Zircons - Rare Earth Elements in Ultramafic and Mafic Rocks and their Minerals - page 140

of almost straight lines with positive slope, are complicated by intense positive Ce
anomalies.
Eclogites. While isotopic dating of eclogites from some metamorphic provinces
of Norway by using U-Pb zircon method in the latter there have also been estimated
REE contents [Root et al ., 2004]. It was ascertained that the total REE content in
these zircons vary in the range of 28-54 ppm with the average of 42 ppm (Table 4.2).
The zircons from eclogites of Flatraket province (Norway) that were studied in more
detail turned out to be almost identical, both in the general level of REE accumula-
tion and the configuration of REE patterns, that in each case are complicated by
positive Ce anomalies (Figure 4.2). The average value of the intensity index of these
anomalies - (Ce/Ce*) n parameter - is 5.6. For the heavy REE the patterns of these zir-
cons have a form of shallow lines, indicating a weak fractionation of these elements.
Root et al. suggested that the characteristics of REE composition of zircons they stud-
ied are caused by the presence in their crystals of syngenetic or later microinclusions
of garnet, enriched with pyrope component. The zircons from eclogites of Norwegian
province called Verpeneset differ from the mineral of the other provinces by a much
more significant enrichment with HREE and less intense positive Ce anomalies.
In the zircons from eclogites of Monte-Rosa complex (Western Alps) the content
of LREE, excepting Ce, is below the limits of detection by the analytical method used.
In addition, chondrite-normalized contents of Yb and Lu in them exceed 100 t.ch.
[Liati & Froitzheim, 2006] (Table 4.2). In order to finish the description of zircons
from eclogites, we should add that in their samples from eclogites exposed in Kuru-
Vaara manifestation (Kola Peninsula, Russia) [Kaulina, 2010] the total REE contents
range from 10 to 176 ppm and the value of (Ce/Ce*) n parameter varies in the range of
2.4-3.7. Moreover, their patterns often show intense negative Nd anomalies, which
were not observed in the patterns of zircons from eclogites described above.
Minettes. Zircons from these rocks are studied by the example of dikes sam-
ples that are cutting the metamorphic complex within Kirovograd block (Ukraine)
[Yatsenko et al ., 2000]. Note that these minettes have previously been described as
lamproites [Belousova et al ., 1998]. The minette samples were selected from the core
of several holes drilled in order to estimate the prospects for diamond-bearing of these
rocks. They usually have a porphyric structure due to the presence of phenocrysts of
phlogopite, biotite, hornblende, diopside, rarely - of olivine, which are immersed in
the fine- and medium-granular matrix. In the content of the latter there are micro-
crystals of zircon, common potash feldspar, pseudo-leucite, plagioclase and quartz.
The zircons presented in minettes are heterogeneous in size, shape and color of grains.
The dominating ones are well-faceted crystals of different habit; the rarely seen are
fragments of crystals, as well as grains of irregular shape with evidence of melting with
observed fluid microinclusions. The values of Zr/Hf parameter in zircons from this
collection vary in a relatively narrow range. Additionally, the contents of most trace
elements, including REE, vary widely. At the same time the contents of Y are higher
than the contents of U, and the latter are higher than in zircons from kimberlites.
By the general level of REE accumulation the analyzed zircons from minettes of
Kirovograd block were divided into four types. The grains of zircons that are pre-
vailing in this collection were assigned to the 1st type and the total REE content in
them ranges from 160 to 1400 ppm (Table 4.3). Zircons of this type have almost
identical REE patterns by configuration, which usually show positive Ce anomalies of