A review of the structure and stratigraphy of the Moinian of Ardgour, Moidart and Sunart—Argyll and Inverness-shire

Abstract

Synopsis The structural geometry is the result of four episodes of deformation (F 1 –F 4 ), with most major folds belonging to the second or third episodes. Major F 1 folds are probably absent (on stratigraphical evidence) but slides of the F 1 episode are not ruled out. Complex F 2 geometries—with curvilinear axes, and antiforms which turn into synforms when traced along traces—are found where F 2 folds are ‘folded’ by F 3 folds, and also remote from F 3 fold hinges. Intense inhomogeneous flattening explains these features, and it is considered that this flattening may be part of the second, rather than the third deformation. In the prevailing high-temperature conditions, the amount of flattening seems to be a function of rock-type and it is possible to distinguish between the simpler structures in thick psammites and the more complicated, highly flattened, structures in pelitic/striped rocks. The major rock units probably represent a stratigraphic sequence, from bottom to top, 1. Morar Division, 2. Glenfinnan Division and 3. Loch Eil Division.