The Uppermost Allochthon in the Scandinavian Caledonides: From a Laurentian ancestry through Taconian orogeny to Scandian crustal growth on Baltica

Thrust sheets of the Uppermost Allochthon in the Caledonides of Scandinavia are distinguished by lithological assemblages and magmatic units that are, in many ways, quite different from those in subjacent nappe complexes. Supracrustal successions are derived mainly from platformal, shelf-edge and basinal-slope environments and are characterized in particular by extensive developments of carbonate rock units that range in age from Late Riphean to Early Silurian. Metasedimentary iron ore forma-tions are also present. Another prominent feature is the Ordovician, arc-type, gran-itoid plutons and batholiths that dominate the geology in certain parts of the alloch-thon. In addition to these lithological elements, the Uppermost Allochthon carries an Ordovician tectonothermal record and early Caledonian, NW-vergent thrust polarity that is unique in Norway. Taken together, these features are indicative of a history of development and crustal growth along the eastern margin of Laurentia, involving an outboard magmatic arc, or arcs, and Taconian accretionary orogenesis. This was followed by recycling and deposition in Late Ordovician to Early Silurian successor