Chapter 23 Swedish Caledonides: key components of an early–middle Paleozoic Himalaya-type collisional orogen

Abstract

AbstractCaledonian collision of continents Laurentia and Baltica, with at least 1000 km of lateral shortening, dominates the bedrock along the northern margins of the North Atlantic Ocean. Scandian (Silurian–Devonian) underthrusting of Laurentia by Baltica resulted in stacking of the main orogenic wedge and its migration onto the platform edge of Baltica. Complementary thrust sheets, exposed in northeastern Greenland, telescoped the Laurentian continental margin. The Swedish part of the Caledonides, comprising the foreland segment along the central half of this mountain belt, includes the key components of: (1) the Baltoscandian inner margin, including Ordovician and Silurian foreland basins; (2) the Neoproterozoic extended outer margin dominated by mafic magma and continent–ocean transition zone; (3) Iapetus oceanic terranes; and (4) evidence that substantial parts of the outermmost Baltoscandian margin experienced deep subduction and high- and ultrahigh-pressure (HP/UHP) metamorphism during late Cambrian–Ordovician accretion. This evidence, integrated with the Norwegian Caledonides, defines an orogenic pro-wedge comparable to that in the Himalaya today. Orthogonal Scandian collision, lasting for about 60 million years (c. 440–380 Ma), involved late Silurian–Early Devonian HP/UHP metamorphism of the underthrusting Baltoscandian basement. By the Middle Devonian, the hinterland was experiencing orogen-parallel folding and axial extension, accompanying exhumation, while the orogenic pro-wedge continued to migrate eastwards on to the platform.