@article{PAR00012379,
  title = {{E}xperimental derivation of nepheline syenite and phonolite liquids by partial melting of upper mantle peridotites},
  author = {{L}aporte, {D}. and {L}ambart, {S}. and {S}chiano, {P}ierre and {O}ttolini, {L}.},
  editor = {},
  language = {{ENG}},
  abstract = {{P}iston-cylinder experiments were performed to characterize the composition of liquids formed at very low degrees of melting of two fertile lherzolite compositions with 430 ppm and 910 ppm {K}2{O} at 1 and 1.3 {GP}a. {W}e used the microdike technique ({L}aporte et al., 2004) to extract the liquid phase from the partially molten peridotite, allowing us to analyze liquid compositions at degrees of melting {F} down to 0.9%. {A}t 1.3 {GP}a, the liquid is in equilibrium with olivine + orthopyroxene + clinopyroxene + spinel in all the experiments; at 1 {GP}a, plagioclase is present in addition to these four mineral phases up to about 5% of melting ({T} approximate to 1240 degrees {C}). {I}mportant variations of liquid compositions are observed with decreasing temperature, including strong increases in {S}i{O}2, {N}a2{O}, {K}2{O}, and {A}l2{O}3 concentrations, and decreases in {M}g{O}, {F}e{O}, and {C}a{O} concentrations. {T}he most extreme liquid compositions are phonolites with 57% {S}i{O}2, 20-22% {A}l(2){O}3, {N}a2{O} + {K}2{O} up to 14%, and concentrations of {M}g{O}, {F}e{O}, and {C}a{O} as low as 2-3%. {R}eversal experiments confirm that low-degree melts of a fertile lherzolite have phonolitic compositions, and p{MELTS} calculations show that the amount of phonolite liquid generated at 1.2 {GP}a increases from 0.3% in a source with 100 ppm {K}2{O} to 3% in a source with 2000 ppm {K}2{O}. {T}he enrichment in silica and alkalis with decreasing melt fraction is coupled with an increase of the degree of melt polymerization, which has important consequences for the partitioning of minor and trace elements. {T}hus {T}i4+ in our experiments and, by analogy with {T}i4+, other highly charged cations, and rare earth elements become less incompatible near the peridotite solidus. {O}ur study brings a strong support to the hypothesis that phonolitic lavas or their plutonic equivalents (nepheline syenites) may be produced directly by partial melting of upper mantle rock-types at moderate pressures (1-1.5 {GP}a), especially where large domains of the subcontinental lithospheric mantle has been enriched in potassium by metasomatism. {T}he circulation of low-degree partial melts of peridotites into the upper mantle may be responsible for a special kind of metasomatism characterized by {S}i- and alkali-enrichment. {W}hen they are unable to escape by porous flow, low-degree melts will ultimately be trapped inside neighboring olivine grains and give rise to the silica- and alkali-rich glass inclusions found in peridotite xenoliths.},
  keywords = {upper mantle ; lherzolite ; partial melting ; phonolite ; mantle ; metasomatism ; potassium},
  booktitle = {},
  journal = {{E}arth and {P}lanetary {S}cience {L}etters},
  volume = {404},
  numero = {},
  pages = {319--331},
  ISSN = {0012-821{X}},
  year = {2014},
  DOI = {10.1016/j.epsl/2014.08.002},
  URL = {https://www.documentation.ird.fr/hor/{PAR}00012379},
}