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See detailCrystallization history of enriched shergottites from Fe and Mg isotope fractionation in olivine megacrysts
Collinet, Max; Charlier, Bernard ULg; Namur, Olivier ULg 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 detailFe and Mg Isotope Fractionation in Olivine from the NWA 1068 Shergottite
Collinet, Max ULg; Charlier, Bernard ULg; Namur, Olivier et al

Conference (2014, June 09)

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See detailAlkaline Primary Melts from the Primitive Mantle of Mars
Collinet, Max ULg; Médard, Etienne; Vander Auwera, Jacqueline ULg et al

Poster (2014, March)

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See detailShergottites: Partial Melts of a Depleted Martian Mantle
Médard, Etienne; Collinet, Max ULg

Poster (2014, March)

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See detailConstraints on the Parental Melts of Enriched Shergottites from Image Analysis and High Pressure Experiments
Collinet, Max ULg; Medard, Etienne; Devouard, Bertrand et al

Poster (2012, March 20)

Martian basalts can be classified in at least two geochemically different families: enriched and depleted shergottites. Enriched shergottites are characterized by higher incompatible element ... [more ▼]

Martian basalts can be classified in at least two geochemically different families: enriched and depleted shergottites. Enriched shergottites are characterized by higher incompatible element concentrations and initial 87Sr/86Sr and lower initial 143Nd/144Nd and 176Hf/177Hf than depleted shergottites. It is now generally admitted that shergottites result from the melting of at least two distinct mantle reservoirs. Some of the olivine-phyric shergottites (either depleted or enriched), the most magnesian Martian basalts, could represent primitive melts, which are of considerable interest to constrain mantle sources. Two depleted olivine-phyric shergottites, Yamato 980459 and Nothwest Africa (NWA) 5789, are in equilibrium with their most magnesian olivine and their bulk rock compositions are inferred to represent primitive melts. Larkman Nunatak 06319 and NWA 1068, the most magnesian enriched basalts, have bulk Mg# that are too high to be in equilibrium with their olivine megacryst cores. Parental melt compositions have been estimated by subtracting the most magnesian olivine from the bulk rock composition, assuming that olivine megacrysts have partially accumulated. However, because this technique does not account for the actual petrography of these meteorites, we used image analysis to study these rocks history, reconstruct their parent magma and understand the nature of oli-vine megacrysts. Our image analysis results are supported by a series of high-pressure experiments performed on LAR 06319 bulk rock composition to test if it could represent a primitive melt, and understand its crystallization history. [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)

Detailed reference viewed: 49 (11 ULg)