Ti Nb Ta Research Articles

Composition and origin of Ti–Nb–Ta–Zr bearing minerals in the Abu Diab highly evolved granite from the Central Eastern Desert of Egypt

The central Eastern Desert (CED) of Egypt is well-known for its granite-related Nb–Ta mineralization. The garnet-bearing muscovite granite (GMG) of the Abu-Diab composite pluton in the CED consists mainly of quartz, K-feldspar (Or88–98), albite (An0-4) and muscovite, with accessory minerals including garnet, zircon, columbite, ilmenite, Ti-rich hematite, rutile, ilmenorutile, thorite, apatite, xenotime and chlorite. The GMG is weakly peraluminous and has low Nb/Ta (9.6–15.4) and Zr/Hf (16–31) with discernible REEs tetrad effect (TE1-3 = 1.11–1.35), typical of highly evolved granites. Zircon contains high concentrations of U and Th typical of late-magmatic zircon and similar to zircon type from highly evolved granite. The homogenous and weak zoned columbites are classified as manganocolumbite. The formation of Ta-rich rim in the columbite may indicate that later fluids were from the GMG granite itself at advanced fractionation into exsolving fluids, and not from an external source. Ilmenite is greatly enriched in MnO, which indicates the significant pyrophanite (up to 29 mol %) molecules in ilmenite through simple substitution of Mn for Fe2+ with increasing oxygen fugacity under magmatic-hydrothermal conditions. Xenotimes show low analytical totals, suggesting probably hydration during their post-magmatic alteration, while apatite is small-grained associated with tiny zircons, suggesting late-crystalized phases. During late magmatic differentiation stage, the interaction of granitic melt with F-rich late magmatic fluids could be resulted in the formation of Ti–Nb–Ta–Zr minerals. Overall, the Abu Diab GMG possesses mineralogical and geochemical features that make it a potential target for Ti–Nb–Ta–Zr minerals.

Duality in dislocation density-superelasticity correlation in a TNTZ bio alloy processed by cold rolling and subsequent annealing

The effect of restoration mechanisms on the superelastic behavior of a Ti–Nb–Ta–Zr (TNTZ) bio-alloy was investigated in terms of dislocation density-superelasticity correlation. For this purpose, the cold-rolled material (by 70% reduction) was subjected to various annealing temperatures ranging from 500 to 900 °C (30 min) to obtain microstructures with different restoration conditions. The characterization of microstructures was mainly performed by SEM/EBSD, OM, and TEM analysis, although X-ray analysis was also employed to calculate the dislocation densities of the obtained microstructures. The superelasticity of specimens was evaluated by loading-unloading tensile tests. A dual correlation between dislocation density and pseudoelastic (S) ratio was observed in the studying microstructures. A very low superelasticity was observed in dislocation dense structures of cold-rolled and 500 °C annealed specimens. The S value significantly increased in the 600 °C annealed specimen (S = 49%) as dislocation density decreased in the structure. However, further reduction of dislocation density degraded the superelasticity in the specimens annealed at the higher temperature range of 700–900 °C. This nonlinearity behavior was explained by the dissimilar effect of microstructure dislocation density on the direct and reverse transformation of martensite.

The age and geochemistry of the Bardkish syenite, northwest Iran: Syenite formation during Neo‐Tethyan subduction

AbstractSHRIMP U–Pb dating of zircon from two representative samples of the Bardkish syenitic pluton, Urumieh plutonic complex, northwestern Iran, yielded a Late Cretaceous weighted mean 206Pb/238U age of 91.1 ±0.8 Ma (Turonian). The pluton is characterized by high K2O content, Ti–Nb–Ta depletion, enrichment in light rare earth elements and large ion lithophile elements compared to high field strength element, Mg‐rich biotite and calcic amphibole, suggesting a shoshonitic affinity. Geochemical features of the Bardkish syenite are consistent with derivation by fractional crystallization of initial mafic parent magmas. It is most likely that primary magma of the syenite originated from a metasomatized subcontinental lithospheric mantle source with minor crustal component, and underwent a fractional crystallization process during its emplacement. The estimates of trapping pressures and temperatures suggest that crystallization began at the middle crustal level (less than 11 km) near 700–730 °C. The generation of the Bardkish syenite could be related to the subduction of Neo‐Tethyan oceanic crust beneath the Central Iranian microcontinent and it possibly marks a major magmatic episode prior to the final closure of the Neo‐Tethyan ocean in northwest Iran.

Petrogenesis and Tectonic Setting of Ore-Associated Intrusive Rocks in the Baiyinnuoer Zn–Pb Deposit, Southern Great Xing’an Range (NE China): Constraints from Zircon U–Pb Dating, Geochemistry, and Sr–Nd–Pb Isotopes

The Baiyinnuoer skarn Zn–Pb deposit, located in the Southern Great Xing’an Range, Northeast China, is the largest Zn–Pb deposit of the northern China, with a total reserve of 32.74 Mt at average grades of 5.44% Zn and 2.02% Pb. The Zn–Pb ore bodies are hosted in the Lower Permian Huanggangliang Formation. The results of zircon U–Pb geochronology show that the ore-associated granodiorite porphyry, granodiorite, and diorite were emplaced at 248 ± 1.3, 251 ± 1.8, and 249 ± 1.4 Ma, respectively. The granodiorites and granodiorite porphyry have low P2O5 (0.13–0.23 wt %) and A/CNK (0.79–1.05) values, and their SiO2 and P2O5 contents are negatively correlated, indicating I-type affinity. The positive εNd(t) values (+1.3 to +1.8) and young two-stage model ages (TDM2) (880–916 Ma) of the Baiyinnuoer intrusive rocks suggest that they might have formed by the mixing of both mantle and crustal materials. The variations in the major elements, Rb, Sr, and Ba, and the negative Nb–Ta–Ti anomalies indicate that fractional crystallization might have occurred during magma ascent. In combination with the regional geology, the new geochronological, geochemical, and isotopic data reveal that the ore-associated intrusive rocks at Baiyinnuoer were formed in a post-collision setting in the Late Permian.

Microstructure and compressive properties of porous Ti–Nb–Ta–Zr alloy for orthopedic applications

Abstract

Identification of lateral inhomogeneity of arc basement by reconstructing the Late Devonian arc belt in the southwestern Central Asian Orogenic Belt

A reconstruction of the Late Devonian arc belt in the West Junggar and adjacent Kazakhstan regions is crucial for understanding the architecture of the southwestern part of the Central Asian Orogenic Belt. Here, we report zircon U–Pb age, elemental, and Sr–Nd isotopic data for the firstly recognized Late Devonian pluton in the central West Junggar terrane (NW China) to constrain the component of the inner arc belt (IAB) of the Kazakhstan Orocline. Dioritic rocks from the pluton, dated at ∼368 Ma, are calc-alkaline and display negative Nb–Ta–Ti anomalies and positive εNd(t) values ranging from +6.6 to +7.0, implying a juvenile arc setting. Such a Late Devonian arc may thus represent the eastern part of the northern limb of the IAB, but it was built on early Paleozoic accreted terranes, which is distinct from a Precambrian continental basement for the coeval arcs in the central and southern parts of IAB. This difference could be attributed to the lateral inhomogeneity of arc basement, similar to the Aleutian arcs.

Paleoproterozoic ($$\sim$$1.88–1.89 Ga) ultramafic–mafic sills, Cuddapah basin, India—revisited: Implications for interaction between mantle plume and metasomatized subcontinental lithospheric mantle

A number of mafic–ultramafic sills, which are supposed to be part of the widespread ~1.88–1.89 Ga Hampi–Bastanar Large Igneous Province of the Indian shield, are reported to intrude into sedimentary/meta-sedimentary rocks of the Proterozoic Cuddapah basin. Mineral chemistry of chrome-spinel, olivine and pyroxene from the cumulate ultramafic rocks of the Pulivendla sills, emplaced at the base of Tadpatri Formation of the Cuddpaha basin, is presented for better understanding on their nature and genesis. The intermediate Cr#, low Mg#, high Fe3+# and Ti (apfu) coupled with relatively low Al (apfu) content of studied spinel indicate their Alaskan-type nature. Moreover, the Ca-rich clinopyroxene together with classic variations of Al2O3, TiO2 and SiO2 follow the trend of arc type of intrusions. The calculated Al2O3 content of parental melt of the studied rocks also suggests arc-type characteristics. Whole-rock geochemistry show fractionated chondrite-normalized REE patterns, higher Ba/Nb and low Nb/La that suggest contribution from an enriched mantle source, whereas higher Th/Yb and negative Ta–Nb–Ti anomaly on the primitive mantle-normalized multi-element spidergrams emphasize the involvement of a subducted component in the lithospheric mantle source. Although, the mineral chemistry and geochemistry is akin to Alaskan-type intrusion, lack of concentric zoning of lithologies (olivine-rich ultramafic rocks in centre surrounded by mafic rocks), rarity of primary hornblende and abundance of orthopyroxene contradict it to be an Alaskan-type intrusion. It is suggested that the mantle source region of the Pulivendla ultramafic–mafic rocks was modified by a fluid-induced metasomatism during an ancient subduction event. Further, Al-in-olivine thermometry suggests crystallization temperature between 1410° and 1484°C, which is 260°C higher than the average temperature of MORB. Similarly, the estimated mantle potential temperature is also significantly higher (>1600°C) than the different secular cooling models of the earth at ~1.88–1.89 Ga and consistent with the thermal regime of a mantle plume. The existence of mantle plume during 1.88–1.90 Ga, which has played an important role in the genesis of mafic–ultramafic sills of the Cuddapah basin, is also well supported by a radiating mafic dyke swarm, domal uplift and magmatic underplating.

Plastic deformation mechanism of Ti–Nb–Ta–Zr–O alloy at cryogenic temperatures

The deformation behavior and mechanism of Ti–36Nb–2Ta–3Zr-0.35O alloy at room and cryogenic temperatures (77 and 200K) were investigated. The microstructure near the fracture was observed with electron backscattered diffraction analysis (EBSD) and transmission electron microscopy (TEM). The results show that the plastic deformation behavior of the alloy is sensitive to test temperature and cold deformation history of the alloy. For the alloy without cold deformation, both tensile strength and ductility have a significant enhancement at cryogenic temperatures, mainly due to the occurrence of mechanical twinning. Moreover, with the decrease of the temperature, the density of mechanical twinning increases. For the alloy cold swaged by 85%, an increase in strength accompanied by a decrease in uniform elongation was found at cryogenic temperatures. The unique temperature dependence of the deformation behavior was due to the low stability of β phase. At 200K, ω phase precipitated in β phase; while at 77K, an interesting transformation (β phase to β′ phase) was observed.

Geochemistry and Sr–Nd–Hf isotopes of granitoids from the Xiaotuergen porphyry Cu deposit, Altay orogenic Belt, Xinjiang, Northwest China: Implications for petrogenesis, tectonic setting, and mineralization

The Xiaotuergen deposit is the first porphyry Cu deposit to be identified in the northern Xinjiang Altay, Northwest China. Voluminous granitoids comprising granite porphyry, granodiorite porphyry, biotite monzogranite, and quartz porphyry are present in the ore district. Granodiorite porphyry hosts the main Cu mineralization, in disseminated, veinlet, veinlet-disseminated, and stockwork forms. The Xiaotuergen intrusions are weakly metaluminous to peraluminous calc-alkaline to alkaline granitic rocks, and exhibit typical subduction-related geochemical signatures comprising light rare earth element (LREE) enrichment, high field strength element (HFSE) depletion, and low Sr/Y and La/Yb ratios. They are depleted in Nb–Ta–Ti, P, and Eu–Sr, yield moderate Mg# values (41.10–55.38), and show negative but near-zero εNd(t) values (−2.0 to −0.1) and variable positive εHf(t) values (+1.52 to +11.08). Geochemical constraints indicate that the Xiaotuergen granitoids are highly evolved I-type granites which were derived from strong fractional crystallization of a parental magma, mixed with materials derived from partial melting of both subducting oceanic sediments and the overlying mantle wedge. The Xiaotuergen granitoids are products of the same tectono-magmatic activity as that which produced the synchronous magmatic rocks of the Xinjiang Altay, having been formed in a continental arc setting during the early Devonian. The Xiaotuergen ore-bearing porphyries are identified as the shoshonite series, rather than the adakite series. Mantle-derived contributions played a crucial role in the formation of magmas with Cu and S contents that were high enough to produce economic mineralization. The mature arc environment and long-lived magmatism provided favorable conditions for the development of porphyry Cu mineralization.

High-entropy oxide thin films based on Al–Cr–Nb–Ta–Ti

Single-phase crystalline (Al,Cr,Nb,Ta,Ti)O2 high-entropy oxide thin films were synthesized at 400 °C by reactive magnetron sputtering of an equimolar Al–Cr–Nb–Ta–Ti-compound target. These show similar chemistry as well as the same rutile structure, even when varying the relative oxygen flow-rate ratio (fO2) during deposition over a wide range. Upon increasing fO2 from 30 to 80%, their hardness increases from 22 to 24 GPa and their indentation moduli increased from 380 to 410 GPa. The materials stayed single-phase crystalline with the rutile structure during vacuum annealing up to 1200 °C, only their orientation changed from random-like to highly 101-textured.

Microstructure and Mechanical Properties of Cold Drawn Ti–Nb–Ta–Zr–O Wires for Orthodontic Applications

Ti–36Nb–2Ta–3Zr–0.35O (TNTZO) alloy is an excellent candidate for biomedical applications. In this study, a new method combining cold-swaging and cold-drawing was used to fabricate the TNTZO alloy wires with 0.3 mm diameter for orthodontic applications. The microstructure and mechanical properties of cold-drawn and annealed TNTZO wires (referred to as TNTZO0.3 and TNTZO0.3(HT), respectively) were investigated. The results show that the microstructure of cold drawn TNTZO0.3 consists of main-sized elongated grains with 70 nm width. After annealing at 700 °C for 5 min, the microstructure of TNTZO0.3(HT) wires becomes equiaxial with a grain size of ~ 5 μm. The cold drawn TNTZO0.3 wires exhibit improved mechanical properties, higher tensile strength (about 1000 MPa) and similar elastic modulus (69 GPa), compared to annealed TNTZO0.3(HT) wires. Besides, TNTZO0.3 has higher creep resistance and lower stress exponent (around 2), compared to Ti wires and TC4 wires with the same diameter. These results prove that TNTZO0.3 wires have most of the ideal characteristics of orthodontic wires.

Geochronology and geochemistry of Late Carboniferous dykes in the Aqishan–Yamansu belt, eastern Tianshan: Evidence for a post-collisional slab breakoff

With aim of providing constraints on the Late Paleozoic tectonic evolution of the southern Central Asian Orogenic Belt (CAOB), an integrated study was conducted on the geochronological and geochemical data for dioritic, granitic and diabase dykes from the Aqishan–Yamansu belt in the eastern Tianshan, NW China. Zircon U-Pb dating indicates that the dioritic and granitic dykes were both emplaced in the Late Carboniferous (∼311 Ma and ∼315 Ma). The dioritic dykes show adakitic characteristics and have high Na2O and positive εHf(t) values (+12 to +17), which suggest an origin from partial melts of a subducted oceanic slab. The granitic dykes have high SiO2 and K2O contents and are characterized by enriched light rare earth elements (LREE) and slightly flat heavy rare earth elements (HREE), with negative Eu and Nb–Ta–Ti anomalies. These dykes are alkali-calcic and show geochemical features of highly fractionated I-type granites. Their positive εHf(t) values (+16 to +17) suggest that they were derived from a juvenile accreted oceanic crustal source. The coeval diabase dykes have low SiO2 and K2O contents but high TiO2, MgO and Mg# (54–59). They are enriched in LREE and show characteristics of enriched mid-ocean ridge basalts (E-MORB). The relatively high Ba/Th, slightly low Th/Ta ratios, and negative Nb-Ta anomalies imply a mantle source metasomatised by slab-derived fluids. Thus, these basic dykes were generated likely by partial melting of the upwelling asthenosphere mantle with a slight influence of slab-derived fluids. Therefore, we suggest that the formation of these Late Carboniferous dykes were triggered by a post-collisional slab breakoff and the Aqishan–Yamansu belt was a continental arc formed by south-dipping subduction of the Kangguer oceanic plate.

Preparation of Ti–Nb–Ta–Zr alloys for load-bearing biomedical applications

Ti–Nb–Ta–Zr alloys for biomedical applications were successfully fabricated by arc melting (AM) and diffusion bonding. The microstructure, mechanical properties and electrochemistry behavior in a simulated body fluid (SBF) were studied. It shows that melted Ti–Nb–Ta–Zr alloy mainly contains β phase although there are a few Ti-rich phases and micropores, the number of which is lower than that in sintered sample with a few Ti-rich and Ta-rich phases. The melted alloys present higher strength (1224 MPa), Young’s modulus (15.3 GPa) and corrosion potential (− 0.34 V) in SBF, while total recovery strain ratio (67.5%) and pseudoelastic strain ratio (8.4%) of sintered Ti–Nb–Ta–Zr alloy keep higher value than 35.7% and 5.0% for melted Ti–Nb–Ta–Zr. The reasons were discussed based on the microstructure of the Ti–Nb–Ta–Zr alloys.

Nb–Ta–Ti Oxides in Topaz Granites of the Geyersberg Granite Stock (Erzgebirge Mts., Germany)

Oxide minerals (Nb–Ta-rich rutile, columbite-group minerals and W-bearing ixiolite) represent the most common host for Nb, Ta and Ti in high-F, high-P2O5 Li-mica granites and related rocks from the Geyersberg granite stock in the Krušné Hory/Erzgebirge Mts. batholith. This body forms a pipe like granite stock composed of fine- to middle-grained, porphyritic to equigranular high-F, high-P2O5 Li-mica granites, which contain up to 6 vol. % of topaz. Intrusive breccia’s on the NW margin of the granite stock are composed of mica schists and muscovite gneiss fragments enclosed in fine-grained aplitic and also topaz- and Li-mica-bearing granite. Columbite group minerals occur usually as euhedral to subhedral grains that display irregular or patched zoning. These minerals are represented by columbite-(Fe) with Mn/(Mn + Fe) ratio ranging from 0.07 to 0.15. The rare Fe-rich W-bearing ixiolite occurs as small needle-like crystals. The ixiolite is Fe-rich with relatively low Mn/(Mn + Fe) and Ta/(Ta + Nb) values (0.10–0.15 and 0.06–0.20, respectively). Owing to the high W content (19.8–34.9 wt. % WO3, 0.11–0.20 apfu), the sum of Nb + Ta in the ixiolite does not exceed 0.43 apfu. The Ti content is 1.7–5.7 wt. % TiO2 and Sn content is relatively low (0.3–4.1 wt. % SnO2).

Neoarchean suprasubduction zone magmatism in the Sonakhan greenstone belt, Bastar Craton, India: Implications for subduction initiation and melt extraction

The Neoarchean Sonakhan greenstone belt (SGB) in the north‐eastern Bastar Craton is mainly composed of an association of pillowed and massive tholeiitic basalts emplaced within an intraoceanic environment. Two types of ultrabasic rocks were identified and are designated as TH‐1 and TH‐2 on the basis of geochemical parameters. Both sample suites exhibit depletion of HFSE with reference to LILE and LREE, LREE/HFSE ratios, and negative Nb–Ta–Ti anomalies in the primitive mantle‐normalized multi‐element diagrams. The geochemical characters of TH‐1 and TH‐2 are consistent with Island arc tholeiites (IAT) and boninite‐like rocks of both Archean and Phanerozoic terranes. Mineral chemistry of clinopyroxenes from both volcanic suites indicate an oceanic arc affinity. The chromite chemistry indicate its derivation from a boninite‐like magma in a suprasubduction zone (SSZ) environment. Trace element modelling depicts that source depletion with significant influence of fluids derived from the subducting oceanic slab collectively controlled the trace element inventory of the mantle wedge, which result to the higher abundance of LREE and LILE compared to HREE and HFSE. The occurrence of lower basalt sequence followed by IAT and boninite‐like rocks in the SGB define a magmatic evolution which is comparable to the Phanerozoic ophiolite suites that exhibit subduction initiation prior to forearc rifting and suprasubduction zone magmatism. The subduction initiation in the intraoceanic lithosphere and the initial decompression melting followed by the upwelling of the MORB‐related magmas were attributed to the formation of the lower pillow basalts. Dehydration of the subducting plate and the melt extraction processes in the hydrous lherzolite mantle wedge account for the formation of TH‐1. Subsequent depletion and significant modification of a more refractory harzburgite source by the slab‐derived fluids generated the TH‐2 rocks. The compositionally diverse magmatic imprints with IAT and boninite affinity in the SGB indicate the significance of episodic melt extraction processes, dehydration of the subducting plate, and hydrous fluxing in SSZ tectonic setting.

Post-collisional calc-alkaline lamprophyres from the Kadiri greenstone belt: Evidence for the Neoarchean convergence-related evolution of the Eastern Dharwar Craton and its schist belts

Lamprophyres from the greenstone belts play a crucial role in deciphering tectonic and geodynamic processes operating during the Archean. This study presents a comprehensive mineralogical and geochemical study of three lamprophyre dykes with calc-alkaline to shoshonitic affinities from the Neoarchean Kadiri schist belt, eastern Dharwar craton, southern India. These rocks display porphyritic-panidiomorphic texture, typical of the lamprophyres with amphibole (magnesio-hornblende) as phenocrysts, biotite as microphenocrysts and feldspar, epidote, titanite and apatite confined to the groundmass. Alteration of biotite to chlorite is observed along with mild deformation in the amphibole phenocrysts. Based on mineralogy and major oxide geochemistry, these rocks are classified as the calc-alkaline lamprophyres. Higher Ba/Nb and low Nb/La points to their derivation from an enriched lithospheric mantle source and higher Th/Yb ratio along with negative TNT (Ti-Nb-Ta) and Zr-Hf anomalies on the primitive mantle (PM) normalized multi-element diagram indicates dehydrated fluids from the foundering slab could be the possible metasomatic agent. Fractionated HREE ratios (GdN/YbN >1.9) and higher SmN/YbN suggests that the source region lies in the garnet stability field. Higher than PM Rb/Sr along with positive correlation between K/La and Rb/La reveals presence of metasomatic phlogopite in the source region. Strong negative initial εNd along with radiogenic 87Sr/86Sr ratios further support an enriched mantle reservoir involved in their genesis. Non-modal batch melting (1–5%) of a mixed source (phlogopite-garnet peridotite) assuming 5% mixing of subducted sediment with ambient mantle wedge (depleted mantle) satisfies the multi-element concentration pattern shown by the Kadiri lamprophyres. The source enrichment can be linked to the accretion-related growth of Dharwar craton and its schist belts during Neoarchean. Our study shows that a majority of lamprophyres associated with the Archean greenstone belts display a shoshonitic character; this highlights the role of subduction-related processes in the growth and evolution of the greenstone belts

Geochemistry and geochronology of Mississippian volcanic rocks from SW Mongolia: Implications for terrane subdivision and magmatic arc activity in the Trans-Altai Zone

Baaran and Baytag “terranes” form important part of the Trans-Altai Zone of the Central Asian Orogenic Belt in the SW Mongolia. The Trans-Altai Zone represents an oceanic domain built by Ordovician to Devonian ophiolites covered by Devonian–Carboniferous oceanic sediments. This oceanic assemblage was intruded by a spectrum of Carboniferous volcanic rocks ranging from basalts to rhyolites (325.6 ± 1.4 Ma to 351.0 ± 5.9 Ma; LA-ICP-MS U–Pb dating on zircon) that display similar whole-rock trace-element and Sr–Nd isotopic signatures regardless their silica contents and the “terrane” they belong to. They are normal-K calc-alkaline rocks whose NMORB-normalized multielement patterns show an arc-like enrichment in LILE (Large Ion Lithophile Elements) and deep negative TNT (Ta, Nb, Ti) anomalies. Based on the relatively high Nb/Yb and Th/Yb ratios, the arc was probably formed on immature continental rather than typical oceanic crust. Low (87Sr/86Sr)i (0.7043–0.7047), high εNd350(+5.2 to = +5.8) and the observed in-situ Hf isotopic variation in dated zircons (εHft = +7.4 to +13) are all attributed to a partial melting of primitive and youthful (Neoproterozoic–Ordovician) arc-type lower continental crust (metamorphosed intermediate–acid igneous rocks and/or arc-derived greywackes), augmented with, and most likely facilitated by, contemporaneous arc-related basaltic intrusions. A distinct possibility remains the previously formulated model assuming that the Carboniferous magmatism in Gobi-Altai and Trans-Altai zones sampled the juvenile Neoproterozoic to Cambrian arc crust relaminated under the Ordovician–Devonian oceanic crust. In any case, the studied arc association, together with lithological sequence of ophiolites, can be closely correlated with the Dulate arc in eastern Junggar. It is proposed that the two arc sequences form a single belt, c. 500 km long, that represents one of the main known arc structures in the Central Asian Orogenic Belt.

Fully Depleted Ti-Nb-Ta-Zr-O Nanotubes: Interfacial Charge Dynamics and Solar Hydrogen Production.

Poor kinetics of hole transportation at the electrode/electrolyte interface is regarded as a primary cause for the mediocre performance of n-type TiO2 photoelectrodes. By adopting nanotubes as the electrode backbone, light absorption and carrier collection can be spatially decoupled, allowing n-type TiO2, with its short hole diffusion length, to maximize the use of the available photoexcited charge carriers during operation in photoelectrochemical (PEC) water splitting. Here, we presented a delicate electrochemical anodization process for the preparation of quaternary Ti-Nb-Ta-Zr-O mixed-oxide (denoted as TNTZO) nanotube arrays and demonstrated their utility in PEC water splitting. The charge-transfer dynamics for the electrodes was investigated using time-resolved photoluminescence, electrochemical impedance spectroscopy, and the decay of open-circuit voltage analysis. Data reveal that the superior photoactivity of TNTZO over pristine TiO2 originated from the introduction of Nd, Ta, and Zr elements, which enhanced the amount of accessible charge carriers, modified the electronic structure, and improved the hole injection kinetics for expediting water splitting. By modulating the water content of the electrolyte employed in the anodization process, the wall thickness of the grown TNTZO nanotubes can be reduced to a size smaller than that of the depletion layer thickness, realizing a fully depleted state for charge carriers to further advance the PEC performance. Hydrogen evolution tests demonstrate the practical efficacy of TNTZO for realizing solar hydrogen production. Furthermore, with the composition complexity and fully depleted band structure, the present TNTZO nanotube arrays may offer a feasible and universal platform for the loading of other semiconductors to construct a sophisticated heterostructure photoelectrode paradigm, in which the photoexcited charge carriers can be entirely utilized for efficient solar-to-fuel conversion.

Late Paleocene–early Eocene granitoids in the Jiamusi Massif, NE China: Zircon U–Pb ages, geochemistry, and tectonic implications

ABSTRACTNortheast (NE) China is characterized by large areas of Mesozoic and Paleozoic granitoids, whereas Cenozoic granitoids are scarce. This paper reports LA-ICP-MS zircon U–Pb ages and whole-rock geochemical data for late Paleocene–early Eocene granitoids from the Jiamusi Massif, NE China, in order to determine their petrogenesis and tectonic implications. Geochronological data indicate that the granodiorite and dioritic porphyry from the Wudingshan pluton formed at 51.5 ± 0.3 Ma and 56.3 ± 0.8 Ma, respectively. The biotite–quartz diorite, biotite granodiorite, and dioritic porphyry have high SiO2 (68.38–70.06 wt.%), Al2O3 (15.34–15.79 wt.%), and Na2O (3.96–4.49 wt.%) contents, low MgO contents (1.10–1.26 wt.%), A/CNK ratios of 0.99–1.11, and are classified as medium- to high-K calc-alkaline and weakly peraluminous I-type granitoids. They are enriched in LREEs and LILEs, and depleted in HFSEs, with Nb/Ta ratios of 10.4–15.0. Moreover, they have negative Nb–Ta–Ti anomalies, indicating that they were derived from continental crust. Combining with the previously published isotopic data and regional geological results, we suggest that the late Paleocene–early Eocene granitoids (56–52 Ma) were probably derived from partial melting of juvenile lower crust, and formed in an active continental margin setting, possibly related to subduction slab rollback of the Paleo-Pacific Plate.

Timing of the final closure of the Irtysh–Zaysan Ocean: New insights from the earliest stitching pluton in the northern West Junggar, NW China

A tight constraint on the closure time of the Irtysh–Zaysan Ocean, a major southwestern branch of the Paleo‐Asian Ocean, is crucial for understanding the final amalgamation of the Central Asian Orogenic Belt; however, no agreement has been reached. This study presents new zircon U–Pb ages and whole‐rock geochemical data for the Keluke composite pluton in the Zharma–Saur arc of the northern West Junggar (NW China). The Keluke composite pluton mainly includes the hornblende gabbro, gabbroic diorite, and K‐feldspar granite. The laser ablation inductively coupled plasma mass spectrometry zircon U–Pb dating indicates that the hornblende gabbro and K‐feldspar granite formed at 334 ± 1 Ma and 319 ± 4 Ma, respectively. The gabbroic and dioritic rocks are calc‐alkaline and arc‐related plutonism characterized by strong depletions in Nb–Ta–Ti, thus being the product of the subduction of the Irtysh–Zaysan Ocean. By contrast, the K‐feldspar granite is geochemically similar to the post‐collisional highly fractionated I‐type granite. In particular, when compared with regional magmatic events, the Keluke K‐feldspar granite represents the first stitching plutonism in response to the termination of the Irtysh–Zaisan Ocean, which strongly indicates that the Irtysh–Zaisan Ocean was closed prior to the earliest late Carboniferous.