SOME PECULIAR OF A CONSTRACTION PROCEDURE T-P-PHASE DIAGRAM MgO-Al2O3-SiO2 WITH THE ACCOUNT OF EQUILIBRIUMS WITH THE ASSISTANCE OF SOLID SOLUTIONS
Surkov N.V.
Institute of Geology & Mineralogy, SB RAS, Koptyug Pr. 3, Novosibirsk, 630090, Russia, E-mail: diagrams@uiggm.nsc.ru, 
The phase diagram of system MgO-Al2O3-SiO2 is observationally investigated at pressures up to 40-45 кбар [1, 2, 3]. At pressures up to 40-45 кбар in this system following phases are known: periclase - Per (MgO); corundum - Crd (Al2O3); silicon group (SiO2) - cristoballite - Crs, -quartz - -Qtz, -quartz - -Qtz, coesite - Co; tridimite (it is close on a composition to SiO2) - Trd, spinel - Spl (MgAl2O4); group of a alumia-silikate (Al2SiO5) - kyanite (disten) - Ky, andolusite - And, sillimanite - Sil; mullite - Mul (Al4OSi2Al2O12 or Al6Si2O13); group enstatite (Mg2Si2O6) - En, orthoenstatite - OEn, clinoenstatite - CEn, protoenstatite - PEn; forsterite (Mg2SiO4) - Fo; pyrope (Mg3Al2Si3O12) - Prp; cordoerite (Mg2Al4Si5O18) - Crd; sapphirine (Mg2Al4SiO10) - Spr. In this conditions the stability fields of the all phases existing in this system are experimental investigated and the monovariant equilibriums restricting this field is spotted. Monovariant responses restricting stability fields of a phases allow to carry out practically univalently the analysis mono - divariant equilibriums for this phase diagramme. The standing experimental research (in P-T co-ordinates) separate the eutectic or peritectic equilibriums in rare instances is required. Solid solutions which noticeably influence topology of the phase diagramme, are discovered for polymorphic modifications of group enstatite. With participation of these solid solutions are oozed same singular nonvariant equilibriums and  singular monovariant reactions. The account of a stability of solid solutions of phases allows to constracted of the phase diagramme of system MgO-Al2O3-SiO2 with the account of all possible equilibriums, it is correct from a formalistic approach position to topology of phase diagrammes. 

References

1. Doroshev A.M., Malinovsky I.Yu.. The Topological analysis of system MgO-Al2O3-SiO2. - Experimental researches on mineralogy. (1972-1973), ed. A.A.Godovikov, etc., Novosibirsk, 1974, p. 81-85 
2. Gasparik T.. A petrogenetic grid for the system MgO-Al2O3-SiO2. - Journal of Geology, 1994, v. 102, N 1, p. 97-109
3. Podlesskii K. K., Aranovich L. Y., Gerya V., Kosyakova N. A.. Sapphirine-bearing assemblages in the system MgO-Al2O3-SiO2: a continuing. - European Journal of Mineralogist, 2008, v. 20, N 5, p. 721-734