Terrane transfer during the Caledonian orogeny: Baltican affinities of the Liverpool Land Eclogite Terrane in East Greenland

摘要

The Liverpool Land basement horst, East Greenland, comprises two allochthonous Caledonian terranes with very different tectonomagmatic and metamorphic histories, separated by the composite Gubbedalen Shear Zone. The Liverpool Land Eclogite Terrane in the footwall consists of orthogneiss formed at 1645-1640 Ma, affected by eclogite-facies metamorphism at 400 Ma and subsequently migmatized and intruded by granites at 388-385 Ma. The Liverpool Land Eclogite Terrane contrasts with the upper plate, which consists of arc-related Late Ordovician to Early Silurian magmatic rocks and was not affected by the Devonian metamorphism seen in the lower plate. Conversely, Ordovician-Silurian rocks are absent from the lower plate. Mesoproterozoic protolith ages, Early Devonian high-pressure metamorphism, and the occurrence of garnet peridotite distinguish the Liverpool Land Eclogite Terrane from all other terranes in East Greenland, including the large North East Greenland Eclogite Province, whereas these features are characteristic for the Western Gneiss Region in Norway. These observations indicate that the Liverpool Land Eclogite Terrane is exotic with respect to Laurentia and a Baltican origin seems likely. The amalgamation of the Baltican crustal slice with Laurentia probably occurred by imbrication of subducted Baltican crust in a bulk transpressional setting.