Compositional evolution and cryptic variation in pyroxenes of the peralkaline Lovozero intrusion, Kola Peninsula, Russia

摘要

The Lovozero alkaline massif is the largest of the world’s layered peralkaline intrusions (~650 km2). We describe the evolution of clinopyroxene from the liquidus to the late residual stage throughout the whole vertical section (2.5 km thick) of the Lovozero Complex. Microprobe data (~990 analyses) of the clinopyroxenes define a relatively continuous trend from diopside containing 15–20% hedenbergite and 10–12% aegirine components, to pure aegirine. The main substitutions during the evolution of the Lovozero pyroxenes are (Na,Fe3+,Ti) for (Ca,Mg,Fe2+). The composition of the pyroxene changes systematically upwards through the intrusion with an increase in Na, Fe3+ and Ti and decrease in Ca and Mg.