Anders Scherstén

The Idefjorden Terrane of the Sveconorwegian Orogen, Fennoscandia, is known to be an area of comparatively juvenile Mesoproterozoic continental growth. Here we provide an improved model of crustal growth based on new coupled zircon U-Pb-O-Lu-Hf isotopic data on thirteen samples of mafic to intermediate plutonic rocks from different domains of the Idefjorden Terrane. The new data support a retreating volcanic arc system, with shorter pulses of accretion. A gradual increase of radiogenic Hf (mean slif from 3.5 to 5.4) in plutonic rocks intruded between ca. 1630 Ma and 1560 Ma reflects an increase in juvenile mantle-derived magma in the genesis of the plutonic suites. This trend is consistent with development of an extensional back-arc rift geotectonic setting, accommodating deposition of the Stora Le-Marstrand greywacke dominated metasediment sequence. Combined isotopic information and the detrital zircon record of the Stora Le-Marstrand Formation support the interpretation that the Idefjorden Terrane was separated from the Fennoscandian Shield before the Sveconorwegian Orogeny. (C) 2015 Elsevier B.V. All rights reserved.