Eclogites in Quartzo-Feldspathic Gneisses of Nordfjord, West Norway
ECLOGITES IN QUARTZO-FELDSPATHIC GNEISSES OF NORDFJORD, WEST NORWAY INGE BRYHNI, HALDIS J. BOLUNGBERG AND PER-REIDAR GRAFF Mineralogisk-Geologisk Museum, Oslo, Norway.- Mineralogisk Museum, Copenhagen, Denmark.- Norges Geologiske Undersökelse, Trondheim, Norway BRYHNI, J., BOLLINGBERG, H. J., & GRAFF, P.-R. 1968: Edogites in quartzo-feldspathic gneisses of Nordfjord, West Norway. Norsk Geologisk Tidsskri/t, Vol. 49, pp. 193-225. Oslo 1969. Edogites in quartzo-feldspathic gneisses of Nordfjord are similar to the oceanic tholeiitesin their low content of titanium, ferric iron, potassium, and phosphorus. The chemical composition of the eclogites varies, how ever, within wide limits, and it is probable that alterations of bulk chemical compositions have taken place if the eclogites were indeed formed by transformations from other basic rocks. The garnets contain 36-50% Alm, 0.4-1.9% Spess, 23-43% Py, 0.3-2.1% And, and 13-25% Gross. Clinopyroxenes contain 3-9% Ac, 23-42% Jd, 8-13% Tsch, 3-7% Hd, and 38-56% Di. Titanium, nickel, chromium, and strontium are concentrated in dino pyroxene relative to garnet, while cobalt, manganese, scandium, and zirconium are relatively concentrated in garnet. Eclogites from gneiss of Nordfjord differ from the eclogites endosed in ultrabasites of Sunnmöre both in bulk chemistry, composition of garnet and clinopyroxene, and in the partition of elements between garnet and dinopyroxene. The ultrabashes occur in leetonised zones and might represent rocks which are tectonically emplaced, but the eclogites enclo3ed in gneiss are Iikely to be original crustal rocks. They occur as disrupted layers or boudins in paragneiss in harmony with a formation from dry basic igneous and sedimentary rocks endosed in a thick geosynclinal pile of supracrustals which were rapidly buckled down to great depths and metamorphosed there.
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