Compositional variation of perovskite-group minerals from the carbonatite complexes of the Kola Alkaline Province, Russia

Perovskite-group minerals from the carbonatite complexes of the Kola Alkaline Province, Russia, are in most instances members of the perovskite - lueshite - loparite-(Ce) - latrappite solid-solution series. From early ultramafic rocks to late calcite carbonatite, the composition of primary perovskite evolves by enrichment in Na, Nb and Fe, and represents a combination of evolutionary trends toward lueshite and latrappite. These trends culminate with the appearance of lueshite and cerian lueshite in late-stage dolomite carbonatite, and Nb-Fe-rich perovskite in some examples of calcite carbonatite. The enrichment of perovskite in the lueshite and latrappite components results in an increase in the unit-cell parameter and tilt angle of the (Ti,Fe,Nb)O-6 octahedra. Secondary perovskite and loparite occur as a replacement and overgrowth mantle on primary perovskite in ultramafic rocks, foidolite and carbonatite. These compositions define a loparite evolutionary trend, represented by increases in Na and LREE, that is commonly accompanied by an increase in Nb and Th contents. The crystallization of secondary cerian perovskite and loparite results from either deuteric or metasomatic processes, and involves the interaction of primary perovskite with fluids derived from a cognate alkaline or carbonatitic source.