The geochemistry of the Ben Hope sill suite, northern Scotland, U.K.

Abstract

Immobile trace-element geochemistry may be used successfully to obtain additional information about the magmatic character and tectonic setting of amphibolite-facies basic rocks, in which former textures have been destroyed. This method is illustrated in a study of the Ben Hope suite of sills which were intruded into the Morar Division Moine sediments before the area was deformed in late Precambrian time. These orthoamphibolites emerge as a series of chemically discrete, but related, variously fractionated tholeiitic sills. Amphibolites from the nearby ‘Meadie Sill’ belong to the same suite, which can, however, be chemically distinguished from other early basic bodies in northern Scotland. Chemical discrimination of the tectonic setting confirms a within-plate environment, for most segments of the Ben Hope sill suite. However, some amphibolites apparently have “plate-margin characteristics” which conflict with the field evidence. This may reflect magmatic effects rather than a change in the tectonic environment.