Mantle-wide sequestration of carbon in silicates and the structure of magnesite II

Details Mantle-wide sequestration of carbon in silicates and the structure of magnesite II Mantle-wide sequestration of carbon in silicates and the structure of magnesite II

Jul 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008georl..3514307p&link_type=abstract

Geophysical Research Letters, Volume 35, Issue 14, CiteID L14307

Physics

6

Mineralogy And Petrology: Reactions And Phase Equilibria (1012, 8412), Mineral Physics: High-Pressure Behavior, Mineral Physics: Physical Thermodynamics, Mineralogy And Petrology: Mineral And Crystal Chemistry (1042), Mineralogy And Petrology: Mantle Processes (1038)

Scientific paper

The participation of the deep mantle in the global carbon cycle and its ability to sequester carbon over billion-year time scales depends upon the mineralogical host for carbon. Density-functional theory calculations for MgCO3-magnesite and structures with tetrahedrally coordinated carbon reveal the stability of magnesite up to ~80 GPa, with a bulk modulus of 110 (+/-2) GPa. Magnesite undergoes a structural transition to a pyroxene-like structure at ~80-100 GPa, with a density increase of 4.5-7.1%. Combined with thermodynamic models for the MgSiO3-MgCO3 system, the inter-solubility of MgCO3 with MgSiO3 orthoenstatite and perovskite constrains the carbon content in the silicates to an upper bound of 4 and 20 ppm (wt), respectively. The carbon content in lower mantle silicates is estimated to be no more than 1% of the mantle's total carbon budget for degassed regions, such that in even the mantle's most depleted regions, most carbon must be stored in carbonates or diamond.

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