Ti Nb Ta Research Articles

Geochemical and geochronological constraints on Late Jurassic volcanic rocks at Tuen Mun, Hong Kong, with implications for the Palaeo-Pacific subduction

Widespread Mesozoic igneous rocks in Hong Kong form part of the giant Mesozoic igneous province in Southeastern China. The Tuen Mun Formation in the Northwestern New Territories is the oldest volcanic unit known in Hong Kong. This formation contains a lower unit composed of dominantly volcanic breccia, minor dacite, rhyolite, and tuff, and an upper unit of basaltic andesitic to andesitic lava. The volcanic rocks from the lower unit contain zircon grains with a mean U–Pb age of 163.4 ± 0.9 Ma, synchronous with the adjacent Tsuen Wan Volcanic Group in the region. Good inter-correlations between different elements in the Harker diagrams indicate that the volcanic rocks with high SiO2 (e.g. >65 wt.%) are essentially physical mixtures of intermediate magmas and various xenoliths of country rocks, characterizing the palaeo-volcanic plug facies. Preservation of large amounts of xenoliths of sandstone and marble in the volcanic rocks, which is revealed both in field and under microscopic observation, further supports this hypothesis. The original andesitic magma, represented by the intermediate volcanic rocks with SiO2 <65 wt.%, exhibit enrichments of LILEs and LREEs compared with N-MORB, but have negative Nb–Ta–Ti anomalies in the primitive-mantle normalized diagram, similar to those derived from metasomatized mantle wedge in an arc environment. Large ranges of SiO2, MgO, and CaO contents, and negative Eu and Ce anomalies are consistent with significant fractional crystallization of likely olivine/pyroxene and plagioclase. We propose that during the Late Jurassic subduction of the Palaeo-Pacific Plate underneath the coastal continental arc in Southeast China generated prolonged and cyclic volcanism in the northern part of Hong Kong.

“Grenvillian” intra-plate mafic magmatism in the southwestern Yangtze Block, SW China

Tectonic affinity of Grenvillian magmatism in the South China Block is important for understanding the role of the block in the reconstruction of the Rodinia supercontinent during the Mesoproterozoic. In the southwestern Yangtze Block, South China, late Mesoproterozoic metabasalts occur as layers in the Pudeng Formation of the Julin Group. Most metabasalts are highly metamorphosed to be amphibolites composed of dominantly plagioclase and amphibole with minor Fe–Ti oxides, titanite and apatite. Two metabasalt samples have identical zircon U–Pb ages of ∼1050Ma. These basalts are tholeiitic in compositions and have high and variable TiO2 (1.1–3.2wt.%) and low Mg# values (=Mg/(Mg+Fe2+); 35–60). In the primitive mantle-normalized diagram, they are characterized by enrichments in Th, Nb, Ta and light REE without significant Zr–Hf–Nb–Ta–Ti anomalies. The samples have ɛNd(t) values ranging from −1.4 to +4.0 and their zircon grains have ɛHf(t) values from −1.7 to +11.0. The low Mg# values and Cr (55.1–261ppm) and Ni (13.5–76.5ppm) contents suggest fractional crystallization of olivine and/or clinopyroxene, whereas minor negative Eu anomalies indicates slightly fractional crystallization of plagioclase. High positive ɛNd(t) and ɛHf(t) values suggest derivation of the parental magma from a depleted asthenospheric mantle source. On the other hand, variable ɛNd(t) and ɛHf(t) values and La/Sm and Nb/La ratios are consistent with significant crustal assimilation by the Paleoproterozoic rocks in the region. These samples have high Ti and Ti/V ratios (mostly >40), typical of within-plate basalts. In the Zr–Nb–Y and Th–Ta–Hf diagrams for tectonic discrimination, the samples with least crustal contamination are plotted in the ‘within-plate’ and ‘E-MORB’ fields, indicating an intra-continental rifting setting. In view of subsequent Neoproterozoic arc magmatic activities (950–730Ma) in the region, we suggest that these basalts were likely produced at a rifting basin in a passive margin. Results presented here demonstrate that the Grenville-age magmatism in the southwestern Yangtze Block was not orogenic in origin, thus arguing against the existence of Grenvillian Orogen in the region that was traditionally used to place the South China Block in the central part of the Rodinia supercontinent.

In situ X-ray diffraction strain-controlled study of Ti–Nb–Zr and Ti–Nb–Ta shape memory alloys: crystal lattice and transformation features

Phase and structure transformations in biomedical Ti–21.8Nb–6.0Zr (TNZ) and Ti–19.7Nb–5.8Ta (TNT) shape memory alloys (at.%) under and without load in the −150 to 100°С temperature range are studied in situ using an original tensile module for a low-temperature chamber of an X-ray diffractometer. Alpha″- and beta-phase lattice parameters, the crystallographic resource of recovery strain, phase and structure transformation sequences, and microstress appearance and disappearance are examined, compared and discussed. For both alloys, the crystallographic resource of recovery strain decreases with temperature increase to become 4.5% for TNZ and 2.5% for TNT alloy (at RT). Loading at low temperatures leads to additional α″-phase formation and reorientation. Heating under load, as compared to strain-free heating, affects the reverse transformation sequence of both alloys in different ways. For TNZ alloy, strain-free heating results in simultaneous ω→β and α″→β transformations, whereas during heating under stress, they are sequential: β+ω→α″ precedes α″→β. For TNT alloy, strain-free heating results in reverse α″→β transformation, whereas during heating under stress, α″→β transformation is preceded by α″-phase reorientation.

Late Miocene K-rich volcanism in the Eslamieh Peninsula (Saray), NW Iran: Implications for geodynamic evolution of the Turkish–Iranian High Plateau

Post-collisional volcanism in northwestern Iran is represented by the Saray high-K rocks including leucite-bearing under-saturated and leucite-free silica saturated rocks. We report Ar–Ar age data which constrain the age as ca. 11Ma (late Miocene). Most of clinopyroxene phenocrysts from the volcanic rocks have complex oscillatory zoning, with high Ti and Al cores, low Ti and high Al mantled clinopyroxenes, grading into low Ti and Al outer rims. All the rocks are highly enriched in incompatible trace elements and have identical Sr–Nd–Pb isotopes. Enrichment in incompatible elements and other geochemical features for the Saray lavas suggest a metasomatized sub-continental lithospheric mantle (SCLM) as the magma source. The negative Nb–Ta–Ti anomalies for the Saray lavas compare with the features of subduction-related magmatism with negligible contamination with ancient crustal components. The highly radiogenic 87Sr/86Sr and 207Pb/204Pb isotopic values of the Saray lavas imply the involvement of slab terrigenous sediments and/or a continental lithosphere. Isotopically, the volcanic rocks define a binary trend, representing 5–8% mixing between the primary mantle and sediment melts. Our melting models suggest residual garnet in the source and are incompatible with partial melting of amphibole and/or phlogopite bearing lherzolites, although the complex geochemical features might indicate the result of mixing between melts produced by different sources or a homogenous melt passing through a compositionally-zoned mantle during multiple stages of partial melting and melt migration. The geochronological, geochemical and isotopic data for the Saray rocks suggest that these Late Miocene magmas were derived from a small degree of partial melting of subduction-metasomatized (subcontinental) lithospheric mantle source in a post-collisional setting.

Geochemistry, zircon U–Pb ages and Lu–Hf isotopes of early Paleozoic plutons in the northwestern Chinese Tianshan: Petrogenesis and geological implications

The northwestern Chinese Tianshan is a key part of the southern Central Asian Orogenic Belt. Voluminous arc-related igneous rocks in this region have recorded the opening and closure of several oceanic basins that may represent southern branches of the Paleo-Asian Ocean. We have conducted geochemical, geochronological and Hf-in-zircon isotopic studies on mafic and felsic intrusive rocks in the northwestern Chinese Tianshan to provide important clues for the evolution of the Junggar Ocean and to understand the early Paleozoic crustal growth in the Central Asian Orogenic Belt. The mafic plutons are composed of metagabbro (453.8±2.0Ma) and fine-grained diorite (461.1±2.0Ma). These rocks are mostly sub-alkaline in composition and belong to calc-alkaline series. The mafic rocks are enriched in LILE (such as Rb, Sr, Ba, Pb) with pronounced negative Nb–Ta–Ti anomalies. Depleted εHf (t) (−0.03–+8.32), high Ba/Th (>79) and Ba/La (>11) as well as low Th and Th/Yb suggest that these mafic rocks were likely generated by partial melting of slab fluid-metasomatized mantle peridotite. The felsic plutons consist of quartz diorite (463.1±2.0Ma, 462.4±2.0Ma), granodiorite (460.2±3.0Ma) and muscovite-bearing granite (448.9±6.0Ma) and show characteristics of calc-alkaline igneous rocks. These felsic rocks are also enriched in LILE and display HFSE depletion with obvious Nb–Ta–Ti troughs, showing typical geochemical features of arc-related magmas. The quartz diorite is characterized by slightly depleted juvenile εHf (t) values (−0.69–+4.52) and relatively young Hf crustal model ages (TDMC: 1.16–1.49Ga), indicating a relatively juvenile magmatic source. The occurrence of Neoproterozoic zircon xenocrysts suggests that the quartz diorite was produced, at least in part, by partial melting of Precambrian basement rocks with limited involvement of a juvenile mantle component. The granodiorite and muscovite-bearing granite both exhibit enriched εHf (t) values (−3.88–+0.11), relatively old TDMC ages (1.44–1.69Ga) and contain numerous early Paleozoic to Meoproterozoic inherited zircons (493–1012Ma). Their εHf (t) values plot on the evolution trend of the Neo- to Mesoproterozoic basement rocks and demonstrate an origin through partial melting of the Precambrian basement. Therefore, the petrogenesis of the mafic and felsic rocks unravels an arc-related tectonic setting in the early Paleozoic. The ages of these intrusive rocks suggest that the onset of a southward subduction of the Junggar Ocean beneath the Yili block predates the middle Ordovician. The subduction process produced extensive arc-related granitoid complexes and triggered the involvement of juvenile mantle components in producing new continental crust and probably played an important role in vertical crustal growth in the CAOB during the early Paleozoic. In combination with new data from adjacent regions, the Middle Ordovician arc-related magmatism in the northwestern Chinese Tianshan and Cambrian to early Ordovician arc-derived magmas in the southern West Junggar was likely produced by bidirectional subduction of the Junggar Ocean.

Titaniferous heavy mineral aggregates as a tool in exploration for pegmatitic and aplitic rare-metal deposits (SE Germany)

Black heavy mineral (HM) aggregates of metallic luster and composed of ilmenite and rutile were named “nigrine” (amount of rutile>ilmenite) and “antinigrine” (amount of ilmenite>rutile). They contain inclusions of, e.g., columbite-(Fe), pyrochlore group minerals, wolframite solid solution series (=s.s.s.), monazite, zircon, Fe oxides and sulfides as well as alteration minerals such as pseudorutile and Fe–Ti–Nb–Ta–Al–P compounds, whose precise chemical composition and mineralogical affiliation cannot be determined. These titaniferous HM aggregates are of widespread occurrence in gneisses and shear zones cutting through them as well as alluvial, fluvial and colluvial deposits at different distances from rare-element phosphate pegmatites within the crystalline basement in SE Germany. “Nigrine” and “antinigrine” may be subdivided into three types which formed at different periods relative to the Variscan tectonic disturbances and which show different qualities as markers for the origin and presence of Nb-bearing pegmatites along the western edge of the Bohemian Massif, SE Germany.Type A developed pre- to synkinematically within or near deep-seated shear zones which formed below 730°C as early as 321 to 329Ma. These HM aggregates are poor in Nb and impoverished in accessory minerals. The HM aggregates having developed in shear zones mark the “kitchen” where friction and heating contributed to the formation of felsic intrusive bodies, such as pegmatites and aplites. This type of Ti-bearing HM aggregates may be held as distal proximity indicator.Type B is early postkinematic and enriched in niobian rutile, rife with lots of inclusions, especially columbite-(Fe). It precipitated in the crystalline country rocks at temperatures around 600°C concomitant with the nearby rare-element pegmatites between 302 and 311Ma. It is the most proximal member of this group of HM aggregates.Type C “nigrine” is enriched in W and late postkinematic relative to the shearing processes in the crystalline basement. It formed around 470°C during the same period of time as type C. It does, however, not qualify as a marker for rare-element pegmatites, as it is unrelated to these felsic intrusives.During the late Neogene the Variscan basement was strongly uplifted and many pegmatites were stripped off their roof rocks. As a consequence of this, “nigrine” and “antinigrine” were released from their host rocks and became part of the terrigenous sediments laid down in the drainage systems which upstream cut into the crystalline basement and the pegmatites/aplites. Due to their high resistance to chemical weathering these titaniferous HM aggregates acted as “armored relics” for less resistant minerals such as columbite and pyrochlore. When these titaniferous HM aggregates got decomposed by attrition these mineral inclusions of lesser stability appear in the fluvial sediments further afield from their source than expected, considering the low stability to weathering of single crystals of columbite- and pyrochlore group minerals.“Antinigrine” and “nigrine” may be spotted in the HM suites of drainage systems around pegmatites at a distance of ≤10km with correlation coefficient of RNb–Ti=+0.42, while in the range 2–5km RNb–Ti increases to +0.77, in the range 1–2km RNb–Ti is +0.85 and around 1km from the rare-element pegmatite RNb–Ti stands at +0.92.“Nigrine” and “antinigrine” are no ideal mineral aggregates to form placer-type deposits of their own due to their variegated mineralogy, excluding some Ta-enriched subtypes in Colombia and Sierra Leone. The variable mineralogy detrimental to its use as a source of Ti, is the strong point as an exploration tool for rare-element pegmatites.

In-situ trace elements and Li and Sr isotopes in peridotite xenoliths from Kuandian, North China Craton: Insights into Pacific slab subduction-related mantle modification

The trace element, Li and Sr isotopic compositions of major minerals in peridotite xenoliths from Kuandian, North China Craton (NCC) were analyzed in situ to investigate Pacific slab subduction-related mantle modification beneath the eastern NCC. The 87Sr/86Sr ratios (0.70282–0.70553) are positively correlated with the La/Nb and U/Nb ratios for clinopyroxenes (Cpx). Based on the trace element distribution patterns, three types of Cpx were identified. Type 1 Cpx are characterized by significant Nb–Ta–Ti depletions and the highest Sr isotopic ratios (up to 0.70553); Type 2 Cpx display Nb (or Ta) depletions and highly variable Nb and Ta fractionation; and Type 3 Cpx show no significant Nb or Ta depletion or even weak Ta enrichment and have the lowest Sr isotopic ratios (0.70282–0.70323). Some Cpx display a pattern of increasing Ca+Mg±Si from the cores to the rims, indicating addition of Ca+Mg±Si-rich fluids derived from a serpentinized peridotite layer above the subducting slab. These features indicate an ancient mantle metasomatic event associated with the subduction of the altered Pacific oceanic crust, which may contribute substantially to the destruction of the eastern NCC.The variations in the Li contents and isotopic compositions of major minerals in the Kuandian peridotite xenoliths encode both the melt/fluid metasomatism and the cooling process. The Li contents in the Cpx (up to 34.8ppm) and orthopyroxenes (Opx) (up to 28.0ppm) are typically higher than those in the coexisting olivines (Ol) (<9.19ppm), suggesting silicate melt metasomatism. Considering the rapid diffusion rate of Li in minerals at mantle temperature, the Li enrichment and low δ7Li values in the rims of most Ol, Cpx and Opx may have arisen from diffusive fractionation due to faster diffusion of 6Li compared to 7Li during a latest Li-rich melt/fluid metasomatic process shortly before the host magma eruption. On the other hand, a few Ol grains show decreased Li contents and higher δ7Li values from the cores to the rims. This could imply Li isotope fractionation caused by cooling-induced Li redistribution during and/or after the host magma eruption, because DLiOl/Cpx decreases significantly with decreasing temperature and 6Li diffuses faster than 7Li.

A Late Carboniferous–Early Permian slab window in the West Junggar of NW China: Geochronological and geochemical evidence from mafic to intermediate dikes

The Late Carboniferous to Early Permian is a critical period for the formation of particular high-temperature magmatic associations in West Junggar, NW China and the geodynamic processes of ridge subduction and related slab windows in the Central Asian Orogenic Belt. Mafic to intermediate dikes, exposed in the central and southeastern West Junggar extensively, mainly consist of Nb-enriched and magnesian suites. The Nb-enriched dikes (305Ma) are characterized by high Nb contents (5.63–9.08ppm) and large variations of major element contents, exhibiting high-K to medium-K calc-alkaline characteristics with high Na2O/K2O (1.33–3.85) and low Sr/Y (9–32) ratios. The dikes have moderate Mg# (44.6–52.9), LREE-rich and sub-horizontal HREE patterns ((La/Yb)N=3.05–7.18; (Gd/Yb)N=1.43–1.78) with weak Eu anomalies (Eu⁎/Eu=0.81–1.10) and positive εNd (t) values (+5.2 to +8.0), and likely originate from partial melting of mantle peridotite that was metasomatized by subducted sediment-derived melts and slab fluids. The medium-K magnesian dikes (305Ma) are characterized by high MgO (3.05–7.28wt.%), Cr (22.3–311ppm) and Ni (32.6–199ppm) contents and all plot in the field of high-Mg andesite. Some have very high Mg numbers (Mg#>60), suggesting a primitive melt composition. These samples display positive Ba, Sr, K and negative Nb–Ta–Ti anomalies as well as strongly-depleted HREE patterns with weak positive Eu anomalies. They have high Sr/Y (27–126) and relatively high εNd (t) values (+6.0 to +8.3), which suggest a similar petrogenesis as the Nb-enriched dikes, but were metasomatized by adakitic melts. The high-K magnesian dikes (284Ma) are high-K calc-alkaline and have lower MgO (3.63–5.57wt.%) compared with the medium-K suite. They have high Sr (422–819ppm), Sr/Y (26–62) ratios and εNd (t) values (+7.0 to +7.1) with relatively flat REE patterns ((La/Yb)N=2.4–5.5), probably originating from partial melting of K-enriched mantle wedge peridotite metasomatized by adakitic slab melts. Based on these petrogenetic features, we suggest that a ridge subduction regime likely prevailed in West Junggar in the Late Carboniferous. The opening of related slab windows and upwelling asthenosphere have possibly triggered the formation of Late Carboniferous–Early Permian magmatic associations in West Junggar.

Microstructural evolution and final properties of a cold-swaged multifunctional Ti–Nb–Ta–Zr–O alloy produced by a powder metallurgy route

Body centred cubic (BCC) β-phase multifunctional titanium alloys have been developed with a very unique combination of thermal and mechanical properties. In this investigation, a very low porosity Ti–36.8–Nb–2.7Zr–2.0Ta–0.44O (wt%) alloy was produced by powder sintering, hot forging, solution treatment and cold swaging. X-ray diffraction and transmission electron microscopy (TEM) of the solution treated alloy revealed the presence of a small amount of ω-phase in a predominantly BCC β-phase matrix. Electron backscatter diffraction (EBSD) of the swaged alloy revealed a highly elongated and fragmented microstructure, and a strong 〈110〉 fibre texture. TEM also revealed the existence of stress-induced twin lamella, dislocations and ω-phase. Consistent with previous studies on these types of alloys, the swaged alloy exhibited non-linear elasticity during tensile straining, low elastic modulus (45.4GPa), high elastic limit (2.3%), high elongation to failure (8.1%), and a high yield strength (880MPa) and tensile strength (940MPa). The coefficient of thermal expansion was also low (∼5×10−6K−1 between 50 and 300°C) in this alloy.

Post-collisional, K-rich mafic magmatism in south Tibet: constraints on Indian slab-to-wedge transport processes and plateau uplift

Post-collisional (23–8 Ma), potassium-rich (including ultrapotassic and potassic) mafic magmatic rocks occur within the north–south-trending Xuruco lake–Dangre Yongcuo lake (XDY) rift in the Lhasa terrane of the southern Tibetan Plateau, forming an approximately 130-km-long semi-continuous magmatic belt. They include both extrusive and intrusive facies. Major and trace element and Sr–Nd–Pb isotopic data are presented for all of the known exposures within the XDY rift. The potassium-rich, mafic igneous rocks are characterized by high MgO (5.9–10.8 wt.%), K2O (4.81–10.68 wt.%), Ba (1,782–5,618 ppm) and Th (81.3–327.4 ppm) contents, and relatively high SiO2 (52.76–58.32 wt.%) and Al2O3 (11.10–13.67 wt.%). Initial Sr isotopic compositions are extremely radiogenic (0.712600–0.736157), combined with low (206Pb/204Pb) i (18.28–18.96) and (143Nd/144Nd) i (0.511781–0.512046). Chondrite-normalized rare earth element patterns display relatively weak negative Eu anomalies. Primitive mantle-normalized incompatible trace element patterns exhibit strong enrichments in large ion lithophile elements relative to high-field-strength elements and display strongly negative Ta–Nb–Ti anomalies. The combined major and trace element and Sr–Nd–Pb isotopic characteristics of the K-rich igneous rocks suggest that the primitive magmas were produced by 1–10 % partial melting of an asthenospheric mantle source enriched by both fluids and partial melts derived from Indian passive continental margin sediments subducted into the shallow mantle as a consequence of the northward underthrusting of the Indian continental lithosphere beneath Tibet since the India–Asia collision at ~55 Ma. The best-fit model results indicate that a melt with trace element characteristics similar to those of the K-rich rocks could be generated by 8–10 % partial melting of a metasomatized mantle source in the south and 1–2 % melting in the north of the XDY rift. Trace element and Sr–Nd–Pb isotopic modeling indicate that the proportion of fluid derived from the subducted sediments, for which we use as a proxy the Higher Himalayan Crystalline Sequence (HHCS), in the mantle source region increases from north (rear-arc) to south (front-arc), ranging from 0 to 5 %, respectively. Correspondingly, the proportion of the melt derived from the subducted HHCS in the source increases from north (2 %) to south (15 %). The increasing proportion of the fluid and melt component in the mantle source from north to south, together with a southward decreasing trend in the age of the K-rich magmatism within the XDY rift, is inferred to reflect rollback of the subducted Indian lithospheric mantle slab during the period 25–8 Ma. Slab rollback may be linked to a decreasing convergence rate between India and Asia. As a consequence of slab rollback at 25 Ma beneath the Lhasa terrane, its geodynamic setting was transformed from a convergent (55–25 Ma) to an extensional (25–8 Ma) regime. The occurrence of K-rich magmatism during the period 25–8 Ma is a consequence of the decompression melting of an enriched mantle source, which may signal the onset of extension in the southern Tibetan Plateau and provide a petrological record of the extension process.

Characterization of electrochemical behavior and surface oxide films on superelastic biomedical Ti–Nb–Ta alloy in simulated physiological solutions

Abstract This paper focuses on study of the kinetics and the mechanism of passive film formation on novel superelastic biomedical Ti–22Nb–6Ta (at.%) alloy in simulated physiological solutions using AES, XPS and electrochemical techniques in comparison with commercially pure titanium and Nitinol. Ti–22Nb–6Ta alloy manifests a strong trend to protective passive film formation during first stage of oxidation in simulated physiological solutions. It is shown that Ti–Nb–Ta electrochemical characteristics are comparable to those of titanium and Nitinol and the alloy can be recommended for use in implantology.

Nanostructured titanium alloys and multicomponent bioactive films: Mechanical behavior at indentation

Structure and mechanical properties of nanostructured Ti and TiNi, TiNbZr, TiNbTa shape memory alloys, and TiCaPCON biocompatible coatings were characterized by metallographic analysis and instrumented indentation. Discussed is the mechanism of localized deformation of the coatings deposited onto nanostructured substrates. Deformation was found to proceed inhomogeneous, through formation of shear bands during penetration of a Vickers diamond indenter into TiCaPCON coatings on the substrates with high elastic modulus especially.

ω Transformation in cold-worked Ti–Nb–Ta–Zr–O alloys with low body-centered cubic phase stability and its correlation with their elastic properties

The ω transformation and its correlation with elastic properties were investigated in cold-worked Ti–36Nb–2Ta–3Zr–xO mass% alloys with low body-centered cubic (β) phase stability, known as gum metal. Analysis of the temperature dependence of the ω (hexagonal) phase formation using transmission electron microscopy and of the elastic properties of solution-treated and cold-worked alloys using resonant ultrasound spectroscopy revealed that in the solution-treated 0.36% and 0.51% O alloys, the high concentration of oxygen suppressed ω-phase formation from room temperature to a fairly low temperature of ∼13K. However, the ω phase was formed by cold working at room temperature in the 0.30% and 0.47% O alloys. Importantly, the fraction of the ω phase clearly increased upon cooling, which indicates that the formation of the ω phase is thermodynamically favorable near and below room temperature in the cold-worked 0.30% and 0.47% O alloys. This formation of the ω phase and the low stability of the β phase related to the low electron/atom (e/a) ratio were the dominant factors determining the elastic properties near and below room temperature in the cold-worked Ti–Nb–Ta–Zr–O alloys.

Geochronology and geochemistry of Cenozoic basalts from eastern Guangdong, SE China: constraints on the lithosphere evolution beneath the northern margin of the South China Sea

The 40Ar–39Ar dating reveals three episodes of basaltic volcanism in eastern Guangdong of SE China since the late Eocene (i.e., 35.5, ~20 and 6.6 Ma). The Miocene alkali olivine basalts (~20 and 6.6 Ma) have OIB-like trace element characteristics, which is coupled with low (87Sr/86Sr)i, high eNd(t), and high eHf(t). In contrast, the late Eocene basalts (35.5 Ma) have overall characteristics of “Island Arc” basalts with strong negative Ta–Nb–Ti anomalies in the primitive mantle-normalized multi-element diagram with high (87Sr/86Sr)i, negative eNd(t), and relatively low eHf(t). All basalts have unexpectedly high 207Pb/204Pb and 208Pb/204Pb, delineating a DUPAL signature in the sources. The late Eocene Arc-like basalts may reflect contributions of relict ancient metasomatized mantle lithosphere that melted as the result of extension-induced asthenospheric upwelling and heating, whereas the Miocene OIB-like basalts may represent partial melting of the asthenospheric mantle beneath the thickened lithosphere. We propose that the Cenozoic basaltic volcanism in eastern Guangdong records an overall lithospheric thickening process beneath SE China, that is, a continental rift system from its maximum extension in the late Eocene to its waning in the Miocene. This interpretation is consistent with the evolution of the South China Sea, whose origin is most consistent with the development of a passive continental margin. The seafloor spreading of the South China Sea during ~ 32–16 Ma may not result from the effect of the “Hainan” mantle plume, but rather played a positive role in allowing the mantle plume to express on the surface.

Structure and mechanical behavior during indentation of biocompatible nanostructured titanium alloys and coatings

The structure of biocompatible titanium alloys and coatings, nanostructured by rapid plastic deformation technology, thermomechanical treatment, and magnetron sputtering, is studied. Measured indentation is used to obtain a mechanical property database. Values of hardness, elasticity modulus, and elastic recovery of titanium, and also Ti–Ni alloys with shape memory and a superelasticity effect Ti–Nb–Zr, Ti–Nb–Ta that are in microstructured and nanostructured conditions, are measured. It is shown that with indentation of a Vickers diamond indenter into a TiCCaPCON coating deformation proceeds inhomogeneously by periodic formation of shear steps.

Oxide minerals in the granitic cupola of the Jálama Batholith, Salamanca, Spain. Part II: Sn, W and Ti minerals in intra-granitic quartz veins

*Corresponding author The mineralized quartz veins hosted by the distal granitic facies of the Jalama Batholith were generated by successive processes of the fractures opening and filling by hydrothermal fluids enriched in volatiles. Cassiterite I, wolframite I and rutile I crystallized during an early stage, followed – after a ductile deformation – by a main Fe–Zn sulphide deposition, composed initially by subordinate cassiterite II and wolframite II. Later during this main sulphide deposition, ixiolite and Nb–Ta-rich rutile II filled fractures. Finally, the late open spaces and cavities were sealed by quartz and carbonates. The crystallization of wolframite II indicates enrichment in Mn of the fluid, compared with wolframite I, suggesting a normal evolutionary trend from the early Sn–W deposition to the first stage of the main Fe–Zn sulphide precipitation in the quartz veins. The scarcity of Sn during the latest stages of the ore deposition prevented the crystallization of cassiterite, favoring instead the incorporation of this element into the ixiolite and rutile II structure. This hydrothermal evolution from the crystallization of wolframite II to ixiolite and rutile II responded to enrichment in Ti and Fe of the late fluid, thus favoring a partially reversed trend in the Nb–Ta–Ti oxides composition. The late enrichment in Ti and Fe of the hydrothermal fluid could be explained by contamination by external metamorphic and/or meteoric fluids en riched in these elements. The incorporation of Ti, Nb and Ta into the ixiolite and rutile structure was favored by high F concentrations in the hydrothermal fluids, inherited from the residual melts of the Jalama Batholith.

Oxide minerals in the granitic cupola of the Jálama Batholith, Salamanca, Spain. Part I: accessory Sn, Nb, Ta and Ti minerals in leucogranites, aplites and pegmatites

*Corresponding author Sn–Nb–Ta–Ti oxides occur as accessory minerals in the granitic facies of the External Unit in the Jalama Batholith (Salamanca, Spain) and in the related LCT pegmatite dikes of the rare-element class. Moreover, abundant cassiterite and columbite-group minerals crystallized in the Cruz del Rayo peribatholithic pegmatite dikes, cutting the pre-Ordovician low-grade metasedimentary rocks of the surrounding Schist-Graywacke Complex. Cassiterite, rutile, ilmenite and tantalite-(Fe) occur disseminated in the border facies of the External Unit, especially throughout the tourmaline-bearing leucogranite and the apical aplites. Additionally, cassiterite, rutile and Ta-rich rutile developed locally in the intragranitic pegmatite dikes. Two types of peribatholithic pegmatites can be distinguished at Cruz del Rayo: (i) granite-like pegmatites, with columbite-(Fe) I and II and cassiterite, in which the influence of metasomatic fluids led to formation of the late albite unit and crystallization of tantalite-(Fe), and (ii) greisen-like bodies, which contain high amounts of columbite-(Fe), columbite(Mn), tantalite-(Mn) I and II as well as cassiterite. The primary oxide assemblage in both types of the peribatholithic pegmatite dikes would have crystallized as a result of magmatic differentiation of the residual melts coming from the Jalama granitic cupola. However, crystallization of the secondary assemblage, richer in Fe and Ta, is interpreted mainly as a consequence of interaction with external fluids coming from the metamorphic host rocks, more or less mixed with meteoric fluids, although partial dissolution and re-precipitation could have played an important role, as well.

Arc picrite–potassic adakitic–shoshonitic volcanic association of the Neoarchean Sigegudda greenstone terrane, western Dharwar craton: Transition from arc wedge to lithosphere melting

A rare association of basalt, andesite, dacite and ultrapotassic volcanic flows is present, together with basalts, komatiites, and banded iron formation (BIF), in the Neoarchean Sigegudda greenstone terrane of the western Dharwar craton. Andesites and dacites are porphyritic, preserving biotite, K-feldspar, and relict fine-grained leucite. Ultrapotassic flows preserve phenocrysts of relict leucite, relict pyroxene, and K-feldspar. Compositionally, basaltic samples are tholeiitic, andesites and dacites are calc-alkaline, and the ultrapotassic samples shoshonites to leucitites. High-Mg basaltic flows have Mg# 0.67–0.52, Ni 1126–260ppm, fractionated REE [(La/Sm)N=1.02–1.75, (Gd/Yb)N=1.41–1.74], and negative anomalies of Nb, Ta, and Ti on primitive mantle normalized diagrams; they are interpreted as arc picrites generated by slab dehydration and high-temperature, low degree, melts of subarc mantle wedge. Andesites qualify as high-Mg andesites. With dacites, these flows have some of the characteristics of adakitic rocks in being aluminous (Al2O3=14–24, 15–18wt.%), with fractionated REE [(La/Sm)N=1.90–2.56, 1.99–2.85, (Gd/Yb)N=1.60–2.64, 1.31–2.50 respectively], with flat to positive anomalies of Zr–Hf relative to MREE, but are potassic relative to “normal” arc andesites–dacites, and possess low abundances of Cr, Co, Ni relative to true adakites. Given the relict mineralogy, with LREE-enrichment the potassic character appears primary. These flows are interpreted as melts of lower arc crust, akin to potassic adakites documented from orogenic belts. Shoshonites and leucitites (SiO2=53–66, 48–53, K2O=3–8, 8–9wt.% respectively) are aluminous at 15–33wt.% Al2O3, with extreme enrichment of LREE at La 200–1000 times chondrite, fractionated REE [La/Sm)N=2.01–3.06, 1.32–3.94, (Gd/Yb)N=2.01–3.65, 1.33–4.50, respectively], and pronounced negative troughs at Nb–Ta–Ti: these compositions are consistent with decompressional melting of arc mantle lithosphere, previously metasomatized by subduction-derived fluids, during arc rifting. Accordingly, this volcanic association records a transition from subarc wedge melting to melts of arc crust and mantle lithosphere, likely in response to arc rifting.

Effects of cold deformation on microstructure, texture evolution and mechanical properties of Ti–Nb–Ta–Zr–Fe alloy for biomedical applications

Abstract The effects of cold deformation on the microstructure, texture evolution and mechanical properties of Ti–25Nb–10Ta–1Zr–0.2Fe (TNTZF) alloy during cold rolling (CR) were investigated. The results showed that the dominant deformation mechanisms changed from stress-induced α″ martensitic transformation and dislocation tangles to twinning, shear bands and nanostructuring with the increase of cold reduction. Meanwhile, the transition from {1 1 1}〈1 1 0〉 to {1 1 1}〈1 1 2〉 orientation took place during CR and a dominant {1 1 1}〈1 1 2〉 texture was obtained after 80% cold deformation. The hardness and strength increased with the increase of cold reduction owing to the effects of the increase of dislocation density and the grain refinement caused by cold deformation. The decrease in Young's modulus after CR is mainly attributed to the stress-induced α″ martensitic transformation accompanying with the disappearance of ω phase. The cold deformed TNTZF alloy with reduction of 60% has a great potential to become a new candidate for biomedical applications since it possesses high strength-to-modulus ratio and appropriate plasticity.

Optical analysis of adsorption sensitivity of titanium, Ti-6Al-4V, and Ti-35Nb-6Ta

Here we report the optical analysis of protein adsorption sensitivity of titanium (Ti), Ti(6)Al(4)V, and Ti(35)Nb(6)Ta. The optical sensor used was a diffractive optical element based sensor, which analyzes magnitude and coherence of probe beam reflected from the measured surfaces. Also, the roughness and other necessary parameters were taken into account on the final verdict. The material Ti(35)Nb(6)Ta showed positive initial reaction to the human plasma fibrinogen, which was the protein used. The Ti(35)Nb(6)Ta was observed to be more active than the grade 2 titanium.