Abstract

The Sørfold area, within the Salta region, Norway, provides a section through a major depression of Caledonian cover sequences bounded to E and W by Precambrian basement gneisses, which allows study of the basement/cover relationships on both sides of the depression. The cover sequences are disposed in major fold-nappes, most of which are represented in the Sørfold area. Geochemically, the basement gneisses exposed in the Salta domes are akin to the rapakivi granites of Finland. This geochemical affinity and the irregularity of dome distribution suggests that the Precambrian basement is heterogeneous in character due to the intrusion of numerous, light, Precambrian rapakivi granites. The Caledonian D1 emplacement of the large fold-nappes created a gravitationally metastable system of heavier cover rocks over locally lighter basement. The less dense areas of basement that consisted of rapakivi granite rose in response to these gravitational forces when activated by rising temperatures, producing the mantled gneiss domes and their associated deformation effects. Experimental and theoretical models of mantled gneiss dome development are relevant in interpreting these structures. The role of the basement was critical in the evolution of the Salta region, and geochemical and spatial evidence suggests that pre-Caledonian patterns influenced the distribution of the domes, the behaviour of the rest of the basement, and the intensity of Caledonian deformation in the cover fold-nappes.

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