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The Koyna region, located in Western India, is a region of recurrent triggered seismicity that started post-impoundment of the Koyna Dam in 1962. Though previous studies have established a relationship between recurrent seismicity and the water level of the Koyna reservoir, little is understood about the possible role of the reservoir water in triggering seismic activity in the region. In the present study, mesoscopic and micro-structural studies of core samples from the basement granitoids provide evidence of fracture networks for fluid percolation and chemical alteration at depth. Salient findings are as follows: (1) presence of brittle deformation features such as fault breccias, fractures, fracture networks, and faults, which can act as water pathways, (2) presence of a cataclastic zone that may act as an impermeable zone and thus prohibit percolation of water thereof, acting as a potential storage area for fluids, in turn promoting dissolution and alteration of minerals, (3) evidence of the presence of fluid such as Fe-staining along fractures and occurrences of secondary precipitation such as calcite, and silica, and alterations such as epidote, chlorite along fractures and networks of mineral veins of epidote and chlorite, (4) low values of Sr and Ba at depth constitute direct evidence of hydrous alteration, (5) presence of fractures and fracture networks in microscopic scale in the thin sections prepared from the apparently intact part of the core signify that fracture networks might be persistent at all depths although it may not appear in mesoscale. Together with the strong correlation between earthquake activity and water levels of the Koyna reservoir and confirmation of the extension of surface fissure and fracture zone to the basement granitoids as brought out by previous studies, the present study provides compelling evidence in support of the percolation of water to the seismogenic depths. So, the weakening of pre-existing fault planes due to the chemical effects of water and an increase in the pore pressure by water infiltration may increase instability that may lead to a movement along the pre-existing faults, and aid repeated seismic slips in the region. Research highlights: The article presents a comprehensive overview of the reservoir-triggered seismicity observed after the impoundment of the Koyna Dam. The study focuses on the role of subsurface infiltration of water from the reservoir to seismogenic depths that may help in facilitating short-term, low-magnitude earthquakes in the region. The design of the article is straightforward; it primarily focuses on reporting the meso- to microstructural observations that bear the evidence of fluid-induced physicochemical alterations of the basement rock, followed by a qualitative discussion on the role of the fluid that may have weakened the pre-existing deformation signatures. The present study provides compelling evidence in support of the percolation of water to the basement granite, thereby increasing pore pressure, and the long-term chemical effects over the fault plane may aid in instability of the fault that may lead to a movement along pre-existing faults, and aid repeated seismic slips in the region. [ABSTRACT FROM AUTHOR]

In the Earth's upper crust, rocks deform mostly by means of brittle fracturing processes. At the micro‐scale these processes involve the formation and growth of microcracks in the vicinity of defects such as open fissures, pores and other cavities. Large defects can produce strong enough perturbations of the stress field to activate and/or intensify brittle damage around them. Here we considered the ideal cases of smooth cylindrical and spherical pores inside an infinite solid body subjected to remote triaxial compressive stresses (i.e., the intermediate and minimum principal stresses are assumed equal). We first established the resulting local stress field around one of those large pores and then verified whether certain brittle damage processes could be activated in these conditions. We mainly considered the formation of tensile microcracks and micro shear bands. The former requires the presence of tensile stresses in some regions around the pore, while the latter needs sufficiently large shear stresses on pre‐existing optimally inclined microcracks to overcome their frictional resistance to sliding. We find that shear driven deformation remains localized in the vicinity of the pore. On the other hand, dilatational, tensile cracks can propagate large distances away from the pore but cannot form at and above some threshold ratio of the least to the largest principal stresses. Faulting associated with interacting tensile cracks is therefore suppressed with increasing depth. Our analysis leads to conclusions generally consistent with published experimental observations and provides some clues to discuss the physical cause of the brittle‐ductile transition in rocks. Plain Language Summary: Rocks close to Earth's surface contain various pores and gas or fluid‐filled voids surrounded by the solid rock matrix. As the rock masses are stressed by tectonic motions, these pores can perturb the local stress field and intensify damage and deformation in their vicinity. In this contribution, we derive the stress fields surrounding large cylindrical and spherical pores and study the brittle damage processes that could be activated. We find that dilatational, tensile cracking can propagate large distances away from the pores but is suppressed with increasing pressure, corresponding to increasing depth at which rocks deform. Importantly, tensile cracking ceases to be possible at some threshold ratio of the least principal stress to the largest principal stress. Other brittle deformation processes driven by shear instead of tensile stresses such as formation of micro shear bands take over at these conditions. However these shear bands cannot extend far away from the pores, thus limiting deformation to the vicinity of the pores. Our model is consistent with experimental observations and provides insights on the physical cause of delocalization of deformation with increasing depth in nature. Key Points: Tensile cracks propagate larger distances away from the pore walls than brittle micro shear bandsTensile stresses around pores cease to exist at a threshold ratio of the least to the largest principal stresses, σ3/σ1 (>1/3 in 2D)The suppression of tensile cracking and consequent delocalization of deformation helps to explain the "brittle‐ductile" transition in rocks [ABSTRACT FROM AUTHOR]

In this work, the multiple inversion method and a field collection of brittle deformation markers were used to assess the paleo-stress in the Koleh Sangi deformed area to the north of Zahedan. The features of fault surfaces and associated slickenside were gathered for this purpose from different sites. The principal stress values and stress ellipse shape for each location were determined using MIM software and the multiple inversion method. Drawing diagrams and analyzing figures demonstrates the influence of several tectonic phases throughout the region's, including three compressional phase 1) N84°E compressional phase 2) Compressive N59°E phase that youngest rocks impacted. 3) N10 compressive phase, which compatible with Major fault in this region. 4) The The youngest phase reveal a transtension regime. In other words, in the studied area, a compressive phase has worked with the change of the northeast-southwest trend from old to new. This indicates a counter-clockwise rotation from N84 degrees in to N59 and then to N10 degrees, which can be attributed to the convergence of the Arabian plate with Eurasia. The compressive phase was followed by a transtension regime with a northwestsoutheast trend, which impacted by the Zahedan fault. [ABSTRACT FROM AUTHOR]

Brittle deformation is prevalent in both geological processes and engineered structures, so probing its actions is an important task as much for Earth materials and engineered ones. To characterize brittle deformation, acoustic waves are especially useful in revealing deformation processes. To promote the use of acoustic techniques, we present an integrated characterization approach that includes both acoustic data collection and analysis. By customizing a rock sample and acoustic sensor assembly, we incorporate acoustic data acquisition into a core holder system that accommodates relatively small samples (2.54 cm diameter) under triaxial loading. Along with fast and high-resolution acoustic waveform recording, the compact design facilitates convenient collection of high-quality acoustic data. To meet the challenge of efficiently and accurately picking P-wave arrivals for hundreds of thousands of acoustic waveforms, we modified and implemented a deep neural network model from the seismology literature called PhaseNet. After training with an augmented dataset of manually-picked arrivals (a total of around 50,000 waveforms), the modified PhaseNet model achieved more than 88% (96%) picking accuracy within ±1 μs (±2 μs) time residual relative to manual picks. This demonstrates the potential of integrating deep learning techniques into the workflow of acoustic data analysis for rapid and accurate extraction of valuable information from a large acoustic dataset. Finally, we conducted high-resolution micro-computed tomography (micro-CT) to inform and complement acoustic characterization at micron- and centimeter-scales. Microscopic observations validate the spatial development of two macroscopic fractures, and suggest that deformation-induced changes in velocity need to be incorporated for accurately locating microcracking events. Thus, integrating acoustic monitoring, a deep neural network, and micro-CT imaging offers an effective means to understand brittle deformation from micro to centimeter scales.

We study the deformation features preserved in basement granitoids recovered by scientific core drilling from an active seismic zone in the Koyna region, Deccan Traps, India. The region is characterized by recurrent reservoir triggered seismicity for the past 55 years, including the 1967 M6.3 Koyna earthquake, which produced the Donichawadi fissure zone. We investigate the basement granitoids down to a depth of 1.5 km in a set of four boreholes. Salient findings are as follows: (1) Basement rocks are composed of granite, granite-gneiss and migmatitic gneiss, characterized by greenschist to amphibolite facies metamorphism, (2) Distinctive brittle deformation features, such as fault breccias, fault gouge, prominent slickenlines and slickensides on fractures and pseudotachylites indicate proximity to a fault zone, (3) Fault zones are enriched with secondary precipitations of ferruginous and calcium-rich material which are the evidences of fluid-filled fractures at depth, (4) Fault breccia and gouge are preserved along with intense shattering of cores in zones of near-vertical fractures. Combined with information from downhole geophysical logs in a 3 km deep scientific borehole and the distribution of hypocentres, the study provides strong constraints for the subsurface extension of the Donichawadi fissure zone that is active to this day. The new datasets provide evidence for multiple episodes of fracturing and fault rock formation in an intraplate, near-vertical, fault zone and chemical changes of the fault rocks in the presence of water at seismogenic depth. [ABSTRACT FROM AUTHOR]

Abstract Structural studies carried out on mesoscopic scale of planar and linear brittle structures from quarries in Precambrian rocks of the central-southern portion of the Catarinense Shield led to a characterization of four main fault directions: NE-SW, NW-SE and some around N-S and E-W. The older dextral (~ N-S) and sinistral (~ E-W) strike-slip faults are explained through a paleostress field approximately NE-SW oriented. The younger dextral (NE-SW) and sinistral (NW) strike-slip faults are compatible with an approximately E-W oriented paleostress field. The oldest event fits between the Cretaceous and Cenozoic and the younger event fits between the Neogene and Quaternary.

Fault zones in porous siliciclastic rocks can be dominated by deformation bands (DBs), which are small-scale tabular structures that usually occur as cluster features. DBs can reduce permeability, contributing to the compartmentalization of oil reservoirs and aquifers. DBs cannot be imaged by seismic methods, but can be imaged by Ground-penetrating radar (GPR). Although DBs and host rocks share the same lithology, GPR imaging is possible because DBs can cause small vertical offsets and reduce the amplitude of the GPR signals. We present an automatic approach for extracting the three-dimensional (3D) architecture of DBs from GPR cubes using multiattribute analysis. We used a 200 MHz GPR cube surveyed on an outcrop of a sandstone formation highly impacted by DBs in the Rio do Peixe Basin, northeastern Brazil. The multiattribute analysis is based on edge evidence and sequential ant-tracking, a combination that can identify narrow zones of attenuated GPR signals. Furthermore, the 3D architecture of DBs was extracted as a geobody using an opacity balancing operator. The geological reliability and limitations of the geobody were demonstrated by comparing slices of the geobody with images of exposed DBs in similar positions, in addition to structural measurements obtained in field and in the geobody. • An outcrop of a sandstone highly impacted by deformation bands was selected. • A 200 MHz Ground Penetrating Radar cube was surveyed in the outcrop. • Deformation bands appear as small offsets and/or reduced amplitude events. • A multi-attribute workflow is designed to extract deformation bands as a geobody. • Reliability of the geobody is shown by comparing its slices with photographs. [ABSTRACT FROM AUTHOR]

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We have investigated the deformation history of the Keszthely Hills (Transdanubian Range, W Hungary), which belongs to the uppermost slice of the Austroalpine nappe system. This Upper Triassic to Upper Miocene sedimentary rock sequence documented the deformation of the upper crust during repeated rifting and inversion events. We investigated the structural pattern and stress field evolution of this multistage deformation history by structural data collection and evaluation from surface outcrops. Regarding the Mesozoic deformations, we present additional arguments for pre-orogenic (Triassic and Jurassic) extension (D1 and D2 phases), which is mainly characterized by NE–SW extensional structures, such as syn-sedimentary faults, slump-folds, and pre-tilt conjugate normal fault pairs. NW–SE-striking map-scale normal faults were also connected to these phases. The inversion of these pre-orogenic structures took place during the middle part of the Cretaceous; however, minor contractional deformation possibly reoccurred until the Early Miocene (D3 to D5 phases). The related meso- and map-scale structures are gentle to open folds, thrusts and strike-slip faults. We measured various orientations, which were classified into three stress states or fields on the basis of structural criteria, such as tilt-test, and/or superimposed striae on the same fault planes. For this multi-directional shortening we presented three different scenarios. Our preferred suggestion would be the oblique inversion of pre-orogenic faults, which highly influenced the orientation of compressional structures, and resulted in an inhomogeneous stress field with local stress states in the vicinity of inherited older structures. The measured post-orogenic extensional structures are related to a new extensional event, the opening of the Pannonian Basin during the Miocene. We classified these structures into the following groups: immediate pre-rift phase with NE–SW extension (D6), syn-rift phase with E–W extension (D7a) and N–S transpression (D7b), and post-rift phase with NNW–SSE extension (D8). [ABSTRACT FROM AUTHOR]

Tectonically deformed coals (TDCs) are of great importance to coalbed methane exploitation and coal mining safety. Compared to primary coals, reservoir properties of TDCs have been transformed greatly by tectonic stress. Here, the pore structure and mechanical properties of primary coal and brittle TDCs were obtained with atomic force microscopy and software. The results showed that tectonic stress generally promotes pore development and Young’s modulus of brittle TDCs. According to the variation in pore structure and Young’s modulus, two stages were identified: weak brittle deformation stage (primary coal–cataclastic coal–schistose coal–mortar coal) and strong brittle deformation stage (mortar coal–granulitic coal–flaky coal). The extent of tectonic impact varies greatly between these two stages. In weak brittle deformation stage, tectonic stress has little impact on coal pore structure. The mean pore number increases slowly, and the mean pore size decreases slowly. In this stage, half of the pore number increment is provided by macropores of 100–200 nm diameter. In strong brittle deformation stage, tectonic stress has a major impact on coal pore structure. The mean pore number increases quickly, and the mean pore size decreases quickly. Most of the pore number increment comes from mesopores of 10–50 nm diameter and macropores of 50–100 nm diameter. In addition, the Young’s modulus of primary coal and different brittle TDCs varies from 1.5 to 2.0 GPa. In weak brittle deformation stage, the Young’s modulus of different samples levels off. While in strong brittle deformation stage, the Young’s modulus increases gradually. Combined with former studies, it is inferred that tectonic stress can influence coal’s Young’s modulus by transforming its chemical structure.

The thickness of the brittle lithosphere—the outer portion of a planetary body that fails via fracturing—plays a key role in the geological processes of that body. The properties of both a planet and its host star can influence that thickness, and the potential range of those properties exceeds what we see in the Solar System. To understand how planetary and stellar parameters influence brittle lithospheric thickness generally, we modeled a comprehensive suite of combinations of planetary mass, surface and mantle temperature, heat flux, and strain rate. Surface temperature is the dominant factor governing the thickness of the brittle layer: smaller and older planets generally have thick brittle lithospheres, akin to those of Mercury and Mars, whereas larger, younger planets have thinner brittle lithospheres that may be comparable to the Venus lowlands. But certain combinations of these parameters yield worlds with exceedingly thin brittle layers. We predict that such bodies have little elevated topography and limited volatile cycling and weathering, which can be tested by future telescopic observations of known extrasolar planets. Plain Language Summary: The outer layer of a rocky planetary body is generally rigid and behaves in a brittle manner. The thickness of this layer is important in governing numerous aspects of that body's geological character, including whether it can support plate tectonics and even retain habitable conditions at the surface. Factors inherent to the planet, such as size, interior temperature, composition, and even climate affect the thickness of this outer layer, but so too do factors specific to the host star, including how luminous and far away it is. We ran a large set of computer models to see how various combinations of planetary and stellar properties influence the thickness of a planetary body's outer layer. Our models predict that worlds that are small, old, or far from their star likely have thick, rigid layers but, in some circumstances, planets might have an outer brittle layer only a few kilometers thick. These worlds, which we call "eggshell planets," might resemble the lowlands on Venus, and we suggest that at least three such extrasolar planets are already known. We propose that these planets be examined with planned and future space telescopes to test if our models are correct. Key Points: We modeled the effects of planetary mass, age, and surface temperature on brittle lithospheric thicknessSurface temperature is the primary determinant of the thickness of brittle exoplanet lithospheresCertain combinations of these parameters yield "eggshell planets"—worlds with ultra‐thin brittle lithospheres [ABSTRACT FROM AUTHOR]

This paper presents a preliminary experimental study on methane adsorption capacity in shales before and after artificial deformation. The experimental results are based on uniaxial compression and methane isothermal adsorption tests on different shale samples from the Silurian Longmaxi Formation, Daozhen County, South China. Two sets of similar cylindrical samples were drilled from the each same bulk sample, one set was subjected to a uniaxial compressive simulation test and then crushed as artificial deformed shale sample, the other set was directly crushed as the original undeformed shale sample. And then we conducted a comparative experimental study of the methane adsorption capacity of original undeformed and artificially deformed shales. The uniaxial compression simulation results show that the failure mode of all samples displayed brittle deformation. The methane isothermal adsorption results show that the organic matter content is the main controlling factor of shale methane adsorption capacity. However, the comparative results also show that the compression and deformation have an effect on methane adsorption capacity, with shale methane adsorption capacity decreasing by about 4.26–8.48% after uniaxial compression deformation for the all shale samples in this study.

The self-developed TRTP-2000 high temperature and high pressure deformation experimental system is used to test the deformation of coal under sub-high temperature and high pressure deformation conditions. Micro-Raman and Micro-FTIR in-situ test methods are used to observe the microscopic deformation of coal after deformation. The typical brittle and ductile deformation points in the domain are analyzed for macromolecular structure. The results show that with the decrease of strain rate, the toughness deformation phenomenon in the sample develops gradually, which promotes the increase of secondary structural defects and the disorder of molecular structure. The brittle deformation is produced by the coupling of mechanical force and frictional heat. The oxygen-containing functional groups of coal macromolecules break and fall off with side chains, resulting in increased disorder and secondary structural defects. The ductile deformation acts on the coal macromolecular structure through the continuous accumulation of strain energy, due to the difference in strain rate. The deformation time changes. The high strain rate (≧1×10-6) toughness deformation leads to an increase in the total amount of aromatic carbon, a decrease in molecular structure disorder, and a relative decrease in secondary structural defects; a deformation at a low strain rate (=2×10-7) There is sufficient time to accumulate a large amount of strain energy in the process, which leads to dislocation slip of the aromatic layer. The accumulation of dislocations causes the aromatic ring to disintegrate, the total amount of aromatic carbon is relatively reduced, and the secondary structural defects are increased. [ABSTRACT FROM AUTHOR]

Coal organic macromolecular structure can be significantly altered by tectonic stress, but such macromolecular models are seldom reported. Here, based on the ultimate analysis, FT-IR, XPS, and 13C NMR results, three molecular models of primary coal (P1) and TDCs (the brittle coal model B2 and ductile coal model D3) within periodic boundary conditions were constructed through the molecular mechanics (MM) and molecular dynamics (MD) calculation methods. By comparing the morphology characteristics of the above three models, the crystal parameters decrease with the increasing deformation intensity, which leads to a tighter configuration. Bridge bonds are easier to be stretched and even broken up within deformed coal, which can furtherly crack the coal molecules into several smaller segments. Oxygen functional groups and methyl can be lost by the deformation on coal, which leads to an increase of the disorder units within coal molecules. On the one hand, the ductile deformation increases the condensation degree of the aromatic layers through promoting the small disorder units (viz. CO) embed into the secondary structural defects. On the other hand, it can also improve the order degree and the stacking degree of aromatic layers. By comparative analysis, the evolution path of tectonically deformed coal molecules is furtherly proposed. The ultra micropore volumes of three models are several orders of magnitude larger than the pore volume within the range of 2–50 nm, indicating that ultra micropores are important storage spaces for excess methane resulting in coal and gas outburst. [ABSTRACT FROM AUTHOR]

In the following work, sacrificial claddings filled with different brittle materials were investigated, from concrete foam to granular media. They were subjected to blast loading using an explosive driven shock tube, while a sensor measures the load transmission and a high speed camera records the compression of the core. From a macroscopic point of view, concrete foam and granular media can act efficiently as a crushable core but differs greatly in terms of energy dissipation mechanisms. To compare them, granular media was at first treated as a cellular material, and different key parameters (plateau stress, densification strain) were computed using the energy absorption efficiency methodology. The presented tests results, coupled with observation in literature, allow a better understanding on the crushing process of a granular media. In particular, granular media tend to work as a core even for low intensity load, contrary to more classical crushable core.

Folded reservoir rocks (Eumeralla Formation) within the Otway Basin are of significant exploration interest for their geothermal and tight gas reservoir potential. Brittle deformation within the Eumeralla Formation (ca 113–100 Ma), along the Otway coastline of Victoria, reflects a protracted history of extension, contraction, erosion and uplift, since Australian–Antarctic separation in the Early Cretaceous. This paper investigates the relative timing of heterogeneously distributed fracture populations within both folded and unfolded areas along the Otway coastline. Data collection occurred across two stratigraphic units spanning the Early Cretaceous (Eumeralla Formation) to the late Cenozoic (Demons Bluff Group), in order to measure fracture geometries and determine the relative timing of fracture formation. An unmanned aerial vehicle has been used to facilitate the systematic and inexpensive acquisition of high-resolution orthophotographs along coastal platforms, in order to complement traditional field mapping of fracture populations. A NE–SW-orientated fracture set is observed exclusively within the Eumeralla Formation (St George fold hinge), while a NW–SE-orientated fracture set pre-dates hinge-parallel fractures. Significant fracture formation has been linked to a period of mid-Cretaceous uplift within the eastern Otway Basin (ca 95 Ma). The Eumeralla Formation and Demons Bluff Group also host a NNW–SSE-orientated fracture set that is inferred to largely post-date mid-Cretaceous folding. Sinistral displacement of fold hinges within the Eumeralla Formation, combined with thrust faulting within Cenozoic sediments, is interpreted to have occurred during an episode of late Miocene to early Pliocene shortening. This paper provides new insights into the history of brittle deformation in the eastern Otway Basin. [ABSTRACT FROM AUTHOR]

This article performs particle (/material point) tracking for ideal brittle faults with translational and rotational slip components. The fault planes are considered to be planar and step-like in separate cases. In the latter case the hangingwall block is considered to behave ductilely. For a specific choice of the three Cartesian co-ordinate axes, dip-slip fault will change two out of the three ordinates of any point in the faulted block that moves. A strike slip faulting can change one out of the three ordinates. On the other hand, whatever be the orientation of the orthogonal co-ordinate axes, an oblique slip fault of any dip amount and a purely rotational fault with dip ≠ 0, 90° alter all the three ordinates, except the pivot point in the latter case. As expected, oblique-slip faulting modifies the co-ordinates of the shifted material points depending on both (i) the pitch of stretching lineation, and (ii) the dip of the fault plane. • Particle tracking in faulted blocks using 3D coordinate geometry. • Translational, rotational and roto-translational faults explained with planar fault planes with and without steps. • Fault modeling in petroleum geosciences and in pure research. [ABSTRACT FROM AUTHOR]

Earthquakes and resulting tsunamis are important geological phenomena, however their sedimentary paleorecord is difficult to identify because some fabrics can be generated by other processes and the criteria for discrimination of seismic and non-seismic triggers are not fully established. This paper presents several deformation and sedimentary structures in the Middle Triassic carbonates of Upper Silesia and discusses their seismogenic and tsunami origin and controls on the deformation type, intensity, preservation potential, and geographic distribution. The deformation type and intensity were controlled by the primary lithology, whereas the lateral continuity of deformed horizons depended on the lateral extent of hosted facies. The thickness and abundance of these structures increase towards the Kraków-Lubliniec Fault Zone which bounded the area from the east and is considered as the main epicentrum of earthquakes and tsunami initiation. The discussed fabrics have a universal significance and can potentially be found in other shallow-marine carbonate successions. • The intensity and type of deformation depended on the primary lithology. • The lateral continuity of deformed horizons depended on the lateral extent of hosted facies. • The abundance and thickness of structures increase towards the reactivated fault-zone. [ABSTRACT FROM AUTHOR]

The Železné hory Fault represents one of the major tectonic structures of the Bohemian Massif which were proved to be reactivated as reverse faults during the Alpine orogeny. However, the architecture and kinematic history of the fault are known only incompletely due to the fact that the trace of the fault is covered by extensive Quaternary sediments. Three sites in the SE segment of the fault were revised and characterized: they provide exposures of the fault core and brittle-deformed ambient rocks for a direct structural study. At the first site at the Sloupno village near Chotěboř, the fault core is exposed in a gorge of a brook. The second site is the nearby active quarry, which reveals the damage zone cutting crystalline rocks. The study of the fault core and its damage zone at the third site of Horní Studenec near Ždírec nad Doubravou would necessitate its re-opening by minor excavations. Parameters of four stress events were estimated by the paleostress analysis of first few fault-slip datasets. The results were compared with previously known styles of brittle deformation of the Upper Cretaceous sediments. The oldest, probably dominant NE compression reactivated the Železné hory Fault as an oblique reverse fault. It was responsible for transpressional brittle and ductile deformations of rocks in its surroundings. The succeeding compression, of similar orientation, reactivated most faults in the area as strike-slips. The subsequent two events, characterized by NNW and WNW extension, are probably the relatively youngest ones. They were responsible for reactivation of the faults as oblique normal faults. Fault movements during the three younger deformation events resulted in frequent transverse segmentation of the structure of the Železné hory Fault. Recognition of the sites and the first results of paleostress analysis demonstrated its possibilities and marked the trends in further study, including the adaptation of some of these sites as educational sites for the public. [ABSTRACT FROM AUTHOR]

Microscale heterogeneities influence failure mechanisms in the crust. To track the microstructural changes in rock samples when loaded until failure, we employed a novel experimental technique that couples dynamic X‐ray microtomography imaging with a triaxial deformation apparatus. We studied the brittle failure of Carrara marble under triaxial compression. Dynamic tomographic data revealed the spatial organization of microfractures and damage increments characterizing the precursory activity toward catastrophic failure. We quantified the emergence of scaling relationships between microstructural parameters, including total damage volume, incremental damage volume, the largest connected microfracture, and the applied differential stress. The total volume of microfractures accumulated from the beginning of the experiment as well as the incremental damage showed power law increase. The growth of the largest connected microfracture was related to differential stress as a power law with divergence at failure. The microfracture volume increments were distributed according to a power law with an upper cutoff that itself spanned the entire volume toward failure. These characteristic features of brittle failure in Carrara marble under compression are in agreement with theoretical models that consider failure as a critical phase transition. We also observed that, very close to failure, several power law relationships broke down, which we interpret to be related to the coalescence of the largest microfractures in a finite size volume. Scaling laws and associated exponents computed from our data are compared with predictions made from theoretical and numerical models. Our results show that precursors of macroscopic brittle failure in Carrara marble follow predictable trends. Key Points: Microfracture dynamics explains complex physical processes guiding the macroscopic failure in Carrara marbleStatistical parameters measuring microfracture volume, growth, and spatial organization showed power law scaling with applied stressEvolution of several microstructural parameters is in agreement with models that establish compressive failure as a critical phase transition [ABSTRACT FROM AUTHOR]

Abstract The relationships between deformation and fluid flow have been investigated in the Paleozoic basement of an isolated horst of the Catalan Coastal Ranges. A structural, petrological and geochemical study has been performed in a complex fracture network that resulted from a long-lived tectonic history (from Carboniferous to Miocene). Nine fracture types, developed from a ductile regime in the greenschist facies to a shallow brittle regime, have been characterized in order to establish P, T and fluid compositions during the evolution of the horst. Syn-cleavage and late-cleavage quartz veins (qtz 1 -chl 1 ± mu and late qtz 2 -chl 2 -dol 1) formed during the Hercynian ductile deformation. These minerals precipitated from metamorphic fluids, possibly evolved from seawater, at temperatures between 240 and 340 °C. En-echelon albite vein arrays (ab-qtz 3 -chl 3 ± ti-an) and NE-SW normal faults generating breccias mark the change from ductile to brittle, from compression to extension and from a closed to an open hydrologic regime. This paragenesis precipitated from the mixing of metamorphic and magmatic fluids at temperatures between 180 and 290 °C during the early Permian extension. Dolomite veins (dol 2 -chl 4 -qtz 4), precipitated at 210–280 °C from the mixing of previous fluids with hypersaline oxidizing external brines, possibly during the late stage of the early Permian extension. Reverse faults and calcite veins (Cc1-ba) formed either during the Paleogene compression or during the Langhian to early Serravallian minor compression. Calcite and barite precipitated from meteoric or marine waters in an open hydrological system at temperatures below 50 °C. The Miocene extension is represented by NE-SW normal faults with fault gouges and NNW-SSE normal faults cemented by calcite 2 that precipitated at temperatures below 50 °C from meteoric fluids in an open basin-scale hydrological system. The studied horst was part of a relay zone between two segments of the NNW-SE Llobregat fault during the early Permian, explaining the high fracture density and the fast upflowing of hydrothermal fluids at that time, thus controlling the development of albite veins exclusively in this area. Highlights • Ductile to shallow brittle deformation structures recorded in crystalline basement. • Mineral paragenesis are controlled by the host rock, fluid origin, fO 2 and T. • A coupled fluid flow system (channelized and pervasive) occurs during metamorphism. • An Early Permian relay zone generates a dense network of hydrothermal veins. • During the Miocene, shallow deformation linked to an open basin-scale fluid flow occurs. [ABSTRACT FROM AUTHOR]

The Northern Apennines (NA) orogenic wedge formed during Oligocene‐Miocene convergence and westward subduction of Adria beneath the European Plate. Extension ensued in the Mid‐Late Miocene in response to Adria roll‐back, causing opening of the back‐arc Northern Tyrrhenian Sea. Whether extension continues uninterrupted since the Mid‐Late Miocene or it was punctuated by short‐lived compressional events, remains, however, uncertain. We used the K‐Ar method to date a set of brittle‐ductile and brittle deformation zones from the Island of Elba to contribute to this debate. We dated the low‐angle Zuccale Fault (ZF), the Capo Norsi‐Monte Arco Thrust (CN‐MAT), and the Calanchiole Shear Zone (CSZ). The CN‐MAT and CSZ are moderately west dipping, top‐to‐the‐east thrusts in the immediate footwall of the ZF. The CSZ slipped 6.14 ± 0.64 Ma (<0.1 μm fraction) and the CN‐MAT 4.90 ± 0.27 Ma ago (<0.4 μm fraction). The ZF, although cutting the two other faults, yielded an older age of 7.58 ± 0.11 Ma (<0.1 μm fraction). The ZF gouge, however, contains an illitic detrital contaminant from the Paleozoic age flysch deformed in its hanging wall and the age thus is a maximum faulting age. Removal of ~1% of a 300‐Ma‐old contaminant brings the ZF faulting age to <4.90 Ma. Our results provide the first direct dating of brittle deformation in the Apennines, constraining Late Miocene‐Early Pliocene regional compression. They call for a refinement of current NA geodynamic models in the framework of the Northern Tyrrhenian Sea extension. Key Points: We provide the first isotopic geochronological constraints on brittle deformation in the NA by illite K‐Ar dating of brittle fault rocksA combined structural‐geochronological approach constrains a Late Miocene‐Early Pliocene regional compressive stress stateResults call for a refinement of geodynamic models of the North Tyrrhenian Sea extension to account for Late Miocene‐Pliocene compression [ABSTRACT FROM AUTHOR]

Abstract: The Andes of southern Patagonia experienced a Miocene shift towards faster and higher angle subduction followed by the approach and collision of the Chile oceanic ridge. We present a kinematic study characterizing palaeostress fields computed from brittle tectonics to better constrain upper crustal deformation during this complex scenario. Although previous studies already suggested variable kinematics, it is striking that in a long‐lasting subduction environment, the computed palaeostress tensors are mostly strike‐slip (55%), while 35% are extensional, and only 10% compressive which are concentrated along a main frontal thrust. Cross‐cutting relationships and synsedimentary deformation indicate that a long‐lived strike‐slip regime was punctuated by a lower Miocene extensional event in the foreland before the main compressional event. The results are discussed in contrasting geodynamic models of plate coupling/decoupling versus direction and rate of convergence of the subducting plate, to explain the main mechanisms that control back‐arc deformation. [ABSTRACT FROM AUTHOR]

Abstract: Spreading processes at the axes of fast spreading ridges are mainly controlled by magmatic activity, whereas tectonic activity dominates further away from the axis. High‐resolution near‐bottom bathymetry data, photographs, videos, and human observations from submersible surveys are used to develop a detailed tectonic analysis of the 16°N segment of the East Pacific Rise (EPR). These data are used to evaluate how a highly magmatic segment, close to a hot spot, affects the nucleation and evolution of faulting patterns and impacts the evaluation of tectonic strain within 2 km of the spreading axis. Our study shows that (1) the growth of tectonic features differs in response to dike intrusion and tectonic extension, (2) the initiation of brittle extension is strongly controlled by the location of the axial magma lens and the development of layer 2A, and (3) the high magmatic budget and the off‐axis magma lens in the west part of the plateau do not significantly impact the initiation of brittle extension along the central portion of the 16°N segment. Within the axial summit region, more than 2% of plate separation at 16°N on the EPR is accommodated by brittle extension, as is observed at other EPR segments. The interaction of the Mathematician hot spot with this EPR segment has no significant influence on the initiation of the tectonic deformation, but it does reduce the development of the brittle deformation. [ABSTRACT FROM AUTHOR]

The Alpine Fault is capable of generating large (M W  > 8) earthquakes and is the main geohazard on South Island, NZ, and late in its 250–291-year seismic cycle. To minimize its hazard potential, it is indispensable to identify and understand the processes influencing the geomechanical behavior and strength-evolution of the fault. High-resolution microstructural, mineralogical and geochemical analyses of the Alpine Fault's core demonstrate wall rock fragmentation, assisted by mineral dissolution, and cementation resulting in the formation of a fine-grained principal slip zone (PSZ). A complex network of anastomosing and mutually cross-cutting calcite veins implies that faulting occurred during episodes of dilation, slip and sealing. Fluid-assisted dilatancy leads to a significant volume increase accommodated by vein formation in the fault core. Undeformed euhedral chlorite crystals and calcite veins that have cut footwall gravels demonstrate that these processes occurred very close to the Earth's surface. Microstructural evidence indicates that cataclastic processes dominate the deformation and we suggest that powder lubrication and grain rolling, particularly influenced by abundant nanoparticles, play a key role in the fault core's velocity-weakening behavior rather than frictional sliding. This is further supported by the absence of smectite, which is reasonable given recently measured geothermal gradients of more than 120 °C km −1 and the impermeable nature of the PSZ, which both limit the growth of this phase and restrict its stability to shallow depths. Our observations demonstrate that high-temperature fluids can influence authigenic mineral formation and thus control the fault's geomechanical behavior and the cyclic evolution of its strength. [ABSTRACT FROM AUTHOR]

The antimony-gold deposits at Costerfield are a swarm of ‘dyke-like’ antimony-gold lodes within a brittle transpressional fault system. They are hosted in the Lower Silurian sedimentary rocks of the Melbourne Zone of the Lachlan Orogen. Individual lodes are dominated by stibnite or stibnite-gold and widths vary from 1 cm to ∼200 cm (averaging 30 cm) and lengths can exceed 1 km. Lodes occur as fault-parallel layers or lenses mantled by deformed quartz-rich margins or overgrowths of hydrothermal quartz and carbonate. Inclusions in the stibnite-rich lodes include vuggy randomly oriented prismatic crystals, crack-sealed and stretched quartz with sugary mosaics of equant quartz grains and quartz breccias. Randomly oriented quartz and stibnite textures, common in the centre of the lodes, indicate free growth from a fluid. Throughout the mineralized system, the hydrothermal stibnite has replaced and overgrown the earlier quartz. Deformed lode margins preserve sub-horizontal lineations and evidence of oblique crack-seal re-opening that reflect emplacement associated with late sinistral strike-slip movements in bounding faults. Crystallographic orientation data collected from the marginal quartz, using neutron diffraction and supported by microstructural observations, reveal that lode emplacement also involved dissolution-precipitation creep and pressure solution. Both the marginal quartz and the lodes are overprinted by later microfractures, within which there has been precipitation of stibnite, pyrite, arsenopyrite, sphalerite and minor gold. 3 D neutron tomography revealed individual gold crystals, with gold voxel sizes ranging from 140 µm to ∼580 µm, were located in late arsenopyrite-gold domains that overprint the stibnite. The mechanical evolution of the lodes involved short-lived brittle processes in combination with dissolution-precipitation crystallization in active fault zones. These ore bodies provide insights about the dynamics of fluid flow and flow velocities when faults breach over-pressured reservoirs of hydrothermal fluid. Our results also suggest that the Costerfield deposit was formed directly from metal-rich metamorphic fluids produced during Tabberabberan (∼375 Ma) prograde metamorphism of sedimentary rocks near the base of the Lower Paleozoic Melbourne Zone, which lie above the Proterozoic Selwyn Block. From a reinterpretation of seismic reflection data, the deformation in the Melbourne Zone sedimentary wedge is characterized by thrusts isolating relatively undeformed packages of sedimentary units, which were moved in a piggyback manner up west-dipping faults. The ore-bearing fluids migrated upwards, at least in part, along these footwall thrusts from the base of the Heathcote Fault Zone. In the upper levels of the sedimentary package, out-of-sequence strike-slip, sub-vertical splays from these second order faults carried the mineralizing fluids to the orebodies. East-west compression during the Tabberabberan Orogeny preceded a northwest-southeast-oriented stress field which reflects the collision of VanDieland against the Gondwanan margin. This produced the sinistral strike-slip faults, which in turn controlled the overall permeability of the hydrothermal system. [ABSTRACT FROM AUTHOR]

The diachronous rifting of the Pangea supercontinent, with the dispersion of the continental masses, resulted in the formation of numerous rift systems, which primarily evolved into passive margins, such as the Brazilian Equatorial Margin (BEM). In the South American counterpart, basement structures serve as the primary markers for direct analysis of the nucleation and development of the BEM since much of the rift record occurs in the subsurface. The geodynamic models that explain the evolution of this margin are largely based on geophysical and numerical modeling data. In this paper, we carried out an onshore, multitool, and multiscale structural analysis of the brittle deformation overprinted on the Precambrian basement of the Potiguar and Ceará basins, which led to the proposition of four superimposed events. The D 1 event (Late-Brasiliano) is mainly represented by the NE-SW (dextral) stepped fracture systems and the unfilled and quartz- or chalcedony-filled NE-SW to E-W-trending extensional joints. This event is related to NE-SW intraplate transpression, associated with the progressive exhumation of the Brasiliano-Pan African orogenic belt. The D 2 event (Jurassic to early Aptian) represents the intracontinental deformation related to the initial rupture of the Pangea. The brasiliano-age ductile shear zones were reactivated (brittle) along with the development of NE-SW normal faults, NNE-SSW en échelon fractures, NE-SW joints, as well as the emplacement of the basic dykes (NE-SW and E-W) related to the Rio Ceará-Mirim magmatism. This event is associated with the NW-SE extension responsible for the origin of the Cariri-Potiguar trend basins. At the beginning of the installation of the equatorial proto-margin, a significant cataclastic process took place, marking the D 3 event (post-early Aptian). This enabled the nucleation of hybrid (WNW-ESE, E-W, and NW-SE), shear fractures (WNW-ESE, NNW-SSE, E-W, NNE-SSW, and ENE-WSW), and NW-SE unfilled or filled (chalcedony, iron oxide and hydroxide, and calcite) dilatational joints, which express an E-W dextral transtensional regime related to this event. E-W and NW-SE pull-apart dilatational jogs are characteristic of this event and may be analog to the E-W Messejana and Jacaúna transtensional grabens (western part of the Potiguar Basin). The younger event (D 4) is characterized by N–S normal faults and joints, and dry or filled (calcite and iron oxide/hydroxide) NNW-SSE hybrid shear fractures. A clockwise rotation of the South American plate with respect to the African plate and the paleostress field change to N–S compression and E-W extension, are responsible for the formation of D 4 structures. The brittle structures developed in the crystalline basement of the Potiguar and Ceará basins represent the intracontinental record of the deformation related to the formation of the Atlantic equatorial margin under a dextral transtensional regime. • The Brazilian Equatorial margin (BEM) shows a complex superposition of brittle events. • Intracontinental brittle structures point to a dextral transtensional regime. • E-W transtensional pull-apart structures may indicate offshore depocenters with similar geometry. [ABSTRACT FROM AUTHOR]

Heterogeneous deformation is intrinsic in natural deformation, but often underestimated in the analysis and interpretation of mesoscopic brittle shear faults. Based on the analysis of 11,222 faults from two distinct tectonic settings, the Central Andes in Argentina and the Sudbury area in Canada, interpolation of principal strain directions and scaled analogue modelling, we revisit controversial issues of fault-slip inversions, collectively adhering to heterogeneous deformation. These issues include the significance of inversion solutions in terms of (1) strain or paleo-stress; (2) displacement, notably plate convergence; (3) local versus far-field deformation; (4) strain perturbations and (5) spacing between stations of fault-slip data acquisition. Furthermore, we highlight the value of inversions for identifying the kinematics of master fault zones in the absence of displaced geological markers. A key result of our assessment is that fault-slip inversions relate to local strain, not paleo-stress, and thus can aid in inferring, the kinematics of master faults. Moreover, strain perturbations caused by mechanical anomalies of the deforming upper crust significantly influence local principal strain directions. Thus, differently oriented principal strain axes inferred from fault-slip inversions in a given region may not point to regional deformation caused by successive and distinct deformation regimes. This outcome calls into question the common practice of separating heterogeneous fault-slip data sets into apparently homogeneous subsets. Finally, the fact that displacement vectors and principal strains are rarely co-linear defies the use of brittle fault data as proxy for estimating directions of plate-scale motions. [ABSTRACT FROM AUTHOR]

NASA's Curiosity rover identified a formerly habitable environment within strata informally known as the Yellowknife Bay formation. The stratigraphic relationship, and thus depositional age, of these rocks relative to other geologic units in Gale crater is not clear from orbital data alone. If part of lower Aeolis Mons (informally known as Mount Sharp), the Yellowknife Bay rocks have been deeply buried and exhumed prior to 3.2–3.3 Ga. If part of younger alluvial fan deposits, however, they likely have never experienced more than ∼100 m of burial. Knowledge of burial history can thus constrain the stratigraphic placement of Yellowknife Bay and the habitable environment preserved therein. The mechanics of natural hydraulic fractures observed in mudstone at YKB allow us to evaluate its burial history and imply a minimum burial depth of 1.2 km. This is consistent with burial by the entirety of lower Mount Sharp and a depositional age of ∼ 3.6 – 3.8 Ga, providing observation-based evidence that Mount Sharp was once much more laterally extensive than its present form. Rocks of the Yellowknife Bay formation thus represent the oldest strata that Curiosity will encounter during its journey in Gale crater, and any additional habitable environments discovered along Curiosity's future path represent conditions at younger times. [ABSTRACT FROM AUTHOR]

The Madeira granite is one of the Paleoproterozoic (1.82 Ga) A-type granite intrusions in the Amazonian Craton. It is elongated in the NE–SW direction and is composed of four facies. Classical structural techniques and the anisotropy of magnetic susceptibility (AMS) method were applied to the study of its internal fabric. Magnetic susceptibility measurements, thermomagnetic curves, remanent coercivity spectra, optical microscopy and SEM (scanning electron microscopy) analyses were carried out on the earlier and later facies of the Madeira granite: the rapakivi granite (RG) and the albite granite (AG) respectively. The last one is subdivided into the border albite granite (BAG) and the core albite granite (CAG) subfacies. AMS fabric pattern is controlled by pure magnetite in all facies, despite significant amounts of hematite in the BAG subfacies. Microstructural observations show that in almost all sites, magnetic fabric correlates to magmatic state fabrics that are defined by a weak NE–SW orientation of mafic and felsic silicates. However, strain mechanisms in both subfacies of AG also exhibit evidence for solid-state deformation at high to moderate temperatures. Pegmatite dyke, strike slip fault (SF A–B–C ), hydrothermal vein, normal fault (F 1–2 ) and joint (J) structures were observed and their orientation and kinematics is consistent with the magmatic and solid-state structures. Dykes, SF A–C and F 1 , are usually orientated along the N70°E/40°N plane, which is nearly parallel to the strike of AMS and magmatic foliations. In contrast, veins, SF B , F 2 and some J are oriented perpendicular to the N70°E trend. Kinematic analysis in these structures shows evidence for a dextral sense of movement in the system in the brittle regime. The coherent structural pattern for the three facies of Madeira granite suggests that the different facies form a nested pluton. The coherence in orientation and kinematics from magmatic to high-temperature solid-state, and into the brittle regime indicates the continuity in the stress regime from the last magmatic stages until the complete cooling of the pluton, likely along a NE–SW dextral corridor related to the regional deformation in the Uatumã–Anauá Domain of the Amazonian Craton. [ABSTRACT FROM AUTHOR]

The deformation of brittle material is primarily accompanied by micro-cracking and faulting. However, it has often been found that continuum fluid models, usually based on a non-Newtonian viscosity, are applicable. To explain this rheology, we use a fiber-bundle model, which is a model of damage mechanics. In our analyses, yield stress was introduced. Above this stress, we hypothesize that the fibers begin to fail and a failed fiber is replaced by a new fiber. This replacement is analogous to a micro-crack or an earthquake and its iteration is analogous to stick-slip motion. Below the yield stress, we assume that no fiber failure occurs, and the material behaves elastically. We show that deformation above yield stress under a constant strain rate for a sufficient amount of time can be modeled as an equation similar to that used for non-Newtonian viscous flow. We expand our rheological model to treat viscoelasticity and consider a stress relaxation problem. The solution can be used to understand aftershock temporal decay following an earthquake. Our results provide justification for the use of a non-Newtonian viscous flow to model the continuum deformation of brittle materials. [ABSTRACT FROM AUTHOR]

The analogue materials play a critical role in dynamically scaled experiments, defining the processes that can be simulated and the structures observable in the model. The dynamic scaling enables the direct comparison between the model and its natural counterpart. To obtain such a model the physical and mechanical properties of the analogue material must be scaled with respect to the rock prototype. A large variety of materials have been applied in analogue modelling studies to address the physical and mechanical requirements for the simulation of (i) upper crust, (ii) middle crust and (iii) lower crust and mantle processes. Nevertheless, the development of new model materials represents a continuous improvement of the analogue modelling techniques. We investigated the mechanical and physical properties of a new Granular Rock-Analogue Material (GRAM) (introduced in Massaro et al. (2022)) and its component materials. GRAM is an ultra-weak artificial sandstone composed of quartz sand cemented with gypsum, capable to deform by tensile and shear failure under variable stress conditions. GRAM aggregates in different mixing ratios (from 1% to 4% in weight of hemihydrate powder) were systematically tested with ring-shear tests and uniaxial compression tests. The relationships between the hemihydrate content and the mechanical properties of GRAM were examined. Additionally, the sample preparation procedure of GRAM was investigated, evaluating the impact of the residual water content on the mechanical properties of GRAM aggregates and defining a standard preparation procedure. Finally, GRAM was compared to natural rocks and to other granular materials applied in analogue modelling studies, in terms of physical and mechanical properties, application to physical modelling and dynamic scaling. It was underlined how the application of GRAM aggregates in dynamically scaled experiments can enhance the comprehension of the fault and fracture processes occurring at the scale of the damage zone. • The physical and mechanical properties of a new model material were investigated. • Preparation workflow and moisture content impact the mechanical properties. • Compressive and shear strength, elastic properties and strain softening analysed. • Dynamic scaling and model-nature length ratio modified by varying the mixing ratios. • Simulation of brittle deformation processes in fault zones at a novel model resolution. [ABSTRACT FROM AUTHOR]

Exhumed faults hosting hydrothermal systems provide direct insight into relationships between faulting and fluid flow, which in turn are valuable for making hydrogeological predictions in blind settings. The Grimsel Breccia Fault (Aar massif, Central Swiss Alps) is a late Neogene, exhumed dextral strike-slip fault with a maximum displacement of 25-45 m, and is associated with both fossil and active hydrothermal circulation. We mapped the fault system and modelled it in three dimensions, using the distinctive hydrothermal mineralisation as well as active thermal fluid discharge (the highest elevation documented in the Alps) to reveal the structural controls on fluid pathway extent and morphology. With progressive uplift and cooling, brittle deformation inherited the mylonitic shear zone network at Grimsel Pass; preconditioning fault geometry into segmented brittle reactivations of ductile shear zones and brittle inter-shear zone linkages. We describe 'pipe'-like, vertically oriented fluid pathways: (1) within brittle fault linkage zones and (2) through along-strike-restricted segments of formerly ductile shear zones reactivated by brittle deformation. In both cases, low-permeability mylonitic shear zones that escaped brittle reactivation provide important hydraulic seals. These observations show that fluid flow along brittle fault planes is not planar, but rather highly channelised into sub-vertical flow domains, with important implications for the exploration and exploitation of geothermal energy. [ABSTRACT FROM AUTHOR]

El Dúplex Caleta Coloso es una estructura de rumbo desarrollada durante la deformación frágil del Sistema de Falla de Atacama (SFA) en el Cretácico Temprano. En su interior hay un sistema de vetas hidrotermales que documentan la naturaleza de la relación entre el transporte de fluidos y el desarrollo del dúplex. El sistema de vetas de orientación dominante NW se localiza en la roca de caja, adyacentes a las zonas de falla. Según su mineralogía dominante hay vetas de clorita, epidota-cuarzo y calcita-limonita, y según las relaciones de corte o su estructura interna, se definieron vetas tempranas (clorita), intermedias (epidota-cuarzo) y tardías (calcita-limonitas). Algunas vetas muestran cristales perpendiculares u oblicuos a sus paredes (vetas de extensión y de extensión oblicua) o fibras minerales orientadas paralelas a las estrías de las fallas (vetas-fallas). Estas últimas tienen indicadores cinemáticos compatibles con las fallas, evidenciando que fueron sincinemáticas con el desarrollo del dúplex. Según su microestructura, ellas se habrían formado en fracturas abiertas llenas de fluidos, bajo condiciones de presión inferior a la hidrostática, lo cual indicaría que la precipitación mineral ocurrió por caídas abruptas de la presión en una corteza somera (The Caleta Coloso Duplex is a brittle strike-slip structure developed along the Atacama Fault System during the Early Cretaceous. A hydrothermal vein system existing within the duplex documents the nature of the link between fluid transport and progressive structural development. The dominantly NW-striking vein system occurs near or at the damage zone of the duplex fault zones. Veins can be classified according to their composition and crosscutting relationships into early chlorite veins, intermediate epidotic-quartz veins and late calcite-limonite veins. Some of them exhibit minerals with their long axes oriented orthogonally or obliquely with respect to the vein walls (extension veins and oblique-extension veins), whereas others show mineral fibers that are parallel to striae of the hosting faults (fault-veins). The latter show kinematic indicators that are compatible with those of the faults, suggesting they were synkinematic with strike-slip duplex development. The vein microstructure suggests that they form from fluid-filled open fractures under subhydrosthatic pressures suggesting that mineral precipitation was triggered by pressure drops at shallow crustal levels (

The repeated north and southward migration of the Chile Triple junction, offshore the Península de Taitao, is expected to have imposed contrasting stress fields in the forearc for the last 6 Ma because of changes in convergence direction and rate of subducting plates. NNW-SSE to E-W and minor NE-SW striking brittle faults developed in the plutonic units of the Mio-Pliocene Taitao Ophiolite, whereas NNE-SSW and minor NW-SE trending faults developed in its eastern border (Bahía Barrientes fault-zone). These brittle faults are studied to elucídate the style of ophiolite emplacement and the tectonic effects resulting from the alternated migration of the Chile Triple junction in the área. Analyses of heterogeneous fault-slip data on both áreas suggest that faults were activated by different stress fields. Two different compressional stress fields were identified in the plutomc units (A and B), whereas three different stress fields, ranging from compressional to strike-slip, were identified in the BahíaBarrientos fault-zone (C, D and E). Calculated directions of Oj axes for A, C, D and E solutions are mostly E-W trending, roughly similar to the convergence direction of subducting plates, whereas that for B solution is counterclockwise rotated ca. 60° with respect to the previous E-W trend. Brittle structures related to solution B were attributed to an early deformation of the ophiolite, most probably developed shortly after its emplacement {ca. 6 Ma). These structures were further counterclockwise rotated, while new structures (related to solution A) developed in the plutomc units in order to absorb the continuous deformation. In the eastern margin of the ophiolite, the stress field divided inte compressional and strike-slip components. During periods of relatively strong compression (fast subduction of the Nazca píate), the fault-zone experienced well defined compressional and strike-slip movements (solutions C and D). In contrast, during periods of relatively weak compression (slow subduction of the Antarctic píate), the fault-zone experienced a complex mixture of thrust and strike-slip movements (solution E). Thus, the wide range of calculated stress ratios for all solutions could be attributed to the alternated change in convergent velocity of the subducting plates beneath the Taitao área.Es esperable que la repetida migración norte-sur del Punto Triple de Chile cercana a la costa de la Península de Taitao haya impuesto campos de esfuerzos distintos en el antearco por los últimos 6 Ma debido a cambios en la dirección de convergencia y tasa de subducción. Fallas con rumbos NNO-SSE y E-O y otras menores con rumbos NE-SO se desarrollaron en las unidades plutónicas de la Oflolita Miocena-Pliocena de Taitao, mientras que fallas con rumbos NNE-SSO y otras menores con rumbos NO-SE se desarrollaron en el borde Este de esta (Zona de falla de Bahía Barrientes). Estas estructuras frágiles son estudiadas para dilucidar el estilo de emplazamiento de la oflolita y los efectos tectónicos resultantes de la migración alternada del Punto Triple de Chile en al área. Análisis de datos heterogéneos de fallas en ambas áreas sugieren que fueron activadas por campos de esfuerzos diferentes. Dos campos de stress compresionales distintos fueron identificados en las unidades plutónicas (A y B), mientras que 3 campos de stress diferentes, desde compresionales a transcurrentes, lo fueron en la zona de falla de Bahía Barrientes (C, D y E). Las direcciones de los ejes a1 calculadas para las soluciones A, C, D y E son principalmente este-oeste, similares a la dirección de convergencia de las placas subductantes, mientras que aquella para la solución B está rotada antihorario ca. 60° con respecto del patrón anterior este-oeste. Las estructuras frágiles relacionadas con la solución B fueron atribuidas a una deformación temprana de la ofiolita, muy probablemente desarrolladas después de su emplazamiento (ca. 6 Ma). Estas estructuras fueron posteriormente rotadas antihorario, mientras nuevas estructuras (relacionadas con la solución A) se desarrollaron en las unidades plutónicas para absorber la deformación continua. En el margen este de la ofiolita, el campo de esfuerzo se dividió en componentes compresionales y transcurrentes. Durante períodos de compresión relativamente alta (subducción rápida de la placa de Nazca) la zona de falla experimentó movimientos compresionales y transcurrentes bien definidos (soluciones C y D). En contraste, durante períodos de relativa baja compresión (lenta subducción de la placa Antartica) la zona de falla experimentó una compleja mezcla de movimientos inversos y transcurrentes (solución E). Así, el amplio rango de radios de stress calculados para todas las soluciones puede ser atribuido al cambio alternado en la velocidad de convergencia de las placas subductantes bajo el área de Taitao.

We combine field observations, drone photogrammetry, and petrographic and XRD analysis to document the internal lithological and structural variability of an exceptionally well-exposed strike-slip fault pressure ridge, in the northern Tibetan foreland. The ridge exposes alternating dm-m thick discolored zones of fault gouge, breccia, and cataclasite likely reflecting the original Riedel shear array and progressive widening of the fault zone as comminution, fluid pressures, mineral alteration, and strain hardening and weakening processes evolved and migrated vertically and laterally within the core. The principal fabric defines an internal foliation fan, and sinistral, oblique-thrust faults bound the ridge supporting a transpressive squeeze-up origin. Outcrop- and micro-scale grain size reduction, gouge formation, and calcite precipitation suggest that thermal pressurization, mechanical lubrication, fault-valve fluid cycling, and periodic gouge zone lock-up may have been important factors controlling fault slip behavior and seismic energy release. Local variations in the distribution and thicknesses of brittle fault rocks, strain intensity, alteration mineralogy and fault core fabrics are a sobering reminder that a single 2-dimensional exposure across any regional fault system will fail to capture the complex petrological, mineralogical, mechanical and rheological heterogeneity that is typical of an evolving intraplate strike-slip fault system, especially where it reactivates an older fault/shear zone. • Detailed structural and lithological variations of a pressure ridge are documented. • Alternating zones of gouge, breccia and cataclasite are common and complexly arranged. • The ridge is a sinistral transpressive squeeze-up with an internal foliation fan. • Mineralogical and structural variations in core suggest complex slip behavior evolution. • A single cross-fault exposure will not capture geometrical and mechanical complexity. [ABSTRACT FROM AUTHOR]

The integrated evaluation of borecores from theMezősas-Furta fractured metamorphic hydrocarbon reservoirsuggests significantly distinct microstructural androck mechanical features within the analysed fault rocksamples. The statistical evaluation of the clast geometriesrevealed the dominantly cataclastic nature of the samples.Damage zone of the fault can be characterised byan extremely brittle nature and low uniaxial compressivestrength, coupled with a predominately coarse fault brecciacomposition. In contrast, the microstructural mannerof the increasing deformation coupled with higher uniaxialcompressive strength, strain-hardening nature andlow brittleness indicate a transitional interval betweenthe weakly fragmented damage zone and strongly grindedfault core. Moreover, these attributes suggest this unit ismechanically the strongest part of the fault zone. Gougerichcataclasites mark the core zone of the fault, with theirwidespread plastic nature and locally pseudo-ductile microstructure.Strain localization tends to be strongly linkedwith the existence of fault gouge ribbons. The fault zonewith ∼15 m total thickness can be defined as a significantmigration pathway inside the fractured crystalline reservoir.Moreover, as a consequence of the distributed natureof the fault core, it may possibly have a key role in compartmentalisationof the local hydraulic system.

We investigated the potential of common crystalline rocks to facilitate the geochemical evolution of continental basement brines and to serve as a metal source for hydrothermal ore deposits. We performed leaching experiments on typical crystalline basement rocks (granite and gneiss), a redbed sandstone and their mineral separates (feldspar, quartz and biotite) at variable T (25, 180, 275 and 350 °C), P (ambient pressure, 0.9, 1.4 and 1.9 kbar), grain-size fractions (< 0.01 mm, 0.063–0.125 and 2–4 mm) and variable fluid/rock ratios (10 to 1.1) with ultrapure water and 25 wt.% NaCl solution as solvents. The modification of the fluid chemistry during water–rock interaction strongly depends on grain-size: leachates (using pure H 2 O) of fine-grained rock powders have lower Na/Cl and Cl/Br ratios but much higher chlorinities (by a factor of up to 40) compared to leachates from coarse-grained rock powders. The Cl/Br ratios of all leachates are lower than that of their respective whole-rocks. Smaller grain-sizes of the starting materials yield element ratios (Cl/Br and Na/Cl) similar to those found in natural fluids, emphasizing the influence of cataclastic deformation on the fluid chemistry of crustal fluids. During our leaching experiments, Pb, Zn, Cu and W are released by felsic minerals, while biotite alteration releases Ni, As and additional Zn and Cu. Our experiments confirm that crystalline rocks may serve as metal source for hydrothermal ore deposits. Short-term water–rock interactions along cataclastic fault zones in the brittle crust may influence the geochemical evolution of upper crustal fluids. This is further suggested by low F/Cl and Cl/Br ratios in some of the leachates being very similar to halogen systematics in natural fluid samples. [ABSTRACT FROM AUTHOR]

This study combines structural and thermochronological analysis with published geochronological data to evaluate the tectonic evolution of the ductile Main Mylonite Zone and the adjacent brittle Ragga-Teuchl fault to the southeast of the Tauern Window. The Main Mylonite Zone experienced ductile deformation with top-to-the-NW transport direction. From microstructural analysis and published K/Ar and Ar/Ar data the timing for this ductile deformation is proposed to be Late Cretaceous in age, contemporaneous to a well documented extensional collapse that affected large parts of the Eastern Alps. Subsequent brittle faulting affected the Main Mylonite Zone and neighbouring units. Apatite fission track data suggest that brittle deformation along the Ragga-Teuchl fault and adjacent units occurred in the middle- and late Miocene (~23 and ~11 Ma), contemporaneous with the main phase of lateral extrusion. Our results show that a rather small study area may comprise information about the evolution of the Eastern Alps from Late Cretaceous to late Miocene times. We also demonstrate that low-temperature thermochronology is a viable tool to resolve the timing of brittle faulting and accompanied fluid activity. [ABSTRACT FROM AUTHOR]