scholarly journals The late Archaean mobile belt through Godthabsfjord, southern West Greenland: a continent-continent collision zone?

1991 ◽  
Vol 39 ◽  
pp. 179-197
Author(s):  
V. R. McGregor ◽  
C. R. L. Friend ◽  
A. P. Nutman
Keyword(s):  
Continental Crust ◽  
Oceanic Crust ◽  
Mobile Belt ◽  
High Grade ◽  
Late Archaean ◽  
West Greenland ◽  
North West ◽  
The North ◽  
Collision Zone ◽  
Different Parts

In the Godthabsfjord region of southern West Greenland a NE-SW-trending belt of rocks of very varied age and origin, here named the Akulleq terrane, is separated by major faults from more extensive blocks of typical high-grade Archaean rocks that, although they are superficially similar, have different ages and metamorphic histories. The continental crust that forms the block to the north-west, the Akia terrane, was accreted between ea. 3200 and 2980 Ma, and that forming the block to the south-east, the Tasiusarsuaq terrane, between 2920 and 2800 Ma. It is suggested that the Godthabsfjord belt is the result of collision of the two continental blocks between 2800 and 2650 Ma. The rocks of the Akulleq terrane are interpreted as fragments of different parts of the crust that originally separated the two continents. They include early Archaean continental crust, possible oceanic crust, and acid to intermediate rocks of intrusive and possibly also extrusive origin that may have been generated in a subduction-related environment.

Deformation at the southern boundary of the late Archaean Atâ tonalite and the extent of Proterozoic reworking of the Disko terrane, West Greenland

1999 ◽  
pp. 155-169 ◽  
Author(s):  
John Grocott ◽  
Steven C. Davies
Keyword(s):  
Large Scale ◽  
Hanging Wall ◽  
Shear Zones ◽  
High Grade ◽  
Southern Boundary ◽  
Late Archaean ◽  
West Greenland ◽  
North West ◽  
North East ◽  
The North

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Grocott, J., & Davies, S. C. (1999). Deformation at the southern boundary of the late Archaean Atâ tonalite and the extent of Proterozoic reworking of the Disko terrane, West Greenland. Geology of Greenland Survey Bulletin, 181, 155-169. https://doi.org/10.34194/ggub.v181.5123 _______________ The c. 2800 Ma old Atâ tonalite in the area north-east of Disko Bugt, West Greenland has largely escaped both Archaean and Proterozoic regional deformation and metamorphism. At its southern margin the tonalite is in contact with migmatitic quartz-feldspar-biotite gneiss and to the south both are progressively deformed in a high-grade gneiss terrain. The main deformation in the high grade gneisses involved hanging wall north-west displacements on a system of low-angle ductile shear zones that structurally underlie the Atâ tonalite. This shear zone system is folded by a large-scale, steeply inclined and north-west-trending antiform defined by the change in dip of planar fabrics. Minor folds related to the antiform are present and there is some evidence that folding was synkinematic with emplacement of a suite of c. 1750 Ma old ultramafic lamprophyre dykes. In much of the north-east Disko Bugt area it remains difficult to separate Archaean from Proterozoic structures and hence the extent of the Archaean terrane that has escaped intense Proterozoic reworking remains uncertain.

scholarly journals Etah meta-igneous complex and the Wulff structure: Proterozoic magmatism and deformation in Inglefield Land, North-West Greenland

1988 ◽  
Vol 139 ◽  
pp. 1-24
Author(s):  
P.R Dawes
Keyword(s):  
Large Scale ◽  
Mobile Belt ◽  
Magmatic Complex ◽  
Igneous Complex ◽  
West Greenland ◽  
North West ◽  
High Deformation ◽  
Precambrian Geology ◽  
North East ◽  
The North

A hitherto uninvestigated collection of crystalline rocks from north-eastem Inglefield Land (c. 79°N) allowanew interpretation of the Precambrian geology of the region. The majority of the samples - high-grade basic, intermediate and granitoid rocks - are referred to the Etah meta-igneous complex, which has been shown to be mid-Proterozoic in age in the type area in south-western Inglefield Land. In areas of high deformation there is a gradation from massive rocks of igneous aspect into folded and variably migmatised gneisses. Thus the magmatic complex provides a gauge of the nature and intensity of Proterozoic (Hudsonian) deformation and metamorphism. In Inglefield Land Proterozoic deformation produced different structural styles; thus in the north-east the Wulff structure - a large-scale refolded isoclinal structure - characterises a region that lacks an obvious preferred regional foliation direction, while in the south-west, linear E-W trending belts with steep dips dominate the structural pattem. The Proterozoic evolution is outlined from the formation of the Etah Group, a supracrustal sequence that pre-dates the Etah meta-igneous complex, to uplift, peneplanation, deposition and magmatism in the late Proterozoic. Inglefield Land is not part of the Rinkian mobile belt of West Greenland, and it is stressed that the obvious continuation of the Proterozoic geology is into Ellesmere Island.

scholarly journals Field work in the north of the Ivisârtoq region, inner Godthåbsfjord, southern West Greenland

1983 ◽  
Vol 115 ◽  
pp. 49-56
Author(s):  
B Chadwick ◽  
M.A Crewe ◽  
J.F.W Park
Keyword(s):  
Field Work ◽  
Geological Survey ◽  
West Greenland ◽  
North West ◽  
The North ◽  
Field Investigations ◽  
New Findings ◽  
Host Rocks

The programme of field investigations in the north of the Ivisartoq region begun in 1981 by Chadwick & Crewe (1982) was continued in 1982. Julia Park began mapping the Taserssuaq granodiorite, its host rocks and the Ataneq fault in the north-west. Dur team was joined by D. Bellur, Geological Survey of India, nominally as an assistant. In this report we present only summary notes of new findings relevant to the interpretation of the geometry and chronology of this segment of the Archaean crust in southern West Greenland. We use the established terminology for the Archaean rocks of the Godthåbsfjord region.

Iridescent anthophyllite-gedrite from Simiuttat, Nuuk district, southern West Greenland composition, exsolution, age

1996 ◽  
Vol 60 (403) ◽  
pp. 937-947 ◽  
Author(s):  
K. A. Rodgers ◽  
P. D. Kinny ◽  
V. R. McGregor ◽  
G. R. Clark ◽  
G. S. Henderson
Keyword(s):  
Single Crystal ◽  
Powder Diffraction ◽  
Diffraction Grating ◽  
Plan View ◽  
Late Archaean ◽  
Space Group ◽  
X Ray ◽  
West Greenland ◽  
The North ◽  
Afm Imaging

AbstractGolden iridescent, <1–100 mm crystals of alternating lamellae of anthophyllite and gedrite constitute the bulk of orthoamphibolite pods within quartz-cordierite gneisses of the Akulleq terrane at Simiuttat, SW Greenland. X-ray powder diffraction powder gave a = 18.526(7),b = 17.979(15), c = 5.285(23) Å; a single crystal has a = 18.546(7), b = 17.950(16), c = 5.280(1) Å, space group Pnma with some reflections being notably broader than others. Spot EMPA yielded composite analyses: AlIV = 0.89–1.3, Mg/(Mg+Fe2+) = 0.57–0.61, Na/AlIV = 0.22–0.26. AFM imaging of {210} cleavage surfaces, showed a uniform corrugated morphology parallel to [001]; wavelength was 190–350 nm, mean 250 nm, amplitude 3 nm. A plan view resembles TEM images of (010)-parallel exsolution textures of orthoamphiboles. A second set of corrugations may crosscut the [001]-parallel ridges at 20–25°, akin to reported lamellar intergrowths developed parallel to both (010) and (120). Unequivocal evidence linking topography with lamellae is absent. In contrast to the conventional multi-layer reflector model, the ridged surface provides an additional origin for iridescence, acting as a diffraction grating. Included zircons, 50–10 μm, have Hf/Zr = 0.008–0.012, Hf+FeIIc. 0.16. 207Pb/206Pb ages are from 2690 to 2770 Ma, averaging 2732±10 Ma. Coexisting, included Th-, La-, Ce-, Pr-, Nd-, Gd-, Y-monazites have 207Pb/206Pb ages from 2680 to 2720 Ma, averaging 2707±12 Ma. The included crystals grew during a late Archaean metamorphism that produced overgrowths on zircons within gneisses to the north, but with Simiuttat grains showing a more complex history. The lamellae may have developed at the same time, or during a reheating c. 2550 Ma, or in a subsequent Proterozoic metamorphism.

scholarly journals The Archaean gneiss complex of northern Labrador A review of current results, ideas and problems

1991 ◽  
Vol 39 ◽  
pp. 153-166
Author(s):  
D. Bridgwater ◽  
L. Schiøtte
Keyword(s):  
Major Part ◽  
Granulite Facies ◽  
High Grade ◽  
Late Archaean ◽  
West Greenland ◽  
Metamorphic History ◽  
Gneiss Complex ◽  
History Of ◽  
Augen Gneiss ◽  
Dominant Phase

1. The early Archaean rocks in northern Labrador can be subdivided into the ea. 3.78 Ga Nulliak supracrus­tal association, the migmatitic Uivak I gneisses, the dominant phase of which was emplaced at ea. 3.73 Ga, and the Uivak II augen gneiss. Inherited low-U rounded inclusions within igneous zircons in the Uivak I gneisses have ages between 3.73 and 3.86 Ga and are more likely to have been derived from a pre-existing high-grade metamorphic gneiss complex than from the Nulliak association. In the early Archaean there were probably several rapid cycles of sedimentary deposition and volcanism followed by emplacement of major plutons. Mid Archaean gneisses are more abundant in northern Labrador than previously realised. The late Archaean metamorphic history of these gneisses is different from the history of the early Archaean gneisses. Whereas an important part of the mid Archaean suite was emplaced in granulite facies and retrogressed at the time of granitoid veining at ea. 2.99 Ga, the major part of the early Archaean rocks were reworked under granulite facies conditions in a sequence of closely spaced events between 2. 7 and 2.8 Ga. The two groups of gneisses had different metamorphic histories until ea. 2.7 Ga, but late and post-tectonic granites of 2.5- 2. 7 Ga age cut across both. It is suggested that the terrane model in southern West Greenland can be extended to Labrador and that tectonic intercalation of early and mid Archaean gneisses took place around 2.7 Ga. Correlation between the Maggo gneisses around Hopedale, mid Archaean gneisses in northernmost Labrador and gneisses from the Akia terrane in West Greenland is suggested. Like the Malene supracrustals in West Greenland the Upernavik supracrustals in Labrador are composite associations, the youngest of which are thought to have been deposited around 2. 7 Ga.

scholarly journals The structure of south Renland, Scoresby Sund. With special reference to the tectono-metamorphic evolution of a southern internal part of the Caledonides of East Greenland

1975 ◽  
Vol 112 ◽  
pp. 1-67
Author(s):  
B Chadwick
Keyword(s):  
Granulite Facies ◽  
Normal Faults ◽  
Mobile Belt ◽  
Minimum Thickness ◽  
East Greenland ◽  
North West ◽  
The North ◽  
South West ◽  
Igneous Activity ◽  
Group Form

Renland occupies an internal position within the southern extreme of the outcrop of the Caledonian mobile belt of East Greenland exposed between latitudes 70° and 82° N. In south-west Renland migmatised paragneisses derived from sediments comparable to the late Precambrian Lower Eleonore Bay Group form a multilayered sequence with a minimum thickness of 1500 m. The migmatites are interleaved with thick concordant sheets of garnetiferous augen granite, the formation of which may be linked with the low-pressure granulite or transitional amphibolite-granulite facies conditions attained during migmatisation of the paragneisses. These conditions persisted during the folding together of paragneisses and granites into regional structures of nappe dimensions which had a north or north-west direction of transport. Refolding of the nappes under continued high-grade conditions gave rise to structures locally coaxial with nappe axes. Reversals of facing of nappes occur in backfolds. Linear fabrics of sillimanite and biotite and prolate ellipsoidal augen of feldspar are parallel to fold axes and show that constrictional deformation dominated the later stages of the nappe phase and the refolding event. The constriction is attributed to compressing of rocks in south-west Renland between nappes advancing from the south and a rising mass of granite and basement gneisses in the north. Intrusion of concordant sheets of biotite-rich hypersthene monzonite (mangerite) followed the nappe deformation in south-east Renland. The principal sheet, which is 500 m thick, forms the rim to part of a lopolithic basin. Thinner sheets of monzonite injected into migmatites within the basin have been disrupted by further migmatisation and granitisation. Stable assemblages in pyribolite restite suggest this later event, which was restricted largely to the basin, attained conditions of hornblende-granulite facies. Open warps attributed to monzonite injection and the basin formation are superimposed on nappes west of the principal sheet. Normal faults with downthrow to east and west relate to the formation of troughs filled with Upper Palaeozoic and Mesozoic sediments in the Scoresby Sund region. The distribution of the faults suggests Renland was a horst area in Upper Palaeozoic times. Tertiary igneous activity in south Renland is represented by rare dykes of olivine dolerite and scattered plugs of pyroxenite which locally contain large blocks of host gneisses.

scholarly journals The Proterozoic mobile belt in the Ammassalik region, South-East Greenland (Ammassalik mobile belt): an introduction and re-appraisal

1989 ◽  
Vol 146 ◽  
pp. 5-12
Author(s):  
B Chadwick ◽  
P.R Dawes ◽  
J.C Escher ◽  
C.R.L Friend ◽  
R.P Hall ◽  
...  
Keyword(s):  
Shear Zones ◽  
Granulite Facies ◽  
Mobile Belt ◽  
The South ◽  
Southern Limit ◽  
Late Archaean ◽  
Early Proterozoic ◽  
The North ◽  
Layer Cake ◽  
Dyke Swarms

The Ammassalik mobile belt is characterised by a regional layer cake structure of tectonically interleaved sheets of quartzo-feldspathic orthogneisses and supracrustal rocks. The sheets of supracrustal rocks are most abundant in the north of the belt and they include semi-pelitic kyanite-sillimanite gneisses, graphitic schists, marble, amphibolites and local peridotite. The sheets are regarded as parts of a disrupted supracrustal sequence, here termed the Siportoq supracrustal association. Preliminary isotopic age data suggest that most of the orthogneisses are late Archaean, although some have early Proterozoic ages. The Siportoq supracrustal association has yielded an early Proterozoic age. Amphibolite dyke swarms were emplaced at various stages in the evolution of the mobile belt. The Ammassalik belt has an ill-defined northern limit marked by heterogeneous retrogression of a granulite facies terrain up to 100 km wide. Most of the belt is at amphibolite facies, with its southern limit lying to the south of the area considered here. The structure in the south is dominated by nappes and shear zones dipping NE within a wide tract of late Archaean orthogneisses intruded by amphibolite dyke swarms with relatively well preserved primary characteristics. The structure in the north is characterised by more pervasive deformation which gave rise to complex sequences of thrusting and nappe development propagating from the north. Large domes were superimposed on the nappe pile, perhaps as buoyancy phenomena. The dioritic Ammassalik Intrusive Complex (c. 1885 Ma) with its granulite facies assemblages is regarded as a late kinematic phenomenon. Major post-tectonic complexes of granite, diorite and gabbro (c. 1580 Ma) were intruded at a high level well after the close of the tectonism in the Ammassalik mobile belt.

Some remarks on the continental margins in the Aquitaine and French Pyrenees

1984 ◽  
Vol 121 (5) ◽  
pp. 407-412 ◽  
Author(s):  
G. Boillot
Keyword(s):  
Iberian Peninsula ◽  
Continental Crust ◽  
Oceanic Crust ◽  
Late Eocene ◽  
Continental Margins ◽  
Bay Of Biscay ◽  
Transform Faults ◽  
The North ◽  
Transform Zone ◽  
Aquitaine Basin

AbstractFrom the Triassic to the Late Eocene, the Iberian Peninsula underwent three successive rotations with respect to the stable European plate, (a) Prior to the Late Aptian, a nearly 150 km southwestward motion resulted in stretching and thinning of the continental crust beneath the North Pyrenean zone, the Aquitaine Basin and the Bay of Biscay continental margins (rifting). Distensive structures trended 90° N to 130° N, and were shifted by 30° N to 50° N transform faults. (b) During the Late Aptian to Santonian interval, an approximately 400 km southeastward motion resulted in the opening of the Bay of Biscay and sinistral slipping of Iberia along the North Pyrenean transform zone (drifting), (c) During palaeocene–Eocene time, a 150 km northwestward convergent motion resulted in limited subduction of the oceanic crust of the Bay of Biscay beneath the Iberian plate, and folding of the Pyrenean chain. The folded belt resulted from squeezing of the former European and Iberian margins (rifted or transform margins, depending on the segment considered).

scholarly journals Dykes and deformation in the Ikertoq zone of the Nagssugtoqidian at S0ndre Str0mfjord Airport, West Greenland - a discussion

1985 ◽  
Vol 34 ◽  
pp. 213-217
Author(s):  
Feiko Kalsbeek ◽  
Hubert P. Zeck
Keyword(s):  
Combined Effect ◽  
Border Zone ◽  
Mobile Belt ◽  
Sr Isotope ◽  
Late Archaean ◽  
West Greenland ◽  
Isotope Evidence

Rb-Sr isotope evidence indicates that deformation in the border zone between the Archaean craton and the Nagssugtoqidian mobile belt in West Greenland took place both during the late Archaean (at ea. 2600 Ma) and during the Proterozoic Nagssugtoqidian orogeny (1850-1600 Ma). The structure (fabric) of the rocks is the combined effect of these two episodes of deformation.

scholarly journals An investigation of the igneous rocks on Hareøen and western Nûgssuaq, West Greenland

1971 ◽  
Vol 35 ◽  
pp. 11-13
Author(s):  
N Hald
Keyword(s):  
East Coast ◽  
Geological Mapping ◽  
Igneous Rocks ◽  
South Coast ◽  
The South ◽  
West Greenland ◽  
North West ◽  
North East ◽  
The North ◽  
Basaltic Lavas

Hareøen is an island north-west of Disko in western Greenland. It has the form of a plateau, whose highest point - 512 metres - is found near the south coast. Like the neighbouring parts of Nugssuaq and Disko, Hareøen consists chiefly of Tertiary basaltic lavas. The island first attracted attention on account of the presence of interbasaltic, coal-bearing sediments on the north-east coast. These were already examined by Giesecke in 1811 (Giesecke, 1910) and later among others by Steenstrup (1874) and B.E. Koch (1959). A petrographie investigation of the basalts was first undertaken by Holmes (1919), who described loose fragments rich in K2O. Lavas from the south coast, colleeted and analysed by Pedersen (1970), also have a high content of potash. V. Miinther in the years 1948-49 untertook geological mapping of the island, on which the present investigation is supported (Miinther, in press).

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