| Abstract: | To evaluate the scale of tectonic movements within the northern sector of the 500-400 Ma Caledonian orogenic belt and its Precambrian foreland zone between the Great Glen Fault (GGF) zone to the southeast and the Laurentian Block to the northwest, we have studied the palaeomagnetism of minor intrusive rocks within the Northern Highlands terrain. These rocks include 1. (1) amphibolites and other metamorphic rocks predating deformation, 2. (2) microdiorities, dolentes and related suites emplaced, and probably magnetised, between 450 and 420 Ma, and 3. (3) Lower-Middle Devonian lamprophyres. A range of predominantly NNE negative and SSW positive components are resolved by cleaning treatment with a dispersion of declinations towards a minority WNW-ESE axis; isolated southerly negative directed hematite-held components suggests limited, but no widespread, remagnetisation in Devonian-Carboniferous times.Comparison is made with data from other tectonic divisions in the Caledonian orogenic belt and the bordering forelands. Palaeopoles from the Northern Highlands closely conform in part with North American Ordovician poles and in part with the post-Ordovician palaeopoles from Britain south of the GGF. The definitive motions of the British Caledonides to emerge from the palaeomagnetic analysis are an anticlockwise rotation of the Caledonian terrain in early Ordovician times, small relative motions during the remainder of Ordovician times followed by large clockwise and then anticlockwise rotations during late Ordovician to early Silurian times contemporary with the last major movements on the Moine Thrust (ca. 430 Ma). Late Silurian-Devonian movements along the GGF were probably below the limits of palaeomagnetic detectability. The collective data require that apparent polar wander movements and concomitant continental movements have currently been incompletely recovered by North American studies and the path for Lower Palaeozoic times is more complex than recognised hitherto. |
