Diamond formation in Earth's mantle: The role of C-O-H fluid composition and host-rock lithology

Dr. Christopher Beyer, Prof. Dr. Sumit Chakraborty, Dr. Niels Jöns

Cooperation partners: Prof. Dr. Dan Frost (BGI)

Ph.D. student: Niklas Ottersberg

Funding source: DFG Grant BE6053/1-1 (2017 – 2020)
 

The central goal of this project is to identify the mechanisms of diamond formation in sublithospheric environments, which is an important step towards the understanding of Earth s deep carbon cycle. Deciphering the coupling between diamond formation, redox state, and mantle lithologies will aid to improve the understanding of regional differences in diamond inclusions and their association with upwelling and downwelling regimes within the convecting mantle of the Earth. The very recently discovered strong affinity to pyroxenites of inclusions found in diamonds that come from a depth below 300 km within the Earth is of particular interest.

Up to the present, only little attention has been payed to the role of pyroxenites in the formation of diamonds. Hence, this study will focus on the mechanisms that are responsible for the formation of pyroxenites and the syngenetic precipitation of diamonds under conditions of the lowermost upper mantle and Earth’s transition zone. This also involves the systematic analysis of C-O-H fluids reacting with oxidized eclogites and derived partial melts.

Finally, to understand the striking difference in diamond yields, we will investigate the effect of isochemical decompression and cooling of C-O-H fluids and the capability to isochemically precipitate macroscopic diamonds independent from the host rock’s composition. This process would explain high yields of large diamonds in harzburgitic rocks, that otherwise lack the oxygen buffer capacity to crystallize diamonds.