Metasomatism and Partial Melting in Upper-Mantle Peridotite Xenoliths from the Lashaine Volcano, Northern Tanzania

REE (LREE) into the glass with respect to clinopyroxene, but the A group of chrome-spinel peridotite upper-mantle xenoliths from the reverse for Sr and Y, in both mica-bearing and mica-free parageneses. Lashaine volcano, northern Tanzania, differs from other xenoliths In a mica-bearing melt pocket, Rb and Ba partition preferentially at this locality in containing glassy melt pockets. Modal, mineral into mica relative to both clinopyroxene and glass. Similar patterns chemical and isotopic evidence indicates that, before the melting that of partitioning exist in a similar xenolith from Labait (another was coincident with the xenolith entrainment and eruption in the Tanzanian xenolith locality) except that Sr is highly concentrated Pleistocene, the sub-Tanzanian mantle lithosphere had a complex in the glass; and the glass and mica contain high Ba. Comparison history. A major element depletion at >3·4 Ga gave rise to a of the chemistry of the melt pockets in the xenoliths from Lashaine high-olivine restite protolith, and this was followed by an episode and other northern Tanzanian volcanoes (Labait and Olmani) of K, Fe, Ca, Ti and Rb metasomatism at >2·0 Ga (Metasomatic indicates that the melting in each xenolith suite was accompanied Event I) resulting in the formation of well-equilibrated Cr-diopside by a distinctive metasomatic influx. and phlogopite. A later episode of metasomatism (Metasomatic Event II), first reported here, is recognized by texturally and chemically non-equilibrated titanian phlogopite, Ti–Cr-diopside, enstatite–bronzite, ilmenite and rutile, interpreted as due to an influx