Palaeomagnetic investigations across Hinlopenstretet border zone: from Caledonian metamorphosed rocks of Ny Friesland to foreland facies of Nordaustlandet (NE Svalbard)

Abstract

New demagnetization results of 286 palaeomagnetic specimens from 15 sites in Neoproterozoic–Lower Paleozoic sequences of Ny Friesland–Nordaustlandet (the Caledonian Eastern Svalbard Terrane) are presented. New in situ 40 Ar/ 39 Ar ultraviolet mass spectrometry (Uv-MS) age determinations on amphibolites and mylonites from the Ny Friesland cluster in the 340–460 Ma interval correspond broadly to the Caledonian thermal event. Older ages are observed but are more scattered and probably reflect partial resetting or argon gain of Proterozoic micas. Palaeomagnetic, petrological and structural data confirm a west to east decrease in the degree of the Caledonian metamorphism and remagnetization across Hinlopenstretet, which is interpreted here to coincide with the limit of Caledonian east-directed overthrusting. No pre-Caledonian palaeomagnetic record was identified in investigated amphibolites and metacarbonates of Ny Friesland. Pre-folding pre-Caledonian, potentially Neoproterozoic (primary?) magnetization was recognized only in non-metamorphosed Murchisonfjorden (Nordaustlandet) carbonates. However, selective palaeomagnetic palaeopoles from Murchisonfjorden also fall into Caledonian sensu lato and Mesozoic sectors of the Laurussia reference path. This also indicates that regions east of Hinlopenstretet and east of the Caledonian front could be partially subjected to Caledonian remagnetization. Mesozoic palaeomagnetic overprints are potentially related to the injection of Mesozoic dolerites in eastern Svalbard. Here, we discuss two concepts of post-Caledonian rotations that could affect the palaeomagnetic record of the Eastern Svalbard Terrane: rotations around vertical axes related to strike-slip faults and rotations around horizontal axes related to normal listric faults that originated during extension in the Devonian basin and the opening of the Atlantic and Arctic oceans. Supplementary material: (1) A detailed description of applied rock-magnetic and palaeomagnetic procedures, (2) detailed description of investigated geochronological samples, (3) in situ Uv-MS 40 Ar/ 39 Ar isotopic age determination results, (4) mineralogy of ferromagnetic phases, (5) hysteresis parameters, (6) distribution of the NRM components and great circles in palaeomagnetic sites and (7) anisotropy of magnetic susceptibility are available at https://doi.org/10.6084/m9.figshare.c.6132018