The Assynt alkaline suite

Abstract

Summary The alkaline intrusives in Assynt overlap the thrust movements and can be used to put limits on their magnitude and timing. The Ailsh syenite is the earliest igneous body within the thrust belt; the Borralan complex is later and overlapped major movements on the Assynt thrust. Large scale displacements on the Sole and Assynt thrusts ended before movement ceased on the Moine thrust. Pyroxene variation in the Ailsh complex confirms that the leucosyenites form a series fractionated before emplacement, but the pyroxene range is unusual for an igneous series and consistent with a metasomatic origin for pyroxene-rich members.