Late Neoproterozoic–Silurian tectonic evolution of the Rödingsfjället Nappe Complex, orogen-scale correlations and implications for the Scandian suture

Abstract

The Scandinavian Caledonides consist of disparate nappes of Baltican and exotic heritage, thrust southeastwards onto Baltica during the Mid-Silurian Scandian continent-continent collision, with structurally higher nappes inferred to have originated at increasingly distal positions to Baltica. New U-Pb zircon geochronological and whole-rock geochemical and Sm-Nd isotopic data from the Rödingsfjället Nappe Complex reveal 623 Ma high-grade metamorphism followed by continental rifting and emplacement of the Umbukta gabbro at 578 Ma, followed by intermittent magmatic activity at 541, 510, 501, 484 and 465 Ma. Geochemical data from the 501 Ma Mofjellet Group is indicative of arc magmatism at this time. Syntectonic pegmatites document pre-Scandian thrusting at 515 and 475 Ma, and Scandian thrusting at 429 Ma. These results document a tectonic history that is compatible with correlation with peri-Laurentian and/or peri-Gondwanan terranes. The data allow correlation with nappes at higher and lower tectonostratigraphic levels, including at least parts of the Helgeland, Kalak and Seve nappe complexes, implying that they too may be exotic to Baltica. Neoproterozoic fragmentation of the hypothesized Rodinia supercontinent probably resulted in numerous coeval, active margins, producing a variety of peri-continental terranes that can only be distinguished through further combined geological, palaeomagnetic and palaeontological investigations.

A review of the Caledonian Wilson cycle from a North Atlantic perspective

“…S ́rodońet al 2023) and late c. 578 Ma dykes in the SDC at Kebnekaise (Kirsch and Svenningsen 2016), or it might be related to the more abundant c. 570-550 Ma Laurentian and Gondwanan CIMP rocks and the opening of the West Iapetus Ocean at c. 550 Ma (Corfu et al 2007;Larsen et al 2018). Slagstad et al (2021) correlated the c. 578 Ma Umbukta gabbro in the Rödingsfjellet Nappe Complex of the northern Scandinavian Caledonides, traditionally thought to originate from the Laurentian margin, with the SIP, also suggesting a non-Baltican origin of the SIP magmatism. Gumsley et al (2020) also compare c. 560 Ma alkali and OIB-like mafic rocks from the southwestern province of Svalbard with the SIP, pointing at the difficulties in palaeogeographically reconstructing these occurrences within the wide Baltica-Laurentia-Gondwana system.…”

“…The CIMP-related magmatic rocks definitively represent important witnesses for final continental break-up and initial Iapetus spreading, but more detailed palaeomagnetic constraints for remnants within allochthonous units are needed before the validity of contrasting palaeogeographic reconstructions at c. 610-550 Ma (e.g. Tegner et al 2019;Slagstad et al 2021) can be addressed. Finding and documenting a true break-up unconformity in sedimentary successions of clear palaeogeographic affinity might also help to constrain the Iapetus break-up history and should be the goal of further studies.…”

Early­­­­–Middle Ordovician sedimentation and bimodal volcanism at the margin of Iapetus: the Trollhøtta–Kinna Basin of the central Norwegian Caledonides

“…Models depend on the palaeogeographic interpretation of subduction-related high-pressure rocks preserved within the allochthonous Seve Nappe Complex, which may be taken to indicate either onset of subduction outboard of Baltica in the early Ordovician (e.g. Gee et al 2013), or a derivation of these high-pressure units from outboard Gondwana (e. g. Slagstad et al 2020). The youngest ophiolitic rocks documented from the Iapetus realm are from a Late Ordovician (ca.…”