Caledonian geology of Scoresby Sund region, central East Greenland

The Geological Survey of Greenland has completed the first 3 years of a 5-year mapping campaign in the Scoresby Sund region which includes the southernmost Caledonian fold belt of East Greenland.

The preliminary results show that it is possible to distinguish 4 main geologic units in the Caledonian fold belt. (1) A Precambrian crystalline basement with a cover of Precambrian metasediments and metavolcanics. These rocks are reworked by Caledonian folding to a varying degree. (2) A metamorphosed but nonmigmatized supracrustal complex composed of psammitic and pelitic rocks with occasional bands of calcareous rocks and totaling several kilometers in thickness. These rocks represent Caledonian geosynclinal deposits of miogeosynclinal aspect and are probably of very late Precambrian age. (3) A Caledonian infracrustal complex of mainly gneisses, migmatites and synkinematic granites. This unit is formed by migmatization of Caledonian geosynclinal deposits. (4) Late- to post-Caledonia intrusions, mainly of granitic type.

Westward directed thrust-sheets with a displacement of several tens of kilometers are present along the western rim of the fold belt. They comprise largely Caledonian supracrustal rocks, but in places basement rocks are incorporated in the thrust sheets. The central part of the N-S directed fold belt is characterized by infracrustal rocks which exhibit simple low-dipping macroscopic structures, which in parts of the area can be shown to be the limbs of major recumbent folds.

The Caledonian supracrustal rocks in the western part of the region were metamorphosed under high-pressure facies conditions and are characterized by kyanite-bearing rocks, whereas the central migmatitic part of the region was formed under low-pressure conditions and is characterized by cordierite-bearing assemblages.