Origin of the White Allivalite, Western Cuillin, Isle of Skye

Abstract

Tholeiitic contact rocks and a wide zone (White Allivalite) rich in primary precipitate calcic plagioclase are marginal to a layered allivalite series in a funnel-shaped intrusion. The high structural level apparently precludes the possibility that the ultrabasic layered rocks are the basal part of an accumulate from a tholeiitic magma. It is suggested, therefore, that a suspension of calcic plagioclase in a liquid more basic than basalt gave rise to an approximately equal volume of layered ultrabasic rocks by fractional crystallization. Emplacement was probably initiated as a tholeiitic cone-sheet complex, followed by the injection of the ultrabasic suspension in a volume sufficiently large to form a funnel-shaped body within the cone-sheet complex.