U–Pb age and Lu–Hf signatures of detrital zircon from Palaeozoic sandstones in the Oslo Rift, Norway

Abstract

U–Pb and Lu–Hf isotope analyses of detrital zircon from the latest Ordovician (Hirnantian) Langøyene Formation, the Late Silurian Ringerike Group and the Late Carboniferous Asker Group in the Oslo Rift were obtained by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Overall the U–Pb dating yielded ages within the range 2861–313 Ma. The U–Pb age and Lu–Hf isotopic signatures correspond to virtually all known events of crustal evolution in Fennoscandia, as well as synorogenic intrusions from the Norwegian Caledonides. Such temporally and geographically diverse source areas likely reflect multiple episodes of sediment recycling in Fennoscandia, and highlights the intrinsic problem of using zircon as a tracer-mineral in ‘source to sink’ sedimentary provenance studies. In addition to its mostly Fennoscandia-derived detritus, the Asker Group also have zircon grains of Late Devonian – Late Carboniferous age. Since no rocks of these ages are known in Fennoscandia, these zircons are inferred to be derived from the Variscan Orogen of central Europe.

Rare late Neoproterozoic detritus in SW Scandinavia as a response to distant tectonic processes

“…c). The detrital zircon data from samples Ring1b (this study), replicate sample Ring 1 (Slama and Pedersen, ) and sample R‐2010‐2 from the same sedimentary sequence (Kristoffersen et al ., ) all document this significant change in the geotectonic regime of SW Scandinavia (Fig. ).…”

“…In sample Ring 1 (Slama and Pedersen, ) and four different Silurian samples reported by Kristoffersen et al . (), the Archaean, Neoproterozoic and Cambrian detrital zircons are almost absent, documenting a very subdued role of the zircon‐poor Cambro‐Ordovician sediments as a source for the newly formed Caledonian foreland basin.…”

“…The derivation of Neoproterozoic detrital zircon from rocks similar to the Egersund dolerite dykes of southern Norway [616 ± 3 Ma (Bingen et al ., )] has been considered improbable because no coeval zircon‐bearing rocks have been found in SW Scandinavia (Kristoffersen et al ., ; Põldvere et al ., ). However, the original rock assemblages from which the Neoproterozoic sedimentary rocks were sourced are not known and cannot be studied in situ.…”

“…The original interpretation of these zircons as representing the rift‐related mafic intrusions at Baltica (Bingen et al ., ) now seems unlikely as no zircon‐bearing rocks of such ages are known from SW Scandinavia (Nystuen and Lamminen, ); the results were ultimately re‐interpreted as Sveconorwegian zircons with Neoproterozoic lead‐loss (Andersen et al ., ). In recent years, with a growing number of provenance data and Neoproterozoic detrital zircon ages being reported from diverse sedimentary formations throughout Baltica (Kristoffersen et al ., ; Andresen et al ., ; Lamminen et al ., ; Slama and Pedersen, ), it has become clear that such zircon ages represent a genuine detrital component and must be taken into account in provenance interpretations.…”

Visualizing, interpreting and comparing detrital zircon age and Hf isotope data in basin analysis – a graphical approach

“…In the example data, the discordance is calculated as described in Kristoffersen et al . (). Other equations for the calculation of discordance, e.g.…”