Chromium-rich sapphirine from the Bjørnesund area, southern West Greenland and its bearing on the conditions of crystallisation of the Fiskenæsset anorthosite complex

Abstract

Windley et al. (1973) have postulated that the Fiskenæsset anorthosite complex crystalIised under conditions of high water vapour pressure. This hypothesis readily explains several of the distinct characteristics of the complex. In particular, the late precipitation of chromitite layers towards the top of the complex in the anorthosite sensu stricto (Ghisler & Windley, 1967) is not normally expected in large layered intrusions (Wager & Brown, 1968), and is explained because the early precipitation of chromite is suppressed under such conditions (Shiraki, 1966). AIso, Windley et al. (1973) have suggested that chromium amphibole, rather than pyroxene, was precipitated in association with the chromite as a direct consequence of the enrichment of volatiles in the upper parts of the intrusion.