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See detailDual origin of Fe-Ti-P gabbros by immiscibility and fractional crystallization of evolved tholeiitic basalts in the Sept Iles layered intrusion
Namur, O.; Charlier, Bernard ULg; Holness, M. B.

in Lithos (2012), 154

We present a detailed study of two ca. 200m-thick apatite-bearing ferrogabbro horizons of the Sept Iles layered intrusion (Canada). These rocks are the most evolved cumulates of the megacyclic units (MCU ... [more ▼]

We present a detailed study of two ca. 200m-thick apatite-bearing ferrogabbro horizons of the Sept Iles layered intrusion (Canada). These rocks are the most evolved cumulates of the megacyclic units (MCU) I and II, and mark the transition between basaltic and silicic magmatism. They are made up of plagioclase (An 55-34), olivine (Fo 66-21), clinopyroxene (Mg#75-55), ilmenite, magnetite, apatite, ±pigeonite and are a significant source of Fe-Ti-P ore. Ferrogabbros have relatively uniform bulk-rock compositions in MCU I but are bimodal in MCU II. The liquid lines of descent for major elements in equilibrium with cumulates of MCU I and II have been calculated using a forward model formalism. Both trends evolve towards SiO 2-enrichment and FeO t-depletion after saturation in Fe-Ti oxides. However, because of magma mixing in MCU II, they do not follow the same path. Evolved liquids from MCU II are shown to enter the experimentally-determined two liquid stability field, while MCU I liquids do not. Immiscibility in MCU II and its absence in MCU I are supported by the presence of contrasted reactive symplectites in cumulate rocks. Apatite-bearing ferrogabbros in MCU II have crystallized from distinct immiscible Fe-rich and Si-rich silicate melts which have physically segregated in the slow-cooling magma chamber. Two different types of cumulate rocks are thus produced: leucocratic and melanocratic gabbros. This is consistent with the presence of Si-rich and Fe-rich melt inclusions in apatite. In contrast, homogeneous ferrogabbros from MCU I were produced by simple fractional crystallization of a homogeneous liquid. Our data suggest that immiscibility could also explain the large geochemical variability of ferrogabbros in the Upper Zone of the Bushveld Complex (South Africa). © 2012 Elsevier B.V. [less ▲]

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See detailExperiments on liquid immiscibility along tholeiitic liquid lines of descent
Charlier, Bernard ULg; Grove, T. L.

in Contributions to Mineralogy and Petrology (2012), 164(1), 27-44

Crystallization experiments have been conducted on compositions along tholeiitic liquid lines of descent to define the compositional space for the development of silicate liquid immiscibility. Starting ... [more ▼]

Crystallization experiments have been conducted on compositions along tholeiitic liquid lines of descent to define the compositional space for the development of silicate liquid immiscibility. Starting materials have 46-56 wt% SiO 2, 11.7-17.7 wt% FeO tot, and Mg-number between 0.29 and 0.36. These melts fall on the basaltic trends relevant for Mull, Iceland, Snake River Plain lavas and for the Sept Iles layered intrusion, where large-scale liquid immiscibility has been recognized. At one atmosphere under anhydrous conditions, immiscibility develops below 1,000-1,020°C in all of these compositionally diverse lavas. Extreme iron enrichment is not necessary; immiscibility also develops during iron depletion and silica enrichment. Variations in melt composition control the development of silicate liquid immiscibility along the tholeiitic trend. Elevation of Na 2O + K 2O + P 2O 5 + TiO 2 promotes the development of two immiscible liquids. Increasing melt CaO and Al 2O 3 stabilizes a single-liquid field. New data and published phase equilibria show that anhydrous, low-pressure fractional crystallization is the most favorable condition for unmixing during differentiation. Pressure inhibits immiscibility because it expands the stability field of high-Ca clinopyroxene, which reduces the proportion of plagioclase in the crystallizing assemblage, thus enhancing early iron depletion. Magma mixing between primitive basalt and Fe-Ti-P-rich ferrobasalts can serve to elevate phosphorous and alkali contents and thereby promote unmixing. Water might decrease the temperature and size of the two-liquid field, potentially shifting the binodal (solvus) below the liquidus, leading the system to evolve as a single-melt phase. © 2012 Springer-Verlag. [less ▲]

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See detailWater storage and early hydrous melting of the Martian mantle
Pommier, A.; Grove, T. L.; Charlier, Bernard ULg

in Earth and Planetary Science Letters (2012), 333-334

We report an experimental investigation of the near-solidus phase equilibria of a water-saturated analog of the Martian mantle. Experiments were performed at low temperatures (700-920°C) and high pressure ... [more ▼]

We report an experimental investigation of the near-solidus phase equilibria of a water-saturated analog of the Martian mantle. Experiments were performed at low temperatures (700-920°C) and high pressure (4-7GPa) using multi-anvil apparatus and piston cylinder device (4GPa). The results of this study are used to explore the role of water during early melting and chemical differentiation of Mars, and to further our understanding of the near-solidus behavior in planetary mantle compositions at high pressure. Water has a significant effect on the temperature of melting and, therefore, on accretion and subsequent differentiation processes. Experiments locate the wet solidus at ~800°C, and is isothermal between 4GPa and 7GPa. The Martian primitive mantle can store significant amounts of water in hydrous minerals stable near the solidus. Humite-group minerals and phase E represent the most abundant hydrous minerals stable in the 4-7GPa pressure range. The amount of water that can be stored in the mantle and mobilized during melting ranges from 1 to up to 4wt% near the wet solidus. We discuss thermal models of Mars accretion where the planet formed very rapidly and early on in solar system history. We incorporate the time constraint of Dauphas and Pourmand (2011) that Mars had accreted to 50% of its present mass in 1.8Myr and include the effects of 26Al radioactive decay and heat supplied by rapid accretion. When accretion has reached 30% of Mars current mass (~70% of its present size), melting starts, and extends from 100 to 720km depth. Below this melt layer, water can still be bound in crystalline solids. The critical stage is at 50% accretion (~80% of its size), where Mars is above the wet and dry solidi with most of its interior melted. This is earlier in the accretion process than what would be predicted from dry melting. We suggest that water may have promoted early core formation on Mars and rapidly extended melting over a large portion of Mars interior. © 2012 Elsevier B.V. [less ▲]

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See detailAnhydrous melting of a primitive martian mantle: new experiments at 1-2 GPa
Collinet, Max ULg; Médard, Etienne; Vander Auwera, Jacqueline ULg et al

Conference (2012)

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See detailPrediction of plagioclase-melt equilibria in anhydrous silicate melts at 1 atm
Namur, Olivier ULg; Charlier, Bernard ULg; Toplis, Michael et al

in Contributions to Mineralogy & Petrology (2012), 163

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See detailAnorthosite formation by plagioclase flotation in ferrobasalt and implications for the lunar crust
Namur, Olivier ULg; Charlier, Bernard ULg; Pirard, Cassian et al

in Geochimica et Cosmochimica Acta (2011), 75

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See detailCrystallization sequence and magma chamber processes in the ferrobasaltic Sept Iles layered intrusion, Canada
Namur, Olivier ULg; Charlier, Bernard ULg; Toplis, Michael et al

in Journal of Petrology (2010), 51

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See detailA-type granite of the ferrobasaltic Sept Iles layered intrusion: a product of large-scale silicate liquid immiscibility
Charlier, Bernard ULg; Namur, Olivier ULg; Schiano, P. et al

in EOS : Transactions, American Geophysical Union (2009), 90(52), 14-06

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See detailTwo parent magmas for the same anorthosite pluton? The Egersund-0gna case
Duchesne, Jean Clair; Charlier, Bernard ULg; Vander Auwera, Jacqueline ULg

in EOS : Transactions, American Geophysical Union (2009), 90(22), 11-02

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See detailCumulate origin and polybaric crystallization of Fe-Ti oxide ores in the Suwalki anorthosite, northeastern Poland
Charlier, Bernard ULg; Namur, Olivier ULg; Duchesne, Jean Clair et al

in Economic Geology (2009), 104

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