Russian Journal of Earth Sciences
Vol. 4, No. 3, June 2002
Rare earth elements in rocks and minerals
from alkaline plutons of the Kola Peninsula,
NW Russia, as indicators of alkaline magma evolution
A. A. Arzamastsev, F. Bea, L. V. Arzamastseva,
and P. Montero
Abstract
In order to elucidate evolutionary paths for the alkaline ultramafic series of the
Kola province, we studied distribution of rare earth elements (REE) in rocks and constituent
minerals of the rock sequence dunite, clinopyroxenite, melilitolite, meltejgite,
ijolite, nepheline syenite. Abundances of REE and other trace elements were measured in olivine,
melilite, clinopyroxene, nepheline, apatite, perovskite, titanite, and magnetite.
Distribution of
most trace elements in Kovdor-type rocks is shown to differ fundamentally from that in the
Khibiny alkaline ultramafic suite and to have been controlled by perovskite crystallization.
Primary olivine melanephelinitic melts of the Kovdor series are demonstrated to be
characterized by early crystallization of perovskite, the most important REE mineral.
Perovskite co-precipitating with olivine and clinopyroxene leads to a sharp REE depletion
of the residual melt, to produce REE-depleted derivatives, ijolites and nepheline syenites.
By contrast, the genesis of the Khibiny alkaline ultramafic series was complicated by
mixing of minor batches of phonolitic melt with the primary olivine melanephelinitic magma,
which led to changes in the crystallization order of REE-bearing titanates and Ti-silicates
and to enrichment of late melt batches in the most incompatible elements. As a result, Khibiny
ijolites have the highest REE abundances, which are accommodated by high-REE apatite
and titanite.