The offshore continuation of the Moine Thrust north of Shetland as deduced from basement isotopic ages

Abstract

Synopsis Caledonian isotopic ages from the southern section of the Scotland–Norway Basement Ridge effectively separated the Archaean–Proterozoic Lewisian Complex and the Lofoten-Vesterålen Complex forming the SW and NE ends of the ridge. The distribution of Caledonian and Lewisian age data to the north and west of Shetland confirm suggestions that the Moine Thrust merges generally within the region of the west margin of the Caledonian mobile belt, as seen on east Greenland. The Moine Thrust between Orkney and Shetland is offset in a dextral sense by c. 25 km. The Walls Boundary Fault intersects the West Shetland Platform edge to the north of Shetland, with the basement displaying an apparent c. 15 km sinistral offset.

Evidence from Rb–Sr mineral ages for multiple orogenic events in the Caledonides of Shetland, Scotland

“…This sector of North Roe is of particular importance, as it appears to be the only area in the Scottish Caledonides where the dominant metamorphic fabrics are Knoydartian, and do not appear to have been extensively reworked during subsequent Caledonian events. However, some very localized Caledonian reworking may be indicated by the Ordovician (466 ± 6 Ma) 40 Ar/ 39 Ar muscovite age reported by Flinn (2009 Ritchie et al 1987;Flinn 1992Flinn , 1993McBride & England 1994). No evidence currently precludes the suggestion that the Wester Keolka Shear Zone is essentially a highly tectonized basement-cover unconformity (Pringle 1970), and therefore not a significant regional structure.…”

“…The latter have been compared lithologically with the early Neoproterozoic Moine Supergroup of the Northern Highland Terrane in mainland Scotland (Flinn 1985(Flinn , 1988. It logically follows that the Wester Keolka Shear Zone could therefore be correlated with the Moine Thrust, which defines the western limit of the Caledonides in mainland Scotland, separating the foreland Lewisian Gneiss Complex from the Moine Supergroup (Andrews 1985;Ritchie et al 1987;Flinn 1992Flinn , 1993McBride & England 1994). However, two lines of field evidence suggest that this correlation needs to be treated with caution.…”

U–Pb zircon geochronology and geodynamic significance of ‘Newer Granite’ plutons in Shetland, northernmost Scottish Caledonides

“…These are succeeded to the east by the metasedimentary Sand Voe Group, which has been correlated with the Neoproterozoic Moine Supergroup of NW Scotland (Pringle 1970;Flinn 1988). The intervening east-dipping Wester Keolka Shear Zone has been correlated with the Silurian Moine Thrust, which defines the western margin of the Caledonides on mainland Scotland (Andrews 1985;Ritchie et al 1987;Flinn 1992Flinn , 1993McBride & England 1994).…”

Caledonian and Pre-Caledonian orogenic events in Shetland, Scotland: evidence from garnet Lu–Hf and Sm–Nd geochronology

“…This structure has been regarded as an extension of the Moine Thrust Zone which defines the northwest margin of the Caledonides in mainland Scotland (Fig. 1A; Andrews 1985;Ritchie et al 1987;Flinn 1992;1993;McBride & England 1994). However, the lowermost part of the SVG contains pebbles that are lithologically similar to the underlying Uyea Gneiss Complex (Pringle 1970, Kinny et al 2019, indicating that the WKSZ may in fact be a tectonically modified unconformity.…”