element mapping
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Optica ◽  
2021 ◽  
Author(s):  
Yishay Klein ◽  
Or Sefi ◽  
Hila Schwartz ◽  
Sharon Shwartz

2021 ◽  
Vol 8 ◽  
Author(s):  
Linjie Wu ◽  
Yongjia Zhang ◽  
Zhongquan Nie ◽  
Ensi Cao

Introducing magnetism into the ferroelectric Ca2Nb2O7 with high Curie temperature can make it a potential multiferroic material at room temperature. Stoichiometric Ca2Nb2O7, nonstoichiometric Ca1.9Nb2O7-δ and Ca2Nb1.9O7-δ single phase films were deposited on STO (110) substrate by pulsed laser deposition under appropriate conditions. The films were characterized by XRD, FE-SEM, Element mapping and XPS. Both stoichiometric Ca2Nb2O7 and Ca1.9Nb2O7-δ films were diamagnetic in the magnetic measurement and ab initio calculations, while the Ca2Nb1.9O7-δ film with the complex vacancy of VNb+O exhibited ferromagnetic behavior at room temperature, with the saturated magnetization of 3.6 emu/cm3. Calculations on the Ca2Nb2O7 (010) surface indicate that the VNb+O can induce spin polarization on the residual O atoms around the Nb vacancies, and the system was most stable when the Nb and O vacancies were the 4th nearest-neighbored, with FM coupling energetically more stable than the AFM coupling. Our work verified experimentally and theoretically the feasibility of introducing ferromagnetism into Ca2Nb2O7 film by the intrinsic complex vacancy of VNb+O.


Author(s):  
Pim Kaskes ◽  
Thomas Déhais ◽  
Sietze J. de Graaff ◽  
Steven Goderis ◽  
Philippe Claeys

ABSTRACT Quantitative insights into the geochemistry and petrology of proximal impactites are fundamental to understand the complex processes that affected target lithologies during and after hypervelocity impact events. Traditional analytical techniques used to obtain major- and trace-element data sets focus predominantly on either destructive whole-rock analysis or laboratory-intensive phase-specific micro-analysis. Here, we present micro–X-ray fluorescence (µXRF) as a state-of-the-art, time-efficient, and nondestructive alternative for major- and trace-element analysis for both small and large samples (up to 20 cm wide) of proximal impactites. We applied µXRF element mapping on 44 samples from the Chicxulub, Popigai, and Ries impact structures, including impact breccias, impact melt rocks, and shocked target lithologies. The µXRF mapping required limited to no sample preparation and rapidly generated high-resolution major- and trace-element maps (~1 h for 8 cm2, with a spatial resolution of 25 µm). These chemical distribution maps can be used as qualitative multi-element maps, as semiquantitative single-element heat maps, and as a basis for a novel image analysis workflow quantifying the modal abundance, size, shape, and degree of sorting of segmented components. The standardless fundamental parameters method was used to quantify the µXRF maps, and the results were compared with bulk powder techniques. Concentrations of most major elements (Na2O–CaO) were found to be accurate within 10% for thick sections. Overall, we demonstrate that µXRF is more than only a screening tool for heterogeneous impactites, because it rapidly produces bulk and phase-specific geochemical data sets that are suitable for various applications within the earth sciences.


2021 ◽  
Author(s):  
Lorraine Tual ◽  
Matthijs Smit ◽  
Jamie Cutts ◽  
Ellen Kooijman ◽  
Melanie Kielman-Schmitt ◽  
...  

<p>Unravelling the timing and rate of subduction-zone metamorphism requires linking the composition of petrogenetic indicator minerals in blueschists and eclogites to time. Garnet is a key mineral in this regard, not in the least because it best records P-T conditions and changes therein and can be dated, using either Lu-Hf or Sm-Nd chronology. Bulk-grain garnet ages are the norm and can provide important and precise time constraints on reactions across both facies. Domain dating, i.e., dating of individual growth zones, moves beyond that. Domain dating by combining mechanical micro-milling and Sm-Nd chronology yielded important constraints on garnet-growth and fluid-release rates for blueschists (e.g., Dragovic et al., 2015). Developing this method for Lu-Hf chronology and, importantly, for "common-sized" garnet (≤1 cm) provides an important opportunity to further explore the potential of this approach.</p><p>We combined a low-loss micro-sampling technique in laser cutting with a refined Lu-Hf routine to precisely date multiple growth zones of a sub-cm-sized garnet in a blueschist. The targeted grain from a glaucophane-bearing micaschist from Syros Island, Greece, was chemically characterized by major- and trace-element mapping (EPMA, LA-ICPMS) and five zones were extracted using a laser mill. The three core and inner mantle zones are chemically comparable and identical in age within a 0.1 Myr precision (2σ). The outer two zones are chemically distinct and are resolvably younger (0.2-0.8 Myr). The timing of these two major garnet-growth episodes, together with the variations in trace-element chemistry, constrain important fluid-release reactions, such as chloritoid-breakdown. The data show that the integral history of garnet growth in subduction zones may be extremely short (<1 Myr), but may, even in that short timeframe, consist of multiple short pulses. Garnet-forming reactions clearly are localized and, thus, associated with focussed high-flux fluid flow. Beyond subduction-zone processes, our new protocol for zoned garnet Lu-Hf geochronology of "common-sized" garnet opens possibilities for constraining the causes and rates of garnet growth and in turn, the pace of tectonic processes in general.</p><p> </p><p><sub><em>Dragovic, B., Baxter, E.F. and Caddick, M.J., 2015. Pulsed dehydration and garnet growth during subduction revealed by zoned garnet geochronology and thermodynamic modeling, Sifnos, Greece. Earth and Planetary Science Letters, 413, pp.111-122.</em></sub></p>


2021 ◽  
Author(s):  
Ingride Jesus Van Der Kellen ◽  
Delphine Derrien ◽  
Jaafar Ghanbaja ◽  
Marie-Pierre Turpault

<p>Forest soils are a major contributor to soil organic carbon (C) storage in terrestrial ecosystems and play a key-role in climate change mitigation. Mineral weathering in soils is expected to promote chemical and physical interactions between soil organic matter and mineral phases. These interactions are known to enhance the protection of organic matter from decomposition. The investigation of the mineral-organic associations (MOA) formation mechanisms during weathering is therefore crucial to understand carbon storage processes in soils. Until now studies have been mainly conducted through laboratory experiments in simplified and controlled conditions or over very long-term time scales using pedosequences. But knowledge about MOA formation processes occurring in situ is lacking, notably during the first stage of mineral weathering.</p><p>To fill this gap, we performed a mesh bag incubation of large Na-saturated vermiculite particles (100-200 µm in size) in a Typic Dystrochrept soil of a Douglas-fir forest, in the Beaujolais area (France). The incubated particles were deposited at the interface under the forest floor. After 20 years, the weathered vermiculite particles were collected and characterized at the macro-scale (XRD and physico-chemical analysis), at the micro-scale (Scanning Electron Microscopy – SEM, imaging and element mapping) and at the nano-scale (Transmission Electron Microscopy - TEM imaging, element mapping and speciation).</p><p>Cation exchange capacity, exchangeable cations and elemental analysis showed significant differences between the mineral structures of the initial (V0) and 20 year incubated (V20) vermiculite particles. The exchangeable Na was completely depleted. Cation exchange capacity strongly decreased in V20 (49.2 cmol<sub>c</sub> kg<sup>-1</sup>) compared to V0 (173.6 cmol<sub>c</sub> kg<sup>-1</sup>). The V20 lost its specific interlayer collapsing property (≈1.4 -> ≈1.0 nm) with K saturation. V20 interlayer collapsing was only observed with a 330°C heating treatment, suggesting the interlayer hydroxylation of vermiculite. High sheet dissolution, around 10%, was also observed. All these changes were attributed to chemical weathering, during which total C analysis showed significant enrichment in V20 (5.7 mg g<sup>-1</sup>) compared to V0 (0.8 mg g<sup>-1</sup>).</p><p>Macro, micro and nano-scale images and elemental mapping of V0 particles showed a highly flat, smooth surface morphology with no detected C. In contrast, V20 particles showed irregular outer and inner surfaces marked by multiple cracks of chemical dissolution. We also observed internal nano-sized exfoliation spaces filled with C and enriched in Ca, and micro-sized exfoliation spaces filled with C entrapped in nano-crystalline Mn oxides or K-rich aluminosilicates precipitates. The nature of the organic matter found strongly differed between small and large exfoliation spaces. It was characterized by alcohol, carboxyl functional groups and C=C bonds in small exfoliation spaces, while the obtained EELS spectra were more difficult to interpret in large exfoliations spaces. These results provide new evidence that over 20 years in situ weathering induces a significant dissolution, among other physical and chemical changes in large vermiculite particles. They reveal that the mineral weathering processes are responsible for the organic matter entrapment (i) in the newly formed mineral nano-sized spaces, possibly mediated by Ca, and (ii) in association with secondary minerals deposits in micro-sized spaces.</p>


2021 ◽  
Author(s):  
Daniela Rubatto ◽  
Lanari Pierre ◽  
Marcel Burger ◽  
Bodo Hattendorf ◽  
Gunnar Schwarz ◽  
...  

<p>Garnet is one of the most robust and ubiquitous minerals that record element zoning during crustal metamorphism. In addition to major element distribution, zoning in trace elements can provide a wealth of information to document the changing conditions of garnet growth and modification. Trace element distribution in garnet grains was mapped in 2D in thin section with laser ablation inductively coupled plasma time of flight mass spectrometry (LA-ICP-TOFMS) and conventional LA-ICP-MS to achieve a lateral resolution of 15-5 µm and limits of detection for the heavy rare earth elements (REE) down to 0.2 µg/g (Rubatto et al. 2020).</p><p>In granulite-facies garnet, major elements show diffusional resetting, whereas trace elements still largely document the growth history. Enrichment of trace elements in the garnet mantle is attributed to the consumption of biotite (V, Cr) and the dissolution of zircon (Zr) and monazite (Y+REE) in the coexisting melt. Lu is notably enriched in the garnet mantle with implications for geochronology. The gradual zoning of Y+HREE between mantle and core is reconcilable with diffusion over ~200 µm in 10 My at temperatures of 750–800°C</p><p>In amphibolite facies garnet, Y+REE trace element zoning closely matches the growth zoning in Ca with no notable diffusive modification. Y+REE zoning is dominated by Rayleigh fractionation in the core and in the outer zones it shows annuli that mark the sporadic breakdown of accessory phases.</p><p>Garnet in eclogite facies samples that underwent fluid-rock interaction show growth zoning in major and trace elements, with local oscillations and sectors. In certain samples, the overall distribution of REE can be reconciled with diffusion-limited uptake. Where garnet displays fluid-related veinlets, visible in major elements, that cross-cut the primary growth zoning, the regular Y+REE and Cr growth zoning is not affected by the veinlets. This indicates that the veinlets did not form by a crack-seal mechanism but are rather related to a selective replacement process.</p><p> </p><p><strong>References </strong></p><p>Rubatto D, Burger M, Lanari P, Hattendorf B, Schwarz G, Neff C, Keresztes Schmidt P, Hermann J, Vho A, Günther D (2020) Identification of growth mechanisms in metamorphic garnet by high-resolution trace element mapping with LA-ICP-TOFMS. Contrib Mineral Petrol 175:61 doi.org/10.1007/s00410-020-01700-5</p>


2021 ◽  
Author(s):  
Graham Hagen-Peter ◽  
Yue Wang ◽  
Olle Hints ◽  
Aivo Lepland

<p>Primary phases in carbonate rocks archive a wealth of geochemical information about depositional conditions and environmental changes. Secondary phases may record additional—albeit more cryptic—information, potentially complicating interpretation of primary signatures. The ability to compositionally characterize and date multiple, texturally distinct generations of primary, diagenetic, and metamorphic carbonate phases enables deciphering of complex depositional and post-depositional histories carbonate successions have experienced. Combined trace-element mapping and U-Pb geochronology of calcite <em>in situ</em> (in thin sections) by LA-ICP-MS provides opportunities to assign absolute ages to calcite crystallization and recrystallization with petrographic and geochemical context. We have applied this approach to two samples of apparently pristine, unmetamorphosed Ordovician bioclastic limestones from the Viki drill core (western Estonia), representing the eastern part of the Baltoscandian Basin. The depositional ages of the samples are constrained by biostratigraphic correlation to ca. 460 and 445 Ma (Hints et al., 2014). Several lines of evidence—such as very low organic-matter maturation and properties of clay minerals—indicate that this sequence did not experience temperatures above 100 °C, and likely not above 50 °C, since deposition (Kirsimäe et al., 2020). Optical petrography and backscatter-electron (“BSE”) imaging reveal low-porosity “BSE-bright” calcite spar cement in pore spaces between “BSE-dark” micro-porous calcite bioclasts. Trace-element mapping of several areas (several mm<sup>2</sup> each) in each thin section by LA-quadrupole-ICP-MS reveals variably elevated Mn/Sr, U concentration, and U/Pb in the calcite spar cement. The trace-element maps were subsequently used to guide the placement of laser spots for U-Pb dating by LA-multicollector-ICP-MS. Primary bioclastic calcite in both samples has low U/Pb (<sup>238</sup>U/<sup>206</sup>Pb < 7) and, thus, does not yield precise Concordia-intercept dates. The primary calcite does, however, yield imprecise intercept dates within uncertainty of the depositional ages. Calcite spar cement has higher U/Pb (<sup>238</sup>U/<sup>206</sup>Pb up to ~15.7) and including all analyses, yields intercept dates of ca. 415 Ma in each sample. Additionally, several of the domains with the highest U/Pb from each sample yield slightly younger dates of ca. 400­-380 Ma. The timing of calcite (re)crystallization and cementation identified here overlaps with the timing of continent collision during the Caledonian orogeny in Scandinavia. We tentatively interpret this to be a result of fluid flow in response to the collision far-inboard (>500 km) from the orogenic front. Furthermore, this work demonstrates that apparently pristine carbonates may have experienced recrystallization (or at least chemical-isotopic perturbation) in open systems long after deposition.</p><p>References</p><p>Hints, O., Martma, T., Männik, P., Nõlvak, J., Põldvere, A., Shen, Y., Viira, V. 2014. New data on Ordovician stable isotope record and conodont biostratigraphy from the Viki reference drill core, Saaremaa Island, western Estonia. GFF 136, 100–104.</p><p>Kirsimäe, K., Somelar, P., Jõeleht, A. 2020. Illitization of the lower Cambrian (Terreneuvian) Blue Clay in the northern Baltic Palaeobasin. Estonian Journal of Earth Sciences 69, 200–213.</p>


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