Manu Pimenta Silva

American Mineralogist:
The effect of H2O on the crystallization of orthopyroxene in a high-Mg andesitic melt
Lennart Koch, et al.
doi.org/10.2138/am-2...
Koch et al. experimentally investigated the crystallization behavior of OPX in a silicate melt at varying H2O concentrations and pressures.

Taking advantage of the government shutdown to finally advertise our paper! We constrained cooling rates and crystal residence times in the Adamello batholith combining Ti-in-quartz and Sr- and Ba-in-plagioclase diffusion - doi.org/10.1007/s004...

And I got to work with internally heated pressure vessels during two great months in Hannover!

The role of oxygen fugacity in hydrous basaltic phase equilibria: experimental constraints at 0.2 and 0.8 GPa - Contributions to Mineralogy and Petrology 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 + 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, 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.

Great to see my new paper finally out! 🌋
We looked into the effects of pressure and fO2 on arc basalt differentiation - it's not just oxide stability!

Plots showing the sulfur isotope compositions of metalavas and granitoid gneisses of the Innuksuaq Complex

⚒️ Article: Combined sulfur and neodymium isotopes suggest volatile cycling at subduction zones began at or prior to 3.8 Ga

@crpg-nancy.bsky.social

www.nature.com/articles/s41...

Mantle Melting Conditions of Mare Lavas on South Pole–Aitken Basin of Lunar Farside Remote sensing data of the South Pole–Aitken basin are utilized to estimate lunar mantle-derived primitive melt compositions Calculations of multiple saturation of primary melts with mantle miner...

Where and how the lavas in farside South Pole were generated? In this work led by Rice Uni, together with Raj Dasgupta @dianji.bsky.social @cintylee.bsky.social and collaborators, we explore the possibilities with a petrological approach 1/5

agupubs.onlinelibrary.wiley.com/doi/full/10....