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40Ar/39Ar geochronologic evidence of Eurekan deformation within the West Spitsbergen Fold and Thrust Belt

By
David A. Schneider
David A. Schneider
Department of Earth and Environmental Sciences, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada
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Karol Faehnrich
Karol Faehnrich
Faculty of Geology, Geophysics and Environment Protection, AGH–University of Science and Technology, 30-059 Kraków, Poland
Department of Earth Sciences, Dartmouth College, Hanover, New Hampshire 03755, USA
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Jarosław Majka
Jarosław Majka
Faculty of Geology, Geophysics and Environment Protection, AGH–University of Science and Technology, 30-059 Kraków, Poland
Department of Earth Sciences, Uppsala University, 752 36 Uppsala, Sweden
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Maciej Manecki
Maciej Manecki
Faculty of Geology, Geophysics and Environment Protection, AGH–University of Science and Technology, 30-059 Kraków, Poland
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Publication history
21 May 201828 September 2018

ABSTRACT

Eocene Eurekan deformation has proven to be an enigmatic sequence of tectonic episodes dominated by tectonic plate compression and translation in the circum-Arctic region. Prins Karls Forland on western Spitsbergen is composed of Neoproterozoic siliciclastic metasediments of Laurentian affinity regionally metamorphosed to greenschist facies conditions. A crustal-scale ductile to brittle deformation zone, here named the Bouréefjellet fault zone, contains the amphibolite facies Pinkiefjellet Unit exposed between the lower metamorphic grade, upper structural unit of the Grampianfjella Group and the Scotiafjellet Group in the footwall. A preliminary age for the amphibolite facies metamorphism (ca. 360–355 Ma) indicates Ellesmerian tectonism, unlike other higher-grade basement rocks on Svalbard. Ten metasedimentary rocks from within the fault zone were collected for multiple single-grain fusion 40Ar/39Ar geochronology, with up to ten muscovite crystals dated per sample. High strain in the rocks is evinced by mylonitic structure, mica fish, and C’ shear zones, and dynamically recrystallized quartz with significant grain bulging and subgrain rotation, indicative of >350 °C temperatures. There is notable dispersion in the 40Ar/39Ar ages between samples, with single muscovite dates ranging from ca. 300 Ma to as young as 42 Ma, reflecting recrystallization and resetting of the muscovite. Younger, reproducible ages were obtained from samples that possess chemically homogeneous muscovite, yielding dates of 55–44 Ma for the Eurekan deformation on Prins Karls Forland. We suggest that Ellesmerian structures on Prins Karls Forland were reactivated during the Eocene (commencing as early as 55 Ma) progressing under warm, yet brittle, conditions that continued to 44 Ma. These 40Ar/39Ar muscovite dates are the first documented Eurekan deformation ages from Svalbard and enable a better understanding of the stages of Eurekan deformation in the Eocene to improve correlations across the circum-Arctic region.

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Contents

GSA Special Papers

Circum-Arctic Structural Events: Tectonic Evolution of the Arctic Margins and Trans-Arctic Links with Adjacent Orogens

Geological Society of America
Volume
541
ISBN electronic:
9780813795416

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