Abstract
Mid-crustal deformation of an Early Proterozoic high-grade gneiss complex in western Dove Bugt gave rise to at least two sets of nappes. Structures in mylonites in low-angle ductile shear zones associated with the younger nappes indicate north-easterly-directed displacements. The nappes and mylonites are folded by upright to inclined folds that verge north-west and which appear to be associated with decollements that dip south-east. Hornblende, sillimanite and anatectic partial melts that developed with the nappes, mylonites and younger folds show that deformation took place under amphibolite facies conditions. Several lines of evidence suggest that the younger nappes, the mylonites and the upright to inclined folds formed during the Caledonian orogeny. Some pre-Caledonian deformation may be represented by the oldest isoclinal folds. Numerous, small-scale, ductile extensional shear zones and more brittIe fractures that were superimposed across the Caledonian structures are believed to have formed during orogen-parallel collapse which may be related IO Devonian basin development farther south in central East Greenland. Younger fauIts and major joints are correlated with Carboniferous, Mesozoic and Tertiary basin development in North-East Greenland.
Highlights
Mid-crustal deformation of an Early Proterozoic high-grade gneiss complex in western Dove Bugt gave rise to at least two sets of nappes
As the effeets ol' the youngest period 01' folding are traeed ø across strike, say from Godfred Hansen to Kap Stop, the antiforms appear to be preferentially cut out on thrusts compared with the synforms. This effeet suggests that the mid-crustal deformation of the Early Proterozoic layercake arrangement ol' high-grade gneisses in western Dove Bugt yielded a regional composite contractional structure comparable with those on a much smaller scale reported by Rykelid & Fossen (1992) in the Caledonides of Norway
The eomplex gneiss terrain in western Dove Bugt is separated from the gneisses and cover roeks in the Caledonian forel and in Dronning Louise Land to the west by wide glaeiers feeding from the Inland Ice
Summary
Fabrics in the gneisses and supracrustal roeks in western Dove Bugt are commonly composite, comprising several distinct components which were the result of polyphase deformation. Older linear (L) and planar (S) fabrics were reoriented and reinforced during periods of deformation which gave rise to the nappes, mylonites, north-westerly verging folds and the late-stage extensional structures. Some of the older fabrics are probably related to Early Proterozoic gneiss-forming events which occurred prior to the emplacement ol' the sheets of pink granites. Many of the folds that are related to the periods of deformation younger than the sheets of pink granites have S fabrics which forrned as aresult of new mineral growth that was superimposed on folded gneissic foliations and mylonite fabrics. Many of the fabrics in the folds and mylonites that are younger than the Early Proterozoic granites are composite in the sense that they
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