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During heating stage experiments with round, relatively small (40-60 µm) melt inclusions,
melting begins at ~160 o C, as indicated by jolting movements of either solid phases or
vapour bubbles. At 420-580 o C bubble movements increase, indicating the appearance of the
liquid phase (melt). Daughter phases experience some changes in their relative position, size
and shape at 540-600 o C. At >600 o C we record a number of liquid globules that move freely
and change shape continuously (Fig. 8d). The outline of a single globule is always smoothly
curved: it can instantaneously change from spherical to cylindrical, embayed or lopsided,
similar to an amoeba. With further heating, the number and size of the globules, as well as
the number and size of vapour bubbles, gradually decreases. Homogenisation of the
inclusions (except some opaque crystals) occurs when the globules and vapour bubbles
disappear almost simultaneously (within 20-30 o C) at 660-760 o C (Fig. 8e).
During slow cooling (5-20 o C/min), vapour bubbles nucleate at 690-650 o C and then
progressively increases in size. Cooling to 610-580°C, the inclusions acquire a 'foggy”
appearance for a split second. This process can be best described as the formation of
emulsion, i.e, microglobules of liquid in another liquid (melt immiscibility). Microglobules
coalesce immediately into elongate or sausage-like pinkish globules. The neighbouring
globules (“boudins”) are subparallel, and are grouped into regularly aligned formations
with a common angle of ~75-80 o . A resemblance to a skeletal or spinifex texture is evident
for several seconds, after which the original “pinch-and-swell structure” pulls apart giving
rise to individual blebs of melt. The latter coalesce and become spherical with time or
further cooling. They continue floating, but slow down with decreasing temperature and
further coalescence. The exact moment of crystallisation or complete solidification is not
detected.
5. Chloride-carbonate nodules in kimberlite
The major component of the kimberlite groundmass, carbonate-chloride in composition,
sometimes form large segragations (“nodules”, Fig. 10; Kamenetsky et al., 2007a;
Kamenetsky et al., 2007b). Such samples were collected from fresh kimberlite at the
stockpiles of the Udachnaya-East pipe. The assumed depth of their origin in the mine pit is
~500 m. The nodules vary in size from a few cm to 0.5 x 1.5 m, but are commonly 5 to 30 cm
across. The shapes are usually round and ellipsoidal, but angular nodules were also
encountered. The nodules have very distinct contacts with the host kimberlite, but without
any thermometamorphic effects. The contacts are composed of thin (< 1mm) breccia-like
aggregate of olivine, calcite, sodalite, phlogopite-tetraferriphlogopite, humite-clinohumite,
Fe-Mg carbonates, perovskite, apatite, magnetite, djerfisherite (K 6 (Cu,Fe,Ni) 25 S 26 Cl) and
alkali sulphates in a matrix of chlorides. Olivine grains present at the contact with nodules
belong to two types: zoned euhedral crystals similar to the Udachnaya-East groundmass
olivine-II, and grains with highly irregular shapes and “mosaic” distributions of Fe-Mg.
Based on mineralogy the nodules can be separated into two major groups - chloride (Fig.
10a, b) and chloride-carbonate (Fig. 10 c-e). Chloride minerals are mainly represented by
halite with included round grains of sylvite. The grain size, halite colour and transparency
are highly variable, ranging from translucent to milky white and from white to all shades of
blue. White and blue halite is often randomly interspersed, although in some coarse-grained
nodules the interior parts are blue and dark-blue coloured, whereas rims are almost
colourless (Fig. 10b). Chloride nodules always contain variable amount of fine-grained
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