@article{PAR00011609,
  title = {{Z}onation of {H}2{O} and {F} concentrations around melt inclusions in olivines},
  author = {{L}e {V}oyer, {M}. and {A}simow, {P}. {D}. and {M}osenfelder, {J}. {L}. and {G}uan, {Y}. {B}. and {W}allace, {P}. {J}. and {S}chiano, {P}ierre and {S}tolper, {E}. {M}. and {E}iler, {J}. {M}.},
  editor = {},
  language = {{ENG}},
  abstract = {{S}tudies of both naturally quenched and experimentally reheated melt inclusions have established that they can lose or gain {H}2{O} after entrapment in their host mineral, before or during eruption. {H}ere we report nano{SIMS} analyses of {H}2{O}, {C}l and {F} in olivine around melt inclusions from two natural basaltic samples: one from the {S}ommata cinder cone on {V}ulcano {I}sland in the {A}eolian arc and the other from the {J}orullo cinder cone in the {T}rans-{M}exican {V}olcanic {B}elt. {O}ur results constrain olivine/basaltic melt partition coefficients and allow assessment of mechanisms of volatile loss from melt inclusions in natural samples. {C}l contents in olivine from both samples are mostly below detection limits (0 center dot 03 +/- 0 center dot 01 ppm), with no detectable variation close to the melt inclusions. {A}ssuming a maximum {C}l content of 0 center dot 03 ppm for all olivines, maximum estimates for {C}l partition coefficients between olivine and glass are 0 center dot 00002 +/- 0 center dot 00002. {O}livines from the two localities display contrasting {H}2{O} and {F} compositions: {S}ommata olivines contain 27 +/- 11 ppm {H}2{O} and 0 center dot 28 +/- 0 center dot 07 ppm {F}, whereas {J}orullo olivines have lower and proportionately more variable {H}2{O} and {F} (11 +/- 12 ppm and 0 center dot 12 +/- 0 center dot 09 ppm, respectively; uncertainties are two standard deviations for the entire population). {T}he variations of {H}2{O} and {F} contents in the olivines exhibit clear zonation patterns, increasing with proximity to melt inclusions. {T}his pattern was most probably generated during transfer of volatiles out of the inclusions through the host olivine. {H}2{O} concentration gradients surrounding melt inclusions are roughly concentric, but significantly elongated parallel to the crystallographic a-axis of olivine. {B}ecause of this preferential crystallographic orientation, this pattern is consistent with {H}2{O} loss that is rate-limited by the 'proton-polaron' mechanism of {H} diffusion in olivine. {P}artition coefficients based on olivine compositions immediately adjacent to melt inclusions are 0 center dot 0007 +/- 0 center dot 0003 for {H}2{O} and 0 center dot 0005 +/- 0 center dot 0003 for {F}. {T}he {H}2{O} and {F} diffusion profiles most probably formed in response to a decrease in the respective fugacities in the external melt, owing to either degassing or mixing with volatile-poor melt. {V}olatile transport out of inclusions might also have been driven in part by increases in the fugacity within the inclusion owing to post-entrapment crystallization. {I}n the case of {F}, because of the lack of data on {F} diffusion in olivine, any interpretation of the measured {F} gradients is speculative. {I}n the case of {H}2{O}, we model the concentration gradients using a numerical model of three-dimensional anisotropic diffusion of {H}, where initial conditions include both {H}2{O} decrease in the external melt and post-entrapment enrichment of {H}2{O} in the inclusions. {T}he model confirms that external degassing is the dominant driving force, showing that the orientation of the anisotropy in {H} diffusion is consistent with the proton-polaron diffusion mechanism in olivine. {T}he model also yields an estimate of the initial {H}2{O} content of the {S}ommata melt inclusions before diffusive loss of 6 wt % {H}2{O}. {T}he findings provide new insights on rapid {H}2{O} loss during magma ascent and improve our ability to assess the fidelity of the {H}2{O} record from melt inclusions.},
  keywords = {diffusion ; melt inclusion ; volatile elements ; degassing ; nano{SIMS} ; {MEXIQUE} ; {ITALIE}},
  booktitle = {},
  journal = {{J}ournal of {P}etrology},
  volume = {55},
  numero = {4},
  pages = {685--707},
  ISSN = {0022-3530},
  year = {2014},
  DOI = {10.1093/petrology/egu003},
  URL = {https://www.documentation.ird.fr/hor/{PAR}00011609},
}