Showing papers by "Gerhard P. Brey published in 1976"

Solubility of CO2 in olivine melilitite at high pressures and role of CO2 in the earth's upper mantle

Abstract: The positions of the liquidi and the near-liquidus phases of olivine-melilitite+CO2 have been determined under MH-buffered and ‘furnace-buffered’ conditions up to 40 kb. It is found that CO2 alone lowers the liquidus compared to ‘dry’ conditions, yet its influence is minor compared to H2O. The major role of CO2 is to favour the growth of orthopyroxene and garnet over that of olivine at least at high pressures. CO2-contents of glasses from experiments just above the liquidus (MH-buffered) were determined as 5.1 % at 10kb; 7.5 % at 20kb, 9.3 % at 30kb and 10–11 % (estimated) at 40 kb. Experiments on (pyrolite −40 % olivine)+H2O+CO2 show that CO2 occurs under mantle conditions as carbonate under subsolidus conditions and dissolved in a melt above the solidus. At 30kb, the solidus lies between 1,000 ° C and 1,050 ° C for vapour-saturated conditions, at \(X_{{\text{H}}_{\text{2}} {\text{O}}} = 0.5 = X_{{\text{CO}}_{\text{2}} } \) and at \(X_{{\text{H}}_{\text{2}} {\text{O}}} = 0.9,{\text{ }}X_{{\text{CO}}_{\text{2}} } = 0.1\).

CO 2 solubility and solubility mechanisms in silicate melts at high pressures

Abstract: CO2 solubility has a slight negative temperature dependence in olivine melilitite at 30 kb with 9% CO2 dissolved at 1,450 °C, 8.5% at 1,550 °C and 8.3% at 1,650° C. CO2 is dissolved as the carbonate molecule (CO32−) only. Feldspar melts (albite-anorthite) dissolve much less CO2 at 30 kb (around 2%) with a slight increase with increasing anorthite content. A CO2 absorption peak in infrared spectra of albite-rich glasses diappears in favour of the CO32−peak with increasing anorthite content. It is inferred that CO2 was present as CO32−in albite-rich melts also, but reverts to CO2 during quenching because of bonding differences related to Ca2+ and Na+ in the melts.