33 research outputs found

    Precise Measurement of Magnesium Isotopes in Fe-Mg Minerals Using a Multi-collector SHRIMP Ion Microprobe

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    The distribution of Mg isotopes in minerals is becoming increasingly relevant in Earth science. Usually, they are determined by dissolving mineral concentrates and, after purifying Mg with ion exchange resins, analysing the resulting solutions by TIMS or, most often, MC-ICP-MS. When applied to individual minerals, these methods are slow and prone to contamination from impurities in the concentrates, inconveniences that may be avoided using spot analysis techniques such as LA-MC-ICP-MS or SIMS, albeit at the price of a large instrumental mass fractionation (IMF) and isobaric interferences, most prominent in the former. Here, we studied the potential of the multi-collector SHRIMP II ion microprobe for measuring Mg isotopes in Fe-Mg silicates and oxides. We found that, when corrected for the divergence of the Mg ion paths within the sample chamber caused by the Earth’s magnetic field, the SHRIMP’s IMF overwhelmingly depends on the mineral species, and the effects of variable chemical composition are negligible. We propose that the IMF is caused by the force constant difference, ΔF, between "hard" and "soft" bonds linking the ions of the studied element to the mineral lattice. Given that ΔF is a constant for each mineral species, we calculated IMF-correction factors for the most common Mg-bearing minerals. The thus-calculated correction factors permit the analysis in the same session, and with reasonable accuracy (within ~0.3‰ of the δ26Mg determined by SN-MC-ICP-MS analyses of concentrates), of samples from different mineral species, facilitating the application of Mg isotopes to terrestrial studies.Andalucian-FEDER grant P18-FR-1696Spanish grant PID2020-114872GB-I0

    Nickel Isotopic Evidence for Late-Stage Accretion of Mercury-Like Differentiated Planetary Embryos

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    © 2021, The Author(s). Earth’s habitability is closely tied to its late-stage accretion, during which impactors delivered the majority of life-essential volatiles. However, the nature of these final building blocks remains poorly constrained. Nickel (Ni) can be a useful tracer in characterizing this accretion as most Ni in the bulk silicate Earth (BSE) comes from the late-stage impactors. Here, we apply Ni stable isotope analysis to a large number of meteorites and terrestrial rocks, and find that the BSE has a lighter Ni isotopic composition compared to chondrites. Using first-principles calculations based on density functional theory, we show that core-mantle differentiation cannot produce the observed light Ni isotopic composition of the BSE. Rather, the sub-chondritic Ni isotopic signature was established during Earth’s late-stage accretion, probably through the Moon-forming giant impact. We propose that a highly reduced sulfide-rich, Mercury-like body, whose mantle is characterized by light Ni isotopic composition, collided with and merged into the proto-Earth during the Moon-forming giant impact, producing the sub-chondritic Ni isotopic signature of the BSE, while delivering sulfur and probably other volatiles to the Earth

    Discrepancy between bulk-rock and zircon Hf isotopes accompanying Nd-Hf isotope decoupling

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    Zircon is an important accessory mineral for studying the crust-mantle interaction and crustal growth through time because zircon crystals not only allow precise dating but also record initial Hf isotope ratios of the host magmas. Our study on a suite of gabbronorite, mafic diorite cumulates, diorite and granite from the Kekeli Batholith in the North Qilian Orogenic Belt, northern Tibetan Plateau, shows (1) a significant Hf isotope discrepancy between zircons and their bulk rocks; and (2) bulk-rock Nd-Hf isotopic decoupling. These observations thus demonstrate that zircons do not always capture the full history of magmatic system. The significant positive correlation between bulk-rock Hf isotope ratios and TiO2 content (R2=0.94) indicates that Ti-rich minerals (e.g., ilmenite, amphibole) are likely important Hf hosts. The early-formed Ti-rich minerals possibly record different Hf isotopes from those of zircons crystallized subsequently, thus causing discrepancy between zircons and bulk-rocks and leading to bulk-rock Nd-Hf isotope decoupling. Correlations between bulk-rock TiO2 content, Mg isotopes and Hf isotopes indicate a mixing process, with granite and gabbronorite representing two compositional endmembers. Because Ti minerals have higher crystallization temperatures than zircons, when the mixing melts have contrasting isotopes (or from heterogeneous sources/ have a strong crustal contamination), the bulk-rock and zircon Hf isotope discrepancies reflect mineral crystallization sequence during mafic and felsic magma mixing. It is thus imperative to consider early formed minerals such as Ti-rich minerals and the bulk rock composition, not just zircons, when using Hf isotopes to track melt evolution and precisely constrain mantle contribution to granitoid petrogenesis

    A novel purification method for high precision measurement of Ni isotopes by double spike MC-ICP-MS

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    Nickel (Ni) isotopes have been developed as a potential biosignature and proxy for tracing the occurrence of the Great Oxidation Event. However, the precise measurement of Ni isotopes is still hindered by the costly operation, complicated procedures and/or high procedural blanks of the chemical purification schemes. Here, a novel purification scheme, utilizing only dimethylglyoxime (DMG) and acetone as organic reagents, is proposed to separate Ni from samples through a four-step procedure with five chromatographic columns. Steps I, II and III are designed to effectively eliminate major matrix elements, including 99% Fe, Ca, Ti, and Al, 85% Mn, 55% K, even for samples with [Ca]/[Ni] approximate to 4600 and [Mg]/[Ni] approximate to 1900. Step IV utilizes the formation of Ni(DMG)(2) complexes in an aqueous medium containing 0.5 M HCl, 95% acetone and 0.1 M DMG, which can remove residual elements such as 45% K; this step avoids the use of Ni-specific resin, which requires careful pH tuning. Steps III and I can be repeated to obtain high-purity Ni. The Ni yield through these four steps is greater than 92%, with a maximum loss of similar to 8% occurring in Step II for low-Ni samples. The total procedural blank is 0.4 to 1.2 ng. When double spiking (Ni-61-Ni-60) is used to correct for instrument mass bias and purification-related isotope fractionation, small sample sizes (600-800 ng) are sufficient for achieving high-precision Ni isotope determination. Nickel isotopes for standards such as SRM 986 and geological reference materials (GRMs) such as BHVO-2, NOD-P-1, and NOD-A were determined on a Nu Plasma III MC-ICP-MS. The long-term reproducibility is 0.05 parts per thousand (2SD, n = 134) for pure solution and 0.06 parts per thousand (2SD, n = 18) for GRMs, and the average delta Ni-60 values are in excellent agreement with previous studies. These results show that our new purification method can be applied to various samples. Using this new method, we measured a set of granite, sediment, diamictite and loess samples and preliminarily constrained the delta Ni-60 of the upper continental crust to be 0.11 +/- 0.14 parts per thousand (2SD, n = 17)

    Revision hip arthroplasty as a treatment of Vancouver B3 periprosthetic femoral fractures without bone grafting

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    Background: It is conventionally considered that bone grafting is mandatory for Vancouver B3 periprosthetic femoral fractures (PFF) although few clinical studies have challenged the concept previously. The aim of the current study was to investigate the radiographic and functional results of Vancouver B3 PFF treated by revision total hip or hemiarthroplasty (HA) in combination with appropriate internal fixation without bone grafting. Materials and Methods: 12 patients with Vancouver B3 PFF were treated by revision THA/HA without bone grafting between March 2004 and May 2008. There were nine females and three males, with an average age of 76 years. PFFs were following primary THA/HA in nine patients and following revision THA/HA in three. Postoperative followup was 5.5 years on average (range, 3.5-6.5 years). At the final followup, radiographic results were evaluated with Beals and Tower′s criteria and functional outcomes were evaluated using the Merle d′Aubigné scoring system. Results: All fractures healed within an average of 20 weeks (range, 12-28 weeks). There was no significant deformity and shortening of the affected limb and the implant was stable. The average Merle d′Aubignι score was 15.8. Walking ability was regained in 10 patients without additional assistance, while 2 patients had to use crutches. There were 2 patients with numbness of lateral thigh, possibly due to injury to the lateral femoral cutaneous nerve. There were no implant failures, dislocation and refractures. Conclusions: Revision THA/HA in combination with appropriate internal fixation without bone grafting is a good option for treatment of Vancouver B3 periprosthetic femoral fractures in the elderly

    Primary tumorectomy promotes angiogenesis and pulmonary metastasis in osteosarcoma-bearing nude mice

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    PURPOSE: To investigate the effect of primary tumorectomy on angiogenesis and pulmonary metastasis in osteosarcoma-bearing nude mice. METHODS: Osteosarcoma was introduced to nude mice via subcutaneous injection of MG-63 cells. One hundred and eighty osteosarcoma-bearing mice were used equally in 3 parallel experiments. The effect of tumorectomy (TR) on the expression of vascular endothelial growth factor (VEGF) and endostatin was investigated by ELISA. Meanwhile, the effect on angiogenesis was evaluated by Matrigel plug assay, and pulmonary metastasis assessed by calculating the metastatic foci. Sham-operation (SO) and untreated (UT) groups served as controls. RESULTS: The VEGF (TR: 79.55 ± 7.82 pg/mL vs. SO: 110.01 ± 5.69 pg/mL, UT: 123.50 ± 10.41 pg/mL; p < 0.01) and endostatin (TR: 47.09 ± 6.22 ng/mL vs. SO: 117.64 ± 7.39 ng/mL, UT: 126.73 ± 6.55 ng/mL; p<0.01) were down-regulated significantly after tumorectomy, and angiogenesis was significantly promoted simultaneously. The incidence of pulmonary metastatic foci was 80.0% in the TR group, 40.0% in the SO group and 35.0% in the UT group. CONCLUSION: Primary tumorectomy can down-regulate the expression of VEGF and endostatin and promote angiogenesis which leads to the acceleration of pulmonary metastasis. These findings imply that anti-angiogenic treatment can be considered after primary tumorectomy
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