Extreme Zr stable isotope fractionation during magmatic fractional crystallization

Zirconium is a commonly used elemental tracer of silicate differentiation, yet its stable isotope systematics remain poorly known. Accessory phases rich in Zr⁴⁺ such as zircon and baddeleyite may preserve a unique record of Zr isotope behavior in magmatic environments, acting both as potential drivers of isotopic fractionation and recorders of melt compositional evolution. To test this potential, we measured the stable Zr isotope composition of 70 single zircon and baddeleyite crystals from a well-characterized gabbroic igneous cumulate. We show that (i) closed-system magmatic crystallization can fractionate Zr stable isotopes at the >0.5% level, and (ii) zircon and baddeleyite are isotopically heavy relative to the melt from which they crystallize, thus driving chemically differentiated liquids toward isotopically light compositions. Because these effects are contrary to first-order expectations based on mineral-melt bonding environment differences, Zr stable isotope fractionation during zircon crystallization may not solely be a result of closed-system thermodynamic equilibrium

Comprehensive Management model for increasing the competitiveness of small and medium artisan jewelry enterprises in Peru

Today, many small and medium enterprises (SMEs) either go out of business or see their growth being stalled due to poor activity management and organization, which is why they are often unprepared to engage against large companies leading their competitive markets. This study aims to develop a comprehensive management model, exclusively designed for SMEs in the jewellery sector, which may encompass all areas that create value and make them competitive. The development of this comprehensive management model was deployed in 21 steps classified into three tiers based on three major philosophies. This study uses lean manufacturing to identify activities that add value and reduce waste, and lean green was used to provide the environmental care and culture approach required for a friendly and fair workplace environment. The selected scenario is a jewelry workshop, wherein techniques and tools were completely applied and yielded a 20% increase in operating performance and a 15% increase in annual return

Reliability of detrital marine sediments as proxy for continental crust composition: the effects of hydrodynamic sorting on Ti and Zr isotope systematics

The isotopic composition of the detrital sediment record harbours a valuable proxy for estimating the composition of the erodible upper crust since the Archaean. Refractory elements such as titanium (Ti) and zirconium (Zr) can display systematic variations in their isotopic composition as a result of magmatic differentiation. Hence, for such elements, the isotope composition of detrital sediments could potentially be used to infer the average composition (e.g., SiO₂ content) of their source region, even when elemental systematics are obfuscated by weathering and diagenetic processes. A key premise of this approach is that the isotopic composition of sediments remains unbiased relative to their protolith. To what extent isotopic fractionation can occur during sedimentary processes, notably the hydrodynamic sorting of heavy mineral assemblages with contrasting isotopic compositions, remains poorly understood. We investigate the effects of such processes on the Ti and Zr isotope composition of a suite of detrital sediments from the Eastern Mediterranean Sea (EMS). These sediments are binary mixtures of two main provenance components, Saharan dust and Nile sediment, with strongly contrasting mineralogical and geochemical signatures. The EMS sediments display clear evidence for hydrodynamic sorting of zircon, expressed as a large variation in Zr/Al₂O₃ and deviation of εHf relative to the terrestrial εNd-εHf array. Our new data, however, do not show pronounced Zr isotope variation resulting from either hydrodynamic sorting of zircon or sediment provenance. Although this agrees with theoretical models that predict negligible equilibrium zircon-melt Zr isotope fractionation, it contrasts with recent observations suggesting that kinetic Zr isotope fractionation might be a common feature in igneous rocks. For the EMS sediments, the negligible shift in Zr isotope composition through hydrodynamic sorting means that fine-grained samples accurately reflect the composition of their source. The nearly overlapping Zr isotope compositions of Sahara- and Nile-derived sediment, however, means that Zr isotopes, in this case, have insufficient resolution to be a useful provenance proxy. Titanium behaves differently. A small but resolvable, systematic difference in Ti isotope composition is observed between the Sahara and Nile provenance components. Samples with a strong Saharan dust signature show some Ti isotope evidence for hydrodynamic sorting of oxides in tandem with zircon, but a much stronger effect is inferred for Nile sediment. Regression of the EMS sediment samples shows that the Ti isotope composition of the Nile-derived component is strongly fractionated compared to its protolith, the Ethiopian flood basalts. Whereas Ti in Nile sediment is carried in essentially unmodified concentration, and by inference isotope composition, from its sources to the delta, large-scale hydrodynamic sorting of Fe-Ti oxides occurs in the delta. This process decreases TiO₂/Al₂O₃ of the residual fine-grained sediment fraction and shifts its Ti isotope composition to heavier compositions. The potential of such an “oxide effect” in detrital sediments has implications for crustal evolution models that use Ti isotopes as a proxy for the proportion of felsic crust and can account for the observed scatter in the shale record

Hadaean to Palaeoarchaean stagnant-lid tectonics revealed by zircon magnetism.

Plate tectonics is a fundamental factor in the sustained habitability of Earth, but its time of onset is unknown, with ages ranging from the Hadaean to Proterozoic eons1-3. Plate motion is a key diagnostic to distinguish between plate and stagnant-lid tectonics, but palaeomagnetic tests have been thwarted because the planet's oldest extant rocks have been metamorphosed and/or deformed4. Herein, we report palaeointensity data from Hadaean-age to Mesoarchaean-age single detrital zircons bearing primary magnetite inclusions from the Barberton Greenstone Belt of South Africa5. These reveal a pattern of palaeointensities from the Eoarchaean (about 3.9 billion years ago (Ga)) to Mesoarchaean (about 3.3 Ga) eras that is nearly identical to that defined by primary magnetizations from the Jack Hills (JH; Western Australia)6,7, further demonstrating the recording fidelity of select detrital zircons. Moreover, palaeofield values are nearly constant between about 3.9 Ga and about 3.4 Ga. This indicates unvarying latitudes, an observation distinct from plate tectonics of the past 600 million years (Myr) but predicted by stagnant-lid convection. If life originated by the Eoarchaean8, and persisted to the occurrence of stromatolites half a billion years later9, it did so when Earth was in a stagnant-lid regime, without plate-tectonics-driven geochemical cycling

Hyperoxemia and excess oxygen use in early acute respiratory distress syndrome : Insights from the LUNG SAFE study

Publisher Copyright: © 2020 The Author(s). Copyright: Copyright 2020 Elsevier B.V., All rights reserved.Background: Concerns exist regarding the prevalence and impact of unnecessary oxygen use in patients with acute respiratory distress syndrome (ARDS). We examined this issue in patients with ARDS enrolled in the Large observational study to UNderstand the Global impact of Severe Acute respiratory FailurE (LUNG SAFE) study. Methods: In this secondary analysis of the LUNG SAFE study, we wished to determine the prevalence and the outcomes associated with hyperoxemia on day 1, sustained hyperoxemia, and excessive oxygen use in patients with early ARDS. Patients who fulfilled criteria of ARDS on day 1 and day 2 of acute hypoxemic respiratory failure were categorized based on the presence of hyperoxemia (PaO2 > 100 mmHg) on day 1, sustained (i.e., present on day 1 and day 2) hyperoxemia, or excessive oxygen use (FIO2 ≥ 0.60 during hyperoxemia). Results: Of 2005 patients that met the inclusion criteria, 131 (6.5%) were hypoxemic (PaO2 < 55 mmHg), 607 (30%) had hyperoxemia on day 1, and 250 (12%) had sustained hyperoxemia. Excess FIO2 use occurred in 400 (66%) out of 607 patients with hyperoxemia. Excess FIO2 use decreased from day 1 to day 2 of ARDS, with most hyperoxemic patients on day 2 receiving relatively low FIO2. Multivariate analyses found no independent relationship between day 1 hyperoxemia, sustained hyperoxemia, or excess FIO2 use and adverse clinical outcomes. Mortality was 42% in patients with excess FIO2 use, compared to 39% in a propensity-matched sample of normoxemic (PaO2 55-100 mmHg) patients (P = 0.47). Conclusions: Hyperoxemia and excess oxygen use are both prevalent in early ARDS but are most often non-sustained. No relationship was found between hyperoxemia or excessive oxygen use and patient outcome in this cohort. Trial registration: LUNG-SAFE is registered with ClinicalTrials.gov, NCT02010073publishersversionPeer reviewe

Drivers of zirconium isotope fractionation in Zr-bearing phases and melts: The roles of vibrational, nuclear field shift and diffusive effects

Conflicting results exist regarding the mechanisms, direction, and magnitude of Zr isotope fractionation in igneous systems. To better understand the origin of the fractionations observed in magmatic Zr-bearing minerals and bulk rocks, we theoretically investigated the main potential driving processes: thermodynamic equilibrium effects driven by either (i) vibrational energy or (ii) nuclear volume, and (iii) diffusion-driven kinetic effects. Vibrational equilibrium fractionation properties were estimated for zircon (^(VIII)ZrSiO₄), baddeleyite (^(VII)ZrO₂), gittinsite (^(VI)ZrCaSi₂O₇), sabinaite (Na₄^(VIII)Zr₂TiC₄O₁₆), and vlasovite (Na₂^(VI)ZrSi₄O₁₁). These properties show dependency on Zr coordination, as well as the presence of strong covalent bonds (C O, Si O by order of decreasing effect) in the material. More importantly, despite the large variety of structures investigated, the predicted mass-dependent equilibrium fractionations (Δ⁹⁴/⁹⁰Zr ∼±0.05‰ relative to zircon at 800 °C) are systematically one order of magnitude smaller than required to explain the natural variability observed to date in natural settings (δ⁹⁴/⁹⁰Zr from ∼+1 to −5‰). Likewise, careful evaluation of expected nuclear field shift (NFS) effects predict a magnitude of fractionation of ∼0.08‰ (at 800 °C), further supporting the conclusion that equilibrium effects cannot be invoked to explain extreme δ⁹⁴/⁹⁰Zr zircon values. Furthermore, the mass-dependency of all Zr isotope ratios reported in zircon crystals precludes a contribution of NFS effects larger than ∼0.01‰ on δ⁹⁴/⁹⁰Zr. On the other hand, we show that diffusion, and in particular the development of Zr diffusive boundary layers in silicate magmas during fractional crystallization, provides a viable and most likely mechanism to produce permil-level, mass-dependent isotope fractionations similar to those observed in natural systems. We propose testable scenarii to explain the large and contrasting Zr isotopes signatures in different magmatic zircons, which underline the importance of magmatic composition, Zr diffusivity, and crystallization timescales

Tectonic juxtaposition of Triassic and Cretaceous meta-(ultra)mafic complexes in the Central Cordillera of Colombia (Medellin area) revealed by zircon U-Pb geochronology and Lu-Hf isotopes

The amphibolites and associated ophiolitic rocks/metapelites in the Aburrá Valley, Colombian Central Cordillera, are commonly considered oceanic fragments accreted to the Permian-Triassic Cajamarca Complex of the north Andes. Nevertheless, the complex tectonostratigraphic architecture of the Central Cordillera and the general paucity of accurate geochronologic data in this region preclude robust interpretations of their origin and accretionary/metamorphic history. To better understand the age and tectonic significance of these oceanic units, we have conducted a geochronologic study using modern U-Pb zircon dating methods. Our new ages, in combination with Lu-Hf isotopic results from the same dated crystals, allow us to place constraints on the origin of these units, their timing of accretion to the continental margin, as well as the source of the liquids/fluids from which zircon (re)-crystallized. Our new geochronologic results indicate that the unit known as the La Espadera-Chupadero amphibolites (LECh), which is associated with the Medellin Metaharzburgitic Unit, consists of late Triassic (ca. 228 Ma) metabasalts and metagabbros (El Picacho Metagabbros) that were metamorphosed shortly after at ca. 221 Ma. Based on the structural position of the LECh amphibolites and other metabasites of the Aburrá Ophiolite, we interpret them as the metamorphic sole of the Medellín Metaharzburgitic Unit, in line with previous proposals. Thus, the age of metamorphism of the LECh marks the time of subduction initiation in the oceanic basin where the Aburrá Ophiolite formed, a process that favored its obduction onto de continental margin. On the other hand, the nearby Santa Elena amphibolites and associated metasediments represent early Cretaceous (≤130 Ma) oceanic protoliths that were metamorphosed at ca. 101 Ma. The early Cretaceous protolith and metamorphic ages of the Santa Elena unit are similar to those of the Arquía Group in the Central Cordillera. Nevertheless, we suggest a distinct origin based on their younger age of metamorphism and lack of high-pressure assemblages. We propose that the Aburrá Ophiolite represents an oceanic arc/back-arc lithospheric fragment obducted onto the Tahami terrane following a period of regional extension in the mid- to late-Triassic, whereas the Santa Elena unit may represent a fragment of the early-Cretaceous Colombian-Ecuadorian oceanic back-arc which was accreted and metamorphosed during mid-Cretaceous back-arc closure. Juxtaposition of the two units after their accretion to the continental margin along the Rodas fault took place between the Cenomanian and the Coniacian, as constrained by the dated cross-cutting Media Luna tonalite stock for which we obtained a new age of 88.849 ± 0.065 Ma. We hence conclude that the Rodas Fault represents a fossilized late Cretaceous structure

To sink or not to sink: The thermal and density structure of the modern northern Andean arc constrained by xenolith petrology

The thermal and compositional structure of arcs influence magmatic differentiation and lower-crustal foundering, two key processes impacting the evolution of the continental crust. Although many studies have proposed time scales of lithospheric recycling based on convective downwelling calculations, these models depend on the composition, density (ρ), and thermal structure of the lower crust and mantle, which are difficult to quantify in active continental arcs. Here, we constrained these properties for the Andean Northern Volcanic Zone using direct petrologic observations from a unique suite of lower-crust and mantle xenoliths from Mercaderes, Colombia. Chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb dates for zircons within the host tuff indicate the xenoliths erupted no earlier than 238 (±19) ka and thus capture a recent snapshot of the arc and subarc mantle. Equilibrium pressure-temperature (P-T) estimates for 81 xenoliths define three distinct thermal domains, interpreted as (1) a steep conductive geothermal gradient in the lower arc crust; (2) a convecting mantle wedge; and (3) cooled mantle in proximity to the subducting slab. Our results indicate the presence of an ~10–14-km-thick, high-density lithospheric root that is ~0.1 g/cm3 denser than the underlying mantle. Unlike records from exhumed paleoarcs, Rayleigh-Taylor instability calculations using our P-T-ρ constraints are unrealistically short for the northern Andes. We suggest the presence of partial melts in this hot arc root as a potential source of buoyancy preventing or significantly slowing down foundering.ISSN:0091-7613ISSN:1943-268