The contact zone of the Rhum ultrabasic intrusion: evidence of peridotite formation from magnesian magmas

Abstract

The Eastern Layered Series of the Rhum ultrabasic complex formed in situ, and was not tectonically emplaced as previously suggested. Field relations along the contact show no evidence for the existence of a late ‘Marginal Gabbro’, instead peridotite and allivalite layers can be traced to within 2 m of the surrounding partially melted country rocks. Local preservation of a chilled margin to one peridotite layer indicates that the parental magma consisted of an olivine tholeiite liquid carrying approximately 19% (vol.) olivine crystals in suspension.