Abstract
Evidence is presented for a carbonate-immiscibility phenomena in the upper mantle based on data from a set of strongly metasomatized xenoliths in a basanitic lava flow from Fernando de Noronha Island (southwest Atlantic). A petrological and geochemical study of lherzolitic and harzburgitic xenoliths reveals that the oceanic mantle of this region has been affected by very strong carbonate metasomatism. The metasomatism led to wehrlitization of the primary mantle mineral assemblage (ol, opx, sp). The wehrlitization was the result of interaction between a possibly ephemeral sodic dolomitic melt or fluid with the mantle peridotite according to the following reactions, which include sodic components:
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