Abstract
Mantle peridotites are interpreted as either residues after partial melting and melt extraction or products of igneous refertilization of refractory peridotites. The simple distinction between these models is difficult to assess because in chemical variation diagrams, both processes lead essentially to the same results. The only exception is the Ti-in-Cpx versus Ti-in-whole-rock plots, which can successfully discriminate between these models. In this study, a modified version of Ti-in-Cpx versus Mg#-in-olivine plots was applied to ∼1,500 spinel peridotite xenoliths from worldwide localities. The results showed that the vast majority of shallow mantle samples are consistent with the partial melting model; however, a minority of samples may indicate refertilization of formerly refractory mantle domains.
Highlights
Four-phase spinel peridotite xenoliths occurring in alkaline basaltic rocks provide direct information about the conditions prevailing in the shallow subcontinental and oceanic lithospheric mantles
In the last decades, the refertilization model has gained an ever wider acceptance among earth scientists working with tectonically emplaced orogenic ultramafic bodies. Some of these scientists think that the same model may or should be applicable to peridotite xenoliths found in alkaline basaltic rocks as well, in spite of the general belief that these samples indicate a depletion trend due to progressive extraction of basaltic melt from a fertile mantle source
Compared with orogenic peridotite massifs, the much smaller size and the accidental nature of xenoliths minimize the chances of tracing textural and chemical variations in the source mantle. This makes it difficult to tell the two types of model apart in any given region, all the more so in that partial melting and refertilization produce the same trend on variation diagrams
Summary
Four-phase spinel peridotite xenoliths occurring in alkaline basaltic rocks provide direct information about the conditions prevailing in the shallow subcontinental and oceanic lithospheric mantles. It occurs that xenoliths severely depleted in FeO, CaO, Al2O3, and alkalis are highly enriched in LREE, e.g., some of the Ray Pic mantle xenoliths in the Massif Central, France (Zangana et al 1997) or those of Szentbékkálla, western Pannonian Basin, Hungary (Embey-Isztin et al 1989) This clearly indicates a decoupling of the processes governing the major element and the incompatible trace element variations. The interpretation of the processes affecting the geochemical evolution of peridotite xenoliths from the lithospheric mantle and those of tectonically emplaced mantle bodies has been essentially the same Fertile lherzolite massifs such as that of the Étang de Lherz in the French Pyrenees (type locality of lherzolite; Lacroix 1917) were generally regarded as pristine mantle, only weakly affected by partial melting and depleted harzburgites as residues, left after melt extraction. It follows that carefully selected xenoliths may prove to be a better choice, even if refertilization processes have been reported on mantle xenoliths in a few cases (e.g., Carlson et al 2004; Tang et al 2008)
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