Low Zr Contents Research Articles

Zircon geochronology of the Koraput alkaline complex: Insights from combined geochemical and U–Pb–Hf isotope analyses, and implications for the timing of alkaline magmatism in the Eastern Ghats Belt, India

Zircon formation and modification during magmatic crystallization and high-grade metamorphism are explored using TIMS and LA-ICP-MS U–Pb geochronology, Lu–Hf isotope chemistry, trace element analysis and textural clues on zircons from the Koraput alkaline intrusion, Eastern Ghats Belt (EGB), India. The zircon host-rock is a granulite-facies nepheline syenite gneiss with an exceptionally low Zr concentration, prohibiting early magmatic Zr saturation. With zircon formation occurring at a late stage of advanced magmatic cooling, significant amounts of Zr were incorporated into biotite, nearly the only other Zr-bearing phase in the nepheline syenite gneisses. Investigated zircons experienced a multi-stage history of magmatic and metamorphic zircon growth with repeated solid-state recrystallization and partial dissolution–precipitation. These processes are recorded by complex patterns of internal zircon structures and a wide range of apparently concordant U–Pb ages between 869±7Ma and 690±1Ma. The oldest ages are interpreted to represent the timing of the emplacement of the Koraput alkaline complex, which significantly postdates the intrusion ages of most of the alkaline intrusion in the western EGB. However, Hf model ages of TDM=1.5 to 1.0Ga suggest an earlier separation of the nepheline syenite magma from its depleted mantle source, overlapping with the widespread Mesoproterozoic, rift-related alkaline magmatism in the EGB. Zircons yielding ages younger than 860Ma have most probably experienced partial resetting of their U–Pb ages during repeated and variable recrystallization events. Consistent youngest LA-ICP-MS and CA-TIMS U–Pb ages of 700–690Ma reflect a final pulse of high-grade metamorphism in the Koraput area and underline the recurrence of considerable orogenic activity in the western EGB during the Neoproterozoic. Within the nepheline syenite gneisses this final high-grade metamorphic event caused biotite breakdown, releasing sufficient Zr for local saturation and new subsolidus zircon growth along the biotite grain boundaries.

Variations of trace element concentration of magnetite and ilmenite from the Taihe layered intrusion, Emeishan large igneous province, SW China: Implications for magmatic fractionation and origin of Fe–Ti–V oxide ore deposits

In situ LA–ICP–MS trace elemental analysis has been applied to magnetite and ilmenite of the Taihe layered intrusion, Emeishan large igneous province, SW China, in order to understand better fractionation processes of magma and origin of Fe–Ti–V oxide ore deposits. The periodic reversals in Mg, Ti, Mn in magnetite and Mg, Sc in ilmenite are found in the Middle Zone of the intrusion and agree with fractionation trends as recorded by olivine (Fo), plagioclase (An) and clinopyroxene (Mg#) compositions. These suggest the Taihe intrusion formed from open magma chamber processes in a magma conduit with multiple replenishments of more primitive magmas. The V and Cr of magnetite are well correlated with V and Cr of clinopyroxene indicating that they became liquidus phases almost simultaneously at an early stage of magma evolution. Ilmenite from the Middle and Upper Zones shows variable Cr, Ni, V, Mg, Nb, Ta and Sc contents indicating that ilmenite at some stratigraphic levels crystallized slightly earlier than magnetite and clinopyroxene. The early crystallization of magnetite and ilmenite is the result of the high FeOt and TiO2 contents in the parental magma. The ilmenite crystallization before magnetite in the Middle and Upper Zones can be attributed to higher TiO2 content of the magma due to the remelting of pre-existing ilmenite in a middle-level magma chamber. Compared to the coeval high-Ti basalts, the relatively low Zr, Hf, Nb and Ta contents in both magnetite and ilmenite throughout the Taihe intrusion indicate that they crystallized from Fe–Ti–(P)-rich silicate magmas. Positive correlations of Ti with Mg, Mn, Sc and Zr of magnetite, and Zr with Sc, Hf and Nb of ilmenite also suggest that magnetite and ilmenite crystallized continuously from the homogeneous silicate magma rather than an immiscible Fe-rich melt. Therefore, frequent replenishments of Fe–Ti–(P)-rich silicate magma and gravitational sorting and settling are crucial for the formation the massive and apatite-rich disseminated ores in the Lower and Middle Zones of the Taihe intrusion.

Provenance and paleoweathering reconstruction of the Mesoproterozoic Hongshuizhuang Formation (1.4 Ga), northern North China

This is the first study presenting major and trace elemental data from the Mesoproterozoic Hongshuizhuang Formation shales in Yanshan basin, North China, in order to reconstruct its provenance and chemical weathering history. The shales are strongly depleted in Na2O and Sr and enriched in Y and transition metal elements relative to upper continental crust. Low Zr concentrations and various discriminant plots (e.g., Th/Sc–Zr/Sc and Al2O3–TiO2–Zr) indicate insignificant mineral sorting or recycling of these shales. The rocks show light rare earth element (REE) enrichment (La/YbCN = 3.99–6.92), flat heavy REE, and significantly negative Eu anomalies (Euan = 0.57–0.68) in chondrite-normalized REE patterns, similar to post-Archean Australian average shales. The fairly uniform REE patterns and trace element ratios indicate that the Hongshuizhuang Formation shales were derived from a felsic source area with granodiorite as the dominant contributor. Mixing calculations suggest a mixture of 30 % granite porphyry, 5 % basalt, and 65 % granodiorite as the possible source of the shales, also supporting that granodiorite was the predominant source. Intense chemical weathering of the source terrain is indicated by high values of the premetasomatized chemical index of alteration, plagioclase index of alteration, Rb/Sr, a strong positive correlation between TiO2 and Al2O3, depletion of CaO, Na2O, and Sr, and mineral compositions. Such strong chemical weathering suggests a warm and wet paleoclimate, perhaps due to high atmospheric CO2 and CH4 concentrations, and a near-equatorial location of the North China Craton in the Columbia supercontinent at 1.4 Ga.

Carboniferous arc magmatism in the Qiangtang area, northern Tibet: Zircon U–Pb ages, geochemical and Lu–Hf isotopic characteristics, and tectonic implications

The Longmu Co–Shuanghu suture zone (LSSZ), which lies between the southern Qiangtang–Baoshan block and northern Qiangtang–Qamdo block on the Tibetan Plateau, represents remnants of the Paleo-Tethys Ocean. Previous investigations have focused on the ophiolite, high-pressure zone, and metamorphic belt in this zone, whereas few studies have considered the arc magmatism. The present study examines a suite of Carboniferous arc-magmatic rocks in the western region of the LSSZ that consist of acidic to basic volcanic rocks, including rhyolite, dacite, andesite, basaltic andesite, basalt, and pyroclastics. Zircon U–Pb dating of three samples (two andesites and one dacite) by laser ablation–inductively coupled plasma–mass spectrometry demonstrates that these rocks were emplaced at ca. 351–346 Ma. The basalts have low Cr and Ni abundances, indicating that they were generated by varying degrees of partial melting of an enriched lithospheric mantle that was metasomatized by subduction-derived components. Zircons in the felsic rocks have positive εHf(t) values of 0.8–14.8, indicating an origin by varying degrees of partial melting of juvenile basaltic lower crust, consisting mainly of underplated magmas with similar compositions to the basalts. Geochemical data show that the volcanic rocks are enriched in light rare earth elements and large ion lithophile elements (e.g., Th, U, and Pb) but are strongly depleted in high field strength elements (e.g., Nb, Ta, and Ti), have high Al2O3 and low Zr concentrations, and are calc-alkaline. These magmas are therefore subduction-related volcanic arc rocks, indicating that Paleo-Tethys subduction began in the early Carboniferous.

Phase evolution during high energy ball milling of immiscible Nb–Zr alloys

Mechanical alloying (MA), a solid-state processing technique used extensively to synthesize metastable phases, was employed to synthesize solid solution and amorphous phases in Nb-rich Nb–Zr powder blends. These metastable phases could be synthesized by MA, under different processing conditions, even though the heat of mixing between Nb and Zr is positive, which makes alloying them difficult. The effect of alloy composition, milling time, and the ball-to-powder weight ratio (BPR) were varied and their effect studied on phase evolution and microstructure in the milled powders. The composition of the milled powders was varied starting from a low value of 5 to about 50at.% Zr. At a Zr content below 40at.%, amorphization was achieved at a higher BPR of 30:1, i.e. more milling energy. The formation of an amorphous phase at Zr contents lower than 40% was achieved for the first time in this work and confirmed using TEM. However, this amorphous phase crystallized rapidly on continued milling (mechanical crystallization) to form an FCC phase. Additionally, milling of powders with low Zr contents primarily resulted in the formation of Nb-based Nb–Zr solid solutions.

Pre‐Alpine discordant granitic dikes in the metamorphic core of the Betic Cordillera: tectonic implications

AbstractPegmatite dikes bearing andalusite crosscut foliation S2 in Alpujarride gneisses and schists. Post‐S2 andalusite is transposed by a foliation S3, defined by fibrolite, which affects the dikes. The dikes represent highly differentiated granitic magmas with low REE and Zr contents and a positive Eu anomaly. U‐Pb SHRIMP dating of magmatic zircons provided Pan‐African ages (cores) and late Variscan ages (rims). However, U‐rich rims also provided metamorphic Alpine ages, supporting a polyorogenic tectonometamorphic history for pre‐Mesozoic Alpujarride rocks.

Influence of Zr alloying on the mechanical properties, thermal stability and oxidation resistance of Cr–Al–N coatings

Cr–Al–N coatings with Zr alloying (Zr contents from 0 to 29.5at.%) were deposited by d.c. reactive magnetron sputtering. The chemical composition and the morphology of as-deposited coatings were characterized, and the phase structure, mechanical properties and wear resistance of the coatings before and after thermal annealing were analyzed and evaluated. With the increase of Zr content, both Cr and N contents decrease whereas Al shows a growing trend. Low Zr (<26.9at.%) coatings are stoichiometric and present a fcc NaCl-type B1 structure with columnar morphology, while high Zr (≥26.9at.%) coatings are in N deficiency and have low crystallinity degree. The alloying of low contents of Zr improves the coating hardness and H/E ratio; however, for low ordered coatings these properties decrease significantly. After thermal annealing, fcc structure is kept in low Zr films whereas the crystalline degree is improved in the high Zr ones and their mechanical properties were slightly improved. Two coatings were selected for further testing, representatives of low (CrAlZr5N) and high (CrAlZr27N) Zr contents. The onset oxidation temperature is ∼900°C and 600°C for CrAlZr5N and CrAlZr27N coatings, respectively. Mainly Cr2O3 is formed on low Zr coatings whereas mixed oxides of ZrO2 and Cr2O3 are detected on CrAlZr27N sample after thermal exposure. In all tribological tests, low Zr coating presents lower wear rate than the CrAlZr27N coating. In general, the addition of very high Zr contents (>20at.%) with N deficiency markedly weakens the mechanical properties and the oxidation resistance of Cr–Al–Zr–N coatings.

In situ LA-(MC)-ICP-MS trace element and Nd isotopic compositions and genesis of polygenetic titanite from the Baogutu reduced porphyry Cu deposit, Western Junggar, NW China

Titanite (sphene, CaTiSiO5) is sensitive to changes in temperature, oxygen and water fugacity, and fluid composition. In order to understand formation processes and the nature of hydrothermal fluids, various types of titanite from Cu ores at the Baogutu reduced porphyry Cu deposit were chosen for detailed study. Magmatic titanite is associated with biotite, plagioclase and K-feldspar, whereas hydrothermal titanite occurs with K-feldspar, chlorite, actinolite and calcite. The formation of hydrothermal titanite was related to hydration of igneous minerals under high fH2O, whereas the widespread replacement of ilmenite by titanite (without magnetite) indicates a relatively low oxygen fugacity. Magmatic titanite has low Al, high Fe, Y, Sn, Zr, Nb and REE contents, relative to hydrothermal titanite. On the basis of the Zr-in-titanite and Al-in-chlorite geothermometers, formation temperatures for magmatic and hydrothermal titanite are estimated to be 687–739°C and 250–670°C, respectively. The gradual decrease in REE, Y and Sn contents from magmatic to late hydrothermal titanite was probably caused by precipitation of REE-bearing minerals. Magmatic and hydrothermal titanites have similar chondrite-normalized REE patterns with negative Eu anomalies and relatively flat HREE. Randomly selected titanites have Nd isotopic compositions similar to the host rocks. Thus, both magmatic and hydrothermal titanite are believed to have been predominantly derived from a mantle source.

Effects of Zr dopant and sintering temperature on electrical properties of In2O3–SrO based ceramics

Electrical properties of indium oxide ceramics doped by Sr and Zr and sintered at 1473 and 1573K in air were studied and are discussed. In2O3–SrO ceramics exhibit nonlinear current–voltage behavior with the current limiting effect: current rises more weakly than voltage, is saturated and even decreased. The Zr dopant changes the type of current–voltage dependency in such materials. In2O3–SrO–ZrO2 ceramics with low Zr content (5–10wt% ZrO2 in mixture) possess linear current–voltage characteristic and very high conductivity. For ceramics with high content of Zr (60wt% ZrO2 in mixture) the current–voltage dependency is superlinear (current is increased stronger than voltage) but the current limiting effect is not observed. Based on the data of dc and ac measurements, temperature dependence of conductivity, X-ray diffraction, and scanning electron microscopy results, the conductivity features of obtained materials are discussed.

High-temperature distillation and consolidation of U–Zr cathode product from molten salt electrorefining of simulated metallic fuel

High-temperature distillation experiments were performed using U–Zr cathode products of various compositions to obtain knowledge on suitable operation conditions and equipment design such as the container material. The LiCl–KCl–UCl3 electrolyte adhering to the U–Zr cathode products was almost completely vaporized at 1273–1573K, under pressure of 10–300Pa. Massive ingots were obtained from the remaining cathode products by heating them at 1573–1673K. Three different phases were identified in a distillation product of a higher Zr content. A U-rich bulk (3.9wt% Zr) and a deposit of a relatively low Zr content (17.2wt% Zr) were considered to be formed during the cooling process of the distillation product. Another Zr-rich deposit (64.7wt% Zr), which might cause the inhomogeneity of product ingots, was expected to result from Zr-rich spots that originally existed in the cathode product. The Cl content in the cathode product was decreased by distillation to less than 1/200 of that after electrorefining, while it was markedly larger at a higher Zr concentration. To limit the amount of Zr-rich deposit and the Cl content, the amount of Zr in the distillation product should be controlled to a sufficiently low level by optimization of the operating procedures and conditions in the electrorefining and distillation steps. The zirconia coating material developed in this study showed superior performance in inhibiting reaction between the melted U–Zr alloy melt and the graphite crucible and also in the easy release of the U–Zr ingot from the crucible.

Provenance of Cored Sediments from Active Margin off Southwestern Taiwan Deduced from Geochemical Constraints

AbstractThe cored sediments sampled by R/V Marion Dufrense in the active margin off southwestern Taiwan on the east side of the Manila Trench are mostly muds consisting mainly of quartz, feldspar, illite, chlorite + kaolinite with a trace amount of montmorillonite. The cored sediments have higher Fe, Ti, Cr, Cs, Li, Ni, and V but lower Ca, Na, Mn, Hf, Nb, Sr, Ta, U and Zr contents when compared with the upper continental crust (UCC, Taylor and McLennan, 1985). The Eu/Eu* ratios of the sediments averaging 0.69 indicate that the recycling effect on the Eu anomaly may be minor and the contribution of mafic source rock was unimportant, which can also be depicted in the La‐Th‐Sc plot (Cullers, 1994) showing a “mixed origin” close to the felsic end member. The chemistry of the cored sediment can be explained by a mixing model designed by Ho and Chen (1996) with four end members i.e., greywacke, shale, quartzite and limestone, which are widely distributed in the Cenozoic formations of southern Taiwan with greywacke as the dominant contributor followed by shale.

Two episodes of Paleoproterozoic metamorphosed mafic dykes in the Lvliang Complex: Implications for the evolution of the Trans-North China Orogen

Tectonic evolution of the Trans-North China Orogen (TNCO) at ∼2.2–1.8Ga is of great importance considering the prolonged controversial issue of when and how the Eastern and Western blocks were assembled to form the coherent basement of the North China Craton. We identified three types of mafic dykes in the Lvliang Complex, of which one was unmetamorphosed and two were subjected to amphibolite facies metamorphism. Zircon LA-ICP-MS U-Pb dating of six metamorphosed mafic dykes yields magmatic crystallization ages of 1919±18Ma, 1939.6±8.2Ma, 1949.9±9.6Ma, 1944±17Ma, 2116±15Ma and 2116±13Ma, indicating two major phases of mafic dykes emplacement at ∼2.11Ga and ∼1.94Ga, respectively. In situ zircon Hf isotope data of the ∼2.11Ga samples vary in large ranges (over fifteen epsilon units) with the highest ɛHf(t) value approaching the depleted mantle array and the lowest value plotting onto the evolution line of the ∼3.1Ga crust, indicating assimilation of depleted mantle-derived magma by old crustal material. For the 1.94Ga samples, almost all the ɛHf(t) values are positive with abundant data near or equal to the contemporary depleted mantle implying limited crustal assimilation. Geochemical data suggest that, most of the ∼2.11Ga dykes are alkaline whereas almost all the ∼1.94Ga dykes are subalkaline. The ∼2.11Ga dykes show variable LREE enrichment (La/Yb=1.9–10.3), prominent Nb-Ta troughs, high Zr contents and Zr/Y ratios while the ∼1.94Ga dykes display no pronounced fractionation between LREE and HREE, and also significant Nb-Ta-Ti negative anomalies, but low Zr contents and Zr/Y ratios. According to the Hf isotopic and the geochemical features, we suggest that the ∼2.11Ga dykes were probably derived from a sub-continental lithospheric mantle in a continental rift with some asthenospheric contribution, whereas, the ∼1.94Ga dykes were arc-related with little crustal contamination during forming and ascending process and the Nb-Ta troughs were probably attributed to subduction-related fluids and melts. Together with the previous researches of the TNCO and other parts of the North China Craton (NCC), we tend to think that there was a whole rift–subduction–collision cycle during the period of ∼2.2–1.85Ga and the subduction process initiated at ∼1.94Ga at least.

Amorphizing and mechanical properties of co-sputtered Al-Zr alloy films

In order to reveal the reason why mechanical properties of alloy films increase continuously after amorphizing, a series of Al-Zr alloy films with different Zr contents are prepared by magnetron co-sputtering of Al and Zr targets. The microstructure and mechanical properties of the films are characterized through a number of techniques, including X-ray energy dispersive spectroscopy, X-ray diffraction, transmission electron microscopy, and nanoindentation. Results show that the films with low Zr content form highly supersaturated solid solutions due to high dispersibility of vapor particles and non-equilibrium growth of the film in co-sputtering process. The film grains are refined to nanoscale particles due to dramatic lattice distortion and the film hardness increases rapidly. As Zr content increases, the film hardness increases continuously because of the increase of Al-Zr chemical bonds after amorphizing, and reaches a high value of 9.8 GPa at 33.3 at.% Zr. The research results reveal the effect of the Al-Zr chemical bonds on mechanical properties in amorphous films

The effect of Zn addition on the structure and transport properties of BaCe0.9−xZrxY0.1O3−δ

Abstract BaCe 0.9− x Zr x Y 0.1 O 3− δ (0.1 ≤ x ≤ 0.9) are ceramic proton conductors widely investigated for different electrochemical devices, such as Solid Oxide Fuel Cell (SOFC) electrolytes, however, their applications are limited by the high sintering temperatures necessary to achieve densification. Polycrystalline powders of BaCe 0.9− x Zr x Y 0.1 O 3− δ (BCZ) have been prepared by freeze-drying precursor method at 1000 °C. These powders were mixed with a zinc nitrate solution to decrease the sintering temperature to 1200–1300 °C. The addition of Zn has several effects on the structure and microstructure of BCZ: the densification and grain growth are enhanced at lower temperature and a reduction of the crystallographic symmetry is observed for samples with low Zr-content ( x ≤ 0.3). Furthermore, the bulk and specific grain boundary conductivities are only slightly affected by the addition of Zn.

Late Precambrian terrigenous rocks of the Anamakit–Muya zone of the Baikal–Muya belt: geochemistry and results of LA-ICP-MS dating of detrital zircons

A comparative geochemical characteristics of Late Precambrian sedimentary rocks (Ust’-Kelyana and Tuluya rock units) in the Anamakit–Muya zone of the Baikal–Muya belt is given, and the conditions of their sedimentation are considered. The first results of U–Pb (LA-ICP-MS) dating of detrital zircons and Sm–Nd isotope data on the Tuluya unit deposits are presented. Petrogeochemical study showed that the studied sediments are first-cycle rocks similar in composition to terrigenous island-arc sediments. The low contents of Th, Rb, Zr, Hf, and LREE and high contents of Co, Ni, Sc, V, Cr, and Fe2O3* in the sandstones of the Ust’-Kelyana unit evidence that these rocks are similar to oceanic-arc deposits. In contrast, the enrichment of the Tuluya unit rocks in Zr, LREE, Th, Rb, and Nb indicates their similarity to deposits of continental island arcs or active continental margin. Isotope-geochronological studies of the Tuluya rock unit showed the mixing of detrital material resulted from the erosion of Neoproterozoic island-arc igneous rock associations (625–700 Ma), like those in the Karalon–Mamakan zone (Yakor’ and Karalon Formations), and more ancient associations, like the Kelyana (812–824 Ma) and/or Dzhaltuk Groups. Judging from the minimum age of detrital zircon, the lower time bound of sedimentation corresponds to 0.6 Ga.

Alkaline rocks of the Ukrainian Shield: Some mineralogical, petrological and geochemical features

Abstract The Ukrainian Shield (USh) is a typical province of Proterozoic alkaline magmatism where about 50 massifs and occurrences of alkaline rocks and carbonatites have been found. In spite of the wide distribution of Devonian basaltic- and alkaline magmatic rocks in the Dnieper-Donetsk depression adjacent to the USh, and in a marginal zone of the USh adjacent to folded Donbass, only alkaline rocks of Proterozoic age (1.8-2.1 Ga) that have been identified in the central interior of the USh. Some discrete bodies of 2.8 Ga subalkaline rocks also occur in Bogdanivka massif (Azov area). Occurrences of both Proterozoic (prevailing) and Phanerozoic (Devonian) alkaline rocks and kimberlites are only found in the eastern part of the USh (Azov area). Kimberlites in the central part of the Ukrainian Shield (Kirovograd region) are also of Proterozoic age (ca 1.8 Ga). It is this predominance of Precambrian rocks that makes the USh so different from other alkaline provinces where Phanerozoic alkaline rocks and kimberlites commonly prevail over Precambrian rocks. The lack of Phanerozoic alkaline magmatism on USh is poorly understood. Two main complexes of alkaline rocks - alkaline-ultrabasic (carbonatitic) and gabbro- syenitic - are distinguished in the USh. There are also rare occurrences of rock types such as alkaline- and alkaline-feldspar granites that may represent one separate alkaline-granite complex. Alkaline rocks present in the Eastern (Azov) province and in the Western province display essentially different geochemical character. Those of the Eastern province show characteristics typical of alkaline-ultrabasic rocks (e.g. high contents of incompatible rare elementssuch as Nb, REE, Zr, Y, Sr, whereas those in the Western province are characterized by low contents of Nb and Zr, and REE in some cases. This fact is interpreted as reflecting different geodynamic conditions of their origin. The Eastern rocks were formed in rift settings, the Western rocks in crustal compressional settings (collision, subduction). Various mineral deposits of phosphorus (apatite), niobium, REE, yttrium and zirconium, including unusually rich ores of REE, Y and Zr (Azov and Yastrybetsky) are associated with the alkaline rocks and carbonatites of the USh.

Effect of a ZrO2 coating deposited by the sol–gel method on the resistance of FeCrAl alloy in high-temperature oxidation conditions

One-, three- and five-layer protective ZrO2 coatings were deposited on a FeCrAl alloy base by the sol–gel method. A zirconium(IV) isopropoxide isopropanol complex was used as the zirconium precursor. It has been shown that zirconium in the amount of 0.3–0.5 wt.% improves the resistance of FeCrAl alloy in high-temperature oxidation conditions (in air at T = 1060 °C for t = 2400 h). Even a very low Zr content affects the morphology, porosity and composition of the forming scale (SEM, EDS). An analysis of the chemical composition of the material after oxidation indicated to-core Zr diffusion. The presence of zirconium prevents catastrophic corrosion of the FeCrAl alloy during oxidation. In the case of the alloy without the reactive element (Zr) this type of corrosion occurred after about 1800 h. The oxidation of the FeCrAl alloy covered with ZrO2 coatings proceeds in three stages. In the first stage, lasting about 50 h, the mass of the sample grows rapidly, then for 700 h the mass changes minimally and in the third stage the oxidation proceeds according to a parabolic dependence. The presence of Zr on the surface of the FeCrAl alloy significantly contributes to the protective effect of the coatings.

Petrogenesis and tectonic significance of Early Cretaceous high-Zr rhyolite in the Dazhou uranium district, Gan-Hang Belt, Southeast China

Early Cretaceous felsic intrusions and volcanic rocks are widespread in the Gan-Hang Belt, SE China. In this study, we report a distinctive high-Zr rhyolite (802–1145ppm Zr) from the Dazhou uranium district in the eastern Gan-Hang Belt. SHRIMP zircon U–Pb dating shows that the Dazhou rhyolite erupted at 127.3±1.7Ma. Geochemical data indicate A-type characteristics for the Dazhou rhyolite, such as high contents of alkali elements, high Fe2O3∗/MgO and high Ga/Al ratios, enrichment in some LILEs, HFSEs, and REEs, and depletion in Sr, Ba, P, and Ti. Compared to other A-type granitoids reported previously in the same belt, the Dazhou high-Zr rhyolite shows only a slight enrichment in other HFSE elements and LREE, but has similar whole-rock Nd and zircon Hf isotopic compositions to those A-type granitoids with relatively lower Zr concentrations, indicating that all these A-type rocks may have similar magma sources. Hence, the difference of Zr contents in these rocks is not due to their different source rocks. We found that zircon grains in the Dazhou high-Zr rhyolite are generally inheritance-poor, and the calculated zircon saturation temperatures are extremely high at ∼1000°C. It is therefore suggested that the distinctive high-Zr characteristic of the Dazhou rhyolite was a result of high-temperature suppression of zircon crystallization by ambient mafic magmas correlative with the upwelling of the asthenospheric mantle. The fundamental difference in magma temperature and magmatic evolution mechanism between the Dazhou high-Zr rhyolite and other A-type granitoid suites in the eastern Gan-Hang Belt brought about their different Zr concentrations.

Determining low concentrations of Zr, Ce, La, and Y in heat-resistant nickel alloys by inductively coupled plasma atomic emission

A technique for mass fraction determination of microalloying additions—Zr, Ce, La, and Y (from 0.001 to 0.1 wt %)—in heat-resistant nickel alloys by inductively coupled plasma atomic emission is described. Results from samples of nickel alloys are in good agreement with the data of spectrophotometric and chemical-spectral analysis. The values of thecontent of Zr, Ce, La, Y in artificial mixtures of nickel-based alloy are reproduced.

Volcanoplutonic association of felsic rocks in the rare-metal ore units of Transbaikalia: Geochemistry of rocks and melts, age, and P-T conditions of their crystallization

The results of study of chemical composition, mineral-forming medium, P-T conditions of crystallization, and the age characteristics of subvolcanic felsic rocks that are spatially associated with rare-metal granite massifs in the ore units of Transbaikalia (Sherlovaya Gora, Khangilay, Bukuka, Belukha, and Shumilovka) give grounds for defining cogenetic volcanoplutonic associations. These associations within the studied region consist of rare-metal granites, ongonites, rhyolites, ongorhyolites, and trachyrhyodacites, which have much in common, but also many differences. The common chemical features of these rocks are their peraluminium signature, low mafic index and basicity, as well as enrichment (as compared to crust) in trace lithophile elements (Li, Rb, Nb, Ta, Sn, W, and F), the low contents of Zr, REE, and Sr, and the similar distribution of trace and refractory elements. At the same time, these rocks differ in the proportions of sodium and potassium, levels of concentrations of lithophile trace and refractory elements, REE distribution patterns, P-T regimes of crystallization, and the volatile composition.