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 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 Partial melting due to breakdown of an epidote-group mineral during exhumation of ultrahigh-pressure eclogite: An example from the North-East Greenland Caledonides

2018 ◽  
Vol 37 (1) ◽  
pp. 15-39 ◽  
Author(s):  
Wentao Cao ◽  
Jane A. Gilotti ◽  
Hans-Joachim Massonne ◽  
Simona Ferrando ◽  
Charles T. Foster
Keyword(s):  
Partial Melting ◽  
Ultrahigh Pressure ◽  
Group Mineral ◽  
East Greenland ◽  
North East ◽  
The North

scholarly journals The Germania Land deformation zone and related structures, North-East Greenland

1994 ◽  
Vol 162 ◽  
pp. 113-127
Author(s):  
J.M Hull ◽  
J.A Gilotti
Keyword(s):  
Deformation Zone ◽  
Strike Slip ◽  
Low Grade ◽  
High Grade ◽  
Normal Faulting ◽  
East Greenland ◽  
North East ◽  
Parallel Movement ◽  
Land Deformation ◽  
Dextral Strike Slip

The Germania Land deformation zone in North-East Greenland consists of two subparallel, NW-striking strands of mylonites and cataclasites. The quasiplastic mylonites formed under low grade (biotite zone) conditions following high grade Caledonian metamorphism. Displacements on the Germania Land deformation zone and parallel zones at Danmarkshavn were predominantly dextral strike slip. Along with the similar, but sinistral, Storstrømmen shear zone, these zones record a late Caledonian phase of orogen-parallel movement. The Germania Land deformation zone is also the locus of Carboniferous normal faulting and basin development.

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 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 Dabie Extensional Tectonic System: Structural Framework

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Quanlin Hou ◽  
Hongyuan Zhang ◽  
Qing Liu ◽  
Jun Li ◽  
Yudong Wu
Keyword(s):  
Shear Zone ◽  
Shear Zones ◽  
Ultrahigh Pressure ◽  
Metamorphic Complex ◽  
The South ◽  
Magma Intrusion ◽  
The North ◽  
Extensional Tectonic ◽  
Mechanism Transition ◽  
Tectonic System

A previous study of the Dabie area has been supposed that a strong extensional event happened between the Yangtze and North China blocks. The entire extensional system is divided into the Northern Dabie metamorphic complex belt and the south extensional tectonic System according to geological and geochemical characteristics in our study. The Xiaotian-Mozitan shear zone in the north boundary of the north system is a thrust detachment, showing upper block sliding to the NNE, with a displacement of more than 56 km. However, in the south system, the shearing direction along the Shuihou-Wuhe and Taihu-Mamiao shear zones is tending towards SSE, whereas that along the Susong-Qingshuihe shear zone tending towards SW, with a displacement of about 12 km. Flinn index results of both the north and south extensional systems indicate that there is a shear mechanism transition from pure to simple, implying that the extensional event in the south tectonic system could be related to a magma intrusion in the Northern Dabie metamorphic complex belt. Two 40Ar-39Ar ages of mylonite rocks in the above mentioned shear zones yielded, separately, ~190 Ma and ~124 Ma, referring to a cooling age of ultrahigh-pressure rocks and an extensional era later.

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.

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