Abstract

Titanate minerals of the crichtonite series (AM21O38, A = Sr in crichtonite; M = Ti, Fe, Cr) reported from mantle peridotite xenoliths associated with kimberlites appear to be solid solutions of several named end members (mostly Ba, Sr, K, Ca) that contain some rare earth elements (REE). Knowledge of the REE distribution in these titanates could be very important for geochemical modelling of the upper mantle. An instrumental neutron activation analysis (INAA) was obtained for a single titanate grain from a typical veined peridotite xenolith from kimberlite. The data support original electron probe REE analyses showing enrichment in the light REE. The absence of significant heavy REE disagrees with recent structural interpretation for the analogous Ba and K end members (lindsleyite, mathiasite respectively) based on a bimodal light and heavy REE distribution. Similar structural interpretation of bimodal REE in the Ca end member (loveringite) is reexamined and also considered doubtful.

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