Carbonate formations and early NW-directed thrusting in the highest allochthons of the Norwegian Caledonides: evidence of a Laurentian ancestry

Abstract

S tructural, sedimentological and isotope-geochemical investigations on thick, carbonate formations in the Uppermost Allochthon of the Norwegian Caledonides have provided the first direct indications of the Laurentian origins of these shelf and slope/rise successions.Chemostratigraphical ages for marbles mostly range from Vendian to Cambrian. The earliest tectonic deformation, involving NW-vergent thrusts and folds in one of the nappes, is considered to relate to Taconian orogenic development along the margin of Laurentia. Subsequently, during Siluro-Devonian, Baltica-Laurentia collision, these thick successions, and plutonic complexes farther south, were detached from their Laurentian roots and retransported into the higher levels of the Scandian orogenic wedge.

Structural and Metamorphic Implications of the Final Emplacement of the Lyngen Nappe

“…The Uppermost allochthon and the higher units of the Upper allochthon are generally exotic terranes derived from spreading ridges, island arcs, and marginal basins of the Iapetus Ocean (Gee, 1975;Stephens, 1988), and usually infers a Laurentian affinity of the rocks. There is evidence that some of these formations were not only derived from Laurentia, but that they were also initially deformed there during the Taconian Orogeny, before their emplacement onto Baltica during the Scandian event (Roberts et al, 2002). Roberts and Gee (1985); Corfu et al (2004); Torsvik and Cocks (2005).…”

“…The rest of the Upper Allochthon currently includes the Kåfjord and Nordmannvik nappes, and is composed of metamorphic rocks postulated to represent the Baltica-Iapetus continent-ocean transition (Stephens & Gee, 1985;Andréasson, 1994), ophiolites, and island-arc and volcanic rocks (Harland & Gayer, 1972). The Uppermost Allochthon currently consists of the Lyngen, Nakkedal, and Tromsø nappes, and contains Caledonian intrusive rocks interpreted to have originated near or within the continental margin of Laurentia Roberts et al, 2002;Barnes et al, 2007;Roberts et al, 2007;Augland et al, 2012). The Nakkedal Nappe is composed of quartzofeldspathic paragneisses and the Skattøra Migmatite Complex (Augland et al, 2014).…”

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

“…The metamorphism in both the Nakkedal and the Tromsø nappes has been suggested to relate to Taconian orogenesis along the eastern margin of Laurentia (Krogh et al, 1990;Roberts et al, 2007). The rocks of the Uppermost Allochthon as a whole have also been considered to derive from the Laurentian side of the Iapetus Ocean (Stephens & Gee, 1989;Roberts et al, 2002Roberts et al, , 2007Melezhik et al, 2003). Based on radiometric data, the Tromsø Nappe is characterised mainly by intermediate concentration levels of uranium and low concentrations of potassium and thorium associated in part with carbonate rocks.…”

Orogenic degassing, scapolitization and K- metasomatism during Caledonian exhumation, Helgeland, Norway

“…The Upper Allochthon comprises sedimentary and igneous rocks derived from the Iapetus Ocean, including ophiolites and island-arc complexes (e.g., Stephens, 1988;Grenne et al, 1999;Roberts, 2003) with faunas of Laurentian affinity (e.g., Bergström, 1979;Spjeldnaes, 1985;Bruton & Harper, 1988). The Uppermost Allochthon was formed in a continental margin setting of Laurentian origin (e.g., Melezhik et al, 2002;Roberts et al, 2002Roberts et al, , 2007, consisting of various metasedimentary, carbonate and magmatic units, and is divided geographically by the Paleoproterozoic Tysfjord basement window (Skår, 2002). North of the Tysfjord window, a number of unnamed and named thrust sheets, divided into Niingen, Tromsø, Gratangen, Nakkedal, Evenes, Lyngsfjell and Bjerkvik nappe complexes, are included in the Uppermost Allochthon (Barker, 1986;Zwaan et al, 1998;Melezhik et al, 2003).…”

“…South of the Tysfjord window, in tectono stratigraphic order top to bottom, Helgeland Nappe Complex (HNC), Beiarn Nappe Complex (BNC), and Rödingsfjället Nappe Complex (RNC) constitute the Uppermost Allochthon, with the HNC and RNC being the dominating units in terms of areal extent. The Fauske Nappe is in some maps shown as a separate unit (Roberts et al, 2007), but is generally interpreted to form the base of the RNC (Gustavson, 1996;Roberts et al, 2002). Corre lations of the BNC to either the HNC or the RNC ( Gustavson & Gjelle, 1991;Gustavson, 1996) have been proposed, but it may very well be seen as a separate complex (Augland et al, 2012).…”