Field relationship of high-grade Neo- to Mesoarchaean rocks of South-East Greenland: Tectonometamorphic and magmatic evolution

During the 1969 geological expedition to Scoresby Sund, a small migmatite area on the south-west peninsula of island no. 1 of the Bjørneøer (71°08'44"N/25°20' 56"W - see fig. 1) was mapped and sampled in detail. More than 2000 kg of rock were collected for petrographic and isotope geochemical investigations to give an insight into the nature of rock-forming processes induced by high-grade regional metamorphism. The restriction to a very limited sampling area (700 m × 200 m) provided rock samples which were subjected to very similar P-T conditions for at least part of their history. This report presents preliminary results obtained by the comparison of U-Pb systematics of accessory minerals from various rock phases.

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Search for Archaean basement in the Caledonian fold belt of North-East Greenland

Rapport Grønlands Geologiske Undersøgelse ◽

10.34194/rapggu.v162.8254 ◽

1994 ◽

Vol 162 ◽

pp. 129-133

Author(s):

A.P Nutman ◽

F Kalsbeek

Keyword(s):

High Grade ◽

Metamorphic Zircon ◽

Fold Belt ◽

Pb Isotope ◽

Zircon Age ◽

East Greenland ◽

Early Proterozoic ◽

North East ◽

History Of ◽

High Grade Metamorphism

SHRIMP U-Pb isotope data on zircon crystals from a gneiss sample near Danmarkshavn, where the presence of Archaean rocks has earlier been documented, show that the rock has undergone a complex history of igneous and metamorphic zircon growth. At least three generations of zircon are present with ages of c. 3000 Ma, c. 2725 Ma and 1967 ±8 Ma (2 α). Apparently the rock was formed from an Archaean protolith which underwent high grade metamorphism during the early Proterozoic. Another sample from the easternmost exposures of the Caledonian basement, collected further north, yielded only early Proterozoic zircons with an age of 1963 ± 6 Ma. Together with a SHRIMP U-Pb zircon age of 1974 ± 17 Ma reported earlier, these results give evidence of a major igneous and metamorphic event in North-East Greenland about 1965 Ma ago.

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Reaction of Precambrian high-grade gneisses to mid-crustal ductile deformation in western Dove Bugt, North-East Greenland

Rapport Grønlands Geologiske Undersøgelse ◽

10.34194/rapggu.v162.8248 ◽

1994 ◽

Vol 162 ◽

pp. 53-70

Author(s):

B Chadwick ◽

C.R.L Friend

Keyword(s):

Shear Zones ◽

Ductile Deformation ◽

Small Scale ◽

High Grade ◽

East Greenland ◽

North West ◽

North East ◽

Basin Development ◽

Ductile Shear Zones ◽

Partial Melts

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.

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The high-grade gneisses in the south-west of Dove Bugt: an old gneiss complex in a deep part of the Caledonides of North-East Greenland

Rapport Grønlands Geologiske Undersøgelse ◽

10.34194/rapggu.v152.8163 ◽

1991 ◽

Vol 152 ◽

pp. 103-111

Author(s):

B Chadwick ◽

C.R.L Friend

Keyword(s):

Granitic Rocks ◽

Small Scale ◽

High Grade ◽

Deep Part ◽

The South ◽

East Greenland ◽

North East ◽

Gneiss Complex ◽

South West

The complex range of orthogneisses has been subdivided on the basis of field characteristics into an old polyphase group, grey phlebitic gneisses, younger varieties of pink granitic gneisses that occur principally as extensive sheets, mixed orthogneisses with schlieric facies and undifferentiated gneisses with dioritic facies. Mafic sheets, now amphibolites, were emplaced at various stages in the evolution of the gneisses. Enclaves and sheets of supracrustal rocks include paragneisses, graphitic schists, marble, amphibolite and stratiform gabbroic complexes with anorthosite. Nappes with curvilinear hinge lines and belts of mylonite developed in high amphibolite conditions after emplacement of the sheets of pink granitic rocks (now variably deformed gneisses) into the old orthogneisses and supracrustal rocks. Principal displacements in the mylonites were shallow and N-directed. The nappes and mylonites were deformed by upright-inclined folds with north-westerly vergence. The nappes, mylonites and north-westerly verging folds are presumed to be Caledonian. N- and S-directed extensions indicated by small-scale ductile structures younger than the regional folding suggest that longitudinal collapse predominated in this part of the Caledonian belt in the south-west of Dove Bugt.

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