The Early to Late Ordovician rock record of the Oppdal area, Scandinavian Caledonides: Explosive volcanism, element recycling and basin infill during closure of the Iapetus Ocean
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- Institutt for geofag [2331]
Abstract
This thesis describes the Ordovician rocks of the Oppdal area, central Norwegian Caledonides, which record the evolution of a section across the Laurentian margin. By fieldwork, geochronology and geochemistry a revised geological map has been made, and the processes active during rock formation have been examined. A ca 475-470 Ma succession of sandstone and MORB-like basalt coexist with pyroclastic rocks with a conflicting geochemical signature; extreme enrichment in elements associated with evolved continental crust combined with a high content of elements which point to a mantle source and limited fractionation. We suggest that subducted continental material partially melted and reacted with the mantle to form anomalous mantle domains which sourced the enriched rocks, whereas normal mantle sourced the MORB, all in an extensional setting possibly related to the death of a subduction zone close to Laurentia. These rocks are unconformably overlain by a volcanosedimentary unit formed in a continental arc setting >435 Ma, before the collision between Laurentia and Baltica when units described herein were thrusted onto Baltica along with the rest of the western Trondheim Nappe Complex.List of papers
Paper I: Dalslåen, B.H., Gasser, D., Grenne, T.,Augland, L.E. and Corfu, F., 2020. Ordovician shoshonitic to ultrapotassic volcanism in the central Norwegian Caledonides: The result of sediment subduction, mantle metasomatism and mantle partial melting. Lithos, 356. DOI: 10.1016/j.lithos.2020.105372. The article is included in the thesis. Also available at: https://doi.org/10.1016/j.lithos.2020.105372 |
Paper II: Dalslåen, B.H., Gasser, D., Grenne, T., Augland, L.E. and Andresen, A., 2020. Early to Middle Ordovician sedimentation and bimodal volcanism at the margin of Iapetus: The Trollhøtta–Kinna basin of the Central Norwegian Caledonides. In: Murphy, J.B., Strachan, R. & Quesada, C. (eds) Pannotia to Pangaea: Neoproterozoic and Paleozoic Orogenic Cycles in the Circum-Atlantic Region. Geological Society, London, Special Publications, 503. DOI: 10.1144/SP503-2020-37. The article is not available in DUO due to publisher restrictions. The published version is available at: https://doi.org/10.1144/SP503-2020-37 |
Paper III: Dalslåen, B.H., Gasser, D., Grenne, T., Ganerød, M. and Andresen, A. The Skuggliberga unit of the Oppdal area, central Scandinavian Caledonides: calc-alkaline andesitic pyroclastic volcanism in a fluvial to shallow marine basin following mid-Ordovician tectonism. Norwegian Journal of Geology 101, 202107. DOI: 10.17850/njg101-2-2. The article is included in the thesis. Also available at: https://doi.org/10.17850/njg101-2-2 |