Contributions to Mineralogy and Petrology最新文献

{"title":"Syn- and post-depositional thermal history of ignimbrites: insights from the structural hydroxyl defect content of quartz crystals from the Tecoloquillo ignimbrite, Acoculco Caldera Complex, Mexico","authors":"Pérez-Orozco Juan Daniel,&nbsp;Sosa-Ceballos Giovanni,&nbsp;Biró Tamás,&nbsp;Hencz Mátyás,&nbsp;Macías José Luis,&nbsp;Kovács István János","doi":"10.1007/s00410-025-02279-5","DOIUrl":"10.1007/s00410-025-02279-5","url":null,"abstract":"<div><p>In this contribution, the structural hydroxyl-defect (OH) content of quartz crystals from the 0.8 ± 0.1 Ma Tecoloquillo Ignimbrite (TI) from the Acoculco Caldera Complex (Puebla, Mexico) was analyzed to examine syn- and post-depositional thermal history of ignimbrites. Pumice-hosted quartz crystals were examined from 5 zones of the TI representing various heights above the basal contact of the ignimbrite. To separate quartz crystal populations, unpolarized micro-FTIR on unoriented crystal fragments was performed to determine the OH-speciation as well as the structural hydroxyl-defect content. Additionally, Raman spectroscopy was used to identify the mineral inclusions of quartz crystals. Two populations of quartz were identified based on the structural hydroxyl-defect concentrations and mineral inclusions: a “hydrous” group with boron-related OH-content (BOH) with evidence of hydrothermal origin (containing abundant rutile needles) and another “anhydrous” group with the absence of any structural hydroxyl-defect content (as well as lack of BOH). The “hydrous” group showed a diffusion profile of BOH with a maximum gradient of 2.4 ± 0.65 wt ppm between the core and the rim of the crystals. The pre-eruptive temperatures of the TI were calculated using the composition of Fe-Ti oxides found in the pumice fragments. Results indicate a 720 ± 20 °C and 790 ± 20 °C temperature for the non-welded main mass (middle level) and 840 ± 30 °C for the welded lower ~ 25 m thick basal level. Based on the pre-eruptive temperatures, the syn- and post-depositional cooling history of the TI was estimated based on thermal modelling. According to the cooling model, the cooling time can reach up to 50 years in the middle level (slow cooling rate: ~3^− 8 °C/s or ~ 1 °C/yr). In spite of such high and long-lasting temperature, the thermal stability of BOH defects (under 600 °C) compared to the common AlOH defects in quartz crystals implies that the ignimbrite emplacement temperature was high enough to cause the total AlOH content to be lost from the quartz crystals, but not as high as the OH-content associated with boron to be diffusively lost. Thus, the structural hydroxyl-defect content of quartz represents a function of the thermal history of the deposit they are embedded in and that of the structural hydroxyl-defect speciation. This is the first study showing the significantly higher thermal stability of BOH structural hydroxyl-defects over AlOH structural hydroxyl-defects within quartz crystals originated from silicic ignimbrites.</p></div>","PeriodicalId":526,"journal":{"name":"Contributions to Mineralogy and Petrology","volume":"180 12","pages":""},"PeriodicalIF":3.7,"publicationDate":"2025-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00410-025-02279-5.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145613102","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Water, redox, and compositional controls on the crystallization of Rhyacian metaluminous igneous charnockites, Bacajá Domain, SE Amazonian Craton: insights from mineral chemistry and thermodynamic modeling","authors":"Arthur Santos da Silva Neri,&nbsp;Roberto Dall’Agnol,&nbsp;Gilmara Regina Lima Feio,&nbsp;Caio José Mesquita Soares,&nbsp;Ingrid Roberta Viana da Cunha,&nbsp;José de Arimatéia Costa de Almeida","doi":"10.1007/s00410-025-02277-7","DOIUrl":"10.1007/s00410-025-02277-7","url":null,"abstract":"<div>\u0000 \u0000 <p>The crystallization conditions of orthopyroxene and fayalite-bearing granitoids remain critical for understanding the evolution of charnockitic magmas. This study integrates petrography, mineral chemistry, thermobarometry, and thermodynamic modeling to evaluate the P-T-<i>f</i>O₂-H₂O conditions during the crystallization of two contrasting Rhyacian igneous charnockites: the Maravilha (2.09 Ga) and Serra Azul (2.06 Ga) plutons, located in the Bacajá Domain, SE Amazonian Craton. The Maravilha Charnockite comprises (i) fayalite + quartz and (ii) pyroxene-bearing granites, whereas Serra Azul is dominated by pyroxene-bearing tonalites and granodiorites. Fayalite-bearing rocks evolved under reduced conditions (FMQ ± 0.5), with initial H₂O content of ≤ 3 wt%, while the pyroxene-bearing association evolved under more oxidizing conditions (NNO ± 0.5), with ~ 4 wt% initial H₂O. Both associations were emplaced at ~ 0.2–0.5 GPa. Serra Azul Charnockite crystallized under oxidizing conditions (NNO ± 0.7 to NNO + 2), with initial H₂O of ~ 2–3 wt% and pressures between 0.3 and 0.6 GPa. Thermodynamic modeling indicates that fayalite and orthopyroxene can crystallize in moderately hydrous melts, ranging from 2.3 to 6 wt% H₂O for fayalite, and ~ 5–6 wt% for orthopyroxene. Fayalite is restricted to reduced conditions and low pressures (≤ 0.3 GPa), whereas orthopyroxene is stable from reduced to moderately oxidizing conditions and over a wider pressure range. These findings highlight that crystallization of fayalite and orthopyroxene is not restricted to low-H₂O conditions, but instead reflects a complex interaction among H₂O content, melt pressure, redox state, and melt composition.</p>\u0000 </div>","PeriodicalId":526,"journal":{"name":"Contributions to Mineralogy and Petrology","volume":"180 12","pages":""},"PeriodicalIF":3.7,"publicationDate":"2025-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145612343","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ferric/ferrous ratio in silicate melts: a model calibrated for felsic compositions","authors":"Alexander Borisov,&nbsp;Stepan Krasheninnikov,&nbsp;Renat Almeev,&nbsp;Francois Holtz","doi":"10.1007/s00410-025-02275-9","DOIUrl":"10.1007/s00410-025-02275-9","url":null,"abstract":"<div><p>There are several models to account for the compositional effect of mafic silicate melts on ferric/ferrous ratio. However, felsic melts have been poorly investigated. In this study, both synthetic and natural silicic melts with a large compositional range (eighteen experimental series) were equilibrated at oxidizing (atmospheric conditions) and more reducing conditions in the temperature range 1401–1533 °C at 1 bar total pressure. The bulk glass composition was determined with electron probe microanalysis (EPMA) and the ferric/ferrous ratio in experimental glasses was analyzed using a wet-chemical technique. The experimental data were combined with previous data in order to formulate an empirical equation describing ferric/ferrous ratio in silicic melts as a function of oxygen fugacity, temperature and melt composition. The proposed equation predicts the log(X_FeO1.5/X_FeO) ratio of melts with a standard error of 0.077. The mean and standard deviation of the residuals for back-calculations of logfO₂ are 0.00 and 0.36 and are − 1 and 39 °C for the temperature.</p></div>","PeriodicalId":526,"journal":{"name":"Contributions to Mineralogy and Petrology","volume":"180 12","pages":""},"PeriodicalIF":3.7,"publicationDate":"2025-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145561790","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Phase-equilibrium geobarometers for silicic rocks based on rhyolite-MELTS. Part 5: principles for multiple-phase geobarometry with examples from plagioclase + orthopyroxene ± quartz ± magnetite","authors":"Sarah L. Smithies,&nbsp;Guilherme A. R. Gualda,&nbsp;Lydia J. Harmon","doi":"10.1007/s00410-025-02274-w","DOIUrl":"10.1007/s00410-025-02274-w","url":null,"abstract":"<div><p>The quartz + feldspar rhyolite-MELTS phase-equilibrium geobarometer is a useful tool for calculating equilibration pressures of rhyolitic magmas. However, it is somewhat limited by typically requiring quartz saturation in magma. Here, we employ the principles from Parts 1–4 to move beyond modeling a specific mineral assemblage. We demonstrate methods for carefully interpreting rhyolite-MELTS geobarometry results to constrain multiple-phase equilibration pressure in quartz-undersaturated dacites to rhyolites, and where quartz saturation is uncertain. We show examples of storage pressure calculations from quartz-absent rhyodacites to rhyolites from Puyehue-Cordón Caulle (PCC), Chile and examples of equilibration between extracted rhyolitic melt compositions and unknown mush mineral assemblages from the Taupō Volcanic Zone, New Zealand. In these cases, orthopyroxene + plagioclase pressures can be used. However, orthopyroxene saturation pressure results are higher at lower modelled oxygen fugacity (<i>f</i>_<i>O2</i>). This can be resolved by modelling at independently constrained <i>f</i>_<i>O2</i>, or by modelling at a range of <i>f</i>_<i>O2</i> to search for orthopyroxene + magnetite + feldspar co-saturation. We show that orthopyroxene + magnetite + feldspar pressures for PCC are consistent with results from other geobarometers and occur at <i>f</i>_<i>O2</i> values within error of the <i>f</i>_<i>O2</i> calculated from Fe-Ti oxides. If quartz saturation is uncertain, quartz + feldspar pressures are a maximum and pyroxene-bearing pressures at low <i>f</i>_<i>O2</i> are a minimum. For uncertain mineral assemblages, the coincidence of multiple phases (≥3) saturating together at reasonable <i>f</i>_<i>O2</i> could be used to infer the equilibrium mineral assemblage. Careful inspection of rhyolite-MELTS geobarometry results therefore gives nuanced information about equilibration pressure, mineral assemblage, and <i>f</i>_<i>O2</i>.</p></div>","PeriodicalId":526,"journal":{"name":"Contributions to Mineralogy and Petrology","volume":"180 12","pages":""},"PeriodicalIF":3.7,"publicationDate":"2025-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00410-025-02274-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145406174","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Role of amorphous precursors in reaction-induced fracturing during mineral hydration","authors":"Sarah Bonilla-Correa,&nbsp;Cristina Ruiz-Agudo,&nbsp;Pedro Alvarez-Lloret,&nbsp;Yannick Emminger,&nbsp;Carlos Rodriguez-Navarro,&nbsp;Encarnacion Ruiz-Agudo","doi":"10.1007/s00410-025-02276-8","DOIUrl":"10.1007/s00410-025-02276-8","url":null,"abstract":"<div><p>Mineral hydration has fundamental geological and technological implications. Despite extensive research, its reaction mechanism(s) and effects on the progress of key metamorphic reactions such as serpentinization, the damage of ceramics, or the setting/hardening of cements are not fully understood. Here, we studied the hydration of periclase (MgO) single crystals and powders forming brucite (Mg(OH)₂) as an analogue for key mineral hydration reactions. Our results show that hydration occurs through an intermediate amorphous phase, as in other oxide and silicate minerals, and results in an epitaxial relationship between periclase and brucite. Mg(OH)₂ precipitates on MgO despite the bulk solution remaining undersaturated with respect to both the amorphous precursor and brucite. This is related to the development of strong concentration gradients at the periclase-solution interface. Remarkably, the transformation of the amorphous precursor into brucite within periclase etch pits and precritical microcracks generates enough supersaturation and crystallization pressure to fracture MgO crystals, enabling further progress of the hydration reaction. This previously unrecognized mechanism for reaction-induced fracturing has relevant natural and technological implications.</p></div>","PeriodicalId":526,"journal":{"name":"Contributions to Mineralogy and Petrology","volume":"180 12","pages":""},"PeriodicalIF":3.7,"publicationDate":"2025-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145352675","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental differentiation of kimberlitic to carbonatitic melts: crystallization sequence and liquid line of descent","authors":"Rebecca F. Zech,&nbsp;Max W. Schmidt,&nbsp;Andrea Giuliani","doi":"10.1007/s00410-025-02273-x","DOIUrl":"10.1007/s00410-025-02273-x","url":null,"abstract":"<div><p>Kimberlites are volatile-rich, silica-undersaturated, mantle-derived magmas with an important role in studying mantle geochemistry, yet their compositional evolution during crystallization remains poorly constrained. This study defines the crystallization sequence and liquid line of descent of a reconstructed kimberlitic melt, using high-pressure experiments at 1–3 GPa and 1100–1400 °C. Early crystallization is dominated by olivine ± chromite, consistent with petrographic observations of natural samples, followed by clinopyroxene, ilmenite, perovskite, apatite, and phlogopite. The absence of clinopyroxene in natural kimberlitessuggests that kimberlitic melts remain above 1150 °C at 1 GPa, conditions at which clinopyroxene is not observed in our experiments. Substantial cooling of kimberlitic melt and related abundant crystallization likely occur in the crust, possibly linked to extensive degassing at shallow pressures. The experimental melts evolve continuously through decreasing SiO₂ and MgO, and enrichment in CaO, alkalis (Na, K), and volatiles (CO₂, H₂O), ultimately transitioning at ≤ 1150 °C to carbonatitic melts with 7–10 wt% SiO₂, 6.5–7.5 wt% Na₂O + K₂O, and up to 35 wt% volatiles. Olivine (± clinopyroxene) fractionation drives Si depletion at almost constant MgO + FeO + CaO and moderate alkali-enrichment, such that the carbonate-silicate miscibility gap is bypassed. This evolution is in sharp contrast to mafic alkaline silicate melts where olivine + clinopyroxene crystallization causes Si enrichment hence promoting melt evolution towards the carbonate-silicate miscibility gap. Overall, the experimental results demonstrate a petrogenetic continuum between kimberlitic and carbonatitic melts and provide constraints on the crystallization conditions of kimberlitic melts.</p></div>","PeriodicalId":526,"journal":{"name":"Contributions to Mineralogy and Petrology","volume":"180 12","pages":""},"PeriodicalIF":3.7,"publicationDate":"2025-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00410-025-02273-x.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145327655","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Zirconium-rich nanophases in an experimental phonolitic melt","authors":"Chris Ballhaus,&nbsp;Phillip Gopon,&nbsp;Eric Woods,&nbsp;Baptiste Gault,&nbsp;Hassan Helmy,&nbsp;Richard Wirth,&nbsp;Vladimir Roddatis,&nbsp;Anja Schreiber,&nbsp;Thorsten Nagel,&nbsp;Frank Tomaschek,&nbsp;Hanna Cieszynsky","doi":"10.1007/s00410-025-02266-w","DOIUrl":"10.1007/s00410-025-02266-w","url":null,"abstract":"<div><p>Many experimental studies have addressed the crystallisation of zircon, not least because zircon is of paramount importance as a geochronometer. Today, it is well established at what temperature, melt composition, and Zr concentration a silicate melt reaches zircon saturation. It remains unclear though what course a Zr bearing melt takes before zircon appears as a macroscopic phase. Does zircon nucleate directly from the melt, or does it use during nucleation and growth Zr-rich nanoparticles as fundamental building blocks? The question is relevant because Zr⁴⁺ is a high field strength (HFS) cation that should tend to polymerise in silicate melts to (ZrO₂)_n clusters. To fill that gap of knowledge, we performed experiments with a Zr-enriched phonolitic melt at 1200 (outside zircon stability) and 900° C (inside zircon stability). We investigated the glasses with Transmission Electron Microscopy (TEM) and Atom Probe Tomography (APT) for Zr-rich nanoparticles, at a spatial resolution not achieved by previous experiments involving zircon. A wide range of nanoparticles is identified, including baddeleyite, zircon, zirconium titanate ZrTiO₄, and rutile. The diverse range of nanoparticles is probably owed to the fact that local-scale gradients in silica (aSiO₂) among silicate melt pools prevailed despite the high run temperatures. The smallest and presumably earliest phases are (ZrO₂)_n nanoparticles trapped by liquidus corundum. They reach diameters around 2 nm or ~ 200 unit cells if they are crystalline. The results support the assumption that Zr⁴⁺ dissolves in silicate melts as ZrO₂ monomers, then quickly polymerises to (ZrO₂)_n clusters. The same may be valid for other HFS cations. Possible applications to HFS element depletions in arc basalts are discussed. At 900° C inside zircon stability, many examples are noted where zircon grows by peritectic reaction of baddeleyite nanoparticles with SiO₂ of the melt although zircon nanoparticles also exist. Larger baddeleyite grains around 50 nm seem to grow by aggregation of smaller (ZrO₂)_n nanoparticles. That zircon also grows by particle attachment cannot be confirmed. Zircon can also crystallise directly from the melt when in melt pools the aSiO₂ and Zr contents were high enough to stabilise zircon.</p></div>","PeriodicalId":526,"journal":{"name":"Contributions to Mineralogy and Petrology","volume":"180 11","pages":""},"PeriodicalIF":3.7,"publicationDate":"2025-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00410-025-02266-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145256638","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The solubility of molecular hydrogen in silicate melts and the origin of hydrogen in the interiors of terrestrial planets","authors":"Alok Chaudhari,&nbsp;Matteo Masotta,&nbsp;Svyatoslav Shcheka,&nbsp;Hans Keppler","doi":"10.1007/s00410-025-02272-y","DOIUrl":"10.1007/s00410-025-02272-y","url":null,"abstract":"<div><p>The solubility of molecular hydrogen (H₂) was measured in haplogranite, andesite, and basalt (MORB) melt. Experiments were carried out with rapid-quench TZM vessels and a piston cylinder apparatus at 0.2 GPa − 4 GPa, 1100 ˚C − 1400 ˚C, and iron-wüstite (Fe-FeO) buffer conditions. H₂ contents in quenched glasses were measured by infrared (FTIR) spectroscopy. For this purpose, the infrared extinction coefficient of the 4120 cm^− 1 band of H₂ in haplogranitic glass was re-calibrated by two independent methods. This yielded a linear molar extinction coefficient of (2.12 ± 0.05) liter mol^− 1cm^− 1, which is about one order of magnitude larger than a coefficient used in previous studies. The new extinction coefficient was used to quantify H₂ solubility in all glass samples of this study. The solubility of molecular hydrogen increases with increasing pressure, being higher in haplogranite than in andesitic or basaltic melt, as expected from ionic porosity considerations. The data at Fe-FeO buffer conditions can all be reproduced by a simple Henry style solubility law c_H2 = a_Henry P, with a_Henry = (206 ± 10) ppm/GPa for basalt, (362 ± 35) ppm/GPa for andesite, and (500 ± 62) ppm/GPa for haplogranite, where ppm is ppm H₂ by weight (µg/g). However, due to the use of an erroneous infrared extinction coefficient, previous studies may have overestimated H₂ solubility in silicate melts by about one order of magnitude. According to the new data presented here, H₂ dissolution in a magma ocean is not a very efficient mechanism for generating elevated hydrogen contents in planetary interiors. Equilibrium thermodynamic modelling shows that in an Earth with chondritic bulk composition, even at an oxygen fugacity six log units below the Fe-FeO buffer, the molar ratio of H₂/H₂O in the magma ocean is still below unity. At a more plausible oxygen fugacity two log units below Fe-FeO, the ratio is 0.06. However, the strong partitioning of hydrogen into the atmosphere under the very reducing conditions of early accretion may have enhanced hydrogen loss due to hydrodynamic escape and impact erosion. Possibly, this was a decisive mechanism for depleting the Earth in volatiles as compared to its chondritic building blocks.</p></div>","PeriodicalId":526,"journal":{"name":"Contributions to Mineralogy and Petrology","volume":"180 11","pages":""},"PeriodicalIF":3.7,"publicationDate":"2025-10-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00410-025-02272-y.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145256256","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Secondary compositional zoning of garnet from the high-grade metamorphic Gföhl Unit, Moldanubian Zone: constraints on relative cation diffusivities and geodynamic processes","authors":"Rene Asenbaum,&nbsp;Elena Petrishcheva,&nbsp;Tereza Zelinková,&nbsp;Martin Racek,&nbsp;Vojtěch Janoušek,&nbsp;Fred Gaidies,&nbsp;Rainer Abart","doi":"10.1007/s00410-025-02268-8","DOIUrl":"10.1007/s00410-025-02268-8","url":null,"abstract":"<div><p>The garnets in garnet pyroxenites from centimetre- to several-hundred-metre-sized mafic lenses embedded in felsic high-pressure granulites of the Gföhl Unit (Moldanubian Zone, Bohemian Massif) are relics of an early high-pressure–high-temperature metamorphic stage related to Variscan subduction and continental collision. Subsequent isothermal decompression to granulite-facies conditions led to the partial replacement of garnet by plagioclase-bearing assemblages. Associated with the partial replacement, a pronounced secondary compositional zoning developed in the relic garnets, which indicates relatively fast diffusion of Fe and Mg and comparatively slow diffusion of Ca. Based on inverse diffusion modelling, cooling rates in the range of 7–<span>(1501 ^circ )</span>C/Myr were estimated for the garnet pyroxenites, indicating rapid cooling and short-lived granulite-facies overprint after decompression. The petrological evidence is compatible with the extrusion of partially molten, buoyant felsic lithologies, which incorporated slivers of mafic lithologies <i>en route</i>. Through the heat they transported advectively, these lithologies produced perturbations of the thermal structure at mid-crustal levels, the decay times of which varied depending on the volumes of the hot material exhumed in different regions.</p></div>","PeriodicalId":526,"journal":{"name":"Contributions to Mineralogy and Petrology","volume":"180 11","pages":""},"PeriodicalIF":3.7,"publicationDate":"2025-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00410-025-02268-8.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145210545","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The role of oxygen fugacity in hydrous basaltic phase equilibria: experimental constraints at 0.2 and 0.8 GPa","authors":"Manuel Pimenta Silva,&nbsp;Felix Marxer,&nbsp;Stepan Krashenninikov,&nbsp;Lennart Koch,&nbsp;Rebecca F. Zech,&nbsp;François Holtz,&nbsp;Peter Ulmer,&nbsp;Othmar Müntener","doi":"10.1007/s00410-025-02269-7","DOIUrl":"10.1007/s00410-025-02269-7","url":null,"abstract":"<div><p>Crystallisation-differentiation drives arc magma evolution, yet discrepancies remain among field, geochemical and experimental evidence. Whereas other controls are better studied, the effect of fO₂, beyond oxide stability, remains less constrained. We investigate fO₂-pressure effects on olivine-clinopyroxene-spinel phase relations with implications for arc magmas. We conducted phase equilibria experiments at 200 MPa between 1010 and 1100 °C. We used basaltic compositions with different xMg* [MgO/(MgO + FeO^tot)] (0.5 to 0.7) at multiple fO₂ conditions (NNO-0.5 to NNO + 2.3), deconvolving the effects of Fe³⁺/Fe²⁺ and xMg^eff [MgO/(MgO + FeO)] on phase equilibria. Additionally, we ran 800 MPa experiments between NNO-0.4 and NNO + 2.5 to explore the combined effects of fO₂ and pressure. At 200 MPa, increasing fO₂ (1) stabilises Fe³⁺-rich spinel, leading to SiO₂-richer melts and, therefore, less pronounced ASI (alumina saturation index, ASI = Al₂O₃/(CaO + Na₂O + K₂O) molar) increase relative to SiO₂, and (2) expands olivine stability relative to clinopyroxene in ol-cpx cotectic melts, resulting in lower ASI melts (for a given SiO₂ content) that better match arc rocks. This is only observed under spinel-absent conditions. The 800 MPa experiments reveal decreasing spinel stability with increasing pressure, while fO₂ has a negligible effect on the ol-cpx cotectic. This suggests that the previously documented pressure effect on the olivine-clinopyroxene equilibrium is stronger than the effect of fO₂. Our results demonstrate that fO₂ increasingly influences the olivine-clinopyroxene cotectic equilibrium as pressure decreases. This supports models where decompression-driven polybaric crystallisation under oxidising conditions shapes arc magmatic compositions. The reported pressure-fO₂ interplay helps reconcile natural and experimental arc records.</p></div>","PeriodicalId":526,"journal":{"name":"Contributions to Mineralogy and Petrology","volume":"180 11","pages":""},"PeriodicalIF":3.7,"publicationDate":"2025-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00410-025-02269-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145210547","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}