Ti Nb Ta Research Articles

Training machine learning interatomic potentials for accurate phonon properties

Abstract One of the major challenges in the development of universal machine learning interatomic potentials is accurately reproducing phonon properties. This issue appears to arise from the limitations of available datasets rather than the models themselves. To address this, we develop an extensive dataset of phonon calculations using density-functional perturbation theory. We then show how this dataset can be used to train neural-network force fields, by implementing the training and the prediction of force constants in periodic crystals. This approach improves the quality of phonon properties prediction while reducing the number of structures needed for neural network training. We demonstrate the efficiency of this method using two examples of ternary phase diagrams: Ti—Nb—Ta and Li—B—C. In both cases, neural network predictions for the energy and forces show a considerable improvement, while phonon properties are predicted with high precision for all structures across the entire phase diagrams.

The origin of Gangjiang adakite-like intrusions and associated porphyry Cu–Mo mineralization in the central Gangdese porphyry Cu belt, southern Tibet

The Gangjiang Cu–Mo deposit is located in the central Gangdese porphyry Cu belt (GPCB), south Tibet. Geological investigation reveals that the Gangjiang deposit is characterized by early potassic alteration, followed by late phyllic and argillic alteration. Late alteration has different degrees of overprinting over the potassic alteration zone. Copper-Mo orebodies are predominantly hosted in the potassic and phyllic alteration zones of the Miocene monzogranite porphyry (MGP) and granodiorite porphyry (GDP). In this study, we present the chemistry and Sr–Nd–Pb–Hf–O isotope compositions of fertile MGP and GDP, barren tonalite porphyrite (TP), and microgranular mafic enclaves (MMEs). Chemical compositions indicate that these intrusions are I-type granites that show high–K calc-alkaline signatures. The negative correlation between Dy/Yb and SiO2 indicates that the intrusions experienced fractionation of amphibole. They have high Sr/Y (>70) and La/Yb (>38) ratios, strong negative Nb–Ta–Ti anomalies, and positive Pb anomalies are typical for arc magma. The high Mg# of various porphyry intrusions (43–65) and MMEs (47–58) indicate the input of mafic components. Various intrusions have whole-rock 87Sr/86Sr(t=13Ma) ratios of 0.70529 to 0.70674, negative εNd(t=13Ma) (−5.0 to −1.2), positive zircon εHf(t) (1.2–9.8), and homogeneous δ18O (5.8–7.1 ‰, mean 6.6 ‰). The MMEs have similar Sr–Nd–Pb–Hf–O isotopic compositions with their host rocks. The features reveal that the Gangjiang adakite-like intrusions and MME samples were derived from the partial melting of the Lhasa Paleoproterozoic crust, with contributions from the juvenile mantle that has been metasomatized by subducted sediments-derived melts. Note, the MGP, GDP, and two types of MMEs have slightly lower δ18O values (down to 4.76 ‰) but higher εNd(t) (up to −1.2) than barren TP, indicating their formation involves more mantle components. Furthermore, the MMEs in the TP and MGP have high Cu contents (up to 1485 ppm), similar to the phenomenon occurs in the Qulong deposit. The Cu-rich MME is probably formed by Cu-refertilization by the underplate arc magma in the juvenile crust. The εHf(t) and εNd(t) values of fertile porphyries increased from the Jiru, Gangjiang, to Qulong deposit indicating increased mantle material additions from the west to the east section of the GPCB. These variations in mantle components have led to an increase in the size of the porphyry Cu deposits from Jiru to Gangjiang, and then to Qulong.

Petrography, U–Pb geochronology and geochemistry of Varcheh intrusions: Insight into younging trend of mid‐Cretaceous subduction in the northern Sanandaj–Sirjan Zone, western Iran

The Neotethyan Sanandaj–Sirjan Zone of western Iran has recorded major magmatic activities due to its continental arc tectonic setting during the Mesozoic. The Varcheh mafic intrusions were less‐studied plutons in the northern Sanandaj–Sirjan Zone (SSZ). Field evidence, petrography, geochemistry and U–Pb geochronological data were used to determine petrographic composition, geochemical nature, crystallization age and also to suggest a conceptual tectonomagmatic model for their emplacement. Small plutonic bodies are dominantly composed of monzogabbro that have intruded into the Cretaceous sedimentary rocks. Based on U–Pb zircon datings, these rocks have crystallized at 125–118 Ma in late Early Cretaceous (Barremian–Aptian), and are older than the supposed ages reported on geological maps. Varcheh rocks are not just typical calc‐alkaline rocks and some show alkaline affinity. Negative anomalies in Nb–Ta–Ti and enrichments in some large‐ion lithophile elements on spider diagrams are consistent with a subduction‐zone setting. Potential deep source for magma generation is partial melting of subcontinental lithospheric mantle wedge above a subducting slab of oceanic lithosphere. The spaces for the Varcheh mafic intrusions are accommodated by dominant dextral strike‐slip movement in a continental arc experiencing extension during late Early Cretaceous subduction. According to the zircon U–Pb geochronology results in this paper and previous U–Pb ages in the northern part of the SSZ, the mid‐Cretaceous magmatism reveals a significant NW‐ward younging trend and migration of the magmatic arc from the Barremian–Aptian in south‐east to the Albian–Cenomanian in the north‐west.

Additive manufacturing of a low modulus biomedical Ti–Nb–Ta–Zr alloy by directed energy deposition

While β titanium alloys have garnered extensive attention as a new generation of biomedical materials designed to mitigate stress shielding due to their low modulus, the realm of additive manufacturing for these alloys is still in its nascent stages. This study focuses on the additive manufacturing of Ti–35Nb–5Ta–7Zr alloy powder via directed energy deposition (DED). The primary objectives were assessing the feasibility of employing DED for this alloy powder and identifying processing parameters to achieve nearly dense components. Systematic exploration of the effect of various processing parameters was performed, and the resultant impact on the densification of the produced specimens was studied. Comprehensive analysis of the microstructure, mechanical properties, electrochemical behavior, and cell studies of fully dense sample coupons were performed. These fully dense samples were found to exclusively comprise the β phase of titanium, resulting in a reduced modulus of elasticity (approximately 44–47 GPa) resulting in high yield strength to elastic modulus ratio. Microstructural examinations revealed the presence of both columnar and equiaxed dendrites, with grains transitioning from columnar to equiaxed (known as CET). Electrochemical testing of the coupons indicated exceptional corrosion resistance in the additively manufactured TNZT alloy. Pre-osteoblasts cultured on the alloys showed good attachment, viability, and growth to confirm cytocompatibility. These findings unveiled the attainment of high strength, favorable ductility, a low elastic modulus, excellent corrosion resistance, and cytocompatibility in dense samples created via DED of Ti–35Nb–5Ta–7Zr. These outcomes hold immense significance for the production of patient-specific medical implants manufactured from β-Ti alloys.

Large-volume and swift magmatic response to Late Cenozoic segmentation of the subducted Neotethyan oceanic slab: evidence from the Galatian Volcanic Province, northwestern Turkey

ABSTRACT The Miocene Galatian Volcanic Province (GVP) is one of the largest volcanic provinces in central-western Anatolia, with an extent of ~ 8,900 km2. The volcanic activity is extended from 22.5 to 7.5 Ma. The volcanic compositions straddle the alkaline-subalkaline fields, from basic to acid compositions and mostly transitional to sodic affinity. Major oxides show good correlation with SiO2 indicating prolonged effects of fractional crystallization. Primitive mantle-normalized multi-element patterns indicate overall similarities among the different samples of the three geographic sectors, sharing strong negative anomalies in Nb–Ta–Ti, strong positive peaks at Cs and K, coupled with a common, albeit not always present, positive anomaly at Pb. Mineral-melt geothermobarometric estimates indicates ~1070–1235°C and ~7–19 kbar for melting conditions of basaltic compositions and ~1000–1150°C and ~3–12 kbar for andesitic-dacitic rocks. The absence of correlation between radiogenic isotopes and SiO2 and MgO is here interpreted as consequence of assimilation-fractional-crystalization processes involving lower continental crust as contaminant. The GVP parental magmas are generated from ~2% to 10% partial melting of a lherzolitic mantle with high spinel/garnet ratio based on intra-REE fractionation constraints. The subduction-related metasomatism inferred for the GVP mantle sources based on their chemistry is interpreted to be linked to the northward subduction of the northern branch of the Neo-Tethys slab. Successive slab retreat resulted in extension for the critical stress distribution through the Cyprus slab, favouring magma propagation for the GVP volcanic region. The eventual break-off of the slab after the continent-continent collision of Arabian and Eurasian plates could have caused a toroidal mantle flow, favouring the widely distributed 15–16 Ma alkaline magmatism in the eastern GVP, associated with passive hot asthenospheric upwelling imaged by teleseismic P-wave tomography.

Influence of (Ta Nb Ti V) C powders synthesized by molten salt at low temperature on densification and properties of high entropy carbide ceramics

AbstractPowder synthesis is crucial for achieving the densification and facilitating widespread applications of high entropy carbide (HEC). Specifically, the production of fine particle‐size powders is essential to enhance the densification of HECs. Consequently, this paper proposes the molten salt method for synthesizing HEC powders. The synthesis process successfully yielded (Ta Nb Ti V) C powders with a particle size of only 0.44 µm at 1400°C, exhibiting a uniform distribution of each element. Subsequent densification of (Ta Nb Ti V) C within the 1700–1900°C temperature range was carried out using spark plasma sintering. It was observed that as the densification temperature increased, the densification and mechanical properties of HEC significantly improved. This study presents innovative ideas for the preparation of HEC at lower temperatures.

Local lattice distortions and the structural instabilities in bcc Nb–Ta–Ti–Hf high-entropy alloys: An ab initio computational study

Local lattice distortions (LLD) and structural stability of body-centered cubic (bcc) Nb–Ta–Ti–Hf high-entropy alloys (HEAs) are studied as functions of composition employing ab initio density-functional theory calculations, with specific focus on the role of the relative concentrations of group IV (Ti and Hf) versus group V (Nb and Ta) elements. Calculated results are presented as a function of composition x in NbxTa0.25Ti(0.75−x)/2Hf(0.75−x)/2 alloys, for elastic moduli, phonon spectral functions, LLD and structural energy differences for the bcc and competing hexagonal close-packed (hcp) and ω phases. The results highlight the important role of group V elements and LLD in stabilizing the bcc structure. They further reveal how composition x can be tuned to alter both the magnitude of the LLD and structural energy differences. Specifically, the magnitude of the structural energy differences, and elastic and dynamic stability of the bcc phase, are enhanced with increasing x, while the LLD increase in magnitude as this concentration is decreased. The results also show evidence of correlated LLD at lower values of x, reflecting local structural distortions towards the ω phase, but not hcp. The degree of ω-collapse is nevertheless partial i.e., transformation towards this phase is not observed to be complete due to the presence of Ta and Nb. At lower values of x we further find an energy landscape characterized by multiple, nearly degenerate local energy minima for different values of the LLD.

Interdiffusion in refractory metal systems with a BCC lattice: titanium–tantalum and titanium–multicomponent (high-entropy) alloy

In this work, the interdiffusion features in multicomponent (high-entropy) alloys of refractory metals were studied. The following pairs were chosen as the diffusion study objects: titanium–equiatomic alloy (Hf–Nb–Ta–Ti–Zr–Mo) and titanium–tantalum for the sake of comparison. The article covers the issues of sample preparation, microstructure study, sample preparation methodology for diffusion research, and experimental results. Diffusion annealing was carried out for 12 h in a vacuum at a residual argon pressure of 6.65·10–3 Pa and a temperature of 1200 °С. Particular attention was paid to the method of combining diffusion pairs (titanium with tantalum, titanium with alloy) by thermal cycling near the polymorphic transformation temperature in titanium (882 °C) within ± 50 °C. The behaviour of the most characteristic elements (Ta, Zr, Ti) in the weld area after the titanium and alloy diffusion pair joining was demonstrated. This is the first time that data on the dependence of the intensity of the corresponding spectral line for titanium and elements of a multicomponent alloy on the penetration depth were obtained. A change in the signal intensity for system elements was observed at a depth of 150–200 μm, whereas a sharp drop in the signal intensity was seen to occur at depths of about 50 μm. The effective value of the coefficient of diffusion of elements into titanium averaged over all elements of the alloying system (except for titanium) at a temperature of 1200 °C was calculated. The obtained value was compared to reference data: the self-diffusion coefficient in β-titanium and diffusion coefficients in titanium pairs with alloy doping elements.

Structural and Phase Changes in Concentrated Solid Solutions of the V–Nb–Ta–Ti System Irradiated with Helium Ions

Structural and Phase Changes in Concentrated Solid Solutions of the V–Nb–Ta–Ti System Irradiated with Helium Ions

Structural and Phase Changes in Concentrated V–Nb–Ta–Ti Solid Solutions Irradiated by Helium Ions

Structural and Phase Changes in Concentrated V–Nb–Ta–Ti Solid Solutions Irradiated by Helium Ions

Post-Collisional Silica-Undersaturated Bamaoqiongzong Volcanic Rocks from Northern Qiangtang: Indicators of the Mantle Heterogeneity and Geodynamic Evolution of Central Tibet

AbstractThe formation of post-collisional mantle-derived rocks in the Tibetan Plateau has been linked to the deep geodynamic processes that cause surface uplift. Co-existing silica-oversaturated to silica-undersaturated mantle-derived rocks have been identified in the northern Qiangtang Terrane (NQT). However, the origins of silica-undersaturated magmas are controversial, and the mechanisms responsible for variable silica activity in the mantle-derived rocks are unclear. Here, we present 40Ar/39Ar chronology, mineral chemistry, and whole-rock geochemical data for the Bamaoqiongzong (BMQZ) volcanic rocks of the NQT. The BMQZ volcanic rocks consist of olivine leucitites, trachybasalts, and phonolites and were erupted at ca. 29 Ma. All samples are unsaturated in silica and characterized by enrichment in light rare earth elements and large-ion lithophile elements, depletion in high-field-strength elements, and the presence of negative Nb–Ta–Ti anomalies and positive Pb anomalies. All samples show limited variation in (87Sr/86Sr)i (0.7079–0.7085) and εNd(t) values (−6.9 to −5.3). The geochemical compositions of the BMQZ volcanic rocks indicate that they were produced by partial melting of carbonated phlogopite–lherzolite within the lithospheric mantle. The formation of the olivine leucitites-trachybasalts-phonolites suite was controlled by fractional crystallization and magma mixing in a magmatic plumbing system. This plumbing system included several independent reservoirs and conduits within the crust. The enriched mantle sources of the BMQZ volcanic rocks were formed by the addition of carbonate-rich melts released from the southward-subducted Songpan–Ganzi Terrane after the Late Cretaceous. Our new results, together with published data, reveal systematic variations in geochemical compositions between silica-undersaturated and silica-oversaturated rocks in the NQT, which are ascribed to variations in the nature of the subducted continental materials added during intracontinental subduction. Carbonate-rich melts that were formed by the breakdown of carbonate minerals helped to generate the mantle sources of silica-undersaturated rocks, whereas silicate melts produced by the partial melting of sediment diapirs contributed to the generation of the silica-oversaturated rocks. On the basis of published numerical modelling of continental subduction and crustal deformation records in the NQT, we suggest that intracontinental subduction and lithospheric thinning together contributed to the generation of post-collisional mantle-derived rocks in the Tibetan Plateau.

Oligocene calc-alkaline lamprophyres and K-rich association in the eastern Iranian ranges: Products of low-degree melting of subduction-modified lithospheric mantle in post-orogenic setting

Late- to post-orogenic lamprophyric and K-rich associations in the eastern Iranian ranges may be able to reveal some obscure issues about the petrogenesis and the role of tectonics in the formation of this rare group of igneous rocks. In this paper, we investigate new zircon U–Pb ages and elemental and Sr–Nd isotope characteristics of coexisting various rock suites as the post-tectonic products of the Paleogene orogeny . Lamprophyres are found in three occurrence modes in the eastern Iranian ranges. The first group is composed of olivine minette/shonkinite bodies in the Lar Complex, which is expressed as a post-tectonic volcano with Calderon subsidence that occurs currently as a ring-dike association and related explosion breccia . The second group consists of lamprophyric lavas of mainly mafic phonolite composition in Hormak. The last group is appinite/porphyrite occurring as stock/sub-volcanic bodies in Malek Siah Kuh. These three magmatic suites including lamprophyre and associated magmatic rocks are genetically, spatially and temporally related to one common K-rich mantle-derived magma . Zircon U–Pb dating of representative monzonite/syenite samples of the Lar Complex yielded ages of 31.43 ± 0.3 and 31.60 ± 0.40 Ma, respectively. Whole-rock geochemical and Sr–Nd isotope investigations demonstrated similar rare earth element (REE) patterns, with distinct enrichment in large lithophile elements (LILEs) and depletion in Ta–Nb–Ti, and limited variations in εNd (t) (+0.50 − +4.80) and 87 Sr/ 86 Sr (0.7043–0.7066) values. These characteristics, together with modeling of batch melting suggest that they were comagmatic and derived from a metasomatized lithospheric mantle source modified by a precursory subduction episode, through a low degree of partial melting (2–5%) at high-pressure conditions at depths >70 km with garnet in the residue. The Harirud fault activity possibly controlled the path, station and rapidity of magma ascent to the crustal levels, and, consequently, the water pressure of crystallization of the K-rich magmas and diversity of magmatic products. • The lithospheric mantle in the eastern Iranian ranges is highly heterogeneous. • Lamprophyres and K-rich association were products of post-orogenic magmatism. • The Harirud fault has crucial role in generation, transport and evolution of K-rich magmas.

Machine learning accelerated design of non-equiatomic refractory high entropy alloys based on first principles calculation

The properties of High Entropy Alloys (HEAs) strongly depend on the composition and content of elements. However, it was difficult to obtain the optimized element composition through the traditional "trial and error" method. The non-equiatomic HEAs have a large range for composition exploration by changing the content of elements, but the current research methods are difficult to analyze comprehensively. In this work, the prediction model with high accuracy is established by mixture design, the first principles calculation and machine learning. The model is used to predict the elastic properties and Poisson's ratio of non-equiatomic Mo–Nb–Ta–Ti–V HEAs, and the prediction results agree well with experimental data. The optimal element composition range of elastic properties and Poisson's ratio could be obtained. The influence of elements on the elastic properties and Poisson's ratio is analyzed through the calculation of features' importance. The results show that the content of Ti has the greatest contribution to the elastic properties and Poisson's ratio of the alloy. This model can not only obtain a large amount of data quickly and accurately but also help us to establish the relationship between element content and mechanical properties of non-equiatomic Mo–Nb–Ta–Ti–V RHEAs and provide theoretical guidance for experiments.

Phase Decomposition and Elevated Temperature Mechanical Properties of Zr–Ti–Nb–Ta–Sn Complex Concentrated Alloy Annealed at Intermediate Temperatures

Phase Decomposition and Elevated Temperature Mechanical Properties of Zr–Ti–Nb–Ta–Sn Complex Concentrated Alloy Annealed at Intermediate Temperatures

Predicting the thermal expansion of body-centred cubic (BCC) high entropy alloys in the Mo–Nb–Ta–Ti–W system

In this study, the thermal expansion behaviour of equiatomic alloys in the Mo–Nb–Ta–Ti–W system is studied to provide a predictive method to assess the behaviour of this and other high entropy alloy systems. The simulations used are based on first principles density functional perturbation theory and the quasi-harmonic approximation. Calculations have been used to predict the stability and phonon properties of increasingly complex alloys in the Mo–Nb–Ta–Ti–W system and their thermal expansion coefficients have been predicted. These are benchmarked against rule-of-mixtures predictions and experimental observations, where available. We have shown that atomic-scale modelling techniques can be used to reliably predict the thermal expansion of a range of body-centred cubic high entropy alloys and concentrated solid solutions.

A comprehensive review on zircon (U–Pb) geochronology, geochemistry and geological significance of granite rocks, provenance, tectonic implications, exhumation history, current status, and perspectives

The mineralization in this area is more closely related to the shoshonitic Niuxinshan meddling complex (NIC), which helps to depict concurrent edge magmatism metallogeny. In the present investigation, new geochronological and geochemical data are combined with previously disseminated isotopic data from granitic rocks in the NIC to establish the situation of the region's structural setting change and determine its bearing on territorial metallogeny. The new geochronological data suggest that structural change could have occurred between 155 and 185 Ma. The granitic rocks of the NIC can be geochemically divided into two groups. The geochemical signature of one group displays high rare earth element (REE) designs with irrelevant Eu anomalies, lower Yb, higher Sr, and negative Nb–Ta–Ti (NTT) abnormalities, demonstrating a volcanic‐curve climate with a thickened outside layer in a focalized setting. The other group has level REE designs with obvious regrettable Eu anomalies, higher Yb, lower Sr, and moderate NTT anomalies, indicating an intra‐plate extensional climate with a decreasing outside. According to geochronologic and isotopic data, the mineralization is Late Jurassic (155 Ma). This has been deciphered to be hereditarily associated with the crystallization of the complex's shallow crustal‐sourced bits. In addition, a structural model is presented that provides a possible explanation for the abundant polymetallic mineralization that occurs in the northern margin of the NCC after 155 Ma.

Nb–Ta mineralization in Ti-oxide minerals from the Bagolyhegy Metarhyolite Formation (Bükk Mountains, NE Hungary)

Abstract The foliated low-grade metamorphic rocks of the Triassic Bagolyhegy Metarhyolite Formation, mainly of pyroclastic origin, host post-metamorphic quartz-albite veins containing abundant tourmaline and occasionally rutile/ilmenite. The study of the Ti-oxide-mineralized veins with SEM-EDX revealed an unusual mineral assemblage comprising fine-grained Nb–Ta-bearing oxides (columbite-tantalite series, fluorcalciomicrolite and other Nb–Ti–Y–Fe-REE-oxide minerals) intergrown with Nb-rich polymorphs of TiO2 (anatase, rutile), ilmenite and zircon enriched with hafnium. This high field strength elements (HFSE)-bearing paragenesis is unexpected in this lithology, and was not described from any formation in the Paleozoic-Mesozoic rock suite of the Bükk Mountains (NE Hungary) before. The host metavolcanics are significantly depleted in all HFSE compared to the typical concentrations in felsic volcanics and the mineralized quartz-albite veins have even lower Ti–Nb–Ta concentration than the host rock, so the mineralization does not mean any enrichment. From proximal outcrops of the Triassic Szentistvánhegy Metavolcanics, potassic metasomatized lenses with albite-quartz vein fillings containing rutile/ilmenite are known. We studied them for comparison, but they only contain REE mineralization (allanite-monazite-xenotime); the Nb–Ta-content of Ti-oxide minerals is undetectably low. LA-ICP-MS measurements for U–Pb dating of Hf-rich zircon of the Nb–Ta-rich mineral assemblage gave 71.5 ± 5.9 Ma as lower intercept age while dating of allanite of the REE mineralized quartz-albite veins gave 113 ± 11 Ma as lower intercept age. The REE-bearing vein fillings formed during a separate mineralization phase in the Early Cretaceous, while the Nb–Ta mineralization was formed by post-metamorphic alkaline fluids in the Late Cretaceous., controlled by fault zones and fractures.

High‐entropy boride–carbide ceramics by sequential boro/carbothermal synthesis

AbstractA dual‐phase high‐entropy boride (HEB)/carbide (HEC) ceramic with a fine grain size was synthesized by a sequential boro/carbothermal process. In the first step, an Hf–Nb–Ta–Ti–Zr‐containing carbide was synthesized by a carbothermal reduction of oxides followed by the reaction of the carbide with B4C and ZrH2 to convert part of the carbide to boride. The resulting composition was ∼29 vol% HEB with an average grain size of ∼1.1 μm. Solid solution formation occurred at the densification temperature of 1900°C resulting in a relative density higher than 99%. The Vickers hardness was 26.5 ± 1.4 GPa. This is the first report of synthesizing dual‐phase boride–carbide high‐entropy ceramics from carbothermally synthesized, HEC powders.

Petrogenesis of Miocene igneous rocks in the Tafresh area (central Urumieh‐Dokhtar magmatic arc, Iran): Insights into mantle sources and geodynamic processes

Cenozoic tectono‐magmatism in Iran is widely considered to be related to subduction of the Neo‐Tethys Ocean. We employed whole‐rock and mineral geochemistry and isotopic data of intrusive rocks from Tafresh, central Urumieh‐Dokhtar magmatic arc, to evaluate the role of the mantle in magmatism, to assess the timing of emplacement, and to interpret the tectonic setting. Rock compositions range from gabbro or gabbro‐diorite (plagioclase + pyroxene ± olivine), to diorite (plagioclase + amphibole ± pyroxene), to granodiorite (quartz + plagioclase + K‐feldspar + amphibole + biotite), exhibiting high‐alumina calc‐alkaline affinity. Major oxide and trace element variations vary systematically from less to more evolved rocks suggesting a major role for fractional crystallization processes. Zircon LA‐ICP‐MS U–Pb ages of major rock types are in the range of 24–19 Ma, whereas those of gabbroic dikes are ~17.5 Ma. ԐNd values range between −1.8 and 3.7, and (87Sr/86Sr)i is narrowly restricted to 0.705–0.706, suggesting a common mantle source. The enrichment in light rare earth element (REE) enrichment and flat heavy REE patterns couple depletion of Nb–Ta–Ti indicate that subducting oceanic crust had interacted with the overlying mantle wedge. High‐alumina, mid‐Mg# Tafresh plutonic rocks formed from hydrous melts from which Ca‐pyroxene and magnetite crystallized earlier than plagioclase, whereas late‐crystallizing zircon nucleated while magma traversed through lithospheric mantle and Cadomian crust. Modelling of isotope and incompatible‐element patterns suggests the contribution of no more than ~5% molten sediment or other crustal components in Tafresh magma, at a developmental stage before most plagioclase and amphibole had crystallized. The Miocene Tafresh plutons originated during the final stages of subduction, before the collision between the Arabian and Eurasian plates.

Carboniferous variation of crustal thickness and subduction angles in Eastern Tianshan, NW China: evidence from the petrogenesis of the magmatic rocks in the Aqishan–Yamansu Belt

ABSTRACT New geochronological and geochemical data were presented for the Early Carboniferous basaltic to andesitic volcanic rocks and Late Carboniferous granitic intrusions in the Aqishan–Yamansu Belt of Eastern Tianshan, NW China. Zircon U–Pb dating indicates that the andesite and granite were emplaced at 330 Ma and 321 Ma, respectively. The andesitic rocks of the Yamansu Formation (FM) display subalkaline to calc-alkaline characteristics with moderate SiO2, relatively high Mg# values, and low Cr, Co and Ni, indicating an origin from mantle-derived melts. Their relatively low εNd(t) values (–0.02 ~ +0.61) and old TDM ages (TDM = 1.39–1.40 Ga) suggest a mantle source with addition of old crustal materials. Their high Rb/Y and Ba/La, low Nb/Y and Th/Yb ratios elucidate that the magma sources were probably metasomatized by slab-derived fluids. Besides, the high Th and low Ce/Th and Ba/Th ratios of the andesites suggest a contribution from subducted sediment–derived melts. Integrated with the depletion in high field strength elements and enrichment in light rare earth elements (LREEs), we suggest that the Yamansu andesites were formed by partial melting of relatively enriched mantle wedge metasomatized by both subducted sediment-derived melts and fluids. The basalts of the Tugutublak Formation (TF) have high MgO, Mg# (56–58) and εNd(t) (+5.9 ~ +6.3) values with enriched in LREEs and depleted in Nb–Ta–Ti anomalies, implying an arc setting. Their high Ba/Th, Ba/La and low Th/Ta, Th/Yb ratios suggest that the slab-derived fluids were involved. The basaltic andesites of the TF have higher SiO2, lower Mg# (48–50), Cr, Ni and εNd(t) (+1.21) values than the basalts of this formation, indicating that they were evolved from the basaltic magma. Therefore, the Carboniferous volcanic rocks in this study indicate that the Aqishan–Yamansu Belt was in a subduction background. The granites intruding into the TF show typical characteristics of I-type granite. Their highly positive εHf(t) values (+14 ~ +17) suggest a significant contribution from juvenile basaltic lower crust. Moreover, changes in the Dy/Yb and Ho/Yb ratios of Late Paleozoic felsic igneous rocks in the Aqishan–Yamansu Belt imply that the crust underwent four periods of thickening and thinning, which were likely triggered by the variation of subduction angles.