Polyphase Metamorphism in the Granulite Facies Terrain of the Risør Area, South Norway
POLYPHASE METAMORPHISM IN THE GRANULITE FACIES TERRAIN OF THE RISØR AREA, SOUTH NORWAY IAN C. STARMER Starmer, I. C.: Polyphase metamorphism in the granulite facies terrain of the Risør area, South Norway. Norsk Geologisk Tidsskrift, Vol. 52, pp. 43-71. Oslo 1972. The tectonic and metamorphic evolution of this Pre-Cambrian complex is discussed in terms of field relationships and petrofabrics. Events are sum marized in tabular form and correlated with those in the Amphibolite facies terrain immediately to the north. Doleritic sheets, originally intruded into metasediments, now form a 'Py ribolite Series' showing a variety of assemblages inherited from successive metamorphisms. An 'Arendalite Series' of charnockitic, enderbitic and more intermediate lithologies is thought to have formed by Granulite facies alter ation of pre-existing metasediments and migmatites. This metamorphism pro duced a complex of Pyribolites, Arendalites and metasediments which were subsequently intruded by basic rocks and underwent prolonged Amphibolite facies alteration. Regional granitisation converted many of the metasedi ments to rocks of general granitic aspect and obliterated most major struc tures. It is suggested that the Granulite facies metamorphism was part of an orogenic episode pre-dating the Sveconorwegian Regeneration which pro duced the late granitisation: radiometric work appears to lend some support to this hypothesis. X-ray diffractometry and microscope studies demonstrate the disequili brium state of potassium-rich feldspars in the granitised rocks and the Arendalites. l. C. Starmer, Department of Geology, Queen Mary College, University of London, London, E.l, England. Introduction The Granulite facies rocks south of RisØr represent the northern limit of Bugge's 'Arendalite Series' or 'Arendal Charnockites' (Bugge 1940, 1943, 1960).
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