US EPA

7473665 

Journal Article 

Mantle peridotites and processes - the kimberlite sample 

Harte, B 

1983 

46-91 

English 

The peridotites can be subdivided petrographically into coarse, modally metasomatized and deformed types; the coarse and deformed types are further subdivided according to the Mg/(Mg + Fe) ratio of olivine and relatively low- or high-T (cold or hot) characteristics. The commonest xenoliths, which probably represent the bulk of the continental lithosphere, are coarse, Mg-rich cold peridotites, with major and trace elements depleted in basaltic components (though LREE may be enriched). The common LREE enrichment in coarse peridotites does not appear to have any necessary connection to processes involving the formation of modally metasomatized peridotites. The latter are defined by the development of new mineral species (phlogopite, K-richterite, various opaque minerals) as a consequence of infiltration metasomatism prior to kimberlite eruption. Such rocks are rich in incompatible elements and offer a source both for these and for enriched Sr- and Nd-isotope ratios for basaltic eruptive rocks. The most widespread deformed rocks are deformed, Fe-Ti-rich, hot peridotites, with chondritic relative REE abundances. Models are favoured in which the chemical features of the hot deformed peridotites result from exchange with the megacryst magma. The potential importance in magma genesis of diffusional exchange of both major and trace elements at high T is noted. - R.A.H.