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.

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.

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 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 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).

The Precambrian supracrustal rocks of Nunataq, north-east Disko Bugt, West Greenland

1999 ◽  
pp. 79-86
Author(s):  
A.K. Higgins ◽  
N.J. Soper
Keyword(s):  
Structural Interpretation ◽  
Original Series ◽  
West Greenland ◽  
North East ◽  
Lower Proterozoic ◽  
Regional System

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Higgins, A., & Soper, N. (1999). The Precambrian supracrustal rocks of Nunataq, north-east Disko Bugt, West Greenland. Geology of Greenland Survey Bulletin, 181, 79-86. https://doi.org/10.34194/ggub.v181.5116 _______________ Supracrustal rocks preserved in a major syncline in southern Nunataq comprise an Archaean and a Proterozoic sequence. An angular discordance between the two sequences is preserved locally. The basal development of the younger sequence shows similarities with that of the lower Proterozoic Mârmorilik Formation of the Uummannaq region north of Nuussuaq. The major syncline–anticline fold pair of southern Nunataq is part of a regional system of E–Wtrending Proterozoic folds which also deform the supracrustal rocks of Anap Nunaa, south of Nunataq. Recognition of a major syncline in southern Anap Nunaa, largely obliterated by albitisation, permits a simpler structural interpretation than previously suggested.

Review of isotope data for Precambrian rocks from the Disko Bugt region, West Greenland

1999 ◽  
pp. 41-47 ◽  
Author(s):  
Feiko Kalsbeek ◽  
Paul N. Taylor
Keyword(s):  
Sr Isotope ◽  
Yield Model ◽  
Original Series ◽  
Early Proterozoic ◽  
West Greenland ◽  
Precambrian Rocks ◽  
Isotope Data ◽  
Metavolcanic Rocks ◽  
Granitoid Rocks ◽  
Data Yield

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., & Taylor, P. N. (1999). Review of isotope data for Precambrian rocks from the Disko Bugt region, West Greenland. Geology of Greenland Survey Bulletin, 181, 41-47. https://doi.org/10.34194/ggub.v181.5110 _______________ Pb-Pb and Rb-Sr isotope data yield whole-rock isochron ages of c. 2800 Ma for two localities of granitoid rocks in the Disko Bugt region, with little evidence of strong later disturbance. Rb-Sr isotope data on Archaean metasediments from two localities, however, were strongly disturbed during the early Proterozoic. Sm-Nd whole-rock data for acid metavolcanic rocks within Archaean supracrustal sequences yield model ages of c. 2800 Ma. The early Proterozoic age of a younger sequence of supracrustal rocks (the Anap nunâ Group) is confirmed by Sm-Nd data, and Rb-Sr whole-rock data for albitised siltstones show that albitisation took place hundreds of millions of years after the peak of early Proterozoic orogenic activity.

Precambrian geology of Nuussuaq and the area north-east of Disko Bugt, West Greenland

1999 ◽  
pp. 6-40 ◽  
Author(s):  
Adam A. Garde ◽  
Agnete Steenfelt
Keyword(s):  
Hanging Wall ◽  
Shear Zones ◽  
Early Proterozoic ◽  
West Greenland ◽  
Metasedimentary Rocks ◽  
Precambrian Geology ◽  
North East ◽  
Westward Movement ◽  
Area North ◽  
Precambrian Terrain

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Garde, A. A., & Steenfelt, A. (1999). Precambrian geology of Nuussuaq and the area north-east of Disko Bugt, West Greenland. Geology of Greenland Survey Bulletin, 181, 6-40. https://doi.org/10.34194/ggub.v181.5108 _______________ The Precambrian terrain of eastern Nuussuaq and north-east Disko Bugt largely consists of late Archaean (c. 2800 Ma) orthogneisses, intercalated with units of strongly deformed Archaean supracrustal rocks. The latter are up to several kilometres wide and comprise both metavolcanic and metasedimentary rocks within which local occurrences of gold have been found. In central Nuussuaq a layered complex of anorthosite, leucogabbro, gabbro and ultramafic rocks is tectonically intercalated with Archaean orthogneisses, and an intrusive complex of Archaean tonalites and trondhjemites, largely unaffected by Archaean and Proterozoic deformation, occurs in the area north-east of Disko Bugt. Here an up to c. 3.5 km thick sequence of early Proterozoic shallow marine clastic sediments and minor marble unconformably overlies Archaean rocks. Several suites of basic dykes are present, and dykes and small plugs of ultramafic lamprophyre and lamproite (age c. 1750 Ma) are common in the central part of the region. Most of the region was overprinted by early Proterozoic deformation and metamorphism. Prominent Proterozoic flat-lying ductile shear zones with north- or north-westward movement of the hanging wall are overprinted by open folds.

Unreworked Archaean basement and Proterozoic supracrustal rocks from northeastern Disko Bugt, West Greenland: implications for the nature of Proterozoic mobile belts in Greenland

1988 ◽  
Vol 25 (5) ◽  
pp. 773-782 ◽  
Author(s):  
F. Kalsbeek ◽  
P. N. Taylor ◽  
R. T. Pidgeon
Keyword(s):  
Metamorphic Grade ◽  
Field Observations ◽  
Pb Isotope ◽  
West Greenland ◽  
Isotope Data ◽  
Tectonic Processes ◽  
Deforma Tion ◽  
Granitoid Rocks ◽  
Data Yield ◽  
Vast Area

Whole-rock Rb–Sr and Pb–Pb and zircon U–Pb isotope data yield an age of approximately 2800 Ma for the Atâ granite from northeastern Disko Bugt, West Greenland. Field observations and isotope data suggest that the surrounding gneisses were formed by deformation and recrystallization of granitoid rocks similar to the Atâ granite some 100 Ma after the emplacement of the granite. Rb–Sr whole-rock data on siltstones at low metamorphic grade give an age of 1760 ± 185 Ma, which is interpreted as the time of closure of the isotope systems after metamorphism. The initial 87Sr/86Sr ratio demonstrates that the sediments were probably deposited during the early Proterozoic.Field observations and isotope data show that Proterozoic (Hudsonian s.l.) deformation and metamorphism were weak in the investigated area. The Archaean basement is well preserved, and the metasediments have well-preserved sedimentary structures. The area lies between the Proterozoic Nagssugtoqidian and Rinkian mobile belts of West Greenland, which are thus separated by an area of Archaean rocks little affected by mid-Proterozoic tectono-thermal events. Thus the two belts form separate tectonic units and do not constitute a single contiguous vast area of Archaean rocks reworked by Proterozoic deforma-tion and metamorphism. It is suggested that the Proterozoic mobile belts of West Greenland are orogenic zones of restricted width (a few hundreds of kilometres) that may be interpreted in terms of modern plate tectonic processes.

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