Detrital zircon U-Pb analysis of the Neoproterozoic, Timanian, passive-margin successions in North Norway and significance for Arctic reconstructions

Sediment provenance investigations which combine paleocurrent data with isotopic analysis (e.g. U-Pb, Lu-Hf), geochemical studies, and/or heavy-mineral analysis, can help to refine paleogeographic reconstructions by, for example, mapping depositional systems, constraining lateral displacements in orogens, characterizing crust which is no longer exposed, stratigraphic correlation, etc. Hence, sediment provenance analysis can provide insights into circum-Arctic tectonic evolution. Sediment recycling, however, can complicate, obscure, and even mislead in testing regional tectonic scenarios. Consequently, it is important to distinguish between first- and second-cycle detritus, as well as to fully characterize all detrital sources including sedimentary ones. The Neoproterozoic, passive-margin successions of the Timanian margin, Finnmark, northern Norway, include the 9 km-thick, deep-marine to deltaic, Barents Sea Group and, to the south, a fluvial to shallow-marine, platformal domain. A study aiming to assess the primary detrital signature of these successions is ongoing. Many detrital investigations in other Arctic terranes claim to recognize the Timanian ';fingerprint' (c. 610-560 Ma zircon from subduction-related granitoids generated during Timanian orogenesis), yet to what extent the passive-margin sediments are recycled or recognized in younger sediments has not been addressed. Here, we present further results of this U-Pb detrital zircon investigation, extending the study into two of the Caledonian nappes farther west. Our results show the following main features of the detrital zircon populations: 1. Styret Formation, Løkviksfjellet Group, Varanger Peninsula (Sample STY1): a multimodal spread extends from c.2.0-1.1 Ga with four peaks of concordant grains at around 1.20-1.15 Ga, 1.55-1.45 Ga, 1.65-1.60 Ga, and 1.85-1.70 Ga, and subsidiary peaks at 2.90-2.50 Ga. 2. Ifjord Formation, Laksefjord Nappe Complex (Sample IFJ1): one group dominates the probability plot at 2.95-2.50 Ga. 3. Feldspathic sandstone, Nordkinn Peninsula (Sample F1): one major group occurs at 1.95-1.80 Ga and a minor group at 2.80-2.70 Ga. A feature common to all these new analyses, as well as the earlier data, is the presence of a detrital population peak at c. 2.8-2.7 Ga, indicating provenance from the northern Fennoscandian Shield which is dominated by Neoarchaean complexes. The major peak at 1.95-1.8 Ga of F1 is derived from Palaeoproterozoic terranes of this craton deformed during 1.9-1.8 Ga Svecofennian orogeny. A profusion of Mesoproterozoic grains from STY1 on Varanger Peninsula (also found earlier in a deltaic formation) indicates a source possibly concealed beneath the Caledonian nappes and adjacent continental shelf, or a northward extension of the Sveconorwegian/Grenvillian orogeny, or a Tonian-emplaced, sandstone-dominated thrust sheet derived from the margin of Rodinia. The new provenance data help to confirm the interpretation of the Neoproterozoic Barents Sea and Løkviksfjellet group successions as an established passive-margin depositional system with little to no coeval magmatism.