Petrology and geochemistry of high-grade metamorphic and igneous rocks on Langøy, northern Norway.

Abstract

The rocks on Langøy have been considered as representing an igneous rock series including metamorphic sedimentary rocks of \"Caledonian type\". The present work shows that they are for the most part high-grade metamorphic rocks which are intruded by a few post metamorphic igneous rocks. The petrography of the rocks is discussed. They range in composition from ultrabasic to granitic. Rocks in the 50-60 per cent silica range predominate areally. The metamorphic rocks on Lagerøy are divided into: the banded series, the charnokite border series, the amphibolite facies veined gneises, porphyroblastic monzonitic granulites, old red granites, red augengneisses (ofmonzonitic composition), metasedimentary rocks, and diaphtoritic gneisses. The Eidet-Hovden intrusion, young red granites and the Bø gabbro are considered as post metamorphic igneous intrusions. The position of the anorthosite with associated monzonite east of Eidsfjorden is doubtful but may be related to the Eidet-Hovden intrusion. The metamorphic facies and mineral equilibria are discussed. A metamorphic boundary which separates amphibolite facies rocks to the east from granulite facies rocks to the west coincides along the strike with the observed thrust plane under the anorthosite east of Eidsfjorden.