Palaeozoic sedimentation and Caledonian terrane architecture in northwest Svalbard: Indications from U–Pb geochronology and structural analysis

Abstract: Svalbard's Northwestern Basement Province is traditionally divided into the Albert I Land and the Biscayarhalvøya terranes. New U–Pb age data on zircon and monazite, structural and geochemical data provide first evidence of early Palaeozoic deposits south of the Biscayarhalvøya Terrane indicating the possible existence of a third terrane: the Germaniahalvøya Terrane. This area is represented by a Cambro-Ordovician succession of mica schist and marble (Lernerøyane Group) and its higher-grade metamorphic equivalent (Liefdefjorden Migmatite Complex), which were affected by the Taconian phase (migmatization at c. 469 Ma) and the Scandian phase (c. 422–415 Ma) of the Caledonian Orogeny. During the Scandian phase, the ductile Lerner Deformation Zone was formed. New isotopic data from the eclogite-bearing Richarddalen Complex of the Biscayarhalvøya Terrane imply the formation as Ordovician–Silurian collision-related mélange dominantly composed of c. 730 to 600 Ma Timanian island-arc derived detritus and igneous rocks, partly eclogite-facies metamorphosed at c. 656 Ma, and Tonian meta-igneous rocks. After amphibolite-facies metamorphism of the mélange matrix at c. 423 Ma, the Richarddalen Complex and the Stenian–Tonian Biscayarfonna Group were juxtaposed and mylonitized by the dextral Biscayarhalvøya Deformation Zone.