| Summary: | Domes of high-grade metamorphic rocks are found in recent and ancient orogens alike. They commonly expose parts of the deep interior of mountain belts, the so-called orogenic infrastructure. This thesis explores the controversial topic of infrastructure exhumation in two different ways: First, through reviewing the history of tectonic research leading to the concept of metamorphic core complexes (MCCs). Second, in a case study of basement windows in the deeply eroded Paleozoic Caledonian orogen of West Norway. Including the (ultra)high-pressure Western Gneiss Region, these domal windows record Caledonian continental subduction of the Baltic Shield and controversial exhumation mechanisms. Paper 1 explores the lithological and structural composition of the Baltic Shield in the eastern part of the Øygarden Complex, which represents the westernmost Caledonian basement window. Secondary-ion mass spectrometry (SIMS) U-Pb zircon geochronology constrains two pulses of voluminous Sveconorwegian intrusions into a Telemarkian (1506 ± 5 Ma) granitic basement. Bimodal magmatism at 1041 ± 3 Ma, followed by leucogranite magmatism at 1027-1022 Ma, correlate the Øygarden Complex with the Sirdal Magmatic Belt in South Norway. A low-temperature resetting of metamict grains at ~482 Ma is the only Caledonian record in zircon. The Sveconorwegian intrusions were strongly reworked by Caledonian ductile deformation. Starting at amphibolite facies conditions, retrograde top-to-E shearing involved fluid-induced phyllonitization that localized ductile-to-brittle low-angle shear zones. Structural features of the Øygarden Complex are discussed in the light of MCC exhumation. Paper 2 investigates the southernmost culmination of the eclogite-bearing Western Gneiss Region in the footwall of the Nordfjord-Sogn detachment (Gulen dome). Semi-quantitative mapping of ductile strain along glacier-polished fjords reveals two distinct structural levels. The amphibolite-facies core domain involved fluid-controlled eclogite retrogression and records ...
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