U-PB DETRITAL ZIRCON ANALYSIS OF NEOPROTEROZOIC, TIMANIAN-MARGIN SUCCESSIONS AND A BASAL CALEDONIAN NAPPE IN NORTHERN NORWAY

U-Pb detrital zircon analysis of ten samples from pre-Timanian passive-margin formations and selected Caledonian nappe rocks from Finnmark, northern Norway, yield the following results.

1) A single sample (STP1) from the Late Ediacaran Stáhpogieddi Formation, Gaissa Nappe Complex, has a dominant peak at c. 550 Ma and is likely to represent deposition in the Timanian foreland basin. Another sample (BRE1) from the same region is much different with two major peaks at 2.8-2.7 Ga and 2.4 Ga; its significance remains to be determined, but renewed paleocurrent flow from the south may explain this change.

2) Seven samples show Baltican affinity, including FUG1, GRN1 and GMS1 from parautochthonous/autochthonous formations in the Tanafjorden-Varangerfjorden Region (TVR), and VEI1 and F-4 from formations lying unconformably upon in-situ Paleoproterozoic- Archean metamorphic complexes. Their provenance includes: i) age peaks at c. 2.8-2.7 Ga, indicating input from the northern Fennoscandian Shield which is dominated by Neoarchaean complexes; ii) age peaks at 1.95-1.8 Ga representing grains derived from Palaeoproterozoic terranes of the craton and deformed during the 1.9-1.8 Ga Svecofennian orogeny; iii) Mesoproterozoic peaks in TVR samples are of uncertain provenance, possibly derived from a source beneath the Caledonian nappes or adjacent continental shelf, a northward extension of the Sveconorwegian/Grenvillian orogen, or from Mesoproterozoic igneous and sedimentary rocks farther south on the shield.

3) Samples (STY1, SF1 and KG1) from formations in the Barents Sea Region have similar 1.8 Ga and 2.8-2.7 Ga peaks and abundant Mesoproterozoic grains which were likely derived from the passive margin before Timanian orogenesis (no detrital zircon grains younger than 1000 Ma are present).

The new data help to constrain sediment provenance in the region and confirms the Neoproterozoic Barents Sea Group succession as an established passive-margin depositional system with little or no coeval magmatism. The Timanian 'fingerprint' found in the Stáhpogieddi Formation suggests that further remnants of the Timanian foreland basin (which is represented in Russia as the Mezen Basin) may eventually be detected in the shallow-marine, platformal domain of the TVR or in similar rocks of the juxtaposed Gaissa Nappe Complex.