Pressure-temperature evolution of retrogressed kyanite eclogites, Weinschenk Island, North-East Greenland Caledonides

Caledonian eclogites and associated high-pressure rocks are present in a 400 x 100-km long belt along the coast of North-East Greenland. Kyanite and clinozoisite eclogites on Weinschenk Island (77 degrees 54'N, 21 degrees 17'W) occur as lenses within amphibolite facies, quartzofeldsparhic gneisses. The eclogites have been extensively overprinted by lower pressure assemblages and exhibit a variety of coronitic and symplectitic reaction textures that record the exhumation path of the rocks. Textural relationships and mineral composition data indicate that the initial high-pressure, plagioclase-free assemblage was garnet + omphacite +/- kyanite +/- clinozoisite + rutile. Compositional growth zoning in garnet, together with distribution of mineral inclusions within it, record a prograde evolution from epidote-amphibolite facies progressing into the eclogite facies, Post-peak pressure reaction textures include clinopyroxene-plagioclase intergrowths after omphacite; the replacement of kyanite by sapphirine-plagioclase, spinel-plagioclase and corundum-plagioclase symplectites; and resorption of garnet by amphibole-plagioclase kelyphites. The replacement textures indicate that post-eclogite facies decompression took place while the rocks remained at elevated temperatures (upper amphibolite/granulite facies conditions). The metamorphic evolution of the eclogites is in agreement with eclogite formation by thick-skinned crustal imbrication and subhorizontal shortening of the Laurentian margin during Caledonian collision, exhumation to amphibolite facies by emplacement of the eclogite-bearing thrust sheet on the Laurentian margin and accompanying erosion, and final exhumation to the surface by post-Caledonian crustal thinning. (C) 2000 Elsevier Science B.V. All rights reserved.