Concentration Profiles Of Elements Research Articles

Using Fin Ray Elemental Signatures and Growth Zone Width to Estimate Onset of Sexually Maturity in Lake Sturgeon (Acipenser fulvescens)

Characterizing inter- and intra-population levels of variability in age at sexual maturation for long-lived fishes provides insight into year-class strength and recruitment dynamics, allowing for more effective management practices. Here we analyzed the ontogenetic chronology of pectoral fin ray annuli trace elemental concentration profiles as well as changes in annuli growth in Lake Sturgeon (Acipenser fulvescens) to determine onset of sexual maturity (OSM). Elemental concentrations and growth-zone width were used to build a random forest classification model to discriminate year-specific signatures to before or after OSM from 98 individual fin rays from both sexes across multiple populations and watersheds. The model demonstrated an overall accuracy of 98.8%. Ba was the most important variable related to OSM discrimination success followed by zone width, Pb, Mn, Mg, Zn, Cu, and Sr. Fin ray elemental concentrations began to increase at approximately age 24 (± 4.7) in females and 15 (± 3.1) in males while zone width decreased. This study implies that new applications for fin ray microchemistry are possible and could benefit future fisheries management strategies specifically by adding nonlethal or less invasive sampling techniques for evaluating OSM in sturgeon.

Недеструктивный количественный элементный анализ поверхности материалов

The paper presents the possibilities of the Rutherford backscattering and proton-induced X-ray emission methods, as well as the features of their application for non-destructive elemental diagnostics of the surface of materials. It is shown that the combined use of these methods makes it possible to quantitatively characterize the chemical composition of the surface layers of various objects and to determine the elemental concentration profile over the thickness of these layers with nanoscale resolution. The use of the methods is demonstrated by examples of thin-film coatings, samples of oil and textile industry.

Substantially excess uranium in the waters of an intertidal salt marsh: A case study of eastern Chongming Beach

Knowledge of the geochemical behavior of uranium is key to an accurate tracing of the decay chain of the uranium series nuclides for material transportation processes on different temporal scales. However, direct observations for understanding dissolved uranium input in tidal water are very limited. Therefore, dissolved uranium was measured in tidal creek water, overlying water, and pore water collected from the central cross section of eastern Chongming Beach, Changjiang Estuary, from November 2012 to October 2013, to observe the spatiotemporal distribution of uranium. The results indicated that the behavior of dissolved uranium is conservative in the tidal creek waters during the flooding process, and an excess of dissolved uranium is observed during the ebbing process; excess uranium phenomena are dominant in the overlying and pore waters throughout the year, particularly at the middle and high tidal flats. The element concentration profiles in pore water showed that uranium release follows Mn oxide reduction in the subsurface suboxic zone. Hence, the exchange process between tidal water and pore water, coupled with ebb tide, represents a potential path for uranium release into the estuary. The three-end-member (Changjiang River, seawater, and pore water) model estimates that 35% of the amount of uranium in ebbing water is derived from pore water. The exchange rate between tidal water and pore water is 196.4 nmol/(cm2·d), with an export flux of 2.34 × 104 mol/a. We suggest that the release of uranium from intertidal salt marshes is an important uranium source in estuarine and coastal regions.

Nutritional characterization on growth and ionome profiles in Japanese wasabi cultivars (Eutrema japonicum) under hydroponics

ABSTRACT Japanese wasabi is traditionally cultivated in terraced fields with running stream water conditions which typically produce a high-quality of yield. Previous studies have explored some of the effects of water nutrient status under such conditions; however, the relationship between water nutrient status in these cultivation conditions and the growth and quality of wasabi is still completely unknown. We evaluated the effects of nutrient strength, inorganic nitrogen sources, and pH of the medium on the growth of wasabi plants. Then, we analyzed the photosynthetic capacity and the ionomes of two major Japanese wasabi cultivars (‘Onimidori,’ an early-growing green-stem type; and ‘Mazuma No.1,’ a late-growing red-stem type) grown under a range of pH conditions. These experiments were conducted using a hydroponic system. Wasabi plants showed the best shoot and root growth in 1/10- and 1/2-strength Hoagland’s solution with a 50:50 ratio of NH4-N:NO3-N. On the basis of the accumulation patterns of NO3 −, amino acids, and chlorophylls, the 1/10-strength nutrient solution provided optimal conditions for wasabi growth. For both wasabi cultivars, the best shoot and root growth was in medium at pH 6.0. The photosynthetic capacity of ‘Onimidori’ was greater than that of ‘Mazuma No.1,’ suggesting that this may contribute to the faster growth of ‘Onimidori.’ Ionome analyses revealed tissue-specific mineral accumulation patterns and their differences among different pH conditions and between the two cultivars. Ionome-based multiple-regression analysis revealed a relationship between element concentration profiles in the wasabi plants, especially those in root, and the shoot growth. Wasabi plants are ammonium-sensitive and nitrate-preferring plants, in addition to relatively low nutrient requirements for optimal growth. The results of this study describe the basic nutritional characteristics of wasabi plants. These findings represent an important step toward optimizing fertilization to control wasabi quality and growth in the traditional flooded cultivation system.

Deposition order and physicochemical process visualization of ink intersections using X‐ray photoelectron spectroscopy imaging for forensic analysis

The physicochemical events at ink intersections are largely understudied. Chemical imaging techniques and multivariate analyses applied to this problem thus far lack the performance characteristics to make confident conclusions about these processes. This deficiency leads to subjective and controversial deposition order determinations in forensic investigations. In this comprehensive report, 44 unique crossings involving laser toners and stamps, as well as felt‐tip, rollerball, gel, and ballpoint pen inks, were imaged with X‐ray photoelectron spectroscopy (XPS), using a 50‐μm X‐ray spot size and 100‐μm steps. The specificity and surface sensitivity of XPS enabled the objective visualization of the inks' chemistry upon deposition via spatial elemental distribution in‐situ. Signal intensity and atomic concentration were mapped for each element detected. Discrimination was possible in 100% of written and printed inks analyzed, and the relationship between the elemental concentration profile in each intersection was compared with the known sequence. Formation of ink layers, mixing, and separation of ink components by way of electrostatic forces were observed. Insights into the known complexity of ink intersection processes were revealed and highlight the need for understanding the chosen analytical technique's information depth and for complementary analyses to increase sequencing confidence. We also provide evidence that these processes invalidate the utility of principal component analysis for analyzing ink intersections. However, sequencing accuracy was 84% for all samples analyzed, and its success was highly dependent on the presence of physical features (i.e., thick coatings and embossed regions). In some intersection types, especially toners, the features exposed with XPS imaging enabled a sequencing accuracy of 100%.

Reverse Engineering Analysis of Optical Properties of (Ti,Cu)Ox Gradient Thin Film Coating

Analysis of the optical properties of a gradient (Ti,Cu)Ox thin film is presented in this paper. The thin film was prepared using reactive co-sputtering of Ti and Cu targets. The desired elemental concentration profiles of Cu and Ti versus the thin film thickness were obtained by changing the power delivered to the magnetron equipped with Cu, while the powering of the magnetron equipped with the Ti target was maintained at a constant level during the film deposition. Optical properties were analysed using the reverse engineering method, based on simultaneously measured optical transmittance and reflectance. Detailed microstructure analysis performed using transmission electron microscopy investigations revealed that the thin film consisted of at least four areas with different structural properties. Finding a satisfying fit of theoretical to experimental data required taking into account the heterogeneity in the material composition and microstructure in relation to the depth in the prepared gradient thin film. On the basis of the built equivalent layer stack model, the composition profile and porosity at the cross-section of the prepared gradient film were evaluated, which agreed well with the obtained elemental and microscopy studies.

Ion migration in GaSb/Mn multilayers for memories applications: Study of Mn diffusion into the GaSb layers

This work presents a study of bilayer and multilayer systems of GaSb/Mn, obtained via DC magnetron sputtering at room temperature for memories applications. These architectures were observed through HR-SEM, which determined that the GaSb and Mn layers had an average thickness of 186,01±5,582 nm and 10,71±0,323 nm, respectively. Through the deconvolution of AES spectra, it was possible to identify the chemical element concentration profiles for each system and propose a model of diffusion layers. The GaSb/Mn systems were analyzed in two cases; in the cases of Mn deposited on the surface of GaSb wafer and bilayer systems, the Mn diffusion process was studied by the conventional Fick’s second law, considering the Mn layer as a constant source, and the Mn diffusion coefficient values correspond to 1,6×10−15cm2/s and 5,8×10−15cm2/s, respectively. The superposition of Fick´s second law solutions in each section of the multilayer architecture was used to describe the experimental concentration profile. Through, the model proposed to calculate the different diffusion coefficients of Mn layers, the description of the diffusion process in the bilayer and multilayer systems and their correlation with synthesis parameters, such as deposition time, has been satisfactory. In the multilayer architecture case, the Mn diffusion coefficients have been reported, considering the Mn layer position, and their values corresponding are 1,105×10−14cm2/s and 6,5×10−15cm2/s for Mn inner and middle layer respectively. Finally, the resistive behavior of the multilayers was studied through I-V curves. It was possible to establish the bipolar resistive behavior of the multilayer and contribution to the formation of conductive filaments or the space charge limited current like conductive mechanism of the multilayer thin films.

Влияние продолжительности боромеднения на толщину диффузионного слоя и микротвердость углеродистых и легированных сталей

Introduction. Borocoppering is one of the methods of thermochemical treatment (TCT) aimed at forming diffusion layers with high physical and mechanical properties on the surface of carbon and alloy steels. The thickness of the diffusion layer is the most important characteristic of the TCT, which determines the depth of hardening. Consequently, the intensity and main characteristics of the TCT (layer thickness, alloying element concentration profile) depend on the process conditions (temperature, duration, and amount of alloying element). The purpose of this work is to determine the temperature-time parameters of diffusion borocoppering, which contribute to the formation of diffusion layers with a maximum thickness. The paper considers the results of surface hardening of carbon and alloy steels (for example, Steel 45 (0.45% C), Steel U10 (1.0% C), and 0.5C-Cr-Ni-Mn steel) by high-temperature soaking in powder mixtures containing boron and copper. Borocoppering was carried out in sealed containers with the powder mixture consisting of boron carbide, copper oxide, and sodium fluoride as an activator at a temperature of 950 °C for 3–5 h. The resulting specimens with a diffusion layer were examined using an optical microscope and a scanning electron microscope (SEM); the microhardness, elemental and phase composition of the layers were also determined, as well as the roughness of the obtained surfaces. Results and discussions. The microstructure of the obtained diffusion layers is studied; diagrams of the changes in the layers’ thickness and the microhardness distribution over the layers’ thickness are shown. It is established that with an increase in the soaking time from 3 to 5 h, the thickness of the diffusion layer increases from 120 to 170 μm on Steel 45 (0.45% C); from 110 to 155 µm on Steel U10 (1.0% C) and from 130 to 230 µm on 0.5C-Cr-Ni-Mn steel. A gradual decrease in the concentration of boron and copper along the layer thickness from 15–16% and 2–3% on the surface, respectively, to zero values at the boundary with the base metal is revealed. It is established that borocoppering to the formation of more thick boride layers on the surface of carbon and alloy steels compared to pure boriding. Moreover, an increase in the duration of soaking during the process contributes to the greatest increase in the thickness of the layer on 0.5C-Cr-Ni-Mn steel. A study of microgeometry is carried out, microtopographies and profilograms of specimens’ surfaces are shown before and after borocoppering. It is established that the roughness after borocoppering increases by 2-3 times compared to the initial one, and an increase in the duration of the process does not have a significant effect on the roughness.

Antisite Defects and Chemical Expansion in Low‐damping, High‐magnetization Yttrium Iron Garnet Films

AbstractYttrium iron garnet is widely investigated for its suitability in applications ranging from magneto‐optical and microwave devices to magnonics. However, in the few‐nanometer thickness range, epitaxial films exhibit a strong variability in magnetic behavior that hinders their implementation in technological devices. Here, direct visualization and spectroscopy of the atomic structure of a nominally stoichiometric thin film, exhibiting a small damping factor of 3.0 ⋅ 10−4, reveals the occurrence of Y‐excess octahedral antisite defects. The two‐magnon strength is very small, Γ0≈10−6 Oe, indicating a very low occurrence of scattering centers. Notably, the saturation magnetization, 4πMs=2.10 (±0.01) kOe, is higher than the bulk value, in consistency with the suppression of magnetic moment in the minority octahedral sublattice by the observed antisite defects. Analysis of elemental concentration profiles across the substrate‐film interface suggests that the Y‐excess is originated from unbalanced cationic interdiffusion during the early growth stages.

Significant contribution of seamounts to the oceanic rare earth elements budget

The rare earth elements (REEs) are a crucial resource frequently used as proxies for reconstructing paleomarine environmental conditions. However, there is limited understanding regarding the marine REEs cycling. In addition, the relationship between benthic diffusion of REEs and seamounts, remain unclear. Here we present the concentration profiles of REEs and trace elements in porewater and seawater from both the seamounts area and abyssal plain. Our results evidenced that the concentration of dissolved porewater REEs, Mn and Al in sediments in proximity of seamount are much higher than those at the abyssal plain. This is attributed to the substantial benthic diffusion of REEs to the ocean. The REEs enrichment processes in porewater at uneven seafloor are based mainly on re-suspension associated with the strong currents and/ or partial dissolution of detrital from seamounts. We suspect this process may occur in other world regions with seamounts and infer that these sediments may account for a significant contributor to the oceanic REEs budget.

Neodymium Isotopic Composition and Rare Earth Element Concentration Variations in the Coral and Solomon Seas

Significant progress has been made in the last decade on the understanding of the role of the Coral and Solomon Seas as major suppliers of waters and chemical elements to the equatorial Pacific. Yet, the location, depth, and processes of chemical enrichment of these waters remain poorly constrained. Neodymium (Nd) isotopic compositions (εNd) and rare earth element concentrations (REE) are powerful tracers of land-ocean chemical exchanges. Combined, they can greatly refine the characterization of these exchanges. Here we report profiles of εNd at 21 stations located in the Coral and Solomon Seas as part of the GEOTRACES GP-12 cruise that complement the rare earth element concentration (REE) profiles of Pham (Chemical Geology, 2019, 524 (May), 11–36). Waters exiting the Solomon Sea are generally slightly more radiogenic than the incoming ones, suggesting inputs of radiogenic material along their pathways across the Solomon Sea. This radiogenic material is brought to the surface waters via natural processes (rivers, volcanic dusts) and likely local mining activities. Noticeable εNd increases are also observed in subsurface and intermediate layers. All these processes indicate the occurrence of local Boundary Exchange (BE) processes, which are estimated to occur within a few days. Coupling hydrological and chemical tracers allows highlighting the land-ocean interactions affecting some water layers and quantifying the exchanged fluxes of Nd. Modifications of the Nd concentration and isotopic composition in the lower thermocline layer require an external flux of 7.9 ± 2.0 t(Nd)/yr only partly balanced by a scavenging flux of 1.8 ± 2.3 t(Nd)/yr, leading to a net influx of 6.1 ± 1.7 t(Nd)/yr. Regarding the Upper Circumpolar Deep Water, a total net flux of 105 ± 50 t(Nd)/yr is estimated, the external flux is relatively high (86 ± 31 t(Nd)/yr while the scavenging flux remains. These results refine the role of the Solomon Sea as a supplier of continental chemical elements to the Pacific equatorial waters.

Fabrication of gradient cemented carbide with Ni3Al binder: Simulations and experiments

Ni3Al phase with an ordered fcc structure has been extensively investigated as alternative binder in WC/TiC/Ti(C, N)-based cermets. Due to the excellent stability, high temperature performance and oxidation resistance, it shows great potential in γ-free gradient cemented carbides. The possibility to fabricate WC-Ti(C,N)–Ni3Al gradient cemented carbide using powder metallurgical method was investigated in the present work through both simulations and experiments. The alloys composition and sintering parameters were carefully designed with the guidance of thermodynamic calculations and DICTRA simulations. A gradient layer free of cubic Ti(C, N) phase and enriched in Ni3Al binder at surface of the cemented carbide sintered at 1723 K for 2 h was generated, with thickness of about 20 μm. The microstructure, elemental concentration distributions and concentration profiles of the new-type gradient cemented carbide with Ni3Al binder have been analyzed by means of XRD, SEM, EDS and EPMA. The gradient layer formation by DICTRA simulations is in accordance with the experimental data. The present work shows the potential for further design of the gradient cemented carbide with Ni3Al binder under the powerful guidance of thermodynamic calculations and DICTRA simulations.

Chemical characterisation of natural and anthropogenic inputs of dust in the seasonal snowpack (2017–2020) at Calderone Glacier (Gran Sasso d’Italia)

Environmental context We present a chemical characterisation of the seasonal snowpack sampled for four consecutive years at the Calderone, the southernmost glacier still surviving in peninsular Italy. This debris covered glacier recently split into two little ice bodies, whose evolution could be influenced by the snowpack properties. In particular the impact of long-range aerosol advections on concentrations of impurities in the snowpack over the local background is discussed. Rationale The Calderone Glacier (Central Apennine, Gran Sasso d’Italia mountain group) is the southernmost glacial apparatus in Europe, split into two glacierets (Upper and Lower Calderone) since the end of the last millennium. Because of its location and altitude, this site is mainly characterised by the long-range transport of air masses which arise from different Mediterranean source regions. Therefore, the seasonal snowpack’s chemistry is strongly affected by the dry and wet deposition of contaminants associated with anthropogenic and natural sources. Methodology In the present study, the seasonal snowpack stratified on the Calderone glacier has been characterised for four consecutive years (2017–2020) in the same monitoring site (2700 m asl), where a snow pit has been dug yearly, to observe the modification of chemical and physical properties depending on local and long-range atmospheric contributions. We determined the concentrations and fluxes of major inorganic ions (MIs) by ion chromatography and of 31 trace elements (TEs) by triple quadrupole ICP-MS. Results Major and trace element concentration profiles along the snowpack allowed to discriminate the snow layers contaminated by long range advections from the uncontaminated ones. The uncontaminated snow layers’ concentrations were used to calculate regional background values. The results have been compared to other remote sites to assess their robustness. Discussion Different source contributions have been recognised using enrichment factors for the trace elements, particularly crustal, marine and anthropogenic. Deposited atmospheric aerosols, found in the snowpack as distinct layers generated during intense air mass advections, have been correlated to these contributions.

Phase transformation and morphological features in a cold-worked CrMnFeCoNi high entropy alloy with Al addition

Addition of Al to equiatomic high entropy alloy CrMnFeCoNi alloy with a single phase FCC structure is known to promote formation of a BCC phase. In addition, tetragonal intermetallic phase σ was also found to form in a (CrMnFeCoNi)92Al8 alloy when subjected to processing by caliber rolling (8 passes) at room temperature followed by annealing at 800 ∘C. Microstructure of the as-rolled alloy is complex, containing a high dislocation density and planar faults (including twins) which can be parallel and perpendicular to the rolling direction. Morphological features of the transformations induced by straining by caliber rolling have been determined by transmission electron microscopy (TEM). Two main morphologies have been determined. In one type of morphology, bundles of elongated domains of B2 ordered BCC phase form preferentially on {111} matrix planes, inside which σ phase particles nucleate on interface with the matrix. In another type of morphology called “aggregate” here, “spines” of elongated grains of σ phase form, over which domains of B2 phase nucleate driven by change in solute concentration ahead of the interface. The σ phase forms by nucleation on planar faults in the matrix with its (001) plane, forming the known orientation relationship (OR) {001}σ ∥ {111}FCC and 〈110〉σ ∥ 〈110〉FCC. Since the planar faults in a caliber rolled alloy form parallel as well as perpendicular to the rolling direction, spines of the σ phase elongated in three mutually perpendicular directions are shown to exist. OR of the B2 phase with the matrix is Kurdjumov-Sachs. The B2 phase matched pairs of close packed planes with σ phase, but no particular OR was found. Elemental concentration profiles across interfaces suggests that σ and B2 phases grow into the matrix. All the evidence suggests that the σ phase nucleates on the planar faults in the matrix, and then B2 phase forms by elemental concentration changes in the matrix caused by growth of the σ phase, forming the aggregate morphology.

Response of toxic metal distributions and sources to anthropogenic activities and pedogenic processes in the Albic Luvisol profile of northeastern China

Intensive agricultural activities generally influence the distribution and sources of toxic metals in the soil profile. This study aimed to investigate the distribution characteristics and mechanisms of toxic metals and mineral matrix elements in the Albic Luvisol of the Sanjiang Plain and assess their anthropogenic effects. Soil cores (0–50 cm depth) were collected at 33 sites in the northeastern agricultural field of the Sanjiang Plain and then sliced into 10 cm slices. The soil pH, organic matter (SOM), and 17 elements were determined. The results showed that SOM content was higher in horizon A, whereas mineral matrix elements Al, Fe, and Mg contents were higher in horizon B. Ca and P contents gradually decreased with soil depth due to the influence of fertilizer. Three types of trace element concentration profiles were identified: (1) decrease with depth for Cd and Hg; (2) highest in horizon B for As, Co, and Pb; and (3) lowest in horizon E the middle layers for Cr, Cu, Ni, Sc, and V. The vertical changes in Cd and Hg concentrations were generally as a result of P fertilizer use and atmospheric deposition, respectively. In addition, Cd and Hg are preferentially associated with SOM. Vertical changes in As, Co, and Pb concentrations were mainly due to their sorption on Fe and Mn oxides, whereas vertical changes in Cr, Cu, Ni, Sc, and V concentrations were mainly derived from soil matrix minerals. The 26% of Cd and 14–16% of As, Co, Hg, and Pb in the 0–40 cm depth soil layer were from anthropogenic sources such as fertilizer use and atmospheric deposition, whereas Cr, Cu, Ni, and V in the soil generally originated from geogenic sources. Therefore, the long-term accumulation of Cd, As, Co, Hg, and Pb in agricultural soils may be a concern in the future and should be monitored regularly.

Differentiating hurricane deposits in coastal sedimentary records: two storms, one layer, but different processes

Hurricanes Gustav and Ike consecutively impacted coastal Louisiana in 2008. Two sediment cores taken from Bay Champagne, a coastal backbarrier lake near Port Fourchon, Louisiana, contain a depositional layer of clastic sediment up to 21 cm thick attributable to these two storms. X-ray fluorescence measurements and statistical analysis suggest the two storm events can be distinguished from one another based on contrasting geochemical profiles. The bottom portion of the layer, attributable to Gustav, contains high concentrations of marine-derived elements, suggesting a strong influence from storm surge. The top portion of the layer, attributed to Ike, contains higher concentrations of terrestrially-derived elements, indicative of contributions from fluvially-driven deposition. The elemental concentration profiles and corresponding environmental data suggest the storm deposits in each core were deposited through two distinct hydrological processes: a storm surge-driven marine intrusion event during Gustav, followed by a mixture of storm-surge and fluvial deposition resulting from Ike. Results show that hurricane-generated deposition in coastal environments is a bi-directional process in which the role of fluvial freshwater deposition cannot be ignored.

Lithium distribution and isotopic composition in zircon megacrysts as constraints for their mantle origin and volcanic transfer timescales

Lithium in zircon has attracted considerable attention for identifying magma sources and as a diffusion chronometer, despite the exact diffusion mechanisms remaining controversial. Zircon megacrysts sourced from Quaternary intraplate basaltic volcanoes in the Ratanakiri Volcanic Province of northeastern Cambodia were analyzed here for Li isotopic and elemental concentration profiles to constrain diffusion behavior of Li in zircon megacrysts entrained in high temperature melts. This is complemented by high-spatial resolution U-Pb geochronology, O-Hf isotope compositions and trace element abundances to refine the long-term pre-eruptive history of these zircon megacrysts. Ratanakiri zircon megacrysts yield a Tera–Wasserburg regression U-Pb age of 0.98 ± 0.02 Ma (n = 615 spot analyses) that is indistinguishable from eruption ages reported for the host basalts, although zircon was unstable in the enclosing magma as evidenced by marginal corrosion and abundant tubular channels within the crystals. Extreme Li-isotopic variations (within −30 to +96‰ on the δ7LiLSVEC scale) of the zircon megacrysts require kinetic Li fractionation due to diffusive mobilization, which is further supported by offsets in intracrystalline domain boundaries with different Li and Y abundances detected in scanning ion images. Complex abundance and isotopic ratio patterns for Li in zircon megacrysts point to multi-mode Li diffusion that is influenced by variable trace element inventories within individual crystals, which correlate with minor differences in the O-Hf isotopic compositions. The overall tendency of decreasing Li abundances along with increasing δ7Li values toward crystal rims indicates diffusion-driven equilibration between zircon and Li-depleted basaltic melt. Diffusion modeling of Li and δ7Li on domain-boundaries within crystals show pre-eruptive heating timescales of about 18 days, which is consistent with the magma transfer duration estimated from zircon megacryst settling rate calculations, implying the zircon megacrysts should be transported from their source region to the surface by ascending alkali basaltic magma within few weeks. Nearly one to two orders of magnitude longer Li diffusion model timescales were computed for crystal rim domains. This apparent faster diffusion of Li is attributed to H+ loss into a volatile phase during eruption, providing an additional driving force for Li+ diffusion, which might become more pronounced at the crystal boundary where zircon is exposed to strong chemical gradients in volatile elements due to decompression and concomitant degassing. Lithium isotope compositions for the innermost domains of zircon megacrysts are relatively heavy with δ7Li values of +12 to +22‰. These values are considered to be less influenced by Li-loss after entrainment by the host basalts than rim compositions. These values in combination with O (δ18O = +3.5 to +5.3‰) and Hf (εHf(0.98 Ma) = +6.5 to +7.9) isotopic compositions as well as inclusions and internal structures suggest that zircon megacrysts were originally derived from partial melting of a metasomatized lithospheric mantle source altered by fluid released from dissolved carbonates during subduction. Lithium isotopes in Ratanakiri zircon megacrysts provide novel insights into using Li isotopes as a tool to constrain the durations of magma transfer from the mantle to the surface, although Li diffusion mechanisms in zircon need to be further scrutinized.

Pegmatitic granite fluid compositions and thermochronometry in the Seridó Belt, Borborema Province, Brazil: Insights from trace element advection-diffusion-partitioning halos in host schist and gneiss

At the Seridó Belt pegmatitic province, fluid advection from dykes and sills led to trace element diffusion and partitioning in biotite, producing sub metric concentration halos in host mica schist and gneiss. We analyzed trace element concentration vs. distance profiles in the host rock of pegmatitic granite intrusions showing enrichments in Li, F, Cl, Zn, Rb, Nb, Sn, Cs, Ta, U and depletions in Sr and Ba. We estimated fluid temperatures in the range 600 to 700 °C using methods of Ti in biotite, F-OH in biotite-apatite and Tschermak component in biotite-muscovite. We analytically modeled thermal profiles around pegmatitic planar intrusions and found that cooling by thermal flats in the first meters into the host rock is reached in 100 years for a 10 m thick sill. The model constraints sustained heat flow during pegmatitic melt emplacement into a colder host rock. The measured trace element profiles were fitted with solutions of differential equations modeling advection-diffusion-partitioning in porous media under isothermal and cooling conditions. Each trace element profile is equally fitted by values of pegmatitic fluid concentration vs. fluid flux duration plotting as a straight line. We obtained a theorical framework combining pegmatitic fluid trace element composition, fluid flux duration and velocity, rock/fluid trace element partition coefficient, and cooling rate. Using published fluid inclusion trace element composition, we obtained fluid flux duration between tens of years to several centuries for the studied profiles. In the case of low temperature fluid flux at 450 °C the modeled flux duration is increased by less than one order of magnitude. The results allow us to interpret the trace element halos as sub millennial hot isothermal fluid influx from the pegmatites into their host rock. Trace element partitioning from the fluid into host rock falls mostly within the range of 0.01 to 25 and decreases in the order Nb, Cu, Rb, Zn-Li, Cs-Sn. The model constraints fluid advection velocity between 1 × 10−11 m/s and 1 × 10−9 m/s, typical of regional metamorphism to shear focused fluid flow regimes. The trace element enrichment of biotite along the profiles reproduces the observed pattern for whole rock, indicating that biotite is their main sink during pegmatitic fluid influx. Using experimental F in biotite diffusivity we obtained a minimal planar diffusion distance, or the effective porosity, between 7 and 15 μm for the total F re-homogenization of metamorphic biotite by pegmatitic fluid. As shown from others fluid-present petrogenetic systems, the trace element contents of biotite in host rock at the contact with pegmatitic intrusions can be a potential tool for the assessment of their rare metal potential.

Using Volatile Element Concentration Profiles in Crystal‐Hosted Melt Embayments to Estimate Magma Decompression Rate: Assumptions and Inherited Errors

AbstractMagma decompression rate has profound impacts on volcanic eruption style as it determines the time available for most kinetic processes (e.g., volatile exsolution, crystal nucleation and growth) that influence the explosive‐effusive eruption transition. Thus, accurately quantifying decompression rate is a critical goal for understanding volcanic eruption dynamics. A recently developed technique uses crystal‐hosted pockets of melt that remain open to the host magma (melt embayments) to calculate an average decompression rate. Diffusion of volatile elements (e.g., H2O, CO2) out of the embayment during decompression creates “frozen” concentration gradients upon quenching that can be modeled to calculate the time needed to create the gradients. This geospeedometer is increasingly used, but inherent assumptions associated with the modeling and their impact on calculated decompression rates are poorly quantified. Therefore, we have conducted a numerical investigation to assess the impact of three common model simplifications pertaining to rhyolitic magmas: 1D diffusion models, equilibrium degassing, and isothermal decompression. We find that the greatest deviation between imposed and calculated decompression rates occur when 1D models are applied to “necked” embayments that have a constriction where the embayment joins with the far field melt. Simplifying to equilibrium degassing can also introduce modeling errors when disequilibrium conditions exist, though the prevalence of one or the other condition in nature is currently under debate. Assuming isothermal conditions introduces little error into modeled timescales. All of our modeling results are summarized into a list of best practices to minimize error in modeled timescales due to modeling assumptions.

Some features of linear scanning of the chemical composition of mineral aggregates using LA-ICP-MS: the modes and limits of the method

A routine linear and 2D scanning procedure using the inductively coupled plasma mass spectrometry with laser ablation (LA-ICP-MS) is often used when studying the composition of zonal and polyphase solid objects (crystals, rocks, alloys, etc.). However, the proper interpretation of the data necessitates taking into account the features inherent to the procedure. One of the most important features of the results obtained for the objects contrasting in composition is the asymmetry of the concentration profile of elements when going from high to low and, to a lesser extent, when going from low to high contents. Physical processes accompanying the analysis of rocks with the aforementioned features are considered. The duration of the time of signal distortion upon change of one crystal phase to another at large differences in the content of elements is estimated. To obtain the correct data for linear and 2D scanning using LA-ICP-MS, the scanning should be performed point by point: to avoid the influence of crater effects, points should be spaced 1.5 – 2.0 laser beam diameter apart. The goal of obtaining of reliable results requires also keeping the time intervals between measurements of at least 2 – 5 sec.