THE PROTEROZOIC EVOLUTION OF THE BAMBLE SECTOR SHEAR BELT, SOUTHERN NORWAY - CORRELATIONS ACROSS SOUTHERN SCANDINAVIA AND THE GRENVILLIAN CONTROVERSY

The Bamble Sector contains a parautochthon, which is a southward continuation of the (now separate) Kongsberg Sector, and an autochthon, which is part of the Telemark Basement Gneiss Complex (TBGC), the northwest bounding block of the Kongsberg-Bamble shear belt. The parautochthon formed at approximately 1100 Ma in the Sveconorwegian Orogeny and produced a distinctive gravity anomaly. The shear belt originated in the Kongsbergian Orogeny (approximately 1700-1500 Ma). Supracrustal rocks (deposited at approximately 1700-1650 Ma) were deformed by D1 (approximately 1650 +/- 50 Ma), developing a bend from the north-south Kongsberg Sector to the NE-SW Bamble Sector. The shear belt (of the Bamble parautochthon and Kongsberg Sector) absorbed high strains relative to surrounding blocks, particularly around this bend. The Late-Kongsbergian, D3 angular shearing (approximately 1500 Ma), in the parautochthon, absorbed a dextral strike-slip past the TBGC. Magmatism of the Post-Kongsbergian anorogenic period (between 1500 and 1250 Ma) included large alkaline suite-augen gneiss complexes, intruded (before approximately 1395 Ma) in a folded zone across the parautochthon. An Early-Sveconorwegian orogenic phase of deformation and granite intrusion (approximately 1250 Ma) was concentrated at the interface of the shear belt with the TBGC. The ensuing Sveconorwegian anorogenic phase of crustal extension (approximately 1200-1100 Ma) was localised in the shear belt, where much basic magma was intruded. The Main Sveconorwegian orogenic phase started (approximately 1100 Ma) with thrusting of the shear belt over the relatively cratonic, higher levels of the TBGC and Bamble autochthon, where later deformations and magmatism (ca. 1050-950 Ma) were concentrated. Controversy about the existence of Grenvillian (Sveconorwegian) orogenic effects in South Norway arose because of the shifting focus of successive events, which preserved a record of older effects in parts of the Bamble parautochthon. Other general features include the variation in response of different lithologies to one deformation phase, and the location of intrusions by earlier fold structures. The Bamble Sector also shows the reaction of deep crustal levels to a dextral strike-slip, which was absorbed by the development of large, overlapping domains of complementary angular shear. The sequence established in the Bamble Sector permits detailed correlations of Mid- and Late-Proterozoic events across southern Scandinavia.