Protolith ages and timing of deformation in the eastern, marginal part of the Sveconorwegian orogen, southwestern Sweden

U-Pb zircon and titanite ages from variably metamorphosed, igneous rocks in the eastern, marginal part of the Sveconorwegian orogen (Eastern Segment), north of lake Vanern, Sweden, suggest that these rocks belong to the young er (c. 1.71-1.65 Ga) igneous suite of the c. 1.85-1.65 Ga Transscandinavian Igneous Belt (TIB). Two porphyritic meta-granites and one isotropic monzon ite yield U-Pb zircon ages of 1661 +/- 27, 1674 +/- 7 and 1674 +/- 7 Ma, re spectively. These ages support earlier interpretations that the Eastern Seg ment north of lake Vanern contains tectonically reworked TIE rocks and that there is no major lithological discontinuity either across the Sveconorweg ian Frontal Deformation Zone or within the Eastern Segment. Igneous, brown- coloured titanites from five samples yield similar U-Pb ages as the zircons . In contrast, colourless and oblate-shaped titanites from the western, pen etratively deformed parts of the Eastern Segment give concordant ages of 97 6 +/- 4 and 956 +/- 6 Ma. Further to the east, similar titanite from both a penetratively deformed meta-granite and a ductile shear zone within a porp hyritic quartz monzonite are strongly discordant close to late Sveconorwegi an lower intercept ages. This type of titanite is interpreted to be syntect onic and formed during the upper greenschist (east)- to amphibolite (west)- facies, fabric-forming event in the Eastern Segment. Since the brown, igneo us titanites and the zircons share a common igneous origin, and the single type of metamorphic titanites are either concordant or strongly discordant towards late Sveconorwegian intercept ages, it is inferred that no major te ctonothermal event occurred between the time of TIE emplacement and the lat e Sveconorwegian tectonothermal reworking. Pre-Sveconorwegian, Palaeo- to M esoproterozoic deformational and metamorphic events (Gothian), which have b een inferred west of and further south within the Eastern Segment, appear t o be absent in the northern part of this crustal unit. (C) 1999 Elsevier Sc ience B.V. All rights reserved.