A novel experimental V-Sc olivine-melt oxybarometer for arc magmas

Article Article scientifique Article A novel experimental V-Sc olivine-melt oxybarometer for arc magmas eng 2025-12-15 2026-02 author Cacciatore Enzo-Enrico 0009-0007-4136-6219 947981 author Gennaro Ivano 0000-0002-9903-781X 947698 author Kouzmanov Kalin 0000-0002-7327-8949 529239 Services communs du département des sciences de la terre (DETCO) author Tsay Alexandra 936004 Services communs du département des sciences de la terre (DETCO) author Zajacz Zoltan 0000-0001-6528-7717 930159 Services communs du département des sciences de la terre (DETCO) 106-129 10.1016/j.gca.2025.12.025 0016-7037 https://linkinghub.elsevier.com/retrieve/pii/S0016703725007069 Redox conditions significantly affect phase equilibria, the availability and mobility of heterovalent elements, including volatiles (e.g., S) and metals (e.g., Fe, Cu) in silicate melts. Gaining a deeper understanding of the initial redox state of magmas may help better understand magmatic ore fertility, volcanic degassing, and the redox evolution of Earth’s crust and atmosphere. This study reports optimized V and novel V-Sc olivine-melt oxybarometers, developed using existing V-partitioning data and new results from a series of fractional crystallization experiments. Experiments were conducted in a rapid-quench molybdenum-hafnium carbide pressure vessel apparatus equipped with a custom-designed hydrogen membrane for flexible, precise, and accurate oxygen fugacity (fO2) control. In some experiments, solid buffers were additionally applied. They were performed at constant pressure (P = 200 MPa) and variable temperatures (T = 1019–920 °C), under water-saturated conditions at fO2 ranging from −1 to + 3.5 log units relative to the FMQ buffer. The impact of the system’s composition (X) was evaluated by comparing two distinct liquid lines of descent (medium-K-calk-alkaline and shoshonitic) through simultaneous experiments using two capsules in parallel. The results show that the partition coefficient of V between olivine and melt (D-V[Ol/melt]) is not systematically affected by varying P-T-X and highly correlates with changing fO2, thus suggesting that the minor variations observed on a global fO2 scale rather reflect analytical and experimental uncertainties. The updated empirical calibrations allow the determination of logfO2 as ΔFMQ from measured 1) D-V[Ol/melt] and 2) KD-[V/Sc][Ol/melt], expressed by the following equations: 1) ∆FMQ = -1.723±0.047 -[log10[(1.230-log[D-V[Ol/melt]]/(log[D-V[Ol/melt]]+3.119))]/-0.099±0.002] for NBO/T (non-bridging oxygens per tetrahedrally coordinated cation) ≤ 0.6: 2) ∆FMQ =(log[KD-[V/Sc][Ol/melt]]+0.981±0.022)/-0.206±0.012. In the logfO2 range of FMQ -1 to FMQ + 3.5, relevant for arc magmatism, and at hydrous conditions, both oxybarometers show 2σ calibration uncertainty below 0.5 log units. The updated and new V-based oxybarometers enhance robustness across a wide P-T-X-fO2 range, enabling accurate quantification of the redox state of magmatic systems. They can, in turn, be applied to volcanic rocks ranging from basaltic to andesitic compositions by using suitable olivine-hosted silicate melt inclusions to reconstruct the redox history of deep-seated magma reservoirs in subduction zones. In addition, we confirm that the olivine-melt FeT-Mg exchange coefficient (where FeT is total iron expressed as FeO) correlates with changing fO2 and can serve as an Fe-Mg oxybarometer within the calibrated range of this study. Owing to the rapid diffusion of Fe in olivine, this approach can record rapid redox fluctuations and provides complementary constraints to the more robust V-based oxybarometers. Experimental oxybarometers Olivine-melt equilibrium V-Sc partitioning Fe-Mg exchange coefficient Fractional crystallization Hydrous arc magmas Dewey 550 European Commission The redox evolution of arc magmas: from the oxygenation of the Earth’s atmosphere to the genesis of giant hydrothermal ore deposits 864792 OXYGEN EU H2020 42 Département des sciences de la Terre 154 false 692 Mineral Resources and Geofluids https://doi.org/10.17632/ty679nzgfx.1 Geochimica et cosmochimica acta 415 4aa6157c-ded7-4e1b-a84e-c436df2d3504 Article (Published version) Public A_novel_experimental_V-Sc_olivine-m.pdf 19296993 application/pdf CC BY-4.0 e4f622c1e070ac677fe7d8944382e156b9f51de83e8269ab934c97e14ac65ec6 openAccess Faculté des sciences / Section des sciences de la Terre et de l'Environnement / Département des sciences de la Terre

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A novel experimental V-Sc olivine-melt oxybarometer for arc magmas	Geochimica et cosmochimica acta			2026	11	213

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