Nano-inclusions in diamond: Evidence of diamond genesis

Abstract:

The use of Focused Ion Beam technology (FIB) for TEM sample preparation introduced approximately 15 years ago revolutionized the application of TEM in Geosciences. For the first time, FIB enabled cutting samples for TEM use from exactly the location we are interested in. Applied to diamond investigation, this technique revealed the presence of nanometre-sized inclusions in diamond that have been simply unknown before. Nanoinclusions in diamond from different location and origin such as diamonds from the Lower and Upper Mantle, metamorphic diamonds (Kazakhstan, Erzgebirge, Bohemia), diamonds from ophiolites (Tibet, Mongolia, Xinjiang, Ural Mountains), diamonds from igneous rocks (Hawaii, Kamchatka) and impact diamonds (Popigai Crater, Siberia) have been investigated during the last 15 years. The major conclusion of all these TEM studies is, that the nanoinclusions, their phases and phase composition together with the micro- and nanostructure evidence the origin of diamond and genesis of diamond. We can discriminate Five different mechanisms of diamond genesis in nature are observed:

Diamond crystallized from a high-density fluid (Upper mantle and metamorphic diamond).

Diamond crystallized from carbonatitic melt (Lower mantle diamond).

Diamond precipitates from a metal alloy melt (Diamond from ophiolites).

Diamond crystallized by gas phase condensation or chemical vapour condensation (CVD) (Lavas from Kamchatka, xenoliths in Hawaiian lavas).

Direct transformation of graphite into diamond.