scholarly journals Middle Proterozoic ultramafic lamprophyre dykes in the Archaean of the Atâ area, central West Greenland

1989 ◽  
Vol 145 ◽  
pp. 23-28
Author(s):  
M Marker ◽  
C Knudsen
Keyword(s):  
Spatial Relation ◽  
Wall Rock ◽  
Thin Sections ◽  
West Greenland ◽  
Dolerite Dyke ◽  
Ultramafic Lamprophyre ◽  
Preliminary Account ◽  
Mode Of Occurrence ◽  
Middle Proterozoic

During the mapping of gneisses and supracrustal rocks around Eqe in the eastern part of the Atâ area in 1988 a series of ultramafic dykes of lamprophyric affinity were discovered by the authors. The dykes are conspicuous in the field because of their lithology, with often high contents of carbonate, and the occurrence of brownish phlogopite phenocrysts. Their ductile type of deformation and aggressive aiteration of the wall-rock are distinctive. The purpose of this paper is to give a preliminary account of the mode of occurrence and lithology of the dykes based on the mapping results and a provisional inspection of a dozen thin sections. Their possibie age is discussed on the basis of their spatial relation to a large NNW-SSE trending dolerite dyke dated at 1645 ± 35 Ma by Kalsbeek & Taylor (1986).

Timing of kimberlite, carbonatite, and ultramafic lamprophyre emplacement in the alkaline province located 64°–67° N in southern West Greenland

Lithos ◽  
2009 ◽  
Vol 112 ◽  
pp. 400-406 ◽  
Author(s):  
K. Secher ◽  
L.M. Heaman ◽  
T.F.D. Nielsen ◽  
S.M. Jensen ◽  
F. Schjøth ◽  
...  
Keyword(s):  
West Greenland ◽  
Ultramafic Lamprophyre

scholarly journals Preliminary palaeomagnetic results of an Archaean dolerite dyke of west Greenland: geomagnetic field intensity at 2.8 Ga

1997 ◽  
Vol 128 (3) ◽  
pp. 585-593 ◽  
Author(s):  
Chiyo Morimoto ◽  
Yo-ichiro Otofuji ◽  
Masako Miki ◽  
Hidefumi Tanaka ◽  
Tetsumaru Itaya
Keyword(s):  
Field Intensity ◽  
Geomagnetic Field ◽  
West Greenland ◽  
Dolerite Dyke ◽  
Geomagnetic Field Intensity

Formation of wide-blocky calcite veins by extreme growth competition

2020 ◽  
pp. jgs2020-104
Author(s):  
Liene Spruženiece ◽  
Michael Späth ◽  
Janos L. Urai ◽  
Estibalitz Ukar ◽  
Michael Selzer ◽  
...  
Keyword(s):  
High Resolution ◽  
Growth Rates ◽  
Polarized Light ◽  
Wall Rock ◽  
Scattered Electron ◽  
Thin Sections ◽  
Content Type ◽  
Calcite Veins ◽  
Supplementary Material ◽  
Electron Back Scattered Diffraction

Liassic limestones on the coast of Somerset in the UK contain dense arrays of calcite microveins with a common, but poorly understood microstructure, characterized by laterally wide crystals that form bridges across the vein. We investigated the mechanisms of formation and evolution of these ‘wide-blocky’ vein microstructures using a combination of high-resolution analytical methods, including virtual petrography, optical cathodoluminescence and scanning electron microscopy techniques (e.g. energy-dispersive X-ray spectrometry, back-scattered electron imaging, cathodoluminescence and electron back-scattered diffraction), laboratory experiments and multiphase field modelling. Our results indicate that the studied veins formed in open, fluid-filled fractures, each in a single opening and sealing episode. As shown by the optical and electron back-scattered diffraction images, the vein crystals grew epitaxially on grains of the wall rock and we hypothesize that their growth rates differed depending on whether the crystals were on a wall rock grain substrate that fractured intergranularly (slow growth rates) or transgranularly (rapid growth rates). Our multiphase field models support this hypothesis, showing that wide, blocky crystals only form where there are significant differences in the growth rate and are dependent on the type of seed grain. These results provide strong evidence for extreme growth competition, a process that we propose controls vein-filling in many micritic carbonate reservoirs, as well as demonstrate that the characteristics of the fracture wall can affect the filling processes in syntaxial veins.Supplementary material: The description and images of the studied thin sections are available at https://doi.org/10.6084/m9.figshare.c.5172371. High-resolution optical microscopy mosaics (under plane-polarized- and crossed polarized light) of the thin section collection in PetroScan file format are available on request from the authors.

scholarly journals Archetypal kimberlite from the Maniitsoq region, southern West Greenland and analogy to South Africa

2006 ◽  
Vol 10 ◽  
pp. 45-48 ◽  
Author(s):  
Troels F.D. Nielsen ◽  
Martin Jebens ◽  
Sven M. Jensen ◽  
Karsten Secher
Keyword(s):  
South Africa ◽  
South African ◽  
The West ◽  
West Greenland ◽  
Ultramafic Lamprophyre ◽  
Mineral Assemblages ◽  
Bona Fide ◽  
Indicator Mineral

Ultramafic dyke rocks with kimberlitic megacrysts and mantle nodules have been known for decades from the northern part of the Archaean block and adjacent Proterozoic terranes in southern West Greenland (Fig. 1; Escher & Watterson 1973; Goff 1973; Scott 1981; Larsen & Rex 1992; Mitchell et al. 1999). Some of the dykes have proved to be diamondiferous (see Jensen et al. 2004a, b, for exploration results, diamond contents, and references). The c. 600 Ma old dykes werecalled ‘kimberlitic’ by Larsen & Rex (1992), but Mitchell et al. (1999) concluded that they were best referred to a ‘carbonatiteultramafic lamprophyre’ suite (aillikites or melnoites). Mitchell et al. (1999) further suggested that the West Greenland province represents “one of the few bona fide examples of ultramafic lamprophyre which contain diamonds”. Reports on indicator mineral assemblages (Jensen et al. 2004b) and diamond contents (e.g. Hudson Resources Inc. 2005) have re-opened the discussion on the classification of the dykes. The results of an investigation of the Majuagaa dyke (Nielsen & Jensen 2005) are summarised below, together with the preliminary results of a regional investigation of the groundmass minerals of the dykes. It is concluded that dykes in the Maniitsoq region are similar to archetypal, South African, on-craton, Type 1 kimberlites, and that all regions of the West Greenland province of ultramafic magmatism are favourable for diamond exploration.

Paleomagnetism, paleointensity and geochronology of a Proterozoic dolerite dyke from southern West Greenland

2020 ◽  
Vol 139 ◽  
pp. 101752
Author(s):  
Masako Miki ◽  
Hanae Seki ◽  
Yuhji Yamamoto ◽  
Chitaro Gouzu ◽  
Hironobu Hyodo ◽  
...  
Keyword(s):  
West Greenland ◽  
Dolerite Dyke

An erosional structure in a layered dolerite dyke, West Greenland

1976 ◽  
Vol 113 (1) ◽  
pp. 77-82 ◽  
Author(s):  
H. R. Williams
Keyword(s):  
Water Vapour ◽  
Vapour Pressure ◽  
Vertical Channel ◽  
Channel Structure ◽  
Water Vapour Pressure ◽  
West Greenland ◽  
Dolerite Dyke

SummaryA vertical channel structure within a layered dolerite dyke resulted from differential magmatic flow. Layering in both dyke and channel is formed of more feldspathic dolerite attributed to fluctuations in water vapour pressure and supercooling during crystallization.

scholarly journals Crustal structure over the Nagssugtoqidian deformation front in West Greenland: Receiver Function analysis

1969 ◽  
Vol 35 ◽  
pp. 79-82 ◽  
Author(s):  
Trine Dahl-Jensen ◽  
Peter H. Voss ◽  
Tine B. Larsen
Keyword(s):  
Crustal Structure ◽  
Receiver Function ◽  
Function Analysis ◽  
Marked Change ◽  
Crustal Thickness ◽  
The South ◽  
Deformation Front ◽  
West Greenland ◽  
Ultramafic Lamprophyre ◽  
Receiver Function Analysis

A marked change in crustal thickness is seen at the deformation boundary between the undisturbed Archaean core in the south and reworked Archaean gneiss in the foreland of the Nagssugtoqidian orogen in West Greenland. In addition, intra-crustal boundaries can be tentatively interpreted. This is the first information on crustal structure in the area, which is known for kimberlite, carbonatite and ultramafic lamprophyre occurrences, and diamond exploration.

scholarly journals Diamonds and lithospheric mantle properties in the Neo - proterozoic igneous province of southern West Greenland

1969 ◽  
Vol 17 ◽  
pp. 65-68 ◽  
Author(s):  
Agnete Steenfelt ◽  
Sven Monrad Jensen ◽  
Troels F.D. Nielsen ◽  
Karina K. Sand ◽  
Karsten Secher
Keyword(s):  
Lithospheric Mantle ◽  
International Research ◽  
Chemical Data ◽  
Research Groups ◽  
Mantle Material ◽  
West Greenland ◽  
The Past ◽  
Ultramafic Lamprophyre ◽  
Igneous Province ◽  
Mineral Data

The search for diamonds in Greenland has resulted in the discovery of many new dykes of kimberlite and ultramafic lamprophyre and, most importantly, in the acquisition of a wealth of chemical data on rocks and minerals representing mantle material entrained by the dyke magmas. The discovery of a diamondiferous sheet at Garnet Lake in southern West Greenland stimulated the research (Hutchison 2005). Over the past five to ten years, the Geological Survey of Denmark and Greenland together with the Bureau of Minerals and Petroleum in Greenland and international research groups have acquired, processed and interpreted data with the objective of identifying diamond-favourable regimes within the lithospheric mantle below the Archaean craton in West Greenland. Here we present mineral data from drift samples that allow us to identify where mantle conditions in terms of lithology and depth may be favourable for the occurrence of diamonds.

II.—On the Organic Origin of the Chert in the Carboniferous Limestone Series of Ireland, and its Similarity to that in the Corresponding Strata in North Wales and Yorkshire

1887 ◽  
Vol 4 (10) ◽  
pp. 435-446 ◽  
Author(s):  
George Jennings Hinde
Keyword(s):  
Microscopic Structure ◽  
General Description ◽  
Joint Paper ◽  
Thin Sections ◽  
Upper Carboniferous ◽  
North Wales ◽  
Mode Of Occurrence ◽  
The Subject ◽  
Water Holding ◽  
Carboniferous Limestone

The first references in any detail to the nature of the Chert in Carboniferous rocks appeared in 1878, when Messrs. Hull and Hardman published a joint paper on the subject, treating more particularly of the Chert in the Upper Carboniferous Limestone of Ireland. Prof. Hull gave a general description of the distribution and mode of occurrence of the Chert, and a detailed notice of its microscopic structure, as shown in fifteen thin sections of the rock from various localities in Ireland. Prof. Hull gave a general description of the distribution and mode of occurrence of the Chert, and a detailed notice of its microscopic structure, as shown in fifteen thin sections of the rock from various localities in Ireland. The author reached the conclusion that the Chert is essentially a pseudomorphic rock, consisting of gelatinous silica replacing limestone of organic origin, chiefly foraminiferal, crinoidal, and coralline; the replacement was believed to have taken place before the shales overlying it were deposited, whilst the limestone was in a more or less plastic condition, admitting the fine percolation of water holding silica in solution. The sea was believed to have been largely charged with silica in solution, and the chemical process was accelerated by the warm surface waters of a shallow sea. The origin of the Chert from the siliceous skeletons of Biatomaceas, Polycystinas, and the spicules of sponges is distinctly denied, and it is affirmed that it can only be considered as a secondary product due to the replacement of lime-carbonate by silica.

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