| dc.description.abstract | Abstract In the Kragerø area in South Norway, tourmaline is commonly found in Sveconorwegian Nb-Y-F pegmatites. In general, magmatic tourmaline is rare in Nb-Y-F pegmatites. The local tourmaline enrichment in the Kragerø pegmatites, and consequently, the origin of Boron is under debate, since the Sveconorwegian basement is poor in B elsewhere. The tourmalines from the following pegmatites were investigated: (1) from the Bamble sector, the Kragerø pegmatites: Lindvikskollen, Tangen, Dalane and Havredal; and the (2) Ramfoss and (3) Spro pegmatites, from the Kongsberg Sector and Idefjorden ‘Terrane’, respectively. The Lindvikskollen pegmatite area was the focus of field work and sampling of rocks and tourmalines. Additional tourmaline samples were provided by the Natural History Museum of the University of Oslo. The methodologies used included whole-rock analysis, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and secondary ion mass spectrometry (SIMS). The Kragerø pegmatites (which occur a few km apart from each other) have different B isotope signatures, which hints to separate melt sources. Because a common melt source of the Kragerø pegmatites can be excluded, it is suggested that they formed by local partial melting. This conclusion is supported by the fact that no granite pluton with similar ages to the pegmatites is exposed in the area. In the case of the Lindvikskollen pegmatite, which intruded a metagabbro body and its albitized parts, tourmaline and bulk rock chemistry indicates that the pegmatite was probably formed by mixed partial melting of its metagabbro and albitite host rocks. In addition, the nearby Tangen pegmatite intrudes the same metagabbro, and its overlapping δ11B data with the Lindvikskollen tourmaline indicates that they share a common source. The Dalane and Havredal tourmalines, are most likely the result of partial melting of their metasedimentary host rocks, amphibolites and gneisses. The Ramfoss tourmalines show affinity to carbonates, which can be found in calcite veins that infiltrated the area’s rocks. The Spro tourmaline chemical and isotopic compositions point to their host rock tourmaline-bearing gneiss to be the pegmatite melt source. This thesis concludes that the source of B of the investigated pegmatites originated by low degree partial melting of their respective host rocks, which contain B-bearing minerals (borosilicates and micas) in addition to the fractional crystallization of the melt under conditions that increased the tourmaline stability range. | eng |