Abstract

Because solid-solution trace elements in olivine have significant influence on upper mantle rheology, it is important to establish whether inclusions in olivine are exsolved from an intrinsic solid solution or are introduced by metasomatism. In a study of olivine in hot deformed peridotite xenoliths from kimberlites, we have found a new type of multiphase inclusion that contains Fe-Ti-rich and Si-Fe-Al-rich phases. Microstructural relations indicate that these inclusions form by a process involving metasomatic fluid infiltration along a fine network of cracks shortly before entrainment of the xenoliths, followed by crack healing during xenolith transport in the magma.

The high trace-element content of Ti, Ca, Al, and Na found in Fe-Ti-rich, hot deformed olivine is related to metasomatic enrichment that occurred shortly before kimberlite eruption. Assessment of the effects of the Fe-Ti metasomatism indicates that the Cr-C-rich inclusions found in olivine from other hot deformed xenoliths are formed by precipitation from an intrinsic solid solution in olivine that has not been affected by Fe-Ti-rich metasomatism.

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