Geochemistry International最新文献

The mineral ferrodimolybdenite (FeMo₂S₄) and the associated mineral assemblage were identified for the first time in an extraterrestrial environment: in a sulfide–metal veinlet of the Kunya-Urgench (H5) ordinary chondrite. They were studied using optical microscopy, SEM, EPMA, and EBSD. Ferrodimolybdenite was found as an inclusion in troilite in terrestrial pyrometamorphic rocks in 2023. Its synthetic analogue has been known as a semiconductor since 1960. Experimental data and properties of the natural mineral assemblage suggest that ferrodimolybdenite should have crystallized from troilite melt at a temperature close to 1100–1000°C. The quenching of metal–sulfide melt enriched in Mo, Cu, and Mn probably formed the metastable phase FeMo₂S₄ in association with native copper, alabandite, and mercury sulfides. The presence of alabandite can indicate strongly reducing conditions (log fO₂ < –4 IW), which are atypical of the impact melting of ordinary chondrites. The fact that this phenomenon occurs locally suggests that a reducing agent may have been locally involved, which was probably a carbon phase contained in the groundmass of the chondrite or brought from the meteoroid that initiated the impact event with the formation of the veinlet. The anomalously high concentrations of Mo (2 × 10² CI), Mn, Cu, and Hg in the Fe–S melt could not have been reached either during the fractional crystallization of large volumes of Fe–FeS melt or during the recurrent partial melting of metal sulfide and silicates during impact events. The ferrodimolybdenite and associated mineral phases were most likely formed during the impact melting of an foreign sulfide–metal aggregate that had been formed under conditions different from those characteristic of the formation of the chondrite matrix in which carbonaceous chondrites were presumably formed. An alternative explanation is hydrothermal activity on the parent body of H chondrites. Although prerequisites for this activity have been identified, its P–T boundary parameters remain uncertain.

A meteorite of a new type, NWA 13202, was revealed for the first time in the collection of the Russian Academy of Sciences. It was assigned to metal-rich ungrouped chondrites and is paired with the NWA 12379/12273 chondrites. These chondrites consist of, on average, ∼70 vol % Fe–Ni metal and ∼20 vol % chondrules and contain small silicate inclusions embedded in the metal. Similar to other known metal-rich chondrites (G, CH, CBa, and CBb), these is no fine-grained matrix in NWA 13202. The chondrules are mainly of the porphyritic olivine–pyroxene, olivine, and pyroxene varieties (POP, OP, and PP). Nonporphyritic chondrules (BO, SO, CC, RC, and GC) are rare. Olivine has an L-chondrite composition, Fa25.9 ± 3.5 mol %, and low-Ca pyroxene is Fs17.2 ± 5.7 mol %, which resembles more closely H-chondrites. The degree of olivine heterogeneity corresponds to chondrites of petrological types 3–4. Accessory minerals are phosphates and chromite. The metal includes low-Ni kamacite and high-Ni taenite and tetrataenite, and the only sulfide is troilite. The oxygen isotope composition of silicates from the chondrules of these ungrouped chondrites supports their affinity to the oxygen isotope reservoir of LL chondrites (Jansen et al., 2019). The metal underwent partial melting, and was formed ~2.4 My after the formation of Ca–Al-rich inclusions (Liu et al., 2023). Chondrites of this type were probably formed by a catastrophic collision of metal and chondrite bodies. The intensity and conditions during this event were not sufficient to form chondrules with chondrules with quench textures, such as the CC and SO types. After the reaccretion of a new parent body of the metal-rich ungrouped chondrite, the material of NWA 13202 and NWA 12379/12273 was affected by aqueous alteration and metamorphism at a temperature of ∼600°C, which produced phosphates and rims of Fe-rich olivine around low-Ca pyroxene.

Na–Fe and Na–Ca–Mg–Fe phosphates were found in the impact melt associations of the Chelyabinsk meteorite (Chebarkul fragment). They drastically differ in composition from phosphates of the initial chondrite (chlorapatite and merrillite). Chladniite Na_2.25Ca_2.14Mg_6.47Fe_3.76Mn_0.17(PO₄)₉ and a merrillite-like phase Na_1.32Ca_6.80Mg_2.07Fe_0.98Mn_0.04(PO₄)₇ were found in the silicate part in quenched interstitial groundmass between olivine grains; merrillite and chlorapatite are rare in it. The spongy metal–sulfide aggregate in the large vugs and metal–sulfide blebs in the silicate part contain Na–Fe phosphate globules. They consist of sarcopside and graftonite (Fe²⁺,Mn²⁺)₃(PO₄)₂, galileiite Na(Fe²⁺,Mn²⁺)₄(PO₄)₃, xenophyllite Na₄(Fe²⁺,Mn²⁺)₇(PO₄)₆, an unidentified Na–Fe phosphate Na₂(Fe²⁺,Mn²⁺)₁₇(PO₄)₁₂, and sometimes chromite-2. Dendritic–skeletal growth of crystals (providing evidence of very rapid quenching) is found in all associations of the impact melt (silicate part, vugs, metal–sulfide aggregate, metal–sulfide blebs, and phosphate globules). The following crystallization sequence is revealed in the Na–Fe phosphate globules: chromite-2 → sarcоpside/graftonite → galileiite → xenophyllite. They are thought to have formed due to the separation of Na–Fe phosphate liquid from homogenous Fe–Ni metal–sulfide melt enriched in Na, P, Cr, and O. The Na–Ca–Mg–Fe phosphates crystallized without involvement of any processes of liquid immiscibility, directly from silicate melt. The paper provides data on the chemical composition and Raman spectroscopy of all studied phosphates and the major minerals of the impact melt associations of the Chelyabinsk meteorite.

Earlier discovery of magnetite in the Chang’E-5 regolith raised the question about a source of oxidized material in young basaltic volcanism area of the landing site. Here we report the find of Fe-oxide microspherule fragment found in the Chang’E-5 sample, which retained its original structure suggesting it could be magnetite polyframboid or dendrite-like microspherule. The size and texture of the object suggest its prolonged formation from a Fe-rich oxidized environment. Shape and the growth morphology observed on the microcrystals surface suggest a possible free growth from gaseous or fluid phase. Volcanic gas/fluid accumulated within erupted lava flow could be an oxidizing agent at the late stage of eruption or during post-eruption fumarolic activity. If fumaroles existed in the volcanic complexes of Oceanus Procellarum, then the products should be reworked during regolith gardening afterwards, having preserved traces of such processes in the regolith.

A melt pocket (MP) found in only one of the silicate inclusions in the Elga iron meteorite was studied using TEM, SEM, EMPA, and Raman spectroscopy methods. The MP demonstrates the liquid immiscibility of the FeCO₃–Fe₃(PO₄)₂–SiO₂–(Fe, Ni)₃P melts, the mineralogical and bulk chemical composition of which is inconsistent with that of the silicate inclusions in the Elga meteorite. Key differences include: (1) The high content of Fe oxide in the MP is inconsistent with the low FeO content (≈3 wt %) in the SiO₂ glass of silicate inclusions; (2) Ca and Mg, the main phase-forming cations of silicate inclusions, are absent in the MP; (3) Siderite and sarcopside, the main oxygen-bearing phases in the MP, were not found in other silicate inclusions of Elga; (4) carbon compounds (aromatized sp² carbon, phenols) identified in the MP were not found in the host silicate substance. These contradictions lead to the conclusion that the melt pocket is a melted fragment of carbonaceous chondrite captured by Elga’s parent body during a collision with carbonaceous asteroid.

Based on the analysis of experimental evidence on the high-temperature thermodynamic properties of oxide compounds occurring in Ca–Al-rich inclusions of chondrites, the enthalpies, entropies, and energies of mixing in molten oxide compounds were recommended. They can be used to calculate the activities of oxides and oxide compounds in melts of refractory inclusions in chondrites at temperatures of 1500–2700 K. The advantages and correctness of the developed approach to the obtaining of thermodynamic data were demonstrated by the agreement of calculated evolutionary changes during fractional evaporation of residual melts of Ca–Al-rich inclusions in chondrites and other meteoritic materials with experimental data.

In central and eastern Inner Mongolia, specifically in the Xilinhot and Chifeng areas, multiple tectonic movements have taken place and strong Cenozoic volcanic activities have occurred, endowing the region with abundant medium and high-temperature geothermal resources. Identifying the sources and causes of geothermal water in this area can help to predict the distribution of geothermal resources and provide a reference for the development of geothermal energy here. Therefore, this paper investigates the geochemical genesis and formation mechanism of geothermal water in the target area through major ions and trace element analysis, as well as hydrogen and oxygen isotope analysis. The results show that the geothermal water in the Xilinhot area is HCO₃–Na and HCO₃–Cl–Na types, dominated by fully equilibrated water and partially equilibrated and mixed water. In the Chifeng area, the geothermal water type is SO₄–Na, mainly consisting of partially equilibrated and mixed and immature water. The anomalously high values of trace elements such as B, Li, Rb, and Cs are fixed in both areas. Moerover, their correlation with Cl^– indicate that the geothermal water in this region is generally influenced by deep parent geothermal fluids (mantle magmas). The δD–δ¹⁸O relationship reveals that the Chifeng geothermal water is shallowly buried, mixed with shallow cold water, and influenced by precipitation; whereas the Xilinhot geothermal water is mainly derived from precipitation and magmatic water. Finally, two geothermal water genesis models, namely the Xilinhot-type and Chifeng-type, are established. This study uncovers the evolutionary process of deep geothermal water circulation in the target area, which is of positive significance for the development of geothermal resources in the region.

The reduction of sulfurous species coupled with anaerobic ammonium oxidation (Sammox) processes plays a significant role in the geochemical cycling of sulfur, nitrogen, and carbon, as well as in the emergence of biochemical cycles. Anaerobic ammonium oxidation to nitrate (AAON) occurs within the microbiological Sulfammox process, which involves sulfate reduction coupled with anaerobic ammonium oxidation. We studied the AAON process in Sammox-driven chemical reaction networks (CRNs) by observing nitrate formation resulting from peptide function evolution during short-term hydrothermal and subsequent long-term experiments under ambient conditions. Small quantities of proteinogenic amino acids were produced during a 3-year reaction under ambient conditions, attributed to the autocatalysis of peptides formed in Sammox-driven CRNs after a 48-h reaction at 100^oC. After an additional 3 years of reaction, nitrate was detected in all treatment groups, suggesting that the “biological” Sulfammox process occurs within the systems. Peptides can function as proto-enzymes, while the formation of stable vesicle structures provides an optimal environment and conditions for the evolution of CRNs into enzymatic proto-metabolic systems. Prebiotic evolution may occur much more rapidly than previously believed.