Neoproterozoic stratigraphy of the Southwestern Basement Province, Svalbard (Norway): Constraints on the Proterozoic-Paleozoic evolution of the North Atlantic-Arctic Caledonides

摘要

The Arctic archipelago of Svalbard, Norway, plays an impor tant role in tectonic reconstructions of the Cambrian-Devonian Caledonian orogen in the North Atlantic and circum-Arctic regions. To elucidate the Proterozoic geological history of the Southwestern Basement Province of Svalbard and place its origin and displacement history in the context of regional tectono-stratigraphic events, we present new geological mapping, strati-graphic assignments, carbonate carbon (δ(13)C_(carb)) and strontium (~(87)Sr/~(86)Sr) isotope chemostratigraphy, and detrital/igneous zircon U-Pb geochronology coupled with Hf isotope geochemistry from Neoproterozoic rocks exposed in southwestern Spitsbergen. The examined metasedimentary successions include a Tonian mixed carbonate-siliciclastic succession (the Nordbu-kta/Deilegga groups) that is regionally truncated by a Cryogenian (＜650 Ma) angular unconformity (the Torellian unconformity), the age of which is confirmed herein by field relationships and re-analysis of previously reported detrital monazite data. New detrital zircon U-Pb data from the Nordbukta Group yield ca. 1030-1170, 1280-1400, 1430-1510, and 1580-1680 Ma age populations that are typical of North Atlantic (e.g., North and East Greenland, Scotland, and the Scandinavian Caledonides) Me-soproterozoic-Neoproterozoic sedimentary successions. Overlying Cryogenian-Ediacaran strata of the Sofiebogen, Dunder-bukta, and Kapp Lyell (Bellsund) groups record rift-related sedimentation and host chemostratigraphic data that provide ties to the ca. 640(?)-635 Ma Marinoan snowball Earth glaciation. Detrital zircon U-Pb data from the Cryogenian Slyngfjellet, Jens Erikfjellet, and Konglomeratfjellet formations yield similar age spectra to the underlying Nordbukta and Deilegga groups, while younger Ediacaran strata of the Hoeferpynten and Gshamna formations record a prominent shift to bimodal ca. 1850 and 2850 Ma U-Pb age populations. Integrating these data with previously published geochemical and geochronological datasets from Svalbard and other circum-Arctic Mesoproterozoic-Neoprotero-zoic successions, we propose that the Southwestern Basement Province represents a composite terrane composed of multiple peri-Baltican (Wedel Jarlsberg-Oscar Ⅱ, Berzeliuseggene-Eim-fjellet, and Prins Karls Forland terranes) and peri-Laurentian (Hornsund terrane) crustal fragments that were likely initially juxtaposed and/or amalgamated during the Caledonian orogeny. These terranes were subsequently complexly deformed and modified during the younger Devonian-Carboniferous Ellesmerian and Paleogene-Eocene Eurekan orogenic events that affected western Svalbard.