Fluid regime and diamond formation in the reduced mantle: Experimental constraints

Effect of oxygen fugacity on the H2O storage capacity of forsterite in the carbon-saturated systems

“…The details of this technique have been presented by Sokol et al (2009). It was not necessary to load MoO 2 or FeO into the outer capsule to control the buffer redox reactions.…”

“…Fig. 2 illustrates the fO 2 of the buffer reactions as a function of temperature at 6.3 GPa, calculated according to Sokol et al (2009 (Table 1) were calculated from equilibrium composition of the C-O-H system corresponding to the fO 2 of the Mo-MoO 2 and Fe-FeO buffers. The compositions of fluid were computed through Gibbs free energy minimization using the "Selektor" computer code (Chudnenko et al, 1995;Karpov et al, 2002).…”

“…In the fO 2 range from FMQ-1 to FMQ-2.5 and under the P-T conditions of our experiments the fluid compositions change from CO 2 -rich to H 2 O-rich (near the water maximum) (Sokol et al, 2000(Sokol et al, , 2004Woodland and Koch, 2003;Zhang and Duan, 2009). The compositions of reduced C-O-H fluid in carbon-saturated system at 6.3 GPa and 1400-1600°C were studied by Sokol et al (2009) as H 2 O and CO 2 have high solubilities in silicate melts, and significantly depress the silicate solidus. The higher solidus temperature in the system Mg 2 SiO 4 -C-O-H at low fO 2 is related to much lower solubilities of H 2 and CH 4 in silicate melt than those of H 2 O and CO 2 .…”

“…FMQ) C-O-H fluid will contain much CO 2 , whereas at low fO 2 (ca. FMQ-5) it will essentially be CH 4 -rich (Wyllie and Ryabchikov, 2000;Sokol et al, 2009). Consequently, the H 2 O fugacity in both, oxidized and reduced C-O-H fluids, will be lower than in pure O-H fluids.…”

“…They include: (1) a hydrous-silicic end-member, which is rich in water, Si, Al, and K; (2) a carbonatitic end-member, rich in carbonate, Mg, Ca, Fe, K, and Na; and (3) a brine, hydrous-saline endmember rich in Cl, K, and Na. The nucleation and growth of diamond were experimentally studied in both anhydrous carbonatite and chloride-carbonate melts (Akaishi et al, 1990;Litvin et al, 1997;Pal'yanov et al, 1999Pal'yanov et al, , 2002 and in hydrous melts and fluids (Pal'yanov et al, 1999Akaishi et al, 2000;Sokol et al, 2001;Palyanov et al, 2007;Sokol and Pal'yanov, 2008;Sokol et al, 2009). The study of fibrous/cloudy diamonds combined with experimental data on diamond formation in model systems allows the reconstruction of mantle fluid and melt evolution and reveals the conditions for diamond crystallization (Navon, 1999;Palyanov et al, 2007;Palyanov and Sokol, 2009).…”