Stability relations of coesite (Co), diopside (Di), diamond (Dm), dolomite (Do), enstatite (En), forsterite (Fo), graphite (Gr), magnesite (Ms) and CO2-bearing fluid at XCO2 = 0.1 in the model system CaO-MgO-SiO2-C-O2-H2O were calculated at P = 4 to 8 GPá using available thermodynamic data already published. Isobaric log fO2 -T stabilities of 4 decarbonation reactions and 4 oxidation reactions together with reaction Dm (Gr) + O2 = CO2 and diamond-graphite transition were determined. Parageneses of minerals as function of bulk composition were modeled for eclogite, clinopyroxenite, websterite, Iherzolite, and carbonate rocks. Reaction Co + Ms = En + Dm + O2 stabilizes diamond in SiO2-saturated rocks such as eclogite at fO2 slightly higher than reaction En + Ms = Fo + Dm + O2 (EMOD). Diamond in SiO2-undersaturated rocks such as Iherzolites and websterites, is stable at fo2 lower than EMOD. Bulk carbon content is also important for the appearance of diamond in silicate rocks. Diopside-rich and carbon-rich compositions are favorable for diamond occurrence in silicate rocks. Ca- and Mg-rich carbonate rocks occur 7 diamond-bearing assemblages at wide fO2 conditions. Using calculated log fO2 -T relations, our model PT-fO2 paths during exhumation and corresponding changes in mineral assemblages were predicted.
|ジャーナル||Geologiya i Geofizika|
|出版ステータス||Published - 1997|
ASJC Scopus subject areas
- Earth and Planetary Sciences (miscellaneous)