Mantle-slab interaction and redox mechanism of diamond formation

Redox-freezing and nucleation of diamond via magnetite formation in the Earth's mantle

Diamonds and their inclusions are unique probes into the deep Earth, tracking the deep carbon cycle to >800 km. Understanding the mechanisms of carbon mobilization and freezing is a prerequisite for quantifying the fluxes of carbon in the deep Earth. Here we show direct evidence for the formation of diamond by redox reactions involving FeNi sulfides. Transmission Kikuchi Diffraction identifies ...

The role of mantle ultrapotassic fluids in diamond formation.

Analysis of data on micro- and nano-inclusions in mantle-derived and metamorphic diamonds shows that, to a first approximation, diamond-forming medium can be considered as a specific ultrapotassic, carbonate/chloride/silicate/water fluid. In the present work, the processes and mechanisms of diamond crystallization were experimentally studied at 7.5 GPa, within the temperature range of 1,400-1,8...

Natural diamond formation by self-redox of ferromagnesian carbonate

Formation of natural diamonds requires the reduction of carbon to its bare elemental form, and pressures (P) greater than 5 GPa to cross the graphite-diamond transition boundary. In a study of shocked ferromagnesian carbonate at the Xiuyan impact crater, we found that the impact pressure-temperature (P-T) of 25-45 GPa and 800-900 °C were sufficient to decompose ankerite Ca(Fe2+,Mg)(CO3)2 to for...

Oceanic slab melting and mantle metasomatism.

Modern plate tectonic brings down oceanic crust along subduction zones where it either dehydrates or melts. Those hydrous fluids or melts migrate into the overlying mantle wedge trigerring its melting which produces arc magmas and thus additional continental crust. Nowadays, melting seems to be restricted to cases of young (< 50 Ma) subducted plates. Slab melts are silicic and strongly sodic (t...

Preface: Deep Slab and Mantle Dynamics