Lang, S., Mollo, S., France, L., Misiti, V., Nazzari, M. Partitioning of Ti, Al, P, and Cr between olivine and a tholeiitic basaltic melt: Insights on olivine zoning patterns and cation substitution reactions under variable cooling rate conditions (Article de journal) Dans: Chemical Geology, vol. 601, p. 120870, 2022. @article{Lang_etal2022,
title = {Partitioning of Ti, Al, P, and Cr between olivine and a tholeiitic basaltic melt: Insights on olivine zoning patterns and cation substitution reactions under variable cooling rate conditions},
author = {S. Lang and S. Mollo and L. France and V. Misiti and M. Nazzari},
doi = {10.1016/j.chemgeo.2022.120870},
year = {2022},
date = {2022-01-01},
journal = {Chemical Geology},
volume = {601},
pages = {120870},
abstract = {The mechanism governing the kinetic growth of olivine in dynamic volcanic settings has been the subject of considerable attention in recent years. Under variable cooling rate (CR) and undercooling (−$Delta$T) regimes, the textual maturation of olivine proceeds from skeletal/dendritic crystals to polyhedral morphologies by infilling of the crystal framework. Owing to the establishment of a diffusion-controlled growth regime, a sharp diffusive boundary layer develops in the melt next to the advancing olivine surface. In this context, we have quantified the apparent partitioning of Ti, Al, P, and Cr between olivine and a Hawaiian tholeiitic basaltic melt at P = 1 at},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The mechanism governing the kinetic growth of olivine in dynamic volcanic settings has been the subject of considerable attention in recent years. Under variable cooling rate (CR) and undercooling (−$Delta$T) regimes, the textual maturation of olivine proceeds from skeletal/dendritic crystals to polyhedral morphologies by infilling of the crystal framework. Owing to the establishment of a diffusion-controlled growth regime, a sharp diffusive boundary layer develops in the melt next to the advancing olivine surface. In this context, we have quantified the apparent partitioning of Ti, Al, P, and Cr between olivine and a Hawaiian tholeiitic basaltic melt at P = 1 at |
Lang, S., Mollo, S., France, L., Misiti, V., Nazzari, M. Kinetic partitioning of major-minor cations between olivine and Hawaiian tholeiitic basalt under variable undercooling and cooling rate conditions (Article de journal) Dans: Chemical Geology, vol. 584, p. 120485, 2021. @article{Lang_etal2021,
title = {Kinetic partitioning of major-minor cations between olivine and Hawaiian tholeiitic basalt under variable undercooling and cooling rate conditions},
author = {S. Lang and S. Mollo and L. France and V. Misiti and M. Nazzari},
doi = {10.1016/j.chemgeo.2021.120485},
year = {2021},
date = {2021-01-01},
journal = {Chemical Geology},
volume = {584},
pages = {120485},
abstract = {In order to elucidate the kinetic partitioning of cations between olivine and basalt, we performed undercooling (−$Delta$T) and cooling rate (CR) experiments at atmospheric pressure and QFM-2 buffer. Starting from the superliquidus temperature of 1250 textdegreeC, a Hawaiian tholeiitic basalt was cooled at the rates of 4 (CR4), 20 (CR20), and 60 (CR60) textdegreeC/h to the final target temperatures of 1175 textdegreeC (−$Delta$T = 35 textdegreeC ; −$Delta$T35) and 1125 textdegreeC (−$Delta$T = 85 textdegreeC ; −$Delta$T85). Results show that polyhedral olivine morphologies are obtained at -$Delta$T35, whereas strong disequilibrium skeletal and/or dendritic textures form at -$Delta$T85. The amount of forsterite in olivine decreases from to 85% to 78% with increasing both -$Delta$T and CR. A diffusive boundary layer also develops in the melt next to the olivine surface and its composition becomes progressively enriched in Ca, owing to its incompatible behavior with the lattice site. Residual melts are progressively depleted in silica and enriched in alkali from CR4 to CR60, but silica-rich melts are observed with increasing -$Delta$T. In terms of Fe2+-Mg exchange, olivines obtained at -$Delta$T35 are always in equilibrium with the diffusive boundary layer, comprising both the interface melt next to the olivine surface and the far-field melt where all chemical gradients cease. At -$Delta$T85, however, the Fe2+-Mg exchange indicates two distinct equilibration stages between olivine core and far-field melt, and between olivine rim and interface melt. Partition coefficients (Kd) of Mg, Fe, Mn, Ca, and Cr calculated at the olivine-melt interface preferentially change as a function of -$Delta$T rather than CR. From -$Delta$T35 to -$Delta$T85, KdMg, KdFe, KdMn, and KdCr remarkably increase, whereas the opposite applies to KdCa. Through the application of equilibrium partitioning models, we found that Mg, Fe, Mn, and Ca are incorporated into the olivine lattice site at near-equilibrium proportions. This generally good agreement with modeling data demonstrates that diffusive mass transport of cations in our experiments occurred under the conditions of local equilibrium at the olivine surface. In contrast, marked deviations from the expected equilibrium are found for KCr in response to the major influence of crystal field stabilization energy on cation incorporation.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In order to elucidate the kinetic partitioning of cations between olivine and basalt, we performed undercooling (−$Delta$T) and cooling rate (CR) experiments at atmospheric pressure and QFM-2 buffer. Starting from the superliquidus temperature of 1250 textdegreeC, a Hawaiian tholeiitic basalt was cooled at the rates of 4 (CR4), 20 (CR20), and 60 (CR60) textdegreeC/h to the final target temperatures of 1175 textdegreeC (−$Delta$T = 35 textdegreeC ; −$Delta$T35) and 1125 textdegreeC (−$Delta$T = 85 textdegreeC ; −$Delta$T85). Results show that polyhedral olivine morphologies are obtained at -$Delta$T35, whereas strong disequilibrium skeletal and/or dendritic textures form at -$Delta$T85. The amount of forsterite in olivine decreases from to 85% to 78% with increasing both -$Delta$T and CR. A diffusive boundary layer also develops in the melt next to the olivine surface and its composition becomes progressively enriched in Ca, owing to its incompatible behavior with the lattice site. Residual melts are progressively depleted in silica and enriched in alkali from CR4 to CR60, but silica-rich melts are observed with increasing -$Delta$T. In terms of Fe2+-Mg exchange, olivines obtained at -$Delta$T35 are always in equilibrium with the diffusive boundary layer, comprising both the interface melt next to the olivine surface and the far-field melt where all chemical gradients cease. At -$Delta$T85, however, the Fe2+-Mg exchange indicates two distinct equilibration stages between olivine core and far-field melt, and between olivine rim and interface melt. Partition coefficients (Kd) of Mg, Fe, Mn, Ca, and Cr calculated at the olivine-melt interface preferentially change as a function of -$Delta$T rather than CR. From -$Delta$T35 to -$Delta$T85, KdMg, KdFe, KdMn, and KdCr remarkably increase, whereas the opposite applies to KdCa. Through the application of equilibrium partitioning models, we found that Mg, Fe, Mn, and Ca are incorporated into the olivine lattice site at near-equilibrium proportions. This generally good agreement with modeling data demonstrates that diffusive mass transport of cations in our experiments occurred under the conditions of local equilibrium at the olivine surface. In contrast, marked deviations from the expected equilibrium are found for KCr in response to the major influence of crystal field stabilization energy on cation incorporation. |
France, L., Brouillet, F., Lang, S. Early carbonatite magmatism at Oldoinyo Lengai volcano (Tanzania) : carbonatite--silicate melt immiscibility in Lengai I melt inclusions (Article de journal) Dans: Comptes Rendus. Géoscience ?Ĭ Sciences de la Plan`ete, vol. 353, no. S2, p. 273–288, 2021. @article{France_etal2021,
title = {Early carbonatite magmatism at Oldoinyo Lengai volcano (Tanzania) : carbonatite--silicate melt immiscibility in Lengai I melt inclusions},
author = {L. France and F. Brouillet and S. Lang},
doi = {10.5802/crgeos.99r/geoscience/},
year = {2021},
date = {2021-01-01},
journal = {Comptes Rendus. G\'{e}oscience ?\u{I} Sciences de la Plan`ete},
volume = {353},
number = {S2},
pages = {273--288},
abstract = {Carbonatites are unusual C-rich alkaline magmas that have been reported throughout the geological record. Nevertheless, there is only one currently active carbonatite system on Earth : Oldoinyo Lengai stratovolcano in northern Tanzania (God’s mountain in Maasai culture). Presentday Lengai carbonatites are natrocarbonatites, peculiar Na-rich carbonatites that, under atmospheric conditions, alter and leach to compositions similar to the more common Ca-carbonatites within weeks, preventing any long-term geological record of such Na-rich magmas. It follows that the oldest report of natrocarbonatites at Oldoinyo Lengai dates to the 19th century. Here, by using samples from the Lengai I cone (`E11 ka), we show that immiscible silicate--carbonatite melts were already present at reservoir conditions at that time. Measurements of three-phase (carbonatite + silicate + gas) melt inclusions from Lengai I highlight that their chemical compositions were similar to those of immiscible melts recently present in the reservoir. Alkaline carbonatites in melt inclusions from both Lengai I and historical explosive eruptions are enriched in Ca relative to those historically effused at the surface and likely record higher equilibrium temperatures (\>1100 textdegreeC). We also report chemical maps that qualitatively document elemental partitioning between immiscible silicate--carbonatite melts.We show that at the melt inclusions’ entrapment conditions Si, Fe, K, Na, and Cl are compatible with the silicate phase when C, Ca, P, Sr, Ba, and F are compatible with the carbonate phase.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Carbonatites are unusual C-rich alkaline magmas that have been reported throughout the geological record. Nevertheless, there is only one currently active carbonatite system on Earth : Oldoinyo Lengai stratovolcano in northern Tanzania (God’s mountain in Maasai culture). Presentday Lengai carbonatites are natrocarbonatites, peculiar Na-rich carbonatites that, under atmospheric conditions, alter and leach to compositions similar to the more common Ca-carbonatites within weeks, preventing any long-term geological record of such Na-rich magmas. It follows that the oldest report of natrocarbonatites at Oldoinyo Lengai dates to the 19th century. Here, by using samples from the Lengai I cone (`E11 ka), we show that immiscible silicate--carbonatite melts were already present at reservoir conditions at that time. Measurements of three-phase (carbonatite + silicate + gas) melt inclusions from Lengai I highlight that their chemical compositions were similar to those of immiscible melts recently present in the reservoir. Alkaline carbonatites in melt inclusions from both Lengai I and historical explosive eruptions are enriched in Ca relative to those historically effused at the surface and likely record higher equilibrium temperatures (>1100 textdegreeC). We also report chemical maps that qualitatively document elemental partitioning between immiscible silicate--carbonatite melts.We show that at the melt inclusions’ entrapment conditions Si, Fe, K, Na, and Cl are compatible with the silicate phase when C, Ca, P, Sr, Ba, and F are compatible with the carbonate phase. |
