@article{fdi:010044263, title = {{O}xygen isotopes composition of sapphires from the {F}rench {M}assif {C}entral : implications for the origin of gem corundum in basaltic fields}, author = {{G}iuliani, {G}aston and {F}allick, {A}. and {O}hnenstetter, {D}. and {P}egere, {G}.}, editor = {}, language = {{ENG}}, abstract = {{A}lluvial and colluvial gem sapphires are common in the basaltic fields of the {F}rench {M}assif {C}entral ({FMC}) but sapphire-bearing xenoliths are very rare, found only in the {M}enet trachytic cone in {C}antal. {T}he {O}-isotope composition of the sapphires ranges between 4.4 and 13.9a{E}uro degrees. {T}wo distinct groups have been defined: the first with a restricted isotopic range between 4.4 and 6.8a{E}uro degrees (n = 22; mean delta {O}-18 = 5.6 +/- 0.7a{E}uro degrees), falls within the worldwide range defined for blue-green-yellow sapphires related to basaltic gem fields (3.0 < delta {O}-18 < 8.2a{E}uro degrees, n = 150), and overlaps the ranges defined for magmatic sapphires in syenite (4.4 < delta {O}-18 < 8.3a{E}uro degrees, n = 29). {A} second group, with an isotopic range between 7.6 and 13.9a{E}uro degrees (n = 9), suggests a metamorphic sapphire source such as biotite schist in gneisses or skarns. {T}he delta {O}-18 values of 4.4-4.5a{E}uro degrees for the blue sapphire-bearing anorthoclasite xenolith from {M}enet is lower than the delta {O}-18 values obtained for anorthoclase (7.7-7.9a{E}uro degrees), but suggest that these sapphires were derived from an igneous reservoir in the subcontinental spinel lherzolitic mantle of the {FMC}. {T}he presence of inclusions of columbite-group minerals, pyrochlore, {N}b-bearing rutile, and thorite in these sapphires provides an additional argument for a magmatic origin. {I}n the {FMC} lithospheric mantle, felsic melts crystallized to form anorthoclasites, the most evolved peraluminous variant of the alkaline basaltic melt. {T}he {O}-isotopic compositions of the first group suggests that these sapphires crystallized from felsic magmas under upper mantle conditions. {T}he second group of isotopic values, typified for example by the {L}e {B}ras sapphire with a delta {O}-18 of 13.9a{E}uro degrees, indicates that metamorphic sapphires from granulites were transported to the surface by basaltic magma.}, keywords = {{F}rance ; {F}rench {M}assif {C}entral ; {B}asalt ; {O}xygen isotopes ; {S}apphires}, booktitle = {}, journal = {{M}ineralium {D}eposita}, volume = {44}, numero = {2}, pages = {221--231}, ISSN = {0026-4598}, year = {2009}, DOI = {10.1007/s00126-008-0214-2}, URL = {https://www.documentation.ird.fr/hor/fdi:010044263}, }