Compositional boundary layers trigger liquid unmixing in a basaltic crystal mush

Honour, Victoria; Holness, Marian B.; Charlier, Bernard; Piazolo, Sandra; Namur, Olivier; Prosa, Ty J.; Martin, Isabelle; Helz, Rosalind Tuthill; Maclennan, John; Jean, M. M.

doi:10.1038/s41467-019-12694-5

Cited by 24 publications

(15 citation statements)

References 45 publications

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“…Fig. 6a, c) 46 . Olivine crystals in our Fernandina nodule samples have ubiquitously low Mg# ol , consistent with growth or re-equilibration with evolved liquids.…”

Section: Resultsmentioning

confidence: 97%

Cryptic evolved melts beneath monotonous basaltic shield volcanoes in the Galápagos Archipelago

et al. 2020

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Many volcanoes erupt compositionally homogeneous magmas over timescales ranging from decades to millennia. This monotonous activity is thought to reflect a high degree of chemical homogeneity in their magmatic systems, leading to predictable eruptive behaviour. We combine petrological analyses of erupted crystals with new thermodynamic models to characterise the diversity of melts in magmatic systems beneath monotonous shield volcanoes in the Galápagos Archipelago (Wolf and Fernandina). In contrast with the uniform basaltic magmas erupted at the surface over long timescales, we find that the sub-volcanic systems contain extreme heterogeneity, with melts extending to rhyolitic compositions. Evolved melts are in low abundance and large volumes of basalt flushing through the crust from depth overprint their chemical signatures. This process will only maintain monotonous activity while the volume of melt entering the crust is high, raising the possibility of transitions to more silicic activity given a decrease in the crustal melt flux.

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“…Fig. 6a, c) 46 . Olivine crystals in our Fernandina nodule samples have ubiquitously low Mg# ol , consistent with growth or re-equilibration with evolved liquids.…”

Section: Resultsmentioning

confidence: 97%

Cryptic evolved melts beneath monotonous basaltic shield volcanoes in the Galápagos Archipelago

et al. 2020

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“…Instead, this segment records the secondary effects of an episode of rapid growth where Ni is quickly depleted in the surrounding melt given the high partitioning in olivine (Kd Ni ol/melt > ~10 in basaltic compositions 21 – 25 ) and the subsequent development of a compositional boundary layer (CBL) around the crystal, which is depleted in compatible elements and enriched in incompatible elements (e.g., refs. 16 , 26 , 27 ). Comparatively, Fo is less sensitive to variations in the CBL environment given the higher initial concentrations of Mg and Fe in the melt and its comparatively lower partition coefficients 23 (Supplementary Information Fig.…”

Section: Resultsmentioning

confidence: 99%

“…These chemical changes may induce a slow-down of crystal growth in the boundary layer environment (e.g., ref. 12 , 26 , 37 , 38 ). While local boundary layers may slow down growth, dendritic fast growth of other new frames may continue simultaneously, documented in the advance of multiple frames (e.g.…”

Section: Resultsmentioning

confidence: 99%

Out-of-sequence skeletal growth causing oscillatory zoning in arc olivines

et al. 2021

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Primitive olivines from the monogenetic cones Los Hornitos, Central-South Andes, preserve dendritic, skeletal, and polyhedral growth textures. Consecutive stages of textural maturation occur along compositional gradients where high Fo–Ni cores of polyhedral olivines (Fo92.5, Ni ~3500 ppm) contrast with the composition of dendritic olivines (Fo < 91.5, Ni < 3000 ppm), indicating sequential nucleation. Here we present a new growth model for oscillatory Fo–Ni olivine zoning that contrasts with the standard interpretation of continuous, sequential core-to-rim growth. Olivine grows rapidly via concentric addition of open-structured crystal frames, leaving behind compositional boundary layers that subsequently fill-in with Fo–Ni-depleted olivine, causing reversals. Elemental diffusion modeling reveals growth of individual crystal frames and eruption at the surface occurred over 3.5–40 days. Those timescales constrain magma ascent rates of 40–500 m/h (0.011 to 0.14 m/s) from the deep crust. Compared to ocean island basalts, where dendritic and skeletal olivines have been often described, magmas erupted at arc settings, experiencing storage and degassing, may lack such textures due to fundamentally different ascent histories.

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“…In this situation, chemical equilibration between crystals and Ferich liquid may kinetically out-compete liquid-liquid equilibration and result in metastable, disequilibrium distribution of network formers and network modifiers. Strong empirical support for this proposition has been recently provided by Honour et al (2019b). They observed that continuous films of Fe-rich liquid with distinct interfaces had formed in compositional boundary layers (CBL) around plagioclase crystals growing in basaltic lava of Kilauea Iki lava lake.…”

Section: Natural Immiscible Liquidsmentioning

confidence: 87%

Immiscible silicate liquids: K and Fe distribution as a test for chemical equilibrium and insight into the kinetics of magma unmixing

Борисов

Veksler

2021

Contrib Mineral Petrol

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Silicate liquid immiscibility leading to formation of mixtures of distinct iron-rich and silica-rich liquids is common in basaltic and andesitic magmas at advanced stages of magma evolution. Experimental modeling of the immiscibility has been hampered by kinetic problems and attainment of chemical equilibrium between immiscible liquids in some experimental studies has been questioned. On the basis of symmetric regular solutions model and regression analysis of experimental data on compositions of immiscible liquid pairs, we show that liquid–liquid distribution of network-modifying elements K and Fe is linked to the distribution of network-forming oxides SiO2, Al2O3 and P2O5 by equation: $$\log K_{{\text{d}}}^{{\text{K/Fe}}} = \, 3.796\Delta X_{{{\text{SiO}}_{2} }}^{{{\text{sf}}}} + \, 4.85\Delta X_{{{\text{Al}}_{2} {\text{O}}_{3} }}^{{{\text{sf}}}} + \, 7.235\Delta X_{{{\text{P}}_{2} {\text{O}}_{5} }}^{{{\text{sf}}}} - \, 0.108,$$ log K d K/Fe = 3.796 Δ X SiO 2 sf + 4.85 Δ X Al 2 O 3 sf + 7.235 Δ X P 2 O 5 sf - 0.108 , where $$K_{{\text{d}}}^{{\text{K/Fe}}}$$ K d K/Fe is a ratio of K and Fe mole fractions in the silica-rich (s) and Fe-rich (f) immiscible liquids: $$K_{d}^{{\text{K/Fe}}} = \, \left( {X_{{\text{K}}}^{s} /X_{{\text{K}}}^{f} } \right)/ \, \left( {X_{{{\text{Fe}}}}^{s} /X_{{{\text{Fe}}}}^{f} } \right)$$ K d K/Fe = X K s / X K f / X Fe s / X Fe f and $$\Delta X_{{\text{i}}}^{sf}$$ Δ X i sf is a difference in mole fractions of a network-forming oxide i between the liquids (s) and (f): $$\Delta X_{i}^{sf} = X_{i}^{s} - X_{i}^{f}$$ Δ X i sf = X i s - X i f . We use the equation for testing chemical equilibrium in experiments not included in the regression analysis and compositions of natural immiscible melts found as glasses in volcanic rocks. Departures from equilibrium that the test revealed in crystal-rich multiphase experimental products and in natural volcanic rocks imply kinetic competition between liquid–liquid and crystal–liquid element partitioning. Immiscible liquid droplets in volcanic rocks appear to evolve along a metastable trend due to rapid crystallization. Immiscible liquids may be closer to chemical equilibrium in large intrusions where cooling rates are lower and crystals may be spatially separated from liquids.

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Compositional boundary layers trigger liquid unmixing in a basaltic crystal mush

Cited by 24 publications

References 45 publications

Cryptic evolved melts beneath monotonous basaltic shield volcanoes in the Galápagos Archipelago

Cryptic evolved melts beneath monotonous basaltic shield volcanoes in the Galápagos Archipelago

Out-of-sequence skeletal growth causing oscillatory zoning in arc olivines

Immiscible silicate liquids: K and Fe distribution as a test for chemical equilibrium and insight into the kinetics of magma unmixing

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