Protoliths of the gneisses and mafic rocks in the Hellevik - Flekke Area in Sunnfjord, Western Norway
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The Hellevik-Flekke area comprises Precambrian crystalline rocks that have experienced a complex history of deformational and metamorphic events through both Precambrian and Caledonian times. The area can be divided into four different lithological units. The Basal Gneisses, the Flekke Unit, the Gjøl- anger Unit and the Vardeheia Unit. During the Caledonian Orogeny all units were deformed and metamorphosed under eclogite facies conditions, but relicts of undeformed and unmetamorphosed protholiths from the units can be identified. To the south, granodioritic and monzonitic gneisses occur together with granites, pegmatites, and minor amphibolitic and eclogitic bands and lenses. This assembly of lithologies is similar to those of the Western Gneiss Complex in the middle part of the Sognefjord transect. The Flekke Unit is interpreted to represent an allocthonous nappe containing a layered mafic-ultramafic complex. The gabbroic rocks of th complex are dated to 1522+-55 Ma (Sm-Nd age). The Gjølanger Unit consists of grey and green orthogneisses of dioritic to granitic composition, with geochemical character- istics of rocks formed at an active continental margin. Rb-Sr isotopic data indicate a minimum age for the gneisses of 155 Ma, with subsequent Sr-isotope disturbance. This unit is also interpreted to be an allochthonous nappe. The Vardeheia Unit in the north experienced the strongest Caledonian deformation and is dominated by heterogeneous banded gneisses and mylonites with small lenses of amphibolites and eclogites.