Geology of the Protogine Zone south of Lake Vättern, southern Sweden: A reinterpretation

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Abstract
Influential models describe the Protogine Zone (PZ) as a collisional suture and thrust front and, in particular, as the extension of the Grenvillian thrust front into Scandinavia. These models do not consider the significance of a rich variety of geological features related to Late Riphean-Vendian rifting of the craton. This paper calls attention to steep, northerly trending and anastomosing, narrow deformation zones of ductile or brittle-ductile character. The zones can be mapped out into the Vättern Graben of c. 700–800 Ma age. Uplift of southwestern Sweden after c. 910 Ma must have had a profound tectonic influence on the bedrock along the PZ. The effects of this late deformation must be identified and subtracted from the structural record before the significance of Sveconorwegian-Grenvillian deformation can be assessed. There is no other foliation south of Lake Vättern qualifying for the name “protogine zone foliation”. Rift-related magmatic and metallogenic features are remarkably restricted to the zone. In fact, most of the features along the southern part of the PZ traditionally ascribed to collisional tectonics may instead be extensional in nature. For instance, an asymmetrical rift with footwall rebound and unroofing could account for the normal and reverse faulting of the PZ and the contrasting metamorphism and structures of SW and SE Sweden.