Alta og Gargia Beskrivelse til de berggrunnsgeologiske kart 1834 I og 1934 IV -M 1:50000 (Med fargetrykte kart)

• Main Authors: Gautier, André M., Bouke Zwaan, Klaas
• Format: Book
• Language: unknown
• Published: Universitetsforlaget 1980
• Subjects: info:eu-repo/classification/ddc/550; Geology; Stratigraphic; Stratigraphic Cambrian Maps; Stratigraphic Precambrian Maps; Maps; From 500 million to 5 billion years ago; Cambrian Geologic Period; Alta; Gargia; Raipas; karelian
• Online Access: https://archive-ouverte.unige.ch/unige:163772

General descriptions of the different metasedimentary, metavolcanic and igneous rocks occurring within the area of the two map-sheets are presented. Three principal map-subdivisions are recognized: (a) a Precambrian (supposed Karelian) supracrustal sequence occurring in a tectonic window; (b) autochthonous Late Precambrian to Lower Cambrian metasediments; (c) an allochthonous (Caledonian) complex of Precambrian and Eocambrian metasediments, gneisses and igneous rocks. The major geological subdivisions of the map-area are outlined. The Precambrian Raipas Group was deformed and metamorphosed in low to middle greenschist facies, possibly in Karelian time. The metamorphic lithologies of the allochthon are separated into two main tectonic units, the Gargia Nappe and the Nalganas Nappe. The Gargia Nappe contains an exotic rock assemblage (Nålfjell Group) which is thought to be a slice of Precambrian basement rocks. The allochthonous rocks have undergone at least three phases of Caledonian deformation. The first two phases are characterized by the formation of a blastomylonitic schistosity subparallel to layering. Folding was relatively uncommon, but most pronounced in the second deformation phase and was accompanied by the highest grade of metamorphism; rocks of the Gargia Nappe were metamorphosed in the lower greenschist facies, those of the Nalganas Nappe in the upper greenschist facies. The third fold phase was of brittle character with a retrograde lower greenschist facies metamorphism. In the final chapters, some information is presented on the economic geology, including the important flagstone industry, and geophysical and geochemical investigations. An excursion guide to localities of the most characteristic rock-types is also included.