Fluid inclusions were studied in six octahedrally-grown, eclogitic diamonds from the Ebelyakh River mine, northern Russia, using microthermometry and Raman spectroscopy. The fluids are CO2-N2 mixtures with 40±4mol%N2, which are trapped along fractures that healed in the diamond stability field. The CO2-rich composition of the fluids provides the first empirical evidence that CO2 can be liberated as a free phase in eclogite in the diamond stability field of the lithospheric mantle, as has been previously predicted from theory. This finding means that the interpretation of carbon isotopes in eclogitic diamonds should not overlook isotopic fractionation due to CO2 liberation from carbonatitic diamond-forming media as it percolates through eclogites. Preferential nucleation of CO2 bubbles in eclogite compared to peridotite may lead to a rock type-specific fracturing mechanism and sampling bias that would help explain the overabundance of eclogite xenoliths in kimberlites.Fluid inclusions in octahedrally-grown, non-fibrous diamonds from both the studied Ebelyakh diamonds and those from other cratons do not show detectable amounts of water. In comparison, fibrous diamond fluid inclusions typically contain 10-25. wt.% water. The absence of "dry" fluids in fibrous diamonds and the presence of these in octahedrally-grown diamonds may indicate different compositions of fluids equilibrated with these two types of diamonds. If there is variability in the water content in diamond-forming fluids, it should affect diamond growth morphology. Water could be responsible for causing fibrous diamond growth, by inhibiting the advancement of growth steps within octahedral faces.

Smith, E., Kopylova, M., Frezzotti, M., Afanasiev, V. (2015). Fluid inclusions in Ebelyakh diamonds: Evidence of CO2 liberation in eclogite and the effect of H2O on diamond habit. LITHOS, 216-217(C), 106-117 [10.1016/j.lithos.2014.12.010].

Fluid inclusions in Ebelyakh diamonds: Evidence of CO2 liberation in eclogite and the effect of H2O on diamond habit

FREZZOTTI, MARIA LUCE
Penultimo
;
2015

Abstract

Fluid inclusions were studied in six octahedrally-grown, eclogitic diamonds from the Ebelyakh River mine, northern Russia, using microthermometry and Raman spectroscopy. The fluids are CO2-N2 mixtures with 40±4mol%N2, which are trapped along fractures that healed in the diamond stability field. The CO2-rich composition of the fluids provides the first empirical evidence that CO2 can be liberated as a free phase in eclogite in the diamond stability field of the lithospheric mantle, as has been previously predicted from theory. This finding means that the interpretation of carbon isotopes in eclogitic diamonds should not overlook isotopic fractionation due to CO2 liberation from carbonatitic diamond-forming media as it percolates through eclogites. Preferential nucleation of CO2 bubbles in eclogite compared to peridotite may lead to a rock type-specific fracturing mechanism and sampling bias that would help explain the overabundance of eclogite xenoliths in kimberlites.Fluid inclusions in octahedrally-grown, non-fibrous diamonds from both the studied Ebelyakh diamonds and those from other cratons do not show detectable amounts of water. In comparison, fibrous diamond fluid inclusions typically contain 10-25. wt.% water. The absence of "dry" fluids in fibrous diamonds and the presence of these in octahedrally-grown diamonds may indicate different compositions of fluids equilibrated with these two types of diamonds. If there is variability in the water content in diamond-forming fluids, it should affect diamond growth morphology. Water could be responsible for causing fibrous diamond growth, by inhibiting the advancement of growth steps within octahedral faces.
Articolo in rivista - Articolo scientifico
CO2 liberation; Continental lithospheric mantle; Diamond; Diamond growth habit; Fluid inclusions; Isotopic fractionation; Geochemistry and Petrology
English
feb-2015
2015
216-217
C
106
117
none
Smith, E., Kopylova, M., Frezzotti, M., Afanasiev, V. (2015). Fluid inclusions in Ebelyakh diamonds: Evidence of CO2 liberation in eclogite and the effect of H2O on diamond habit. LITHOS, 216-217(C), 106-117 [10.1016/j.lithos.2014.12.010].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/96480
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