In southern Norway and Sweden, the Sveconorwegian orogenic belt hosts over 5000 pegmatite bodies (1100-900 Ma) usually clustered in local pegmatite fields. The Spro pegmatite, the object of this study, occurs, however, as an isolated body on the Nesodden peninsula approximately 20 km SSW of Oslo. Observations from fieldwork characterize the Spro pegmatite as a vertical dyke, approximately 230 m long, with variable thickness (1 to 25 m). The geological setting comprises the dyke emplaced in a tectonically complex region within a shear zone, transecting the Mesoproterozoic basement. The host rocks consist in deformed Spro granite (1542 -1493 Ma) and amphibole gneiss, both affected by amphibolitefacies metamorphism during the Sveconorwegian orogeny which peaked around 1050 Ma. Field observations and analyzed samples revealed that the otherwise homogenous pegmatite body exhibits late-stage, albite veins hosting an unusual mineral assemblage (including tourmaline, fluorite, topaz, and beryl) compared to other Sveconorwegian pegmatites. The Spro pegmatite particular features generated great interest regarding its relation to the shear zone, its unusual mineral assemblage and orogenic events that highly influenced the region’s geology as well as the pegmatite genesis. Interpretations based on the performed fieldwork and tectonic features indicate that the development of a major regional shear zone occurred almost simultaneously with the amphibolite facies metamorphism. The resulting intense deformation within and close to the shear zone is recognizable in the collected host rocks. The Spro pegmatite devoid of internal zonation was emplaced 1035 Ma along the fault. Recognized leucosomes in the region combined with analyzed mineral assemblages point to P-T conditions around 2-6 kbar and ~650 °C. The water circulation associated with the shear zone is assumed to have decreased the pegmatite protolith’s melting temperature, and suggest lower crystallization temperatures (~400-600 °C). The geochemical signatures from whole rock analysis by solution ICP-MS indicate that the pegmatite protolith, not seen in the field, is a peraluminous (A/CNK and A/NK ratios of 1.8 and 2.10 respectively), anarogenic, A-type granitic rock, genetically unrelated to the host rocks. The Spro pegmatite mineral assemblage and geochemical data characterizes it as a member of the NYF petrogenetic pegmatite family and the muscoviterare- element REE class with three distinct crystallization stages: 1) Primary stage of coarsegrained to megacrystic major minerals microline, muscovite, quartz and oligoclase-albite, and accessory monazite, thorite, samarskite-(Y), columbite-(Fe); 2) Late incompatible-elementenriched stage consisting in sugary albite irregular cross-cutting veins, hosting tourmaline, green muscovite, fluorite, topaz, beryl, microlite, apatite, and calcite; 3) Alteration stage with replacement of pre-existing minerals. EMPA analyses of the Spro micas revealed a systematic increase in Fe, F, Rb, and Na. These concentrations and trends indicate that the initial Spro pegmatite melt was primitive in composition but consistently evolved during pegmatite crystallization from the wall to the core of the body. Micas associated with the late stage albite veins have the most evolved compositions. EMPA analyses of tourmalines occurring exclusively in the albite veins have a relatively homogeneous schorl composition (16.2 wt% FeO and 2.4 wt% Na2O) suggesting a fairly consistent composition of the albite zone forming melts. Additionally, the consistent δ11B values acquired by in-situ microanalysis of the tourmalines by SIMS, averaging −13.2 ‰, suggest a single B source. The B isotopic composition, typical for peraluminous crustal reworked rocks and silicate melts and evidence pointing to partial melting indicate that the pegmatite melt originated from shear zone induced anatexis of a B-rich protolith. Furthermore, the progressive crystallization trends, along with chemical and mineralogical consistency of albite zone veins indicate that these are a product of melt-melt immiscibility.