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Kimberlitic and non-kimberlitic diamondiferous rocks and probable models of diamond generation.

Lapin A.V.*, Belov S.V.**, Kljucharev D.S.

* The Institute of Mineralogy, Geochemistry and Crystal Chemistry of Rare Elements, Moscow, Russia;

** Vernadsky Geological Museum of RAS, Moscow, Russia.

 

In recent years, numerous occurrences of non-kimberlitic diamondiferous igneous and metamorphic rocks of varied composition have been detected in different structural segments of the Earth’s crust. The majority of non-kimberlitic diamondiferous complexes refer to the orogenic collision zones of active continental margins, gneiss-eclogitic ultrametamorphic belts, volcanic island arcs, etc. (Kimberlites and non-kimberlitic diamondiferous rocks generation 2010; Kaminsky,2007). On the geodynamic conditions of formation, these diamondiferous complexes significantly differ from kimberlites typical of the stable ancient cratons.

With this account, the numerous attempts to explain various occurrences of non-kimberlitic diamondiferous rocks, similar to kimberlites, are not productive, and it becomes necessary to analyze possible conditions of diamonds generation different from traditional kimberlitic diamondformation. This is most obvious, because theoretic and experimental works in the recent decades proved possible synthesis of diamonds under varied parental environments and different thermodynamic parameters, including fairly low-temperature and low-baric conditions; this is one the arguments  in favor of the principle conclusion about polygenic position of diamonds in the nature.

Analyzing the modern state of the problem of diamondiferous igneous and metamorphic rocks generation with account of the experimental results in diamond synthesis, the following probable models of diamondiferous rocks generation can be outlined suitable to various thermodynamic conditions and natural geodynamic environments:

“Kimberlitic” model (ancient cratons) – diamond crystallization in the melted matter of the upper mantle and the intermediate zone that is, perhaps, partially continued in the kimberlitic magma in the area of thermodynamic diamond stability (P>4ÃÏà, T>1270°K) according to the diagram of phase equilibrium under static conditions.  In accordance with this model kimberlites are confined to the relatively stable cold blocks with deep lithospheric roots, and they are accompanied by the deepest mantle paragenesis. Thus, kimberlitic diamonds are protominerals of mantle peridotites and eclogites, and they are evacuated by the kimberlitic magma simultaneously with xenogenic material of mantle rocks from the area of thermodynamic stability of minerals; this does not exclude both possible continuation of growth of diamond crystals in the kimberlitic magma and their partial dissolution during transportation to the surface.

“Collision” model (orogenic folded belts and active continental margins) – diamond crystallization in the upper parts of the mantle and low part of the crust in the rocks of varied composition under conditions of the stressed-deformation state due to abnormal stress in the zones of continental collision and subduction accretion-collision zones of active continental margins. (Examples: basalts of volcanoes Drevny Ichinsky and Almazny on Kamchatka [Kutyev, Kutyeva, 1975; Kaminsky and oth. 1979]; carbonatite-like rocks of Chatagaisk complex in the Tein-Shan and oth. [Lapin, Divaev, Kostitsin, 2005; Golovko, Divaev, 2007]). According to M.V. Gzovsky (1975), P.N. Kropotkin (1996) and V.T. Filatova with co-authors (2002), the values of most tangent stresses under these conditions can significantly exceed lithostatic load and at the depth up to 20 km can account for 10-15 kbar and locally reach 50 kbar for short time.

Typical diamond minerals indicators are absent. Reduction conditions , necessary for diamond generation, are provided by abyssal fluids and appear in the presence of moissanite, graphite, native metals (Au, Ag, Pt, Pb, Cu, and oth.) and their alloys.

The model of the gas-fluid synthesis of diamonds in open catalytic systems (zones of cataclasites and metasomatites, in association with regional tectonic faults, powerful thrusts) – diamond crystallization in the rocks of the Earth’s crust under moderate and low pressure, presence of fluid-gas flow of carbon-bearing matters, rather high temperature (above 700 °C), optimal reduction-oxidation potential and presence of catalysts. Intensive graphitization of diamondiferous rocks is typical. Biogenic carbon participates in diamond and graphite generation (Example: Kumdykolsk deposit in  Northern Kazakhstan [Lavrova, Pechnikov and oth., 1999]).

The model of epitaxial growth of diamond - carbonado on the mineral sublayer – surfaces of structure-like cubic carbon silicide in reduction environments at relatively low PT parameters under conditions of high gas saturation and balanced gaseous phase composition. Typical is diamond association with cubic carbon silicide, graphite, native silicon. (Example: carbonado in avachits of Kamchatka [Gorshkov, Seliverstov and oth., 1995]).

“Impact” model – Diamond crystallization due to shock pressure and warm-up as a result of hard-phase transition of graphite into diamond during shock effect of large meteorites on earth rocks. Diamonds are represented by polycrystalline aggregates containing admixture of the mineral hexagonal modification – lonsdeilite, as well as inclusions of graphite scales. High-baric minerals are also presented by coesite and stishovite. (Example: diamondiferous impactites of Popigaisk astroblem [Massaitis, Mikhalev, Selivanovskaya, 1975])

“Cavitation” model – generation of micro- and nanocristaline diamonds in the fluid inclusion in xenolith minerals of the mantle rocks of lamprophyres and alkali-basalts using the energy, which results from cavitation processes in liquid. According to this model, cavitation is an efficient tool for the energy concentration of low dense sound waves into high dense as a result of pulsation and collapse of cavitation bubbles. Energy is accumulated in the process of cavitation bubbles pulsation. Collapse of cavitation bubbles (pressure and temperature in this moment are estimated at ~ 10 ÃÏà and 5000°C) produces shock sound waves that can cause diamond crystallization in preserved bubbles. Inclusions with nanodiamonds, contain high dense carbon dioxide, carbonates and hydrous minerals (Example: lamprophyre dikes) on Japan islands [Mizukami, Wallis et al., 2008], alkali-basalts of Havaiian Islands (Wirth, Rocholl, 2003; Frezzotti, Piccerillo, 2007]).

Thus, analysis of diamondiferous complexes of varied composition and generation conditions presents enough arguments in favor of probable realization of different models of diamond generation depending on geodynamic regimes typical of these or those lithosphere segments. It is noteworthy, that experimentally approved method of artificial synthesis of diamonds corresponds to each natural model. It is obvious that polygenic property of diamond should be taken into consideration during search and prospecting for diamonds, especially in noncratonic environments.

 

References:

Kimberlites and non-kimberlitic diamond generation in the igneous and metamorphic rocks. The authors: A.V. Lapin, G.S. Gusev (ed. N.V. Mezhelovsky, A.F. Morosov) Publishing House GEOS, M.2010. 496 p.(in Russian).

Kaminsky F.V. Non-Kimberlitic Diamondiferous Igneous Rocks: 25 years on.// Journ. Geol. Soc. of India. V.69. March 2007. P.557-575.

Kutyev F.Sh.., Kutyeva T.V. Diamonds in basaltoids of Kamchatka // Dokl. Acad. Sci. USSR. 1975. V.221. N1. P.69-80 (in Russian).

Kaminsky F.V., Patoka M.T., Sheimovich V.S. On geologic-tectonic position of diamondiferous basalts of Kamchatka // Dokl. Acad Sci. USSR. 1979. V.269. N3. P.679-682 (in Russian).

Lapin A.V., Divaev F.K., Kostitsin Yu. A. Petrogeoclimatic typization of carbonatite-like rocks of chatagaisk complex of Tien Shan in connection with the problem of diamond generation // Petrology. 2005. V. 13. N5. P.548-560 (in Russian)

Golovko A.V., Divaev F.K. Non-kimberlitic diamondiferous rocks of Uzbekistan. In “Alkaline magmatism, its sources and plums” Ed. N.V. Vladykin. 2007. Irkutsk. P. 124-140 (in Russian).

Gzovsky M.V. The basics of tectonophysics. M. Nauka. 1975. 535 p. (in Russian).

Kropotkin P.N. Tectonic Stresses in the Earth’s Crust // Geotectonics. N2. 1996. P.3-15 (in Russian).

Filatova V.T. and oth. Tectonophysics of Intraplate Collision // Geology and Mineral Resources of the Kola Peninsula. V. 1. Apatites. 2002. P.57-73 (in Russian).

Lavrova L.D., Pechnikov B.A. and oth. A new genetic type of diamondiferous deposits. M. Nauchny mir. 1999. 228p (in Russian).

Gorshkov A.I., Seliverstov V.A. and oth.  Crystal Chemistry and carbonado genesis from melanocratic basaltoids of Avacha volcano on Kamchatka // Geology of ore deposits. 1995. V.37. N1. P.54-66 (in Russian).

Massaitis V.l., Mikhailov M.V., Selivanovskaya T.V. Popigaisk meteoritic crater. M. Nauka. 1975. 124p. (in Russian).

Mizukami T., Wallis S. et al. Foreark diamond from Japan // Geology. 2008. V.36. N3. P.219-222.

Wirth R., Rocholl A. Nanocristaline diamond from the Earth’s mantle underneath Havaii // Earth and Planet. Sci. Lett. 2003. V.211. N 3-4. P. 357-369.

Frezzotti M.L., Peccerillo A. Diamond-bearing COHS fluids in mantle beneath Havaii // Earth and Planet. Sci. Lett. 2007. V.262. P.273-283.