Taconian and Acadian transpression between the internal Humber Zone and the Gaspé Belt in the Gaspé Peninsula: tectonic history of the Shickshock Sud fault zone

2004 ◽  
Vol 41 (5) ◽  
pp. 635-653 ◽  
Author(s):  
Paul E Sacks ◽  
Michel Malo ◽  
Walter E Trzcienski, Jr ◽  
Alix Pincivy ◽  
Patrice Gosselin
Keyword(s):  
Hanging Wall ◽  
Shear Bands ◽  
Shear Zones ◽  
Strike Slip ◽  
Tectonic History ◽  
Movement Kinematic ◽  
Deformation Features ◽  
History Of ◽  
Laurentian Margin ◽  
Strike Slip Movement

The Shickshock Sud fault has a history of Ordovician (Taconian), Silurian (Salinic), and Devonian (Acadian) movements. Taconian deformation involving ductile dextral oblique-slip faulting is recorded in Cambrian rocks in the footwall of the Shickshock Sud fault. Metabasalt and metaarkose at amphibolite grade are converted into phyllonite and mylonitic schist. Shear bands, asymmetric garnet porphyroclasts, C–S fabrics, and mica-fish textures indicate dextral shearing. The regional sense of shear is top to west and southwest on generally southeast dipping shear zones. Hornblende of metabasalt yielded an 40Ar/39Ar age of 455.9 ± 2 Ma, and muscovite from the mylonitic schist yielded an 40Ar/39Ar age of 454.3 ± 0.9 Ma, which indicate metamorphism and deformation during the Taconian orogeny. Evidence for Silurian activity is indicated by the Salinic unconformity to the south related to normal block-faulting. Deformation features in the Ordovician and Silurian–Devonian rocks in the hanging wall were predominantly brittle and involved dextral transpression. Kinematic indicators point to predominantly dextral strike-slip movement. Kinematic analysis of brittle fault-slip data indicates that the shortening axis direction during strike-slip deformation was northwest–southeast and subhorizontal, which is essentially coaxial to the average pole of Acadian cleavage. Deformation in the hanging wall of the Shickshock Sud fault is Acadian-related. The irregular geometry of the Laurentian margin, including the Grenville basement, might be the cause for Taconian and Acadian transpression in the Gaspé Appalachians.

Zircon geochronology and paleomagnetism of an Archean harzburgite intrusion, eastern Bighorn Mountains, Wyoming

2020 ◽  
Vol 57 (1) ◽  
pp. 21-40
Author(s):  
Alexandra Wallenberg ◽  
Michelle Dafov ◽  
David Malone ◽  
John Craddock
Keyword(s):  
Hanging Wall ◽  
Vertical Axis ◽  
Shear Zones ◽  
Strike Slip ◽  
Zircon Geochronology ◽  
Weighted Mean ◽  
Mafic Complex ◽  
Laramide Orogeny ◽  
Axis Rotation ◽  
Bighorn Mountains

A harzburgite intrusion, which is part of the trailside mafic complex) intrudes ~2900-2950 Ma gneisses in the hanging wall of the Laramide Bighorn uplift west of Buffalo, Wyoming. The harzburgite is composed of pristine orthopyroxene (bronzite), clinopyroxene, serpentine after olivine and accessory magnetite-serpentinite seams, and strike-slip striated shear zones. The harzburgite is crosscut by a hydrothermally altered wehrlite dike (N20°E, 90°, 1 meter wide) with no zircons recovered. Zircons from the harzburgite reveal two ages: 1) a younger set that has a concordia upper intercept age of 2908±6 Ma and a weighted mean age of 2909.5±6.1 Ma; and 2) an older set that has a concordia upper intercept age of 2934.1±8.9 Ma and a weighted mean age 2940.5±5.8 Ma. Anisotropy of magnetic susceptibility (AMS) was used as a proxy for magmatic intrusion and the harzburgite preserves a sub-horizontal Kmax fabric (n=18) suggesting lateral intrusion. Alternating Field (AF) demagnetization for the harzburgite yielded a paleopole of 177.7 longitude, -14.4 latitude. The AF paleopole for the wehrlite dike has a vertical (90°) inclination suggesting intrusion at high latitude. The wehrlite dike preserves a Kmax fabric (n=19) that plots along the great circle of the dike and is difficult to interpret. The harzburgite has a two-component magnetization preserved that indicates a younger Cretaceous chemical overprint that may indicate a 90° clockwise vertical axis rotation of the Clear Creek thrust hanging wall, a range-bounding east-directed thrust fault that accommodated uplift of Bighorn Mountains during the Eocene Laramide Orogeny.

Chapter 8 Outboard-migrating accretionary orogeny at 1.9–1.8 Ga (Svecokarelian) along a margin to the continent Fennoscandia

2020 ◽  
Vol 50 (1) ◽  
pp. 237-250 ◽  
Author(s):  
Michael B. Stephens
Keyword(s):  
Base Metal ◽  
Regional Scale ◽  
Volcanic Rocks ◽  
Shear Zones ◽  
Strike Slip ◽  
Base Metal Sulphide ◽  
Metal Sulphide ◽  
Time Period ◽  
Ductile Shear Zones ◽  
Strike Slip Movement

AbstractAn intimate lithostratigraphic and lithodemic connection between syn-orogenic rock masses inside the different lithotectonic units of the 2.0–1.8 Ga (Svecokarelian) orogen, Sweden, is proposed. A repetitive cyclic tectonic evolution occurred during the time period c. 1.91–1.75 Ga, each cycle lasting about 50–55 million years. Volcanic rocks (c. 1.91–1.88 Ga) belonging to the earliest cycle are host to most of the base metal sulphide and Fe oxide deposits inside the orogen. Preservation of relict trails of continental magmatic arcs and intra-arc basins is inferred, with differences in the depth of basin deposition controlling, for example, contrasting types of base metal sulphide deposits along different trails. The segmented geometry of these continental magmatic arcs and intra-arc basins is related to strike-slip movement along ductile shear zones during transpressive events around and after 1.88 Ga; late orogenic folding also disturbed their orientation on a regional scale. A linear northwesterly orogenic trend is suggested prior to this structural overprint, the strike-slip movement being mainly parallel to the orogen. A solely accretionary orogenic model along an active margin to the continent Fennoscandia, without any trace of a terminal continent–continent collision, is preferred. Alternating retreating and advancing subduction modes that migrated progressively outboard and southwestwards in time account for the tectonic cycles.

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>

Microstructural shear bands in mylonites dated using muscovite sub-spectra from high-definition ultra-high-vacuum (UHV) argon diffusion experiments with phengitic white mica

2020 ◽  
Author(s):  
Marnie Forster ◽  
Ruoran Nie ◽  
Sonia Yeung ◽  
Gordon Lister
Keyword(s):  
High Vacuum ◽  
Microstructural Analysis ◽  
Shear Bands ◽  
Shear Zones ◽  
White Mica ◽  
Ultra High Vacuum ◽  
High Definition ◽  
Thin Sections ◽  
History Of ◽  
Ar Geochronology

<p>With excellent outcrop, the eclogite-blueschist belt exposed in the Cycladic archipelago in the Aegean Sea, Greece, offers a spectacular natural laboratory in which to decipher the structural geology of a highly extended orogenic belt and to ascertain the history of the different fabrics and microstructures that can be observed. Using phengitic white mica we demonstrate a robust correlation of age with microstructure, once again dispelling the myth that <sup>40</sup>Ar/<sup>39</sup>Ar geochronology using this mineral, produces cooling ages alone.</p><p>Further, we show that high-definition ultra-high-vacuum (UHV) <sup>39</sup>Ar diffusion experiments using phengitic white mica routinely allow the extraction of muscovite sub-spectra in the first 10-30% of <sup>39</sup>Ar gas release during <sup>40</sup>Ar/<sup>39</sup>Ar geochronology. The muscovite sub-spectrum is distinct and separate to the main spectrum which is dominated by mixing of gas released from phengite as well as muscovite. The muscovite sub-spectra allow consistent estimates of the timing of the formation of microstructural shear bands in various mylonites, as well as allowing quantitative estimates of temperature variation with time during the cooling history of the eclogite-blueschist belt. Our new data reveals hitherto unsuspected variation in the timing of exhumation of individual slices of the eclogite-blueschist belt, caused by Eocene and Miocene detachment-related shear zones.</p><p>This study thus illustrates a new method for the quantitative determination of the timing of movement in mylonites and/or in strongly stretched metamorphic tectonites. Shear bands formed in such structures are rarely coarsely crystalline enough to allow mineral grains that can be individually dated using laser spot analysis. Where phengitic white mica is involved, interlaying is usually so fine as to preclude the application of laser methods. In any case, laser methods do not have the capability of extracting exact and detailed age-temperature spectra, and can never achieve the definition of the multitudinous steps of the age spectrum evident from our high-definition UHV diffusion experiments.</p><p>Previous work in the Cycladic eclogite-blueschist belt has incorrectly assumed that the diffusion parameters for phengitic white mica were the same as for muscovite. Arrhenius data suggest this is not the case, and that phengitic white mica is considerably more retentive of argon than muscovite. Previous workers have also erred in dismissing microstructural variation in age as an artefact, supposedly as the result of the incorporation of excess argon. This has led to inconsistencies in interpretation, because phengite is able to retain argon at temperatures that exceed those estimated using metamorphic mineral parageneses. In consequence, we discover a robust correlation between microstructure and age, even down to the detail present in complex tectonic sequence diagrams produced during fabric and microstructural analysis of individual thin-sections.</p><p>A critical factor is that the recognition of muscovite sub-spectra requires Arrhenius data in order to recognise the steps dominated by release of <sup>39</sup>Ar from muscovite. In turn this requires precise measurement of temperature during each heating step. To apply percentage-release formula for the estimation of diffusivity, there must be a sharp rise to the temperature in question, then that temperature must be maintained at a constant value, then dropped sharply to relatively low values.</p>

Change of stress magnitudes during the polyphase tectonic history of the Cretaceous Gyeongsang basin, southeast Korea

2013 ◽  
Vol 184 (4-5) ◽  
pp. 467-484 ◽  
Author(s):  
Pom-yong Choi ◽  
Jacques Angelier ◽  
Jean-Paul Cadet ◽  
Jae-Ha Hwang ◽  
Choon Sunwoo
Keyword(s):  
Principal Stress ◽  
Maximum Principal Stress ◽  
Strike Slip ◽  
Rock Mechanic ◽  
Shear Stresses ◽  
Tectonic History ◽  
Tectonic Events ◽  
Gyeongsang Basin ◽  
Relative Chronology ◽  
History Of

Abstract In order to evaluate the change of stress magnitudes in the Gyeongsang basin during its tectonic history, we analyzed multiple faulting episodes in the Barremian-Aptian Hasandong Formation at the Yusu site. As elsewhere in southeast Korea, the recorded sequence consists of a succession of more than fourteen faulting episodes, and the relative chronology shows that a strike-slip faulting episode usually coexisted with a coaxial extensional episode. Likewise, seven couples of synchronous coaxial episodes recognised in the Gyeongsang basin are assigned to seven tectonic events (T_1 to T_7 events). The friction line (in the sense of Byerlee) allows us to determine the ratios between principal stress magnitudes as well as the origin of the dimensionless Mohr diagram. This line can be deduced from tension fractures on fault planes affected by friction and from the lower limit of scattered distribution of the normal stresses vs. shear stresses of faults. Dimensionless failure envelopes drawn for coaxial strike-slip and extensional episodes are adjusted to the experimental Mohr failure envelope derived from rock mechanic tests to determine the complete stress tensors. The maximum principal stress magnitudes of strike-slip episodes show a transition from 169 MPa in the Barremian-Coniacian T_1 Event through 263 MPa and 246 MPa in the T_2 and T_4 events, respectively to 235 MPa in the Quaternary T_7 Event; additional horizontal extension (ΔσT) have changed from −6 MPa in the T_1 Event through −8 MPa in the T_2 Event to −17 MPa in the T_7 Event. Because the studied site is currently exposed, the determined overburden (1.9 km) for the T_7 Event seems to be important, indicating the presumable occurrence of this event during the early Quaternary rather than at the present day.

Tectonic history of the central Humber Zone, western Newfoundland Appalachians: post-Taconian deformation in the Old Man's Pond area

1991 ◽  
Vol 28 (3) ◽  
pp. 398-410 ◽  
Author(s):  
John W. F. Waldron ◽  
John V. Milne
Keyword(s):  
Shear Zones ◽  
Tectonic Activity ◽  
Middle Ordovician ◽  
Tectonic History ◽  
Basement Rocks ◽  
Crenulation Cleavage ◽  
Shelf Sediments ◽  
History Of ◽  
Detachment Surface ◽  
Normal Sense

In the Humber Zone of the west Newfoundland Appalachians, the Middle Ordovician Taconian orogeny led to emplacement of the Humber Arm and other allochthons above a rift and shelf succession of late Precambrian to Early Ordovician age. Later deformation reversed this stacking in the Old Man's Pond area, where shelf sediments are thrust over the Old Man's Pond Group. East-vergent folds were subsequently developed in association with a regional, west-dipping cleavage that overprints the Taconian structures and intensifies eastward. Later, a major episode of shearing along normal-sense, northwest-dipping shear zones juxtaposed the Old Man's Pond Group against metamorphosed rift-related sediments and volcanics of the Hughes Lake Slice. This extensional episode may be related to intrusive events in adjacent central Newfoundland. The shear zones are overprinted by "cross folds," west-vergent folds, crenulation cleavage, and thrusts. These late structures are inferred to be related to westward transport of the rift–shelf succession and the Grenville-age basement rocks of the Long Range massif above a detachment surface, probably in Devonian time. The structural history is difficult to reconcile with a single, Devonian, "Acadian" orogeny, but is consistent with published isotopic data from central Newfoundland that suggest continued protracted tectonic activity in the Humber Zone in Silurian time.

scholarly journals Structural evidence of in-sequence and out-of-sequence thrusting in the Karwendel mountains and the tectonic subdivision of the western Northern Calcareous Alps

2019 ◽  
Vol 112 (1) ◽  
pp. 62-83
Author(s):  
Sinah Kilian ◽  
Hugo Ortner
Keyword(s):  
Hanging Wall ◽  
Strike Slip ◽  
Northern Calcareous Alps ◽  
Deformation History ◽  
Structural Geometry ◽  
Thrust Sheet ◽  
Northern Calcareous ◽  
Nappe Tectonics ◽  
Thrust Sheets ◽  
History Of

AbstractWe present the results of a field study in the Karwendel mountains in the western Northern Calcareous Alps, where we analysed the boundary between two major thrust sheets in detail in a key outcrop where nappe tectonics had been recognized already at the beginning of the 20th century. We use the macroscopic structural record of thrust sheet transport in the footwall and hanging wall of this boundary, such as folds, foliation and faults. In the footwall, competent stratigraphic units tend to preserve a full record of deformation while incompetent units get pervasively overprinted and only document the youngest deformation.Transport across the thrust persisted throughout the deformation history of the Northern Calcareous Alps from the late Early Cretaceous to the Miocene. As a consequence of transtensive, S-block down strike-slip tectonics, postdating folding of the major thrust, new out-of-sequence thrusts formed that climbed across the step, and ultimately placed units belonging to the footwall of the initial thrust onto its hanging wall.One of these out-of-sequence thrusts had been used to delimit the uppermost large thrust sheet (Inntal thrust sheet) of the western Northern Calcareous against the next, tectonically deeper, (Lechtal) thrust sheet. Based on the structural geometry of the folded thrust and the age of the youngest sediments below the thrust, we redefine the thrust sheets, and name the combined former Inntal- and part of the Lechtal thrust sheet as the new Karwendel thrust sheet and the former Allgäu- and part of the Lechtal thrust sheet as the new Tannheim thrust sheet.

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