Petrology and geochemistry of spinel peridotite nodules and host basalt, Vestspitsbergen

Mineral compositions and major and trace element whole-rock analyses for eight spinel peridotite nodules and their host basalt from Quaternary volcanoes in Vestspitsbergen are presented. Modally the nodules range from harzburgite, lherzolite (dominant) and olivine websterite, and they are considered to represent mantle material. The olivines range in composition from Fo 88.1 to 92.0, the orthopyroxenes have
100 Mg /(Mg + Fet) ratios between 88.9 to 92.3. The clinopyroxenes are chromediopside and the oxide phase is Al- or Cr-spinel.
The compatible trace elements of the nodules correlate with their modal composition. Thus Se correlate
positively with clinopyroxene, whereas Ni and Co correlate positively with olivine. La, Ta, Th, U and K show highest concentrations in some of the most refractory nodules, and their REE patterns are very variable.
The refractory nature of some of the nodules is thought to relate to an earlier basalt extraction from the mantle. This 'refractory' mantle was subsequently enriched in the highly incompatible elements, probably by the veining or the metasomatism by alkali basalt. The host basalt can be modelled, in terms of RE elements, to represent a partial melt (around 3% batch melting) of a composite source, represented by the spinel peridotites nodules.