Lithostratigraphic correlation of the Salangen (Ofoten) and Balsfjord (Troms) Groups: evidence for the post-Finnmarkian unconfirmity, North Norwegian Caledonides.

Abstract

Detailed mapping around Ofotfjorden (68-69\u00B0N)demonstrates many tectonostratigraphic and lithostratigraphic similarities with the Caledonian allocthons in the Balsfjord area, 150 km to the north. Lithostratigraphic similarities are particularly striking between the nonfossiliferous Salangen supergroup (Ofoten) and the fossiliferous Upper Ordovician-Silurian Balsfjord Group. Both groups occur at an equivalent level in the respective nappe stacks. The lower contact of both groups is erosional, lying above a basement containing mafic-ultramafic igneous complexes that have been interpreted as ophiolite fragments; the Salangen supergroup lies above the upper part of the Narvik Group (Bjerkvik nappe) and the Balsfjord Group overlies the Lyngen Gabbro\/Ophiolite. Relatively thick marble sequences, including both calcite and dolomolite marbles, and distinctive carbonate pebble diamictites, quartzites, breccias, conglomerates, and mica schists are present in both groups at similar stratigraphic levels. Syntectonic granitoids and pretectonic metadolerites intruded both groups. The combined depositional, magmatic and tectonostratigraphic similarities strongly support that the Upper Ordovician\/Silurian post-Finnmarkian basin recognized within the nappe pile in Balsfjord extended much further south into the Ofoten nappes. This implies that at least the upper part of the Narvik Group is of pre-Scandian age.