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.

scholarly journals Neogene Evolution of the Pacific - Australia Plate Boundary Zone in NE Marlborough, South Island, New Zealand

2021 ◽  
Author(s):  
◽  
Dougal B Townsend
Keyword(s):  
New Zealand ◽  
Late Quaternary ◽  
Plate Boundary ◽  
Vertical Axis ◽  
Strike Slip ◽  
Early Miocene ◽  
Crustal Thickening ◽  
The Pacific ◽  
Axis Rotation ◽  
Dextral Strike Slip

<p>Six new palaeomagnetic localities in NE Marlborough, sampled from Late Cretaceous - Early Tertiary Amuri Formation and Middle Miocene Waima Formation, all yield clockwise declination anomalies of 100 - 150 degrees. Similarity in the magnitude of all new declination anomalies and integration of these results with previous data implies that clockwise vertical-axis rotation of this magnitude affected the entire palaeomagnetically sampled part of NE Marlborough (an area of ~700sq. km) after ~18 Ma. Previous palaeomagnetic sampling constrains this rotation to have occurred before ~7 Ma. The regional nature of this rotation implies that crustal-scale vertical-axis rotations were a fundamental process in the Miocene evolution of the Pacific - Australia plate boundary in NE South Island. The Flags Creek Fault System (FCFS) is a fold-and-thrust belt that formed in marine conditions above a subduction complex that developed as the Pacific - Australia plate boundary propagated through Marlborough in the Early Miocene. Thin-skinned fault offset accommodated at least 20 km of horizontal shortening across a leading-edge imbricate fan. Mesoscopic structures in the deformed belt indicate thrust vergence to the southeast. The palaeomagnetically-determined regional clockwise vertical axis rotation of ~100 degrees must be undone in order to evaluate this direction in the contemporary geographic framework of the thrust belt. Therefore the original transport direction of the thrust sheets in the FCFS was to the NE, in accordance with NE-SW plate motion vector between the Pacific and Australian plates during the Early Miocene. The two new palaeomagnetic localities that are within ~3 km of the active dextral strike-slip Kekerengu Fault have the highest clockwise declination anomalies (up to 150 degrees). Detailed structural mapping suggests that the eastern ends of the FCFS are similarly clockwise-rotated, by an extra 45 degrees relative to the regional average, to become south-vergent in proximity to the Kekerengu Fault. This structural evidence implies the presence of a zone of Plio-Pleistocene dextral shear and vertical-axis rotation within 2-3 km of the Kekerengu Fault. Local clockwise vertical-axis rotations of up to 50 degrees are inferred to have accrued in this zone, and to have been superimposed on the older, regional. ~100 degrees Miocene clockwise vertical-axis rotation. The Late Quaternary stratigraphy of fluvial terraces in NE Marlborough has been revised by the measurement of five new optically stimulated luminescence (OSL) dates on loess. This new stratigraphy suggests that the latest aggradation surface in the Awatere Valley (the Starborough-1 terrace) is, at least locally, ~9 ka old, several thousand years younger than the previous 16 ka thermoluminescence age for the same site. This new surface abandonment age implies that terrace-building events in NE Marlborough lasted well after the last glacial maximum (~17 ka). The timing of terrace aggradation in this peri-glacial region is compared with oxygen isotope data. Downstream transport of glacially derived sediment at the time of maximum deglaciation/warming is concluded to be the primary influence on the aggradation of major fill terraces in coastal NE Marlborough. This interpretation is generally applicable to peri-glacial central New Zealand. Patterns of contemporary uplift and directions of landscape tilting have been analysed by assessing the rates of stream incision and by the evolution of drainage networks over a wide tract of NE Marlborough that includes the termination of the dextral strike-slip Clarence Fault. Relative elevations of differentially aged terraces suggests an increase in rates of incision over the last ~10 ka. Uplift is highest in the area immediately surrounding the fault tip and is generally high where Torlesse basement rocks are exposed. Independently derived directions of Late Quaternary tilting of the landscape display a similar pattern of relative uplift in a broad dome to the north and west of the fault tip. This pattern of uplift suggests dissipation of strike-slip motion at the Clarence Fault tip into a dome-shaped fold accommodating: 1) crustal thickening (uplift) and 2) up to 44 degrees of vertical-axis rotation of a ~40 km2 crustal block, relative to more inland domains, into which the fault terminates. The distribution of incision rates is compared with the pattern of crustal thickening predicted by elastic models of strike-slip fault tips. The observed pattern and spatial extent of uplift generally conforms with the distribution of thickening predicted by the models, although the rate of incision/uplift over the last ~120 ka has been variable. These differences may be due to variability in the strike-slip rate of the Clarence Fault, superimposition of the regional uplift rate or to interaction with nearby fault structures not accounted for in the models.</p>

scholarly journals Neogene Evolution of the Pacific - Australia Plate Boundary Zone in NE Marlborough, South Island, New Zealand

2021 ◽  
Author(s):  
◽  
Dougal B Townsend
Keyword(s):  
New Zealand ◽  
Late Quaternary ◽  
Plate Boundary ◽  
Vertical Axis ◽  
Strike Slip ◽  
Early Miocene ◽  
Crustal Thickening ◽  
The Pacific ◽  
Axis Rotation ◽  
Dextral Strike Slip

<p>Six new palaeomagnetic localities in NE Marlborough, sampled from Late Cretaceous - Early Tertiary Amuri Formation and Middle Miocene Waima Formation, all yield clockwise declination anomalies of 100 - 150 degrees. Similarity in the magnitude of all new declination anomalies and integration of these results with previous data implies that clockwise vertical-axis rotation of this magnitude affected the entire palaeomagnetically sampled part of NE Marlborough (an area of ~700sq. km) after ~18 Ma. Previous palaeomagnetic sampling constrains this rotation to have occurred before ~7 Ma. The regional nature of this rotation implies that crustal-scale vertical-axis rotations were a fundamental process in the Miocene evolution of the Pacific - Australia plate boundary in NE South Island. The Flags Creek Fault System (FCFS) is a fold-and-thrust belt that formed in marine conditions above a subduction complex that developed as the Pacific - Australia plate boundary propagated through Marlborough in the Early Miocene. Thin-skinned fault offset accommodated at least 20 km of horizontal shortening across a leading-edge imbricate fan. Mesoscopic structures in the deformed belt indicate thrust vergence to the southeast. The palaeomagnetically-determined regional clockwise vertical axis rotation of ~100 degrees must be undone in order to evaluate this direction in the contemporary geographic framework of the thrust belt. Therefore the original transport direction of the thrust sheets in the FCFS was to the NE, in accordance with NE-SW plate motion vector between the Pacific and Australian plates during the Early Miocene. The two new palaeomagnetic localities that are within ~3 km of the active dextral strike-slip Kekerengu Fault have the highest clockwise declination anomalies (up to 150 degrees). Detailed structural mapping suggests that the eastern ends of the FCFS are similarly clockwise-rotated, by an extra 45 degrees relative to the regional average, to become south-vergent in proximity to the Kekerengu Fault. This structural evidence implies the presence of a zone of Plio-Pleistocene dextral shear and vertical-axis rotation within 2-3 km of the Kekerengu Fault. Local clockwise vertical-axis rotations of up to 50 degrees are inferred to have accrued in this zone, and to have been superimposed on the older, regional. ~100 degrees Miocene clockwise vertical-axis rotation. The Late Quaternary stratigraphy of fluvial terraces in NE Marlborough has been revised by the measurement of five new optically stimulated luminescence (OSL) dates on loess. This new stratigraphy suggests that the latest aggradation surface in the Awatere Valley (the Starborough-1 terrace) is, at least locally, ~9 ka old, several thousand years younger than the previous 16 ka thermoluminescence age for the same site. This new surface abandonment age implies that terrace-building events in NE Marlborough lasted well after the last glacial maximum (~17 ka). The timing of terrace aggradation in this peri-glacial region is compared with oxygen isotope data. Downstream transport of glacially derived sediment at the time of maximum deglaciation/warming is concluded to be the primary influence on the aggradation of major fill terraces in coastal NE Marlborough. This interpretation is generally applicable to peri-glacial central New Zealand. Patterns of contemporary uplift and directions of landscape tilting have been analysed by assessing the rates of stream incision and by the evolution of drainage networks over a wide tract of NE Marlborough that includes the termination of the dextral strike-slip Clarence Fault. Relative elevations of differentially aged terraces suggests an increase in rates of incision over the last ~10 ka. Uplift is highest in the area immediately surrounding the fault tip and is generally high where Torlesse basement rocks are exposed. Independently derived directions of Late Quaternary tilting of the landscape display a similar pattern of relative uplift in a broad dome to the north and west of the fault tip. This pattern of uplift suggests dissipation of strike-slip motion at the Clarence Fault tip into a dome-shaped fold accommodating: 1) crustal thickening (uplift) and 2) up to 44 degrees of vertical-axis rotation of a ~40 km2 crustal block, relative to more inland domains, into which the fault terminates. The distribution of incision rates is compared with the pattern of crustal thickening predicted by elastic models of strike-slip fault tips. The observed pattern and spatial extent of uplift generally conforms with the distribution of thickening predicted by the models, although the rate of incision/uplift over the last ~120 ka has been variable. These differences may be due to variability in the strike-slip rate of the Clarence Fault, superimposition of the regional uplift rate or to interaction with nearby fault structures not accounted for in the models.</p>

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

&lt;p&gt;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.&lt;/p&gt;&lt;p&gt;&lt;img src=&quot;https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.0cf6ef44e5ff57820599061/sdaolpUECMynit/12UGE&amp;app=m&amp;a=0&amp;c=d96bb6db75eed0739f2a6ee90c9ad8fd&amp;ct=x&amp;pn=gepj.elif&amp;d=1&quot; alt=&quot;&quot;&gt;&lt;/p&gt;

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.

scholarly journals A first estimation of the contraction related to vertical axis rotation: the case of the Ibero-Armorican Arc formation

2020 ◽  
Author(s):  
Josep Maria Casas ◽  
Joan Guimerà ◽  
Joaquina Alvarez-Marron ◽  
Ícaro Días da Silva
Keyword(s):  
Secondary Structure ◽  
Vertical Axis ◽  
Strike Slip ◽  
The Other ◽  
Variscan Orogeny ◽  
The Core ◽  
Rotational Curve ◽  
Southern Branch ◽  
Axis Rotation

Abstract. Different models have been proposed to explain the formation of the Ibero-Armorican Arc, which require significant vertical axis rotations, at the end of the Variscan orogeny. Estimates of the amount of contraction (horizontal shortening) needed for these rotations range from 54 % to 91 % perpendicularly to the arc. These estimates are compared with coeval deformational structures developed in two areas of the orogen, one in the autochthonous hinterland underlying the Galicia-Trás-os-Montes Zone in the southern branch of the arc, and the other in the Cantabrian Zone foreland in the core of the arc. From this analysis it follows that the late Variscan deformation together with the subsequent Alpine contraction is not sufficient to explain the formation of the Ibero-Armorican Arc as a secondary structure by means of vertical axis rotations. Our analysis suggests this arc is mainly a primary, or non-rotational curve, slightly modified by ca. 10 % of superposed contraction during late Carboniferous and/or Alpine times. Moreover, we propose that the assumptions underlying the interpreted geometry of the arc be re-evaluated, and we discuss the role of late-Variscan regional strike-slip faults in the Iberian and in the Armorican massifs that probably acted consecutively before and during the contraction of the arc.

Albian syndepositional block rotation and its geological consequences, Basque–Cantabrian Basin (western Pyrenees)

2013 ◽  
Vol 150 (6) ◽  
pp. 986-1001 ◽  
Author(s):  
LUIS MIGUEL AGIRREZABALA ◽  
JAUME DINARÈS-TURELL
Keyword(s):  
Slip Rate ◽  
Vertical Axis ◽  
Strike Slip ◽  
Block Rotation ◽  
Minimum Block ◽  
Magmatic Intrusions ◽  
Axis Rotation ◽  
High Level ◽  
Basque Cantabrian Basin ◽  
Dextral Strike Slip

AbstractStratigraphic, structural, palaeocurrent and palaeomagnetic analyses of Upper Albian deep-water deposits in and around the Deba block (Northern Iberia) are presented. Results indicate an anticlockwise vertical-axis rotation of this block by 35° during a maximum time span of c. 1 Ma (Late Albian intra-C. auritus ammonite Subzone). This Albian syndepositional block rotation is interpreted to be the consequence of the coeval activity of conjugate major sinistral strike-slip faults and minor (antithetic) dextral strike-slip faults, which border the Deba block. On the base of conservative estimations, a minimum block-rotation rate of 35° Ma−1 and a sinistral strike-slip rate of 1.2 km Ma−1 are calculated. As a consequence of the interaction of the rotated Deba block with adjacent non-rotated blocks, its corners experienced coeval transpressive (NW and SE corners) and transtensional deformations (SW and, possibly, NE corners). At the transtensional SW corner, two domal high-reflective seismic structures have been recorded and interpreted as high-level magmatic laccoliths. These magmatic intrusions triggered the development of a mineralizing hydrothermal system, which vented to the Late Albian seafloor warm to hot hydrocarbon-rich fluids. Vented hydrocarbon was generated from Albian organic-rich sediments by contact alteration with hydrothermal fluids.

Three-Dimensional Computation during Off-Vertical Axis Rotation (OVAR) in Monkeys

2006 ◽  
Vol 65 (6) ◽  
pp. 429-439 ◽  
Author(s):  
Keisuke Kushiro ◽  
Jun Maruta
Keyword(s):  
Three Dimensional ◽  
Vertical Axis ◽  
Axis Rotation

scholarly journals Mapping and classifying large deformation from digital imagery: application to analogue models of lithosphere deformation

2021 ◽  
Author(s):  
Taco Broerse ◽  
Nemanja Krstekanić ◽  
Cor Kasbergen ◽  
Ernst Willingshofer
Keyword(s):  
Large Deformation ◽  
Finite Deformation ◽  
Large Strain ◽  
Shear Zones ◽  
Strike Slip ◽  
Strain Measure ◽  
Lithospheric Deformation ◽  
Analogue Models ◽  
Strain Tensors ◽  
Shape Changes

Summary Particle Image Velocimetry (PIV), a method based on image cross-correlation, is widely used for obtaining velocity fields from time series of images of deforming objects. Rather than instantaneous velocities, we are interested in reconstructing cumulative deformation, and use PIV-derived incremental displacements for this purpose. Our focus is on analogue models of tectonic processes, which can accumulate large deformation. Importantly, PIV provides incremental displacements during analogue model evolution in a spatial reference (Eulerian) frame, without the need for explicit markers in a model. We integrate the displacements in a material reference (Lagrangian) frame, such that displacements can be integrated to track the spatial accumulative deformation field as a function of time. To describe cumulative, finite deformation, various strain tensors have been developed, and we discuss what strain measure best describes large shape changes, as standard infinitesimal strain tensors no longer apply for large deformation. PIV or comparable techniques have become a common method to determine strain in analogue models. However, the qualitative interpretation of observed strain has remained problematic for complex settings. Hence, PIV-derived displacements have not been fully exploited before, as methods to qualitatively characterize cumulative, large strain have been lacking. Notably, in tectonic settings, different types of deformation - extension, shortening, strike-slip - can be superimposed. We demonstrate that when shape changes are described in terms of Hencky strains, a logarithmic strain measure, finite deformation can be qualitatively described based on the relative magnitude of the two principal Hencky strains. Thereby, our method introduces a physically meaningful classification of large 2D strains. We show that our strain type classification method allows for accurate mapping of tectonic structures in analogue models of lithospheric deformation, and complements visual inspection of fault geometries. Our method can easily discern complex strike-slip shear zones, thrust faults and extensional structures and its evolution in time. Our newly developed software to compute deformation is freely available and can be used to post-process incremental displacements from PIV or similar autocorrelation methods.

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