A structural, stratigraphic and petrologic study of anorthosites, eclogites and ultramafic rocks and their country rocks, Tafjord area, western South Norway.

Abstract

The Tafjord area of the central basal gneiss region contains Caledonized metamorphic rocks divided into two groups. The 1000 m.y. old Fetvatn Geniss is a homogeneous zone of granodioritic gneiss that was intruded as part of a large plutonic complex during the Sveconorwegian Cycle. The heterogeneous Vikvatn Sequence contains obvious metasedimentary and metavolcanic rocks and is comprised of the Øyen, Øvste Rødal and Svartegga groups. In addition, anothosite, eclogite and anhydrous peridotite occur within the Øyen and Øvste Rødal groups. The quartizite-rich Svartegga group may form the basal (Eocambrian) part of the Caledonian supracrustal sequence typical of the eastern basal gneiss region. The Øyen and Øvste Rødal groups would then be Precambrian metasedimentary sequences seperated from the Svartegga group by a major unconformity. Structures include two early generations (F1A og F1B) of east-plunging, reclined, isoclinal, similar folds. Later (F2) folds generally have a concentric geometry, disharmonic profiles and variable axes. The F1 and F2 fabrics are identical to stuctures in the eastern basal geniss region that are believed to have formed during the Caledonian orogeny; but the F1A fabric may be a heterogeneous assemblage of Precambrian structures that were homogenized (Caledonized) during the intense F1B deformation.