Provenance characteristics of the Brumunddal sandstone in the Oslo Rift derived from U-Pb, Lu-Hf and trace element analyses of detrital zircons by laser ablation ICMPS
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The 800 m thick Brumunddal sandstone is partly an eolian, partly a fluvial sandstone deposited in a fault-bounded basin in the northern part of the Oslo Rift in Permian time.The sandstone is the youngest rift-related deposit in the northern part of the Oslo Rift. Well rounded detrital zircons are common accessory mineral grains in the sandstone. U-Pb dating of detrital zircon from a sample of the Brumunddal sandstone by LAM-ICPMS gives a range of ages from (rare) late Archaean ages to Permian (283±4 Ma). The age and initial ?Hf pattern of zircons in the sediment match the main rock- forming events in Fennoscandia from Archaean to Phanerozoic time. This kind of diverse provenance was most likely obtained by repeated recycling of clastic sediments of Fennoscandian origin, with Silurian, continental sandstones as the most probable direct precursors. Trace element distributions show a conspicuous absence of patterns with the high level of U and Th enrichment typical of zircon from granitic rocks. This is consistent with a complex transport and redepositional history: High U-Th, metamict zircons were selectively removed by abrasion during repeated transport-deposition-erosion cycles. In addition to recycled material, Caledonian syn-orogenic intrusions and Permian intermediate to felsic plutonic rocks in the Oslo Rift itself were minor, but still significant sources of detrital zircon.

tom.andersen@geo. uio.no