scholarly journals Magnetic susceptibility ellipsoids in Nagssugtoqidian and Archaean rocks in South-East Greenland.

2008 ◽  
Vol 56 ◽  
pp. 11-25
Author(s):  
George, E.J. Beckmann
Keyword(s):  
Magnetic Susceptibility ◽  
Vertical Component ◽  
Shear Zones ◽  
Mobile Belt ◽  
Boundary Area ◽  
East Greenland ◽  
Precambrian Rocks ◽  
North East ◽  
The North ◽  
Hand Specimen

Measurements of magnetic susceptibility have been carried out on Precambrian rocks in south-east Greenland in the Nagssugtoqidian mobile belt from Ammassalik northwards to its boundary with the Archaean craton, and slightly beyond. Directions of maximum susceptibility are the best defined, and are as follows: Ammassalik: Declination = 3º, Inclination = 40º,α95 = 7º; Nagssugtoqidian/Archaean “boundary”: Declination = 311º, Inclination = 62º, α95 = 10º; area enclosing post-tectonic plutons: Declination = 194º, Inclination = 87º, α95 = 17º. The boundary is invisible to the directions of maximum susceptibility. A shear zone near the boundary has been studied in detail. The maximum directions of the samples are tightly grouped and lie in the plane of the zone, whilst the intermediate directions rotate about the maximum direction as the zone is approached, until they lie in its plane. Such rotation is widespread in the boundary area. A plate tectonic explanation for the maxima from the boundary and from Ammassalik is proposed as follows: the maximum direction from the boundary is attributed to subduction and collision of the Archaean plate arriving from the north-east, followed by a vertical component imprinted by the emplacement of the plutons. The maximum direction at Ammassalik is due to overriding Archaean crust coming from the north. Anisotropy of magnetic susceptibility is useful in detecting shear zones and rock fabric when these are not apparent in the field or hand specimen.

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.

Geology and timing of dextral strike-slip shear zones in Danmarkshavn, North-East Greenland Caledonides

2006 ◽  
Vol 143 (4) ◽  
pp. 431-446 ◽  
Author(s):  
C. SARTINI-RIDEOUT ◽  
J. A. GILOTTI ◽  
W. C. McCLELLAND
Keyword(s):  
Deformation Zone ◽  
Shear Zones ◽  
Amphibolite Facies ◽  
Ultrahigh Pressure ◽  
High Mass ◽  
Weighted Mean ◽  
East Greenland ◽  
North East ◽  
The North ◽  
Land Deformation

The North-East Greenland eclogite province is divided into a western, central and eastern block by the sinistral Storstrømmen shear zone in the west and the dextral Germania Land deformation zone in the east. A family of steep, NNW-striking dextral mylonite zones in the Danmarkshavn area are geometrically and kinematically similar to the ductile Germania Land deformation zone, located 25 km to the east. Amphibolite facies deformation at Danmarkshavn is characterized by boudinage of eclogite bodies within quartzofeldspathic host gneisses, pegmatite emplacement into the boudin necks and subsequent deformation of pegmatites parallel to gneissosity, a widespread component of dextral shear within the gneisses, and localization of strain into 10–50 m thick dextral mylonite zones. The gneisses and concordant mylonite zones are cut by a swarm of weakly to undeformed, steeply dipping, E–W-striking pegmatitic dykes. Oscillatory-zoned zircon cores from two boudin neck pegmatites give weighted mean 206Pb/238U sensitive, high mass resolution ion microprobe (SHRIMP) ages of 376 ± 5 Ma and 343 ± 7 Ma. Cathodoluminescence images of these zircons reveal complex additional rims, with ages from ranging from c. 360 to 320 Ma. Oscillatory-zoned, prismatic zircons from two late, cross-cutting pegmatites yield weighted mean 206Pb/238U SHRIMP ages of 343 ± 5 Ma and 332 ± 3 Ma. Zircons from the boudin neck pegmatites record a prolonged growth history, marked by fluid influx, during amphibolite facies metamorphism beginning at c. 375 Ma. The cross-cutting pegmatites show that dextral deformation in the gneisses and ductile mylonite zones had stopped by c. 340 Ma. Ultrahigh-pressure metamorphism in the eastern block at 360 Ma requires that the Greenland Caledonides were in an overall contractional plate tectonic regime. This, combined with 20% steep amphibolite facies lineations in the eclogites, gneisses and mylonites suggests that dextral transpression may have been responsible for a first stage of eclogite exhumation between 370 and 340 Ma.

scholarly journals Complex basal conditions influence flow at the onset of the North East Greenland Ice Stream

2020 ◽  
Author(s):  
Steven Franke ◽  
Daniela Jansen ◽  
John Paden ◽  
Olaf Eisen
Keyword(s):  
Shear Zones ◽  
Surface Flow ◽  
Ultra Wideband ◽  
Ice Flow ◽  
Systematic Analysis ◽  
East Greenland ◽  
North East ◽  
The North ◽  
Ice Surface ◽  
Ice Stream

<p>The onset and high upstream ice surface velocities of the North East Greenland Ice Stream (NEGIS) are not yet well reproducible in ice sheet models. A major uncertainty remains the understanding of basal sliding and a parameterization of basal conditions. In this study, we assess the slow-flowing part of the NEGIS in a systematic analysis of the basal conditions and investigate the increased ice flow. We analyze the spectral basal roughness in correlation with basal return power from an airborne radar survey with AWIs ultra-wideband radar system in 2018 and compare our results with current ice flow geometry and ice surface flow. We observe a roughness anisotropy where the ice stream widens, indicating a change from a smooth and soft bed to a harder bedrock as well as the evolution of elongated subglacial landforms. In addition, at the upstream part of the NEGIS we find a clear zoning of the bedrock return power, indicating an increased water content at the base of the ice stream. At the downstream part, we observe an increased bedrock return power throughout the entire width of the ice stream and outside its margins, indicating enhanced melting and the distribution of basal water beyond the shear zones.</p>

scholarly journals The geology of the north-eastern corner of Greenland - photogeological studies and 1993 field work

1994 ◽  
Vol 161 ◽  
pp. 21-33
Author(s):  
H.F Jepsen ◽  
J.C Escher ◽  
J.D Friderichsen ◽  
A.K Higgins
Keyword(s):  
Field Work ◽  
Tectonic Activity ◽  
Mobile Belt ◽  
North East ◽  
The North ◽  
Upper Proterozoic ◽  
North Eastern ◽  
Field Season ◽  
Upper Boundary ◽  
Middle Proterozoic

Late Archaean and Early Proterozoic crust-forming events in North-East and eastern North Greenland were succeeded by Middle Proterozoic sedimentation and volcanic activity; Late Proterozoic through Tertiary sedimentation was interrupted by several periods of tectonic activity, including the Caledonian orogeny in East Greenland and the Mesozoic deformation of the Wandel Hav mobile belt. Photogeological studies helped pinpoint areas of special interest which were investigated during the short 1993 field season. Insights gained during field work include: the nature of the crystalline basement terrain in the Caledonian fold belt, redefinition of the upper boundary of the Upper Proterozoic Rivieradal sandstones, revision of Caledonian nappe terminology, and the northern extension of the Caledonian Storstrømmen shear zone.

scholarly journals Caledonian and pre-Caledonian geology of the region between Grandjean Fjord and Bessel Fjord (75°–76°N), North-East Greenland

1989 ◽  
Vol 145 ◽  
pp. 90-97
Author(s):  
N Henriksen ◽  
J.D Friderichsen ◽  
R.A Strachan ◽  
N.J Soper ◽  
A.K Higgins
Keyword(s):  
Amphibolite Facies ◽  
Sedimentary Sequence ◽  
East Greenland ◽  
Early Proterozoic ◽  
Late Proterozoic ◽  
North East ◽  
The North ◽  
Group A ◽  
Metasedimentary Sequence

The area between Grandjean Fjord and Bessel Fjord was the focus in 1988 of regional geological investigations and 1:500000 mapping during the North-East Greenland project (Henriksen, 1989). The greater part of the area forms part of the East Greenland Caledonides and can be divided into three distinct rock groups: infracrustal gneisses and granites of possibie Archaean or early Proterozoic origin; a metasedimentary sequence which has probably suffered both mid-Proterozoic and Caledonian migmatisation and metamorphism; and the late Proterozoic Eleonore Bay Group, a thick sedimentary sequence which has undergone amphibolite facies Caledonian metamorphism in its lower parts and is intruded by Caledonian granites. Aspects of the stratigraphy and sedimentology of the Eleonore Bay Group are described by Sønderholm et al. (1989); only the structures affecting the sequence are described here.

scholarly journals Petroleum potential of the Upper Jurassic Hareelv Formation, Jameson Land, East Greenland

2018 ◽  
pp. 85-113 ◽  
Author(s):  
Jørgen A. Bojesen-Koefoed ◽  
Morten Bjerager ◽  
H. Peter Nytoft ◽  
Henrik I. Petersen ◽  
Stefan Piasecki ◽  
...  
Keyword(s):  
Significant Proportion ◽  
Upper Jurassic ◽  
Geochemical Data ◽  
Eastern Canada ◽  
Petroleum Potential ◽  
East Greenland ◽  
North East ◽  
The North ◽  
Clay Formation

The marine, mudstone-dominated Hareelv Formation (Upper Jurassic) of Jameson Land, East Greenland is a representative of the widespread Kimmeridge Clay Formation equivalents, sensu lato, known from the greater North Atlantic region, western Siberia and basins off eastern Canada. These deposits constitute the most important petroleum source-rock succession of the region. The present study reports petroleum geochemical data from the 233.8 m thick succession penetrated by the fully cored Blokelv-1 borehole, and includes supplementary data from outcrop samples and other boreholes in Jameson Land. The succession consists of basinal mudstone intercalated with a significant proportion of gravity-flow sandstones, both in situ and remobilised as injectites. The mudstones are generally rich in organic carbon with values of TOC reaching nearly 19 wt% and high pyrolysis yields reaching values of S2 up to nearly 43 kg HC/ton. Hydrogen Indices are up to 363. The data presented herein demonstrate that weathering of abundant pyritic sulfur adversely affects the petroleum potential of the kerogen in outcrop samples. The succession is thermally immature to early mature, except where intrusions have locally heated adjacent mudstones. The documentation of rich gas/oil-prone Upper Jurassic successions in Jameson Land is important for the assessment of the regional petroleum potential, including the North-East Greenland continental shelf.

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.

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