Kanairiktok shear zone: the boundary between the Paleoproterozoic Makkovik Province and the Archean Nain Province, Labrador, Canada.

2000 ◽  
Vol 37 (9) ◽  
pp. 1245-1257 ◽  
Author(s):  
N Culshaw ◽  
T Brown ◽  
P H Reynolds ◽  
J WF Ketchum
Keyword(s):  
Shear Zone ◽  
Quartz Vein ◽  
Shear Zones ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Low Grade ◽  
Early Stages ◽  
Oblique Convergence ◽  
Andean Type ◽  
Early Activity

The polyphase Kanairiktok shear zone (KNSZ) separates gneissic rocks of the Archean Nain craton from their reworked equivalents in the Paleoproterozoic Kaipokok domain of the Makkovik Province. In its early stages, the KNSZ bounded the Kaipokok domain as it was thermally softened by 1895-1870 Ma Andean-type magmatism, accompanied by dextral oblique convergence and resultant penetrative deformation. The amphibolite-facies tectonite that developed in this stage was widely overprinted by greenschist-facies mylonite. Laserprobe and spectral 40Ar/39Ar ages of recrystallized and porphyroclastic muscovite, from the greenschist-facies mylonite and from muscovite in a syntectonic quartz vein, bracket the age of deformation between 1740 and 1710 Ma with the best estimate at 1715 Ma. These ages are similar to those of A-type granites within the Makkovik Province and amphibole cooling ages from the province interior. Together with the petrological similarity of the greenschist-facies mylonite to localized low-grade shear zones elsewhere in the Makkovik Province, they are suggestive of a widespread, lithosphere-scale event. The 40Ar/39Ar data do not provide good constraints on the early activity of the KNSZ. However, preservation of relationships between granitoid sheets correlated with the 1895-1870 Ma Island Harbour Bay plutonic suite and early fabrics imply that the granites were emplaced syntectonically in the KNSZ. Thus, the KNSZ was a major, long-lived structure in the Makkovik Province that decoupled events in the reactivated Nain craton from an inert cratonic region.

scholarly journals Brittle–viscous deformation of vein quartz under fluid-rich low greenschist facies conditions

2015 ◽  
Vol 7 (1) ◽  
pp. 213-257 ◽  
Author(s):  
H. J. Kjøll ◽  
G. Viola ◽  
L. Menegon ◽  
B. E. Sørensen
Keyword(s):  
Quartz Vein ◽  
Basal Slip ◽  
Boundary Migration ◽  
Fluid Pressure ◽  
Shear Zones ◽  
Progressive Increase ◽  
Greenschist Facies ◽  
Coarse Grained ◽  
Low Grade ◽  
Viscous Deformation

Abstract. A coarse grained, statically crystallized quartz vein, embedded in a phyllonitic matrix, was studied by EBSD and optical microscopy to gain insights into the processes of strain localization in quartz deformed under low-grade conditions, broadly coincident with the frictional–viscous transition. The vein is from a high strain zone at the front of the Porsa Imbricate Stack in the Paleoproterozoic Repparfjord Tectonic Window in northern Norway. The vein was deformed under lower greenschist facies conditions during deformation along a large out-of-sequence phyllonitic thrust of Caledonian age. The host phyllonite formed at the expense of metabasalt wherein feldspar broke down to form interconnected layers of fine, synkinematic phyllosilicates. In the mechanically weak framework of the phyllonite, the studied quartz vein acted as a relatively rigid body deforming mainly by coaxial strain. Viscous deformation was initially accommodated by basal ⟨a⟩ slip of quartz during the development of a mesoscopic pervasive extensional crenulation cleavage. Under the prevailing boundary conditions, however, dislocation glide-accommodated deformation of quartz resulted inefficient and led to dislocation tangling and strain hardening of the vein. In response to hardening, to the progressive increase of fluid pressure and the increasing competence contrast between the vein and the weak foliated host phyllonite, quartz crystals began to deform frictionally along specific, optimally oriented lattice planes, creating microgouges along microfractures. These were, however, rapidly sealed by nucleation of new grains as transiently over pressured fluids penetrated the deforming system. The new nucleated grains grew initially by solution-precipitation and later by grain boundary migration. Due to the random initial orientation of the vein crystals, strain was accommodated differently in the individual crystals, leading to the development of remarkably different microstructures. Crystals oriented optimally for basal slip accommodated strain mainly viscously and experienced only minor fracturing. Instead, the crystals misoriented for basal slip hardened and deformed by pervasive domainal fracturing. This study indicates the importance of considering shear zones as dynamic systems wherein the activated deformation mechanisms vary transiently in response to the complex temporal and spatial evolution of the shear zone, often in a cyclic fashion.

Complex kinematics in a major ductile shear zone, NW Shetland: Evidence of ductile extrusion during Caledonian transpression

2021 ◽  
Author(s):  
Timothy Armitage ◽  
Robert Holdsworth ◽  
Robin Strachan ◽  
Thomas Zach ◽  
Diana Alvarez-Ruiz ◽  
...  
Keyword(s):  
Shear Zone ◽  
Hanging Wall ◽  
Regional Scale ◽  
Shear Zones ◽  
White Mica ◽  
Strike Slip ◽  
Amphibolite Facies ◽  
Lateral Extrusion ◽  
Shear Sense ◽  
Ductile Shear

<p>Ductile shear zones are heterogeneous areas of strain localisation which often display variation in strain geometry and combinations of coaxial and non-coaxial deformation. One such heterogeneous shear zone is the c. 2 km thick Uyea Shear Zone (USZ) in northwest Mainland Shetland (UK), which separates variably deformed Neoarchaean orthogneisses in its footwall from Neoproterozoic metasediments in its hanging wall (Fig. a). The USZ is characterised by decimetre-scale layers of dip-slip thrusting and extension, strike-slip sinistral and dextral shear senses and interleaved ultramylonitic coaxially deformed horizons. Within the zones of transition between shear sense layers, mineral lineations swing from foliation down-dip to foliation-parallel in kinematically compatible, anticlockwise/clockwise-rotations on a local and regional scale (Fig. b). Rb-Sr dating of white mica grains via laser ablation indicates a c. 440-425 Ma Caledonian age for dip-slip and strike-slip layers and an 800 Ma Neoproterozoic age for coaxial layers. Quartz opening angles and microstructures suggest an upper-greenschist to lower-amphibolite facies temperature for deformation. We propose that a Neoproterozoic, coaxial event is overprinted by Caledonian sinistral transpression under upper greenschist/lower amphibolite facies conditions. Interleaved kinematics and mineral lineation swings are attributed to result from differential flow rates resulting in vertical and lateral extrusion and indicate regional-scale sinistral transpression during the Caledonian orogeny in NW Shetland. This study highlights the importance of linking geochronology to microstructures in a poly-deformed terrane and is a rare example of a highly heterogeneous shear zone in which both vertical and lateral extrusion occurred during transpression.</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.0cf6ef44e5ff57820599061/sdaolpUECMynit/12UGE&app=m&a=0&c=d96bb6db75eed0739f2a6ee90c9ad8fd&ct=x&pn=gepj.elif&d=1" alt=""></p>

Strain localization mechanism of graphitic carbon-bearing rocks: Constraints from microstructure, texture and graphite geothermometry

2021 ◽  
Author(s):  
Meixia Lyu ◽  
Shuyun Cao
Keyword(s):  
Shear Zone ◽  
Strain Localization ◽  
Carbonaceous Material ◽  
Shear Zones ◽  
Graphitic Carbon ◽  
Maximum Temperature ◽  
Low Grade ◽  
High Grade ◽  
Grade Metamorphism ◽  
Average Temperature

<p><strong>Abstracts:</strong></p><p>Graphitic carbon-bearing rocks can occur in low- to high-grade metamorphic units. In low-grade matamorphic rocks, graphitic carbon is often associated with brittle fault gouge whereas in middle- to high-grade metamorphic rocks, graphitic carbon commonly occurs in marble, schist or paragneiss. Previous studies showed that carbonaceous material gradually ordered from the amorphous stage, e.g. graphitization, is mainly controlled by increasing thermal metamorphism and has a good correlation with the metamorphic temperature. Besides, this ordered process is irreversible and the resulting structure is not affected by late metamorphism. Subsequently, the degree of graphitization is believed to be a reliable indicator of peak temperature conditions in the metamorphic rock. In this contribution, based on detailed field observations, the variably deformed and metamorphosed graphitic gneisses to phyllites, located within the footwall and hanging-walls unit of the Cenozoic Ailaoshan-Red River strike-slip shear zone are studied. According to lithological features and temperature determined by Raman spectra of carbonaceous material, these graphitic rocks and deformation fabrics are divided into three types. Type I is represented by medium–grade metamorphism and strongly deformed rocks with an average temperature of 509 °C and a maximum temperature of 604 °C. Type II is affected by low-grade metamorphism and deformed rocks with an average temperature of 420 °C. Type III is affected by lower–grade metamorphism and occurs in weakly deformed/undeformed rocks with an average temperature of 350 °C. Slip–localized micro–shear zone and laterally continuous or discontinuous slip planes constituted by graphitic carbon aggregates are developed in Types I and II. The electron back–scattered diffraction (EBSD) lattice preferred orientation (LPO) patterns of graphitic carbon grains were firstly observed in comparison with LPO patterns of quartz and switch from basal <a>, rhomb <a> to prism <a> slip systems, which indicate increasing deformation temperatures. According to the graphitic slip–planes, micro–shear zones and mylonitic foliation constituted by graphitic carbon minerals, we also propose that the development of fine–grained amorphous carbon plays an important role in rheological weakening of the whole rock during progressive ductile shearing.</p><p><strong>Key Words:</strong> graphitic carbon, strain localization, graphitic thermometry, slip–localized micro–shear zone, rheological weakening</p>

Early Devonian sinistral strike-slip in the Caledonian basement of Oscar II Land advocates for escape tectonics as a major mechanism for Svalbard terranes assembly

2020 ◽  
Author(s):  
Grzegorz Ziemniak ◽  
Jarosław Majka ◽  
Maciej Manecki ◽  
Katarzyna Walczak ◽  
Pauline Jeanneret ◽  
...  
Keyword(s):  
Shear Zone ◽  
Barents Sea ◽  
Weighted Average ◽  
Shear Zones ◽  
Structural Features ◽  
Greenschist Facies ◽  
Western Boundary ◽  
Structural Development ◽  
Early Devonian ◽  
Mylonitic Foliation

<p>The Svalbard’s Southwestern Basement Province in contrary to the Northwestern and Eastern Basement Provinces is commonly correlated with the Pearya Terrane or Timanides and bears a complicated internal structure. Here, we present new data from Oscar II Land supporting the model of Svalbard’s Basement being divided into the Laurentia and Barentsia plates in the late-Caledonian period.</p><p>In Oscar II Land the enigmatic Müllerneset Formation is tectonically juxtaposed against the remaining greenschist facies metamorphosed basement. It consists of Mesoproterozoic to Neoproterozoic metapelites and metapsammites that experienced a polymetamorphic history. The progressive amphibolite facies event M1 of unknown age reached the pressure-temperatures conditions of 5-7 kbar at 500-560 °C. The subsequent greenschist facies overprint (M2) is associated with mylonitization strongly pronounced across the whole Müllerneset Formation. Mylonitic foliation S2 dips steeply to the SW and it is associated with a stretching lineation dipping moderately-to-shallowly to the SE. In the western part of the unit, monazite is growing within the S2 foliation and related shear bands mainly replacing allanite. Th-U-total Pb dating of homogenous monazite population yielded a weighted average age of 410 ± 7 Ma with MSWD = 0.26 and p = 0.997. In the western part, where mylonitic foliation is less prevalent, monazite growths within M1 porphyroblasts and within the S2 foliation. Th-U-total Pb dating revealed an array of ages between 480 – 280 Ma with no correlation of chemical or structural features allowing divisions into subgroups.</p><p>Dating results indicating an early Caledonian signal should be attributed to the progressive M1 event. Uniform monazite age of 410 ± 7 Ma in the western part represents the timing of the M2 greenschist facies overprint. Younger ages obtained in the eastern part suggest fluid related disturbance of Th-U-Pb system during late Caledonian, Ellesmerian and Eurekan events. The timing of monazite growth during the M2 event is identical with the 410 ± 2 Ma <sup>40</sup>Ar/<sup>39</sup>Ar cooling age reported by Dallmeyer (1989). Geochronological evidence combined with structural observations suggests that the Müllerneset Formation in the Early Devonian was tectonically exhumed on the NW-SE trending left-lateral strike- to oblique-slip shear zone. Similarly oriented tectonic zones within the Southwestern Basement Province, in the Berzeliuseggene unit and the Vimsodden-Kosibapasset Shear Zone are also of similar age. This set of anastomosing shear zones is roughly parallel to the proposed orientation of the suture between Barentsia and Laurentia (Gudlaugsson et al. 1998). The documented Early Devonian sinistral displacement may mark the western boundary of the Barentsia microplate laterally extruded during the final Caledonian collision in a style similar to present day Anatolian Plate escape.</p><p>This work is funded by NCN research project no. 2015/17/B/ST10/03114, AGH statutory funds 16.16.140.315 and RCN Arctic Field Grant no. 282546.</p><p>Dallmeyer, R. D. (1989). Partial thermal resetting of<sup> 40</sup>Ar/<sup>39</sup>Ar mineral ages in western Spitsbergen, Svalbard: possible evidence for Tertiary metamorphism. Geological Magazine, 126(5), 587-593.</p><p>Gudlaugsson, S. T., Faleide, J. I., Johansen, S. E., & Breivik, A. J. (1998). Late Palaeozoic structural development of the south-western Barents Sea. Marine and Petroleum Geology, 15(1), 73-102.</p>

Upper Carboniferous-Permian tectonics in Central Mediterranean: an updated revision

2020 ◽  
Author(s):  
Giancarlo Molli ◽  
Andrea Brogi ◽  
Alfredo Caggianelli ◽  
Enrico Capezzuoli ◽  
Domenico Liotta ◽  
...  
Keyword(s):  
Shear Zone ◽  
Regional Scale ◽  
Sedimentary Basins ◽  
Sedimentary Facies ◽  
Shear Zones ◽  
Low Grade ◽  
Central Mediterranean ◽  
Upper Carboniferous ◽  
Fold And Thrust Belt ◽  
Splay Faults

<p>An updated revision of the upper Carboniferous-Permian tectonics recorded in Corsica, Calabria and Tuscany is here proposed. We combine our and literature data to document how the sedimentary, tectono-metamorphic and magmatic upper Carboniferous-Permian record fits with a regional-scale tectonic scenario characterized by trascurrent fault systems associated with stretched crustal domains in which extensional regional structures, magmatism and transtensional basins developed. In Corsica, altogether with well-known effusive and intrusive Permian magmatism, the alpine S.Lucia nappe exposes a kilometer-scale portion of the Permian lower to mid-crust, with many similarities to the Ivrea-Verbano zone. The two distinct Mafic and Leucogranitic complexes, which characterize this crustal domain are juxtposed by an oblique-slip shear zone named as S.Lucia Shear Zone. Structural and petrological data document interaction between magmatism, metamorphism and shearing during Permian in the c. 800-400 °C temperature range. In Calabria (Sila, Serre and Aspromonte), a continuous pre-Mesozoic crustal section is exposed. The lower crust portion of such section is mainly made up of granulites and migmatitic paragneisses with subordinate marbles and metabasites. The mid-crustal section includes an up to 13 km thick sequence of granitoids of tonalitic to granitic composition, emplaced between 306 and 295 Ma and progressively deformed during retrograde extensional shearing to end with a final magmatic activity between 295 and 277 Ma, consisting in the injection of shallower dykes in a transtensional regime. The section is completed by an upper crustal portion mainly formed by a Paleozoic succession deformed as a low-grade fold and thrust belt, locally overlaying medium-grade paragneiss units, and therefore as a whole reminiscent of the external/nappe zone domains of Sardinia Hercynian orogen. In Tuscany we document, how late Carboniferous/Permian shallow marine to continental sedimentary basins characterized by unconformity and abrupt change in sedimentary facies (coal-measures, red fanglomerate deposits) and acid magmatism well fit a transtensional setting with a mid-crustal shear zone linked with a system of E-W trending (in present orientation) upper crust splay faults. We will frame the whole dataset in a regional framework of first-order transcurrent shear zones network which includes a westernmost S.Lucia Shear Zone and an easternmost East Tuscan Shear Zone, with intervening crustal domains in which extensional to transtensional shearing occured.</p>

scholarly journals Switching deformation mode and mechanisms during subduction of continental crust: a case study from Alpine Corsica

Solid Earth ◽  
2017 ◽  
Vol 8 (4) ◽  
pp. 767-788 ◽  
Author(s):  
Giancarlo Molli ◽  
Luca Menegon ◽  
Alessandro Malasoma
Keyword(s):  
Shear Zone ◽  
Continental Crust ◽  
Ambient Pressure ◽  
Deformation Mode ◽  
Shear Zones ◽  
Small Scale ◽  
Low Grade ◽  
Stick Slip ◽  
Brittle Ductile Transition

Abstract. The switching in deformation mode (from distributed to localized) and mechanisms (viscous versus frictional) represent a relevant issue in the frame of crustal deformation, being also connected with the concept of the brittle–ductile transition and seismogenesis. In a subduction environment, switching in deformation mode and mechanisms and scale of localization may be inferred along the subduction interface, in a transition zone between the highly coupled (seismogenic zone) and decoupled deeper aseismic domain (stable slip). However, the role of brittle precursors in nucleating crystal-plastic shear zones has received more and more consideration being now recognized as fundamental in some cases for the localization of deformation and shear zone development, thus representing a case in which switching deformation mechanisms and scale and style of localization (deformation mode) interact and relate to each other. This contribution analyses an example of a millimetre-scale shear zone localized by brittle precursor formed within a host granitic protomylonite. The studied structures, developed in ambient pressure–temperature (P–T) conditions of low-grade blueschist facies (temperature T of ca. 300 °C and pressure P ≥ 0. 70 GPa) during involvement of Corsican continental crust in the Alpine subduction. We used a multidisciplinary approach by combining detailed microstructural and petrographic analyses, crystallographic preferred orientation by electron backscatter diffraction (EBSD), and palaeopiezometric studies on a selected sample to support an evolutionary model and deformation path for subducted continental crust. We infer that the studied structures, possibly formed by transient instability associated with fluctuations of pore fluid pressure and episodic strain rate variations, may be considered as a small-scale example of fault behaviour associated with a cycle of interseismic creep and coseismic rupture or a new analogue for episodic tremors and slow-slip structures. Our case study represents, therefore, a fossil example of association of fault structures related to stick-slip strain accommodation during subduction of continental crust.

Dating ductile deformation using U–Pb geochronology: examples from the Gilbert River Belt, Grenville Province, Labrador, Canada

1993 ◽  
Vol 30 (7) ◽  
pp. 1458-1469 ◽  
Author(s):  
D. J. Scott ◽  
N. Machado ◽  
S. Hanmer ◽  
C. Gariépy
Keyword(s):  
Isotopic Analysis ◽  
Shear Zones ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Ductile Deformation ◽  
Grenville Province ◽  
Southern Limit ◽  
Zircon Age ◽  
Intense Deformation ◽  
Host Rocks

The Gilbert River Belt, in the Grenville Province in southeastern Labrador, is a distinctive, west–northwest-trending zone of locally intense deformation and voluminous granitoid plutonism, up to 30 km in width. In an attempt to directly quantify the timing of deformation in ductile shear zones within the belt, rocks interpreted as having been intruded synchronously with ongoing deformation were sampled for U–Pb isotopic analysis. Three of these samples are <2 m wide granitic veins that have sharp intrusive contacts that truncate ductile deformation fabrics, but are themselves deformed at metamorphic conditions similar to their host rocks and are therefore interpreted as having intruded after the initiation of deformation and fabric development, but prior to cessation of this deformation. The first vein is syntectonic with respect to amphibolite-facies deformation and yielded a zircon age of [Formula: see text]. The second vein intruded synchronously with the development of a zone of amphibolite-facies straight gneisses, which defines the southern limit of the Gilbert River belt at [Formula: see text]. The third vein is syntectonic with respect to greenschist-facies deformation and yielded a zircon age of [Formula: see text] and a monazite age of 1078 ± 2 Ma. A sample of the K-feldspar megacrystic granite that underlies much of the belt and is interpreted as having intruded during ongoing amphibolite-facies deformation yielded a zircon age of [Formula: see text]; a mildly deformed granitic vein that crosscuts the megacrystic granite at the same location contained zircon that indicate a [Formula: see text] crystallization age. Monazite from a granodioritic gneiss yielded a concordant age of 1077 ± 3 Ma, interpreted as the time of final cooling during gneiss formation. These results indicate that much of the amphibolite-facies deformation (1664 – 1644 Ma) in the Gilbert River Belt is correlative with the regionally extensive Labradorian orogenic event, whereas greenschist-facies deformation (1113 – 1062 Ma) and monazite growth (1078 Ma) are the result of renewed tectonomagmatic activity during Grenvillian orogenesis.

Geology of the shear-hosted Brookbank gold prospect in the Beardmore–Geraldton belt, Wabigoon subprovince, Ontario

2007 ◽  
Vol 44 (7) ◽  
pp. 925-946 ◽  
Author(s):  
Jerry C DeWolfe ◽  
Bruno Lafrance ◽  
Greg M Stott
Keyword(s):  
Shear Zone ◽  
Hanging Wall ◽  
Shear Zones ◽  
Gold Deposits ◽  
Iron Formation ◽  
Alteration Zone ◽  
Gold Deposition ◽  
Low Grade ◽  
Metasedimentary Rocks ◽  
Polymictic Conglomerate

The Beardmore–Geraldton belt consists of steeply dipping, intercalated panels of metavolcanic and metasedimentary rocks along the southern margin of the granite–greenstone Wabigoon subprovince in the Archean Superior Province, Ontario. It is an important past-producing gold belt that includes classic epigenetic iron-formation-hosted deposits near Geraldton and turbidite-hosted deposits, north of Beardmore. The Brookbank gold prospect belongs to a third group of related gold deposits that formed along dextral shear zones localized at contacts between panels of metasedimentary and metavolcanic rocks. The Brookbank prospect occurs along a steeply dipping shear zone at the contact between footwall polymictic conglomerate and hanging-wall calc-alkaline arc basalt. Early during shearing the basalt acted as a structural and chemical trap that localized brittle deformation, veining, and gold deposition, ankerite–sericite–chlorite–epidote–pyrite alteration, and the replacement of metamorphic magnetite and ilmenite by gold-bearing pyrite. This produced a low grade (≤5 g/t Au) ankerite-rich alteration zone that extends up to 20 m into the hanging-wall basalt. Later during shearing, gold was deposited within higher grade (≤20 g/t Au) quartz–orthoclase–pyrite alteration zones superimposed on the wider ankerite-rich alteration zone. Auriferous quartz–carbonate veins oriented clockwise and counter-clockwise to the shear zone walls are folded and boudinaged, respectively, consistent with dextral slip along the shear zone. A key finding of the study is that different groups of gold deposits in the belt, including epigenetic iron formation gold deposits near Geraldton, formed during post-2690 Ma regional dextral transpression across the belt.

Structural evolution and tectonic significance of the Eastern Highlands shear zone in Cape Breton Island, the Canadian Appalachians

1995 ◽  
Vol 32 (5) ◽  
pp. 545-554 ◽  
Author(s):  
Shoufa Lin
Keyword(s):  
Shear Zone ◽  
Structural Evolution ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Movement Direction ◽  
Cape Breton Island ◽  
Cape Breton ◽  
Shear Sense ◽  
Eastern Highlands ◽  
Canadian Appalachians

The Eastern Highlands shear zone in Cape Breton Island of the Canadian Appalachians is characterized by an amphibolite-facies deformation zone over 5 km wide overprinted by a greenschist-facies mylonite zone about 1 km wide. Deformation zones in both metamorphic grades dip steeply to the southeast with movement direction pitching steeply to the southwest, and shear sense indicators indicate the same sense of shear, that is, an east-over-west dip-slip movement with minor sinistral strike-slip component. Deformation in both conditions is constrained to the Late Silurian to Early Devonian (mainly Late Silurian). It is suggested that the greenschist-facies deformation represents the last stage of a single episode of deformation that occurred initially under amphibolite-facies conditions. The west-vergent shearing along the shear zone is antithetic to the westward subduction that led to the Silurian continent-continent collision, which is interpreted by tectonic wedging in this part of the Canadian Appalachians.

scholarly journals Structure of the Storstrømmen shear zone, eastern Hertugen af Orléans Land, North-East Greenland

1994 ◽  
Vol 162 ◽  
pp. 103-112
Author(s):  
R.A Strachan ◽  
I.R Tribe
Keyword(s):  
Shear Zone ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Fold Belt ◽  
East Greenland ◽  
North East ◽  
Mineral Assemblages ◽  
Basement Gneiss

The Storstrømmen shear zone is a NNE-trending belt of steep, heterogeneously deformed gneisses and mylonites, at least 8 km wide, which transects the basement gneiss complexes of the Caledonian fold belt between Dronning Louise Land and Hertugen af Orleans Land. Shear criteria indicate a consistent sinistral sense of displacement parallel to a gently-plunging L-S fabric. Mineral assemblages and fabrics within the mylonites indicate that mylonitisation was initiated under low amphibolite facies conditions and continued within the greenschist facies. The shear zone is reworked by late, steep brittle faults which are associated with cataclasis and local metamorphic retrogression.

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