Perovskites - Rare Earth Elements in Ultramafic and Mafic Rocks and their Minerals - page 205

K d (perovskite/kimberlite), Wesselton province
K d (perovskite/melilite-nepheline basalt), experimental data
K d (perovskite/siliceous melt), experimental data
Figure 7.4. The graphs of coefficients REE distribution between perovskites and kimberlites, melilite-
nepheline basalts and siliceous melts (experimental data [Jones & Wyllie, 1984]).
(Tanzania) showed that in the cases when there was absence of titanites in these rocks
the values of K d (perovskite/apatite) were: La-9, Ce-16, Nd-9,5. However, when sam-
ples of the same rocks contained titanites, the values of K d (perovskite/apatite) for
these elements were much lower [Dawson et al ., 1994].
Having considered very scarce data on the contents of REE in perovskites, we
emphasize again that this mineral, presented as an accessory phase in some varieties of
magmatic rocks, can accumulate in its structure very substantial LREE amounts and
much smaller quantities of medium and heavy elements. Therefore, if there is a sig-
nificant modal content of perovskite in the rocks it might have a noticeable effect on
the REE distribution in these rocks, which is well illustrated by the kimberlites. The
high values of LREE distribution coefficients between perovskite and its parent melts
indicate that during the isomorphic incoming into its structure the LREE usually pos-
sessed properties of compatible elements.
Taking into account the ability of perovskites to accumulate in its structure very
significant amounts of REE, one should pay attention to another important geochemi-
cal aspect. Thus, the estimates show that a significant portion of the Earth's mantle at
depths greater than 670 km for about 70% might consist of a high-pressure perovskite-
like phase [Urusov & Puscharovskii, 1999; Puscharovskii, Yu., Puscharovskii, D.,
2010]. In this regard, with a considerable degree of conditionality we can assume that
if the perovskite-like phase is similar to normal perovskite not only in its crystal struc-
ture but also in geochemical properties, than those REE, which are accumulated in the
matter of undepleted mantle are probably concentrated in these high-pressure phases
such as CaSi-perovskite and CaTi-perovskite pointed out by Garanin [2006].