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Article by IGV's affiliated senior researcher in GFF

with the title: U-Pb baddeleyite age for the Ottfjället Dyke Swarm, central Scandinavian Caledonides: new constraints on Ediacaran opening of the Iapetus Ocean and glaciations on Baltica

Abstract: The Ottfjället Dyke Swarm (ODS) is a prominent component of the Ediacaran mafic magmatism associated with opening of the Iapetus ocean, and hosted in the Särv Nappe, Middle Allochthon of the Scandinavian Caledonides. A U-Pb baddeleyite age of 596.3 ± 1.5 Ma for a thick, well preserved, plagioclase-phyric dolerite dyke in Härjedalen, Sweden, dates emplacement of the swarm. The age represents a robust, inheritance-free reference age for variably deformed and metamorphosed tholeiitic dykes in sandstone-dominated sequences of the lower part of the Middle Allochthon, representing the proximal, rifted Baltoscandian margin preceding the opening of Iapetus. The new age is within the narrow time span between 610 and 595 Ma defined by the most reliable age estimates for mafic dykes in structurally higher nappes (upper part of Middle Allochthon), representing the distal margin during the opening of Iapetus. The Ottfjället Dyke Swarm cuts the Tossåsfjället Group succession, which includes sabkha-related carbonate platform and diamictite couples, one of several correlated Neoproterozoic glaciogenic successions in Scandinavia. The intrusion age of ca. 596 Ma therefore sets a minimum age for the glaciogenic successions. It implies that Neoproterozoic glaciations in Scandinavia predate the ca. 580 Ma Gaskiers glaciation event and are probably part of the ca. 635 Ma Marinoan “Snowball-Earth”-type glaciation.

Kumpulainen, R.A., Hamilton, M.A., Söderlund, U. and Nystuen, J.P., 2021. U-Pb baddeleyite age for the Ottfjället Dyke Swarm, central Scandinavian Caledonides: new constraints on Ediacaran opening of the Iapetus Ocean and glaciations on Baltica. GFF: 143:1, 40–54,
DOI: 10.1080/11035897.2021.1888314

 

 

Sketch map showing positions of dyke swarms of the Baltoscandian Dyke Swarm (BDS) in a palaeogeographic setting of the Neoproterozoic Baltoscandian marginal zone, modified from Pease et al. (2008), with data on the BDS components from Andréasson et al. (2005) and Jakob et al. (2017). Egersund, Ottfjället, Sarek and Kebnekaise indicate inferred original position of dyke swarms. The map area of Figure 2 in relation to the present-day geography is indicated approximately by a broken circle. VB, Valdres Basin; HB, Hedmark Basin; EB, Engerdalen Basin; Ottfjället gives the approximate position of the Tossåsfjället Basin; RB, Risbäck Basin; TVR, Varangerfjorden-Tanafjorden Region