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prior to obliteration by common pervasive alteration. Study of melt inclusions trapped in
magmatic phenocrysts during crystallisation allows seeing compositions beyond effects of
postmagmatic modifications. The study of other least altered kimberlites emplaced into
magmatic or metamorphic rocks in the terranes containing little or no sedimentary cover,
namely the Gahcho Kué, Jericho, Aaron and Leslie pipes in the Slave Craton (Canada) and
the Majuagaa dyke in southern West Greenland, helped to further enhanced the significance
of the carbonate-chloride melt composition (Kamenetsky et al., 2009b).
The study of olivine and olivine-hosted melt inclusions in partially altered kimberlites from
Canada and Greenland (Kamenetsky et al., 2009b), aimed at comparison with the fresh
Udachnaya-East kimberlite and followed by implications of sodium- and chlorine-rich
compositions of the parental kimberlite melt, has a precedent in the history of petrological
and mineralogical studies of carbonatites. Unlike all ancient intrusive and extrusive
carbonatite rocks composed of calcite and/or dolomite, the presently erupting carbonatitic
magmas of the Oldoinyo Lengai volcano in Tanzania provides evidence for alkali- and
halogen-rich anhydrous melts forming carbonatites. Following the discovery of these
natrocarbonatite lavas (Dawson, 1962b) and building on the ideas of von Eckermann (1948),
the primary/parental nature of such compositions was defended in a number of empirical
(e.g., Clarke & Roberts, 1986; Dawson et al., 1987; Deans & Roberts, 1984; Gittins & McKie,
1980; Hay, 1983; Keller & Zaitsev, 2006; Le Bas, 1987; Schultz et al., 2004; Turner, 1988) and
experimental (Safonov et al., 2007; Wallace & Green, 1988) studies. A strong support for the
role of alkalies and halogens in magmas parental to mafic silicate intrusions and related
carbonatites is further provided by melt/fluid inclusion research (e.g., Andreeva et al., 2006;
Aspden, 1980; Aspden, 1981; Kogarko et al., 1991; Le Bas, 1981; Le Bas & Aspden, 1981;
Panina, 2005; Panina & Motorina, 2008; Veksler et al., 1998). Syn- and postmagmatic release
of alkalies from carbonatite magmas and rocks is recorded respectively in alkaline (mainly
soda-dominant) metasomatic “fenitisation halos” around intrusive carbonatite bodies (e.g.,
(Bailey, 1993; Buhn & Rankin, 1999; Le Bas, 1987; McKie, 1966; Morogan & Lindblom, 1995)
and references therein) and rapid decomposition of alkali- and chlorine-bearing minerals in
the natrocarbonatites (Dawson, 1962b; Genge et al., 2001; Keller & Zaitsev, 2006; Mitchell,
2006). Same processes can be applicable to kimberlitic magmas in general, during and after
their emplacement, as recorded in fenitisation of country rocks (Masun et al., 2004; Smith et
al., 2004 and references therein) and gradation from Na-rich “deep” to Na-poor “shallow”
kimberlite in the Udachnaya-East pipe.
The groundmass of most kimberlites, including altered kimberlites from the Udachnaya
pipe, contain no alkali carbonates and chlorides and have very little Na
2
O (<0.2 wt%). We
believe that alteration disturbs original melt compositions, with the alkaline elements and
chlorine being mostly affected. However, the compositions of melt inclusions and Cl-rich
serpentine are indicative of the chemical signature of a melt in which olivine crystallised
and accumulated. It appears that enrichment in alkalies and chlorine, as seen in unaltered
Udachnaya-East kimberlites, has been significant in other kimberlites prior to their
alteration, and thus can be assigned deep mantle origin.
7.6 Two populations of olivine in kimberlites: Fellow-travellers or close relatives?
Our work on the uniquely unaltered Udachnaya-East kimberlite concurs with what has
been shown in other mineralogical studies of other kimberlites, namely, the presence of
morphologically distinct populations of olivine. One population is represented by large
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