Compositional, structural and vibrational spectroscopic characteristics of feldspar megacrysts from southern Slovakia

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Marco E. Ciriotti
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Compositional, structural and vibrational spectroscopic characteristics of feldspar megacrysts from southern Slovakia

Messaggio da Marco E. Ciriotti » mer 24 ott, 2018 11:18

Referenza:
▪ Huraiová, M., Lengauer, C.L., Abart, R., Hurai, V. (2018): Compositional, structural and vibrational spectroscopic characteristics of feldspar megacrysts in alkali basalts from southern Slovakia. Journal of Geosciences, 63, 215-226.

Abstract:
Feldspar megacrysts in Late Miocene-Pliocene maars, diatremes and basaltic lava flows in the northern part of the Pannonian Basin span the compositional range from Na-sanidine, through anorthoclase to oligoclase and andesine. Newly formed An82 plagioclase (bytownite) crystallized within composite melt inclusions hosted by the oligoclase. Powder X-ray diffraction data indicate strong structural disorder diagnostic of the high albite-high sanidine series typical of magmatic feldspars. The magmatic origin is also corroborated by chemical compositions, which plot along the 700 ± 50 °C solvus, with the exception of the most sodic Ab79 plagioclase megacryst projecting along the 600 °C isotherm. Vibrational spectroscopic records document that the basic groups of magmatic feldspars can be identified by the specific pattern of the group I and IV bands in the 350-600 cm-1 range. The IVa band at 560-570 cm-1 is diagnostic for triclinic feldspars. The anorthite and orthoclase contents can be inferred from the 506-515 cm-1 (Ia) and 473-486 cm-1 (Ib) peak separation values combined with the Ia bandwidth.
Marco E. Ciriotti

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