Some observations on the structure of the early Proterozoic, Ammassalik mobile belt in the Ammassalik region, South-East Greenland

Abstract

Ammassalikian deformation appears to have given rise in the first instance to a regional layer cake structure of tectonically interleaved sheets of the early Proterozoic Siportoq supracrustal association and Archaean quartzo-feldspathic orthogneisses, the latter containing locally abundant amphibolite dykes. Younger orthogneisses were emplaced magmatically in parts of the structure. The layer cake structure was progressively modified by fold nappes and later domes with steep intervening cusps. The early Ammassalikian structure is attributed to thrust stacking during ensialic crustal shortening with tectonic instability spreading from north to south. Some of the nappes and upright structures may be buoyancy phenomena which resulted from thermal instabilities generated at depth within the thrust pile.