scholarly journals Reconnaissance P,T studies of Proterozoic crustal evolution of the Ammassalik area, East Greenland

1989 ◽  
Vol 146 ◽  
pp. 48-53
Author(s):  
A.P Nutman ◽  
C.R.L Friend
Keyword(s):  
Regional Metamorphism ◽  
Crustal Thickening ◽  
Mobile Belt ◽  
Crustal Evolution ◽  
Intrusive Complex ◽  
East Greenland ◽  
Early Proterozoic ◽  
Northern Half

The Ammassalik area of East Greenland lies in the centre of a 300 km wide early Proterozoic mobile belt, dominated by Archaean gneisses and early Proterozoic metasediments. Regional Proterozoic synkinematic metamorphism was associated with crustal thickening by southerly-directed thrusting and isoclinal folding. Maximum P, T conditions recorded during the regional metamorphism are found in the northern half of the mobile belt and are 9.5 kbar (equivalent to 30 km burial) and c. 700°C. Following some erosion and uplift, the late kinematic 1885 Ma Ammassalik Intrusive Complex (AIC) was intruded at pressures of c. 7 kbar (equivalent to a depth of 20 km). Temperatures in the metamorphic aureole of the AIC reached 800°C. Following further erosion and uplift, post kinematic, c. 1575 Ma granite-diorite-gabbro complexes were intruded, under pressures of 2.5 kbar (equivalent to a depth of 8 km).

scholarly journals The Blokken gneisses: a re-appraisal

1989 ◽  
Vol 146 ◽  
pp. 83-86
Author(s):  
P.R Dawes ◽  
C.R.L Friend ◽  
A.P Nutman ◽  
N.J Soper
Keyword(s):  
Field Data ◽  
Mobile Belt ◽  
East Greenland ◽  
Early Proterozoic ◽  
Distinct Unit

A group of quartzo-feldspathic gneisses – the Blokken gneisses – is described in the literature as a syn-tectonic igneous suite intruded into the central part of the Nagssugtoqidian mobile belt of South-East Greenland in early Proterozoic time. The gneisses are reported to be transgressive to early structures (Nag. 1) and to show only later (Nag. 2) tectonic fabrics. Field data are at variance with this interpretation. No grounds exist for maintaining the gneisses in question as a distinct unit separable from the regional Archaean gneisses. Consequently the term should be abandoned.

scholarly journals Some observations on the structure of the early Proterozoic, Ammassalik mobile belt in the Ammassalik region, South-East Greenland

1989 ◽  
Vol 146 ◽  
pp. 29-40
Author(s):  
B Chadwick ◽  
V.N Vasudev
Keyword(s):  
Mobile Belt ◽  
East Greenland ◽  
Early Proterozoic ◽  
Crustal Shortening ◽  
Layer Cake

Ammassalikian deformation appears to have given rise in the first instance to a regional layer cake structure of tectonically interleaved sheets of the early Proterozoic Siportoq supracrustal association and Archaean quartzo-feldspathic orthogneisses, the latter containing locally abundant amphibolite dykes. Younger orthogneisses were emplaced magmatically in parts of the structure. The layer cake structure was progressively modified by fold nappes and later domes with steep intervening cusps. The early Ammassalikian structure is attributed to thrust stacking during ensialic crustal shortening with tectonic instability spreading from north to south. Some of the nappes and upright structures may be buoyancy phenomena which resulted from thermal instabilities generated at depth within the thrust pile.

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.

scholarly journals Outline of the Nagssugtoqidian mobile belt of East Greenland

1979 ◽  
Vol 89 ◽  
pp. 9-18
Author(s):  
D Bridgwater ◽  
J.S Myers
Keyword(s):  
Shear Zones ◽  
Granulite Facies ◽  
Tectonic Activity ◽  
Mobile Belt ◽  
East Greenland ◽  
The North ◽  
Marginal Areas ◽  
High Level ◽  
North And South ◽  
Wide Zone

The Nagssugtoqidian mobile belt is a 240 km wide zone of deformation and plutonic activity which cuts across the Archaean craton of East Greenland. The belt was established 2600 m.y. ago by the formation of vertical E-W shear zones and the syntectonic intrusion of basic dykes. Tectonic activity along the E-W shear zones was followed by the emplacement of tonalitic intrusions, the Blokken gneisses, 2350 m.y. ago in the central parts of the mobile belt. The emplacement of the Blokken gneisses was accompanied and followed by further emplacement of basic dykes. These are synplutonic in the centre of the mobile belt but are emplaced into more rigid crust in the marginal areas of the belt and in the Archaean craton to the north and south. During a second major tectonic and thermal episode circa 1900 m.y. ago, the region was deformed by thrusting from the north. In the southem part of the mobile belt the earlier steep shear zones are cut by shear zones dipping gently northwards in which rocks are downgraded to greenschist facies. The grade of metamorphism increases northwards and shear zones are replaced by open folds with axial surfaces which dip gently northwards. The increasing ductility in the centre of and northem part of the belt is associated with the intrusion of charnockitic plutons and their granulite facies aureoles. Regional uplift occurred before the intrusion of high level post-tectonic plutons of diorite and granite 1550 m.y. ago.

Granites and early Proterozoic crustal evolution in Sweden: evidence from SmNd, UPb and O isotope systematics

1985 ◽  
Vol 72 (4) ◽  
pp. 376-388 ◽  
Author(s):  
M.R. Wilson ◽  
P.J. Hamilton ◽  
A.E. Fallick ◽  
M. Aftalion ◽  
A. Michard
Keyword(s):  
Crustal Evolution ◽  
Early Proterozoic ◽  
O Isotope ◽  
Isotope Systematics

The possible roles of Precambrian biota in the origin of magmatogene and hydrothermal silver-bearing vein deposits

1987 ◽  
Vol 24 (2) ◽  
pp. 291-295 ◽  
Author(s):  
Roger D. Morton ◽  
Amarendra Changkakoti
Keyword(s):  
Regional Metamorphism ◽  
Hydrothermal Systems ◽  
Metals And Metalloids ◽  
Early Proterozoic ◽  
Sedimentary Environments ◽  
Characteristic Spectrum ◽  
Bear Lake ◽  
Lake Region ◽  
The World ◽  
Vein Deposits

The origins of silver-bearing, polyelement vein associations in the Great Bear Lake region and elsewhere in the world might be traced back to possible organic-rich, Precambrian sedimentary protoliths. These protoliths could have yielded a characteristic spectrum of elements to hydrothermal systems during regional metamorphism or during anatexis to form S-type granitoids. Wholesale capture of metals and metalloids by microbiota and their remains may have been a characteristic of some Early Proterozoic marginal marine, mesosaline environments. Two possible atmosphere–hydrosphere–lithosphere models are considered in light of recent theories. The metallogenic effects of Early Proterozoic organic-rich sedimentary environments could be of great significance: they might account for the polyelemental signatures of many younger, remobilized metal liferous systems.

scholarly journals Isotopic evidence for a Precambrian metamorphic event within the Charcot Land window, East Greenland Caledonian fold belt

1981 ◽  
Vol 29 ◽  
pp. 151-160
Author(s):  
B. T. Hansen ◽  
R. H. Steiger ◽  
A. K. Higgins
Keyword(s):  
Regional Metamorphism ◽  
Metamorphic Event ◽  
Low Grade ◽  
Fold Belt ◽  
Thrust Sheet ◽  
East Greenland ◽  
Grade Metamorphism ◽  
Isotopic Evidence ◽  
Tectonic Window

Rb-Sr, U-Pb and K-Ar analyses on rocks and minerals from a tectonic window below a Caledonian thrust sheet in the westernmost part of the Scoresby Sund region (70°-72°N) give evidence for a Precambrian age of formation. The Charco't Land supracrustal sequence rests on a basement that is probably of Archaean development and older than at least 2100 m.y. The major regional metamorphism of the supracrustal rocks is probably not much older than the intrusion of two post-kinematic bodies, i.e. about 1840 m.y. Low-grade metamorphism in a tillite and low-grade retrogressive overprinting of the supra­crustal rocks are related to Caledonian orogenesis.

scholarly journals U-Pb age determinations on zircons and monazites from a migmatite area on Bjørneøer, Scoresby Sund, East Greenland

1973 ◽  
Vol 58 ◽  
pp. 63-74
Author(s):  
F Oberli ◽  
R.H Steiger
Keyword(s):  
Regional Metamorphism ◽  
High Grade ◽  
Sampling Area ◽  
Accessory Minerals ◽  
East Greenland ◽  
Preliminary Results ◽  
Limited Sampling ◽  
South West ◽  
Insight Into ◽  
Age Determinations

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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