Evolution of diamond resorption in a silicic aqueous fluid at 1–3 GPa: Application to kimberlite emplacement and mantle metasomatism

Diamond resorption features as a new method for examining conditions of kimberlite emplacement

“…Previous work on the diamond morphology for the three studied kimberlites established differences in the depth of fluid separation (Zhang et al 2015) and fluid retention during the ascent as well as the effect of both factors on the kimberlite ascent rate, kimberlite composition (volcaniclastic vs. coherent), and diamond grade preservation (Fedortchouk et al 2010). The established here variations in the composition of the magmatic fluid in the three kimberlites infer differences in their emplacement (Fig.…”

“…Thus, based on the AFM-derived parameters of the etch trigons, we propose the following conditions of diamond resorption in the three examined kimberlites: In Koala, magmatic fluid had very low CO 2 /H 2 O ratio at low T < 1150 °C, in Grizzly the fluid had higher T and similar or slightly higher CO 2 /H 2 O, and in Misery the fluid had the highest CO 2 /H 2 O at higher T > 1250 °C. The recent study Zhang et al (2015) demonstrated that higher P promotes faster rounding of diamond without a notable weight loss, which explained the paradox of high diamond grade accompanied by high proportion of rounded stones in Misery kimberlite. The AFM data presented here for trigonal pits on Misery diamonds suggest that this early (deep) separated fluid was also more CO 2 rich than the fluid separated at shallower depth in Koala and Grizzly kimberlites.…”

Microrelief of Rounded Diamond Crystals as an Indicator of the Redox Conditions of Their Resorption in a Kimberlite Melt

“…Based on experimental data, the conditions of natural resorption of diamond were reconstructed, under which rounded forms of diamond crystals are formed. These forms were shown to emerge upon dissolution of plane-faced diamond crystals in water-bearing carbonate, silicate, and carbonate-silicate melts, or fluids in a wide range of temperatures (1100-1500 • C) and pressures (1.0-6.3 GPa) [13][14][15][16][17][18][19][20]. However, despite similar macromorphology of natural rounded diamonds, their surfaces have different reliefs.…”

Three styles of diamond resorption in a single kimberlite: does crustal xenolith assimilation play a role?

“…Most distinctive is the kimberlite-induced resorption on CK-B diamonds, which yielded severely corroded rounded crystals (Fig. 2C) resembling experimental products of diamond dissolution in carbonate melt (Zhang et al, 2015). SEM imaging revealed similarities between the corroded surfaces of CK-B diamonds and micro-cavities on CK-A diamonds, implying that these cavities represent an initial stage of the same resorption event that affected CK-B diamonds.…”

“…H 2 O and CO 2 reach saturation in kimberlite magma only within the last 2.5 km of ascent (Moussallam et al, 2016). The high proportion of rounded THH diamonds and the character of resorption on BK1 and AK15 diamonds require fluid presence at a much greater depth (> 1 GPa) (Zhang et al, 2015). CO 2 degassing can be triggered by dissolution of silicate-rich material in carbonate-rich magma.…”