Tectonostratigraphic development of the Trondheim region Caledonides, Central Norway

Abstract

The metamorphic allochthon of the central Norwegian Caledonides comprises a complex of discrete nappes of metasediments and igneous rocks ranging in age from probable Svecofennian through Vendian to Silurian. This southeastward-translated allochthon overlies a thin cover of autochthonous Vendian to Cambrian sediments deposited upon a crystalline Precambrian basement, and is superseded by late-orogenic, intermontanebasinal sediments of latest Silurian to Middle Devonian age. Stratigraphical sequences in higher allochthonous units are floored by oceanic tholeiitic basalts with rare, subjacent sheeted-dyke and gabbro units, considered as fragments of an ophiolite assemblage which suffered initial eastward transport in pre-Middle Arenig times, an important orogenic event which is well represented in northern and southwestern Norway. The overlying Ordovician—Silurian sequences, disturbed by episodic parorogenic events, embrace a variety of sedimentary facies from shallow-water carbonates to deep-marine terrigenous turbidites and include both island arc and marginal basin lavas and intrusives. Polyphase Middle Silurian metamorphism and deformation resulted in a complex telescoping and dissection of the Lower Palaeozoic rocks and their Precambrian substrate, with nappe translation in the order of several hundred kilometres. Folding and thrusting of Old Red Sandstone molasse sediments attests to continuing tectonism well into Devonian times.