Other
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995e%26psl.134..297l&link_type=abstract
Earth and Planetary Science Letters, vol. 134, Issue 3-4, pp.297-305
Other
6
Scientific paper
The phase behaviour of the carbonates in the system MgO-CaO-SiO 2 -CO 2 have been studied in a diamond-anvil press employing YAG laser heating from about 40 to 260 kbar at ~ 1000°C. It is already known that at the CaCO 3 -MgCO 3 join calcite (CaCO 3 ) is stable only at relatively low pressures (< 30 kbar), that aragonite (CaCO 3 ) is stable between 30 and 400 kbar, and that magnesite (MgCO 3 ) is stable between 7 and 550 kbar at ~ 1000°C. In the present study it has been found that the intermediate mineral dolomite (CaCO 3 · MgCO 3 ) decomposes into the mixture aragonite + magnesite in the pressure range 60-70 kbar at ~ 1000°C. Another intermediate mineral, huntite (CaCO 3 · 3MgCO 3 ), transforms to a new phase at pressures below 40 kbar, and then decomposes to the mixture dolomite + magnesite at pressures greater than ~ 60 kbar. The new phase with the huntite composition possesses an orthorhombic cell with a 0 = 9.933 ± 0.002, b 0 = 6.712 ± 0.001 and c 0 = 24.06 ± 0.02 å at ambient conditions. There are only two well-known silicate-carbonate minerals in the CaO-SiO 2 -CO 2 system. These are spurrite and tilleyite. Both were found to decompose into their component silicates and carbonates at pressures below 40 kbar at ~ 1000°C. On the basis of the present study it can be concluded that aragonite and magnesite are the only two carbonates in the entire CaO-MgO-SiO 2 -CO 2 system which are stable at pressures greater than about 70 kbar at ~ 1000°C, if no interaction occurs between carbonates and silicates at still higher pressures.
Chung-Cherng Lin
Lin-Gun Liu
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