scholarly journals Stratigraphy and structural development of the Precambrian rocks in the area north-east of Disko Bugt, West Greenland

1967 ◽  
Vol 13 ◽  
pp. 1-28
Author(s):  
A Escher ◽  
M Burri
Keyword(s):  
Transition Zone ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Structural Development ◽  
West Greenland ◽  
Precambrian Rocks ◽  
The Third ◽  
North East ◽  
Area North

The Precambrian rocks in the area north-east of Disko Bugt can be divided into a lower gneiss group and an upper supracrustal group. The lower part of the supracrustal group consists of quartzites, amphibolites and garnet-staurolite schists, while the upper part is mainly semipelitic schist. The gneisses were affected by three successive phases of deformation, while in the supracrustals only the two latest phases of folding can be recognized. Evidence is given in support of the idea that the supracrustals were deposited on a gneiss basement after the first phase of folding, the basement being later reactivated mainly during the third and last deformation. Two main tectonic compLexes can be distinguished in the area mapped: a southern complex characterized by a predominarit ENE direction of the fold axes and a northern complex in which the main fold axes are strongly curved around a central gneiss dorne. The transition zone between the southern and northern complex is marked by the presence of severaL important faults and mylonites. The gneiss dorne is flanked in its northern part by a thick granite sheet. The dorne structure appears to have been forrned by a combination of diapiric movements and the interference between two successive deformations. The gneisses and lower supracrustals recrystallized under amphibolite facies conditions, while greenschist facies conditions prevaiLed during the recrystallisation of the upper supracrustals.

scholarly journals Some border relations between supracrustal and infracrustal rocks in South-West Greenland

1966 ◽  
Vol 9 ◽  
pp. 1-43
Author(s):  
B.F Windley ◽  
N Henriksen ◽  
A.K Higgins ◽  
E Bondesen ◽  
S.B Jensen
Keyword(s):  
Transition Zone ◽  
Metamorphic Grade ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Granitic Rocks ◽  
Second Phase ◽  
Concomitant Increase ◽  
West Greenland ◽  
South West ◽  
Volcanic Series

Three types of border relation between supracrustal and intracrustal rocks are described from South-West Greenland. In the Ravns Storø area a largely volcanic series, possibly equivalent in age to the Tartoq Group, passes downwards into the underlying gneisses via a transitional migmatite front. The supracrustal bedding passes conformably downwards into the gneissic foliation and there is a progressive downward increase in metamorphic grade and degree of mineral orientation. In the northern part of the Ivigtut region Ketilidian supracrustals lie with a major unconformity on pre-Ketilidian gneisses (and Tartoq Group) supracrustals; between which there is a migmatite front relation. Passing southwards the autochthonous unconformity between the Ketilidian supra­crustals and the underlying rocks is affected by a series of progressive tectonic modifications. Faulting parallel to the axial planes of Ketilidian second phase folds in the supracrustals is followed by thrusting along the unconformity, giving rise to a parautochthonous border, which further south passes into an allochthonous border modified by gneissification and associated with the formation of granitic rocks. Earlier basic dykes together with the gneissic foliation are dragged along the transitional border which simulates a transition zone between a superstructure and an infrastructure. In association with this increase in tectonisation there is a concomitant increase in grade of metamorphism of the supracrustal rocks from an almost unmetamorphosed state through greenschist facies and epidotemphibolite facies to amphibolite facies.

scholarly journals Structures in an area north-east of Fiskenæsset, West Greenland

1976 ◽  
Vol 73 ◽  
pp. 16-21
Author(s):  
A.M Hopgood
Keyword(s):  
Large Scale ◽  
The Other ◽  
Minor Importance ◽  
The South ◽  
Rock Unit ◽  
West Greenland ◽  
The Third ◽  
North East ◽  
South West ◽  
Area North

The area under discussion borders the Inland lce 75 km north-east of Fiskenæsset and consists of about 250 km2 of predominantly anorthositic gneisses, with streaky biotitic and homblendic gneisses forming the other major rock unit. Amphibolites and late rectilinear, unmetamorphosed basic dykes are of relatively minor importance, constituting probably less than 5% of the whole. All these units with the exceptionof the dolerite dykes are parallel or sub-parallel to one another and are disposed in a series of large, moderately tight folds with axial planes symmetrically related to the lithological banding. These folds in places are isoc1inal and their axial traces are gently curved, trending on average south-east (fig. 9). Immediately to the south of the area the trend of the major lithological units swings from south-east to south and then curves to the south-west, an effect ascribed to the influence of folds developed during the third and fourth fold episodes in the deformational sequence which is discussed here. On a large scale the tight to isoclinal folds refold other, attenuated isoclinal folds considered to belong to the first (Fl) set in the sequence recognised. All the major lithological units have been affected by the Fl episode of folding. Curvature of the axial traces of the first and second fold sets is due to a combination of effects arising predominantly from deformation during the fifth, sixth and seventh fold episodes. The effects of these on a large scale have not been distinguished individually, although the reversal of plunge sense in the central part of the area is almost certainly the result of folding on easterly trending Fs axial planes. Perhaps the most striking faet which emerges from the present investigation is the broad similarity between the fold sequence in this area and that determined from an area adjacent to the Frederikshåbs Isblink approximately 50 km to the south (Hopgood, 1973). The principal distinction between the two sequences is merelyadifference in orientation ofaxial planes of equivalent fold sets, especiaIly the earlier ones.

The Archaean Atâ intrusive complex (Atâ tonalite), north-east Disko Bugt, West Greenland

1999 ◽  
pp. 103-112
Author(s):  
Feiko Kalsbeek ◽  
Lilian Skjernaa
Keyword(s):  
Intrusive Complex ◽  
The South ◽  
Original Series ◽  
Early Proterozoic ◽  
West Greenland ◽  
North East ◽  
The North ◽  
Southern Border ◽  
Area North ◽  
Igneous Layering

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Kalsbeek, F., & Skjernaa, L. (1999). The Archaean Atâ intrusive complex (Atâ tonalite), north-east Disko Bugt, West Greenland. Geology of Greenland Survey Bulletin, 181, 103-112. https://doi.org/10.34194/ggub.v181.5118 _______________ The 2800 Ma Atâ intrusive complex (elsewhere referred to as ‘Atâ granite’ or ‘Atâ tonalite’), which occupies an area of c. 400 km2 in the area north-east of Disko Bugt, was emplaced into grey migmatitic gneisses and supracrustal rocks. At its southern border the Atâ complex is cut by younger granites. The complex is divided by a belt of supracrustal rocks into a western, mainly tonalitic part, and an eastern part consisting mainly of granodiorite and trondhjemite. The ‘eastern complex’ is a classical pluton. It is little deformed in its central part, displaying well-preserved igneous layering and local orbicular textures. Near its intrusive contact with the overlying supracrustal rocks the rocks become foliated, with foliation parallel to the contact. The Atâ intrusive complex has escaped much of the later Archaean and early Proterozoic deformation and metamorphism that characterises the gneisses to the north and to the south; it belongs to the best-preserved Archaean tonalite-trondhjemite-granodiorite intrusions in Greenland.

Stratigraphy, structure and geochemistry of Archaean supracrustal rocks from Oqaatsut and Naajaat Qaqqaat, north-east Disko Bugt, West Greenland

1999 ◽  
pp. 65-78
Author(s):  
Henrik Rasmussen ◽  
Lars Frimodt Pedersen
Keyword(s):  
Tectonic Setting ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
West Greenland ◽  
North West ◽  
North East ◽  
Metavolcanic Rocks ◽  
Arc Setting ◽  
Area North ◽  
Back Arc

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Rasmussen, H., & Frimodt Pedersen, L. (1999). Stratigraphy, structure and geochemistry of Archaean supracrustal rocks from Oqaatsut and Naajaat Qaqqaat, north-east Disko Bugt, West Greenland. Geology of Greenland Survey Bulletin, 181, 65-78. https://doi.org/10.34194/ggub.v181.5114 _______________ Two Archaean supracrustal sequences in the area north-east of Disko Bugt, c. 1950 and c. 800 m in thickness, are dominated by pelitic and semipelitic mica schists, interlayered with basic metavolcanic rocks. A polymict conglomerate occurs locally at the base of one of the sequences. One of the supracrustal sequences has undergone four phases of deformation; the other three phases. In both sequences an early phase, now represented by isoclinal folds, was followed by north-west-directed thrusting. A penetrative deformation represented by upright to steeply inclined folds is only recognised in one of the sequences. Steep, brittle N–S and NW–SE striking faults transect all rock units including late stage dolerites and lamprophyres. Investigation of major- and trace-element geochemistry based on discrimination diagrams for tectonic setting suggests that both metasediments and metavolcanic rocks were deposited in an environment similar to a modern back-arc setting.

Proterozoic thermal activity in the Archaean basement of the Disko Bugt region and eastern Nuussuaq, West Greenland: evidence from K-Ar and 40Ar-39Ar mineral age investigations

1999 ◽  
pp. 55-64
Author(s):  
Henrik Rasmussen ◽  
Paul Martin Holm
Keyword(s):  
Structural Development ◽  
Thermal Activity ◽  
Excess Argon ◽  
Original Series ◽  
West Greenland ◽  
Precambrian Rocks ◽  
North Eastern ◽  
The Matrix ◽  
Radiogenic Argon

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Rasmussen, H., & Holm, P. M. (1999). Proterozoic thermal activity in the Archaean basement of the Disko Bugt region and eastern Nuussuaq, West Greenland: evidence from K-Ar and 40Ar-39Ar mineral age investigations. Geology of Greenland Survey Bulletin, 181, 55-64. https://doi.org/10.34194/ggub.v181.5113 _______________ K-Ar and 40Ar-39Ar analyses of amphiboles from Archaean amphibolites and gneisses show that Proterozoic tectono-thermal activity has played an important role in the metamorphic and structural development of the Precambrian rocks around north-eastern Disko Bugt and in eastern Nuussuaq. Proterozoic thermal activity lead to resetting of the K-Ar ages of amphiboles in eastern Nuussuaq, resulting in ages of c. 1750 to 1925 Ma; in the Disko Bugt area the effects are seen in total or partial resetting with K-Ar ages scattering mostly between 2750 and 1870 Ma. Resetting is caused either by total diffusion of earlier accumulated radiogenic argon or by complete recrystallisation of the amphiboles. Archaean 40Ar-39Ar ages obtained from mafic xenoliths within the Atâ tonalite show that not all parts of the area suffered argon loss during Proterozoic reheating. Incorporation of significant proportions of excess argon in some amphiboles is seen from 40Ar-39Ar mineral age spectra obtained for samples from supracrustal rocks and from mafic xenoliths in the Atâ tonalite. Phlogopite phenocrysts from a lamproite stock yielded a K-Ar age of 1764 ± 24 Ma, identical to a previously determined K-Ar age of the matrix phlogopite. These ages probably date the emplacement of the lamproite, and mark the time after which no tectono-thermal events affected the area.

scholarly journals Continued 1:500 000 reconnaissance mapping in the Precambrian of the Sukkertoppen region, southern West Greenland

1978 ◽  
Vol 90 ◽  
pp. 50-54
Author(s):  
J.H Allaart ◽  
C.R.L Friend ◽  
R.P Hall ◽  
S.B Jensen ◽  
I.W.N Roberts
Keyword(s):  
Coastal Areas ◽  
West Greenland ◽  
North East ◽  
Base Camp ◽  
Area North

The reconnaissance mapping programme for the 1:500000 map sheet Frederikshåb Isblink - Søndre Strømfjord (62°30'-66°45'N), in the Godthåb-Sukkertoppen region that started in 1976 (Allaart et al., 1977), was continued in 1977. This summer's activity was concentrated in the areas between the inner part of Fiskefjord and Taserssuaq, from Taserssuaq to north of Majorqaq and from Søndre Isortoq to Evighedsfjord (fig. 19). Between Fiskefjord and Søndre Isortoq detailed mapping has been carried out by geologists of Kryolitselskabet Øresund A/S during the summers of 1965-1976. The coastal areas have been investigated previously by GGU geologists (Berthelsen, 1960; Noe-Nygaard & Ramberg, 1961). The mapping team of five geologists, supported by two Bell G3 helicopters and by the GGU motor cutter F. Johnstrup, operated from a base camp at the head of the fjord Kangerdluarssuk, 30 km north-east of Sukkertoppen. The reconnaissance mapping programme will be completed in 1978, when the area north of Evighedsfjord as far as latitude 66°45'N will be mapped.

scholarly journals Compilation of 1:500 000 reconnaissance mapping in the Precambrian of the Evighedsfjord – Søndre Strømfjord – Itivdleq region, southern West Greenland

1979 ◽  
Vol 95 ◽  
pp. 72-76
Author(s):  
J.H Allaart ◽  
S.B Jensen
Keyword(s):  
Summer Season ◽  
West Greenland ◽  
North East ◽  
Area North ◽  
The University

The three years reconnaissance mapping programme for the 1:500 000 map sheet Frederikshåb Isblink - Søndre Strømfjord (Allaart et al., 1977,1978) was completed during the 1978 summer season. This summer's activity was concentrated in the area between Evighedsfjord and the northem boundary of the map sheet at latitude 66°45'N, and west of longitude 51°30'W (fig. 26). The area north-east of the Sukkertoppen Iskappe was reconnoitred during the summer of 1969 (Eseher et al., 1970). The area around Itivdleq and further north has been mapped more recently by geologists from the University of Liverpool under the direction of J. Watterson (1974). The mapping team in 1978 comprised two geologists based on the GGU cutter J. F. Johnstrup; periodic reconnaissance with Jet Ranger and Bell 204 helicopters was undertaken. The guidance of J. Watterson in the area around Itivdleq and Kangerdluarssuk fjords was greatly appreciated.

scholarly journals Measurements of ice thickness on glaciers at Isortuarssûp tasia, southern West Greenland and Pâkitsoq, central West Greenland

1989 ◽  
Vol 145 ◽  
pp. 59-63
Author(s):  
L Thorning ◽  
E Hansen
Keyword(s):  
Short Distance ◽  
Ice Thickness ◽  
West Greenland ◽  
Ice Cap ◽  
North East ◽  
The North ◽  
Electromagnetic Resonance ◽  
Area North ◽  
Inland Ice ◽  
Ice Radar

Two separate geophysical projects were carried out in 1988 as part of glacier-hydrological investigations of the margin of the Inland Ice. We made a reconnaissance electromagnetic resonance survey over the ice margin adjacent to Sermilik and Isortuarssup tasia, south-east of Nuuk/Godthåb and measured ice thickness along some lines in the area of Qamanârssûp serrnia, Kangiata nunâta sermia and Kangaussarssup sermia a short distance to the north, as well as a few profiles over a local ice cap just east of Isortuarssup tasia. In the Pâkitsoq area, north east of Ilulissat/Jakobshavn, we finished the mono-pulse ice radar work started last year (Thorning & Hansen, 1988a).

scholarly journals Structure of the Storstrømmen shear zone, eastern Hertugen af Orléans Land, North-East Greenland

1994 ◽  
Vol 162 ◽  
pp. 103-112
Author(s):  
R.A Strachan ◽  
I.R Tribe
Keyword(s):  
Shear Zone ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Fold Belt ◽  
East Greenland ◽  
North East ◽  
Mineral Assemblages ◽  
Basement Gneiss

The Storstrømmen shear zone is a NNE-trending belt of steep, heterogeneously deformed gneisses and mylonites, at least 8 km wide, which transects the basement gneiss complexes of the Caledonian fold belt between Dronning Louise Land and Hertugen af Orleans Land. Shear criteria indicate a consistent sinistral sense of displacement parallel to a gently-plunging L-S fabric. Mineral assemblages and fabrics within the mylonites indicate that mylonitisation was initiated under low amphibolite facies conditions and continued within the greenschist facies. The shear zone is reworked by late, steep brittle faults which are associated with cataclasis and local metamorphic retrogression.

SHRIMP U-Pb zircon ages for Archaean granitoid rocks, Ataa area, north-east Disko Bugt, West Greenland

1999 ◽  
pp. 49-54
Author(s):  
Allen P. Nutman ◽  
Feiko Kalsbeek
Keyword(s):  
Field Observations ◽  
Intrusive Complex ◽  
Ion Microprobe ◽  
Granitoid Rock ◽  
Original Series ◽  
West Greenland ◽  
North East ◽  
Granitoid Rocks ◽  
Area North ◽  
Age Determinations

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Nutman, A. P., & Kalsbeek, F. (1999). SHRIMP U-Pb zircon ages for Archaean granitoid rocks, Ataa area, north-east Disko Bugt, West Greenland. Geology of Greenland Survey Bulletin, 181, 49-54. https://doi.org/10.34194/ggub.v181.5111 _______________ Zircons from four samples of granitoid rocks from the Ataa area have been studied by SHRIMP ion microprobe. A trondhjemite from the Atâ intrusive complex (Atâ tonalite) yielded an age of 2803 ± 4 Ma, in agreement with earlier age determinations. A sample from the regional migmatitic biotite gneisses gave 2815 ± 4 Ma. A homogeneous granitoid rock, from field observations believed to be younger than the regional gneisses, has two main zircon populations, 2835 ± 4 Ma and c. 2800 Ma, respectively, and a granite that intrudes the Atâ complex yielded an age of 2758 ± 2 Ma.

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