scholarly journals Shape of plutons in crustal shear zones: A tectono-magmatic guide based on analogue models

2021 ◽  
Author(s):  
Maria Michail ◽  
Michael Rudolf ◽  
Matthias Rosenau ◽  
Alberto Riva ◽  
Piero Gianolla ◽  
...  
Keyword(s):  
Shear Zones ◽  
Analogue Models ◽  
Crustal Shear Zones

scholarly journals Shape of plutons in crustal shear zones: A tectono-magmatic guide based on analogue models

2021 ◽  
pp. 104417
Author(s):  
Maria Michail ◽  
Michael Rudolf ◽  
Matthias Rosenau ◽  
Alberto Riva ◽  
Piero Gianolla ◽  
...  
Keyword(s):  
Shear Zones ◽  
Analogue Models ◽  
Crustal Shear Zones

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.

Tectonic modelling state of the art and future challenges 

2021 ◽  
Author(s):  
Laetitia Le Pourhiet
Keyword(s):  
Numerical Modelling ◽  
Continuum Mechanics ◽  
Plate Tectonics ◽  
Shear Bands ◽  
Plate Boundary ◽  
Shear Zones ◽  
Thermal Dependence ◽  
Brittle Behavior ◽  
Viscous Shear ◽  
Analogue Models

<p>Tectonic modelling is a very wide area of application over a large range of time scale and length scale. What mainly characterize this modelling field is the coexistence of brittle fractures which relates to the field of fracture mechanics and plastic to viscous shear zones which belongs to the two main branch of continuum mechanics (solid and fluid respectively).</p><p>This type of problems arises sometimes in engineering but material do not change their behavior with loading rate or with time or with temperature, and rarely are engineers interested in modelling large displacement in post failure stage.  As a result, tectonicists cannot use commercial packages to simulate their problems and need to develop methodologies specific to their field.</p><p>Historically, the first tectonics models made use of simple analogue materials and corresponded more to modelism than actual analogue models. While the imaging of the models, and the characterization of the analogue materials have made a lot of progress in the last 15 years, up to recently, most analogue models still relied on sand and silicone putty to represent the brittle and viscous counter part of tectonic plates.</p><p>Since the late 80’s, but mostly during the years 2000, numerical modelling has exploded on the market, as contrarily to analogue modelling, it was easier to capture the thermal dependence of frictional-viscous transition, I use frictional here because most models in tectonics use continuum mechanics approach and in fine do not include brittle material s.s. but rather frictional shear bands. Some groups run these types of simulation routinely in 3D today but this performance has been made at the cost of a major simplification in the rheology: the disappearance of elasticity and compressibility which was present in late 90’s early 2000 simulations and is still very costly because the treatment of “brittle” rheology seriously amped code performances.</p><p>Until recently, in both analogue and numerical modelling, I have some kind of feeling that we have been running the same routine experiments over and over again with better performance, or better acquisition.  </p><p>We are now entering a new exciting era in tectonic modelling both from experimental and numerical side: a ) emergence of complex analogue material or rheological laws that efforts in upscaling from micro-mechanical process observed on the field to plate boundary scale, or from earthquake cycle to plate tectonics, b) emergence of new interesting set up’s in terms of boundary conditions in 3D, c) development of robust numerical technics for brittle behavior d) development of new applications to make our field more predictive that will enlarge the community of end-users of the modelling results</p><p>I will review these novelties with some of the work develop with colleagues and students but also with examples from the literature and try to quickly draw a picture of where we are at and where we go.</p>

Fluid controlled eclogitization of granulites in deep crustal shear zones, Bergen arcs, Western Norway

1990 ◽  
Vol 104 (2) ◽  
pp. 184-193 ◽  
Author(s):  
Bj�rn Jamtveit ◽  
Kurt Bucher-Nurminen ◽  
H�kon Austrheim
Keyword(s):  
Shear Zones ◽  
Western Norway ◽  
Crustal Shear Zones

Cratonic Reactivation in the Precambrian Basement of Western Canada. III. Crustal Evolution

1973 ◽  
Vol 10 (2) ◽  
pp. 283-291 ◽  
Author(s):  
R. A. Burwash ◽  
J. Krupička ◽  
R. R. Culbert
Keyword(s):  
Shear Zones ◽  
Western Canada ◽  
Upward Movement ◽  
Low Velocity ◽  
Reflection And Refraction ◽  
Refraction Seismic ◽  
Southern Alberta ◽  
Crustal Shear Zones ◽  
Crustal Reflection ◽  
Velocity Zone

Relative to the Superior and Slave provinces, the Churchill province is enriched in K and Rb. The inferred mechanism of alkali enrichment involves diapiric uprise of mantle material from the base of the low velocity zone, in response to upward movement of water from the deep mantle. Intergranular fluid in the peridotite is enriched in K and Rb. At the base of the crust this fluid separates to enter deep-seated crustal shear zones. At upper crustal levels, reaction with permeable cataclasites causes K-metasomatism, involving especially the change of plagioclase into K-feldspar.Eclogite bodies within the peridotite, on moving upward to the base of the crust yield andesitic magma which separates to form sialic underplating. The existence of a discrete lower crust beneath southern Alberta, western Ontario, and northern Manitoba is shown by deep crustal reflection and refraction seismic studies.Generation of juvenile sial during the Hudsonian orogeny is indicated by initial ratios of whole-rock Rb–Sr isochrons for igneous rocks. During metasomatism, potassium and rubidium were added in the ratio of about 350:1. This ratio makes it unlikely that these alkalis were derived by anatexis of Kenoran crystalline basement.

CRUSTAL SHEAR ZONES AND THE VISCOSITY OF THE LOWER CRUST

2017 ◽  
Author(s):  
Greg Hirth ◽  
◽  
Mark Behn ◽  
William Shinevar
Keyword(s):  
Lower Crust ◽  
Shear Zones ◽  
Crustal Shear Zones

RELATIONSHIPS AMONG TRANSIENT BRITTLE AND DUCTILE DEFORMATION AND METAMORPHIC REACTIONS IN CRUSTAL SHEAR ZONES

2017 ◽  
Author(s):  
Kevin H. Mahan ◽  
◽  
Philippe Goncalves ◽  
Omero F. Orlandini ◽  
Thomas Leydier ◽  
...  
Keyword(s):  
Shear Zones ◽  
Ductile Deformation ◽  
Crustal Shear Zones

A discussion of the (re)activation of basement structures during multi-phase shortening in thin- and thick-skinned styles

2021 ◽  
Author(s):  
Nicolas Molnar ◽  
Susanne Buiter
Keyword(s):  
Structural Evolution ◽  
Shear Zones ◽  
Fault Reactivation ◽  
Swiss Alps ◽  
Lateral Strain ◽  
Thrust Belts ◽  
Experimental Apparatus ◽  
Analogue Models ◽  
Fold And Thrust Belts ◽  
Multi Phase

<p>Shortening in fold-and-thrust belts can be accommodated with little or substantial basement involvement, with the former, thin-skinned, style arguably being the more common (Pfiffner, GSA Special Paper, 2006). Experimental studies on thin-skinned fold-and-thrust belts have confirmed critical taper theory and have highlighted the roles of bulk rheology, embedded weak layers, décollement strength, and surface processes in structural evolution. However, analogue models of thick-skinned fold-and-thrust belts are less common, which may be related to practical challenges involved in shortening thick layers of brittle materials. Here we focus on basement fault reactivation, which has been suggested for several fold-and-thrust belts, such as the Swiss Alps, the Laramide belt in North America and the Sierras Pampeanas in South America, which show evidence of deep-rooted thrust systems, pointing to a thick-skinned style of shortening.</p><p>Within an orogenic system, the shortening style may change between thin- and thick-skinned in space (foreland to hinterland) and time. This raises the question how inherited structures from one shortening phase may influence the next. We aim to use analogue experiments of multi-phase shortening to discuss the effects of deep-seated shortening-related inherited structures, such as thrusts and basement topography, on the structural evolution of fold-and-thrust belts.</p><p>We employ a push-type experimental apparatus that can impose shortening in both thick- and thin-skinned style. The device has two independently moving backstops, permitting to change between these shortening styles over time, allowing the simulation of multiple contractional scenarios. We start with an initial stage of thick-skinned shortening, followed by either thin- or thick-skinned reactivation. We use quartz sand to simulate crustal materials and microbeads for embedded weak (sedimentary) layers. Surface and lateral strain, as well as topography, is quantified using a high-resolution particle imaging velocimetry and digital photogrammetry monitoring system.</p><p>We will present preliminary results of this innovative experimental approach with the objective of discussing to what extent pre-existing conditions in the basement control the geometric, kinematic, and mechanical evolution of thick-skinned and basement-involved thin-skinned tectonics. In this presentation, we hope for a discussion of mechanisms of localisation of shortening in brittle analogue models, of sequences of thin- and thick-skinned deformation expected during multi-phase shortening, and comparisons to ongoing research and natural observations. Questions we aim to discuss are: Can weaknesses and anisotropies within the basement influence and control later structural evolution? Are pre-existing structures, such as thrusts or shear zones within the basement, responsible for subsequent fault nucleation, thin-skinned folding or basement uplift? What role does the rheology of the basement-cover interface play in the reactivation of basement thrusts? Can we model these reactivations with an analogue setup?</p>

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