Abstract

Magmatic barian titanian phlogopite (BaO = 4.2−11.2 wt% and TiO2 = 10.1−13.1 wt%) occurs in the groundmass and in a magmatic inclusion of olivine leucitites from northeast China. In addition, titanian phlogopite (BaO < 0.3 wt% and TiO2 ≤ 6.4 wt%) formed by reaction between olivine phenocrysts and late fluids also occurs as coronas rimming olivine phenocrysts in associated leucite basanites. Compositions of the barian titanian phlogopite vary systematically; Al2O3 and TiO2 increase and SiO2, MgO, FeO, and K2O decrease with increasing BaO. Substitutions deduced from such variations include Ba + (Al,Fe3+) = K + Si and 2(Mg,Fe2+) = Ti + ☐. Ti-O and Ti-Tschermak's substitutions may also be present in subordinate amounts. The Ba + Al = K + Si substitution is common to most magmatic barian micas, except for some lamproitic micas. In contrast, no general Ti substitution scheme is applicable, as Ti substitutions vary with melt compositions and intensive variables.

These phlogopite samples crystallized as a late phase at low pressures and temperatures. Differences in mineral assemblages between olivine leucitites and leucite basanites contribute significantly to the observed disparities in chemical composition between the barian titanian phlogopite and the corona phlogopite and, in general, among phlogopite from other alkalic magmatic rocks.

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