Correlation of supracrustal sequences and origin of terranes in the Sveconorwegian orogen of SW Scandinavia: SIMS data on zircon in clastic metasediments

Ton probe U-Pb data on detrital zircons were acquired in five pre-Sveconorw egian elastic metasedimentary units in the Sveconorwegian orogen in S Norwa y. Turbidite-type sediments in the Veme complex (Begna sector, west of the Oslo rift) display zircons between 1.67 and 1.53 Ga (9 grains). This comple x is interpreted as a westward, younger extension of the Stora Le-Marstrand metasedimentary belt (less than or equal to 1.58 Ga) of the Idefjorden ter rane (east of the Oslo rift). The belt formed in an outboard setting, and t he detritus in the sediments was probably mainly derived from subduction-re lated complexes exposed in the Idefjorden terrane. To the west, a quartzite of the Hallingdal complex in the Telemark sector has zircon populations at 3.13-2.68 and 2.03-1.71 Ga (34 grains). It was deposited between 1.7 and 1 .5 Ga and attests the presence of differentiated continental crust older th an 1.5 Ga in S Norway. Two samples of the Hettefjorden and Festningsnutan G roups from the Hardangervidda plateau have zircon populations at 3.25-2.42 and 2.03-1.54 Ga (47 grains). The 1.90-1.85 Ga frequency maximum of the age distribution in these three epicontinental sediments corresponds with the peak of Svecofennian magmatic activity in central Sweden, and to the age of the main zircon populations in late-Svecofennian sediments. This is an ind ication of a Fennoscandian origin for the Telemark-Bamble and Rogaland-Hard angervidda terranes, at the margin of the Svecofennian domain; alternative exotic provenances are possible. A quartzite sample of the Modum complex in the Kongsberg sector displays 2.07-1.48 Ga Proterozoic zircon populations (28 grains) and minor Archaean populations. The Modum complex represents, p robably together with the Kragero complex in the Bamble sector and the Selj ord Group in the Telemark sector, parts of a quartzite-rich epicontinental cover deposited after 1.48 Ga on the Telemark-Bamble terrane. The juxtaposi tion of the Telemark-Bamble and Rogaland-Hardangervidda terranes with the s ubduction-related Idefjorden terrane, can be explained by a transpressive t ranslation of these terranes at the margin of the Fennoscandian shield duri ng the Sveconorwegian orogeny. Sveconorwegian sinistral strike-slip shearin g probably took place along an amphibolite-facies banded gneiss unit situat ed at the boundary. (C) 2001 Elsevier Science B.V. All rights reserved.