Early Silurian mafic–ultramafic and granitic plutonism in contemporaneous flysch, Magerøy, northern Norway: U–Pb ages and regional significance

Abstract

The Caledonian Magerøy sequence comprises Earliest Silurian clastic metasedimentary rocks, which underwent folding and regional metamorphism and were intruded by a mafic-ultramafic complex and various granitic plutons. U-Pb ages of 438.2 AE 0.7 Ma for gabbro in the Honningsvåg Igneous Complex, 438.4 AE 0.9 Ma for an associated granite and 437.7 AE 1.6 Ma for the Finnvik granite coincide within error with the age of deposition inferred from fossils demonstrating a very rapid geological evolution. Plutons of peraluminous affinity are somewhat younger at 436.0 AE 1.0 Ma (Skarsvåg granite) and 434.5 AE 1.5 Ma (a granitic dyke in the Skarsvåg Nappe). The association of flysch deposition, folding and mafic-felsic magmatism suggests formation at a trench-ridge intersection. These Early Silurian events are the expression of a period of major magmatism in a variety of settings all along the Caledonides, probably reflecting rapid convergence and subduction during closure of the Iapetus Ocean. Re-evaluation of the palaeomagnetic signature of the Honningsvåg Igneous Complex indicates that at the time of formation the suite was located in an equatorial position, probably close to the Laurentian margin, and was subsequently translated southward by some 1350 km prior to and during emplacement onto the Baltic margin.

Middle to Late Devonian–Carboniferous collapse basins on the Finnmark Platform and in the southwesternmost Nordkapp basin, SW Barents Sea

“…The West Troms Basement Complex consists of tonalitic, trondhjemitic, and granitic gneisses; metasupracrustal rocks; and mafic and felsic igneous rocks (Corfu et al, 2003;Bergh et al, 2010). These rocks were deformed during the Svecofennian orogeny, which resulted in the formation of NW-SE-trending steep foliation, ductile shear zones, and upright and vertical macrofolds, which were only weakly reworked during the Caledonian Orogeny (Corfu et al, 2003;Bergh et al, 2010).…”

Mid/Late Devonian-Carboniferous collapse basins on the Finnmark Platform and in the southwesternmost Nordkapp basin, SW Barents Sea

“…The Magerøy Nappe is characterized by asymmetrical, NNE-SSW trending, east-verging folds and lowangle, NW-and SE-dipping thrusts similar in trend to those observed within the Kalak Nappe Complex (Andersen, 1981), and is intruded by granitic and gabbroic plutons, e.g. the Silurian 195 Honningsvåg Igneous Complex (Corfu et al, 2006) and the Finnvik Granite (Andersen, 1981).…”

New high-resolution aeromagnetic and radiometric surveys in Finnmark and North Troms: linking anomaly patterns to bedrock geology and structure

“…The oldest formations are mainly of shallow-marine origin and are succeeded by a distinctive turbiditic, flysch sequence (Andersen, 1984). The latter also occurs in imbricate thrust slices on the mainland and on Sørøya (Kirkland et al, 2005;Corfu et al, 2006). Scandian deformation commenced shortly after the flysch deposition and was interrupted by intrusion of mainly ultramafic and mafic plutons of the late Early Silurian Honningsvåg Igneous Complex (Robins, 1998;Corfu et al, 2006).…”