Omphacite paradox in mantle peridotites |
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| Institution: | 1. Lomonosov Moscow State University, Leninskie Gory 1, 119234, Russia;2. Institute of Experimental Mineralogy, Russian Academy of Sciences, ul. Institutskaya 4, Chernogolovka, Moscow Region, 142432, Russia;1. Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton T6G 2E3, Canada;2. School of Earth and Environmental Sciences, Burnaby Building, University of Portsmouth, Portsmouth PO1 3QL, United Kingdom;3. Department of Earth and Environmental Sciences, University of St. Andrews, College Gate, St Andrews, Fife, KY16 9AJ Scotland |
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| Abstract: | Omphacite is a typomorphic mineral of eclogites, which is inappropriate to mineral assemblages of peridotites. Nevertheless, findings of this mineral in inclusions in peridotitic diamonds can be considered as indirect evidence for the existence of this paradoxical mineral assemblage.In this paper we present experimental results on the interaction between carbonate-bearing amphibolite and olivine that model processes operated at the crust–mantle boundary in subduction zones. The experiments demonstrate growth of omphacite at the interface between acid melt and peridotite media at 2.9 GPa and 850–900 °C; the omphacite coexists either with garnet and orthopyroxene or with phlogopite. The synthetic omphacite is exclusively of reactive-magmatic origin and does not form in metasomatic way. Findings of omphacite inclusions in peridotitic diamonds and in some pyroxenites from kimberlites are discussed in scope of the obtained experimental data. |
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