Diamonds metamorphism

Carbon and oxygen isotope analyses were carried out on marbles occurring in the epidote amphibolite masses from the Iratsu and Tonaru areas of the Sanbagawa metamorphic belt, central Shikoku, Japan and on diamond-bearing dolomitic marbles from the Kumdy-Kol site of the Kokchetav Massif, to compare them and to elucidate their origin. 

The Kokchetav Massif of northern Kazakhstan is a very large, fault-bounded metamorphic complex of Late Proterozoic-Paleozoic protolith age, surrounded by the Caledonian rocks of the Ural-Mongolian fold belt. The Kokchetav UHP and HP belt runs NW-SE extending at least 150 km long and 17 km wide. This massif has attracted much interest since the discovery of metamorphic diamonds. It is the first locality where microdiamonds were found within metamorphic rocks derived from crustal material. 

Shatsky, V.S., Sobolev, N.V., Vavilov, M.A. 1995. Diamond-bearing metamorphic rocks of the Kokchetav Massif (northern Kazakhstan). Ultrahigh-Pressure... 

Sobolev, N.V. Shatsky, V.S. 1990. Diamond inclusions in garnets from metamorphic rocks. Nature, 343, 742-746. 

A/xjkT. In recent investigations on cut stones, an example showing, for the first time, the presence of a seed in the crystal growth of natural diamonds has been discovered [18]. It is also the first example to show the relation between diamonds formed by ultra-high-pressure metamorphic rocks and those formed in ultramafic magma. 

Ultra-high-pressure metamorphic rocks. Diamonds occur sporadically in crystals of garnet or zircon in various ultra-high-pressure metamorphic rocks formed in deep subduction zones. Crystals are of micrometer size, and the morphology is mostly spherulitic or cuboid, but octahedral is also... 

The characteristics of the presolar diamonds also change with the metamorphic grade of the host meteorite. F igure 5.15 shows the typical bimodal release of heavy noble gases (here illustrated by xenon) in Orgueil, an unheated chondrite. This pattern is compared to the xenon-release patterns of two ordinary chondrites that have experienced different degrees of mild metamorphism. The amount of low-temperature gas, labeled P3 for historical reasons, is a sensitive function of temperature. Its abundance correlates well with other indicators of... 

Huss, G. R. (1990) Ubiquitous interstellar diamond and silicon carbide in primitive chondrites abundances reflect metamorphism. Nature, 347, 159-162. 

The source of diamond-bearing kimberlites is uncertain but the stability field of diamond implies a deep-seated origin. Kimberlites are generally believed to have resulted from metamorphism or melting at the deep end of a subducted oceanic plate, the source material being the oceanic lithosphere with... 

Pearson D. G., Davies G. R., and Nixon P. H. (1995) Orogenic ultramafic rocks of UHP (diamond facies) origin. In Ultrahigh Pressure Metamorphism (eds. R. G. Coleman and X. Wang). Cambridge University Press, Cambridge, pp. 456—511. 

Figure 1 Worldwide distribution of UHP localities with diamond (filled diamond) and coesite (filled circle) occurrences. Age of UHP metamorphism in millions of years.

Claoue-Long J. C., Sobolev N. V., Shatsky V. S., and Sobolev A. V. (1991) Zircon response to diamond-pressure metamorphism in the Kokchetav massif. Geology 19, 710—713. 

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