The timing of Svalbard's assembly in relation to the mid‐Paleozoic Caledonian collision between Baltica and Laurentia remains contentious. The Svalbard archipelago consists of three basement provinces bounded by N–S‐trending strike–slip faults whose displacement histories are poorly understood. Here, we report microstructural and mineral chemistry data integrated with 40Ar/39Ar muscovite geochronology from the sinistral Vimsodden‐Kosibapasset Shear Zone (VKSZ, southwest Svalbard) and explore its relationship to adjacent structures and regional deformation within the circum‐Arctic. Our results indicate that strike–slip displacement along the VKSZ occurred in late Silurian–Early Devonian and was contemporaneous with the beginning of the main phase of continental collision in Greenland and Scandinavia and the onset of syn‐orogenic sedimentation in Silurian–Devonian fault‐controlled basins in northern Svalbard. These new‐age constraints highlight possible links between escape tectonics in the Caledonian orogen and mid‐Paleozoic terrane transfer across the northern margin of Laurentia.
<p>The Svalbard&#8217;s Southwestern Basement Province in contrary to the Northwestern and Eastern Basement Provinces is commonly correlated with the Pearya Terrane or Timanides and bears a complicated internal structure. Here, we present new data from Oscar II Land supporting the model of Svalbard&#8217;s Basement being divided into the Laurentia and Barentsia plates in the late-Caledonian period.</p>
<p>In Oscar II Land the enigmatic M&#252;llerneset Formation is tectonically juxtaposed against the remaining greenschist facies metamorphosed basement. It consists of Mesoproterozoic to Neoproterozoic metapelites and metapsammites that experienced a polymetamorphic history. The progressive amphibolite facies event M1 of unknown age reached the pressure-temperatures conditions of 5-7 kbar at 500-560 &#176;C. The subsequent greenschist facies overprint (M2) is associated with mylonitization strongly pronounced across the whole M&#252;llerneset Formation. Mylonitic foliation S2 dips steeply to the SW and it is associated with a stretching lineation dipping moderately-to-shallowly to the SE. In the western part of the unit, monazite is growing within the S2 foliation and related shear bands mainly replacing allanite. Th-U-total Pb dating of homogenous monazite population yielded a weighted average age of 410 &#177; 7 Ma with MSWD = 0.26 and p = 0.997. In the western part, where mylonitic foliation is less prevalent, monazite growths within M1 porphyroblasts and within the S2 foliation. Th-U-total Pb dating revealed an array of ages between 480 &#8211; 280 Ma with no correlation of chemical or structural features allowing divisions into subgroups.</p>
<p>Dating results indicating an early Caledonian signal should be attributed to the progressive M1 event. Uniform monazite age of 410 &#177; 7 Ma in the western part represents the timing of the M2 greenschist facies overprint. Younger ages obtained in the eastern part suggest fluid related disturbance of Th-U-Pb system during late Caledonian, Ellesmerian and Eurekan events. The timing of monazite growth during the M2 event is identical with the 410 &#177; 2 Ma <sup>40</sup>Ar/<sup>39</sup>Ar cooling age reported by Dallmeyer (1989). Geochronological evidence combined with structural observations suggests that the M&#252;llerneset Formation in the Early Devonian was tectonically exhumed on the NW-SE trending left-lateral strike- to oblique-slip shear zone. Similarly oriented tectonic zones within the Southwestern Basement Province, in the Berzeliuseggene unit and the Vimsodden-Kosibapasset Shear Zone are also of similar age. This set of anastomosing shear zones is roughly parallel to the proposed orientation of the suture between Barentsia and Laurentia (Gudlaugsson et al. 1998). The documented Early Devonian sinistral displacement may mark the western boundary of the Barentsia microplate laterally extruded during the final Caledonian collision in a style similar to present day Anatolian Plate escape.</p>
<p>This work is funded by NCN research project no. 2015/17/B/ST10/03114, AGH statutory funds 16.16.140.315 and RCN Arctic Field Grant no. 282546.</p>
<p>Dallmeyer, R. D. (1989). Partial thermal resetting of<sup> 40</sup>Ar/<sup>39</sup>Ar mineral ages in western Spitsbergen, Svalbard: possible evidence for Tertiary metamorphism. Geological Magazine, 126(5), 587-593.</p>
<p>Gudlaugsson, S. T., Faleide, J. I., Johansen, S. E., & Breivik, A. J. (1998). Late Palaeozoic structural development of the south-western Barents Sea. Marine and Petroleum Geology, 15(1), 73-102.</p>
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.