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Title: The geology of Northern Sotra : Precambrian gneisses west of the Bergen Arcs, Norway
Author: Johns, C. C.
Awarding Body: Royal Holloway, University of London
Current Institution: Royal Holloway, University of London
Date of Award: 1981
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Northern Sotra forms part of a hitherto poorly studied area of Precambrian gneisses within the Western Gneiss Complex at the core of the Bergen Arcs. The oldest rocks comprise gneisses of acidic to intermediate composition, ortho-amphibolites and metasediments, which were variably migmatised during the Svecofennian orogeny (c.1850Ma). These were deformed and metamorphosed, and subsequently intruded by a suite of gabbros and dolerites, and by Sveconorwegian granites (c.1000Ma). The predominant deformation structures are Caledonian in age, and overprint, and frequently obliterate, earlier structures. Two Caledonian orogenic phases are recognised: the Finmarkian (Cambrian to L.Ordovician) and Scandinavian (M. to L.Silurian). During the Finmarkian deformation, overfolds developed in response to the overthrusting of a thick nappe pile. Collapse of the nappe pile caused intense flattening and the formation of thick protomylonite zones. Synto post-tectonic, amphibolite facies metamorphism indicates a cover thickness of approximately 20 -2Skm. Uplift to a near surface level occurred by U.Ordovician to L.Silurian times. The Scandinavian orogenic activity followed further nappe overthrusting, and is restricted to major doming, accompanied by greenschist facies metamorphism. The dome may be explained by fold superimposition or gravity induced diapirism, and is responsible for the arcuate shape of the Bergen Arcs. Post-doming, brittle deformation occurred, developing faults, joints, and cataclasite and pseudotachylite zones. Joint planes are the site of basalt dyke intrusion and hydrothermal mineralisation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Geology Geology Mineralogy Sedimentology