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Abstract
XRF and AAS analyses of amphibolite facies metadolerites intruding both basement and cover rocks in the west coast (Vestranden) gneiss region of the central Scandinavian Caledonides to the south of Trondheimsfjord (Snillfjord) suggest the presence of three distinctive intrusive suites: two in the basement and one in the cover. The more numerous basement suite represents a continental tholeiitic magma type whilst the less common group for which limited geochemical data are available shows affinities with plate margin calcalkali basalts (this latter group may also have a chemistry similar to komatiites). The metadolerites within the cover sequence are different from those of the basement in their petrography, field relationships and geochemistry; they are indicated as having transitional chemical characteristics with both within-plate and ocean-floor affinities (possibly representing early stages in the formation of the lapetus ocean). Comparisons with the Ottfjället metadolerites intruding the Särv Nappe to the east in the region of well documented thrust tectonics indicate that the two sets of basement metadolerites are different geochemically from the Ottfjället intrusives and that therefore this part of Vestranden (Snillfjord) is not the root-zone for the Caledonian nappes. There is however the possibility that the cover metadolerites are analogous to the Ottfjället intrusives which would imply a thrust (or tectonic slide) contact between basement and cover. The root-zone must thus lie further to the west, off west-coast Norway. The emplacement of high density rocks into this core-adjacent mobile region may well have set up a gravitationally unstable environment causing the complex pattern of deformation, involving both basement and cover alike.