Compositional, structural and vibrational spectroscopic characteristics of feldspar megacrysts in alkali basalts from southern Slovakia
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.
SNIP (Scopus, 2017): 1.120
IF (ISI, 2017): 1.415
5 YEAR IF (ISI, 2017): 1.738
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