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    Experimental shock synthesis of diamonds in a graphite gneiss
    Meteoritics and Planetary Science (2005)
    T. KenkmannU. HornemannD. Stöffler
    Abstract— The occurrence of diamonds in terrestrial impact craters and meteorites is related to dynamic shock loading during hypervelocity impacts. To understand the mechanism of impact diamond formation in natural rocks, shock‐recovery experiments with graphite gneiss were carried out at shock pressures between 35 and 79 GPa. This is the first report on the successful shock synthesis of microdiamonds in a natural rock. Micrometer‐size diamonds and a wide range of intermediate, presently unclassified, amorphous, and disordered carbon phases were observed within vesiculated biotite melts in the vicinity of relic graphite grains using microRaman spectrometry. We explain these findings by jetting mechanisms of carbon and graphite clusters, originating at the edges of graphite grains, into the very hot and volatile rich biotitic melt veins during shock loading. This environment enabled the thermally activated crystallization of diamonds during shock compression in a period of less than 0.5 μsec. Regraphitization of diamonds during pressure release was widespread and caused the formation of the amorphous to disordered carbon phases recorded frequently with microRaman spectroscopy. The surviving diamonds must have cooled down to 2000 K during the compression phase at local thermal sinks and cooler interfaces to avoid regraphitization.
    Shock metamorphism
    Thermal shock
    Carbon fibers
    Amorphous carbon
    Hypervelocity
    Crystal (programming language)
    Citations (14)
    Diamond stability in silicate-halogenide melts at high pressure
    Doklady Earth Sciences (2009)
    В. М. СонинЕ. И. ЖимулевА. А. ЧепуровN. P. Pokhilenko
    Citations (1)
    Kinetic Control on the Depth Distribution of Superdeep Diamonds
    Geophysical Research Letters (2018)
    Feng ZhuJie LiJiachao LiuXiaojing LaiBin Chen
    Abstract Superdeep diamonds contain unique information from the sublithospheric regions of Earth's interior. Recent studies suggest that reaction between subducted carbonate and iron metal in the mantle plays an important role in the production of superdeep diamonds. It is unknown if this reaction is kinetically feasible in cold slabs subducted into the deep mantle. Here we present experimental data on real‐time tracking of the magnesite‐iron reaction at high pressures and high temperatures to demonstrate the production of diamond at the surface conditions of cold slabs in the transition zone and lower mantle. Our data reveal that the diamond production rate has a positive temperature dependence and a negative pressure dependence, and along a slab geotherm it decreases by a factor of three at pressures from 14.4 to 18.4 GPa. This rate reduction provides an explanation for the rarity of superdeep diamonds from the interior of the mantle transition zone.
    Slab
    Magnesite
    Citations (13)