STRUCTURAL CHARACTERIZATION OF THE EASTERN SEGMENT IN THE GLASSVIK AREA (HALLAND PROVINCE, SW SWEDEN)

The Sveconorwegian Province is a ~500 km wide mobile belt in SW Scandinavia, considered as a tectonic counterpart to the Grenvillian Province in North America. The Eastern Segment (ES) is the easternmost parautochthonous basement of the Sveconorwegian Province, and mainly consists of migmatitic orthogneisses, and different generations of high-grade metaigneous mafic rocks. These rocks have been affected by at least two high-grade metamorphic episodes: a c. 1.43 Ga pre-Sveconorewegian and a c. 0.97 Ga Sveconorwegian event. In the Glassvik area (Halland Province, SW Sweden) a layered sequence dominated by grey quartz-feldspathic gneisses (Qtz + Fsp + Bt ± Grt ± granitic leucosome), layered migmatitic garnet amphibolite (Hbl + Bt + Fsp + Grt + Qtz ± Cpx + Opx-bearing leucosome), and coarse grained garnet amphibolite (Hbl + Cpx + Plg + Grt ± Bt ± Qtz, ± Opx) is characterized by a strong NNE-SSW to NE-SW tectonic banding (S₁), in which intrafolial folds (F₁) and concordant leucosome veins are preserved. S₁ is folded by cm- to km-scale asymmetric F₂ folds that are characterized by angular hinges, N-S to NE-SW trending axes, and an axial planar cleavage (S₂). A predominantly east-trending mineral lineation defined by oriented polymineralic aggregates is also observed in the area. Cm- to km-scale cylindrical F₃ folds with steeply SE-plunging axes and SW dipping axial planes fold and deflect all previous structures. Some of the amphibolitic rocks show gradational enrichment in cm-scale leucosome veins of granitic composition that are subparallel to the main banding (S₁, S₂). A younger generation of leucosome veins cuts the S₁ and S₂ at high angles, and is likely associated to F₃. At least 2 generations of cm- to m-scale granitic pegmatites intrude the sequence: the oldest generation (dated by U-Pb zircon at 1.4 Ga) intruded the sequence subparallel to the tectonic banding prior to F₂, as suggested by their internal tectonic fabrics. A younger generation of mostly cm-scale pegmatitic veins (0.95 Ga) intrudes the tectonic banding at a high angle, and is syn- to post-F₃. Future work to further resolve the relative ages and geometry of the fold sets along strike of this area will provide important constraints to better understand the tectonometamorphic evolution of the Eastern Segment.