New Identity of the Kimberlite Melt: Constraints from Unaltered Diamondiferous Udachnaya – East Pipe Kimberlite, Russia - Advances in Data, Methods, Models and Their Applications in Geoscience - page 181

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New Identity of the Kimberlite Melt:
Constraints from Unaltered
Diamondiferous Udachnaya -
East Pipe Kimberlite, Russia
Vadim S. Kamenetsky, Maya B. Kamenetsky and Roland Maas
University of Tasmania,
University of Melbourne,
Australia
1. Introduction
Kimberlite magmas are in many aspects unusual compared to other terrestrial magmatic
liquids. They are very rare and occur in small volumes, but their intimate relationships with
diamonds make them invaluable to the scientific and exploration communities. The
association of kimberlite rocks with diamonds and deep-seated mantle xenoliths links the
origin of parental kimberlite magmas to the highest known depths (> 150 km) of magma
derivation (e.g. Dawson, 1980; Eggler, 1989; Girnis & Ryabchikov, 2005; Mitchell, 1986;
Mitchell, 1995; Pasteris, 1984). Kimberlite magmas would have one of the lowest viscosities
and highest buoyancies that enable exceptionally rapid transport from the source region
(Canil & Fedortchouk, 1999; Eggler, 1989; Haggerty, 1999; Kelley & Wartho, 2000; Sparks et
al., 2006) and preservation of diamonds.
Despite significant research efforts, there is still uncertainty about the true chemical identity
of kimberlite parental melts and their derivates. Kimberlite magmas are always
contaminated by large quantities of lithic fragments and crystals, unrelated to the evolution
of the parental melt. In most cases kimberlites are severely modified by syn- and post-
magmatic changes that have altered the original alkali and volatile element abundances.
These problems are reflected in the definition of the kimberlite rock as “ both a contaminated
and altered sample of its parent melt ” (Pasteris, 1984). Numerous other definitions of the
kimberlite commonly reflect on ultramafic compositions and enrichment in volatiles (CO 2
and H 2 O; Clement et al., 1984; Kjarsgaard et al., 2009; Kopylova et al., 2007; Mitchell, 1986;
Mitchell, 2008; Patterson et al., 2009; Skinner & Clement, 1979) which are supposedly
inherited from parental magmas.
The physical properties of a kimberlite magma directly, and occurrence of diamonds
indirectly, relate to the enrichment in carbonate components which are represented in
common kimberlites by calcite and dolomite. The abundant carbonate component in
kimberlite rocks is counter-balanced by a more abundant olivine (ultramafic) component,
represented by olivine fragments and crystals that are commonly affected by
serpentinisation. The ultramafic silicate compositions of kimberlites are ascribed to