Archean Gray Gneisses and the Origin of the Continental Crust: Evidence the Godthåb Region, West Greenland

1979 ◽  
pp. 169-204 ◽  
Author(s):  
V.R. McGregor
Keyword(s):  
Continental Crust ◽  
West Greenland

scholarly journals Reaction between picrite magma and continental crust: early Tertiary silicic basalts and magnesian andesites from Disko, West Greenland

1985 ◽  
Vol 152 ◽  
pp. 1-126
Author(s):  
A.K Pedersen
Keyword(s):  
Continental Crust ◽  
Transition Element ◽  
Crystal Fractionation ◽  
West Greenland ◽  
Crustal Rocks ◽  
Early Tertiary

The Kûgánguaq Member is a lava and tuff sequence comprising about 7.S km3 of magnesian silicic basalts (92%), magnesian andesites (7%) and feldspar-phyric silicic basalts ( 18%) through reaction with crustal rocks, presumably Cretaceous sand or siltstones. The reaction led to sulphide fractionation and to magma modification which cannot be explained in terms of crystal fractionation or by simple mixing between magma and contaminants. The transition element (Fe, Ti, Vand Cr) concentrations in rocks, glasses and minerals indicate that the Kûgánguaq Member rocks equilibrated at oxygen fugacities several orders of magnitude below the FMQ buffer, but above the IW-buffer. The partitioning of vanadium between olivine and glass and between chromite and glass show particularly large variations and appears to be the most sensitive recorder of fo2 variations in the range between the FMQ and IW buffers at high igneous temperatures.

Accretion and evolution of an Archaean high-grade grey gneiss – amphibolite complex: the Fiskefjord area, southern West Greenland

1997 ◽  
pp. 1-115 ◽  
Author(s):  
Adam A. Garde
Keyword(s):  
Continental Crust ◽  
Granulite Facies ◽  
Ductile Deformation ◽  
Repeated Injection ◽  
High Grade ◽  
Volcanic Origin ◽  
Granulite Facies Metamorphism ◽  
West Greenland ◽  
Facies Metamorphism ◽  
Grey Gneiss

NOTE: This monograph was published in a former series of GEUS Bulletin. Please use the original series name when citing this series, for example: Garde, A. A. 1997: Accretion and evolution of an Archaean high-grade grey gneiss – amphibolite complex: the Fiskefjord area, southern West Greenland. Geology of Greenland Survey Bulletin 177, 115 pp. _______________ The Fiskefjord area in southern West Greenland, part of the Akia tectono-stratigraphic terrane, comprises a supracrustal association and two groups of grey quartzo-feldspathic orthogneises c. 3200 and 3000 Ma old. The supracrustal association forms layers and enclaves in grey gneiss and may comprise two or more age groups. Homogeneous amphibolite with MORB-like but LIL element enriched tholeiitic composition predominates; part, associated with cumulate noritic and dunitic rocks, represents fragments of layered complexes. Heterogeneous amphibolite of likely submarine volcanic origin, (basaltic) andesitic amphibolite, leucogabbro-anorthosite, and minor pelitic metasediment occur. Disruption by magmatic and tectonic events and geochemical alteration have obscured primary origin: the supracrustal association may represent oceanic crust. Grey orthogneiss of the tonalite-trondhjemite-granodiorite (TTG) association was generated during continental accretion at c. 3000 Ma, most likely by partial melting of wet and hot tholeiitic basaltic rocks subducted in a convergent plate setting. Most dioritic gneiss is c. 220 Ma older. A 3040 Ma dioritic to tonalitic phase, enriched in P2O5 , Ba, Sr, K, Pb, Rb and LREE, probably was derived from metasomatised mantle. Intense deformation and metamorphism accompanied the 3000 Ma magmatic accretion.Thrusts along amphibolite-orthogneiss contacts were succeeded by large recumbent isoclines, upright to overturned folds, and local domes with granitic cores. Syntectonic granulite facies metamorphism is thought to be due to heat accumulation by repeated injection of tonalitic magma. Strong ductile deformation produced steep linear belts before the thermal maximum ceased, whereby folds were reorientated into upright south-plunging isoclines. Two large TTG complexes were then emplaced, followed by granodiorite and granite. Post-kinematic diorite plugs with unusually high MgO, Cr and Ni, and low LIL and immobile incompatible element contents, terminated the 3000 Ma accretion. Hybrid border zones and orbicular textures suggest rapid crystallisation from superheated magma. The diorites most likely formed from ultramafic magma contaminated with continental crust. Widespread high-grade retrogression preserved a granulite facies core in the south-west; to the east the retrogressed gneiss grades into amphibolite facies gneiss not affected by granulite facies metamorphism and retrogression. LIL elements were depleted during granulite facies metamorphism and reintroduced during retrogression, probably transported in anatectic silicate melts and in fluids. Rb-Sr isotope data, and relationships between retrogression, high-strain zones and granite emplacement, show that retrogression took place shortly after the granulite facies metamorphism, before terrane assembly at c. 2720 Ma, probably by movement of melts and fluids into the upper, marginal zone of granulite facies rocks from deeper crust still being dehydrated. Retrogression during Late Archaean terrane assembly was in narrow reactivated zones of ductile deformation; in the Proterozoic it occurred with faulting and dyke emplacement.Geochemical data are presented for Early Proterozoic high-Mg and mafic dykes. A rare 2085 Ma microgranite dyke strongly enriched in incompatible trace elements was formed by partial anatexis of Archaean continental crust.  

Deformation of the Isua block, West Greenland: a remnant of the earliest stable continental crust

1976 ◽  
Vol 13 (6) ◽  
pp. 816-823 ◽  
Author(s):  
Patrick R. James
Keyword(s):  
Continental Crust ◽  
Simple Shear ◽  
Vertical Displacement ◽  
Yield Strain ◽  
West Greenland ◽  
Structural Style ◽  
A Value ◽  
Supracrustal Belt ◽  
Strain Paths ◽  
Unit Yield

The Isua block of West Greenland is composed of a belt of supracrustal rocks and surrounding granitic gneisses, both of which yield dates of approximately 3750 m.y. This age is equivalent to that of the Amitsoq gneisses of the nearby Godthaabsfjord area. From the lilhological variation and structural style, two major deformalional events are recognised in both the supracrustals and the gneisses: D1, a phase of fabric formation caused by a vertical simple shear mainly affecting rocks of the supracrustal belt; and D2. a phase of major and minor folding of the earlier structures probably caused by an ENE–WSW ductile dextral simple shear movement. Measurements of the amount of strain from a distinctive conglomeratic unit yield strain paths for the two deformations and a value of vertical displacement of approximately 7 km for D1. Two dyke sets invade the supracrustals and gneisses, a tangential set during D2 and a radial set after D2.

scholarly journals New zircon ages from the Tasiusarsuaq terrane, southern West Greenland

2008 ◽  
Vol 15 ◽  
pp. 73-76 ◽  
Author(s):  
Tomas Næraa ◽  
Anders Scherstén
Keyword(s):  
Continental Crust ◽  
Spatial Relationship ◽  
Outer Part ◽  
The South ◽  
West Greenland ◽  
North East ◽  
Geological Processes ◽  
South West ◽  
Terrane Accretion ◽  
Inland Ice

In the last three field seasons the Geological Survey of Denmark and Greenland (GEUS) has undertaken mapping in the south-eastern part of the Nuuk region in southern West Greenland, and here we present new zircon ages that help constrain the northern boundary of the Tasiusarsuaq terrane. The Archaean geology of the Nuuk region is commonly interpreted as a tectonic collage assembled through lateral accretion and collision of oceanic and continental slivers and blocks (e.g. Friend & Nutman 2005). Popular jargon de scribes these as terranes, bounded by faults or mylonite zones and characterised by rocks of contrasting origin on either side of their tectonic boundaries (Coney et al. 1980). The Isukasia and Færingehavn terranes (Figs 1, 2) are the oldest terranes at ≥3.75 Ga, and extend from the outer part of Godthåbsfjord in the south-west to the margin of the Inland Ice in the north-east, but they might not have a common geological history (Friend & Nutman 2005). The Tre Brødre terrane is mainly represented by the Ikkatoq gneiss and occurs in close spatial relationship with the Færingehavn terrane, and also as a pronounced thrust unit along the Qarliit Nunaat thrust between the Færingehavn and Tasiusarsuaq terranes (Fig. 1; Nutman et al. 1989). The terrane boundaries in the inner fjord region near the Inland Ice margin are less well constrained; the Tre Brødre terrane extends into the region from the south-west, the Kapisilik terrane is defined from the northern and eastern part and borders the Tasiusarsuaq terrane to the south and possibly to the east. The terrane accretion is believed to have taken place in two events. The first terrane accretion is defined from the northern part of the region, and possibly involves the Isukasia, Kapisilik and Akia terranes. The thermal event stitching these terranes is dated to c. 2.99–2.95 Ga (Fig. 2; Hanmer et al. 2002; Friend & Nutman 2005). The second accretion phase of the major continental blocks is believed to have occurred at around 2.725–2.71 Ga. This second event is well described, and in- cludes anatexis and emplacement of continental crust-derived granites, which are associated with contemporaneous metamorphism (Friend et al. 1996). Figure 2 outlines regional plutonic, metamorphic and su- pracrustal events. Individual terranes were formed during relatively short time periods with active geological processes of creation and recycling of continental crust, and most of the terranes follow a similar pattern of development. The first plutonic events consisted of primitive magmas and produced ton a- lite–trondhjemite–granodiorite (TTG) and dioritic gne isses. Younger, more evolved granitic magmas were often intruded simultaneously with high-grade metamorphism. This development may reflect a stabilisation of the individual terranes.

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.

Evidence for continental crust in the offshore Palaeogene volcanic province, central West Greenland

2002 ◽  
pp. 97-102 ◽  
Author(s):  
Nina Skaarup
Keyword(s):  
Continental Crust ◽  
Seismic Data ◽  
Geological Survey ◽  
Primary Data ◽  
Volcanic Province ◽  
Original Series ◽  
West Greenland ◽  
Primary Data Source ◽  
Data Source

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Skaarup, N. (2002). Evidence for continental crust in the offshore Palaeogene volcanic province, central West Greenland. Geology of Greenland Survey Bulletin, 191, 97-102. https://doi.org/10.34194/ggub.v191.5135 _______________ The Palaeogene volcanic province of central West Greenland extends for 550 km from north to south and 200 km from east to west (Henderson 1973; Henderson et al. 1981; Whittaker 1996). In a preliminary interpretation of the area offshore Disko and Nuussuaq, based on older seismic data, Whittaker (1996) described a number of large rotated fault blocks containing structural closures at top volcanic level that could indicate leads capable of trapping hydrocarbons. This work, combined with the discovery of oil in the basalts onshore, led the Geological Survey of Denmark and Greenland (GEUS) to acquire 1960 km of multi-channel 2D seismic data in the area between 68°N and 71°N in 1995 (Fig. 1). These seismic data are the primary data source for the interpretation presented in this paper.

scholarly journals Rapid maturation and stabilisation of middle Archaean continental crust: the Akia terrane, southern West Greenland

2000 ◽  
Vol 47 ◽  
pp. 1-27
Author(s):  
A.A. Garde ◽  
C.R.L. Friend ◽  
A.P. Nutman ◽  
M. Marker
Keyword(s):  
Continental Crust ◽  
Isotope Geochemistry ◽  
Granulite Facies ◽  
West Greenland ◽  
Relative Chronology ◽  
Deformation Phase ◽  
Thermal Maximum ◽  
Final Maturation ◽  
Arc Setting ◽  
Grey Gneiss

from the Akia terrane, southern West Greenland, supported by Sm-Nd isotope geochemistry, document its middle Archaean accretional history and provide new evidence about the location of its northern boundary. Zircon populations in grey gneiss and inherited zircons in granite show that magmatic accretion of new continental crust, dominated by intrusion of tonalite sheets in a convergent island arc setting, occurred between c. 3050 and 3000 Ma, around and within a c. 3220 Ma continental core. In the central part of the terrane, tonalite sheets were intercalated with older supracrustal rocks of oceanic affinity by intrusion, thrusting and folding during the Midterhøj and Smalledal deformation phases of Berthelsen (1960). Continued tonalite injection led to a thermal maximum with granulite facies conditions at c. 2980 Ma, dated by metamorphic zircons in grey gneiss. The metamorphic maximum was contemporaneous with upright, angular folds of the Pâkitsoq deformation phase. Within a few million years followed high-grade retrogression and intrusion of two large dome-shaped tonalite-granodiorite complexes, granites s.l. derived from remobilisation of grey gneiss, and post-kinematic diorite plugs. Whereas the relative chronology of these events is firmly established from field observations, zircons from the post-granulite facies intrusions all yielded statistically indistinguishable emplacement ages of c. 2975 Ma. These results show that crustal growth occurred in several short-lived events starting at c. 3220 Ma, and that final maturation and stabilisation of new, thick continental crust took place rapidly (within c. 20 Ma) at c. 2975 Ma.

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