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 and Y approximate to Z brown. The studied oxykinoshitalite, characterized by micro-Raman spectroscopy, electron microprobe WDS (wavelength-dispersive system), and secondary-ion mass spectrometry (SIMS), was compared with the type material from the Fernando de Noronha 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)(Sigma 0.97)(Mg1.98Fe0.55Ti0.48)(Sigma 3.01)(Si2.42Al1.56)(Sigma 3.98) O-10[O1.17F0.62(OH)(0.21)](Sigma 2.00). The lack of chemical zoning and the enrichment in Zr and Nb in the groundmass crystals of the Hyblean oxykinoshitalite suggest formation during the final crystallization stage of a basaltoid magma with ocean island basalt (OIB) affinity. Most likely, the magma originated by partial melting of metasomatized ultramafic rocks in the Hyblean crustal basement.
Micro-Raman spectroscopy and SIMS characterization of oxykinoshitalite in an olivine nephelinite from the Hyblean Plateau (Sicily, Italy)
Ottolini Luisa;
2012
Abstract
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 and Y approximate to Z brown. The studied oxykinoshitalite, characterized by micro-Raman spectroscopy, electron microprobe WDS (wavelength-dispersive system), and secondary-ion mass spectrometry (SIMS), was compared with the type material from the Fernando de Noronha 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)(Sigma 0.97)(Mg1.98Fe0.55Ti0.48)(Sigma 3.01)(Si2.42Al1.56)(Sigma 3.98) O-10[O1.17F0.62(OH)(0.21)](Sigma 2.00). The lack of chemical zoning and the enrichment in Zr and Nb in the groundmass crystals of the Hyblean oxykinoshitalite suggest formation during the final crystallization stage of a basaltoid magma with ocean island basalt (OIB) affinity. Most likely, the magma originated by partial melting of metasomatized ultramafic rocks in the Hyblean crustal basement.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
