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,
title = {The effects of superheating and cooling rate on olivine growth in chondritic liquid},
author = {M. Auxerre and F. Faure and D. Lequin},
doi = {10.1111/maps.13830},
year = {2022},
date = {2022-01-01},
journal = {Meteoritics \& Planetary Science},
pages = {1--22},
abstract = {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--750textdegreeCh\^{a}1) 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 (\<10textdegreeCh\^{a}1). 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},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
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 |
Florentin, L., Faure, F., Deloule, E., Tissandier, L., Gurenko, A., Lequin, D. Origin of Na in glass inclusions hosted in olivine from Allende CV3 and Jbilet Winselwan CM2: Implications for chondrule formation (Article de journal) Dans: Earth and Planetary Science Letters, vol. 474, p. 160–171, 2017. @article{Florentin_etal2017,
title = {Origin of Na in glass inclusions hosted in olivine from Allende CV3 and Jbilet Winselwan CM2: Implications for chondrule formation},
author = {L. Florentin and F. Faure and E. Deloule and L. Tissandier and A. Gurenko and D. Lequin},
doi = {10.1016/j.epsl.2017.06.038},
year = {2017},
date = {2017-01-01},
journal = {Earth and Planetary Science Letters},
volume = {474},
pages = {160--171},
abstract = {Glass inclusions trapped in Mg-rich olivines within type I chondrules from the Allende (CV3) and Jbilet Winselwan (CM2) chondrites were analyzed by EPMA (Electron Probe Microanalysis) for major elements and by SIMS (Secondary Ion Mass Spectrometry) for Cl and S (analyzed here for the first time in chondrule-hosted glass inclusions). The inclusions from Jbilet Winselwan are poor in Na2O, whereas those from Allende are Na-rich, displaying up to 8wt.% Na2O. The source of Na is a central issue in terms of chondrule origins because of the volatility of Na at high temperature. The wide scatter in Na2O contents of olivine-hosted glass inclusions from chondrules has led the community to propose that Na2O came from late interactions of chondrules with a Si/Na-rich gas. To gain new insights into the origins of the Na2O recorded in glass inclusions, heating experiments (up to 1810◦C) were performed on Allende inclusions in an effort to constrain the initial composition of the trapped melts. Our results demonstrate that sodium (although volatile) does not escape from inclusions during heating, thus confirming that glass inclusions behave as closed systems. Furthermore, heated olivines still bear inclusions containing up to 7.2wt.% of Na2O. Olivines are thought to form at temperatures at which Na is volatile. This implies that (1) Na from glass inclusions cannot come from condensation but rather results from trapping in a Na-rich environment, which implies a high pressure, as in a melting planetasimal (2) there may be two distinct origins for the sodium: an indigenous origin for the sodium trapped inside glass inclusions and a gaseous origin for the sodium recorded in mesostasis from chondrules. Consequently, these results are in favor of a planetesimal origin for olivine from chondrules.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Glass inclusions trapped in Mg-rich olivines within type I chondrules from the Allende (CV3) and Jbilet Winselwan (CM2) chondrites were analyzed by EPMA (Electron Probe Microanalysis) for major elements and by SIMS (Secondary Ion Mass Spectrometry) for Cl and S (analyzed here for the first time in chondrule-hosted glass inclusions). The inclusions from Jbilet Winselwan are poor in Na2O, whereas those from Allende are Na-rich, displaying up to 8wt.% Na2O. The source of Na is a central issue in terms of chondrule origins because of the volatility of Na at high temperature. The wide scatter in Na2O contents of olivine-hosted glass inclusions from chondrules has led the community to propose that Na2O came from late interactions of chondrules with a Si/Na-rich gas. To gain new insights into the origins of the Na2O recorded in glass inclusions, heating experiments (up to 1810◦C) were performed on Allende inclusions in an effort to constrain the initial composition of the trapped melts. Our results demonstrate that sodium (although volatile) does not escape from inclusions during heating, thus confirming that glass inclusions behave as closed systems. Furthermore, heated olivines still bear inclusions containing up to 7.2wt.% of Na2O. Olivines are thought to form at temperatures at which Na is volatile. This implies that (1) Na from glass inclusions cannot come from condensation but rather results from trapping in a Na-rich environment, which implies a high pressure, as in a melting planetasimal (2) there may be two distinct origins for the sodium: an indigenous origin for the sodium trapped inside glass inclusions and a gaseous origin for the sodium recorded in mesostasis from chondrules. Consequently, these results are in favor of a planetesimal origin for olivine from chondrules. |
Tissandier, L., Florentin, L., Lequin, D., Baillot, P., Faure, F. A new heating stage for high temperature/low fO2 conditions (Article de journal) Dans: Journal of Crystal Growth, vol. 458, p. 72–79, 2017. @article{Tissandier_etal2017,
title = {A new heating stage for high temperature/low fO2 conditions},
author = {L. Tissandier and L. Florentin and D. Lequin and P. Baillot and F. Faure},
doi = {10.1016/j.jcrysgro.2016.11.043},
year = {2017},
date = {2017-01-01},
journal = {Journal of Crystal Growth},
volume = {458},
pages = {72--79},
abstract = {Understanding the processes involved in the formation of intracrystalline inclusions can be valuable for both geological studies and industrial production. In view of this, we developed a new heating stage that can operate in extreme conditions. The use of tungsten as the heating material allows temperatures of over 2000 textdegreeC to be reached and also requires that experiments are run under reducing atmospheres. Small samples of metal are needed to calibrate the temperature for each experiment and the fO2 is achieved by a flow of mixed gases (CO, Ar, He). The first experiments run on this device highlight the good agreement between the different ways of estimating the temperature (by the amount of power delivered, the use of a thermocouple or by chemical composition), and a precision of textpm 20 textdegreeC is obtained for temperature determinations. As well as the homogenization of magmatic inclusions in ultramafic rocks, processes such as whisker crystal formation or transcrystalline migration of inclusions can be investigated using the new stage thanks to its very high maximum temperature and to the thermal gradients observed close to the heating wires. This new device looks to be a very promising tool that could easily be adapted for a range of studies by changing the nature and shape of the heating filaments.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Understanding the processes involved in the formation of intracrystalline inclusions can be valuable for both geological studies and industrial production. In view of this, we developed a new heating stage that can operate in extreme conditions. The use of tungsten as the heating material allows temperatures of over 2000 textdegreeC to be reached and also requires that experiments are run under reducing atmospheres. Small samples of metal are needed to calibrate the temperature for each experiment and the fO2 is achieved by a flow of mixed gases (CO, Ar, He). The first experiments run on this device highlight the good agreement between the different ways of estimating the temperature (by the amount of power delivered, the use of a thermocouple or by chemical composition), and a precision of textpm 20 textdegreeC is obtained for temperature determinations. As well as the homogenization of magmatic inclusions in ultramafic rocks, processes such as whisker crystal formation or transcrystalline migration of inclusions can be investigated using the new stage thanks to its very high maximum temperature and to the thermal gradients observed close to the heating wires. This new device looks to be a very promising tool that could easily be adapted for a range of studies by changing the nature and shape of the heating filaments. |
