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Paper No. 11
Presentation Time: 8:00 AM-6:00 PM


PROUTY, Jonathan M.1, AUGLAND, L.E.2, AGYEI-DWARKO, Nana Y.3, ANDRESEN, Arild3 and STELTENPOHL, Mark1, (1)Geology and Geography, Auburn University, Auburn, AL 36849, (2)Dept. Geosciences, University of Oslo, PO Box 1047, Blindern, Oslo, 0316, Norway, (3)Department of Geosciences, University of Oslo, PO Box 1047, Blindern, Oslo, 0316, Norway,

New structural and 40Ar/39Ar and U-Pb geochronological data are reported for the Salten and Ofoten regions of north-central Norway allowing for tectonostratigraphic correlations to be made across the E-W-trending Tysfjord orogenic culmination, improving our understanding of basement-cover relations over a vast part of the northern Scandinavian Caledonides. In Salten, large areas previously interpreted as pre-Caledonian (ca 1.8 Ga) Baltic basement (Heggmovatn and Landegode domes) are in fact Caledonian thrust sheets belonging to the exotic (Laurentian) Uppermost Allochthon. Orthogneisses that intrude metasedimentary units within the Heggemovatn allochthon are dated to ca 930 Ma, and these are intruded by ca 430 Ma leucogranites; U-Pb analysis of detrital zircons from metasiliciclastic rocks constrain the age of deposition to between 1100-930 Ma. The Bratten orthogneiss, which we lithologically correlate with the Landegode basement dome, is ca 950 Ma. Our mapping implies that the Steigtinden and Mikkelharn gneiss domes also are allochthonous and have potential Laurentian links. 40Ar/39Ar step-heating analysis of hornblende and K-feldspar suggest pre-Scandian thermal effects, whereas muscovites and phlogopites record Siluro-Devonian metamorphism and cooling from Scandian thrust emplacement. In Ofoten, a ca 470 Ma U-Pb date on the Snaufjell granite, which intrudes a thick section of the nappe pile exposed in the core of the Ofoten synform, documents continuity of Uppermost Allochthon tectonostratigraphy and structures across the erosionally breached Tysfjord culmination. The Ofoten synform appears to be the northern counterpart of the Engeloy synform. Pre-Scandian Caledonian relics within the Lofoten-Vesteralen region also imply that slivers of Uppermost Allochthon exist far to the west of areas previously mapped as Baltic basement. We outline our current thoughts on the distribution of Baltican versus Laurentian crust in Scandinavia between 67o and 69o N latitudes.
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