Carbonate Melt Research Articles

Integrating a High Temperature Fuel Cell with СО<sub>2</sub> Capture System into Thermal Power Plant Energy Cycle

The molten carbonate fuel cell allows for capturing, separating and concentrating CO2 as it passes through the carbonate melt from the cathode side to the anode side, while simultaneously generating electricity and heat. The article presents the technology and flow diagram of a system for capturing CO2 from flue gases of a thermal power plant in a high-temperature fuel cell on molten carbonates with subsequent conversion and utilization of gaseous combustible products in the energy cycle of a thermal power plant. The fuel cell runs on natural gas with internal reforming. After the fuel cell, the gas leaving the anode is sent to the conversion unit where, in reaction with carbon at high temperatures, combustible gases are formed that are suitable for re-combustion in the turbine. For power plants and a system for capturing and converting carbon dioxide, thermodynamic, technical and economic calculations were carried out. The efficiency of a high-temperature fuel cell is 42 %. In the baseline scenario, the net energy efficiency of the plant is 61 % while a CO2 capture ration is 80–85 %. The return of fuel gases after the conversion of carbon dioxide, taking into account their calorific value, makes it possible to additionally increase the electric power of the thermal power plant up to 20 %. With a unit cost of a fuel cell of 1300 EUR/kW and a price of natural gas of 0.04 EUR/kW, the total electricity cost of the plant is 0.074 EUR/kW. The results show that the proposed system is attractive for natural gas power generation with CO2 capture.

Revision of the CaMgSi2O6-CO2P-T phase diagram at 3–6 GPa

Abstract We reexamined the phase relationships in the system diopside-CO2 in the range of 3–6 GPa and 850–1500 °C in multi-anvil experiments, including reversal ones lasting up to 169 h. The reaction CaMgSi2O6 (clinopyroxene) + 2CO2 (fluid) = 2SiO2 (quartz/coesite) + CaMg(CO3)2 (dolomite) passes through 3 GPa/950 °C with a slope of 6 MPa/°C and terminates at an invariant point near 4.5 GPa/1200 °C, where carbonate liquid coexists with clinopyroxene, coesite, dolomite, and CO2 fluid. The newly determined boundary has the equation P(GPa) = 0.006 × T(°C) – 2.7. As temperature increases to 1250 °C at 4.5 GPa, liquid, dolomite, and coesite disappear, and clinopyroxene coexists with CO2 fluid. As pressure increases to 6 GPa, the solidus temperature increases to 1300 °C revealing a slope of 15 MPa/°C. At 4.5 and 6 GPa, solidus melts contain about 1 wt% SiO2. As temperature increases to 1400 and 1500 °C at 6 GPa, the silica contents in the carbonate melt increase to 6 and 13 wt%, respectively. Our data, combined with that of Luth (2006), indicate that above 4.5 GPa the liquidus reaction involving clinopyroxene and CO2 sweeps down through 350 °C via a pressure maximum near 5.3 GPa to meet the invariant point at 4.5 GPa. The shape of the diopside-CO2 solidus resembles that of lherzolite-CO2 (Wyllie and Huang 1975a) but shifted by 2 GPa to higher pressure. Thus, the deep depression along the solidi in the system CaO-MgO-SiO2-CO2 is a fundamental feature of both ultramafic and mafic assemblages at depths of 70–150 km.

Elongational viscosity of poly(propylene carbonate) melts: tube-based modelling and primitive chain network simulations

In fast elongational flows, linear polymer melts exhibit a monotonic decrease of the viscosity with increasing strain rate, even beyond the contraction rate of the polymer defined by the Rouse time. We consider two possible explanations of this phenomenon: (a) the reduction of monomeric friction and (b) the reduction of the tube diameter with increasing deformation leading to an Enhanced Relaxation of Stretch (ERS) on smaller length scales. (Masubuchi et al. (2022) reported Primitive Chain Network (PCN) simulations using an empirical friction reduction model depending on segmental orientation and could reproduce the elongational viscosity data of three poly(propylene carbonate) melts and a polystyrene melt. Here, we show that the mesoscopic tube-based ESR model (Wagner and Narimissa 2021) provides quantitative agreement with the same data set based exclusively on the linear-viscoelastic characterization and the Rouse time. From the ERS model, a parameter-free universal relation of monomeric friction reduction as a function of segmental stretch can be derived. PCN simulations using this friction reduction relation are shown to reproduce quantitatively the experimental data even without any fitting parameter. The comparison with results of the earlier PCN simulation results with friction depending on segmental orientation demonstrates that the two friction relations examined work equally well which implies that the physical mechanisms of friction reduction are still open for discussion.

Five-Membered Loop-Initiated Nucleation of Unlayered Graphene Sheets in a Carbon Melt, with Diffusion Barrier Possibilities

Five-Membered Loop-Initiated Nucleation of Unlayered Graphene Sheets in a Carbon Melt, with Diffusion Barrier Possibilities

Interaction of carbonates with peridotite containing iron metal: Implications for carbon speciation in the upper mantle

Due to the significantly reduced conditions in the mantle below ~250 km, carbonates transported by the subducting oceanic plates will inevitably interact with Fe-saturated mantle peridotites to form diamonds or other reduced carbon species. In this study, we present the reaction experiments at 6 and 10 GPa, and 1100–1400°С between carbonates and peridotite with iron to model the behaviors of subducted carbonates in the reduced mantle. Magnesiowüstite (Mws), ferropericlase, metastable graphite, or diamond crystallization showed the occurrence of the redox reactions. The reactions in Ca‑carbonate and dolomite-containing systems were accompanied by the appearance of carbonate melt already at 1100 and 1200 °C. Formation of the melt at such a low temperature in the studied systems shows that the redox gradient between iron-containing mantle peridotites and carbonate-containing subduction lithologies could trigger deep mantle melting at the hot subduction zone conditions, even in the anhydrous and alkali-free systems. Carbonate melts, and oxides, formed in the redox reactions, would further interact with olivine, pyroxenes , and garnet with the formation of merwinite , Ca-rich garnet, and Fe-rich olivine. Here we confirm that merwinite could be an indicator of the mantle metasomatism and may originate via interaction of Ca-rich carbonate melt with peridotite. The kinetic calculations reflect that, in natural systems where carbonates and iron are separated by silicate media, the redox reactions are limited due to slow chemical diffusion rates in silicates and will not have any significant effect on the preservation of carbonates in the anhydrous and melt free environment. On the contrary, the presence of carbonate melt during the reaction between carbonate and metallic Fe will lead to significant consumption of carbonates. • We studied the carbonate-iron reactions in the complex peridotite systems at 6,10 GPa • We observed formation of magnesiowüstite, diamond, graphite and carbonate melt • The redox gradient between mantle peridotites and subduction lithologies could trigger deep mantle melting. • Merwinite in diamond inclusions is linked to the carbonate metasomatic activity in the ultramafic assemblages.

Zinc isotopic evidence for recycled carbonate in the deep mantle

Carbonate, the major carbon reservoir on Earth’s surface, can enter into the mantle by subduction. However, evidence for recycled surficial carbonates in the deep mantle is still scarce. Ocean island basalts from Cook-Austral islands and St. Helena Island, widely called HIMU basalts because of their high μ = 238U/204Pb sources, are thought to be fed by mantle plumes originating in the lower mantle. Here we report exceptionally high δ66Zn values (δ66Zn = 0.38 ± 0.03‰) of these HIMU lavas relative to most published data for oceanic basalts (δ66Zn = 0.31 ± 0.10‰), which requires a source contributed by isotopically heavy recycled surficial carbonates. During subduction of the oceanic lithosphere, melting of mixed surficial carbonates and basaltic crust in the deep mantle generates carbonatite melts, which metasomatizes the nearby mantle and the resultant carbonated mantle ultimately evolves into a high-δ66Zn HIMU source. High-δ66Zn signatures of HIMU basalts, therefore, demonstrate that carbonates can be transported into Earth’s deep mantle.

Melting relations of Ca–Mg carbonates and trace element signature of carbonate melts up to 9 GPa – a proxy for melting of carbonated mantle lithologies

Abstract. The most profound consequences of the presence of Ca–Mg carbonates (CaCO3–MgCO3) in the Earth's upper mantle may be to lower the melting temperatures of the mantle and control the melt composition. Low-degree partial melting of a carbonate-bearing mantle produces CO2-rich, silica-poor melts compositionally imposed by the melting relations of carbonates. Thus, understanding the melting relations in the CaCO3–MgCO3 system facilitates the interpretation of natural carbonate-bearing silicate systems. We report the melting relations of the CaCO3–MgCO3 system and the partition coefficient of trace elements between carbonates and carbonate melt from experiments at high pressure (6 and 9 GPa) and temperature (1300–1800 ∘C) using a rocking multi-anvil press. In the absence of water, Ca–Mg carbonates are stable along geothermal gradients typical of subducting slabs. Ca–Mg carbonates (∼ Mg0.1–0.9Ca0.9–0.1CO3) partially melt beneath mid-ocean ridges and in plume settings. Ca–Mg carbonates melt incongruently, forming periclase crystals and carbonate melt between 4 and 9 GPa. Furthermore, we show that the rare earth element (REE) signature of Group-I kimberlites, namely strong REE fractionation and depletion of heavy REE relative to the primitive mantle, is resembled by carbonate melt in equilibrium with Ca-bearing magnesite and periclase at 6 and 9 GPa. This suggests that the dolomite–magnesite join of the CaCO3–MgCO3 system might be useful to approximate the REE signature of carbonate-rich melts parental to kimberlites.

Paleomagnetic study of impactites from the Karla impact structure suggests protracted postimpact hydrothermalism

AbstractWe present a paleomagnetic study of the ~10 km diameter Karla impact structure in Russia. We sampled the target carbonate rocks, and a yet undocumented fragmental melt‐bearing lithic breccia layer. This impact breccia, which contains carbonate melt, is enriched in stoichiometric magnetite by a factor of ~15 compared to the target lithologies, and carries a stable natural remanent magnetization. The weak remanent magnetization and the presence of both normal and reverse polarities down to the centimeter scale indicate that the breccia does not carry a thermoremanent magnetization (TRM), but rather a chemical remanent magnetization (CRM). The presence of stoichiometric magnetite and the absence of TRM suggest that the magnetite was formed during relatively low‐temperature postimpact hydrothermalism that affected the porous impact breccia layer. During this process, the breccia acquired a CRM. The paleomagnetic direction is compatible with a Cenozoic age for the impact event, but cannot bring more precise constraint on the age because of the stable position of the Eurasian plate over the last 60 Myr. However, the presence of both polarities indicates that mild hydrothermalism took place over a period of time long enough to span at least one reversal of the geomagnetic field, that is, over a time scale of the order of 100 kyr. This confirms that protracted hydrothermal systems associated with impact craters are long lived, even in relatively small craters such as Karla, and are key features of the geologic and environmental effects of impacts on Earth.

Evolution of the Munali Intrusive Complex: Host to a carbonate-rich Ni-(Cu-PGE) sulfide deposit

The Munali Intrusive Complex is hosted within supracrustal metasedimentary rocks located along a major structural lineament within the Zambezi Belt in southern Zambia. The complex comprises unmineralised gabbro surrounded by a marginal heterogeneous mafic–ultramafic breccia unit that is host to Ni-Fe sulfide. This marginal unit comprises a range of variably evolved brecciated mafic–ultramafic rocks that include gabbro, olivine-gabbro and dolerite, alongside younger, pegmatitic, apatite-magnetite-bearing clinopyroxenite, wehrlite and dunite. The magmatic evolution is most consistent with a model whereby early mafic rocks interact with hot, MgO- and volatile-rich melts along gabbro contacts, causing localised metasomatism of gabbro and pyroxenites, and progressively replacing pyroxene-rich rocks with olivine, forming pegmatitic ‘replacive dunites’. Sulfide mineralisation is characterised by a carbonate-rich apatite-magnetite-bearing assemblage predominately present as lenses of semi-massive to massive sulfide ore. The complex is enveloped almost entirely within a unit of marble, yet C and O isotope signatures of carbonate at Munali have revealed a clear mantle signature for some of the carbonate associated with sulfide, alongside a more dominant, crustally derived component. The carbonate occurring alongside sulfide displays micro to macro textures signifying the presence of carbonate melts formed from anatectic melting of the country rocks. The presence of fracture sets that define coarse breccia clasts (>1 m) indicate that the host rock was significantly crystallised and brittly deformed prior to carbonate and sulfide melt infiltration. Both carbonate and sulfide melts appear to have independently utilised these pre-existing weaknesses producing a pseudobreccia, and accounting for the seemingly chaotic nature of the orebody. The indication of sulfide being a significantly later phase suggests that the sulfide did not form in situ and was mobilised from elsewhere to be subsequently emplaced late within the Munali system.

Petrology, geochemistry and new U–Pb ages of the Epembe syenites and carbonatite, northwest Namibia

The Epembe Alkaline Carbonatite Complex (EACC) in northwestern Namibia, was emplaced along a fault zone into medium-to high-grade Palaeoproterozoic basement rocks of the Epupa Metamorphic Complex (EMC) and extends over a distance of 9 km in a south-easterly direction with a width of 1 km. Alkaline rocks constitute the main lithologies and are cross-cut by a calcite-carbonatite dyke. The alkaline rocks can be classified as syenite and nepheline-bearing syenites, with alkalic, metaluminous and ferroan affinities. An emplacement age of 1220 ± 3 Ma (2 SE, MSWD = 1.3) is determined for the syenite, whereas two nepheline syenite samples give similar magmatic ages of 1209 ± 3 Ma (2 SE, MSWD = 1.1) and 1205 ± 13 Ma (2 SE, MSWD = 2). The nepheline syenite ages correspond with the 1198 ± 5 Ma (2 SE, MSWD = 1.1) age of the carbonatite interpreted as magmatic. The nepheline-normative syenites define broadly linear trends in Harker plots consistent with evolution by fractional crystallization involving pyroxene and apatite. The rare-earth element (REE) pattern of the syenite shows a negative Eu anomaly, consistent with prior plagioclase formation and fractionation. The syenite is characterized by the absence of a negative Nb anomaly on a Primitive Mantle (PRIMA)-normalized diagram with Ce/Pb and Nb/U ratios of 12 and 19, respectively, suggesting that it was not affected by crustal contamination during ascent and emplacement. The absence of a crustal signature in the evolution of the syenite indicates that the syenite is not related to the nepheline syenite by combined assimilation and fractional crystallization and is likely to have been emplaced as a distinct magma batch derived from the mantle. REE patterns of the nepheline syenite and carbonatite are coherent showing LREE enrichment relative to HREE. On a PRIMA-normalized multi-element diagram both the carbonatite and syenite display depletions in Zr, Hf and Pb with positive Sr. Low Mg number and Cr and Ni contents of the carbonatite and nepheline syenite suggest that these rocks crystallized from an evolved parental magma rather than a primary mantle derived-melt. Geochemical similarities between the carbonatite and nepheline syenite also suggest that the origin of the Epembe carbonatite is not a product of immiscible separation between a carbonate and silicate melt. Instead, the carbonate may represent a melt fraction that formed after partial crystallization of the nepheline syenite. Magma assimilation of the country rocks by the carbonatite magma is evident from the occurrence of biotite, feldspars and syenitic xenoliths in the carbonatite.

Change in carbonate budget and composition during subduction below metal saturation boundary

It is generally accepted that carbonates can be subducted to the mantle depths, where they are reduced with iron metal to produce a diamond. In this work, we found that this is not always the case. The mantle carbonates from inclusions in diamonds show a wide range of cation compositions (Mg, Fe, Ca, Na, and K). Here we studied the reaction kinetics of these carbonates with iron metal at 6–6.5 GPa and 1000–1500 °C. We found that the reduction of carbonate with Fe produces C-bearing species (Fe, Fe-C melt, Fe3C, Fe7C3, C) and wüstite containing Na2O, CaO, and MgO. The reaction rate constants (k = Δx2/2t) are log-linear relative to 1/T and their temperature dependences are determined to bekMgCO3 (m2/s) = 4.37 × 10−3 exp [−251 (kJ/mol)/RT]kCaMg(CO3)2 (m2/s) = 1.48 × 10−3 exp [−264 (kJ/mol)/RT]kCaCO3 (m2/s) = 3.06 × 10−5 exp [−245 (kJ/mol)/RT] andkNa2CO3 (m2/s) = 1.88 × 10−10 exp [−155 (kJ/mol)/RT].According to obtained results at least, 45–70 vol% of carbonates preserve during subduction down to the 660-km discontinuity if no melting occurs. The slab stagnation and warming, subsequent carbonate melting, and infiltration into the mantle saturated with iron metal are accompanied by a reduction of carbonate melt with Fe. The established sequence of reactivity of carbonates: FeCO3 ≥ MgCO3 > CaMg(CO3)2 > CaCO3 ≫ Na2CO3, where K2CO3 does not react at all with iron metal, implies that during reduction carbonate melt with Fe evolves toward alkali-rich. The above conclusions are consistent with the findings of carbonates in inclusions in diamonds from the lower mantle and high concentrations of alkalis, particularly K, in mantle carbonatite melts entrapped by diamonds from kimberlites and placers worldwide.

Raman study of quench products of alkaline carbonate melt at 3 and 6 GPa: Link to the pressure of origin

AbstractInclusions of former alkaline carbonate melts occur in igneous minerals, mantle xenoliths, and diamonds from kimberlites and lamproites. However, the identification of most daughter phases remains undetermined owing to the lack of their Raman spectra. Yet, the phase compositions of the alkali carbonate melt at different pressure are interesting to know because Na‐Ca, Na‐Mg, K‐Ca, and K‐Mg double carbonates have a number of pressure‐induced phase transitions. Here, we studied the quench products of K‐Ca, K‐Mg, and Na‐Ca carbonate melts obtained at 3 and 6 GPa. Scanning electron microscopy coupled with energy‐dispersive spectroscopy with silicon drift detector (EDS‐SDD) and Raman spectroscopy were employed for phase characterization. The following carbonates were detected among the quench products: γ‐Na2CO3, Na4Ca(CO3)3 (Ia3d), Na2Ca3(CO3)3 (P1n1), K2Ca(CO3)2 ( ) bütschliite, disordered K2Ca3(CO3)4 (Pnam), K2Mg(CO3)2 ( ), aragonite, magnesite at 6 GPa; and CaCO3‐bearing K2CO3, K2Ca(CO3)2 ( ) bütschliite, K2Ca2(CO3)3 (R3), and ordered K2Ca3(CO3)4 (P212121) at 3 GPa. The results indicate that the quench products of carbonate melt consist of carbonates thermodynamically stable at the pressure of quenching. Thus, the daughter phases in carbonatitic inclusions could be identified by obtained Raman spectra and reflect the pressure conditions of their entrapment.

Quench Products of K-Ca-Mg Carbonate Melt at 3 and 6 GPa: Implications for Carbonatite Inclusions in Mantle Minerals

Alkali-rich carbonate melts are found as inclusions in magmatic minerals, mantle xenoliths, and diamonds from kimberlites and lamproites worldwide. However, the depth of their origin and bulk melt composition remains unclear. Here, we studied quench products of K-Ca-Mg carbonate melt at 3 and 6 GPa. The following carbonates were detected at 3 GPa: K2CO3, K2Ca(CO3)2 bütschliite (R3¯2/m), o-K2Ca3(CO3)4 (P212121), K2Ca2(CO3)3 (R3), K2Mg(CO3)2 (R3¯m), Mg-bearing calcite, dolomite, and magnesite. At 6 GPa, the variety of quench carbonate phases includes K2CO3, K2Ca(CO3)2 bütschliite (R3¯2/m), d-K2Ca3(CO3)4 (Pnam), K2Mg(CO3)2 (R3¯m), aragonite, Mg-bearing calcite, dolomite, and magnesite. The data obtained indicate that alkali-bearing carbonate melts quench to the alkaline earth and double carbonates that are thermodynamically stable at quenching pressure and can be used as markers reflecting the pressure of their entrapment. Further, in this study, we established the fields of melt compositions corresponding to the distinct quench assemblages of carbonate minerals, which can be used for the reconstruction of the composition of carbonatitic melts entrapped by mantle minerals.

The evolution of refertilized lithospheric mantle beneath the northeastern Siberian craton: Links between mantle metasomatism, thermal state and diamond potential

Although the diamond potential of cratons is linked mainly to thick and depleted Archean lithospheric keels, there are examples of craton-edge locations and circum-cratonic Proterozoic terranes underlain by diamondiferous mantle. Here, we use the results of comprehensive major and trace-element studies of detrital garnets from diamond-rich Late Triassic (Carnian) sedimentary rocks in the northeastern Siberia to constrain the thermal and chemical state of the pre-Triassic mantle and its ability to sustain the diamond storage. The studied detrital mantle-derived garnets are dominated by low- to medium-Cr lherzolitic (∼45%) and low-Cr megacrystic (∼39%) chemistries, with a significant proportion of eclogitic garnets (∼11%), and only subordinate contribution from harzburgitic garnets (∼5%) with variable Cr2O3 contents (1.2–8.4 wt.%). Low-Cr megacrysts display uniform, “normal” rare-earth element (REE) patterns with no Eu/Eu* anomalies, systematic Zr and Ti enrichment (mainly within 2.5–5), which are evidence of their crystallization from deep metasomatic melts. Lherzolitic (G9) garnets exhibit normal or humped to MREE-depleted sinusoidal REE patterns and elevated Nd/Y (up to 0.33–0.41) and Zr/Y ratios (up to 7.62). Rare low- to high-Cr harzburgitic (G10) garnets have primarily “depleted”, sinusoidal REE-patterns, low Ti, Y and HREE, but vary significantly in Zr-Hf, Ti and MREE-HREE contents, Nd/Y (within 0.1–2.4) and Zr/Y (1.53–19.9) ratios. The observed trends of chemical enrichment from the most depleted, harzburgitic garnets towards lherzolitic (including high-Ti high-Cr G11-type) garnets and megacrysts result from either voluminous high-temperature metasomatism by plume-derived silicate melts or recurrent mobilization of less voluminous kimberlitic or related carbonated mantle melts, rather than the initially primitive, fertile nature of the Proterozoic SCLM. Calculated Ni-in-garnet temperatures (primarily within ∼1150–1250 °C) indicate their derivation from at least ∼220 km thick Cr-undersaturated lithosphere at the relevant Devonian to Triassic thermal flow of ∼45 mW/m2 or cooler. We suggest the existence of rare harzburgitic domains in the primarily lherzolitic diamond-facies SCLM beneath the northeastern Siberian craton at least by Triassic, whereas the abundance of eclogitic garnets, predominance of E-type inclusions in placer diamonds and specific morphologies argue for diamondiferous eclogites occurring within a ∼50–65 kbar diamond window of the Olenek province by the same time.

Magnesium and zinc isotopic evidence for the involvement of recycled carbonates in the petrogenesis of Gaussberg lamproites, Antarctica

Lamproites are rare mantle-derived peralkaline ultrapotassic rocks, and they are commonly geographically associated with the ultramafic lamprophyres and kimberlites. Their unique geochemistry and mineralogy make determining their mantle source and origin important because of the significance for inferring specific geodynamic processes. In this study, we further examine lamproite petrogenesis using new Mg and Zn isotopic data for the typical Gaussberg lamproites, Antarctica, the source of which were thought to be contributed by recycled crustal materials. Results show that these lamproites have lower δ26Mg (−0.44‰ to −0.39‰) and higher δ66Zn (0.36‰ to 0.39‰) values than terrestrial mantle (δ26Mg = −0.25 ± 0.04‰, δ66Zn = 0.18 ± 0.05‰). The post-magmatic alteration and crustal contamination as well as fractional crystallization and partial melting cannot account for these anomalous Mg and Zn isotopic values. By contrast, the involvement of sedimentary carbonates which are characterized by light δ26Mg (average approximately −2.0‰) and heavy δ66Zn (average ~ +0.91‰) values in their mantle source can explain these Mg and Zn isotopic anomalies. Quantitative modelling suggests that addition of 10–15% subducted dolomite into the source of Gaussberg lamproites can well reproduce their Mg and Zn isotopic values. The source component with light Mg and heavy Zn isotopic compositions can either be sub-continental lithospheric mantle metasomatized by carbonate melts or residue of subducted carbonate-bearing sediments after deep melting in the mantle transition zone. A lithospheric mantle contribution is indeed required to explain their strongly enriched radiogenic isotopic compositions. However, in terms of carbonate component, their positive ZrHf anomalies (Hf/Hf* = 1.28–2.19), and extremely high K/U (~40, 000) and Ba/Th (~400) ratios lead us to favor the latter deep recycling model in which the recycled carbonate-bearing sediments subducted as K-hollandite and majorite underwent partial melting within the mantle transition zone.

Mg–Fe Isotopes Link the Geochemical Complexity of the Coldwell Complex, Midcontinent Rift to Metasomatic Processes in the Mantle

Abstract Mafic intrusions in the Coldwell Complex have previously been interpreted as forming from a metasomatized mantle source. To build upon our understanding of this metasomatism, the Mg–Fe isotope compositions of these rocks have been determined, and variations are assessed with respect to the magmatic processes that could have occurred at different stages of their formation. The mineralized Marathon Series (δ26Mg = −0.28‰ to −0.19‰), associated metabasalt (δ26Mg = −0.24‰ to −0.23‰), and the Geordie Lake gabbro (δ26Mg = −0.31‰ to −0.22‰) are characterized by δ26Mg values that are within the range of mantle values, whereas the unmineralized Layered Series (δ26Mg = −0.2‰ to −0.05‰) is heavier than mantle. In contrast, the δ56Fe values of all the Coldwell basaltic–gabbroic rocks (δ56Fe = 0.07 ± 0.08‰) are heavier than mantle but within the range of terrestrial basalts and mafic–ultramafic layered intrusions. We propose that the Mg–Fe isotope compositions of these rocks was not significantly modified by processes such as partial melting or garnet retention/fractionation in the mantle, fractional crystallization, or contamination during ascent through the crust, as the isotope values do not correlate with proxies for these processes (e.g. La/Sm and La/Yb, Gd/Yb, MgO–CaO–TiO2, and Th/Nb and Th/La, respectively). Their isotope compositions are, therefore, proposed to reflect the compositions of their metasomatized mantle sources. We conclude that metasomatism was not caused by a carbonate melt, subduction-altered oceanic crust and sediments, or an evolved silicate melt, as these processes generate light δ26Mg, variably fractionated δ56Fe, and heavy δ56Fe values, respectively, which are not observed in our dataset for the Coldwell Complex. The agent that metasomatized the mantle beneath the Coldwell Complex was likely slab-derived fluids characterized by isotopically heavy δ26Mg and basaltic δ56Fe values. This scenario can account for the lack of Fe isotope fractionation from basaltic values in all of the Coldwell rocks. The variably heavier δ26Mg of the Layered Series (−0.20 ± 0.01‰ to −0.05 ± 0.05‰) relative to the mantle (−0.25 ± 0.07‰) suggests that the magmas for the Coldwell rocks were derived by tapping of an isotopically heterogeneous mantle source that had undergone variable degrees of metasomatism. The distinctive geochemistry of mafic sequences in the Coldwell and numerous mafic dykes located in the northeast shoulder of the Midcontinent Rift suggests the presence of a variably metasomatized mantle source beneath a large area of the rift.

Influence of Growth Parameters on the Electrochemical Performance of Electrodeposited Carbons

Generating useful chemicals from CO2 is driving research into carbon capture and utilization. In this work, hard carbons are electrodeposited on various substrates from molten carbonate melts in CO2 atmospheres. These electrodeposited carbons are subsequently used as anodes in sodium-ion batteries, with preliminary investigations into their performance in potassium-ion batteries. The hard carbons were characterized using X-ray diffraction (XRD) and Raman spectroscopy. Hard carbons grown on graphite substrates produced initial reversible capacities of 405 ± 29 mAh/g and capacity retention of 85.2 ± 1.1% after 50 cycles when cycled at 10 mA/g which are amongst the highest capacities reported for hard carbons to date. This work clearly illustrates that the carbons generated via CO2 mediated electrodeposition are suitable for application in next generation batteries.

Differentiation between carbonate and silicate metasomatism based on lithium isotopic compositions of alkali basalts

Abstract Carbonate and silicate metasomatism occurring in subduction zones is an important mechanism underlying mantle heterogeneity and compositional diversity of mantle-derived rocks. However, distinguishing between the two kinds of metasomatism is often difficult. Lithium (Li) and its isotopes have great potential in this regard because of the different Li isotopic compositions of recycled marine carbonate and silicate components. We report Li isotopic data from Cenozoic and Mesozoic alkali basalts of the West Qinling orogen in central China. Relative to those for normal basalts, very high δ7Li values (up to +11.2‰) were observed for the Cenozoic alkali basalts, but significantly and systematically lower values (as low as −3.3‰) were estimated for the Mesozoic alkali basalts. Their abnormal Li isotopic compositions, combined with major- and trace-element contents and Sr-Mg isotope ratios, indicate that the Cenozoic and Mesozoic alkali basalts originated from carbonated and silicated mantle sources, respectively, reflecting metasomatism of the mantle by slab-derived carbonate and silicate melts during Paleotethyan oceanic subduction. Interactions of such melts with the mantle peridotite in subduction channels can account for the elemental and isotopic differences of the studied alkali basalts. The present study demonstrates an effective way to distinguish between carbonate and silicate metasomatism in subduction zones by studying Li isotopic compositions of alkali basalts and highlights the prospect of Li isotopes in tracing the deep carbon cycle.

All-solid-state, long term stable, and embedded pH sensor for corrosion monitoring of concrete

The corrosion process of concrete usually accompanies pH changes of the pore solution. Thus, monitoring the pH value of concrete has great significance for the prediction of concrete corrosion. However, the most commonly used methods for measuring the pH value of concrete pore solution are destructive methods, which are very inefficient and cannot provide the pH value for real-time. In this study, an all-solid-state pH sensor constituted with iridium oxide (IrOx) working electrode and manganese/manganese dioxide (Mn/MnO2) reference electrode was developed. The IrOx electrode fabricated with carbonate melt oxidation method and Mn/MnO2 fabricated with powder compaction method exhibited a dense and homogeneous micro structure. The as-prepared pH sensors showed remarkable long-term stability, ideal potential-pH response, low hysteresis, fast pH response time and strong resistance to ionic interference in solutions. Furthermore, the pH sensor was embedded in the mortar samples and used to monitor pH changes during the accelerated carbonation test. The results indicate that the pH sensor can provide accurate pH value variations of the mortar samples during the carbonation process, and it has great potential for non-destructively monitoring the corrosion process of concrete.

Genetic link between saline and carbonatitic mantle fluids: The system NaCl-CaCO3-MgCO3 ± H2O ± Fe0 at 6 GPa

Melt inclusions in kimberlitic minerals and diamonds indicate that chlorides are important constituents of mantle carbonatite melts. Besides, alkaline chlorides are important constituents of saline high-density fluids (HDFs) found in diamonds from kimberlites and placers around the world. Continuous compositional variations suggest that saline and carbonatitic HDFs could be genetically linked. However, the essence of this link remains unclear owing to the lack of data on phase relations in the chloride-carbonate systems under pressure. Here we studied subsolidus and melting phase relations in the system NaCl–CaCO3–MgCO3 at 6 GPa and 1000–1600 °C using a Kawai-type multianvil press. We found that at 1000 °C, subsolidus assemblage consists of halite, magnesite, and aragonite. At higher temperatures, the stabilization of dolomite splits the subsolidus area into two partial ternary fields: halite + magnesite + dolomite and halite + dolomite + aragonite. The minimum on the liquidus surface corresponds to the halite-dolomite-aragonite ternary eutectic, situated at 1100 °C. The eutectic melt has Ca# 89 and contains 30 wt.% NaCl (26 mol% 2NaCl). The system has two ternary peritectics: halite + dolomite = magnesite + liquid located near the ternary eutectic and magnesite + dolomite = Mg-dolomite + liquid situated between 1300 and 1400 °C. Although under dry conditions incipient melting yields carbonate-dominated melt, the addition of water facilitates the fusion of NaCl and expands the liquid field to NaCl-rich compositions with up to 70 wt.% NaCl. The obtained results favor the idea that hydrous saline melts/fluids (brines) found as inclusions in diamonds could be a lower temperature derivative of mantle carbonatite melts and disagree with the hypothesis on chloride melt generation owing to the chloride-carbonate liquid immiscibility since no such immiscibility was established. We also studied the interaction of the NaCl–CaCO3–MgCO3 system with iron metal and found that carbonate reduction produces C-bearing species (Fe0, Fe-C melt, Fe3C, Fe7C3, C0) and wüstite containing Na2O, CaO, and MgO. Besides, a carbonate chloride compound, Ca2Cl2CO3, was established among the reaction products. The interaction between NaCl-bearing carbonate melt shifts its composition toward Mg-poor and NaCl-rich. Given the above, an alternative hypothesis can be proposed, according to which the interaction of alkaline chloride-bearing carbonate melts formed in the subduction zones with the reduced mantle should be accompanied by diamond crystallization and shift the composition of the melt from carbonatitic to alkali-rich saline.