Proterozoic magmatism in the southern Scandinavian Caledonides, with special reference to the occurrences in the Eikefjord Nappe

Abstract

Caledonian nappes of southern Norway comprise basement slices and sedimentary cover, and generally have close affinity with autochthonous terranes in the Fennoscandian foreland. The nappes can be distinguished in those having Gothian (1700–1600 Ma) character and those of Telemarkian (1550–1480 Ma) type. There were also several periods of variously intense magmatism between these early accretionary events and the end of the Sveconorwegian Orogeny. Most prominent features are the anorthositic-noritic massifs, which formed mainly during the Telemarkian period and in the late stages of the Sveconorwegian Orogeny between 980 and 920 Ma. In this paper, we review the main events affecting the crystalline parts of the nappes and report new results from the Eikefjord Nappe. An augen gneiss yields a crystallization age of 1191 ± 2 Ma, which is an event rarely seen in nappes or the autochthon. An amphibolitic gneiss formed at about 1500 Ma and underwent high-grade metamorphism at 986 ± 3 Ma, followed by lower grade overprints as reflected by titanite dates ranging to 915 Ma. The Sveconorwegian metamorphism was ubiquitous in the nappes, although its intensity was locally highly variable. The association of metamorphism with the second main anorthosite generation event points to intense subcrustal magmatism, heating and deformation of the lithosphere. The various crustal forming events have different geneses, some are clearly related to subduction processes, others more consistent with localized mantle melting. Those closer in character to classical Large Igneous Provinces are the events at 1470–1420, 1280–1240 and 1220–1180 Ma.