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Escamilla Casas, José Cruz


Geological Society of America Abstracts with Programs. Vol. 44, No. 7, p.37


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.

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