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 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.

scholarly journals Reaction of Precambrian high-grade gneisses to mid-crustal ductile deformation in western Dove Bugt, North-East Greenland

1994 ◽  
Vol 162 ◽  
pp. 53-70
Author(s):  
B Chadwick ◽  
C.R.L Friend
Keyword(s):  
Shear Zones ◽  
Ductile Deformation ◽  
Small Scale ◽  
High Grade ◽  
East Greenland ◽  
North West ◽  
North East ◽  
Basin Development ◽  
Ductile Shear Zones ◽  
Partial Melts

Mid-crustal deformation of an Early Proterozoic high-grade gneiss complex in western Dove Bugt gave rise to at least two sets of nappes. Structures in mylonites in low-angle ductile shear zones associated with the younger nappes indicate north-easterly-directed displacements. The nappes and mylonites are folded by upright to inclined folds that verge north-west and which appear to be associated with decollements that dip south-east. Hornblende, sillimanite and anatectic partial melts that developed with the nappes, mylonites and younger folds show that deformation took place under amphibolite facies conditions. Several lines of evidence suggest that the younger nappes, the mylonites and the upright to inclined folds formed during the Caledonian orogeny. Some pre-Caledonian deformation may be represented by the oldest isoclinal folds. Numerous, small-scale, ductile extensional shear zones and more brittIe fractures that were superimposed across the Caledonian structures are believed to have formed during orogen-parallel collapse which may be related IO Devonian basin development farther south in central East Greenland. Younger fauIts and major joints are correlated with Carboniferous, Mesozoic and Tertiary basin development in North-East Greenland.

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).

scholarly journals Large-scale changes of the semidiurnal tide along North Atlantic coasts from 1846 to 2018

Ocean Science ◽  
2021 ◽  
Vol 17 (1) ◽  
pp. 17-34
Author(s):  
Lucia Pineau-Guillou ◽  
Pascal Lazure ◽  
Guy Wöppelmann
Keyword(s):  
Sea Level ◽  
North Atlantic ◽  
Large Scale ◽  
Low Frequency ◽  
Underlying Mechanism ◽  
East Atlantic ◽  
North West ◽  
North East ◽  
The North ◽  
The North Atlantic

Abstract. We investigated the long-term changes of the principal tidal component M2 along North Atlantic coasts, from 1846 to 2018. We analysed 18 tide gauges with time series starting no later than 1940. The longest is Brest with 165 years of observations. We carefully processed the data, particularly to remove the 18.6-year nodal modulation. We found that M2 variations are consistent at all the stations in the North-East Atlantic (Cuxhaven, Delfzijl, Hoek van Holland, Newlyn, Brest), whereas some discrepancies appear in the North-West Atlantic. The changes started long before the 20th century and are not linear. The secular trends in M2 amplitude vary from one station to another; most of them are positive, up to 2.5 mm/yr at Wilmington since 1910. Since 1990, the trends switch from positive to negative values in the North-East Atlantic. Concerning the possible causes of the observed changes, the similarity between the North Atlantic Oscillation and M2 variations in the North-East Atlantic suggests a possible influence of the large-scale atmospheric circulation on the tide. Our statistical analysis confirms large correlations at all the stations in the North-East Atlantic. We discuss a possible underlying mechanism. A different spatial distribution of mean sea level (corresponding to water depth) from one year to another, depending on the low-frequency sea-level pressure patterns, could impact the propagation of the tide in the North Atlantic basin. However, the hypothesis is at present unproven.

Precambrian geology of Nuussuaq and the area north-east of Disko Bugt, West Greenland

1999 ◽  
pp. 6-40 ◽  
Author(s):  
Adam A. Garde ◽  
Agnete Steenfelt
Keyword(s):  
Hanging Wall ◽  
Shear Zones ◽  
Early Proterozoic ◽  
West Greenland ◽  
Metasedimentary Rocks ◽  
Precambrian Geology ◽  
North East ◽  
Westward Movement ◽  
Area North ◽  
Precambrian Terrain

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Garde, A. A., & Steenfelt, A. (1999). Precambrian geology of Nuussuaq and the area north-east of Disko Bugt, West Greenland. Geology of Greenland Survey Bulletin, 181, 6-40. https://doi.org/10.34194/ggub.v181.5108 _______________ The Precambrian terrain of eastern Nuussuaq and north-east Disko Bugt largely consists of late Archaean (c. 2800 Ma) orthogneisses, intercalated with units of strongly deformed Archaean supracrustal rocks. The latter are up to several kilometres wide and comprise both metavolcanic and metasedimentary rocks within which local occurrences of gold have been found. In central Nuussuaq a layered complex of anorthosite, leucogabbro, gabbro and ultramafic rocks is tectonically intercalated with Archaean orthogneisses, and an intrusive complex of Archaean tonalites and trondhjemites, largely unaffected by Archaean and Proterozoic deformation, occurs in the area north-east of Disko Bugt. Here an up to c. 3.5 km thick sequence of early Proterozoic shallow marine clastic sediments and minor marble unconformably overlies Archaean rocks. Several suites of basic dykes are present, and dykes and small plugs of ultramafic lamprophyre and lamproite (age c. 1750 Ma) are common in the central part of the region. Most of the region was overprinted by early Proterozoic deformation and metamorphism. Prominent Proterozoic flat-lying ductile shear zones with north- or north-westward movement of the hanging wall are overprinted by open folds.

scholarly journals Tectonolinament framework of the Black Sea region and the surrounding areas

2021 ◽  
Vol 8 (1) ◽  
pp. 26-44
Author(s):  
Vladimir Pokalyuk ◽  
Igor Lomakin ◽  
Valentyn Verkhovtsev ◽  
Vladimir Kochelab
Keyword(s):  
Black Sea ◽  
Large Scale ◽  
The Black Sea ◽  
Mobile Belt ◽  
Black Sea Region ◽  
North West ◽  
North East ◽  
The North ◽  
Lateral Displacements ◽  
Surrounding Areas

Modern high-precision global digital 3-d models of the relief of the continents and the ocean floor (SRTM, GEBCO) are the objective basis to clarify the structure and features of the organization of the planetary fault network of of the Black Sea region and adjacent areas of the Mediterranean mobile belt and surrounding platform areas, to find out the location of the main transregional supermegalineaments forming the deep structural-tectonic framework of the territory. A complete consistency of the structural plan of faults and fault zones within the sea areas and continental surroundings is established. The structural position of the Black Sea basin as a whole is determined by its location at the intersection area (superposition, interference) of the diagonal (subdiagonal) transcontinental tectonolinament belts: the north-west – Elba-Zagros, Caucasus-Kopetdag, and the north-east – Atlas- Black Sea. The absence of large-scale lateral displacements at the intersection nodes of differently oriented supermegalineament systems indicates the relative autonomous stationarity and inheritance of the formation of the lyneament framework during the entire Mezozoic-Cenozoic and relatively low-shear nature of its implementation. This feature of the Black Sea region structural pattern significantly limits the possibility of using neomobilistic geodynamic models to explain the history of the geological development of the region. The strict consistency and orderliness of the lineament framework can be ensured only by global planetary factors associated with the influence of the rotational regime of the Earth's shells on the stress distribution in the lithosphere.

scholarly journals Climate-scale changes of the semidiurnal tide over the North Atlantic coasts from 1846 to 2018

2020 ◽  
Author(s):  
Lucia Pineau-Guillou ◽  
Pascal Lazure ◽  
Guy Wöppelmann
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Low Frequency ◽  
Underlying Mechanism ◽  
East Atlantic ◽  
North West ◽  
North East ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract. We investigated the long-term changes of the principal tidal component M2 over the North Atlantic coasts, from 1846 to 2018. We analysed 9 tide gauges with time series starting no later than 1920. The longest is Brest with 165 years of observations. We carefully processed the data, particularly to remove the 18.6-year nodal modulation. We found that M2 variations are consistent at all the stations in the North East Atlantic (Newlyn, Brest, Cuxhaven), whereas some discrepancies appear in the North West Atlantic. The changes started long before the XXth century, and are not linear. The trends vary from a station to another; they are overall positive, up to 0.7 mm/yr. Since 1990, the trends switch from positive to negative values. Concerning the possible causes of the observed changes, the similarity between the North Atlantic Oscillation and M2 variations in the North East Atlantic suggests a possible influence of the large-scale atmospheric circulation on the tide. We discuss a possible underlying mechanism. A different spatial distribution of water heights from one year to another, depending on the low-frequency sea-level pressure patterns, could impact the propagation of the tide in the North Atlantic basin. However, the hypothesis is at present unproven.

Major northwest-directed Caledonian thrusting and folding in Precambrian rocks, northwest Mayo, Ireland

1995 ◽  
Vol 132 (1) ◽  
pp. 91-112 ◽  
Author(s):  
J. D. Johnston
Keyword(s):  
Large Scale ◽  
Shear Zones ◽  
Southeastern Part ◽  
Structural Mapping ◽  
Mafic Dykes ◽  
North West ◽  
Precambrian Rocks ◽  
The North ◽  
Subsequent Deformation

AbstractStructural mapping of the North West Mayo Inlier has investigated the kinematics of ductile fault and shear zones within the Dalradian and pre-Dalradian rocks. The area is characterized by an intense east to southeast trending elongation direction. Pre-Caledonian deformation is preserved as west-northwest trending sinistral mylonite zones. These are cross-cut by Grenville pegmatites and by undated mafic dykes. Subsequent deformation has been influenced by the majorbasement structures. During the Caledonian deformation, the pre-existing sinistral structures were reactivated coaxially as steep sinistral shear zones, deforming the mafic dykes. Major northwesterly verging thrusts are widespread in flat-lying zones which occur over much of the inlier. These are interpreted as D2 in age. The S2 fabric is the dominant fabric and contains an east to northeast trending mineral lineation. The southeastern part of the inlier is characterized by very large scale (wavelengths of kilometres) reclined D2 folding. This is interpreted as a crustal scale ramp zone. In the vicinity of this ramp there is evidence of earlier (F1) folds which are possibly the product of ramprelated deformation. All of these structures are interpreted as the product of northwest verging thrusting with crustal scale frontal and lateral ramps.

scholarly journals Sinistral transpression and hydrothermal activity during emplacement of the Early Proterozoic Julianehåb batholith, Ketilidian orogenic belt, South Greenland

1994 ◽  
Vol 163 ◽  
pp. 5-22
Author(s):  
B Chadwick ◽  
P Erfurt ◽  
T Frisch ◽  
R.A Frith ◽  
A.A Garde ◽  
...  
Keyword(s):  
Shear Zones ◽  
Field Work ◽  
Hydrothermal Activity ◽  
Vertical Shear ◽  
Early Proterozoic ◽  
North West ◽  
North East ◽  
The North ◽  
Granitoid Rocks ◽  
Quartz Veining

The first systematic investigations of the central part of the Early Proterozoic Ketilidian orogen in the vicinity of Søndre Sermilik in the early 1960s suggested that this part of the orogen comprised a mixture of the Julianehåb granite, altered supracrustal rocks and older orthogneisses. Recent field work has shown that the area consists only of a variably deformed suite of granitic to dioritic plutonic rocks and a range of hornblende-bearing dykes of the appinite suite which all belong to the Julianehåb batholith. Steep to vertical shear zones with widths from a few centimetres to more than one kilometre are a significant element of the structure. The principal shear zones trend north-east and they are parallel to the schistosity and subhorizontal linear structures in the granitoid rocks. Kinematic indicators in many of the shear zones indicate sinistral transcurrent displacements. The relationships between granite fabrics, shear zones and mafic dykes suggest that the Julianehåb batholith was emplaced during subduction from the south towards the Archaean craton in the north-west in a sinistral transpressional system. Effects of hydrothermal alteration, mainly in the form of quartz veining, silicification, chloritisation, epidotisation and pyritisation, are common within and adjacent to the largest shear zones. These effects are believed to be related to late stages of the evolution of the batholith. Gold anomalies appear to be closely tied to the hydrothermal phenomena.

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