| dc.description.abstract | Fen Carbonatite Complex was formed in different stages. The stage of søvite and dolomite carbonatite emplacement is believed to be accompanied by extensive deformation. However, the mechanism of carbonatite deformation is poorly understood. This thesis presents analyses of the deformation features of søvite and dolomite carbonatite from the Fen Carbonatite Complex through field observations and comprehensive microscopic analyses, which include petrographic microscopy and scanning electron microscope-based techniques such as backscatter electron imaging, energy-dispersive spectroscopy, cathodoluminescence imaging and electron backscatter diffraction. In field exposures, søvite and dolomite carbonatite occur as foliated and lineated dikes, with numerous xenoliths of fenite and mafic intrusions that form porphyroclast systems. Structural analysis indicates that the deformation occurred by a combination of pure and simple shear. Observations with the petrographic microscope were mainly focused on microstructures of carbonate minerals and apatite, which are common phases in søvite and dolomite carbonatite. Based on the carbonate microstructure, temperatures are estimated to be ≥ 600 °C. Backscatter imaging revealed the presence of melt pseudomorphs in the form of intergranular beads, cusps, films, and pools, especially in apatite layers. Based on electron backscatter diffraction analyses, elongated apatite grains deformed by dissolution-precipitation creep. Dissolution-precipitation creep caused core-and-rim zoning in apatite observed with cathodoluminescence. Zoning was accompanied by precipitation of rare earth elements from apatite core to rim during grain elongation. Apatite grain shape depended on core-rim fraction within that grain, where more elongated grains are rim-dominated, while fairly equidimensional grains are core-dominated. The electron backscatter diffraction method showed that apatite does not have intracrystalline distortion, has a homogeneous crystallographic structure, with elongation preferentially oriented parallel to the c-axis. Thus, the deformation of apatite was achieved through dissolution-precipitation in the presence of melt. | eng |