Publication Date:
2017-07-04
Description:
Carbon dioxide is a ubiquitous component of low-silica melts such as kimberlites or melilitites. It is currently assumed that CO 2 molecules dissolving in low-silica melts as carbonate groups (CO 3 2– ) induce a strong polymerization of the silicate network; however, the exact molecular configuration of this dissolution mechanism is still debated. Using 17 O MAS NMR spectroscopy, we have investigated the carbonate molecular environment in a series of synthesized low-silica (31–41 wt% SiO 2 ), CO 2 -bearing (from 2.9 to 13.2 wt% CO 2 ) silicate glasses analogous to melilitites and kimberlites. With the selective { 13 C}-, { 27 Al}-, and { 29 Si}- 17 O J HMQC NMR method, we show that CO 2 dissolved in the studied low-silica glasses is totally disconnected from the silicate network, forming free ionic clusters (FIC) M n+ CO 3 2– with M n+ , a charge compensating cation. The M n+ CO 3 2– FIC are considered as precursors to immiscibility in between carbonate and silicate liquids. Observed in all studied compositions, we suggest that this immiscibility can be produced from moderately to strongly depolymerized silicate melt compositions.
Print ISSN:
0003-004X
Electronic ISSN:
1945-3027
Topics:
Geosciences
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