Geohemija flogopita i biotita iz semilamprofirsko/lamprofirskih stijena Velikog Majdana, Srbija

Micas of the semilamprophyre/lamprophyric rocks from Veliki Majdan, Serbia

Abstract

Fero-magnesian trioctahedral micas occurs in semilamprophyre/lamprophyric dykes from V. Majdan area. The jointly occurrence of phlogopites and biotites in the same rock (magma) is peculiar from petrogenetic and geochemical point of view and is hardly noticeable by routine petrographic examination. The phlogopite from V. Majdan area is highly magnesium with Mg#=0.88-0.89, and with high content of Cr₂O₃ up to 2.35 %. Trace elements chemistry and thermobarometer calculation suggests crystallization from metasomatized upper-mantle source. Relative to phlogopite, geochemical features of biotites from V. Majdan area are very different with much lower Mg# (0.40-0.46), lower content of Cr₂O₃ and higher content of Al₂O₃ and TiO₂. Content of trace-elements and thermobarometer calculation suggests crystallization from the lower parts of the crust. This specific coexistence of two consanguine micas cannot be paragenetic suggesting mingling and mixing of two different types of magma: lamprophyric (upper mantle origin) and acid one (crustal origin).