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Tectonic regimes and terrane boundaries in the high-grade Sveconorwegian belt of SW Norway, inferred from U-Pb zircon geochronology and geochemical signature of augen gneiss suites

par Bingen, Bernard ;Van Breemen, Otto
Référence Journal of the Geological Society, 155, 1, page (143-154)
Publication Publié, 1998-01

Article révisé par les pairs

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Résumé :

Six units from three suites of gneissic megacrystic granitoids in the Sveconorwegian Province of SW Norway were dated by the U-Pb zircon method. The Gjerstad suite crystallized between 1.19 and 1.15 Ga in the Bamble, Telemark and Rogaland Vest Agder terranes; it has an A-type geochemical signature suggesting intrusion in a tensional setting. The Vennesla unit of this suite yields an age of 1166+61 -21 Ma. The Feda suite intruded in Rogaland-Vest Agder during a short period at 1.05 Ga (four units between 1051+2-8 and 1049+2-8 Ma) and has a high-K. calc-alkaline trend suggesting a subduction-related setting. The Fennefoss augen gneiss of Telemark (1035+2 -3 Ma) possesses a geochemical signature transitional between high-K calc-alkaline and A-type. The spatial association of tensional plutonism with the Kristiansand-Porsgrunn shear zone between Bamble and Telemark suggests that crustal thinning occurred along this axis between 1.19 and 1.13 Ga, preceding Sveconorwegian compressive shearing. The boundary between Rogaland-Vest Agder and Telemark, the Mandai line, probably separated, at 1.05 Ga, a mobile belt (Rogaland-Vest Agder) and a colder, more rigid terrane (Telemark). Major strike-slip shearing along the southern section of the Mandal line was probably associated with intrusion of an elongate pluton of the Feda suite and ductile amphibolite-facies deformation along a banded gneiss unit.