In order to better understand the origin and circulation of mantle carbon, recent studies have examined the carbon isotope composition of diamonds from several areas around the world, including the Letlhakane and Orapa kimberlite fields in Botswana, the Finsch mine in South Africa, and the Argyle lamproite field in Western Australia. These investigations discovered a much broader variety of δ13C values, from -18.5 to +2.5 per thousand, compared to previous studies. Diamonds with very unfavourable carbon isotope values were also found in this wider range, pointing to a sizable reservoir of deeply buried sediments or recycled crustal material in the Earth's mantle that has not yet been included in the general carbon cycle. Additionally, the existence of such isotope heterogeneity across various diamond locations implied the existence of chemically and physically separate portions within the earth's mantle.
Beyond carbon isotopes, diamonds can provide vital information about the depths of mantle melting and the origins of the magmas that brought the diamonds to the surface. The concentrations of particular trace elements, such as nitrogen, sulfur, and iron, inside diamonds change as a function of pressure, temperature, and volatile composition under which they are generated. These trace elements allow the creation of growth zones in diamonds that correspond to distinct phases in the evolution of kimberlitic magma and its ascent. For instance, one important outcome from trace element research is that diamonds with different colors, such as colourless and brown diamonds, may develop from the same starting magma but under distinct P-T conditions and volatile components, which further elucidates the intricacy of the diamond-forming process.
Another significant advancement in the study of diamonds for comprehending the Earth's carbon cycle is the discovery of ultra-deep diamonds. These diamonds show extraordinarily high δ13C values of up to +5.5 per thousand, indicating that their carbon source is substantially different from conventional mantle carbon reservoirs. The presence of super-deep diamonds suggests the potential existence of extremely old carbon reservoirs in the Earth's lower mantle, which might include remnants of subducted sediments and/or primordial mantle material.
In summary, diamonds provide vital insights into the Earth's carbon cycle, mantle processes, and diamond-forming circumstances due to their exceptional capacity to maintain stable isotope information and trace element composition. Research on diamonds has resulted in the realization that the earth's carbon cycle is more complex than earlier thought, and that there are sizable, unidentified carbon reservoirs in the Earth's mantle that are critical for comprehending the dynamic processes that shape our planet.
