On origin and evolution of diamond-forming lower-mantle systems: physicochemical studies in experiments at 24 and 26 GPaстатьяИсследовательская статья
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Дата последнего поиска статьи во внешних источниках: 6 февраля 2018 г.
Аннотация:The MgO - FeO - SiO2 - CaO system is representative for the dominant lower-mantle ultramafic assemblage ferropericlase (MgO center dot FeO)(ss) + bridgmanite (Mg,Fe)SiO3 + Ca-perovskite CaSiO3. Melting relations of the system were studied over its polythermal section (MgO)(70)(FeO)(30) - (SiO2)(70)(FeO)(30) at 24 GPa. A peritectic reaction of bridgmanite with melt was revealed to form the mafic assemblage stishovite SiO2 + periclase-wustite solid solution phases (MgO center dot FeO)(ss) (effect of "stishovite paradox"). Experimental phase relations demonstrate the possibility of ultramafic-mafic fractional evolution of the lower-mantle magma and in situ formation of stishovite. Moreover, origin of ultradeep diamonds and associated phases in melts of the MgO - FeO - SiO2 - CaO - (Mg-Fe-Na-K-carbonate) - carbon system have been examined at 26 GPa. A key role of the peritectic reaction of bridgmanite in genesis of mafic inclusions in lower-mantle diamonds is verified.