Mechanisms and conditions of Ti and Cr incorporation in mantle phlogopite: the results of atomistic simulation

Modeling of eight mechanisms for the incorporation Ti4+ and Cr3+ impurity components into phlogopite was carried out by a semi-empirical method using GULP (General Utility Lattice Program) software. The calculation thermodynamic mixing properties in range 1–7 GPa 373–1573 K analysis structure geometry simulated solid solutions provided following energy-preferred schemes isomorphic substitution: VI(Mg2+) + 2IV(Si4+) = VI(Ti4+) 2IV(Al3+) VI(□) 2IV(Ti4+), IV(Si4+) VI(Cr3+) IV(Al3+), 3VI(Mg2+) VI(Al3+) VI(□). It is shown scheme 2VI(Mg2+) illustrating entrance Ti with formation vacancy realized case microconcentrations only. Accumulation high-Ti contents associates octahedral site. This provides via 2IV(Ti4+) (Mg, Fe2+) 2OH− 2O2− that high-Cr concentrations (> 5.5 wt % Cr2O3) accompanied an increase number vacancies site proportion dioctahedral component K(Al, Cr, □)2AlSi3O10(OH)2.