Olivine Phase Research Articles

Mechanochemical synthesis of (Mg1−x Fe x )2SiO4 olivine phases relevant to Martian regolith: structural and spectroscopic characterizations

Abstract To fabricate metals from the base materials for future Mars exploration, synthesis of representative olivine phases and their structural and spectroscopic characterizations are of crucial importance. Using mechanochemical technique that mimics the mechanical weathering, a complete solid solution of (Mg1−x Fe x )2SiO4 has been synthesized to investigate the associated crystal chemical properties. X-ray powder diffraction data Rietveld analysis confirms that each polycrystalline sample crystallizes in space group Pbnm. The average crystallite size ranges between 80(1) nm and 223(4) nm. Each lattice parameter increases with increasing Fe-content due to the larger Fe2+ radius than that of Mg2+, following Vegard’s rule. For a given nominal chemical composition, substitution of Mg with Fe at the M1-site (4a: 0,0,0) is preferred to the M2-site (4c: x,y,¼). As a consequence, the average Fe-content lies slightly below the equivalence line for x = 0.2–0.8, indicating that the Fe/Mg ratio in the amorphous scattering content is most likely greater than unity. Characteristic Raman spectral features of the olivines have been explained in terms of the chemical composition (x). Simple regression models are demonstrated based on both X-ray diffraction and Raman spectroscopic data for the calculation of Mg/Fe in olivines. Diffuse reflectance UV/Vis spectra RATD analysis shows each olivine phase possesses direct band-gap between 3.38(3) eV and 4.90(3) eV. This study could keep valuable information to relevant databases for future human missions on Mars, in particular, for precise estimation of the representative olivines from the remote X-ray diffraction and spectroscopic data.

Stabilizing inverse ringwoodite with defects, and a possible origin for the 560-km seismic discontinuity

Ringwoodite is an important mineral in the mantle transition zone, and its cationic disorder can profoundly affect its physicochemical properties, but there is currently much controversy about this disorder. In this study, we investigate the cation disorder states of pure Mg2SiO4-ringwoodite and defective ringwoodite under mantle transition zone conditions through DFT calculations and thermodynamic models. Two stable endmembers are seen, one with normal ringwoodite structure and the other with inverted structure (its Si atoms and half of its Mg atoms have swapped sites). Our results indicate that pure ringwoodite does not invert (swap Mg and Si cations) under normal mantle temperatures but the introduction of a Si-excess, Mg-deficient defect induces a swap at normal mantle temperatures and this swap is likely induced by a wide range of defects including water. Thus, in the presence of such a defect or similar defects the olivine phase transition sequence may then go from olivine to wadsleyite to inverse ringwoodite, and then normal ringwoodite. We calculate the seismic properties of normal and inverse ringwoodite and find significantly slower wave speeds in inverted ringwoodite. Due to this difference the presence of inverse ringwoodite may provide a potential explanation for the discontinuous interface of seismic waves at the depth of ∼560 km.

Links between Calcite Kimberlite, Aillikite and Carbonatite in West Greenland: Numeric Modeling of Compositional Relationships

Abstract Textural, mineralogical and mineral compositional observations in a suite of Neoproterozoic aillikite and calcite kimberlite dykes from southern West Greenland point to consistent variations in melt major element compositions amongst these silica-undersaturated magma types. The aillikites have notably higher bulk SiO2/CO2, H2O/CO2 and K2O compared to calcite kimberlite. Bulk rock arrays, together with field and petrographic observations, emphasize that flow sorting of olivine and other crystalline phases during magma emplacement is important in controlling the compositions of individual samples from these ultramafic dykes. Flow sorting together with variable overall proportions of entrained lithospheric mantle material result in scatter on element–element plots, which makes the interpretation of regional scale major and trace element geochemical datasets difficult. We argue that a significant proportion of the regional Ni–MgO variation in the ultramafic dyke suite of SW Greenland is due to variation in the proportion of an entrained refractory lithospheric mantle component. Therefore, ratios of elements to MgO can be used as proxies for melt compositions. Ratios of SiO2, TiO2, Al2O3, FeO and K2O over MgO are systematically higher, and CO2/MgO lower, in aillikites compared to calcite kimberlites. The trace element patterns of the calcite kimberlite and aillikite dykes show strong similarities in incompatible element concentrations, resulting in overlapping ratios for the highly to moderately incompatible elements. However, differences in Zr-Hf concentrations between rock types imply differences in mantle source mineralogy. Guided by our observations, we present mixing models that demonstrate that partial flux-melting of phlogopite–ilmenite metasomes within the cratonic mantle lithosphere is capable of produce the geochemical characteristics of aillikites and mela-aillikites in West Greenland. Fusion of cratonic metasomes was initiated by infiltrating asthenosphere-derived carbonatitic melts previously identified as the parental liquids to calcite kimberlite.

OPTIMIZING VANADIUM CONVERTER SLAG UTILIZATION: TARGETED ENRICHMENT AND STABILIZATION OF VANADIUM THROUGH NON-EQUILIBRIUM SOLIDIFICATION

The objective of this research was to optimize the comprehensive utilization of vanadium converter slag through targeted enrichment and stabilization of heavy metal vanadium. Employing the non-equilibrium solidification theory and FactSage software, we investigated the potential of modifying vanadium converter slag. When the original slag failed to generate vanadium-rich spinel with usable V elements, introducing modifying agents Fe and Al proved effective. Fe facilitated the enrichment of Cr within spinel, while Al significantly promoted the V enrichment. Expanding on this, we systematically examined the influence of Fe2O3, Al2O3 and MgO contents on spinel phase precipitation during vanadium slag solidification. The addition of Al resulted in the precipitation of corundum, hematite, spinel, olivine and diopside phases. With an increase in the Fe2O3 content, the precipitation of FeV2O4 and MgV2O4 initially increased, peaking at 9.67 % before subsequently decreasing. Maintaining the Fe2O3 content within a range of 25–30 % proved optimal for enhancing vanadium precipitation and enrichment. In contrast, variations in the Al2O3 content had minor impacts on SP-V phase precipitation, with slight effects on FeV2O4 reaching 10.34 %. Furthermore, the incorporation of MgO facilitated the precipitation of MgV2O4 while concurrently suppressing the FeV2O4 precipitation. By judiciously controlling the MgO content at approximately 20 %, vanadium enrichment in the form of FeV2O4 and MgV2O4 spinel phases reached a remarkable 94.46 %.

Solid-state Zn-ion batteries using composite cellulose polyethylene oxide materials-Illustration of reaction and capacity fading mechanisms

In this work, the composite materials of cellulose and poly(ethylene oxide) (PEO) materials as the solid-electrolyte separator was electrochemically and mechanically characterized before being incorporated into solid-state Zn-ion batteries (SSZIBs) with LiFePO4 cathode and Zn anode. As understanding fading mechanisms and operational settings is essential to developing long lasting batteries, we further investigated the mechanisms of LiFePO4 lithiation and de-lithiation in SSZIBs. The capacity fading mechanism was elucidated using ex-situ high energy synchrotron XANES measurements on our developed Zn-ion devices at varying charge rates. Long-term cycling was the focus of these investigations, which tracked and assessed chemical and structural changes. The results show that an increase in inactive FePO4 proportional to the loss of active lithium is the primary driver of capacity fading once the lithium source is depleted. XRD confirm that LiFePO4 exists in an olivine phase and reveal that the insertion and deinsertion behaviour of lithium ions in LiFePO4 changes with cycling. The two phases (LiFePO4, FePO4) and the loss of the lithium source may contribute to the reduced rate capability and capacity fading of LiFePO4 cells during prolonged cycling.

Enhanced Ionic Conductivity of Fluoride-Doped LiTi<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> as Solid Electrolyte of Lithium-Ion Battery

In this study, LiTi2(PO4)3 (LTP) was synthesized by the addition of lithium fluoride (LiF) of 0 %, 5 %, and 10 wt.%. A wet solid-state reaction method is applied by mixing Li2CO3, TiO2, and NH4H2PO4 into a ball mill, then calcined at 900o C for 12 hr. XRD pattern of Fluoride-doped LTP is indexed and found in two phases. First is the Nasicon phase (LiTi2(PO4)3) with rhombohedral structure, and second, the Olivine phase (LiTiPO5) with orthorhombic structure at the addition of 5 % and 10 wt. % of LiF. The higher LiF decreases the cell volume while the crystallite size, particle size, and material density increase. The morphology of the Fluoride-doped LTP is increasingly homogeneous and more rectangle-shape. LTP 2, adding 10 wt. % of LiF, has high ionic conductivity at 4.77 10-4 S cm-1 as a promising candidate material for solid-electrolyte of lithium-ion battery.

Structural and electrical properties of high energy ball-milled LiMnPO4 for solid-state batteries

Single-phase LiMnPO4 powders were successfully synthesized via High-energy ball-milling by mixing the starting materials in High energy ball-miller at 250 rpm for 8 h, then drying the slurry at 100 C° for 12 h. The resulting powder was characterized by thermal analysis (TGA-DTA-DSC) in the range of 30–1000 C° to study the decomposition and mechanism of chemical reaction for the precursors. It was found that the olivine phase began to crystallize at 416 C°. The calcination process was performed at 700 C° for 2 h without following inert gas during the heat treatment process according to what was concluded from the thermal analysis. X-ray diffraction analysis was used to study the phases and structure of the calcined powder, which shows that pure phase LiMnPO4 was obtained. The morphology and particle size of the calcined powder were estimated by field emission scanning electron microscopy (FESEM), and the results showed the homogenous semi-sphere particles with an average size of range 127 nm. FTIR spectroscopy reveals the internal mods vibration of the olivine structure. Electrical properties for the sintered powder were performed in the range of 20Hz-100kHz to study the electrical conductivity, Also the electrical properties were performed by variation of temperature in the range of 300–410 K. The results for the electrical properties showed poor electrical conductivity of LiMnPO4 and also showed that very low variation of conductivity with temperature, NTC behavior, and moderated value of the dielectric constant.

Northwest Africa 12279: Evidence for the Interaction Between Early Lunar Mantle Melt and Anorthositic Crust

AbstractThe Mg‐spinel‐bearing rocks are an essential component of the lunar crust. They are widely distributed on the Moon's near and far sides. The study of petrogenesis provides a rare opportunity to understand the early lunar crust‐mantle interaction. Northwest Africa 12279 is a unique Mg‐spinel‐bearing troctolitic anorthosite lunar meteorite that is unbrecciated and pristine. The modal content of the spinel‐bearing troctolitic component is ∼95%. Five hundred sixty spinels larger than 100 μm are investigated in this paper, and 38 of them are found to contain magma melt inclusions. These magma melt inclusions represent the mixed composition between mantle melt and crust material during the crystallization of a spinel. They generally show an immiscible liquid phase separation, which can be divided into a magnesium‐rich and silica‐rich phase. The former is similar in chemical composition to the lunar mantle's peridotite or plutonic ultramafic Mg‐suite. The mantle melt reacts successively with Ferroan Anorthosites in the crust to crystallize Mg‐spinel, plagioclase, olivine, pyroxene, and silica phases. The large grains of euhedral Mg‐spinels with homogeneous chemical composition indicate they are the products of equilibrium crystallization, while plagioclase, olivine, pyroxene, and silica phase are the products of differentiated crystallization of mixed magma. This reaction may represent a typical process of lunar Mg‐suite. This work is the first to find petrological evidence that the melt from the lunar mantle intrudes into the crust and then undergoes a liquid phase immiscible separation to form the Mg‐spinel‐bearing troctolitic anorthosite.

Corrosion behavior of CaO–Al2O3–SiO2–MgO-Cr2O3 slag on MgO refractory brick for smelting of chromite

The MgO bricks were generally used as the refractory linings in electric furnace smelting of chromite ore. The reaction mechanisms between the MgO refractory and CaO-Al2O3-SiO2-MgO-Cr2O3 slags were experimentally investigated. The elemental distribution and phase compositions at the contact surface between slags and refractory bricks were studied using thermodynamic calculations and SEM-EDS techniques analysis. The main phase of the refractory brick was MgO, while the main phases of slag were pyroxene ((Ca, Mg) AlSi2O6), chromium spinel (Mg (Al, Cr)2O4), and magnesium olivine (2MgO·SiO2). The EDS analysis showed that the main phases at the contact surface of slag and refractory brick were calcium magnesium olivine and magnesium olivine, and the proportion of calcium magnesium olivine phase increased with the increase of slag basicity. Furthermore, the thermodynamic calculation indicated that the melting temperature and the slag viscosity decreased with the increase of slag basicity, and then the molten slag more easily penetrated the pores of refractory brick and caused brick corrosion.

Study of the behavior of cesium and strontium in co-melting basalt and silica gel containing cesium or strontium nitrates for the development of a potential material for radioactive waste immobilization

The work studied the distribution of cesium and strontium in cast stone matrices obtained by co-melting basalt and silica gel (hereinafter SiO2) containing cesium or strontium nitrates at 1623 K during 5 h. The melt cooling rate was ∼2 °C/min.Co-melting basalt and SiO2 containing CsNO3 or Sr(NO3)2 at a basalt/SiO2 initial mass ratio of 5 : 1 produced cast stone matrices, in which the main phases were Cr–Fe spinel and glass. At the same time co-melting basalt and SiO2 containing CsNO3 or Sr(NO3)2 at an initial mass ratio of 2 : 1 yielded matrices which, apart from Cr–Fe spinel and glass, included pollucite, clinopyroxene, and Ti-containing magnetite phases for Cs-containing system, magnetite and olivine phases for Sr-containing system.For Cs-containing system at a basalt/SiO2 initial mass ratio of 5 : 1 the glass phase showed almost an even distribution of cesium, whereas the spinel phase was virtually free of cesium. At a basalt/SiO2 initial mass ratio of 2 : 1 the major amount of cesium was found in the pollucite phase, where it mainly occurred in parts containing SiO2. Some amount of cesium was found in the glass phase. The other crystal phases found in the matrix were virtually free of cesium.For Sr-containing system at a basalt/SiO2 initial mass ratio of 5 : 1 the process yielded two types of glass: one rich in Ca and the other in Sr. Strontium was mainly found in the glass phases. The spinel phase was virtually free of strontium. At a basalt/SiO2 initial mass ratio of 2 : 1 strontium was mainly found in the glass phases. The magnetite, olivine, and Cr–Fe spinel phases were virtually free of strontium.

Mantle refertilization at high-pressure conditions of continental subduction channel: Evidence from orogenic peridotites in the Sulu UHP terrane, eastern China

Refertilization of depleted peridotites widely occurs in lithospheric mantle but is poorly understood in a continental subduction channel. The Sulu orogenic belt is a typical ultra-high pressure (UHP) terrane formed by continental subduction and collision. To understand the complex metasomatic processes on peridotites during continental subduction, we combined detailed petrographic and geochemical studies for fertile garnet lherzolites (Chijiadian) from the Sulu UHP terrane, as well as refractory peridotites (Xugou and Lijiatun) for comparison. The fertile garnet lherzolites (Chijiadian) are not residues of low-degree partial melting, but they formed from refertilization processes during peak-UHP metamorphic stages (garnet-facies) in a continental subduction channel, as reflected by abundant clinopyroxene (12 vol%) and garnet (12 vol%), low bulk-rock Mg# of 91 and high Al2O3 of 2.4–3.3 wt%. Garnet, clinopyroxene, and orthopyroxene display secondary poikilitic textures and often contain early phases of olivine, spinel, and garnet inclusions, indicating later precipitation of these minerals into depleted peridotite protoliths. The clinopyroxenes show enrichment of large ion lithophile elements (LILE) and high 87Sr/86Sr of 0.7061–0.7084. The estimated pressure-temperature are 720–770 °C at 4.4–4.8 GPa, consistent with previous constraints on UHP conditions. These features suggest strong refertilization processes at UP-UHP conditions (garnet-facies) in continental subduction channels. The metasomatic agents for refertilization would be basaltic-intermediate melts which incorporated continental materials. Similarly, Xugou harzburgites and Lijiatun dunites also record the subducted continental signatures with enrichment of LILE and high Sr isotopes on clinopyroxenes (87Sr/86Sr: 0.7050 to 0.7065). However, Xugou harzburgites and Lijiatun dunites overall do not display the same typical refertilization features as for Chijiadian, as reflected by low abundances of clinopyroxene and high Mg# of 92–93. Consequently, continental subduction could lead to diverse types of metasomatism of refractory peridotites, including refertilization at UP-UHP metamorphic stages in subduction channels, as in other tectonic settings.

High precision measurement of trace F and Cl in olivine by electron probe microanalysis

Fluorine (F) and chlorine (Cl) are important volatiles in olivine and its high-pressure polymorphs, which would significantly affect olivine phase transition, melting temperature, and physical property of the mantle. F and Cl concentrations in olivine can be detected by electron probe microanalysis (EPMA). However, the analytical accuracy and precision can be impeded by severe peak overlaps, low peak intensities of traditional analytical crystals, and secondary fluorescence effects. In this study, we constructed an optimized analytical method with high accuracy and precision to analyze trace F and Cl in olivine. Key parameters of analytical crystals, beam conditions, peak overlaps, and secondary fluorescence effects were discussed. Variations in the levels of the analyzed trace elements fall within ± 10%. The detection limits (3σ) for F and Cl are lowered to 30 ppm and 5 ppm, respectively. This method can provide precise F and Cl analysis for natural olivine samples and help to provide significant information on its formation process.

Life Cycle Analysis of a Green Solvothermal Synthesis of LFP Nanoplates for Enhanced LIBs in Chile.

Despite the structural and electrochemical advantages of LiFePO4 (LFP) as a cathode material, the solid-state reaction commonly used as a method to produce it at the industrial level has known disadvantages associated with high energy and fossil fuel consumption. On the other hand, solution-based synthesis methods present a more efficient way to produce LFP and have advantages such as controlled crystal growth, homogeneous morphology, and better control of pollutant emissions because the reaction occurs within a closed system. From an environmental point of view, different impacts associated with each synthesis method have not been studied extensively. The use of less polluting precursors during synthesis, as well as efficient use of energy and water, can provide new insights into the advantages of each cathode material for more environmentally friendly batteries. In this work, a solvothermal method is compared to a solid-state synthesis method commonly used to elaborate LFPs at the commercial level in order to evaluate differences in the environmental impacts of both processes. The solvothermal method used was developed considering the reutilization of solvent, water reflux, and a low thermal treatment to reduce pollutant emissions. As a result, a single high crystallinity olivine phase LFP was successfully synthesized. The use of ethylene glycol (EG) as a reaction medium enabled the formation of crystalline LFP at a low temperature (600 °C) with a nano-plate-like shape. The developed synthesis method was evaluated using life cycle analysis (LCA) to compare its environmental impact against the conventional production method. LCA demonstrated that the alternative green synthesis process represents 60% and 45% of the Resource Depletion impact category (water and fossil fuels, respectively) of the conventional method. At the same time, in the Climate change and Particular matter impact categories, the values correspond to 49 and 38% of the conventional method, respectively.

Study on the effect of Al2O3 on the crystallization behaviour of MnO–SiO2–MgO inclusions in tire cord steel

ABSTRACT Aiming at avoiding the formation of high melting point inclusions containing Al2O3 and reducing the wire breakage rate of the tire cord steel. MnO–SiO2–10wt.%MgO–(5wt.%, 10wt.%, 15wt.%, 20wt.%) Al2O3 system were designed to investigate the crystallization behaviour by XRD, SEM-EDS, FactSage 8.0. The results indicate that the Mn/Mg element ratio of the Mg-Mn olivine phase precipitated from the system varies. Mg–Mn olivine phase is formed by the interaction of the components in the melt or by the occurrence of homogeneity and the liquidus temperature of the system decreases with the increase of Al2O3 content. Al2O3 lowers the melting point of the whole system by forming the low melting point phase Mn3Al2Si3O12. To obtain low melting point plasticized inclusions, the Al2O3 content of the system needs to be controlled in the range of 15–20 wt.%.

Synthesis of olivine NaMnPO4 single crystals and electrochemical performance as anode material for Li-ion batteries

The direct synthesis of metastable olivine phase NaMnPO4 still remains a challenge. In this study, single crystals of the olivine NaMnPO4 were synthesized for the first time by a facile hydrothermal reaction. Single-crystal X-ray diffraction analysis provides precise structure information on the olivine structure of NaMnPO4. Moreover, the olivine NaMnPO4 can be completely transformed to its maricite phase after heating at 600 ​°C under Ar atmosphere, confirming the metastable nature of the olivine phase. Electrochemical performance of the olivine NaMnPO4 as anode material for Li-ion batteries (LIBs) was characterized. It delivers a capacity of 645.0 mAh g−1 ​at 0.1 ​A ​g−1 after 200 cycles. In contrast, the maricite phase NaMnPO4 exhibits very low lithium storage capacity.

Effect of Fe/SiO2 ratio and cooling regime on As stability in copper smelting slag

The present study investigated the effects of Fe/SiO2 ratio (0.8−1.6) and cooling methods (quenching and cooling with furnace) on the stability of As in typical copper smelting slag (FeO−SiO2−Fe2O3−CaO−MgO−Al2O3). It was determined that iron silicate slag can achieve As vitrification. In addition, the lower Fe/SiO2 contributed to the immobilization and reduced the leaching toxicity of As. FTIR analysis showed that the increase of Fe/SiO2 caused to the depolymerization of the glass structure and promoted the formation of [AlO6]9− octahedra. XPS spectra of O1s and Si2p showed that the amount of non-bridging oxygen (NBO) in the melt increases with increasing Fe/SiO2. In addition, Al2p and As3d spectra indicate that the covalency between the As−O and Al−O bonds decreased with increasing Fe/SiO2 to accommodate glass depolymerization. For the slow-cooled slag, As was mainly enriched in the iron olivine phase, with a small fraction in the silicate matrix. The increase of Fe/SiO2 promoted the precipitation of iron olivine phase and thus the leaching concentration of As increased with the increase of Fe/SiO2.

Geochemistry of shield stage basalts from Baluran volcano, East Java, Sunda arc

We report petrography and geochemistry of basaltic lava flows from the shield stage of Baluran, a Quaternary volcanic center in the rear of East Java, Sunda Arc, Indonesia. These basalts contain abundant plagioclase, clinopyroxene, olivine, and minor magnetite. Geochemically, they resemble other medium-K calc alkaline basalts from eastern Java’s volcanoes, but they are less enriched in light ion lithophile elements (LILE) and Pb. The predicted primary basalt of Baluran lavas can be sourced to a more primitive primary melt composition which may also generate medium-K calc-alkaline magmas in the region. The fractionation trajectory of these primary magmas shows the importance of plagioclase, clinopyroxene, olivine, and magnetite phase removal from the melt. Regardless of the diverse composition of the derivatives, the calculated primary basalts from the eastern Java are all in the field of nepheline-normative. This finding suggests variably small degree of melting of clinopyroxene-rich mantle source is at play in the generation of these magmas. Our result further suggests that the clinopyroxene source rock is possibly present as veins in peridotite mantle which have experienced metasomatism by addition of slab-derived fluids at differing proportion.

Geodynamic predictions of seismic structure and discontinuity topography of the mantle transition zone

SUMMARYThe mantle transition zone (TZ) is expected to influence vertical mass flow between upper and lower mantle as it hosts a complex set of mineral phase transitions and an increase in viscosity with depth. Still, neither its seismic structure nor its dynamic effects have conclusively been constrained. The seismic discontinuities at around 410 and 660 km depth (‘410’ and ‘660’) are classically associated with phase transitions between olivine polymorphs, the pressure of which is modulated by lateral temperature variations. Resulting discontinuity topography is seismically visible and can thus potentially provide insight on temperature and phase composition at depth. Besides the olivine phase changes, the disassociation of garnet may additionally impact the 660 at higher temperatures. However, the volume of material affected by this garnet transition and its dynamic implications have not yet been quantified. This study presents hypothetical realizations of TZ seismic structure and major discontinuities based on the temperature field of a published 3-D mantle circulation model for a range of relevant mineralogies, including pyrolite and mechanical mixtures (MM). Systematic analysis of these models provides a framework for dynamically informed interpretations of seismic observations and gives insights into the potential dynamic behaviour of the TZ. Using our geodynamic-mineralogical approach we can identify which phase transitions induce specific topographic features of 410 and 660 and quantify their relative impact. Areal proportions of the garnet transition at the 660 are ∼3 and ∼1 per cent for pyrolite and MM, respectively. This proportion could be significantly higher (up to ∼39 per cent) in a hotter mantle for pyrolite, but remains low (<2 per cent) for MM. In pyrolite, both slabs and plumes are found to depress the 660—with average deflections of 14 and 6 km, respectively—due to the influence of garnet at high temperatures indicating its complex dynamic effects on mantle upwellings. Pronounced differences in model characteristics for pyrolite and MM, particularly their relative garnet proportions and associated topography features, could serve to discriminate between the two scenarios in Earth.

Accurate analyses of key petrogenetic minor and trace elements in olivine by electron microprobe

Abundances of minor and trace elements in olivine are increasingly used as petrogenetic indicators for mantle source lithologies, mantle metasomatism history, mantle potential temperatures, and magmatic differentiation. As it is common for olivine to be complexly zoned on a fine-scale, high precision analytical methods for EPMA (electron microprobe microanalyzer, or Electron Microprobe) trace element analysis under high spatial resolution have been developed. However, previous studies have focused more on analytical precision with fewer efforts in examining the accuracy of the data. In this study, we used the Cameca SXFive field emission (FE) EPMA to fully evaluate the effects of beam settings, background offsets and background regression models, and primary calibration standards on the data accuracy of 10 key petrogenetic elements (Na, Al, P, Ca, Ti, Cr, Mn, Co, Ni, and Zn) using MongOlSh11–2 olivine as a reference material. Our results indicate that high voltage, high beam current and long counting time not only improve data precision, but also improve data accuracy, especially on elements with low P/B (peak/background) ratios such as Zn and Cr. Importantly, careful background offsets and background regression models need to be obtained via high resolution WDS relative scans or step scans on each target element. Special care needs to be paid to Co element analysis to avoid or correct for peak interference of Fe Kβ. Among 10 minor and trace elements, exponential background regression models need to be applied to Al, Mn, and Ti elements, whereas other elements require linear background regression. Furthermore, to avoid Al and Zn surface contamination due to alumina polishing or brass presence, ultrasonic cleaning between each intermediate polishing steps and plasma cleaning immediately prior to EPMA experiments is highly recommended. Micro-inclusions such as chromite and spinel in olivine or adjacent Ca-rich phases need to be avoided to minimize primary or secondary fluorescence-related contamination on Al, Cr, or Ca. As a volatile element, Na element needs to be analyzed first with appropriate counting time to minimize the Na loss under high beam conditions. It needs mentioning that major elements (Mg, Fe, and Si) are best analyzed using MongOlSh11–2 or San Carlos olivine as primary standards for calibrations, which can yield more accurate data for both major elements and trace elements because of the improved matrix-corrections. Using our recommended analytical protocols, we have successfully discriminated “depleted” mantle olivine cores from an EMORB in northern East Pacific Rise (EPR) via Ca, Ti, Ni, Co, and Mn abundances. Our olivine data from Siqueiros Transform and the nearby 8°20′ N seamounts also help reveal a metasomatized peridotite mantle beneath the northern EPR. Overall, the protocols proposed in this study can serve as a guide for accurate EPMA olivine trace element analyses, which potentially contributes to the efforts of fostering a comparable olivine database worldwide.

Cimmerian block detachment from Gondwana: A slab pull origin?

The Cimmerian blocks are ribbons-like micro-continents that detached from the northern margin of Gondwana during the closure of the Paleotethys ocean at the end of the Permian. While it has been hypothesized that slab pull forces induced by subduction of the Paleotethys beneath Eurasia could have driven extension in the lower plate after the Paleotethys mid-oceanic ridge subduction, so far, numerical modeling studies have concluded that these forces alone are not sufficient to drive continental breakup. However, the previous modeling studies neglect olivine phase transitions in the mantle and likely underestimated the slab pull. Here, we present numerical simulations that consider the evolution of the density of the slab associated with metamorphic reactions and analyze carefully when, where, and how the slab pull can lead to the formation of micro-continents. Our results show that the marked increase in slab density related to olivine phase transitions at 410 km discontinuity, in addition to gravitational potential energy, can cause continental rifting of the lower plate. Nonetheless, continental breakup is only achieved in absence of horizontal shear flow at the base of the continental lithosphere. In these successful experiments, the deformation localizes 100-200 km on shore due to bending stress pointing out that this process probably always leads to the formation of small continental ribbons. Our results confirm that the tensional force induced by the Paleotethys subduction dynamics may have caused the detachment of the Cimmerian blocks. Since continental breakup of the lower plate is promoted in the absence of basal shear below Gondwana's lithosphere (with respect to the underlying mantle), we argue that the formation of the Cimmerian blocks provides information on the relative motion between the tectonic plates and the underlying mantle. Our simulations demonstrate that there is a significant time-lag between ridge subduction and continental breakup (i.e. the time needed for the slab to reach the 410 km discontinuity), which is rarely accounted by paleogeographic reconstructions.