scholarly journals Fault reactivation and strain partitioning across the brittle-ductile transition

Geology ◽  
2019 ◽  
Vol 47 (12) ◽  
pp. 1127-1130 ◽  
Author(s):  
Gabriel G. Meyer ◽  
Nicolas Brantut ◽  
Thomas M. Mitchell ◽  
Philip G. Meredith
Keyword(s):  
Fault Slip ◽  
Fault Reactivation ◽  
Ductile Deformation ◽  
Tectonic Deformation ◽  
Gradual Change ◽  
Bulk Rock ◽  
Total Deformation ◽  
Bulk Strain ◽  
Brittle Ductile Transition ◽  
Ductile Flow

Abstract The so-called “brittle-ductile transition” is thought to be the strongest part of the lithosphere, and defines the lower limit of the seismogenic zone. It is characterized not only by a transition from localized to distributed (ductile) deformation, but also by a gradual change in microscale deformation mechanism, from microcracking to crystal plasticity. These two transitions can occur separately under different conditions. The threshold conditions bounding the transitions are expected to control how deformation is partitioned between localized fault slip and bulk ductile deformation. Here, we report results from triaxial deformation experiments on pre-faulted cores of Carrara marble over a range of confining pressures, and determine the relative partitioning of the total deformation between bulk strain and on-fault slip. We find that the transition initiates when fault strength (σf) exceeds the yield stress (σy) of the bulk rock, and terminates when it exceeds its ductile flow stress (σflow). In this domain, yield in the bulk rock occurs first, and fault slip is reactivated as a result of bulk strain hardening. The contribution of fault slip to the total deformation is proportional to the ratio (σf − σy)/(σflow − σy). We propose an updated crustal strength profile extending the localized-ductile transition toward shallower regions where the strength of the crust would be limited by fault friction, but significant proportions of tectonic deformation could be accommodated simultaneously by distributed ductile flow.

scholarly journals Fluid-mediated, brittle–ductile deformation at seismogenic depth – Part 1: Fluid record and deformation history of fault veins in a nuclear waste repository (Olkiluoto Island, Finland)

Solid Earth ◽  
2019 ◽  
Vol 10 (3) ◽  
pp. 809-838 ◽  
Author(s):  
Barbara Marchesini ◽  
Paolo Stefano Garofalo ◽  
Luca Menegon ◽  
Jussi Mattila ◽  
Giulio Viola
Keyword(s):  
Fluid Inclusion ◽  
Strain Localization ◽  
Damage Zone ◽  
Fluid Pressure ◽  
Fault Reactivation ◽  
Ductile Deformation ◽  
Nuclear Waste Repository ◽  
Structural Level ◽  
Localized Deformation ◽  
Brittle Ductile Transition

Abstract. The dynamic evolution of fault zones at the seismogenic brittle–ductile transition zone (BDTZ) expresses the delicate interplay between numerous physical and chemical processes. Deformation and fluid flow at the BDTZ are closely related and mutually dependent during repeating and transient cycles of frictional and viscous deformation. Despite numerous studies documenting in detail seismogenic faults exhumed from the BDTZ, uncertainties remain as to the exact role of fluids in facilitating broadly coeval brittle and ductile deformation at that structural level. We combine structural analysis, fluid inclusion, and mineral chemistry data from synkinematic and authigenic minerals to reconstruct the temporal variations in fluid pressure (Pf), temperature (T), and bulk composition (X) of the fluids that mediated deformation and steered strain localization along BFZ300, a strike–slip fault originally active at the BDTZ. BFZ300 deforms the Paleoproterozoic migmatitic basement of southwestern Finland and hosts in its core two laterally continuous quartz veins formed by two texturally distinct types of quartz – Qtz I and Qtz II, with Qtz I older than Qtz II. Veins within the damage zone are formed exclusively by Qtz I. Mesostructural and microstructural analysis combined with fluid compositional data indicate recurrent cycles of mutually overprinting brittle and ductile deformation triggered by oscillations of fluid pressure peaking at 210 MPa. Fluid inclusion microthermometry and mineral pair geothermometry indicate that the two documented quartz types precipitated from different fluid batches, with bulk salinities in the 1 wt % NaCleq–5 wt % NaCleq range for Qtz I and in the 6 wt % NaCleq–11 wt % NaCleq range for Qtz II. The temperature of the fluids involved with initial strain localization and later fault reactivation evolved through time from > 350 ∘C during Qtz I precipitation to < 300 ∘C at the time of Qtz II crystallization. The peak fluid pressure estimates constrain pore pressure oscillations between 80 and 210 MPa during the recorded faulting episodes. Our results suggest variability of the physico-chemical conditions of the fluids steering deformation (Pf, T, X), reflecting the ingress and effects of multiple batches of fluid in the fault zone. Initial fluid-mediated embrittlement generated a diffuse network of joints and/or hybrid–shear fractures in the damage zone; subsequent strain localization led to more localized deformation within the fault core. Localization was guided by cyclically increasing fluid pressure and transient embrittlement of a system that was otherwise under overall ductile conditions. Our analysis suggests that fluid overpressure at the BDTZ can play a key role in the initial embrittlement of the deforming rock and steer subsequent strain localization.

Fault (un-)stability and strain partitioning across the brittle-ductile transition

2020 ◽  
Author(s):  
Jérôme Aubry ◽  
François Passelègue ◽  
Javier Escartín ◽  
Damien Deldicque ◽  
Julien Gasc ◽  
...  
Keyword(s):  
Plastic Strain ◽  
Axial Loading ◽  
Confining Pressure ◽  
Fault Slip ◽  
Ductile Deformation ◽  
Strain Partitioning ◽  
Brittle Deformation ◽  
Brittle Ductile Transition ◽  
Fault Roughness ◽  
Slow Earthquakes

&lt;p class=&quot;Abstract&quot;&gt;&lt;span lang=&quot;EN-US&quot;&gt;In the lithosphere, t&lt;span class=&quot;None&quot;&gt;he transition from brittle to ductile deformation corresponds to a regime where brittle fracturing and plastic flow coexist, called the semi-brittle deformation zone. Within these different regimes, a large fault slip spectrum has been observed, from fast to slow earthquakes. &lt;/span&gt;Studying &lt;span class=&quot;None&quot;&gt;the parameters &lt;/span&gt;controlling fault (un-)stability and strain partitioning across this &lt;span class=&quot;None&quot;&gt;transition is fundamental to understand how natural faults behave at varying crustal depths.&lt;/span&gt;&lt;/span&gt;&lt;/p&gt; &lt;p class=&quot;Abstract&quot;&gt;&lt;span lang=&quot;EN-US&quot;&gt;To investigate semi-brittle deformation and the conditions promoting it, we report here the results of experiments &lt;span class=&quot;None&quot;&gt;performed on Carrara marble saw-cut faults in triaxial conditions. We studied the influence of the confining pressure, axial loading rates and initial fault roughness on fault (un-)stability. From mechanical data, we performed strain partitioning calculations to infer elastic, frictional and plastic strain contributions during the deformation process. &lt;/span&gt;&lt;/span&gt;&lt;/p&gt; &lt;p class=&quot;Abstract&quot;&gt;&lt;span class=&quot;None&quot;&gt;&lt;span lang=&quot;EN-US&quot;&gt;We conclude that (laboratory) earthquakes may nucleate within a regime where homogeneous plastic deformation of the bulk and dynamic fault slip may coexist. The contribution of plastic strain is promoted with increasing confining pressure and fault roughness. &lt;/span&gt;&lt;/span&gt;&lt;/p&gt;

scholarly journals Fluid-mediated, brittle-ductile deformation at seismogenic depth: Part I – Fluid record and deformation history of fault-veins in a nuclear waste repository (Olkiluoto Island, Finland)

2019 ◽  
Author(s):  
Barbara Marchesini ◽  
Paolo Stefano Garofalo ◽  
Luca Menegon ◽  
Jussi Mattila ◽  
Giulio Viola
Keyword(s):  
Structural Analysis ◽  
Fluid Inclusion ◽  
Strain Localization ◽  
Damage Zone ◽  
Fluid Pressure ◽  
Ductile Deformation ◽  
Nuclear Waste Repository ◽  
Homogeneous State ◽  
Deformation History ◽  
Brittle Ductile Transition

Abstract. The dynamic evolution of fault zones at the seismogenic brittle-ductile transition zone (BDTZ) expresses the delicate interplay of numerous physical and chemical processes that occur at the time of strain localization. Deformation and flow of aqueous fluids in these zones, in particular, are closely related and mutually dependent during cycles of repeating, transient frictional and viscous deformation. Despite numerous studies documenting in detail seismogenic faults exhumed from the BDTZ, uncertainties remain as to the role of fluids in facilitating deformation in this zone, particularly with regard to the mechanics of broadly coeval brittle and ductile deformation. We combine here structural analysis, fluid inclusion data and mineral chemistry data from synkinematic and authigenic minerals to reconstruct the temporal variations in P, T and bulk composition of the fluids that mediated deformation and steered strain localization in a strike-slip fault from the BDTZ. This is a fault formed within the Paleoproterozoic migmatitic basement of southwestern Finland, hosting in its core two laterally continuous quartz veins formed by two texturally distinct quartz types – Qtz I and Qtz II, where Qtz I is demonstrably older than Qtz II. Veins within the diffuse damage zone of the fault are infilled by Qtz I. Multi-scalar structural analysis indicates recurrent cycles of mutually overprinting brittle and ductile deformation. Fluid inclusion microthermometry and mineral pair geothermometry indicate that both quartz types precipitated from a fluid that was in a homogeneous state during the recurrent cycles of faulting, and whose bulk salinity was in the 0–5 wt % NaCleq range. The temperature of the fluid phase involved with the various episodes of initial strain localization and later reactivation changed with time, from c. 240 °C in the damage zone to c. 350 °C in the core during Qtz I precipitation to < 200 °C at the time of Qtz II crystallization. Fluid pressure estimates show an oscillation in pore pressure comprised between 160 and 10 MPa during the fault activity stages. Our results suggest significant variability in the overall physical conditions during the fault deformation history, possibly reflecting the interaction of several batches of compositionally similar fluids ingressing the dilatant fault zone at different stages of its evolution, each with specific T and P conditions. Initial, fluid-mediated embrittlement of the faulted rock volume generated a diffuse network of joint and/or hybrid/shear fractures in the damage zone, whereas progressive strain localization led to more localized deformation within the fault core. Localization was guided by cyclically increasing fluid pressure and transient embrittlement of a system that was otherwise at overall ductile conditions. Our analysis implies that fluid overpressure at the brittle-ductile transition can play a key role in the initial embrittlment of the metamorphic basement and strain localization mechanisms.

scholarly journals The physics of fault friction: Insights from experiments on simulated gouges at low shearing velocities

2020 ◽  
Author(s):  
Berend A. Verberne ◽  
Martijn P. A. van den Ende ◽  
Jianye Chen ◽  
André R. Niemeijer ◽  
Christopher J. Spiers
Keyword(s):  
Granular Flow ◽  
Shear Bands ◽  
Active Regions ◽  
Strength Properties ◽  
Ductile Deformation ◽  
Unified Framework ◽  
Fault Rock ◽  
Brittle Ductile Transition ◽  
Wide Range ◽  
Individual Grains

Abstract. The strength properties of fault rocks at shearing rates spanning the transition from crystal-plastic flow to frictional slip play a central role in determining the distribution of crustal stress, strain and seismicity in tectonically-active regions. We review experimental and microphysical modelling work aimed at elucidating the processes that control the transition from pervasive ductile flow of fault rock to rate-and-state dependent frictional (RSF) slip and to runaway rupture, carried out at Utrecht University in the past two or so decades. We address shear experiments on simulated gouges composed of calcite, halite-phyllosilicate mixtures, and phyllosilicate-quartz mixtures, performed under laboratory conditions spanning the brittle-ductile transition. With increasing shear rate (or decreasing temperature), the results consistently show transitions from (1) stable, velocity(v)-strengthening to potentially unstable, v-weakening behavior, and (2) back to v-strengthening. Sample microstructures show that the first transition, seen at low shear rates and/or high temperatures, represents a switch from pervasive, fully ductile deformation to frictional sliding, involving dilatant granular flow in localized shear bands, where intergranular slip is incompletely accommodated by creep of individual mineral grains. A recent microphysical model, treating fault rock deformation as controlled by a competition between rate-sensitive (diffusional or crystal-plastic) deformation of individual grains and rate-insensitive sliding interactions between grains (granular flow), predicts both transitions well. Unlike classical RSF approaches, this model quantitatively reproduces a wide range of (transient) frictional behaviors using input parameters with direct physical meaning. When implemented in numerical codes for crustal fault-slip, it offers a single, unified framework for understanding slip patch nucleation and growth to critical (seismogenic) dimensions, and for simulating the entire seismic cycle.

Extrinsic anisotropy of two-phase Newtonian aggregates: fabric characterisation and parametrisation, and application to global mantle convection.

2021 ◽  
Author(s):  
Albert de Montserrat Navarro ◽  
Manuele Faccenda ◽  
Giorgio Pennacchioni
Keyword(s):  
Mantle Convection ◽  
Flow Direction ◽  
Thin Layers ◽  
Ductile Deformation ◽  
Mechanical Anisotropy ◽  
Two Phase ◽  
Bulk Strain ◽  
Wide Range ◽  
Mechanical Models ◽  
Cell Shapes

&lt;p&gt;&lt;span&gt;Rocks of the Earth's crust and mantle commonly consist of aggregates of different minerals with contrasting mechanical properties. During progressive, high temperature (ductile) deformation, these rocks tend to develop an extrinsic mechanical anisotropy related to the strain competition of the different minerals, the amount of accumulated bulk strain and the bulk strain geometry. Extrinsic anisotropy is thought to play an important role in a wide range of geodynamic processes up to the scale of mantle convection. However, the evolution of grain-scale and rock-scale associated with this anisotropy cannot be directly implemented in large-scale numerical simulations. For two-phase aggregates -a good rheological approximation of most Earth's rocks- we propose a methodology to indirectly approximate the extrinsic viscous anisotropy by a combination of (i) 3-D mechanical models of rock fabrics, and (ii) analytical effective medium theories. The resulting 3-D mechanical models, confirm that the weak least abundant phase induces substantial rock weakening by forming an inter-connected network of thin layers in the flow direction. 3-D models further suggest, however, that the lateral inter-connection of these weak layers is quite limited, and the maximum structural weakening is considerably less than previously estimated. &lt;/span&gt;&lt;span&gt;Ont the other hand,&lt;/span&gt;&lt;span&gt; presence of hard inclusions does not have a profound impact in the effective strength of the aggregate, &lt;/span&gt;&lt;span&gt;with&lt;/span&gt;&lt;span&gt; lineations develop&lt;/span&gt;&lt;span&gt;ing only&lt;/span&gt;&lt;span&gt; at relatively low compositional strength contrast. When rigid inclusions become clogged, however, the aggregate viscous resistance can increase over the theoretical upper bound. We show that the modelled grain-scale fabrics can be parameterised as a function of the bulk deformation and material phase properties and can be combined with analytical solutions to approximate the anisotropic viscous tensor. &lt;/span&gt;&lt;span&gt;At last, the resulting parameterisation &lt;/span&gt;&lt;span&gt;of the extrinsic viscous tensor &lt;/span&gt;&lt;span&gt;is implemented in a bi-dimensional global mantle convection code&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;Preliminary results show that extrinsic is responsible for an increase of the upwelling speed of hot material from the lowermost mantle, &lt;/span&gt;&lt;span&gt;different convective cell shapes&lt;/span&gt;&lt;span&gt;, and deflection of mantle plumes at the uppermost mantle.&lt;/span&gt;&lt;/p&gt;

Integrated Reservoir Geomechanics Approach for Reservoir Management

2021 ◽  
Author(s):  
Vai Yee Hon ◽  
M Faizzudin Mat Piah ◽  
Noor 'Aliaa M Fauzi ◽  
Peter Schutjens ◽  
Binayak Agarwal ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Water Injection ◽  
Fluid Pressure ◽  
Integrated Approach ◽  
Fault Slip ◽  
Fault Reactivation ◽  
Analytical Models ◽  
Reservoir Compaction ◽  
Stress Changes ◽  
Reservoir Geomechanics

Abstract An integrated 3D dynamic reservoir geomechanics model can provide a diverse 3D view of depletion-injection-induced field stress changes and the resulting deformation of both reservoir and overburden formations at various field locations. It enables the assessment of reservoir compaction, platform site subsidence, fault reactivation and caprock integrity associated with multiple production and injection reservoirs of the field. We demonstrated this integrated approach for a study field located in the South China Sea, Malaysia, which is planned for water injection for pressure support and EOR scheme thereafter. Reservoir fluid containment during water injection is an important concern because of the intensive geologic faulting and fracturing in the collapsed anticlinal structure, with some faults extending from the reservoirs to shallow depths at or close to the seafloor. Over 30 simulations were done, and most input parameters were systematically varied to gain insight in their effect on result that was of most interest to us: The tendency of fault slip as a function of our operation-induced variations in pore pressure in the reservoir rocks bounding the fault, both during depletion and injection. The results showed that depletion actually reduces the risk of fault slip and of the overburden, while injection-induced increase in pore fluid pressure will lead to a significant increase in the risk of fault slip. Overall, while depletion appears to stabilize the fault and injection appears to destabilize the fault, no fault slip is predicted to occur, not even after a 900psi increase in pore pressure above the pore pressure levels at maximum depletion. We present the model results to demonstrate why depletion and injection have such different effects on fault slip tendency. The interpretation of these geomechanical model results have potential applications beyond the study field, especially for fields with a similar geology and development plan. This is a novel application of 3D dynamic reservoir geomechanics model that cannot be obtained from 1D analytical models alone.

scholarly journals Superposed Sedimentary and Tectonic Block-In-Matrix Fabrics in a Subducted Serpentinite Mélange (High-Pressure Zermatt Saas Ophiolite, Western Alps)

Geosciences ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 358 ◽  
Author(s):  
Tartarotti ◽  
Guerini ◽  
Rotondo ◽  
Festa ◽  
Balestro ◽  
...  
Keyword(s):  
Western Alps ◽  
Ocean Basin ◽  
Transport Processes ◽  
Ductile Deformation ◽  
Geodynamic Setting ◽  
Tectonic Deformation ◽  
Tectonic Block ◽  
Rock Unit ◽  
Deformation Partitioning ◽  
Stratigraphic Succession

The primary stratigraphic fabric of a chaotic rock unit in the Zermatt Saas ophiolite of the Western Alps was reworked by a polyphase Alpine tectonic deformation. Multiscalar structural criteria demonstrate that this unit was deformed by two ductile subduction-related phases followed by brittle-ductile then brittle deformation. Deformation partitioning operated at various scales, leaving relatively unstrained rock domains preserving internal texture, organization, and composition. During subduction, ductile deformation involved stretching, boudinage, and simultaneous folding of the primary stratigraphic succession. This deformation is particularly well-documented in alternating layers showing contrasting deformation style, such as carbonate-rich rocks and turbiditic serpentinite metasandstones. During collision and exhumation, deformation enhanced the boudinaged horizons and blocks, giving rise to spherical to lozenge-shaped blocks embedded in a carbonate-rich matrix. Structural criteria allow the recognition of two main domains within the chaotic rock unit, one attributable to original broken formations reflecting turbiditic sedimentation, the other ascribable to an original sedimentary mélange. The envisaged geodynamic setting for the formation of the protoliths is the Jurassic Ligurian-Piedmont ocean basin floored by mostly serpentinized peridotites, intensely tectonized by extensional faults that triggered mass transport processes and turbiditic sedimentation.

scholarly journals FTIR and Raman Spectral Research on Metamorphism and Deformation of Coal

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Xiaoshi Li ◽  
Yiwen Ju ◽  
Quanlin Hou ◽  
Zhuo Li ◽  
Junjia Fan
Keyword(s):  
Structural Evolution ◽  
Tectonic Stress ◽  
Ductile Deformation ◽  
Frictional Heat ◽  
Structural Defects ◽  
Tectonic Deformation ◽  
Macromolecular Structure ◽  
Brittle Deformation ◽  
Metamorphic Stage ◽  
The Stability

Under different metamorphic environments, coal will form different types of tectonically deformed coal (TDC) by tectonic stress and even the macromolecular structure can be changed. The structure and composition evolution of TDC have been investigated in details using Fourier transform infrared spectroscopy and Raman spectroscopy. The ductile deformation can generate strain energy via increase of dislocation in molecular structure of TDC, and it can exert an obvious influence on degradation and polycondensation. The brittle deformation can generate frictional heat energy and promote the metamorphism and degradation, but less effect on polycondensation. Furthermore, degradation affects the structural evolution of coal in lower metamorphic stage primarily, whereas polycondensation is the most important controlling factor in higher metamorphic stage. Tectonic deformation can produce secondary structural defects in macromolecular structure of TDC. Under the control of metamorphism and deformation, the small molecules which break and fall off from the macromolecular structure of TDC are replenished and embedded into the secondary structural defects preferentially and form aromatic rings by polycondensation. These processes improved the stability of macromolecular structure greatly. It is easier for ductile deformation to induce secondary structural defects than in brittle deformation.

Mapping Tectonic Deformation in the Crust and Upper Mantle Beneath Europe and the North Atlantic Ocean

Science ◽  
2013 ◽  
Vol 341 (6148) ◽  
pp. 871-875 ◽  
Author(s):  
Hejun Zhu ◽  
Jeroen Tromp
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Three Dimensional ◽  
Surface Strain ◽  
Tectonic Deformation ◽  
Crust And Upper Mantle ◽  
The North ◽  
Ductile Flow ◽  
The North Atlantic

We constructed a three-dimensional azimuthally anisotropic model of Europe and the North Atlantic Ocean based on adjoint seismic tomography. Several features are well correlated with historical tectonic events in this region, such as extension along the North Atlantic Ridge, trench retreat in the Mediterranean, and counterclockwise rotation of the Anatolian Plate. Beneath northeastern Europe, the direction of the fast anisotropic axis follows trends of ancient rift systems older than 350 million years, suggesting “frozen-in” anisotropy related to the formation of the craton. Local anisotropic strength profiles identify the brittle-ductile transitions in lithospheric strength. In continental regions, these profiles also identify the lower crust, characterized by ductile flow. The observed anisotropic fabric is generally consistent with the current surface strain rate measured by geodetic surveys.

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