The objectives are: - To understand how the carbon phases, graphite and diamond, can be formed and transported in carbonate-rich igneous rocks, including testing the hypotheses that (1) diamond and graphite can be precipitated from carbonate melts and that (2) the only known diamondiferous carbonatites s.s. (Uzbekistan) are formed in a post-collisional tectonic setting. - To test the hypothesis that carbonatites and kimberlites are closely related and can both originate from diamond-producing mantle depths. Diamonds fascinate scientists and the public alike but the actual mechanism by which they form is still unclear. Studies of diamonds indicate an important role for CO2-rich fluids or carbonate melts. This project takes a distinct and new approach to the relationship between diamond and carbonate melt. Instead of studying minute inclusions in diamonds, it uses new discoveries of diamond- and graphite-bearing carbonatites to investigate whether native carbon can be precipitated from carbonate melts. Previous experiments by our group suggest that this is possible. Two other key examples will also be studied. Graphite-bearing carbonatites at Gremyakha Vyrmes, Kola, Russia will provide a comparison with Transbaikalia. Diamond-bearing calcite-kimberlite dykes in West Greenland represent the most usual diamond host rock, in which it might be expected that the diamonds would be xenocrysts transported by, rather than precipitated from, the kimberlite. However, these rocks are calcite-rich and a good comparison with the Uzbekistan diamondiferous carbonatites. They are closely associated with kimberlite. The research programme consists of (1) analysis and petrological understanding of the four examples, using international collaboration to produce comparable data sets; (2) experimental petrology to test precipitation of diamond and graphite in these rocks; (3) computer modelling of magma mixing and mingling processes in transport and emplacement and (4) geochronology and geochemistry to test whether the rare tectonic setting of Uzbekistan diamond-bearing carbonatites at the western end of the Tien Shan mountains relates to a post-collisional tectonic setting and can be used for exploration elsewhere. Eight organisations are involved (5 NIS and 3 INTAS). This is the first such grouping of project partners and the comparison of the 4 localities gives a unique perspective on the relationships between carbonate and graphite/diamond. The project provides a new dimension to the understanding of native carbon and carbonate melts. The results will be used by scientists studying diamond and graphite genesis, mantle processes, including the deep earth carbon cycle, and magma genesis and evolution. They will provide new insights into the relationship between kimberlite and carbonatite and may provide a new challenge to conventional thinking on the depth of generation of these melts. The conclusions will be directly relevant to diamond exploration.
Chernogolovka, Moscow Region