Diamond Crystallization at High Pressure: The Relative Efficiency of Metal-Graphite and Metal-Carbonate Systems

Doklady Earth Sciences - Data on the interaction of the Fe–Ni melt with CaCO3 and graphite at 5 GPa and 1400°С under the thermogradient conditions used in experiments on the growth...     

Patterns of Phase Formation in Kimberlite under Reducing Conditions at 4 GPa and 1500°C

Doklady Earth Sciences - Experimental data on the interaction of an iron melt with natural kimberlite at a temperature of 1500 ± 25°C and a pressure of 4.0 ± 0.2 GPa corresponding to...     

Experimental estimation of the rate of gravitation fractionating of xenocrysts in kimberlite magma at high P-T parameters

This report considers experimental studies of the gravitation fractionating of xenocrysts (diamond, garnet, and olivine) in kimberlite magma at 4.0 GPa and 1400°C. The values obtained (0.6–0.7 m/h for 0.3-mm diamond crystals, 0.36 m/h for garnet grains, and 0.6–0.29 m/h for olivine grains) point to a high rate of xenocryst sinking in the ultralow-viscous kimberlite magma (as high as 1 m/h and more, depending on the densities and grain sizes of minerals). A high rate of xenocryst sinking in kimberlite magma results in the impossibility of preservation of heterogeneity in these melts for a sufficiently long time.     

Peculiarities of the Composition of Volatiles of Diamonds Synthesized in the Fe–S–C System: Data on Gas Chromatography–Mass Spectrometry

The first chromatography–mass spectroscopy data on volatiles in diamonds synthesized in the Fe–S–C system with 5 wt % S at 1400–1450°C and 5.0–5.5 GPa indicate the evolution of volatile composition during the diamond growth and, correspondingly, the variation in redox conditions of the reaction cell. A significant role is played by various hydrocarbons (HCs) and their derivatives, the content of which can reach 87%. Our data on possible abiogenic synthesis of HCs (components of natural gas and oil) can result in global recalculations (including climate) related to the global C cycle.     

Synthesis of New Polytypic Modifications of Fe7C3 at 5.5 GPa

Doklady Earth Sciences - The results of experimental synthesis of carbide Fe7C3 at 5.5 GPa are presented. It is found that carbide Fe3C and several polytypes of carbide Fe7C3 are formed along with...     

The conservation of an aqueous fluid in inclusions in minerals and their interstices at high pressures and temperatures during the decomposition of antigorite

An experimental study of serpentine decomposition at high pressure (4.5 GPa) was carried out to elucidate if water can be preserved in the system in the form other than structural admixtures in minerals. This problem is of interest because it is water that plays a leading role in the melting in a subducted slab and a mantle wedge. To estimate the possible content of an aqueous fluid in deep-seated rocks, a BARS pressless split-sphere apparatus was used in complex with thermobarogeochemistry and gas chromatography. It has been established that the serpentine decomposition is accompanied by the release of water, which concentrates in inclusions in the produced minerals (olivine and orthopyroxene) and their interstices. Chromatographic analysis with a stepwise heating of samples showed that most of the released water is localized in the interstices, and the rest is conserved in fluid inclusions in the minerals. The produced solid phases conserve 0.13 to 2.43 wt.% fluids as inclusions, with water amounting to 0.1–2.06 wt.%. The content of inclusions determined by microscopic examination falls in this region. Since the mobility of the fluid conserved as inclusions in the olivine and orthopyroxene is significantly lower than that in the interstices, this fluid might be better preserved in olivine-containing rocks subsided to depth.