IMPACT-COSMIC-METASOMATIC ORIGIN OF MICRO-DIAMONDS FROM KUMDYKOL DEPOSIT, KOKCHETAV MASSIV, N. KAZAKHSTAN

Diamond-bearing Kumdykol deposit formation was provoked by impact event followed prograde and retrograde metamorphism with metasomatic alterations of target rocks caused diamond crystallization, everything confirm by evidences:

1. The deposit locates within ring structure; impact created tectonic dislocation system and fracture zones filling out of host rock cataclastic breccia;
2. UHP minerals: diamonds (~10 - 50 µm), lonsdaleite, coesite, omphacite, moissanite, ∝-Fe, Fe-Ni meteoritic globules and the cation’s exchange in shock-activated phases have point out to the passing through these rocks shock wave with pressure ≥ 40- 50 GPa;
3. Intensive metasomatic alteration of diamond-bearing rocks with markers of amphibolite (~ 650-680С, <10 GPa) and greenschist (~ 420°C, ~2–3 GPa) metamorphic facies; phase transformations during the decompression;
4. Carbon represents by diamond, graphite, carbon transition forms (sp³+sp²), lonsdaleite, chaoite, ∝- and β-carbines, X-ray amorphous skeletal forms. Values of diamond carbon isotope composition of δ¹³C (–8.9 to –27 ‰) compare with δ¹³C (-5 to -31 ‰) in meteorites;
5. Polycrystaline nano-inclusions in diamonds represented by oxides Si, Ti, Fe, Cr with trace element impurities: Mg, Са, Al, К, Na, S, Р, Pb, Nb, Cl, Zn, Ni, and also Si-Р-К-containing glasses and K-Si-COH fluid inclusions;
6. Very high ³He/⁴He isotopic ratios (7х10^-1 to 8х10^-9 ‰) of diamonds suggest ³He was trapped by diamonds during its formation outside the Solar System. Ne, Ar, Xe also present in these diamonds;
7. High N (up to 3300 ppm), H, Ni contents, and high enrichment δ¹⁵N (+5.3 to + 25 ‰) in diamonds compare to those of comet coma gases, diamonds from chondrites and presolar diamond grains.

So, diamonds have been formed on cosmic origin carbon seeds from saturated by C, H, O, N fluid-melt. Diamond crystal zonation suggests of multiple, quickly changeable P - T conditions. Small diamond sizes, low N aggregation state, and diamond preservations suggest to short-term diamond grown process. All of above appear to indicate CVD grown process for Kumdykol diamond formation.