Micro-Raman spectroscopy and SIMS characterization of oxykinoshitalite in an olivine nephelinite from the Hyblean Plateau (Sicily, Italy).

A Ba-Ti rich oxymica occurs in an olivine nephelinite from S. Demetrio High in the northern margin of the Hyblean Plateau(Sicily, Italy). The rock sample exhibits a porphyritic texture formed by olivine, clinopyroxene, nepheline, titanian magnetite, apatite,and rare subhedral tabular mica crystals, which have a perfect cleavage on {001}, and a strong pleochroism with X pale brown andYZ brown. The studied oxykinoshitalite, characterized by micro-Raman spectroscopy, electron microprobe WDS (wavelengthdispersivesystem), and secondary-ion mass spectrometry (SIMS), was compared with the type material from the Fernando deNoronha island (Pernambuco, Brazil). Structural formula of the Hyblean oxykinoshitalite, calculated on the basis of 7 (Si, Al, Fe, Mg,Ti), is (Ba0.51K0.41Na0.04Ca0.01)0.97(Mg1.98Fe0.55Ti0.48)3.01(Si2.42Al1.56)3.98 O10[O1.17F0.62(OH)0.21]2.00. The lack of chemicalzoning and the enrichment in Zr and Nb in the groundmass crystals of the Hyblean oxykinoshitalite suggest formation during the finalcrystallization stage of a basaltoid magma with ocean island basalt (OIB) affinity. Most likely, the magma originated by partialmelting of metasomatized ultramafic rocks in the Hyblean crustal basement.