Fonction : Doctorante - 01/10/2018 au 30/08/2021 -Thèse soutenue le 08/04/2022
Coordonnées :
CRPG UMR 7358 CNRS-UL
15 rue Notre Dame des Pauvres
54500 Vandœuvre les Nancy – France
Email : marion.auxerre@univ-lorraine.fr
2022 |
Auxerre, M., Faure, F., Lequin, D. The effects of superheating and cooling rate on olivine growth in chondritic liquid (Article de journal) Dans: Meteoritics & Planetary Science, p. 1–22, 2022. @article{Auxerre_etal2022,Chondrules, the major constituent of chondrites, are millimeter-sized igneous objects resulting from the crystallization of silicate liquids produced by the partial orcomplete melting of chondritic precursors, whose exact nature remains disputed. Variouschondrule textures are observed as a function of the extent of the initial melting event.Here, we report dynamic crystallization experiments performed with a broad range ofcooling rates (2--750textdegreeChâ1) from superliquidus or subliquidus initial conditions todemonstrate the control of nucleation on the final chondrule texture. Classical crypto-porphyritic, micro-porphyritic, and porphyritic olivine textures were reproduced insubliquidus experiments in which heterogeneous nucleation dominates. In contrast, we wereunable to reproduce barred olivine textures, regardless of the cooling rates investigated fromsuperliquidus conditions ; instead, macro-porphyritic textures were systematically obtained atlow cooling rates (<10textdegreeChâ1). The small number and large size of crystals in the macro-porphyritic texture are consistent with the initial step of superheating and the presence oflong embayments that indicate an initial episode of rapid growth due to delayed nucleation.Crystals then acquired polyhedral shapes during a subsequent episode of slow growth.When the growth rate is too slow to decrease the degree of supersaturation in the liquid, anew episode of rapid growth produces a new generation of melt inclusions |
Faure, F., Auxerre, M., Casola, V. Slow cooling during crystallisation of barred olivine chondrules (Article de journal) Dans: Earth and Planetary Science Letters, vol. 593, p. 117649, 2022. @article{Faure_etal2022,Barred olivine (BO) chondrules are small ferromagnesian silicate igneous droplets with unique dendritic textures that are considered to have formed in the early solar system during one or more brief high-temperature episodes, followed by rapid cooling in a gas. Rapid cooling rates of 100--7200 â¦C/h during chondrule formation have been proposed based on experiments attempting to reproduce BO crystal textures. However, the BO texture has never truly been reproduced under such rapid cooling conditions. Here, we experimentally show that true BO textures can be produced either after rapid cooling (>50 â¦C/h) following by reheating step or by cooling rates slower than 10 â¦C/h. Regardless of the thermal history considered, the chemical compositions of glass inclusions trapped within olivines of BO chondrules imply a final slow cooling rate one to two orders of magnitude below previous estimates. Such slow cooling rates are consistent with those estimated for plagioclase-bearing porphyritic chondrules and magmatic type-B Ca-Al-rich inclusions, suggesting that slow cooling rates are common to all similar chondritic objects. |
Feignon, J. G., Cluzel, N., Schiavi, F., Moune, S., Roche, O., Clavero, J., Schiano, P., Auxerre, M. High CO2 content in magmas of the explosive andesitic Enco eruption of MochoâChoshuenco volcano (Chile) (Article de journal) Dans: Bulletin of Volcanology, vol. 84, no. 40, 2022. @article{Feignon_etal2022,Mocho-Choshuenco volcano has produced several highly explosive eruptions during its history, which make it one of the most hazardous volcanoes in the southern volcanic zone of Chile, although it is still relatively little studied to date. We present a geochemical study of the products of the sub-Plinian, andesitic, Enco eruption that occurred about 1600 years ago. We determined the major and trace elements compositions, as well as the volatile (H2O, CO2, Cl, and S) contents of melt inclusions trapped in minerals (olivine, plagioclase, and pyroxene) using electron microprobe, ion microprobe (SIMS), and 3D confocal Raman mapping. Though the whole-rock composition of the Enco magma is andesitic (60.2 textpm 1.1 wt.% SiO2), the melt inclusions have SiO2 contents ranging from 50.3 to 67.3 wt.%, following the magmatic series of Mocho-Choshuenco, and the compositions of the most mafic melt inclusions are close to those of the most mafic erupted magmas. Geochemical modeling indicates that mixing occurred between a mafic magma and an andesitic-to-dacitic magma. Glass analysis revealed typical parental arc magma values for H2O (2.6--3.8 wt.%), S (116--1936 ppm), and Cl (620--1439 ppm). However, CO2 contents are very high in some melt inclusions with concentrations above 4000 ppm (measured in the glass), suggesting trapping depths > 17--22 km. Presence of solid carbonates inside inclusion-hosted bubbles clearly indicates that the CO2 contents measured in the glass phase were minimum values. We conclude that a CO2- rich basaltic magma ascended and mixed with a shallower andesitic magma. The magma cooled and exsolved high amounts of CO2, which may have dramatically increased the pressure and triggered the highly explosive Enco eruption. |
2020 |
Zanon, V., Pimentel, A., Auxerre, M., Marchini, G., Stuart, F. M. Unravelling the magma feeding system of a young basaltic oceanic volcano (Article de journal) Dans: Lithos, vol. 352-353, p. 105325, 2020. @article{Zanon_etal2020,A multidisciplinary approach combining petrological, geochemical, and fluid-inclusion studies with seismic monitoring datawas used to build a model of the magma feeding system of Pico volcano (Azores islands, North Atlantic Ocean).We explore how magma has ascended to the surface in the last 10 ka and how this ascent is associated with the selective activation of the three tectonic systems intersecting the volcano. The deepest and most important ponding level for all ascending magmas is located at 17.3--17.7 km and corresponds to theMoho Transition Zone (MTZ), which marks the transition from mantle rocks to ultramafic cumulates. At shallower depth ascending magmas carry N30 vol% of clinopyroxene and olivine. Each magma ascent followed a distinct path and ponded often for a limited period. Ponding levels common to all feeding systems are present at 16.3--16.7 km, 12.1--14.5 km, 9.4--9.8 km, and 7.7--8.1 km. These depths mark important discontinuities where magmas formed stacked sills and evolved through fractional crystallisation. Dense and un-decrepitated fluid inclusions show rapid ascent from the MTZ along the Lomba do Fogo-S~ao Jo~ao fault (N150textdegree system) and along the N120textdegree regional transtensive system, despite multiple intrusions. Magma ponding at 5.6--6.8 km occurs where the N150textdegree and N60textdegree tectonic systems intersect each other. Here magma evolves towards plagioclase-rich and is only erupted at the summit crater and subterminal vents. This region is the source of the frequent microseismicity recorded at 4 to 7 km beneath the southern flank of Pico volcano, which might be associated with the early stages of formation of a more complex magma reservoir. The local and regional tectonics are of paramount importance in the activation of the different magma feeding systems over time. This new information is fundamental to improve the knowledge on the future eruptive behaviour of Pico volcano and can have significant implications on the mitigation of volcanic risk. This multidisciplinary approach can be applied not only to other volcanoes of the Azores but also to poorly monitored oceanic volcanoes, where magma ascent strongly depends on the activation of tectonic systems. |