Relatively iron-rich lherzolite xenoliths of the Cr-diopside suite: A guide to the primary nature of anorogenic tholeiitic andesite magmas

TLDR: A relatively Fe-rich lherzolite xenolith (mg=79) in analcimite from Spring Mount, New South Wales, belongs to the Cr-diopside inclusion suite and accordingly may be assigned an accidental, upper mantle origin this article.

Abstract: A relatively Fe-rich lherzolite xenolith (mg=79) in analcimite from Spring Mount, New South Wales, belongs to the Cr-diopside inclusion suite and accordingly may be assigned an accidental, upper mantle origin. More Mg-rich variants, transitional to the most common Cr-diopside xenoliths (mg=88–92), are also upper mantle components. The relative abundance of Mg-rich xenoliths may reflect factors controlling xenolith preservation in higher temperature lavas. Significant inhomogeneity with respect to Mg/Fe is indicated for the upper mantle, thereby greatly expanding the spectrum of possible primary melts. The abundance of ‘evolved’ volcanics in continental flood ‘basalt’ provinces in considered in terms of this proposal. Least squares mixing calculations suggest that anorogenic tholeiitic andesites may represent primary magmas in their own right, formed by partial melting of relatively Fe-rich lherzolite.