References of "Geochimica et Cosmochimica Acta"
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See detailIron and silicon isotope behaviour accompanying weathering in Icelandic soils, and the implications for iron export from peatlands
Opfergelt, Sophie; Williams, H; Cornelis, Jean-Thomas ULiege et al

in Geochimica et Cosmochimica Acta (2017)

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See detailCrystallization history of enriched shergottites from Fe and Mg isotope fractionation in olivine megacrysts
Collinet, Max; Charlier, Bernard ULiege; Namur, Olivier ULiege et al

in Geochimica et Cosmochimica Acta (2017), 207

Martian meteorites are the only samples available from the surface of Mars. Among them, olivine-phyric shergottites are basalts containing large zoned olivine crystals with highly magnesian cores (Fo ... [more ▼]

Martian meteorites are the only samples available from the surface of Mars. Among them, olivine-phyric shergottites are basalts containing large zoned olivine crystals with highly magnesian cores (Fo 70–85) and rims richer in Fe (Fo 45–60). The Northwest Africa 1068 meteorite is one of the most primitive “enriched” shergottites (high initial 87Sr/86Sr and low initial ε143Nd). It contains olivine crystals as magnesian as Fo 77 and is a major source of information to constrain the composition of the parental melt, the composition and depth of the mantle source, and the cooling and crystallization history of one of the younger magmatic events on Mars (∼180 Ma). In this study, Fe-Mg isotope profiles analyzed in situ by femtosecond-laser ablation MC-ICP-MS are combined with compositional profiles of major and trace elements in olivine megacrysts. The cores of olivine megacrysts are enriched in light Fe isotopes (δ56FeIRMM-14 = −0.6 to −0.9‰) and heavy Mg isotopes (δ26MgDSM-3 = 0–0.2‰) relative to megacryst rims and to the bulk martian isotopic composition (δ56Fe = 0 ± 0.05‰, δ26Mg = −0.27 ± 0.04‰). The flat forsterite profiles of megacryst cores associated with anti-correlated fractionation of Fe-Mg isotopes indicate that these elements have been rehomogenized by diffusion at high temperature. We present a 1-D model of simultaneous diffusion and crystal growth that reproduces the observed element and isotope profiles. The simulation results suggest that the cooling rate during megacryst core crystallization was slow (43 ± 21 °C/year), and consistent with pooling in a deep crustal magma chamber. The megacryst rims then crystallized 1–2 orders of magnitude faster during magma transport toward the shallower site of final emplacement. Megacryst cores had a forsterite content 3.2 ± 1.5 mol% higher than their current composition and some were in equilibrium with the whole-rock composition of NWA 1068 (Fo 80 ± 1.5). NWA 1068 composition is thus close to a primary melt (i.e. in equilibrium with the mantle) from which other enriched shergottites derived. [less ▲]

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See detailEnhanced silicate weathering of tropical shelf sediments exposed during glacial lowstands: a sink for atmospheric CO2
Wan, Shiming; Clift, Peter D.; Zhao, Debo et al

in Geochimica et Cosmochimica Acta (2017), 200

Atmospheric CO2 and global climate are closely coupled. Since 800 ka CO2 concentrations have been up to 50% higher during interglacial compared to glacial periods. Because of its dependence on temperature ... [more ▼]

Atmospheric CO2 and global climate are closely coupled. Since 800 ka CO2 concentrations have been up to 50% higher during interglacial compared to glacial periods. Because of its dependence on temperature, humidity, and erosion rates, chemical weathering of exposed silicate minerals was suggested to have dampened these cyclic variations of atmospheric composition. Cooler and drier conditions and lower non-glacial erosion rates suppressed in situ chemical weathering rates during glacial periods. However, using systematic variations in major element geochemistry, Sr-Nd isotopes and clay mineral records from Ocean Drilling Program Sites 1143 and 1144 in the South China Sea spanning the last 1.1 Ma, we show that sediment deposited during glacial periods was more weathered than sediment delivered during interglacials. We attribute this to subaerial exposure and weathering of unconsolidated shelf sediments during glacial sealevel lowstands. Our estimates suggest that enhanced silicate weathering of tropical shelf sediments exposed during glacial lowstands can account for ~9% of the carbon dioxide removed from the atmosphere during the glacial and thus represent a significant part of the observed glacial-interglacial variation of ~80 ppmv. As a result, if similar magnitudes can be identified in other tropical shelf-slope systems, the effects of increased sediment exposure and subsequent silicate weathering during lowstands could have potentially enhanced the drawdown of atmospheric CO2 during cold stages of the Quaternary. This in turn would have caused an intensification of glacial cycles. We attribute this to subaerial exposure and weathering of unconsolidated shelf sediments during glacial sealevel lowstands. Our estimates suggest that enhanced silicate weathering of tropical shelf sediments exposed during glacial lowstands can account for ~9% of the carbon dioxide removed from the atmosphere during the glacial and thus represent a significant part of the observed glacial-interglacial variation of ~80 ppmv. As a result, if similar magnitudes can be identified in other tropical shelf-slope systems, the effects of increased sediment exposure and subsequent silicate weathering during lowstands could have potentially enhanced the drawdown of atmospheric CO2 during cold stages of the Quaternary. This in turn would have caused an intensification of glacial cycles. [less ▲]

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See detailStructural characterization by Raman hyperspectral mapping of organic carbon in the 3.46 billion-year-old Apex chert, Western Australia
Sforna, Marie-Catherine ULiege; van Zuilen, Mark; Philippot, Pascal

in Geochimica et Cosmochimica Acta (2014), 124

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See detailCompositional and kinetic controls on liquid immiscibility in ferrobasalt-rhyolite volcanic and plutonic series
Charlier, Bernard ULiege; Namur, O.; Grove, T. L.

in Geochimica et Cosmochimica Acta (2013), 113

We present major element compositions of basalts and their differentiation products for some major tholeiitic series. The dry, low-pressure liquid lines of descent are shown to approach or intersect the ... [more ▼]

We present major element compositions of basalts and their differentiation products for some major tholeiitic series. The dry, low-pressure liquid lines of descent are shown to approach or intersect the experimentally-defined compositional space of silicate liquid immiscibility. Ferrobasalt-rhyolite unmixing along tholeiitic trends in both volcanic and plutonic environments is supported by worldwide occurrence of immiscible globules in the mesostasis of erupted basalts, unmixed melt inclusions in cumulus phases of major layered intrusions such as Skaergaard and Sept Iles, and oxide-rich ferrogabbros closely associated with plagiogranites in the lower oceanic crust. Liquid immiscibility is promoted by low-pressure, anhydrous fractional crystallization that drives the low Al2O3, high FeO liquids into the two-liquid field. Kinetic controls can be important in the development of two-liquid separation. The undercooling that occurs at the slow cooling rates of plutonic environments promotes early development of liquid immiscibility at higher temperature. In contrast rapid cooling in erupted lavas leads to large undercoolings and liquid immiscibility develops at significantly lower temperatures. Unmixing leads to the development of a compositional gap characterized by the absence of intermediate compositions, a feature of many tholeiitic provinces. The compositions of experimental unmixed silica-rich melts coincide with those of natural rhyolites and plagiogranites with high FeOtot and low Al2O3, suggesting the potential role of large-scale separation of immiscible Si-rich liquid in the petrogenesis of late-stage residual melts. No trace of the paired ferrobasaltic melt is found in volcanic environments because of its uneruptable characteristics. Instead, Fe-Ti±P-rich gabbros are the cumulate products of immiscible Fe-rich melts in plutonic settings. The immiscibility process may be difficult to identify because both melts crystallize the same phases with the same compositions. The two liquids might form incompletely segregated emulsions so that both liquids continue to exchange as they crystallize and remain in equilibrium. Even if segregated, both melts evolve on the binodal surface and exsolve continuously with decreasing temperature. The two liquids do not differentiate independently and keep crystallizing the same phases with differentiation. Further evolution by fractional crystallization potentially drives the bulk liquid out of the two-liquid field so that very late-stage liquids could evolve into the single melt phase stability field. © 2013 Elsevier Ltd. [less ▲]

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

in Geochimica et Cosmochimica Acta (2011), 75

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See detailTracing mechanisms controlling the release of dissolved silicon in forest soil solutions using Si isotopes and Ge/Si ratios
Cornelis, Jean-Thomas ULiege; Delvaux, Bruno; Cardinal, D. et al

in Geochimica et Cosmochimica Acta (2010), 74(14), 3913-3924

Abstract : The terrestrial biogenic Si (BSi) pool in the soil plant system is ubiquitous and substantial, likely impacting the land-ocean transfer of dissolved Si (DSi). Here, we consider the mechanisms ... [more ▼]

Abstract : The terrestrial biogenic Si (BSi) pool in the soil plant system is ubiquitous and substantial, likely impacting the land-ocean transfer of dissolved Si (DSi). Here, we consider the mechanisms controlling DSi in forest soil in a temperate granitic ecosystem that would differ from previous works mostly focused on tropical environments. This study aims at tracing the source of DSi in forest floor leachates and in soil solutions under various tree species at homogeneous soil and climate conditions, using stable Si isotopes and Ge/Si ratios. Relative to granitic bedrock, clays minerals were enriched in Si-28 and had high Ge/Si ratios, while BSi from phytoliths was also enriched in Si-28, but had a low Ge/Si ratio. Such a contrast is useful to infer the relative contribution of silicate weathering and BSi dissolution in the shallow soil on the release of DSi in forest floor leachate solutions. The delta Si-30 values in forest floor leachates (-1.38 parts per thousand to -2.05 parts per thousand) are the lightest ever found in natural waters, and Ge/Si ratios are higher in forest floor leachates relative to soil solution. These results suggest dissolution of Si-28 and Ge-enriched secondary clay minerals incorporated by bioturbation in organic-rich horizons in combination with an isotopic fractionation releasing preferentially light Si isotopes during this dissolution process. Ge/Si ratios in soil solutions are governed by incongruent weathering of primary minerals and neoformation of secondary clays minerals. Tree species influence Si-isotopic compositions and Ge/Si ratios in forest floor leachates through differing incorporation of minerals in organic horizons by bioturbation and, to a lesser extent, through differing Si recycling. (C) 2010 Elsevier Ltd. All rights reserved. [less ▲]

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See detailHolocene records of regional dust deposition using peat bogs
Le Roux, G.; De Vleeschouwer, François; Cheburkin, A. et al

in Geochimica et Cosmochimica Acta (2008), 72(12), 535-535

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See detailNd and Pb isotopic signatures of detrital fractions from Labrador Sea and Iceland Basin sediments: Deep oceanic circulation changes over the Holocene
Fagel, Nathalie ULiege; Brasseur; Mattielli, N. et al

in Geochimica et Cosmochimica Acta (2008), 72(12), 251-251

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See detailGenesis of intermediate to silicic igneous rocks at the end of the Sveconorwegian (grenvillian) orogeny
Vander Auwera, Jacqueline ULiege; Bogaerts, M.; Bolle, Olivier ULiege

in Geochimica et Cosmochimica Acta (2007, August), 71(15S), 1054

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See detailSpatial and temporal (30 yr.) variations of lead geochemical signature in a macrotidal highly polluted estuary
Taillez, A.; Jacqmot, A.; Petit, Jérôme et al

in Geochimica et Cosmochimica Acta (2007, August), 71(15, Suppl. S), 993-993

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See detailModelling continental weathering: from the lab to the field
Godderis, Y.; Schott, J.; François, Louis ULiege et al

in Geochimica et Cosmochimica Acta (2007), 71(15), 333-333

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See detailDeciphering the record of early life in Precambrian oceans using combined microscopy and microchemistry of organic-walled microfossils.
Javaux, Emmanuelle ULiege; Marshall, C. P.

in Geochimica et Cosmochimica Acta (2007), 71(15), 442

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See detailThe Sept Iles mafic layered intrusion; an example of ferrobasaltic differentiation
Namur, Olivier ULiege; Charlier, Bernard ULiege; Higgins, Michael et al

in Geochimica et Cosmochimica Acta (2007), 71(15S), 705

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See detailTracking groundwater contribution to rivers by combining hydrogen isotopes and cation concentrations
Bureau, M.; Carignan, J.; France-Lanord, C. et al

in Geochimica et Cosmochimica Acta (2007), 71(15), 134-134

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See detailSpatial and temporal (30 yr.) variations of lead geochemical signature in a macrotidal highly polluted estuary
Taillez, A.; Jacqmot, A.; Petit et al

in Geochimica et Cosmochimica Acta (2007), 71(15), 993-993

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See detailModelling weathering processes at the catchment scale: The WITCH numerical model
Godderis, Y.; François, Louis ULiege; Probst, A. et al

in Geochimica et Cosmochimica Acta (2006), 70(5), 1128-1147

A numerical model of chemical weathering in soil horizons and underlying bedrock (WITCH) has been coupled to a numerical model of water and carbon cycles in forest ecosystems (ASPECTS) to simulate the ... [more ▼]

A numerical model of chemical weathering in soil horizons and underlying bedrock (WITCH) has been coupled to a numerical model of water and carbon cycles in forest ecosystems (ASPECTS) to simulate the concentration of major species within the soil horizons and the stream of the Strengbach granitic watershed, located in the Vosges Mountains (France). For the first time, simulations of solute concentrations in soil layers and in the catchment river have been performed on a seasonal basis. The model is able to reproduce the concentrations of most major species within the soil horizons, as well as catching the first-order seasonal fluctuations of aqueous calcium, magnesium and silica concentrations. However, the WITCH model underestimates concentrations of Mg2+ and silica at the spring of the catchment stream, and significantly underestimates Ca2+ concentration. The deficit in calculated calcium can be compensated for by dissolution of trace apatite disseminated in the bedrock. However, the resulting increased Ca2+ release yields important smectite precipitation in the deepest model layer (in contact with the bedrock) and subsequent removal of large amount of silica and magnesium from solution. In contrast, the model accurately accounts for the concentrations of major species (Ca, Mg and silica) measured in the catchment stream when precipitation of clay minerals is not allowed. The model underestimation of Mg2+ and H4SiO4 concentrations when precipitation of well crystallized smectites is allowed strongly suggests that precipitation of well crystallized clay minerals is overestimated and that more soluble poorly crystallized and amorphous materials may be forming. In agreement with observations on other watersheds draining granitic rocks, this study indicates that highly soluble trace calcic phases control the aqueous calcium budget in the Strengbach watershed. (c) 2005 Elsevier Inc. All rights reserved. [less ▲]

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