The Lochnagar granitic ring complex, Aberdeenshire

Abstract

The Lochnagar granitic ring complex consists of nine concentric annular and crescentic masses of adamellite and granodiorite. The successive members of the complex were emplaced in order of increasing potassium and silica content and decreasing size and grain size from the margin towards the centre of the complex. The early members of the complex, the granodiorites and the first adamellite, are foliated and crowded with inclusions of the contiguous wall rocks. They are partly circumscribed by an adamellite cone sheet and appear to have been forcibly intruded into the complex. The later finer-grained adamellites appear to have been emplaced into the central part of the complex by cauldron-subsidence; the last two phases, the smallest, finest-grained and most felsic adamellites, being emplaced into the centre of the complex under flat roofs of earlier adamellite.