Corrigendum to “Influence of shear heating on microstructurally defined plate boundary shear zones” [J. Struct. Geol. 79 (2015), 80–89]

ABSTRACTLeucogranites are typical products of collisional orogenies. They are found in orogenic terranes of different ages, including the Proterozoic Trans-Hudson orogen, as exemplified in the Black Hills, South Dakota, and the Appalachian orogen in Maine, both in the USA, and the ongoing Himalayan orogen. Characteristics of these collisional leucogranites show that they were derived from predominantly pelitic sources at the veining stages of deformation and metamorphism in upper plates of thickened crusts. Once generated, the leucogranite magmas ascended as dykes and were emplaced within shallower parts of their source sequences. In these orogenic belts, there was a strong connection between deformation, metamorphism and granite generation. However, the heat sources needed for partial melting of the source rocks remain controversial. Lack of evidence for significant intrusion of mafic magmas necessary to cause melting of upper plate source rocks suggests that leucogranite generation in collisional orogens is mainly a crustal process.The present authors evaluate five types of thermal models which have previously been proposed for generating leucogranites in collisional orogens. The first, a thickened crust with exponentially decaying distribution of heat-producing radioactive isotopes with depth, has been shown to be insufficient for heating the upper crust to melting conditions. Four other models capable of raising the crustal temperatures sufficiently to initiate partial melting of metapelites in thickened crust include: (1) thick sequences of sedimentary rocks with high amounts of internal radioactive heat production; (2) decompression melting; (3) thinning of mantle lithosphere; and (4) shear-heating. The authors show that, for reasonable boundary conditions, shear-heating along crustal-scale shear zones is the most viable process to induce melting in upper plates of collisional orogens where pelitic source lithologies are usually located. The shear-heating model directly links partial melting to the deformation and metamorphism that typically precede leucogranite genera

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Tectonic modelling state of the art and future challenges

10.5194/egusphere-egu21-14923 ◽

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

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).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. &#160;As a result, tectonicists cannot use commercial packages to simulate their problems and need to develop methodologies specific to their field.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.Since the late 80&#8217;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&#8217;s early 2000 simulations and is still very costly because the treatment of &#8220;brittle&#8221; rheology seriously amped code performances.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. &#160;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&#8217;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 resultsI 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.

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The internal structure and composition of a plate boundary-scale serpentinite shear zone: The Livingstone Fault, New Zealand

10.5194/se-2019-62 ◽

2019 ◽

Author(s):

Matthew S. Tarling ◽

Steven A. F. Smith ◽

James M. Scott ◽

Jeremy S. Rooney ◽

Cecilia Viti ◽

...

Keyword(s):

New Zealand ◽

Internal Structure ◽

Shear Zone ◽

Plate Boundary ◽

Shear Zones ◽

East Side ◽

Local Dispersion ◽

Fine Grained ◽

Shear Sense ◽

Tectonic Settings

Abstract. Deciphering the internal structural and composition of large serpentinite-dominated shear zones will lead to an improved understanding of the rheology of the lithosphere in a range of tectonic settings. The Livingstone Fault in New Zealand is a > 1000 km long terrane-bounding structure that separates the basal portions (peridotite; serpentinised peridotite; metagabbros) of the Dun Mountain Ophiolite Belt from quartzofeldspathic schists of the Caples or Aspiring Terranes. Field and microstructural observations from eleven localities along a strike length of c. 140 km show that the Livingstone Fault is a steeply-dipping, serpentinite-dominated shear zone tens to several hundreds of metres wide. The bulk shear zone has a pervasive scaly fabric that wraps around fractured and faulted pods of massive serpentinite, rodingite and partially metasomatised quartzofeldspathic schist up to a few tens of metres long. S-C fabrics and lineations in the shear zone consistently indicate a steep Caples-side-up (i.e. east-side-up) shear sense, with significant local dispersion in kinematics where the shear zone fabrics wrap around pods. The scaly fabric is dominated (> 98 vol %) by fine-grained (&ll; 10 μm) fibrous chrysotile and lizardite/polygonal serpentine, but infrequent (

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Strain localization by shear heating and the development of lithospheric shear zones

Tectonophysics ◽

10.1016/j.tecto.2019.05.010 ◽

2019 ◽

Vol 764 ◽

pp. 62-76 ◽

Cited By ~ 1

Author(s):

Katy Willis ◽

Gregory A. Houseman ◽

Lynn Evans ◽

Tim Wright ◽

Andrew Hooper

Keyword(s):

Strain Localization ◽

Shear Zones ◽

Shear Heating

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Rapid fluid-driven transformation of lower continental crust associated with thrust-induced shear heating

10.5194/egusphere-egu2020-2154 ◽

2020 ◽

Author(s):

Bjørn Jamtveit ◽

Kristina G. Dunkel ◽

Arianne Petley-Ragan ◽

Fernando Corfu ◽

Dani W. Schmid

Keyword(s):

Regional Metamorphism ◽

Shear Zones ◽

Amphibolite Facies ◽

Source Rocks ◽

Granitic Rocks ◽

Time Interval ◽

Fluid Infiltration ◽

Facies Metamorphism ◽

Shear Heating ◽

Host Rocks

Caledonian eclogite- and amphibolite-facies metamorphism of initially dry Proterozoic granulites in the Lind&#229;s Nappe of the Bergen Arcs, Western Norway, is driven by fluid infiltration along faults and shear zones. The granulites are also cut by numerous dykes and pegmatites that are spatially associated with metamorphosed host rocks. U-Pb geochronology was performed to constrain the age of fluid infiltration and metamorphism. The ages obtained demonstrate that eclogite- and amphibolite-facies metamorphism were synchronous within the uncertainties of our results and occurred within a maximum time interval of 5 Myr, with a mean age of ca. 426 Ma. &#160;Caledonian dykes and pegmatites are granitic rocks characterised by a high Na/K-ration, low REE-abundance and positive anomalies of Eu, Ba, Pb, and Sr. The most REE-poor compositions show HREE-enrichment. Melt compositions are consistent with wet melting of plagioclase- and garnet-bearing source rocks. The most likely fluid source is dehydration of Paleozoic metapelites, located immediately below the Lind&#229;s part of the Jotun-Lind&#229;s microcontinent, during eastward thrusting over the extended margin of Baltica. Melt compositions and thermal modelling suggest that short-lived fluid-driven metamorphism of the Lind&#229;s Nappe granulites was related to shear heating at lithostatic pressures in the range 1.0-1.5 GPa. High-P (&#8776;2 GPa) metamorphism within the Nappe was related to weakening-induced pressure perturbations, not to deep burial. Our results emphasize that both prograde and retrograde metamorphism may proceed rapidly during regional metamorphism and that their time-scales may be coupled through local production and consumption of fluids.

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The emplacement mode of Upper Cretaceous plutons from the southwestern part of the Sredna Gora Zone (Bulgaria): structural and AMS study

Geologica Carpathica ◽

10.2478/v10096-009-0001-8 ◽

2009 ◽

Vol 60 (1) ◽

pp. 15-33 ◽

Cited By ~ 16

Author(s):

Neven Georgiev ◽

Bernard Henry ◽

Neli Jordanova ◽

Nikolaus Froitzheim ◽

Diana Jordanova ◽

...

Keyword(s):

Magnetic Susceptibility ◽

Shear Zone ◽

Upper Cretaceous ◽

Plate Boundary ◽

Shear Zones ◽

Anisotropy Of Magnetic Susceptibility ◽

Southwestern Part ◽

Structural Investigations ◽

Plate Convergence ◽

Microgranular Enclaves

The emplacement mode of Upper Cretaceous plutons from the southwestern part of the Sredna Gora Zone (Bulgaria): structural and AMS study Several plutons located in the southwestern part of the Sredna Gora Zone — Bulgaria are examples of the Apuseni-Banat-Timok-Sredna Gora type of granites emplaced during Late Cretaceous (86-75 Ma) times. The studied intrusive bodies are spatially related to and deformed by the dextral Iskar-Yavoritsa shear zone. The deformation along the shear zone ceased at the time of emplacement of the undeformed Upper Cretaceous Gutsal pluton, which has intruded the Iskar-Yavoritsa mylonites. A clear transition from magmatic foliation to high-, moderate- and low-temperature superimposed foliation and lineation in the vicinity of the Iskar-Yavoritsa and related shear zones gives evidence for simultaneous tectonics and plutonism. Away from the shear zones, the granitoids appear macroscopically isotropic and were investigated using measurements of anisotropy of magnetic susceptibility at 113 stations. The studied samples show magnetic lineation and foliation, in agreement with the magmatic structures observed at a few sites. Typical features of the internal structure of the plutons are several sheet-like mafic bodies accompanied by swarms of mafic microgranular enclaves. Field observations indicate spatial relationships between mafic bodies and shear zones as well as mingling processes in the magma chamber which suggest simultaneous shearing and magma emplacement. Structural investigations as well as anisotropy of magnetic susceptibility (AMS) data attest to the controlling role of the NWSE trending Iskar-Yavoritsa shear zone and to the syntectonic emplacement of the plutons with deformation in both igneous rocks and their hosts. The tectonic situation may be explained by partitioning of oblique plate convergence into plate-boundary-normal thrusting in the Rhodopes and plate-boundary-parallel transcurrent shearing in the hinterland (Sredna Gora).

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A lifetime of the Variscan orogenic plateau from uplift to collapse as recorded by the Prague Basin, Bohemian Massif

Geological Magazine ◽

10.1017/s0016756817000875 ◽

2017 ◽

Vol 156 (3) ◽

pp. 485-509 ◽

Cited By ~ 3

Author(s):

FRANTIŠEK VACEK ◽

JIŘÍ ŽÁK

Keyword(s):

Bohemian Massif ◽

Three Dimensional ◽

Plate Boundary ◽

Early Carboniferous ◽

Shear Zones ◽

Crustal Thickening ◽

Variscan Orogeny ◽

Prague Basin ◽

Lateral Extrusion ◽

Orogenic Plateau

AbstractThe Ordovician to Middle Devonian Prague Basin, Bohemian Massif, represents the shallowest crust of the Variscan orogen corresponding toc.1–4 km palaeodepth. The basin was inverted and multiply deformed during the Late Devonian to early Carboniferous Variscan orogeny, and its structural inventory provides an intriguing record of complex geodynamic processes that led to growth and collapse of a Tibetan-type orogenic plateau. The northeastern part of the Prague Basin is a simple syncline cross-cut by reverse/thrust faults and represents a doubly vergent compressional fan accommodatingc.10–19 % ~NW–SE shortening, only minor syncline axis-parallel extension and significant crustal thickening. The compressional structures were locally overprinted by vertical shortening, kinematically compatible with ductile normal shear zones that exhumed deep crust in the orogen's interior atc. 346–337 Ma. On a larger scale, the deformation history of the Prague Syncline is consistent with building significant palaeoelevation during Variscan plate convergence. Based on a synthesis of finite deformation parameters observed across the upper crust in the centre of the Bohemian Massif, we argue for a differentiated within-plateau palaeotopography consisting of domains of local thickening alternating with topographic depressions over lateral extrusion zones. The plateau growth, involving such complex three-dimensional internal deformations, was terminated by its collapse driven by multiple interlinked processes including gravity, voluminous magma emplacement and thermal softening in the hinterland, and far-field plate-boundary forces resulting from the relative dextral motion of Gondwana and Laurussia.

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Results from a systematic analysis of fully coupled Thermo-Hydro-Mechanical-Chemical rock models

10.5194/egusphere-egu2020-12896 ◽

2020 ◽

Author(s):

Celso Alvizuri ◽

Yury Podladchikov

Keyword(s):

Strain Rate ◽

Parameter Space ◽

Rheological Model ◽

Grid Point ◽

Shear Zones ◽

Spontaneous Generation ◽

Background Strain ◽

Model Instance ◽

Shear Heating ◽

Fully Coupled

The rheology/mechanical behavior of rock is controlled by several processes including thermal, hydraulic, mechanical, and chemical conditions. (Braeck et al., 2009; Kiss et al., 2019)We conduct a systematic parametric study within a fully coupled Thermo-Hydro-Mechanical-Chemical (THMC) numerical rheological model to identify regions of stable and unstable (brittle?) deformation. The rheological model assumes incompressible viscous deformation and is governed by the equations of conservation of mass, linear momentum, and energy; a constitutive equation, and a creep flow law. Three parameters control the deformation: background strain rate, shear heating, and a Brinkman number that captures the interplay between viscosity and temperature.We setup a grid of points using these parameters, use each grid point as a starting instance of the rheological model, and let each instance evolve with time. We are able to perform a fine-grained study of the parameter space by using a high-performance GPU cluster. Our initial results show that the background strain rate requires relatively low values (near 1) for the computation to remain stable. While keeping a constant (low) strain rate, we next observe how each model instance evolves with respect to shear heating and Brinkman values. This approach allow us to map stable/unstable regions in the 3-parameter space.&#160;Next we analyze the rheological conditions of each model instance (in the stable and unstable regions) and its potential as a rock-weakening mechanism.References Braeck, S., Podladchikov, Y., & Medvedev, S., 2009. Spontaneous dissipation of elastic energy by self-localizing thermal runaway, Phys. Rev. E , 80, 046105, doi:10.1103/PhysRevE.80.046105.Kiss, D., Podladchikov, Y., Duretz, T., & Schmalholz, S., 2019. Spontaneous generation of ductile shear zones by thermal softening: Localization criterion, 1D to 3D modelling and application to the lithosphere, Earth Planet. Sci. Lett., 519, 284&#8211;296, doi:10.1016/j.epsl.2019.05.026.

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