Following the Svecofennian arc accretionary growth and extensive granitoid magmatism in the Transscandinavian Igneous Belt (TIB), new crustal growth occurred west of the TIB to form the Gothian orogen. An early stage is manifested by 1.69–1.65 Ga subduction-related magmatism in the Ätran Terrane. A second stage, forming an 140 km wide segment east of the Permian Oslo Rift, is recorded by three 1.66–1.59 Ga metamorphosed volcano-sedimentary units, exposed in the Horred, Åmål and Stora Le-Marstrand formations in the Idefjorden Terrane. The 1.66 Ga Horred Formation is dominated by felsic volcanics and has geochemical signatures indicative of formation in an island arc setting. In contrast, the lithologically similar volcanic sequences in the 1.61 Ga Åmål Formation have geochemical signatures consistent with a continental-margin setting. The 1.60–1.59 Ga Stora Le-Marstrand Formation is dominated by greywacke-type metasediments with subordinate metabasalts. These volcanics have markedly primitive trace element signatures and depleted Nd isotopic compositions, all consistent with their derivation in an oceanic island arc setting. The sediments document two provenances: a distal continental source and one with Nd isotopic compositions similar to the SLM volcanism. Many of the metasediments in the Stora Le-Marstrand formation have chemical signatures consistent with derivation from continental crust, suggesting that this volcanic arc developed in the vicinity of a continental massif, possibly in a setting similar to the Philippine Sea. Accretion of the Horred and Stora Le-Marstrand arc systems occurred prior to 1.61 and 1.59 Ga, respectively, and was followed by voluminous, ca 1.59 Ga calc-alkaline magmatism.