and depleted in volatile components and the distribution of siderophile elements in the planet offer the possibility of correlating, under certain conditions, the origin of the Moon and its core from an initial material of composition close to CI carbonaceous chondrites. In order to verify the model of the percolation of liquid metallic Fe through a silicate matrix of chondritic composition at low degrees of melting, we have experimentally modeled Fe movement and deposition in the course of high-temperature centrifugation. The starting experimental mixture had the composition 85% Ol, 10% ferropicrite, and 5% Fe-S (95% Fe and 5% S); the experimental conditions were 4000 g “gravity”, T = 1440°C, Δ log fO₂(IW) ～ ?5.5. In our experiments, Fe was segregated in systems with Fe sulfide and silicate melts at partial melting under reduced conditions and the deformation of the silicate framework. Our results indicate that the Moon could be produced from a material of composition close to CI carbonaceous chondrite.     

Nb–Ta–(Ti–Sn) oxide mineral chemistry as tracer of rare-element granitic pegmatite fractionation in the Borborema Province,Northeastern Brazil

The Borborema Pegmatitic Province (BPP), northeastern Brazil, is historically important for tantalum mining and also famous for top-quality specimens of exotic Nb–Ta oxides and, more recently, for the production of gem quality, turquoise blue, ‘Paraíba Elbaite.’ With more than 750 registered mineralized rare-element granitic pegmatites, the BPP extends over an area of about 75 by 150 km in the eastern part of the Neoproterozoic Seridó Belt. The Late Cambrian pegmatites are mostly hosted by a sequence of Neoproterozoic cordierite–sillimanite biotite schists of the Seridó Formation and quartzites and metaconglomerates of the Equador Formation. The trace-element ratios in feldspar and micas allow to classify most pegmatites as belonging to the beryl–columbite phosphate subtype. Electron microprobe analyses (EMPA) of columbite, tapiolite, niobian–tantalian rutile, ixiolite and wodginite group minerals from 28 pegmatites in the BPP are used to evaluate the effectiveness of Nb–Ta oxide chemistry as a possible exploration tool, to trace the degree of pegmatite fractionation and to classify the pegmatites. The columbite group mineral composition allows to establish a compositional trend from manganoan ferrocolumbite to manganocolumbite and on to manganotantalite. This trend is typical of complex spodumene- and/or lepidolite-subtype pegmatites. It clearly contrasts with another trend, from ferrocolumbite through ferrotantalite to ferrowodginite and ferrotapiolite compositions, typical of pegmatites of the beryl–columbite phosphate subtype. Large scatter and anomalous trends in zoned crystals partially overlap and conceal the two main evolution patterns. This indicates that a large representative data set of heavy mineral concentrate samples, collected systematically along cross-sections, would be necessary to predict the metallogenetic potential of individual pegmatites. Other mineral species, e.g. garnets and/or tourmaline, with a more regular distribution than Nb–Ta oxides, would be more appropriate and less expensive for routine exploration purposes. The currently available Nb–Ta oxide chemistry data suggest the potential for highly fractionated Ta–Li–Cs pegmatites in the BPP, so far undiscovered, and encourages further, more detailed research.     

Evidence of sulfide melting and melt fractionation during amphibolite facies metamorphism of the Rajpura–Dariba polymetallic sulfide ores

Partial melting of sulfide ores during prograde metamorphism could have been more prevalent than generally accepted. However, identification of such melting is difficult as sulfide melts do not form glasses and the textures generated on quenching are obliterated due to the tendency of sulfides for ready recrystallization. The polymetallic base metal sulfide deposit at Rajpura–Dariba, Rajasthan, India is a typical stratiform ore metamorphosed to the middle amphibolite facies. The peak metamorphic temperature of 600 °C should have been sufficient to initiate sulfide melting as evident from experimental studies in the ZnS–PbS–Cu₂S–FeS₂–S system. Further, syn-metamorphic melting of the original SEDEX ore was abetted by the high f_S2 condition that prevailed as a consequence of barite dissolution. A Zn–Fe–S melt containing minor Pb, Sb and Cu but no Ag fractionated from an initial melt in the above system resulting in a residual immiscible sulfosalt-bearing PbS melt. The final metallic melts, represented by formation of dyscrasite (Ag₃Sb) from the sulfosalt-bearing melt and breithauptite (NiSb) or ullmannite (NiSbS) from the sulfosalt-absent melt, were a product of independent fractional crystallization of the immiscible sulfide and PbS–sulfosalt melts.     

Ulan-Tologoi Ta–Nb Deposit: the Role of Magmatism in the Formation of Rare Metal Mineralization

The role of magmatic differentiation is considered for the formation of the Ulan-Tologoi Ta–Nb–Zr deposit (northwestern Mongolia) related to the eponymous alkali granite pluton. Data are presented on the structure of the pluton, the composition of its rocks, and distribution of rare metal mineralization. The ores of the pluton include alkali granites with contents of ore elements exceeding the normative threshold for Ta (>100 ppm). The rare metal mineralization includes pyrochlore, columbite, zircon, bastnaesite, monazite, and thorite, which are typical of all alkali–salic rocks; however, their amount varies depending on the REE content of the rocks. The pluton was formed ~298 Ma ago under the influence of a mantle-crustal melt source.

     

Tracking magmatic and hydrothermal Nb–Ta–W–Sn fractionation using mineral textures and composition: A case study from the late Cretaceous Jiepailing ore district in the Nanling Range in South China

The Jiepailing mining district in the Nanling range in South China is well-known for its granite-related Sn–Be–F-mineralization. Recently, drill holes have exposed an Nb–Ta–W–Sn mineralized granitic porphyry and topaz-bearing granite–greisen at depth, which we have studied here, using mineral (columbite, rutile, wolframite, cassiterite, zircon, and mica) major- and trace-element compositional data, mineral textures, and zircon and columbite U–Pb geochronology. Our age data shows that the porphyry and the granite and their mineralization formed at ~ 91–89 ± 1 Ma in the late-Cretaceous, and thus subsequent to the main ore-forming events of the region. Continuous mineral compositional trends indicate that the studied granitoids are related by progressive fractionation. We propose that: (1) subhedral–euhedral, low-Ta columbite crystallized from melt; (2) euhedral–subhedral rutile and wolframite and subhedral and subhedral cassiterite up to ~ 30 μm in size formed at the magmatic–hydrothermal transition of the system; and (3) high-Ta columbite and subhedral cassiterite up to ~ 10 μm in size formed from subsolidus hydrothermal fluids. In combination with the Nb, Ta, W, and Sn compositions of zircon and mica, their textures and compositional variation allow us to track the magmatic to hydrothermal rare-metal fractionation (concentration, mobilization, and deposition) of the system in detail, despite our limited access to it through only two exploration drill cores. Using the Nb, Ta, W, and Sn concentrations in zircon (refractory, early-crystallized) and in micas (late equilibrated), respectively, was particularly useful for tracing the partial loss of Sn and W ore components from the intrusion, and to constrain the information which is crucial for any rigorous ore exploration.     

The effect of bulk composition on the solidus of carbonated eclogite from partial melting experiments at 3 GPa

To explore the effect of bulk composition on the solidus of carbonated eclogite, we determined near-solidus phase relations at 3 GPa for four different nominally anhydrous, carbonated eclogites. Starting materials (SLEC1, SLEC2, SLEC3, and SLEC4) were prepared by adding variable proportions and compositions of carbonate to a natural eclogite xenolith (66039B) from Salt Lake crater, Hawaii. Near-solidus partial melts for all bulk compositions are Fe–Na calcio-dolomitic and coexist with garnet + clinopyroxene + ilmenite ± calcio-dolomitic solid solution. The solidus for SLEC1 (Ca#=100 × molar Ca/(Ca + Mg + Fe_T)=32, 1.63 wt% Na₂O, and 5 wt% CO₂) is bracketed between 1,050°C and 1,075°C (Dasgupta et al. in Earth Planet Sci Lett 227:73–85, 2004), whereas initial melting for SLEC3 (Ca# 41, 1.4 wt% Na₂O, and 4.4 wt% CO₂) is between 1,175°C and 1,200°C. The solidus for SLEC2 (Ca# 33, 1.75 wt% Na₂O, and 15 wt% CO₂) is estimated to be near 1,100°C and the solidus for SLEC3 (Ca# 37, 1.47 wt% Na₂O, and 2.2 wt% CO₂) is between 1,100°C and 1,125°C. Solidus temperatures increase with increasing Ca# of the bulk, owing to the strong influence of the calcite–magnesite binary solidus-minimum on the solidus of carbonate bearing eclogite. Bulk compositions that produce near-solidus crystalline carbonate closer in composition to the minimum along the CaCO₃-MgCO₃ join have lower solidus temperatures. Variations in total CO₂ have significant effect on the solidus if CO₂ is added as CaCO₃, but not if CO₂ is added as a complex mixture that maintains the cationic ratios of the bulk-rock. Thus, as partial melting experiments necessarily have more CO₂ than that likely to be found in natural carbonated eclogites, care must be taken to assure that the compositional shifts associated with excess CO₂ do not unduly influence melting behavior. Near-solidus dolomite and calcite solid solutions have higher Ca/(Ca + Mg) than bulk eclogite compositions, owing to Ca–Mg exchange equilibrium between carbonates and silicates. Carbonates in natural mantle eclogite, which have low bulk CO₂ concentration, will have Ca/Mg buffered by reactions with silicates. Consequently, experiments with high bulk CO₂ may not mimic natural carbonated eclogite phase equilibria unless care is taken to ensure that CO₂ enrichment does not result in inappropriate equilibrium carbonate compositions. Compositions of eclogite-derived carbonate melt span the range of natural carbonatites from oceanic and continental settings. Ca#s of carbonatitic partial melts of eclogite vary significantly and overlap those of partial melts of carbonated lherzolite, however, for a constant Ca-content, Mg# of carbonatites derived from eclogitic sources are likely to be lower than the Mg# of those generated from peridotite.     

Organic geochemistry across the Permian–Triassic transition at the Idrijca Valley,Western Slovenia

Bulk and molecular stable C isotopic compositions and biomarker distributions provide evidence for a diverse community of algal and bacterial organisms in the sedimentary organic matter of a carbonate section throughout the Permian–Triassic (P/Tr) transition at the Idrijca Valley, Western Slovenia. The input of algae and bacteria in all the Upper Permian and Lower Scythian samples is represented by the predominance of C₁₅–C₂₂ n-alkanes, odd C-number alkylcyclohexanes, C₂₇ steranes and substantial contents of C₂₁–C₃₀ acyclic isoprenoids. The occurrence of odd long-chain n-alkanes (C₂₂–C₃₀) and C₂₉ steranes in all the samples indicate a contribution of continental material. The decrease of C_org and C_carb contents, increase of Rock-Eval oxygen indices, and ¹³C-enrichment of the kerogen suggest a decrease in anoxia of the uppermost Permian bottom water. The predominance of odd C-number alkylcycloalkanes, C₂₇ steranes, and C₁₇ n-alkanes with δ¹³C values ∼−30‰, and ¹³C-enrichment of the kerogens in the lowermost Scythian samples are evidence of greater algal productivity. This increased productivity was probably sustained by a high nutrient availability and changes of dissolved CO₂ speciation associated to the earliest Triassic transgression. A decrease of C_org content in the uppermost Scythian samples, associated to a ¹³C-depletetion in the carbonates (up to 4‰) and individual n-alkanes (up to 3.4‰) compared to the Upper Permian samples, indicate lowering of the primary productivity (algae, cyanobacteria) and/or higher degradation of the organic matter.     

Eutectic temperatures and melting relations in the Fe–O–S system at high pressures and temperatures

We have investigated melting relations in the Fe–O–S ternary system in the pressure range of 15–27 GPa and 1873 K. Subsolidus phase relations are Fe, Fe₃S₂, and FeO up to 17 GPa and Fe, Fe₃S, and FeO above this pressure. The eutectic temperature slightly decreases from ambient pressure to 17 GPa, whereas increases above this pressure. The eutectic temperature in this study is 100 K lower than that in the Fe–S binary system. The oxygen content in the Fe–O–S eutectic liquid drops when the coexisting solid phases changes from FeS to Fe₃S₂. The cotectic lines in the ternary phase diagram lie close to the Fe–FeS binary axis. The isothermal sections indicate that oxygen solubility in the Fe–O–S liquid increases with increasing temperature, and with increasing sulfur content. The solubility of sulfur in the solid Fe has a maximum value at the eutectic temperature, and decreases with increasing temperature. Our results could have important implications for formation and composition of the Martian core.     

The Al (Nb,Ta) Ti(in−2) substitution in titanite: the emergence of a new species?

Summary The highest (Nb, Ta) content ever encountered in titanite is reported from the Maríkov 11 pegmatite in northern Moravia, Czech Republic. This dike is a member of a pegmatite swarm of the beryl-columbite subtype, metamorphosed under conditions of the amphibolite facies. The pegmatite carries, i.a., rare tantalian rutile intergrown with titanian ixiolite, titanian columbite-tantalite, fersmite and microlite. Fissures generated in the Nb, Ta oxide minerals during deformation are filled with titanite, formed by reaction of the oxide minerals with metamorphic pore fluids. The titanite displays limited degrees of substitutions Na(Ta > Nb)(CaTi)_–1, (Ta > Nb)₄Ti_–4Si_–1 and AI(OH, F)(TiO)_–1, but an extensive (and occasionally the sole significant) substitution (Al > Fe³⁺)(Ta > Nb)Ti_–2, responsible for widespread oscillatory zoning. This substitution reduces the proportion of the titanite componentsensu stricto, CaTiSiO₄,O, to less than 50 mole % in many analyzed spots. The extreme composition corresponds to (Ca_0.994Na_0.011)(Ti_0.436Sn_0.007Al_0.280Fe³⁺ _0.006Ta_0.199Nb_0.079)Si_0.988O₄(O_0.974F_0.026). However, so far this substitution fails to generate compositions that would define a new species.

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Zusammenfassung Die AI(Nb, Ta)Ti_–2 Substitution im Titanit: Auftauchen einer neuen Mineralspecies? Die höchsten (Nb, Ta) Gehalte, die jemals für Titanit gefunden wurden, werden für den Maríkov II Pegmatit in Nordmähren, Tschechei, berichtet. Der Intrusivgang ist Teil eines Amphibolit-faziell überprägten Pegmatitschwarms vom Beryll-Columbit Subtypus Der Pegmatit führt u.a. seltene tantalbetonte Rutile verwachsen mit titanbetontem Ixiolith, titanbetontem Columbit-Tantalit, Fersmit and Mikrolith. Deformationsbedingte Frakturen in den (Nb, Ta) Oxiden sind mit Titanit, als Folge der Reaktion der metamorphen Porenlösungen mit den Oxidmineralen, verkittet. Titanit zeigt begrenzte Substitutionen Na(Ta > Nb)(CaTi)_–1,(Ta > Nb)₄Ti_–4Si_–1 and Al(OH, F)(TiO)_–1, aber extensive (und gelegentlich einzig bedeutsame) Substitution (Al >> Fe³⁺)(Ta > Nb)Ti_–2, die eine weitverbreitete, oszillierende Zonierung hervorruft. Diese Substitution verringert den Anteil der Titanit-Komponentesensu stricto, CaTiSiO,O, auf weniger als 50 Mol% in vielen Analysen. Die Extremzusammensetzung entspricht Ca_0.994Na_0.11) (T_10.436Sn_0.007Al_0.280Fe³⁺ _0.006Ta_0.199Nb_0.079)Si_0.988O₄(O_0.974F_0.026). Das AusmaB dieser Substitution ist unzureichend, um eine neue Mineralspecies zu definieren.

     

Cenozoic volcanic rocks in the Belog Co area, Qiangtang, northern Tibet, China： Petrochemical evidence for partial melting of the mantle-crust transition zone

Neogene volcanic rocks in the Belog Co area, Qiangtang, northern Tibet, are represented by a typical intermediate-basic and intermediate alkaline rock association, with latite-trachyte as the main rock type. The results of chemical analysis are: SiO2=52%–62%, Al2O3>15%, Na2O/K2O>1 and MgO<3.30%. In addition, the volcanic rocks are LREE-enriched with LREE/HREE=10–13, (La/Yb)N=15–19, and show a weak negative Eu anomaly with δEu=0.71–0.89. The close relationship between Mg# and SiO2 and the co-variation of the magmatophile elements and ultra-magmatophile elements such as La/Sm-La and Cr-Tb indicate that this association of volcanic rocks is the product of comagmatic fractional crystallization. The rock association type and lower Sm/Yb values (Sm/Yb=3.23–3.97) imply that this association of volcanic rocks should have originated from partial melting of spinel lherzolite in the lithospheric mantle. On the other hand, the weak negative Eu anomaly and relative depletion in Nb, Ta and Ti reflect the features of terrigenous magma. So the Neogene Belog Co alkaline volcanic rocks should be the result of partial melting of the special crust-mantle transition zone on the Qinghai-Tibet Plateau.     

Origin of K-rich diamond-forming immiscible melts and CO2 fluid via partial melting of carbonated pelites at a depth of 180–200 km

Melt inclusions in kimberlitic and metamorphic diamonds worldwide range in composition from potassic aluminosilicate to alkali-rich carbonatitic and their low-temperature derivative, a saline high-density fluid (HDF). The discovery of CO₂ inclusions in diamonds containing eclogitic minerals are also essential. These melts and HDFs may be responsible for diamond formation and metasomatic alteration of mantle rocks since the late Archean to Phanerozoic. Although a genetic link between these melts and fluids was suggested, their origin is still highly uncertain. Here we present experimental results on melting phase relations in a carbonated pelite at 6 GPa and 900–1500 °C. We found that just below solidus K₂O enters potassium feldspar or K₂TiSi₃O₉ wadeite coexisting with clinopyroxene, garnet, kyanite, coesite, and dolomite. The potassium phases react with dolomite to produce garnet, kyanite, coesite, and potassic dolomitic melt, 40(K_0.90Na_0.10)₂CO₃·60Ca_0.55Mg_0.24Fe_0.21CO₃ + 1.9 mol% SiO₂ + 0.7 mol% TiO₂ + 1.4 mol% Al₂O₃ at the solidus established near 1000 °C. Molecular CO₂ liberates at 1100 °C. Potassic aluminosilicate melt appears in addition to carbonatite melt at 1200 °C. This melt contains (mol/wt%): SiO₂ = 57.0/52.4, TiO₂ = 1.8/2.3, Al₂O₃ = 8.5/13.0, FeO = 1.4/1.6, MgO = 1.9/1.2, CaO = 3.8/3.2, Na₂O = 3.2/3.0, K₂O = 10.5/15.2, CO₂ = 12.0/8.0, while carbonatite melt can be approximated as 24(K_0.81Na_0.19)₂CO₃·76Ca_0.59Mg_0.21Fe_0.20CO₃ + 3.0 mol% SiO₂ + 1.6 mol% TiO₂ + 1.4 mol% Al₂O₃. Both melts remain stable to at least 1500 °C coexisting with CO₂ fluid and residual eclogite assemblage consisting of K-rich omphacite (0.4–1.5 wt% K₂O), almandine-pyrope-grossular garnet, kyanite, and coesite. The obtained immiscible alkali‑carbonatitic and potassic aluminosilicate melts resemble compositions of melt inclusions in diamonds worldwide. Thus, these melts entrapped by diamonds could be derived by partial melting of the carbonated material of the continental crust subducted down to 180–200 km depths. Given the high solubility of chlorides and water in both carbonate and aluminosilicate melts inferred in previous experiments, the saline end-member, brine, could evolve from potassic carbonatitic and/or silicic melts by fractionation of Ca-Mg carbonates/eclogitic minerals and accumulation of alkalis, chlorine and water in the residual low-temperature supercritical fluid. Direct extraction from the hydrated marine sediments under conditions of cold subduction would be another possibility for the brine formation.     

Geochemical compositional changes at the Pliocene–Pleistocene transition in fluviodeltaic deposits in the Tegelen-Reuver area (southeastern Netherlands)

2 O contents, which can be attributed to the Alpine source supplying fresh, sodic plagioclase-rich material instead of the local, strongly weathered sediments. Increasing K₂O/Al₂O₃ can be attributed to a similar decrease in degree of weathering. However, this trend is disturbed by the loss of K from clay minerals during weathering in organic-rich layers. Local high TiO₂ anomalies, caused by preferential sorting and concentration, are found in most Pliocene sections, but they are absent in the Upper Pliocene and Lower Pleistocene Alpine-derived deposits. This change is probably due to a change in the energy of the fluvial system. Finally, (pyrite-) S contents drop (siderite-) Fe contents rise. Micromorphological observations indicate that the Pliocene pyrite was formed when freshwater deposits were flooded with seawater during short-term events. The decrease in S, and the increase in siderite-Fe, can be attributed to decreasing marine influence, as a result of the marine regression at the Pliocene–Pleistocene transition. Received: 28 August 1999 / Accepted: 2 November 1999     

Magmatic Evolution and Mineralization Process of the Super-Large Shihuiyao Rb–Nb–Ta Deposit, Southern Great Xing’an Range, China

正Objective Rare metal ore reserves are an important strategic resource,and their metallogenic mechanism and mineralization studies have also been received widespread international attention.The Shihuiyao super-large Rb-Nb-Ta deposit from the Southern Great Xing’an Range,NE China is the world’s largest Rb deposit,whose reserves     

Effect of network-forming cations on the oxygen isotope fractionation between silicate melts: Experimental study at 1400–1570°C

We have experimentally studied the behavior of oxygen isotope composition in silicate melts with a wide range of network-forming cations. Isotopic equilibration of the Di-An eutectic melts modified by addition of Si, Al, Ti, and Fe was carried out in a vertical tube furnace within a temperature range from 1400 to 1570°C. It was established that the value ^{10 3}Lnα between silicic and basic melts at 1400 and 1450°C systematically increases with increase of SiO₂ content, reaching ≈1‰ at 20% melt silica enrichment. The effect of the Fe₂O₃, TiO₂, and Al₂O₃ contents was studied at 1500°C. An increase in Fe₂O₃ from 5 to 20 wt % causes a 0.4‰ increase of δ¹⁸O. An increase in Ti and Al contents results in the non-linear behavior of δ¹⁸O, which decreases in the region of the highest TiO₂ (28.4%) and Al₂O₃ (29.3 %) contents. In the region of moderate Fe₂O₃, TiO₂, and Al₂O₃ contents, the values of δ¹⁸O show monotonous linear dependence on the oxide contents. Methods of estimations of oxygen isotope fractionation coefficients at T > 1400°C in the studied range of network-forming oxides are considered on the basis of experimental data. The calculation of fractionation coefficients with the use of I¹⁸O index showed that experimental values with increase of SiO₂ content deviate from calculated values by 0.3‰ for basic melts and 0.5–0.6‰ in the region of silicic melts. Similar pattern is observed during approximation of a melt by normative mineral composition. The calculation with the Garlick index leads to the systematic underestimation (on average, by 0.3‰) of 10³Lnα as compared to the experimental data. The NBO/T ratio appeared the best parameter to describe 10³Lnα in the melt-melt system, including the region of high-Fe melts. Analysis of experimental data leads us to conclude that the degree of polymerization of the melts in the studied temperature-composition region is the most important factor affecting the oxygen-isotope fractionation in the melt-melt system. Empirical index similar to the Garlick index was proposed to take into account oxygen associated with T-cations: $$I^m = (C_{Si} + aC_{Al} + bC_{Ti} + cC_{Fe^{3 + } } )/\Sigma C_i ,$$ where a, b, and c constants are empirically established coefficients: 0.75, 0. 70, and 1.75, respectively.     

A study of rare earth element (REE)–SiO2 variations in felsic liquids generated by basalt fractionation and amphibolite melting: a potential test for discriminating between the two different processes

The origin of felsic magmas (>63% SiO₂) in intra-oceanic arc settings is still a matter of debate. Two very different processes are currently invoked to explain their origin. These include fractional crystallization of basaltic magma and partial melting of lower crustal amphibolite. Because both fractionation and melting can lead to similar major element, trace element and isotopic characteristics in felsic magmas, such lines of evidence have been generally unsuccessful in discriminating between the two processes. A commonly under-appreciated aspect of rare earth element (REE) solid–liquid partitioning behavior is that D _REE for most common igneous minerals (especially hornblende) increase significantly with increasing liquid SiO₂ contents. For some minerals (e.g., hornblende and augite), REE partitioning can change from incomptatible (D < 1) at low liquid SiO₂ to compatible (D > 1) at high liquid SiO₂. When this behavior is incorporated into carefully constrained mass-balance models for mafic (basaltic) amphibolite melting, intermediate (andesitic) amphibolite melting, lower or mid to upper crustal hornblende-present basalt fractionation, and mid to upper crustal hornblende-absent basalt fractionation the following general predictions emerge for felsic magmas (e.g., ∼63 to 76% SiO₂). Partial melting of either mafic or intermediate amphibolite should, regardless of the type of melting (equilibrium, fractional, accumulated fractional) yield REE abundances that remain essentially constant and then decrease, or steadily decrease with increasing liquid SiO₂ content. At high liquid SiO₂ contents LREE abundances should be slightly enriched to slightly depleted (i.e., C _l/C _o ∼ 2 to 0.2) while HREE abundances should be slightly depleted (C _l/C _o ∼ 1 to 0.2). Lower crustal hornblende-bearing basalt fractionation should yield roughly constant REE abundances with increasing liquid SiO₂ and exhibit only slight enrichment (C _l/C _o ∼ 1.2). Mid to upper crustal hornblende-bearing basalt fractionation should yield steadily increasing LREE abundances but constant and then decreasing HREE abundances. At high liquid SiO₂ contents LREE abundances may range from non-enriched to highly enriched (C _l/C _o ∼ 1 to 5) while HREE abundances are generally non-enriched to only slightly enriched (C _l/C _o ∼ 1 to 2). Hornblende-absent basalt fractionation should yield steadily increasing REE abundances with increasing liquid SiO₂ contents. At high SiO₂ contents both LREE and HREE are highly enriched (C _l/C _o ∼ 3 to 4). It is proposed that these model predictions constitute a viable test for determining a fractionation or amphibolite melting origin for felsic magmas in intra-oceanic arc environments where continental crust is absent. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Magmatic–hydrothermal rare-element mineralization in the Songshugang granite (northeastern Jiangxi,China): Insights from an electron-microprobe study of Nb–Ta–Zr minerals

The Songshugang granite, hidden in the Sinian metasedimentary stratum, is a highly evolved rare-element granite in northeastern Jiangxi province, South China. The samples were systematically taken from the CK-102 drill hole at the depth of 171–423 m. Four types of rocks were divided from the bottom upwards: topaz albite granite as the main body, greisen nodules, topaz K-feldspar granite and pegmatite layer. Electron-microprobe study reveals that the rare-element minerals of the Songshugang granite are very different from those of other rare-element granites. Mn^# [Mn/(Fe + Mn)] and Ta^# [Ta/(Nb + Ta)] of columbite-group minerals and Hf^# [Hf/(Zr + Hf)] of zircon are nearly constant within each type of rocks. However, back-scattered electron imaging revealed that Nb–Ta oxides and zircon of the Songshugang granite, especially those of topaz albite granite, topaz K-feldspar granite and greisen, are commonly characterized by a specific two-stage texture on the crystal scale. The early-stage Nb–Ta oxide is simply subhedral-shaped columbite-(Fe) (CGM-I) with low Mn^# (0.16–0.37) and Ta^# (0.05–0.29). Columbite-(Fe) is penetrated by the later-stage tantalite veinlets (CGM-II) or surrounded by complex Nb–Ta–Sn–W mineral assemblages, including tantalite-(Fe), wodginite (sl), cassiterite, and ferberite. Tantalite has wide range of Mn^# values (0.15–0.88) from Fe-dominance to Mn-dominance. Wodginite with Ta>Nb has large variable concentrations of W, Sn and Ti. Cassiterite and ferberite are all enriched in Nb and Ta (Nb₂O₅ + Ta₂O₅ up to 20.12 wt.% and 31.42 wt.%, respectively), with high Ta^# (>0.5). Similar to Nb–Ta oxides and Nb–Ta–Sn–W mineral assemblages, the early-stage zircon is commonly included by the later-stage zircon with sharply boundary. They have contrasting Hf contents, and HfO₂ of the later-stage zircon is up to 28.13 wt.%. Petrographic features indicate that the early-stage of columbite and zircon were formed in magmatic environment. However, the later-stage of rare-element minerals were influenced by fluxes-enriched fluids. Tantalite, together with wodginite, cassiterite, and ferberite implies a Ta-dominant media. An interstitial fluid-rich melt enriched in Ta and flux at the magmatic–hydrothermal transitional stage is currently a favored model for explaining the later-stage of rare-element mineralization.     

Geochemistry of amphibolitized eclogites and cross-cutting tonalitic–trondhjemitic dykes in the Metamorphic Kimi Complex in East Rhodope (N.E. Greece): implications for partial melting at the base of a thickened crust

In the ultra-high pressure Metamorphic Kimi Complex widespread tonalitic–trondhjemitic dykes, with an intrusion age ca. 65–63 Ma, cross-cut boudins and layers of amphibolitized eclogites. Geochemical investigation proclaims the tied genetic relationship of the amphibolitized eclogites and the associated tonalitic–trondhjemitic dykes. The major and trace element contents and rare earth element patterns of the amphibolitized eclogites indicate formation of their protoliths by fractional crystallization of tholeiitic magmas in a back-arc environment. The tonalites and trondhjemites are characterized by moderate to high Sr contents (>130 ppm), and low Y (<8.2 ppm) and heavy rare earth element contents (Yb content of 0.19–0.88 ppm). The chemical composition of the tonalitic and trondhjemitic dykes are best explained by partial melting of a tholeiitic source like the amphibolitized eclogites with residual garnet and amphibole, at the base of a thickened crust during Early Tertiary subduction/accretion at the southern margins of the European continent.     

Paleoenvironmental conditions across the Cretaceous–Paleogene transition at the Apennines sections (Italy): An integrated geochemical and ichnological approach

Two distal Cretaceous–Paleogene (K/Pg) boundary sections in the Central Apennine region (Italy) have been studied: Bottaccione Gorge and Contessa Highway. Geochemical and carbon isotope analyses on the infilling of trace fossils and on the host sedimentary rocks were performed to determine paleoenvironmental conditions during the Cretaceous–Paleogene transition. Major and trace element contents were measured in a 63 cm-thick interval at Bottaccione Gorge (from 22 cm below to 41 cm above the K/Pg boundary) and in a 72 cm-thick interval at Contessa Highway (from 43 cm below to 29 cm above the K/Pg boundary). Even though the K/Pg ejecta layer is now depleted at these sections due to continuous oversampling, the uppermost Maastrichtian and lowermost Danian deposits record the paleoenvironmental conditions prior to and after the K/Pg event. We used redox-sensitive element ratios (V/Al, Cr/Al, Co/Al, Ni/Al Cu/Al, Zn/Al, Mo/Al Pb/Al and U/Mo) and detrital element ratios (K/Al, Rb/Al, Zr/Al and ƩREE/Al) as proxies of certain environmental parameters, used for paleoenvironmental reconstruction. In general, similar values for elemental ratios are registered within Maastrichtian and Danian deposits, which supports similar paleoenvironmental conditions prior to and after the K/Pg event as well as the rapid reestablishment of the pre-impact conditions (i.e., oxygenation, nutrient availability, and/or sedimentary input). An enrichment in certain redox-sensitive elements above the K/Pg at the Bottaccione Gorge section suggests lower oxygenation, as also evidenced by the tracemaker community. Carbon isotope composition data from the infilling material of trace fossils furthermore reveals values similar to those of the host rocks at the corresponding depth, which supports an active infilling by nearly contemporaneous bioturbation during sediment deposition.     

Consistent modeling of a catastrophic flowslide at the Shenzhen landfill using a hydro-elasto-plastic model with solid–fluid transition

Flow-type landslides are an important hazard that can cause great destruction due to the rapid flow velocity and large disaster area. This paper presents a catastrophic flowslide that recently occurred at a landfill in Shenzhen, China. This disaster involved an area about 1100 m in length and 630 m in maximum width, and caused the death of 77 people and the destruction of 33 buildings. The precise reason for the landfill’s failure is still unknown, and therefore we try to contribute an increased understanding of the event for future prevention. In this study, the failure mechanism of the studied slope was analyzed and described under partially saturated condition. The solid–fluid transition during the flowslide occurrence was described using a unified constitutive model. The model was used to perform the hydro-elasto-plastic modeling in the pre-failure stage, the viscous modeling in the post-failure stage, and the second-order work criterion was introduced in between to model the solid–fluid transition. The consistent evolution of the flowslide, including initiation, propagation, and deposit stages, was simulated and analyzed using the finite element method with Lagrangian integration points after careful calibration of the viscous parameters. The numerical results were compared with the real case and used to explain the failure mechanism.