Post-Grampian top-to-WNW Caledonian ductile shear in the Grampian Highlands [abstract only]

The Glendoe Hydro Scheme involves construction of an 4.6 m diameter bored tunnel,
extending 8.6 km SSE-ward from Fort Augustus and the Great Glen, through mainly
Grampian Group Dalradian rocks deformed in the Grampian orogeny. The great prize
though is access to an 8 km long borehole driven perpendicular to regional strike
through the footwall and hanging wall of the Eilrig Shear Zone. The Eilrig Shear Zone
is unique in the geology of the Grampian Highland ‘terrane’ and is revealed as 1.5 km
thick in the NW-end of the continuous tunnel section. The shear zone is a low
temperature ductile (quartz-muscovite mylonite) to brittle-ductile structure. No similar
structure is recorded anywhere else in the Grampian terrane, late stage Grampian
structures in the southern Highlands are represented by ductile folds and crenulation
fabrics. The Grampian Group lithostratigraphical succession (Corrieyairack
Subgroup) in the hanging wall of this structure has experienced a typical NW-vergent
Ordovician (Grampian) orogenic deformation sequence and accompanying garnetamphibolite
facies metamorphism. In stark contrast, the footwall succession (Glen
Buck Pebbly Psammite Formation) comprises fluviatile to shallow marine? deposits
of uncertain stratigraphical affinity and has not experienced the orogenic effects
pervasive in the hanging wall. If Grampian (Ordovician) deformation is absent in the
footwall of the Eilrig Shear zone then that structure represents the Grampian Orogenic
Front.
The net translation on this low temperature/high level shear zone must surely be
considerable (100 km+?). Is the displacement late Grampian (Ordovician) in age or
Scandian (Silurian)? If the latter, what might be the relationship to the Moine Thrust
Zone in the Northwest Highlands terrane across the GGF? Is the footwall succession
to the ESZ comparable in any way to the ‘foreland’ succession in the Northwest
Highlands?