Details
| Originalsprache | Englisch |
|---|---|
| Aufsatznummer | 83 |
| Fachzeitschrift | Contributions to Mineralogy and Petrology |
| Jahrgang | 180 |
| Ausgabenummer | 11 |
| Publikationsstatus | Veröffentlicht - 4 Okt. 2025 |
Abstract
mental evidence. Whereas other controls are better studied, the effect of fO2, beyond oxide stability, remains less con-
strained. 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 com-
positions with different xMg* [MgO/(MgO
+
FeOtot)] (0.5 to 0.7) at multiple fO2 conditions (NNO-0.5 to NNO
+
2.3),
deconvolving the effects of Fe3+/Fe2+ and xMgeff [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, increas-
ing fO2 (1) stabilises Fe3+-rich spinel, leading to SiO2-richer melts and, therefore, less pronounced ASI (alumina satura-
tion 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
ASJC Scopus Sachgebiete
- Erdkunde und Planetologie (insg.)
- Geophysik
- Erdkunde und Planetologie (insg.)
- Geochemie und Petrologie
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in: Contributions to Mineralogy and Petrology, Jahrgang 180, Nr. 11, 83, 04.10.2025.
Publikation: Beitrag in Fachzeitschrift › Artikel › Forschung › Peer-Review
}
TY - JOUR
T1 - The role of oxygen fugacity in hydrous basaltic phase equilibria: experimental constraints at 0.2 and 0.8 GPa
AU - Silva, Manuel Pimenta
AU - Marxer, Felix
AU - Krashenninikov, Stepan
AU - Koch, Lennart
AU - Zech, Rebecca F.
AU - Holtz, François
AU - Ulmer, Peter
AU - Müntener, Othmar
N1 - Publisher Copyright: © The Author(s) 2025.
PY - 2025/10/4
Y1 - 2025/10/4
N2 - Crystallisation-differentiation drives arc magma evolution, yet discrepancies remain among field, geochemical and experi-mental evidence. Whereas other controls are better studied, the effect of fO2, beyond oxide stability, remains less con-strained. We investigate fO2-pressure effects on olivine-clinopyroxene-spinel phase relations with implications for arcmagmas. We conducted phase equilibria experiments at 200 MPa between 1010 and 1100 °C. We used basaltic com-positions with different xMg* [MgO/(MgO+FeOtot)] (0.5 to 0.7) at multiple fO2 conditions (NNO-0.5 to NNO+2.3),deconvolving the effects of Fe3+/Fe2+ and xMgeff [MgO/(MgO+FeO)] on phase equilibria. Additionally, we ran 800 MPaexperiments between NNO-0.4 and NNO+2.5 to explore the combined effects of fO2 and pressure. At 200 MPa, increas-ing fO2 (1) stabilises Fe3+-rich spinel, leading to SiO2-richer melts and, therefore, less pronounced ASI (alumina satura-tion index, ASI=Al2O3/(CaO+Na2O+K2O) molar) increase relative to SiO2, and (2) expands olivine stability relative toclinopyroxene 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 withincreasing pressure, while fO2 has a negligible effect on the ol-cpx cotectic. This suggests that the previously documentedpressure effect on the olivine-clinopyroxene equilibrium is stronger than the effect of fO2. Our results demonstrate thatfO2 increasingly influences the olivine-clinopyroxene cotectic equilibrium as pressure decreases. This supports modelswhere decompression-driven polybaric crystallisation under oxidising conditions shapes arc magmatic compositions. Thereported pressure-fO2 interplay helps reconcile natural and experimental arc records
AB - Crystallisation-differentiation drives arc magma evolution, yet discrepancies remain among field, geochemical and experi-mental evidence. Whereas other controls are better studied, the effect of fO2, beyond oxide stability, remains less con-strained. We investigate fO2-pressure effects on olivine-clinopyroxene-spinel phase relations with implications for arcmagmas. We conducted phase equilibria experiments at 200 MPa between 1010 and 1100 °C. We used basaltic com-positions with different xMg* [MgO/(MgO+FeOtot)] (0.5 to 0.7) at multiple fO2 conditions (NNO-0.5 to NNO+2.3),deconvolving the effects of Fe3+/Fe2+ and xMgeff [MgO/(MgO+FeO)] on phase equilibria. Additionally, we ran 800 MPaexperiments between NNO-0.4 and NNO+2.5 to explore the combined effects of fO2 and pressure. At 200 MPa, increas-ing fO2 (1) stabilises Fe3+-rich spinel, leading to SiO2-richer melts and, therefore, less pronounced ASI (alumina satura-tion index, ASI=Al2O3/(CaO+Na2O+K2O) molar) increase relative to SiO2, and (2) expands olivine stability relative toclinopyroxene 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 withincreasing pressure, while fO2 has a negligible effect on the ol-cpx cotectic. This suggests that the previously documentedpressure effect on the olivine-clinopyroxene equilibrium is stronger than the effect of fO2. Our results demonstrate thatfO2 increasingly influences the olivine-clinopyroxene cotectic equilibrium as pressure decreases. This supports modelswhere decompression-driven polybaric crystallisation under oxidising conditions shapes arc magmatic compositions. Thereported pressure-fO2 interplay helps reconcile natural and experimental arc records
KW - Arc magmatism
KW - ASI evolution
KW - Basaltic phase equilibria
KW - Calc-alkaline magmas
KW - Experimental petrology
KW - Oxygen fugacity
UR - http://www.scopus.com/inward/record.url?scp=105018187430&partnerID=8YFLogxK
U2 - 10.1007/s00410-025-02269-7
DO - 10.1007/s00410-025-02269-7
M3 - Article
VL - 180
JO - Contributions to Mineralogy and Petrology
JF - Contributions to Mineralogy and Petrology
SN - 0010-7999
IS - 11
M1 - 83
ER -