ABSTRACT We apply zircon (U-Th)/He low-temperature thermochronology to metasedimentary sequences of the Southwestern Basement Province of Svalbard to investigate the shallow crustal tectonics of Svalbard and the High Arctic. We resolve Cretaceous through Paleogene time-temperature histories for four areas of the province: Sørkapp Land, Wedel Jarlsberg Land, Oscar II Land, and Prins Karls Forland. Results indicate peak Late Cretaceous temperatures of ~175–185 °C in the south (Sørkapp Land, Wedel Jarlsberg Land) and >200 °C in the north (Oscar II Land) as a consequence of maximum burial and an elevated geothermal gradient (>40 °C/km). Late Cretaceous cooling affected all areas during regional exhumation related to initial rifting in the Eurasian Basin to the north. A subsequent heating event (recorded at Wedel Jarlsberg Land and Oscar II Land) from ca. 53–47 Ma is interpreted to result from tectonic burial during Eurekan deformation and development of the West Spitsbergen Fold-and-Thrust Belt. Our thermal models reveal a subsequent cooling event (47–34 Ma) corresponding to a shift in tectonic regime from compression to dextral strike-slip kinematics during Eurekan deformation; exhumation of the West Spitsbergen Fold-and-Thrust Belt coincided with strike-slip tectonism. Throughout Eurekan deformation, Prins Karls Forland resided at temperatures >200 °C and records cooling during post-34 Ma extension. Our models indicate 2.5–3.5 km of unroofing in Wedel Jarlsberg Land and Oscar II Land, and >4 km of unroofing of Prins Karls Forland, which is a deeper structural level of the West Spitsbergen Fold-and-Thrust Belt than other exposures on Spitsbergen. The results of this study document elevated heat flow in the Late Cretaceous, extend spatial resolution of Late Cretaceous crustal cooling documented across Svalbard, and illustrate the temporal and thermal evolution of the West Spitsbergen Fold-and-Thrust Belt, which is necessary for an improved understanding of Arctic geodynamics.

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 40 Ar/ 39 Ar 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 40 Ar/ 39 Ar 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 40 Ar/ 39 Ar 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.

ABSTRACT Detrital zircon provenance studies of Precambrian metasedimentary rocks in Wedel Jarlsberg Land and Sørkapp Land, Svalbard’s Southwestern Caledonian Basement Province, were conducted to evaluate local stratigraphic correlations and the role of long-distance strike-slip displacements in assembling the basement of the Arctic Caledonides. The detrital zircon U-Pb age spectra of the late Mesoproterozoic to Neoproterozoic metasediments revealed mainly Mesoproterozoic to Paleoproterozoic age signatures characteristic for a Grenville–Sveconorwegian orogen provenance. These results confirmed a stratigraphic correlation between basement units of southern Sørkapp Land and the Isbjørnhamna Group of Wedel Jarlsberg Land and suggest relocation of the tectonic boundary between the Eimfjellet Complex and the Isbjørnhamna Group above the Eimfjellbreane Formation. Moreover, the results support the Vimsodden Kosibapasset Shear Zone (VKZ) as a major tectonic boundary and highlight the inhomogeneity in the Southwestern Caledonian Basement Province. The detrital zircon age signatures south of the VKZ bear similarities with coeval metasediments of the Northwestern Caledonian Basement Province of Svalbard and other localities in the Greenland and Scandinavian Caledonides. In contrast, the detrital zircon age spectra north of the VKZ are comparable with the high Arctic Neoproterozoic sediments of Baltican affinity. In conjunction with previous studies, the results suggest that the basement units may continue across the traditional boundaries of the Svalbard’s Caledonian basement provinces.