Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8910886 | Geochimica et Cosmochimica Acta | 2018 | 17 Pages |
Abstract
In contrast, the 29Si MAS NMR spectra for partially depolymerized, carbon-bearing NS3 glasses show that the fraction of [5,6]Si increases with increasing pressure at the expense of Q3 species ([4]Si species with one non-bridging oxygen as the nearest neighbor). The pressure-induced increase in topological disorder around Si is evident from an increase in peak width of [4]Si with pressure. 17O NMR spectrum shows that the fraction of Naâ¯O[5]Si in carbon-bearing NS3 glasses is less than that of carbon-free NS3 glasses at 6â¯GPa potentially due to the formation of bridging carbonate species. While its presence is not evident from the 17O NMR spectrum primarily due to low carbon concentration, 13C MAS NMR results imply the formation of bridging carbonates, [4]Si(CO3)[4]Si, above 6 GPa. The spin-lattice relaxation time (T1) of CO2 in albite melts increases with increasing pressure from 42â¯s (at 1.5â¯GPa) to 149â¯s (at 6â¯GPa). Taking the pressure-induced change in T1 of carbon species into consideration, total carbon content in carbon-bearing albite melts increases with pressure from â¼1â¯wt% at 1.5â¯GPa to â¼4.1â¯wt% at 6â¯GPa. The results also reveal a noticeable drop in the peak intensity of free carbonates in carbon-bearing NS3 melts at 6â¯GPa, implying a potential non-linear change in the carbon solubility with pressure. The current results of carbon speciation in the silicate melts above 4â¯GPa provide an improved link among the atomic configurations around carbon species, their carbon contents, and isotope composition of carbon-bearing melts in the upper mantle.
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Authors
Eun Jeong Kim, Yingwei Fei, Sung Keun Lee,