Geochemical comparisons of coronitic olivine gabbro and eclogites: metamorphic effects and the origin of eclogite protoliths (Flemsøy, Sunnmøre, Western Norway)

Olivine gabbros on the island of Flemsøy (Skuløy) show different degrees of transition to eclogite. Coronitic olivine gabbro and eclogitized parts within the gabbro have been compared with more typical country-rock eclogites for the rare earth elements (REE), K, Rb, Sr, Y, Zr, Ti and Ni. Eclogite transformation within the gabbro body has not been accompanied by significant changes of Y, Zr, Ni, P and Ti and the REE patterns. The trace element data support the hypothesis of a common origin for the country-rock eclogites and the gabbro. In the country-rock eclogites Y, Zr and Ti have been fairly resistant to metamorphism on a whole-rock (ca. 1 litre) scale. The REE have typically preserved the original compositions of the inferred gabbro protoliths, but may show variable degrees of selective disturbance which tend to 'flatten out' the original LREE enriched patterns. The protoliths are interpreted as continental, low-P gabbro intrusions of tholeiitic to transitional alkaline affinity. High MgO and FeO contents are attributed to accumulation of olivine. REE and P2O5 allow distinction of the Flemsøy eclogites from the more alkaline eclogite compositions in the Sunnfjord area, and from the eclogites with
more depleted tholeiitic and variable REE patterns in the Stadtlandet area. This suggests the presence of provinces with petrogenetically different eclogite protoliths within the Western Gneiss Region.