scholarly journals Search for Archaean basement in the Caledonian fold belt of North-East Greenland

1994 ◽  
Vol 162 ◽  
pp. 129-133
Author(s):  
A.P Nutman ◽  
F Kalsbeek
Keyword(s):  
High Grade ◽  
Metamorphic Zircon ◽  
Fold Belt ◽  
Pb Isotope ◽  
Zircon Age ◽  
East Greenland ◽  
Early Proterozoic ◽  
North East ◽  
History Of ◽  
High Grade Metamorphism

SHRIMP U-Pb isotope data on zircon crystals from a gneiss sample near Danmarkshavn, where the presence of Archaean rocks has earlier been documented, show that the rock has undergone a complex history of igneous and metamorphic zircon growth. At least three generations of zircon are present with ages of c. 3000 Ma, c. 2725 Ma and 1967 ±8 Ma (2 α). Apparently the rock was formed from an Archaean protolith which underwent high grade metamorphism during the early Proterozoic. Another sample from the easternmost exposures of the Caledonian basement, collected further north, yielded only early Proterozoic zircons with an age of 1963 ± 6 Ma. Together with a SHRIMP U-Pb zircon age of 1974 ± 17 Ma reported earlier, these results give evidence of a major igneous and metamorphic event in North-East Greenland about 1965 Ma ago.

scholarly journals Sm-Nd model age of an early Proterozoic gabbro-anorthosite from the Caledonian fold belt in North-East Greenland

1994 ◽  
Vol 162 ◽  
pp. 135-137
Author(s):  
O Stecher ◽  
N Henriksen
Keyword(s):  
Fold Belt ◽  
Crust Formation ◽  
East Greenland ◽  
Early Proterozoic ◽  
North East ◽  
A Value ◽  
Nd Model Age

Metamorphosed anorthositic and gabbro-anorthositic rocks are found as scattered occurrences in the basement gneisses of the Caledonian fold belt of North-East Greenland. A Tm-MD-nd model age determined on a gabbro- anorthositic sample yields a value of 2146 Ma. This model age is in agreement with the general age of crust formation in the region. The result shows that anorthosites, which are of Archaean derivation in many areas in Greenland, cannot on their own be used as an indicator of Archaean crust.

scholarly journals Persistence of melt-bearing Archean lower crust for >200 m.y.—An example from the Lewisian Complex, northwest Scotland

Geology ◽  
2019 ◽  
Vol 48 (3) ◽  
pp. 221-225 ◽  
Author(s):  
Richard J.M. Taylor ◽  
Tim E. Johnson ◽  
Chris Clark ◽  
Richard J. Harrison
Keyword(s):  
Trace Element ◽  
Lower Crust ◽  
Mafic Magma ◽  
High Grade ◽  
Trace Element Data ◽  
Metamorphic Zircon ◽  
Geochronological Data ◽  
Zircon Age ◽  
Gneiss Complex ◽  
High Grade Metamorphism

Abstract Geochronological data from zircon in Archean tonalite–trondhjemite–granodiorite (TTG) gneisses are commonly difficult to interpret. A notable example is the TTG gneisses from the Lewisian Gneiss Complex, northwest Scotland, which have metamorphic zircon ages that define a more-or-less continuous spread through the Neoarchean, with no clear relationship to zircon textures. These data are generally interpreted to record discrete high-grade events at ca. 2.7 Ga and ca. 2.5 Ga, with intermediate ages reflecting variable Pb loss. Although ancient diffusion of Pb is commonly invoked to explain such protracted age spreads, trace-element data in zircon may permit identification of otherwise cryptic magmatic and metamorphic episodes. Although zircons from the TTG gneiss analyzed here show a characteristic spread of Neoarchean ages, they exhibit subtle but key step changes in trace-element compositions that are difficult to ascribe to diffusive resetting, but that are consistent with emplacement of regionally extensive bodies of mafic magma. These data suggest suprasolidus metamorphic temperatures persisted for 200 m.y. or more during the Neoarchean. Such long-lived high-grade metamorphism is supported by data from zircon grains from a nearby monzogranite sheet. These preserve distinctive trace-element compositions consistent with derivation from a mafic source, and they define a well-constrained U-Pb zircon age of ca. 2.6 Ga that is intermediate between the two previously proposed discrete metamorphic episodes. The persistence of melt-bearing lower crust for hundreds of millions of years was probably the norm during the Archean.

Persistence of melt-bearing Archean lower crust for >200 m.y.— An example from the Lewisian Complex, northwest Scotland

2020 ◽  
Author(s):  
Tim Johnson ◽  
Rich Taylor ◽  
Chris Clark
Keyword(s):  
Trace Element ◽  
Lower Crust ◽  
Mafic Magma ◽  
High Grade ◽  
Trace Element Data ◽  
Metamorphic Zircon ◽  
Geochronological Data ◽  
Zircon Age ◽  
Gneiss Complex ◽  
High Grade Metamorphism

<p><strong>Geochronological data in zircon from Archaean tonalite–trondhjemite–tonalite (TTG) gneisses is commonly difficult to interpret. A notable example are TTG gneisses from the Lewisian Gneiss Complex (LGC), northwest Scotland, which have metamorphic zircon ages that define a more-or-less continuous spread through the Neoarchaean, with no clear relationship to zircon textures. These data are generally interpreted to record discrete high-grade events at c. 2.7 Ga and c. 2.5 Ga, with intermediate ages reflecting variable Pb-loss. Although ancient diffusion of Pb is commonly invoked to explain such protracted age spreads, trace element data in zircon may permit identification of otherwise cryptic magmatic and metamorphic episodes. Although zircons from the TTG gneiss analyzed here show a characteristic spread of Neoarchaean ages, they exhibit subtle but key step changes in trace element compositions that are difficult to ascribe to diffusive resetting, but which are consistent with emplacement of regionally-extensive bodies of mafic magma. These data suggest suprasolidus metamorphic temperatures persisted for 200 Myr or more during the Neoarchaean. Such long-lived high-grade metamorphism is supported by data from zircon grains from a nearby monzogranite sheet. These preserve distinctive trace element compositions suggesting derivation from a mafic source, and define a well-constrained U–Pb zircon age of c. 2.6 Ga that is intermediate between the two previously proposed discrete metamorphic episodes. The persistence for hundreds of millions of years of melt-bearing lower crust was probably the norm during the Archaean.</strong></p>

scholarly journals The crystalline rocks of Germania Land, Nordmarken and adjacent areas, North-East Greenland

1991 ◽  
Vol 152 ◽  
pp. 85-94
Author(s):  
J.D Friderichsen ◽  
J.A Gilotti ◽  
N Henriksen ◽  
A.K Higgins ◽  
J.M Hull ◽  
...  
Keyword(s):  
Alkali Feldspar ◽  
Crystalline Rocks ◽  
Fold Belt ◽  
East Side ◽  
Deformation History ◽  
Isotopic Data ◽  
East Greenland ◽  
Metasedimentary Rocks ◽  
North East ◽  
History Of

The crystalline rocks of Germania Land, Nordmarken and adjacent areas are dominated by grey, migmatitic quartzo-feldspathic orthogneisses with a complex history of emplacement and deformation. Ultramafites, eclogites and metasedimentary rocks are preserved as inclusions or trails of enclaves within the migmatitic orthogneisses. Later intrusive suites include metadolerite dykes, alkali feldspar metaporphyries and metagabbros. All these crystalline rocks have suffered thorough metamorphism and deformation, and three fabric events are recognised. Three systems of late mylonite zones are found: west of the study area in Hertugen af Orleans Land, along the east side of Stormlandet and Germania Land, and in northern Store Koldewey and Lille Koldewey. The region lies within the East Greenland Caledonian fold belt. Available isotopic data suggest the crystalline rocks include Archaean and Early Proterozoic suites. These have undergone variable degrees of later reworking on several occasions. It is unclear how much of the deformation history is Caledonian and how much pre-Caledonian. The latest fault displacements are post-Caledonian, as shown by local preservation of fault bounded outcrops of Carboniferous and Jurassic sedimentary rocks.

scholarly journals The crystalline rocks of western and southern Dove Bugt, North-East Greenland

1990 ◽  
Vol 148 ◽  
pp. 127-132
Author(s):  
B Chadwick ◽  
C.R.L Friend ◽  
A.K Higgins
Keyword(s):  
Crystalline Rocks ◽  
Fold Belt ◽  
Deformation History ◽  
Isotopic Data ◽  
East Greenland ◽  
Metasedimentary Rocks ◽  
North East ◽  
Rock Types ◽  
Different Types ◽  
History Of

The land areas around Dove Bugt are dominated by quartzo-feldspathic orthogneisses with a complex history of emplacement and deformation. The oldest rocks recognised are supracrustal units, mainly marbles and rusty-weathering metasedimentary rocks. Locally gabbro-anorthosite units are associated with the supracrustal rocks. These rock units are cut by different phases of the gneisses, of which the most abundant are grey banded orthogneisses. Two different varieties of pink orthogneiss are also recognised. Different types of tabular amphibolitic bodies, relicts of dykes or sills, cut most rock types. The area lies within the East Greenland Caledonian fold belt, but available isotopic data suggest that the crystalline rocks include Archaean and early Proterozoic suites which have undergone uncertain degrees of Caledonian reworking. It is not clear at present how much of the deformation history of at least four periods of deformation and associated mylonitisation is Caledonian, and how much pre-Caledonian.

The Pikwitonei Granulite Domain, Manitoba: a giant Neoarchean high-grade terrane in the northwest Superior ProvinceThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh.N. Machado, T.E. Krogh, and W. Weber are deceased.

2011 ◽  
Vol 48 (2) ◽  
pp. 205-245 ◽  
Author(s):  
L. M. Heaman ◽  
Ch. O. Böhm ◽  
N. Machado ◽  
T. E. Krogh ◽  
W. Weber ◽  
...  
Keyword(s):  
Granulite Facies ◽  
Superior Province ◽  
High Grade ◽  
Metamorphic Zircon ◽  
Special Issue ◽  
Metamorphic History ◽  
Zircon Growth ◽  
The World ◽  
Northwestern Margin ◽  
History Of

The Pikwitonei Granulite Domain located at the northwestern margin of the Superior Province is one of the largest Neoarchean high-grade terranes in the world, with well-preserved granulite metamorphic assemblages preserved in a variety of lithologies, including enderbite, opdalite, charnockite, and mafic granulite. U–Pb geochronology has been attempted to unravel the protolith ages and metamorphic history of numerous lithologies at three main localities; Natawahunan Lake, Sipiwesk Lake, and Cauchon Lake. The U–Pb age results indicate that some of the layered enderbite gneisses are Mesoarchean (3.4–3.0 Ga) and the more massive enderbites are Neoarchean. The high-grade metamorphic history of the Pikwitonei Granulite Domain is complex and multistage with at least four episodes of metamorphic zircon growth identified: (1) 2716.1 ± 3.8 Ma, (2) 2694.6 ± 0.6 Ma, (3) 2679.6 ± 0.9 Ma, and (4) 2642.5 ± 0.9 Ma. Metamorphic zircon growth during episodes 2 and 3 are interpreted to be regional in extent, corresponding to M1 amphibolite- and M2 granulite-facies events, respectively, consistent with previous field observations. The youngest metamorphic episode at 2642.5 Ma is only recognized at southern Cauchon Lake, where it coincides with granite melt production and possible development of a major northeast-trending deformation zone. The timing and multistage metamorphic history recorded in the Pikwitonei Granulite Domain is similar to most Superior Province high-grade terranes and marks a fundamental break in Archean crustal evolution worldwide at the termination of prolific global Neoarchean greenstone belt formation.

scholarly journals Regional geology and 1:500 000 mapping in North-East Greenland

1990 ◽  
Vol 148 ◽  
pp. 16-20
Author(s):  
N Henriksen
Keyword(s):  
Geological Mapping ◽  
Fold Belt ◽  
East Greenland ◽  
Regional Geology ◽  
Field Mapping ◽  
North East ◽  
General Geology ◽  
Geological Map

A three-year field mapping programme was initiated in 1988 aiming at regional geological studies and geological mapping in North-East Greenland between latitudes 75° and 78°N. This region encompasses relatively little known parts of the Caledonian fold belt and the overlying post-Caledonian sequences, which lie north of the better known regions of central East Greenland (Henriksen, 1989). Major aims of the programme include compilation a 1:500 000 geological map, and an understanding of the general geology of the region.

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