Xenoliths, mantle-derived ratios

Distinctive lithospheric mantle He. As discussed in the Possible xenolith noble gas components section, radiogenic production within the lithosphere can lower the He/ He ratio of He derived from the convecting mantle. Therefore, the He represents a distinctive lithospheric component. This may be created in the xenolith source region, or may involve He that is remobilized in the lithosphere. As discussed below, regional studies often contend with distinguishing between distinctive asthenospheric and lithospheric sources for such He. 

The He/ e ratios in ultramafic xenoliths often are similar to those of MORB or low He/ He OIB and indicate that the He in the xenoliths is dominantly derived from the underlying convecting mantle. However, it is not clear whether the He came directly from the underlying mantle, or has had some residence time in the lithosphere prior to incorporation in the xenoliths. 

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