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element abundances in the rims are highly variable (in wt%: NiO 0.15-0.35, CaO 0.03-0.15,
MnO 0.11-0.2, Cr
2
O
3
0.01-0.11 and Al
2
O
3
0-0.04). In general, the rims are richer in MnO, but
poorer in NiO than the cores with the same Fo content (Fig. 6b). The outermost forsteritic
(Fo96) rims are very enriched in CaO (up to 1 wt%).
4. Mineral and melt inclusions in olivine
Inclusions of different composition are present in almost all grains of the Udachnaya-East
olivine. They can be very abundant in some grains, but rare in others. Three main types of
magmatic inclusions are recognized in the studied samples: crystals, fluid and melt.
Inclusion sizes are variable (<1 to ~400 µm) and the distribution of inclusions within a single
olivine crystal is very heterogeneous, with some parts totally devoid of inclusions, and some
parts so packed with inclusions as to make olivine almost opaque (Fig. 3, 8). The highest
density of inclusions is observed along internal fractures and growth planes (Fig. 3). Crystal
inclusions in olivine of both populations are always primary. Inclusions of melt and fluid in
olivine-I and cores of olivine-II are always restricted to fractures healed with olivine of
different composition, and thus are secondary in origin with respect to their host olivine.
Similar inclusions in the rims of olivine-II show features reminiscent of both primary and
secondary origin (Fig. 8). Melt inclusions in olivine of both populations are predominantly
alkali carbonate-chloride in composition (Fig. 8). Silicate melt inclusions have not been
found in our studies.
The rims of olivine-II grains contain abundant inclusions of different minerals that are never
present in the cores (Kamenetsky et al., 2008; Kamenetsky et al., 2009a). Among them, Cr-
spinel, phlogopite, perovskite and rutile are relatively abundant, whereas magnetite and
picroilmenite are less common. Inclusions of low-Ca pyroxene (Mg# 88-92) occur in both
cores and rims (Fo86-91) in clusters of several (10-30) round and euhedral grains
(Kamenetsky et al., 2008; Kamenetsky et al., 2009a). A common association of low-Ca
pyroxene in the rims includes numerous melt and fluid inclusions, and CO
2
-rich bubbles
adhered to surfaces of pyroxene crystals. The compositions of low-Ca pyroxene inclusions
are characterised by high SiO
2
(53.3-58 wt%), Na
2
O (0.1-0.9 wt%), elevated TiO
2
(0-0.5 wt%),
and low Al
2
O
3
(0.7-1.4 wt%), CaO (0.7-1.7 wt%) and Cr
2
O
3
(0.1-0.6 wt%), compared to
mantle orthopyroxene.
Rare inclusions of high-Ca pyroxene in the Udachnaya-East olivine are restricted to olivine-I
and cores of olivine-II (Fig. 9; Kamenetsky et al., 2008; Kamenetsky et al., 2009a). They occur
as single crystals or clusters of several crystals. They vary in size (25-400 µm), colour
(emerald-green to greyish-green) and shape (round to euhedral-subhedral). Most of them
are intimately associated with the carbonate-chloride material, which forms coating on
surfaces and inclusions inside clinopyroxene grains (Fig. 9). The clinopyroxene inclusions
(Mg# 87.5-94.5 mol%) are in Mg-Fe equilibrium with the host olivine Fo
86.3-93
, and
characterised by low Al
2
O
3
(0.65-2.9 wt%), and high CaO (19.5-23.8 wt%), Na
2
O (0.75-2.3
wt%) and Cr
2
O
3
(0.9-2.6 wt%) contents. Individual crystals show fine-scale compositional
zoning, with a general pattern of MgO and CaO increase, and Na
2
O, Cr
2
O
3
and in some
cases Al
2
O
3
, decrease towards the rims. Major and trace element compositions of high-Ca
pyroxene inclusions overlap with compositions of clinopyroxene from lherzolite nodules in
the Udachnaya-East kimberlite (Kamenetsky et al., 2009a).
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