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The origin of crystal‐scale Zr isotopic variation remains enigmatic. Here, we report high‐precision Zr isotopic compositions of thin‐sectioned and hand‐picked zircon crystals from monzodiorites and K‐feldspar granites, which represent the mafic and felsic products of a differentiating magma. Our results reveal that zircons from both rock associations are dominated by a rim‐ward increase in the 94Zr/90Zr ratio and accompanied by ∼1‰ intracrystalline and intercrystalline variations, confirming the preferential incorporation of light Zr isotopes and thus kinetic isotopic fractionation during zircon growth. Notably, zircons enclosed by K‐feldspar in monzodiorites generally yield lower 94Zr/90Zr and higher Zr/Hf ratios than that of separated crystals, while in K‐feldspar granites, tiny zircons intergrown with apatite obtain higher 94Zr/90Zr but lower Zr/Hf ratios relative to that of sizable separates. The diversity in petrographic textures and sizes of zircon crystals, corresponding to their crystallization sequence, potentially accounts for some of the heterogeneity of Zr isotopes at the mineral scale. Plain Language Summary: Stable Zr isotopes of zircon have been proposed as a new and promising tracer for magmatic differentiation. However, how significant heterogeneity of Zr isotopes developed at the mineral scale in an evolving magma is highly debatable. Ab initio simulation calculations, experiments, and natural sampling have suggested that kinetic rather than equilibrium effect plays a dominant role in fractionating Zr isotopes during zircon crystallization, whereas how kinetic effect links with the textural contexts of zircons is not directly constrained. Here, petrographic and geochemical constraints on zircon crystals from the mafic and felsic products of a differentiating magma are provided, which reveal that earlier crystallized domains or crystals are isotopically lighter in Zr than the later ones. Besides, the δ94Zr values of zircon crystals, displaying intra‐grain and inter‐grain variations beyond ∼1‰, correlate well with Zr/Hf ratios that reflect diverse stages of magma differentiation, irrespective of the compositions of host rocks. These findings indicate that crystal‐scale elemental and stable isotopic variations (e.g., Zr isotopes in zircon) could be ascribed to the sequential crystallization of targeting minerals. Key Points: Early‐formed zircon crystals or domains are isotopically lighter in Zr than those crystallized late in both mafic and felsic rocksDiversity in textural occurrences and sizes of zircons potentially explain the Zr isotopic heterogeneity at the mineral scaleGeochemical information extracted from separated minerals does not always reflect the nature of primitive magma [ABSTRACT FROM AUTHOR]

The isotope dilution (ID) method, owing to its high precision, is extensively used for the determination of element mass fractions in a wide range of natural samples. One of the prerequisites of the ID method is knowledge of the isotopic composition of an enriched spike, which is often challenging to accurately determine. In this study, we employ a regression mass bias correction model to accurately and precisely measure the isotopic composition of an enriched Hf spike (Lot No. 159293, Oak Ridge National Laboratory). A NIST SRM 3134 Re solution, whose isotopic composition was calibrated by an NRC IRIS‐1 Ir isotope standard, was used to calibrate the isotopic composition of the Hf spike. The obtained ratios of 176Hf/177Hf, 179Hf/177Hf and 180Hf/177Hf were 0.2406 ± 0.0005 (u, k = 1), 2.8620 ± 0.0005 (u, k = 1) and 384.65 ± 0.05 (u, k = 1), respectively, which meet the required precision levels for Hf isotopes in the application of the ID method. The combined uncertainties of the calibrated Re and Hf isotope ratios were evaluated using a Monte Carlo method, in which the uncertainty of the primary calibrator (IRIS‐1, 193Ir/191Ir = 1.6866 ± 0.0005, u, k = 1) was also taken into consideration. The precision of Hf spike was improved significantly compared with the SSB and C‐SSBIN methods. To the best of our knowledge, this is the first report of isotope ratio calibration in an enriched spike using the regression model. The precisely calibrated spike can lower the uncertainty of the Hf mass fraction significantly, thereby increasing the accuracy of the Lu‐Hf chronometer. [ABSTRACT FROM AUTHOR]

Discontinuous ophiolites within the Indus–Tsangpo suture zone (ITSZ) in southern Tibet represent remnants of Neo‐Tethyan oceanic lithosphere, which are considered to have formed during the late Jurassic to early Cretaceous. We report field observations, petrological and geochronological data for some mafic intrusions in a tectonic mélange in the southern ophiolitic belt of the western ITSZ. Zircon from a gabbro yields an age of 243 ± 1 Ma with εHf(t) values of +7.9 to +13.2. Rare earth element (REE) pattern of this rock resembles that of normal mid‐ocean ridge basalt. We suggest that such gabbro and surrounding mafic–ultramafic rocks represent the remnants of middle Triassic oceanic lithosphere in the ITSZ. Our findings indicate that the Neo‐Tethys Ocean between India and the Lhasa terrane existed from at least the middle Triassic, contrasting with the commonly held view that the Neo‐Tethys Ocean opened along the northern edge of Gondwana during the late Triassic–early Jurassic. [ABSTRACT FROM AUTHOR]

Determination of gold abundances in natural rock is critical for applications, but very challenging. Here, we report a method for determining gold with a very low mass fraction (> 0.01 ng g−1) in rocks. The method involves Carius tube digestion with reverse aqua regia, chromatographic separation to remove most of the sample matrix and measurement by high‐sensitivity ICP‐MS. The mono‐isotopic element gold was quantified by external calibration using an internal standardisation of gold to platinum that was precisely determined by isotope dilution. The method is robust and the obtained results are indistinguishable (< 5–10%, 2s) from those independently obtained by a standard addition technique on the same solution. The results from reference materials TDB‐1 and GPt‐2 are consistent with the certified values and those determined by HF‐aqua regia digestion, confirming the validity of the method. TDB‐1 (n = 20), GPt‐2 (n = 6), BHVO‐2 (n = 9) and other mafic RMs are homogenous for gold (10–20%, 2s) at the 2 g test portion level; however, sample heterogeneity affects some RMs. Gold and platinum‐group elements also display different extents of sample heterogeneity for different RMs. Given the homogeneity observed for TDB‐1, GPt‐2 and BHOV‐2, they are recommended as well‐suited RMs for inter‐laboratory comparison studies of gold. [ABSTRACT FROM AUTHOR]

Bromine and iodine are important tracers for geochemical and environmental studies. In this study, a rapid acid digestion (HNO3 + HF) with ammonia dilution for the simultaneous determination of bromine and iodine in soils and sediments using ICP‐MS was developed. The recoveries of Br and I were controlled by the synergic effect of temperature and time. It took only 15 min at 140 °C for the complete recovery of Br and I in sediment (GSD‐2) and soil (GSS‐24) reference materials, which is a process that needs 2–6 h at 90 °C. A serious loss of Br and I was found at a higher digestion temperature of 190 °C. A 5% v/v NH4OH dilution effectively eliminated the memory effects and stabilised the signals of Br and I. Moreover, ammonia dilution also avoided the corrosiveness of HF on the sample introduction system and torch of ICP‐MS. Tellurium is a more suitable internal standard element than In in the ammonia medium. To avoid the adsorption of residues of dissolution on Te, addition of Te should be carried out after centrifuging the solution. The developed method was successfully applied to determine Br and I in fifty‐three Chinese soil and sediment reference materials. This simple method shows great potential for the rapid determination of Br and I in large batches of geological and environmental samples commonly analysed for mineral exploration and environmental geochemistry studies. [ABSTRACT FROM AUTHOR]

Ilmenite (FeTiO3) is a common accessory mineral and has been used as a powerful petrogenetic indicator in many geological settings. Elemental fractionation and matrix effects in ilmenite (CRN63E-K) and silicate glass (NIST SRM 610) were investigated using 193 nm ArF excimer nanosecond (ns) laser and 257 nm femtosecond (fs) laser ablation systems coupled to an inductively coupled plasma-mass spectrometer. The concentration-normalised 57Fe and 49Ti responses in ilmenite were higher than those in NIST SRM 610 by a factor of 1.8 using fs-LA. Compared with the 193 nm excimer laser, smaller elemental fractionation was observed using the 257 nm fs laser. When using 193 nm excimer laser ablation, the selected range of the laser energy density had a significant effect on the elemental fractionation in ilmenite. Scanning electron microscopy images of ablation craters and the morphologies of the deposited aerosol materials showed more melting effects and an enlarged particle deposition area around the ablation site of the ns-LA-generated crater when compared with those using fs-LA. The ejected material around the ns crater predominantly consisted of large droplets of resolidified molten material; however, the ejected material around the fs crater consisted of agglomerates of fine particles with 'rough' shapes. These observations are a result of the different ablation mechanisms for ns- and fs-LAs. Non-matrix-matched calibration was applied for the analysis of ilmenite samples using NIST SRM 610 as a reference material for both 193 nm excimer LA-ICP-MS and fs-LA-ICP-MS. Similar analytical results for most elements in ilmenite samples were obtained using both 193 nm excimer LA-ICP-MS at a high laser energy density of 12.7 J cm-2 and fs-LA-ICP-MS. [ABSTRACT FROM AUTHOR]

A laser ablation multi-collector inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS) method was developed to obtain precise and accurate Pb isotopic ratio measurements in low-Pb materials (< 10 µg g-1) using a combination of Faraday cups and ion counters (FC-IC). The low abundance 204Pb (~ 1.4%) was collected using an IC. A NBS 981 standard solution was used to cross-calculate the FC-IC gain and to investigate the signal response characteristics of the IC. A significant, continuous and linear decrease in the FC-IC gain was observed within 1 hr, but this drift could be corrected using the calibrator-sample-calibrator bracketing method. In addition, a non-linear response of the IC used in this study was observed and corrected by a non-linear correction algorithm, which was established by measuring a series of gravimetrically prepared NBS 981 standard solutions (NIST SRM 981 ). Compared with the conventional arrangement, the use of the newly designed X skimmer cone and Jet sample cone improved the signal intensities from Pb isotopes by a factor of 1.9. Compared with only Faraday cups, using a combination FC-IC array was found to enhance the measurement repeatability (RSD) of 20xPb/204Pb by approximately one order of magnitude when the 204Pb intensity was < 8 mV. Eight natural glasses and the NIST SRM 612 reference material glass (as a calibration material) were measured to evaluate the new protocol for Pb isotope determination. The analytical results were in agreement with the reference values within 2s measurement uncertainties. For MPI-DING ATHO-G (5.67 lg g-1 total Pb), KL2-G (2.07 µg g-1 total Pb) and ML3B-G (1.38 µg g-1 total Pb), the typical accuracies of 20xPb/204Pb were 0.09% of preferred values with precisions of < 0.33% (2RSD). The Pb isotope ratios in feldspars from granodiorite and within mafic microgranular enclaves (MMEs) from the Fangshan pluton, North China, were measured using the present method. The Pb isotopic compositions of feldspars from the whole host granodiorite show that that are radiogenic in the margin zone and gradually become less radiogenic. For the MMEs, the Pb isotopic compositions of feldspars are highly variable and overlap with those of the whole host granodiorite. For single-grain feldspar, the strong rim-core-rim variations of the Pb isotopic compositions and trace elements are interpreted to have been generated via magma mixing. These results suggest that the Fangshan pluton underwent magma mixing of mantle-derived mafic magmas with felsic magmas, and the proportion of the mafic magma influx decreased overtime. [ABSTRACT FROM AUTHOR]

Fused glass prepared without the addition of a flux is generally more homogeneous than a pressed powder pellet and thus ideal for analysis of bulk samples by LA- ICP- MS. In this work, a new glass-making method using a boron nitride crucible was developed to prepare homogenous glass samples from silicate rock powder. The apparatus consisted of a small boron nitride vessel with net volume of about 34 mm3 and two molybdenum strips. Applying the summed metal oxide normalisation technique, both major and trace element contents in the fused glass were measured by LA- ICP- MS. Analyses of five geochemical reference materials (spanning the compositional range basalt-andesite-rhyolite) indicated that the measured Si O2, Al2 O3 and P2 O5 contents matched the preferred values to within 5%, and the other major elements generally matched the preferred values to within 8%. Except for the transition metals, the measured trace element contents generally matched the preferred values to within 10%. Compared with the iridium heater method developed by Stoll et al. (2008), element volatilisation during high-temperature melting was effectively suppressed in our method, but metal segregation caused by reduction of BN may cause loss of Cr, Ni and Cu. Although analysis with a large spot size has the advantage of improving counting statistics, matrix effects induced by mass loading of the ICP may hamper the accurate determination of some elements. [ABSTRACT FROM AUTHOR]

Discontinuous ophiolite suites along the Yarlung Zangbo suture zone (YZSZ) in southern Tibet representing remnants of the Neo‐Tethyan oceanic lithosphere are considered to be formed between Late Jurassic and Early Cretaceous. Older ophiolite or ophiolitic mélange (e.g. Triassic) to reveal the initial evolution the Neo‐Tethyan ocean within the YZSZ have rarely been documented so far. The western YZSZ extending from the Saga to Ladakh area are composed of the northern ophiolitic sub‐belt, the Zhongba terrane and the southern ophiolitic sub‐belt. In this study, we document structural, petrological and geochronological data of mafic intrusions from the Mayoumu massif in the southern ophiolitic sub‐belt of the western YZSZ. Two lithos‐tectonic sub‐units, the southern ophiolitic complex and the northern ophiolitic mélange, are recognized in the Mayoumu massif in terms of structural pattern and petrology. LA‐ICP‐MS zircon U‐Pb dating of gabbro from the ophiolitic mélange yields an age of 243 ± 1 Ma with zircon ∊Hf(t) values of +7.9 to +13.2. Two samples of diabase samples from the ophiolite yield ages of 131±1 Ma and 124±1 Ma with zircon ∊Hf (t) values ranging from +10.8 to +15.0 and +12.3 to +15.4, respectively. Geochemically, rare earth elements (REEs) patterns show that these mafic intrusions are similar to those of the normal mid‐ocean‐ridge basalt (N‐MORB). Enrichment of fluid‐mobile elements (e.g. Rb and Ba) and depletion of Nb, and Ta suggest that these intrusions were possibly originated from melting of a depleted mantle source influenced by subducted slab. Our data strongly confirms that the Neo‐Tethyan ocean between the Lhasa terrane and Gondwana had been existed since the Middle Triassic at least. The ages of the two diabases from the ophiolitic complex reveal that mafic magma activities within the Neo‐Tethyan ocean could be as a continuing process during 120–130 Ma. Emplacement and preservation of older ophiolitic recorder during evolution of the Neo‐Tethyan Ocean may be closely related to the occurrence of the Zhongba micro‐terrane within the western YZSZ. [ABSTRACT FROM AUTHOR]

Discontinuous ophiolite suites along the Yarlung Zangbo suture zone (YZSZ) in southern Tibet representing remnants of the Neo‐Tethyan oceanic lithosphere are considered to be formed between Late Jurassic and Early Cretaceous. Older ophiolite or ophiolitic mélange (e.g. Triassic) to reveal the initial evolution the Neo‐Tethyan ocean within the YZSZ have rarely been documented so far. The western YZSZ extending from the Saga to Ladakh area are composed of the northern ophiolitic sub‐belt, the Zhongba terrane and the southern ophiolitic sub‐belt. In this study, we document structural, petrological and geochronological data of mafic intrusions from the Mayoumu massif in the southern ophiolitic sub‐belt of the western YZSZ. Two lithos‐tectonic sub‐units, the southern ophiolitic complex and the northern ophiolitic mélange, are recognized in the Mayoumu massif in terms of structural pattern and petrology. LA‐ICP‐MS zircon U‐Pb dating of gabbro from the ophiolitic mélange yields an age of 243 ± 1 Ma with zircon ∊Hf(t) values of +7.9 to +13.2. Two samples of diabase samples from the ophiolite yield ages of 131±1 Ma and 124±1 Ma with zircon ∊Hf (t) values ranging from +10.8 to +15.0 and +12.3 to +15.4, respectively. Geochemically, rare earth elements (REEs) patterns show that these mafic intrusions are similar to those of the normal mid‐ocean‐ridge basalt (N‐MORB). Enrichment of fluid‐mobile elements (e.g. Rb and Ba) and depletion of Nb, and Ta suggest that these intrusions were possibly originated from melting of a depleted mantle source influenced by subducted slab. Our data strongly confirms that the Neo‐Tethyan ocean between the Lhasa terrane and Gondwana had been existed since the Middle Triassic at least. The ages of the two diabases from the ophiolitic complex reveal that mafic magma activities within the Neo‐Tethyan ocean could be as a continuing process during 120–130 Ma. Emplacement and preservation of older ophiolitic recorder during evolution of the Neo‐Tethyan Ocean may be closely related to the occurrence of the Zhongba micro‐terrane within the western YZSZ. [ABSTRACT FROM AUTHOR]