Using palaeomagnetic and isotopic data to investigate late to post-Caledonian tectonothermal processes within the Western Terrane of Svalbard

Abstract

The analytical results of a total of 205 metabasic specimens from 10 palaeomagnetic sites collected from Oscar II Land in Western Spitsbergen are presented. Petrographic, structural and palaeomagnetic data all demonstrate that the pre-Caledonian ferromagnetic fabric of the metabasic rocks has been extensively reoriented and intensively remineralized. New in situ laser ablation inductively coupled plasma mass spectrometry 40 Ar/ 39 Ar age determinations suggest that the host rocks have been subject to three resetting events during the 426 – 380 Ma (Caledonian sensu lato ), 377 – 326 Ma and c. 300 Ma intervals. The latter two resetting events coincide in time with the Barents Shelf-wide rift-controlled subsidence events. The derived palaeomagnetic data do not fall on the expected apparent polar wander path of Laurussia for syn- to post-Caledonian time. Consequently, four models invoking palaeogeographical great and small circle rotations, regional tectonism involving thrusting and normal listric faulting have been investigated to account for this lack of correspondence. The palaeomagnetic data do not lend support to reconstructions linking Western Svalbard with Pearya but point instead to the importance of listric faulting related to the opening of the North Atlantic Ocean that modified the geometry of the West Spitsbergen Fold and Thrust Belt. Supplementary material: (1) Field characteristics of metabasic sites, (2) detailed description of applied rock magnetic and palaeomagnetic procedures, (3) microscopic images of investigated geochronological samples, (4) in situ LA-ICP-MS 40 Ar/ 39 Ar isotopic age determination results, (5) microscopic, SEM and BSE images of investigated metabasites, and (6) anisotropy of magnetic susceptibility are available at https://doi.org/10.6084/m9.figshare.c.3673924 .

Mineralogical, Rock-Magnetic and Palaeomagnetic Properties of Metadolerites from Central Western Svalbard

“…This contribution follows on from previous studies of the metabasites by the authors in the St. Jonsfjorden, Venernbreen, Kinnefjellet, Ommafjellet areas of Western OIIL [14,15]. The metadolerite host rocks of western OIIL have been found, from in situ 40 Ar/ 39 Ar data using a 1059 nm CSI fibre laser and MAP215-50 mass spectrometer, to have been subjected to three thermal events in the 426-380 Ma (Caledonian (sensu lato) metamorphism?…”

“…300 Ma intervals. The two younger resetting ages could be related to the Late Palaeozoic rift-controlled extensional movements in the Barents Shelf as was suggested by Michalski et al [14]. The 377-326 Ma overprint can be also correlated with Devonian-Carboniferous Svalbardian/Ellesmerian events [8,9,[16][17][18].…”

“…All of the listed events could potentially have reset and/or overprinted the palaeomagnetic record. While the pre-metamorphic palaeomagnetic record of the metadolerites of western OIIL can, potentially, survive the Caledonian greenschist-facies metamorphism the rock-magnetic and mineralogical data reported by Michalski et al [14] and Burzyński et al [15] demonstrate that there are no relicts of any pre-Caledonian ferromagnetic carriers. Several palaeogeographic and tectonic models have been tested to explain inconsistency of the calculated palaeopoles with reference to the Apparent Polar Wander Path of Laurussia [14].…”

“…While the pre-metamorphic palaeomagnetic record of the metadolerites of western OIIL can, potentially, survive the Caledonian greenschist-facies metamorphism the rock-magnetic and mineralogical data reported by Michalski et al [14] and Burzyński et al [15] demonstrate that there are no relicts of any pre-Caledonian ferromagnetic carriers. Several palaeogeographic and tectonic models have been tested to explain inconsistency of the calculated palaeopoles with reference to the Apparent Polar Wander Path of Laurussia [14]. From palaeomagnetic and isotopic data it was postulated that listric normal faulting related to, for example, the opening of the North Atlantic, played an important role in the modification of the western OIIL Caledonian basement geometry [14].…”

“…Michalski et al [12] have questioned, from palaeomagnetic and isotopic data, the timing of the amalgamation of Svalbard [1] suggesting that the Eastern and Central Caledonian Svalbard Terranes sensu Harland and Wright [1] had already docked by Late Silurian time. Although several palaeomagnetic attempts have been undertaken to establish the pre-Caledonian palaeogeographic position of the pre-Late Devonian location of Western Svalbard [13,14], it remains unresolved.…”