The Caledonian Mountain Chain of the Southern Troms and Ofoten areas. Part II. Caledonian rocks of igneous origin.

Abstract

Metamorphosed rocks of igneous origin are described fromCaledonian part of the Southern Troms and Ofoten areas. Based onmegascopic and microscopic appearance, on chemistry and on fieldrelations they can be divided into two separate groups whose age andgeologic history differ from each other: The first group comprisesserpentinites, amphibolites, meta-trondhjemites and metamorphozedquartz keratophyres. It is suggested that these rocks represent earlyperidotite intrusions, basalts, gabbros, basalt tuffs and tuffites,trondhjemite intrusives, and quartz keratophyre pytoclastics and lavas,respectively, all rocks having been metamorphosed by progressiveregional metamorphism occurring during the Caledonian orogeny. Theirmineral assemblages are generallly in good accordance with thedistribution of metamorphic facies as this is revealed by the writer'sprevious investigations in adjoining metasediments. This first grouprepresent the initial Caledonian magmatism in the area, largelybelonging to the geosynclinal stage. The second group of igneousrocks includes ultrabasics (peridotites and troctolites), norites,gabbros, diorites, granodioritic and granitic rock types (to a smallerextent also trondhjemites). These rocks were only to a small degreealtered by metamorphic processes.