Abstract

The Ach'uaine hybrids of northern Scotland form a suite of Caledonian minor intrusions with a wide range of cogenetic compositions, ranging from mantle-derived mafic shosonite chemically similar to the lamprophyres of the region, through syenites comparable to the rare Caledonian syenites, to granites typical of the local Newer Granites. They therefore provide a hitherto unsuspected direct link between these major Caledonian magma types and suggest that the Newer Granites in the Northern Highlands may have mantle-derived parental components of subduction-related, shoshonitic affinity. Shoshonite to granite fractionation is thought to have proceeded within a compositionally stratified Caledonian magma chamber. Chemical data, including rare earth element analyses, demonstrate the control of crystal fractionation, but the wide range of silica saturation may imply a significant crustal input.

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