Paleomagnetism and 40Ar/39Ar geochronology of Meso-Neoproterozoic rocks from southwest Norway. Implications for magnetic remanence ages and the paleogeography of Baltica in a Rodinia supercontinent context

Abstract

Here we present new 40Ar/39Ar geochronology, rock magnetic, and paleomagnetic data obtained from rocks from three distinct domains of the Precambrian Sveconorwegian orogen (Southern Norway) that record progressively younger orogenic events from east to west. The first locality is in the Bamble lithotectonic unit and the other two areas are located within the Telemark and Rogaland–Vest Agder sectors in the central and southwestern parts of the Telemark lithotectonic unit, respectively. New and existing geochronology data on metamorphism and cooling, combined with detailed rock magnetic analyses indicate that studied rocks cooled and blocked (acquired) the natural remanent magnetization at ∼ 1090 Ma (Bamble Lithotectonic unit), 1000 Ma (Central Telemark), and at around 900 Ma in the westernmost part of the Telemark Lithotectonic Unit. Accordingly, the new paleomagnetic poles for the Bamble (Plat = -6.6°N, Plong = 218.4°E, N = 38, A95 = 6.1°, K = 15.6), central Telemark (Plat = -17.4° N, Plong = 229.8° E, N = 23. A95 = 6.5 °, K = 22.6), and western Telemark Lithotetonic Unit (Plat = -46.2° N, Plong = 209.4° E, N = 9, A95 = 12.0, K = 19.4) were assigned 1090 Ma, 1000 Ma, and 900 Ma ages, respectively. The new Bamble paleomagnetic pole reconstructs Baltica at ∼ 1090 Ma with noticeable latitudinal gap from the eastern Laurentian margin and thus does not support classical Baltica-Laurentia configuration within the Rodinia supercontinent. The other two younger poles, when used together with the coeval paleomagnetic data from Laurentia do not support the traditionally envisaged Meso- to Neoproterozoic Baltica-Laurentia relationship either. Overall, the new data do not lend any support to the close connection between the two continents during the proposed Rodinia tenure but instead emphasize the problems with the traditional paleogeographic reconstructions of Rodinia. The new data appear more in line with the geological record within the Sveconorwegian orogen, which indicates that the orogeny developed at or behind active continental margins. While Baltica and Laurentia may have resided at broadly similar latitudes between 1000 and 900 Ma, there is no geologic and paleomagnetic evidence for placing them next to each other.