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The Kallintiri area (SW Byala Reka–Kechros Dome, Rhodope) hosts a polymetallic (critical, base, and precious metals) ore deposit, tectonically controlled by the late Eocene–Oligocene, top-to-SW Kallintiri Detachment System. The earliest structure associated with the Kallintiri Detachment is a ductile shear zone at the interface between the high-grade footwall gneisses of the Lower and Intermediate Rhodope Terranes. The detachment zone encompasses the uppermost part of the gneisses and the ultramylonitic Makri Unit marble. The marble is bound by a brittle–ductile shear zone at the base and a knife-sharp, low-angle normal fault at the roof, exhibiting considerable brecciation and ultracataclasite development. The hanging wall includes the Makri Unit phyllites and the overlying mid–late-Eocene–Oligocene supra-detachment sediments, which show syn-depositional slump structures and brittle deformation with low- and high-angle faulting and non-cohesive cataclasites. Extensive hydrothermal fluid circulation along the detachment zone and through NW tension gashes and high-angle faults led to pronounced silicification and ore deposition. Field observations and mineralogical and geochemical analyses revealed two primary types of ore mineralization spatially and temporally associated with different structures. Base and precious metals-rich ores are associated with the detachment, while Sb ore deposition is localized mostly within the NW-trending tension gashes and high-angle faults. [ABSTRACT FROM AUTHOR]

Several Jurassic, ophiolite-hosted Cu-Zn VMS deposits occur in Tuscany. They are hosted by tectonic units of oceanic affinity (Ligurian Units), such as the well-known deposits of nearby Liguria. Industrial production was small and definitively ceased in the 1960s. Locally, massive ore (chalcopyrite-bornite-chalcocite) with an exceptionally high grade was found. The Montecatini Val di Cecina mine exploited the largest "bonanza" and, for few decades in the 19th century, became one of the most profitable copper mines in Europe. This study provides an updated review of these deposits. Tuscan Cu-Zn VMSs mostly occur in proximity of the contact between the serpentinite-gabbro basement and the overlying basalts. Chalcopyrite-pyrite stockworks occur in serpentinite-gabbro cut by dolerite dykes, while the largest massive sulphide bodies are hosted by polymictic-monomictic breccias at the base of pillow basalts. Early chalcopyrite ores were mechanically–chemically reworked and upgraded to bornite-rich nodular ore embedded in a chlorite, calcic amphibole, Fe-rich serpentine, quartz, andradite, ilvaite, and xonotlite assemblage. This bornite-rich ore contains substantial amount of sphalerite and pyrite and ubiquitous grains of clausthalite, hessite, tellurium, and gold. They represent a prime example of the sub-seafloor portion of a hybrid mafic-ultramafic oceanic hydrothermal system formed in an OCC along the slow spreading ridge of the Jurassic Piedmont-Ligurian Ocean. The peculiar mineralogical–textural character of the bornite-rich ore was driven by an interface coupled dissolution–precipitation process mediated by fluids. [ABSTRACT FROM AUTHOR]

Yeşilyurt gold mineralization is located within the provincial borders of Malatya and Adıyaman in the East Anatolian Region. This mineralization is one of the gold deposits which correlated with low-angle normal/detachment fault. Low-angle normal fault associated with a tectonic setting which is potential extensional in Paleogene-Neogene (?) term. Marble-recrystallized limestone which belongs to the metamorphic core is the dominant rock (footwall) type in the bottom plate of the fault zone. There are deformed graphitic calc-schists (hanging wall) in the upper plate of the fault zone. The fault zone is characterized by fault gauge, cataclasite, and breccia. While the cataclasite, and breccia are the principal ore host, there is weaker mineralization in fault gauge. Alteration assemblages are: (1) silica replacements/veinlets and, (2) quartz-pyrite replacements / veinlets. High gold contents are closely related to silicification and quartz-pyrite alteration which damaged the primary textures. Small volume syn-tectonic magmatic rocks are simultaneous and typically monitored in the silicified areas which are border on the high-grade gold mineralization. Mineralization is a non-base metalliferous Au depositthat contains Au/Ag ~ 1.07, As (~0.27%), F (1.59%), and a trace amount of Sb. This deposit will lead to finding new gold deposits in Eastern Taurus Orogenic Belt.

Transient creep during an earthquake cycle is very important to understand the rheology of fault and deformation mechanisms in the brittle–plastic transition zone. In this paper, we analyzed the microstructures of samples for mylonites, pseudotachylyte, and cataclasite under optical microscope, SEM, and EBSD, which were collected from the Red River fault in southwest of China, where we uncovered a series of ductile to brittle deformed rocks which recorded transient creep related to earthquakes. The results show that mylonites formed at the inter-seismic creep were overprinted by pseudotachylyte and cataclasite which were produced during co-seismic rupture, and cracks in cataclasite were healed during the post-seismic relaxation. Based on the analysis of the microstructures and deformation mechanism of fault rocks, we propose the oscillation deformation model to explain transient creep of the brittle–plastic transition zone during the seismic cycle in the Red River fault.

Yeşilyurt gold mineralization is located within the provincial borders of Malatya and Adıyaman in the East Anatolian Region. This mineralization is one of the gold deposits which correlated with low-angle normal/detachment fault. Low-angle normal fault associated with a tectonic setting which is potential extensional in Paleogene-Neogene (?) term. Marble-recrystallized limestone which belongs to the metamorphic core is the dominant rock (footwall) type in the bottom plate of the fault zone. There are deformed graphitic calc-schists (hanging wall) in the upper plate of the fault zone. The fault zone is characterized by fault gauge, cataclasite, and breccia. While the cataclasite, and breccia are the principal ore host, there is weaker mineralization in fault gauge. Alteration assemblages are: (1) silica replacements/veinlets and, (2) quartz-pyrite replacements / veinlets. High gold contents are closely related to silicification and quartz-pyrite alteration which damaged the primary textures. Small volume syn-tectonic magmatic rocks are simultaneous and typically monitored in the silicified areas which are border on the high-grade gold mineralization. Mineralization is a non-base metalliferous Au depositthat contains Au/Ag ~ 1.07, As (~0.27%), F (1.59%), and a trace amount of Sb. This deposit will lead to finding new gold deposits in Eastern Taurus Orogenic Belt. [ABSTRACT FROM AUTHOR]

Hole BT1B of the Oman Drilling Project provides a continuous sampling from listvenite into the metamorphic sole that preserves the deformation, hydration, and carbonation processes of oceanic mantle peridotite at the base of the Samail ophiolite, Oman. We present evidence of multistage brittle deformation in listvenites and serpentinites based on field observations, visual core logging and petrography. About 10 vol% of listvenite and serpentinite in Hole BT1B is composed of cataclasite bands. Cataclasites contain lithic clasts of listvenite with spheroidal, zoned magnesite and quartz, and fragments of chalcedony‐carbonate veins that elsewhere crosscut listvenite—showing that cataclasis postdates listvenite formation. Locally the cataclasites are reworked and cut by thin, sharp faults, pointing to repeated reactivation of brittle structures. SEM‐EDS mapping shows that cataclasis was related to dissolution of carbonate and/or silica cementation. Dolomite veins crosscut cataclasites and breccias, suggesting that part of the Ca gain in BT1B is related to late fluids after listvenite formation. These results indicate a multistage tectonic overprint after peridotite carbonation and listvenite formation, which may be related to the tectonic history of the deformed continental margin under the ophiolite. These relatively late brittle structures should be excluded when trying to understand the carbonation of peridotite to listvenite. Key Points: Abundant cataclasites overprint previously formed listvenite in the Oman Drilling Hole BT1BCataclasis was related to fluid flow, which caused Mg loss and/or Si enrichment, and local redistribution of CrThe multistage tectonic overprint after peridotite carbonation in the Oman ophiolite should be excluded when analyzing early structures [ABSTRACT FROM AUTHOR]

Archaean granitoid gneisses and younger metadolerite and dolerite intrusions in a drill core from the late-Jurassic Morokweng impact structure, host mm- to m-wide aphanitic dykes that are spatially and geometrically associated with cataclasite-bearing reverse-slip faults. The dykes contain lithic and mineral clasts derived from their wallrocks. Petrographic and BSEM analysis indicates that the original dyke matrices are completely altered to a smectite-zeolite-magnetite paragenesis. However, a melt precursor is argued based on evidence for low-viscosity flow, high dyke aspect ratios and intrusive relationships into both the wallrocks and cataclasite, and the sharply contrasting matrix hydrothermal mineral grain size and textures relative to those found in the cataclasites. A subset of cm-wide pink-orange monomictic dykes have a felsic composition closely resembling their granitic wallrocks. More voluminous, polymictic, red dykes show compositions intermediate between the mafic and felsic wallrock endmembers in the drill core, which both occur in close proximity to the dykes. These hybrid compositions are interpreted to have developed either through mixing of mafic and felsic melts along faulted contacts between the doleritic and gneissic rocks, or by mechanical mixing, with or without assimilation, of a dolerite-derived melt with incohesive granitoid-derived cataclasite within the fault zones. The structural, petrographic and geochemical evidence support the dykes originating by friction melting (pseudotachylite, s.s.) caused by high-strain-rate faulting of the crater basement during the excavation and/or modification stages of the Morokweng impact, rather than by contamination of impact melt intrusions. Based on their spatial context relative to the impact melt sheet and the moderately high shock levels of their host rocks, these pseudotachylite dykes are interpreted as part of the parautochthonous peak ring of the Morokweng impact structure. • Aphanitic breccia dykes are linked to cataclastic reverse-slip faults. • Dykes are interpreted as pseudotachylite formed during the Morokweng impact. • Dykes are geochemically distinct from the Morokweng impact melt. • Melts were derived locally from granitoid and dolerite wallrocks. • Mingling of melt with incohesive cataclasite can explain variable dyke compositions. [ABSTRACT FROM AUTHOR]

The spectrum of slip behavior in crustal faults generates various rock types that can inform the mechanics of earthquake genesis. However, a single fault exposure may contain evidence of slip at various depths and temperatures due to progressive fault rock formation and overprinting during exhumation. Here, we unravel the spatiotemporal evolution of mechanical transitions along the Boundary Canyon detachment, a low-angle normal fault northeast of Death Valley, USA. Field, microstructural, and geochemical characterizations of fault rocks are compared to existing laboratory experiments and combined with a thermo-kinematic model of fault evolution. Together, these constrain the depths of mechanical transitions along the fault and reveal the evolution of earthquake nucleation zone thickness. Fault exposures from different initial paleodepths passed through the mechanical transitions during footwall exhumation, resulting in overprinting of mylonite by cataclasite and ubiquitous late formation of foliated, illite-rich gouge within the uppermost crust. We present evidence of coseismic low-angle normal fault slip (e.g., injection veins of cataclasite, laminar and grain-inertial fluidization). Coseismic slip likely nucleated at strength contrasts within the fault zone (i.e., contacts between quartzite breccia and calc-mylonite; quartz ribbons and mylonite matrix; breccia and clay gouge) at ≈ 5–9.5 km depth. Observations including mutually overprinting cataclasite/ultramylonite and exposures of pulverized gouge support that dynamic rupture propagated down-dip through the brittle-ductile transition zone (≈10–11 km depth) and up-dip through velocity-strengthening fault patches (≈0–5 km depth). Rapid fault exhumation increased the geotherm, leading to upward advection of the brittle-ductile transition and shallowing/thinning of the earthquake nucleation zone. This process may explain the rarity of large magnitude earthquakes on low-angle normal faults. [Display omitted] • Field, micro-structural, and geochemical analysis of fault rocks. • Fault rocks reconstructed to paleo-depth and temperature. • Reconstructed mechanical transitions and 2D static stress models. • Coseismic low-angle, normal-sense slip and dynamic rupture. • Thinning and shallowing of earthquake nucleation zone with exhumation. [ABSTRACT FROM AUTHOR]

Quartz/feldspar fragment (‘clast’) sizes were measured in thin sections of three types of fault zone rocks, e.g., melting-dominated pseudotachylyte (M-Pt), crushing-dominated pseudotachylyte (C-Pt) and cataclasite (Ct), from two well-studied Precambrian shear/fault zones in the Indian craton (e.g., the Gavilgarh–Tan Shear zone in central India and the Sarwar–Junia Fault zone in western India). Logarithmic plots of clast area vs. cumulative frequency in the pseudotachylytes demonstrate a fractal clast-size distribution (c.s.d.) for the intermediate size range, whereas the finer and coarser clast size fractions clearly deviate from the fractal trend. Under-representation of the finer size clasts in the pseudotachylyte samples may be attributed to their preferential melting and removal from the clast population. The relative paucity of coarse clasts, on the other hand, is possibly due to a sampling bias against coarse clasts. The c.s.d of the cataclastic rock shows a multi-fractal character with two different slopes (i.e., lower D-value for finer clast sizes) and absence of the left-hand (finer size) fall off. This suggests less efficient crushing in the finer clast size fraction. The proportion of clasts, compared to the matrix, is very small in M-Pt, increases in C-Pt and is highest in Ct, suggesting that melting of rock/mineral fragments is a dominant process in forming M-Pt, whereas it is less significant in C-Pt, and is absent in Ct, which corroborates the microscopic observations. Research Highlights: Clast size and cumulative frequency were measured in pseudotachylyte and cataclasite samples from two shear zones. Size-frequency relationship follows a power law in melting- and crushing-dominated pseudotachylytes. The power law does not hold good for the finest and coarsest size ranges in both types of pseudotachylytes. For cataclasite, a multi-fractal power law relationship exists between the size and cumulative frequency of clasts. The non-uniform power law relationship is explained by selective melting of finer clasts in pseudotachylyte. Clast size distribution in a fault rock is likely controlled by the degree of melting involved in its genesis. [ABSTRACT FROM AUTHOR]

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Frictional heterogeneities within fault zones depend strongly on lithology as well as shear fabric and strain localization structures. Here we investigate the impact of fault rock composition and shear fabric on friction constitutive properties for mature High Zagros (Iran) fault rocks. We present field observations along with results from friction experiments on intact and powdered fault rock from carbonate, quartzofeldspathic and schist. We measured frictional strength and rate/state dependence over normal stresses from 25 to 100 MPa and shear slip velocities from 3 to 300 μm/s. The sliding friction coefficients of intact fault rocks are lower than their powdered equivalents. The foliated quartzofeldspathic and lensoidal carbonate rocks from the Main Zagros Reverse Fault (MZRF) exhibit velocity strengthening friction and stable sliding. In contrast, the cataclasite carbonate rocks from the younger, Main Recent Fault (MRF) exhibit potentially unstable, velocity-weakening frictional behavior, consistent with regional seismicity. Our results suggest that solution seams, cleavage processes, and development of stylolite and calcite veins in the carbonate fault rocks of the MZRF continually rejuvenate and rework shear structures, which leads to dominantly aseismic shear. In contrast, younger fault rocks of the MRF form highly localized shear zones and shear fabric that result in velocity-weakening frictional behavior and seismic slip. Our field observations and laboratory data provide insights for using friction data and fault zone structure to build predictive models of the mode of fault slip in zones of tectonic collision. • Fault zone structures including shear localization zones play a key role in determining frictional properties • Fault rocks from the main Zagros reverse fault exhibit velocity strengthening frictional behavior and aseismic slip • Frictional properties of intact fault rocks differ from their identical powders due to shear fabric and internal structure • The sliding friction coefficients of intact fault rocks are lower than their powdered equivalents [ABSTRACT FROM AUTHOR]

Weathering can alter fault-rock cohesion, which is an important criterion in the classification of fault rocks, and can also alter fault-rock mechanical and hydraulic properties. To investigate the effects of weathering on fault rocks, we studied relatively fresh and weathered fault rocks collected from a drill core and outcrop, respectively, of a granitic fault zone (the Yeongdeok Fault, a northern branch of the Yangsan Fault) on the southeastern Korean Peninsula. At the studied outcrop, the Yeongdeok Fault has juxtaposed Triassic granite against Cretaceous sedimentary rocks. Granitic fault rocks in the outcrop are incohesive, whereas the drill core includes both cohesive and incohesive granitic fault rocks. A detailed correlation of the fault rocks from the drill core with those from the outcrop reveals that some incohesive fault rocks from the outcrop are weathered cataclasite. Cataclasites from the drill core are composed of feldspar, plagioclase, and quartz fragments embedded in a matrix of quartz, plagioclase, muscovite, and chlorite. Locally, foliation defined by the preferred orientation of muscovite is developed. The weathered cataclasite comprises quartz, plagioclase, and feldspar fragments, with a fine-grained matrix composed mostly of clay minerals. The measured Chemical Index of Alteration (CIA) values for cataclasite and weathered cataclasite are 47–49 and 60–67, respectively. Measurements of hydraulic properties show that weathered cataclasite has higher porosity and permeability compared with unweathered cataclasite. Physical and chemical weathering are interpreted to have increased the fracture density of the weathered cataclasite and enhanced the dissolution of vein minerals, respectively. These processes have not only contributed to the higher permeability and porosity of the weathered (cf. unweathered) cataclasite but have also resulted in a loss of cohesion. When cohesion is lost due to weathering, distinguishing between cataclasite and fault breccia becomes challenging. Our study demonstrates that the cohesion-based classification of fault rocks becomes limited for fault rocks with CIA value more than 60. • Weathering alters cohesion and hydraulic properties of fault rocks. • Increase in fracture density is the main cause for loss of cohesion. • Degree of weathering depends on the types of fault rocks. [ABSTRACT FROM AUTHOR]

The spatial distribution and fabric of carbonate fault rocks observed at outcrop are often highly heterogeneous. Therefore, petrophysical properties of fault rock samples may not be representative of the overall sealing capacity of the fault zone. By quantifying the fault rock distributions (i.e. fault rock thickness and fault rock continuity) of several fault zones in Malta, juxtaposing shallow burial limestones, this work investigates the relationship between fault zone architecture, deformation mechanisms, and fault rock distribution. Results from microstructural analyses indicate that high porosity (>15%) grain-dominated limestones deform via grain scale deformation, as opposed to fracture-derived cataclasites often observed in tight carbonates. Low porosity (<15%) grain-dominated limestones and high porosity micrite-dominated limestones deform in a more distributed manner, through extensional fracturing and brecciation. Fault rock continuity estimates suggest displacements of 50–200 m are required to form a continuous low-permeability cataclasite veneer in the studied sequence. However, greater displacements may be required when a distributed damage zone is present, in which strain is accommodated over multiple slip surfaces. This work highlights the heterogeneity in the distribution and fabric of carbonate fault rocks within fault zones hosting tens of meters displacement, and the importance of considering fault rock thickness and continuity when estimating the sealing capacity of a carbonate-hosted fault zone. [ABSTRACT FROM AUTHOR]

The Neoarchean Cundimurra Pluton (Yilgarn Craton, Western Australia) was emplaced incrementally along the transpressional Cundimurra Shear Zone. During syndeformational cooling, discrete networks of cataclasites and ultramylonites developed in the narrowest segment of the shear zone, showing the same kinematics as the earlier synmagmatic structures. Lithological boundaries between aplite/pegmatite veins and host granitic gneiss show more intense pre-cataclasite fabrics than homogeneous material, and these boundaries later became the preferred sites of shear rupture and cataclasite nucleation. Transient ductile instabilities established along lithological boundaries culminated in shear rupture at relatively high temperature (∼500–600 °C). Here, tensile fractures at high angles from the fault plane formed asymmetrically on one side of the fault, indicating development during seismic rupture, establishing the oldest documented earthquake on Earth. Tourmaline veins were emplaced during brittle shearing, but fluid pressure probably played a minor role in brittle failure, as cataclasites are in places tourmaline-free. Subsequent ductile deformation localized in the rheologically weak tourmaline-rich aggregates, forming ultramylonites that deformed by grain-size sensitive creep. The shape and width of the pluton/shear zone and the regime of strain partitioning, induced by melt-present deformation and established during pluton emplacement, played a key role in controlling the local distribution of brittle and then ductile subsolidus structures. [ABSTRACT FROM AUTHOR]

During the second phase of the Alpine Fault, Deep Fault Drilling Project (DFDP) in the Whataroa River, South Westland, New Zealand, bedrock was encountered in the DFDP-2B borehole from 238.5–893.2 m Measured Depth (MD). Continuous sampling and meso- to microscale characterisation of whole rock cuttings established that, in sequence, the borehole sampled amphibolite facies, Torlesse Composite Terrane-derived schists, protomylonites and mylonites, terminating 200–400 m above an Alpine Fault Principal Slip Zone (PSZ) with a maximum dip of 62°. The most diagnostic structural features of increasing PSZ proximity were the occurrence of shear bands and reduction in mean quartz grain sizes. A change in composition to greater mica:quartz + feldspar, most markedly below c. 700 m MD, is inferred to result from either heterogeneous sampling or a change in lithology related to alteration. Major oxide variations suggest the fault-proximal Alpine Fault alteration zone, as previously defined in DFDP-1 core, was not sampled. [ABSTRACT FROM PUBLISHER]

At the northern end of the Cap Corse peninsula, several klippes of ultramafic rocks (peridotite and serpentinite), among which the Monte Maggiore klippe is the least serpentinized one, rest upon continental-crust derived rocks (Centuri gneisses) and basic or metasedimentary schists (Schistes Lustrés). The Monte Maggiore ophiolitic klippe shares several characteristics with the Cima di Gratera klippe located 30 km further south. First, the two units are composed of a lherzolitic peridotite. Second, they record the same succession of metamorphic events. Third, in the Cap Corse tectonic pile, the two units occupy the highest structural position. Several differences are also observed. First, mafic rocks are significantly less abundant in the Monte Maggiore unit, where they are restricted to dykes cross-cutting the peridotite, than in the Cima di Gratera unit, where they constitute an entire sub-unit. Second, pyroxenite layers are more common at Monte Maggiore than at Cima di Gratera. Despite these differences, the Monte Maggiore and Cima di Gratera klippes can be considered as possible lateral equivalents of a single ophiolitic unit having covered the entire Cap Corse before subsequent erosion. Pseudotachylyte of seismic origin is newly discovered in the Monte Maggiore klippe. The host rock is a cataclastic serpentinized peridotite affected by a cataclastic foliation that is either flat-lying or steeply dipping. Pseudotachylyte fault veins are parallel to the host rock cataclastic foliation. The small lateral extension and the small thickness of fault veins along with frequent cross-cutting relationships suggest that the exposed pseudotachylyte most likely results from numerous small magnitude seismic events such as swarms or aftershocks rather than from large magnitude shocks. All these characteristics are also observed at the Cima di Gratera klippe where they are interpreted as the testimonies of a fossil intermediate-depth Wadati-Benioff zone at the time of subduction of the Ligurian Tethys oceanic lithosphere. Mineral assemblages that could constrain the depth of formation of the pseudotachylyte lack in the Monte Maggiore area. Despite this uncertainty, and given the similarities with the Cima di Gratera occurrences, the pseudotachylyte veins newly discovered at Monte Maggiore are tentatively related to the seismic activity linked with the subduction of the Piemonte-Ligurian oceanic lithosphere in Eocene times. This interpretation suggests that the fossil Wadati-Benioff zone could be traced further south in Alpine Corsica and further north in the Piemontese zone of the western Alps.

During earthquakes, comminution and frictional heating both contribute to the dissipation of stored energy. With sufficient dissipative heating, melting processes can ensue, yielding the production of frictional melts or "pseudotachylytes." It is commonly assumed that the Newtonian viscosities of such melts control subsequent fault slip resistance. Rock melts, however, are viscoelastic bodies, and, at high strain rates, they exhibit evidence of a glass transition. Here, we present the results of high-velocity friction experiments on a well-characterized melt that demonstrate how slip in melt-bearing faults can be governed by brittle fragmentation phenomena encountered at the glass transition. Slip analysis using models that incorporate viscoelastic responses indicates that even in the presence of melt, slip persists in the solid state until sufficient heat is generated to reduce the viscosity and allow remobilization in the liquid state. Where a rock is present next to the melt, we note that wear of the crystalline wall rock by liquid fragmentation and agglutination also contributes to the brittle component of these experimentally generated pseudotachylytes. We conclude that in the case of pseudotachylyte generation during an earthquake, slip even beyond the onset of frictional melting is not controlled merely by viscosity but rather by an interplay of viscoelastic forces around the glass transition, which involves a response in the brittle/solid regime of these rock melts. We warn of the inadequacy of simple Newtonian viscous analyses and call for the application of more realistic rheological interpretation of pseudotachylyte-bearing fault systems in the evaluation and prediction of their slip dynamics. [ABSTRACT FROM AUTHOR]

Geochemical changes and authigenic clays were detected in the fault rocks of the Padul Fault. An enrichment from the protolith to the ultracataclasites in Si, Al, Fe, Ca, Ti and also Zn but an impoverishment in Mg was detected. Although the protolith (dolostones) and fault rocks are mostly composed of carbonates, the fault rocks are also characterized by the presence of fine-grained clays in the matrix (mainly chlorite and Mg-rich biotite, but also smectite and punctually talc). Neither chlorite nor talc were detected in the protolith. The application of chlorite thermometry gives temperatures around 140–220 °C for chlorites lamellae located on the fault plane. These chlorites are compositionally homogeneous, whereas the chlorites detected in the cataclasites are more variable, although both of them are Mg-rich and have almost no Fe. As well, chlorites from the cataclasites usually include Zn in their composition and, as observed at nanoscale, they are genetically related to biotites, which come from the protolith. Talc grains (< 1 μm) are always found between dolomite and calcite. These observations point to clay mineral reactions in the fault rocks as the chlorite and talc precipitation promoted by circulation of fault-controlled hydrothermal fluids close to 200 °C. Other clays such as smectite are the result of the final step of the hydrothermal activity in the fault. The identification of authigenic clay minerals, which cause weakening mechanisms, is consistent with the geodetic characterization of the Padul Fault, which plays an important role in aseismic deformation. • Fault rocks are enriched in silicate elements, particularly in a trace element, Zn. • Fault rocks include clay minerals absent in the dolostones (chlorite and talc). • Chlorite thermometry points to low temperature (140–220 °C) origin of the clay minerals. • Clay minerals can contribute to the known aseismic deformation of the Padul Fault. [ABSTRACT FROM AUTHOR]

Abstract: In this study three different sites along the ENE-trending, sinistral Salzach–Ennstal–Mariazell–Puchberg [SEMP] fault zone were investigated with respect to brittle fault zone evolution and fault re-activation. All sites crop out in Triassic carbonates (Ladinian Wetterstein limestone/–dolomite). Simultaneously (re-) activated faults were investigated with focus on fault-slip data and structural inventory of each individual fault zone. Configuration of (internal) structural elements, fault core thickness, strike direction and slip sense in addition to particle analysis of fault core cataclasites add up to three different fault types (Fault Types I, II and III). Fault Type I is classified by a complex internal fault core structure with thicknesses up to several 10s of meters and generally evolve in a strike direction of maximum shear stress (τmax). Type II faults, characterized by cataclastic fault cores with thicknesses up to 1m, as well as Type III faults (thin solitary cataclastic layers) evolve sub-parallel to the main fault direction and in orientation according to R, R' or X shear fractures with variable (σn/τ) ratio. Progressive development from Type III to Type II and Type I faults is consistent with increasing displacement and increasing fault core width. Fault type classification and related paleostress analysis provide evidence from field observation compared to theoretical and analog models of Mohr–Coulomb fracture evolution. [Copyright &y& Elsevier]

Abstract: The 600m-thick Gole Larghe Fault Zone (GLFZ) is hosted in jointed crystalline basement and exposed across glacier-polished outcrops in the Italian Alps. Ancient seismicity is attested by the widespread occurrence of cataclasites associated with pseudotachylytes (solidified frictional melts) formed at 9–11km depth and ambient temperatures of 250–300°C. Previous work focused on the southern part of the fault zone; here we quantitatively document fault zone structure across the full width of the GLFZ and surrounding tonalite host rocks by using a combination of structural line transects and image analysis of samples collected across fault strike. These new datasets indicate that the GLFZ has a broadly symmetric across-strike damage structure and contains distinct southern, central and northern zones distinguished by large variations in fracture density, distribution of pseudotachylytes, volume of fault rock materials, and microfracture sealing characteristics. The c. 100m wide central zone is bound by two thick (~2m) and laterally continuous (>1km) protocataclastic to ultracataclastic horizons. Within and immediately surrounding the central zone, fracture density is relatively high due to cataclastic fault–fracture networks that reworked earlier-formed pseudotachylytes. The fault–fracture networks were associated with pervasive microcracking and fluid–rock interaction, resulting in the development of a c. 200m thick alteration zone delimited by lobate fluid infiltration fronts. In the c. 250m thick southern and northern zones, fracture densities are much lower and pseudotachylytes systematically overprint cataclastic faults that exploited pre-existing magmatic cooling joints. Analysis of the structure of the GLFZ suggests that it shares certain characteristics with the seismogenic source responsible for the 2002 Au Sable Forks intraplate earthquake sequence in the northeastern USA, including seismicity distributed across a fault zone 500–1000m thick and large (>100MPa) static stress drops associated with frictional melting. [Copyright &y& Elsevier]

The Palaeozoic North-Armorican shear zone (NASZ) (Brittany, France) is described as an E-W trending dextral, intracontinental shear zone. In the valley of the Queffleuth river, we outline a well-exposed zone of protocataclasite to cataclasite as the Queffieuth cataclastic zone (QCZ). Four morphological fault classes are defined in the QCZ based on the petrographic characteristics of the fault planes. The first fault class is clearly related to cataclasis, as the matrix/clast ratio increases and the clast size decreases towards the individual fault planes. The other three morphological classes cross-cut the cataclasite and are therefore considered to postdate cataclasis. A palaeostress analysis allowed to distinguish five distinct stress states, which are dominated by oblique to pure strike-slip N-S trending faults, that are oriented antithetic with respect to the overall trend of the NASZ. Both dextral and sinistral E-W kinematics are inferred for the QCZ. Because all morphological fault classes are identified in each of the stress states, dextral and sinistral kinematics must have occurred during and after cataclasis. Based on the kinematic similarities with the active South Iceland seismic zone, it is suggested that the defined stress states reflect local stress permutations during the early, immature stage of the NASZ. [ABSTRACT FROM AUTHOR]

The Alpine chain exposed in the Western Mediterranean area represents a front several kilometres in width, dismembered by more recent tectonics and by opening of the Tyrrhenian Basin. In most exposures of this mountain belt, relics of older metamorphic rocks occur. The deformational sequence of events may be revealed by the recognition of metamorphic records associated with different structures. Within a tract of the Alpine front cropping out in the Peloritani Mountains (NE Sicily), we distinguished two metamorphic complexes characterized by different tectonometamorphic histories. Their present tectonic juxtaposition is a cataclastic thrust linked to the recent Africa-verging Sicilian–Maghrebian fold-and-thrust belt. The Lower Complex is characterized by Hercynian metamorphism (P > 0.2 GPa and T ≈ 350°C) exclusively. It essentially consists of very low-grade metapelites and metavolcanic rocks overlain by an unmetamorphosed sedimentary cover. The Upper Complex, comprising different tectonic slices, consists of medium- to high-grade Hercynian metamorphic rocks (P = 0.3–0.8 GPa and T up to 650°C) with Alpine metamorphic overprint (T > 250°C) affecting also the Mesozoic–Cenozoic cover. Lithotypes, structures, and inferred P–T conditions of investigated rocks suggest the existence of an Alpine accretionary wedge during the Cretaceous deformational collision. Within the Upper Complex, a polyphase Palaeogene mylonitic horizon involving rocks belonging to different tectonic slices fully preserves the tectonometamorphic evolution. For this reason, we focused our attention on these sheared rocks in order to reconstruct the entire tectonic history of this geologically complex area. Our new basic model allows the complex structure of the nappe-pile edifice of the Peloritani Mountains to be simplified, casting new light on the tectonic evolution of this key sector of the southern Calabrian-Peloritani Orogen. [ABSTRACT FROM AUTHOR]

Abstract: Understanding the impact of faults on fluid flow in the subsurface is important for the extraction of oil, gas and groundwater as well as the geological storage of waste products. We address two problems present in current industry-standard workflows for fault seal analysis that may lead to fault rocks not being represented adequately in computational fluid flow models. Firstly, fluid flow properties of fault rocks are often measured only for small-scale faults with throws not exceeding a few centimetres. Large seismic-scale faults (throws >20 m) are likely to act as baffles or conduits to flow but they are seldom recovered from subsurface cores and consequently fault rock data for them is sparse. Secondly, experimental two-phase fluid flow data is lacking for fault rocks and, consequently, uncertainties exist when modelling flow across faults in the presence of two or more immiscible phases. We present a data set encompassing both single- and two-phase fluid flow properties of fault and host rocks from the 90-Fathom fault and its damage zone at Cullercoats Bay, NE England. Measurements were made on low-throw single and zones of deformation bands as well as on slip-surface cataclasites present along the ∼120 m throw main fault. Samples were analysed using SEM and X-ray tomography prior to petrophysical measurements. We show that single deformation bands, deformation band zones and slip-surface cataclasites exhibit dissimilar single- and two-phase fluid flow properties. This is due to grain-size reduction being more pronounced in slip-surface cataclasites and changes in microstructure being fault-parallel for deformation bands but mostly fault-perpendicular for slip-surface cataclasites. A trend of fault rocks with low absolute permeabilities exhibiting lower relative permeabilities than more permeable rocks at the same capillary pressure is evident. [Copyright &y& Elsevier]

Abstract: The characterization and representation of fault zones is of paramount importance for studies of fault and earthquake mechanics, since their rheological and geometric complexity controls seismic/aseismic behaviour and fluid circulation at depth. We present a 3D geological model of a fault system, created by integrating borehole and surface structural data, which allows us to bridge the gap between outcrop-scale descriptions and large-scale geophysical models. The model integrates (i) fault geometry and topology, (ii) fault-rock distribution, and (iii) characterization of fracturing in damage zones at the km scale. The dextral-reverse Pusteria and Sprechenstein-Mules Faults (Italian Eastern Alps) provide an opportunity to study fault rocks and damage distribution as a function of host-rock lithology and fabric, and of fault geometry. A first-order control is exerted by the composition of protoliths (quartzo-feldspathic vs. phyllosilicate-rich) and/or by the presence of an inherited anisotropic fabric (massive vs. foliated), resulting in a marked asymmetry of damage zones. Interestingly, the pervasive foliation typical of some protoliths may explain both this asymmetry and the relative weakness of one of the faults. The importance of geometrical factors is highlighted when the damage zone thickness increases five times in proximity to a km-scale contractional jog. On the other hand, the type of fault rock present within the fault core does not show a direct relationship with damage intensity. In addition, the thickness of damage zones along planar fault segments does not appear to grow indefinitely with displacement, as might be envisaged from some scaling laws. We interpret both of these observations as reflecting the maturity of these large-displacement faults. [ABSTRACT FROM AUTHOR]

Abstract: An important textural component of cataclasites in quartz-rich rocks deformed at low temperatures is a fine-grained (<20μm) matrix composed of anhedral quartz. As cataclasites form during shearing, this component would typically be interpreted to result from extreme grain size reduction through comminution. Tabular bands of fine-grained quartz that texturally resemble cataclasite found in faulted quartz arenites and other quartz-rich, well cemented sandstones have characteristics that are incompatible with a shearing origin. These characteristics include a lack of shear displacement and wall rock fragments, gradational contacts with the wall rock, and a fine-grained quartz fill that has a different cathodoluminescence, water content, oxygen isotope chemistry, and in some cases, mineralogy, than the wall rocks. Rather than being the result of cataclasis, the fine-grained quartz in these tabular bands was precipitated in a dilating fracture. In essence, these structures are veins. In fault zones, where cataclasite is well developed and shearing is unequivocal, the fine-grained quartz matrix representing up to 50% of the fault rock volume has characteristics similar to those in the tabular bands. We interpret these volumes to be in many cases a result of cement precipitation rather than as a product of comminution. If correct, then the brittle deformation of well cemented, quartz-rich rocks deformed at low temperatures involves much more dilation and cementation than previously recognized. [ABSTRACT FROM AUTHOR]

Abstract: Pseudotachylytes and two distinct types of cataclasite in the Otago Schist at Tucker Hill, South Island, New Zealand, provide evidence for both seismic slip and aseismic creep on a normal fault zone during regional crustal extension in late Cretaceous time. Regional geologic evidence suggests that the fault had its present low-angle dip (ca. 10°) at the time it was active. ‘Type A’ cataclasites, presumably aseismic, can be recognized by bi-fractal grain size distributions, monomict composition, angular clasts of uniform textural maturity, and a crude fabric defined by oriented grains and transgranular fractures. ‘Type B’ cataclasites, possibly cosesimic, have characteristics consistent with fluidized grain flow, including heterogeneous clast shapes and types, a bimodal grain size distribution, intrusive relationships with other rocks, and the absence of any fabric or transecting fractures. Pseudotachylyte, which occurs as fault veins, injection veins and more complex types of intrusive structures, consistently cuts across and invades Type A cataclasites but is both intrusive into and included as clasts in Type B cataclasites. These relationships are consistent with a fault evolution model in which the development of a damage zone through aseismic cataclasis (Type A) facilitates the formation of pseudotachylyte in a subsequent seismic event by providing a permeable matrix through which fluids can drain in the early stages of slip, thereby maintaining frictional contact between rock surfaces. The formation of pseudotachylyte, in turn, may seal the fault zone and lead to thermal pressurization in a later seismic cycle, forming fluidized (Type B) cataclasites. Seismic slip on the low-angle normal fault zone at Tucker Hill may have occurred by two distinct modes of dynamic weakening — melt lubrication and thermal pressurization — in successive seismic events. Although there is a perception among geologists that pseudotachylyte is most likely to form in intact, crystalline rocks, geophysical models of fault zones clearly demonstrate that pseudotachylyte formation is actually suppressed in low-permeability rock because any fluids present would be unable to escape the fault zone and thermal pressurization would rapidly reduce frictional resistance. The paradigmatic occurrences of pseudotachylyte in otherwise pristine crystalline rocks probably represent somewhat exceptional circumstances (single rupture events at very high effective stress in dry rock). Coseismic frictional melts may actually be more common in hydrated rocks like the schist at Tucker Hill, but harder to recognize and also vulnerable to overprinting as a fault zone matures. In such rocks, pseudotachylyte may represent an intermediate stage in the evolution of a fault zone, the period between the formation of a high-permeability damage zone and the development of a low-permeability fault core. [Copyright &y& Elsevier]

Abstract: A study of normal faults in the Nubian Sandstone Sequence, from the eastern Gulf of Suez rift, has been conducted to investigate the relationship between the microstructure and petrophysical properties of cataclasites developed along seismic-scale faults (slip-surface cataclasites) and smaller displacement faults (deformation bands) found in their damage zones. The results help to quantify the uncertainty associated with predicting the fluid flow behaviour of seismic-scale faults by analysing small faults recovered from core, a common procedure in the petroleum industry. The microstructure of the cataclasites was analysed as well as their single-phase permeability and threshold pressure. Faulting occurred at a maximum burial depth of ∼1.2km. The permeability of deformation band and slip-surface cataclasites varies over ∼1.5 orders of magnitude for a given fault. Our results suggest that the lowest measured deformation band permeabilities provide a good estimate for the arithmetic-mean permeability of the major slip-surface cataclasites. This is because the cataclastic permeability reduction is mostly established early in the deformation history. Stress at the time of faulting rather than final strain appears to be the critical factor determining fault rock permeability. For viable predictions it is important that the slip-surface cataclasites and deformation bands originate from the same host. On the other hand, a higher uncertainty is associated with threshold pressure predictions, as the arithmetic-mean slip-surface cataclasite threshold pressure exceeds the highest measured deformation band threshold pressure by at least a factor of 4. [Copyright &y& Elsevier]

Abstract: Microstructures and grain size distribution from high velocity friction experiments are compared with those of slow deformation experiments of for the same material (Verzasca granitoid). The mechanical behavior of granitoid gouge in fast velocity friction experiments at slip rates of 0.65 and 1.28m/s and normal stresses of 0.4–0.9MPa is characterized by slip weakening in a typical exponential friction coefficient vs displacement relationship. The grain size distributions yield similar D-values (slope of frequency versus grain size curve=2.2–2.3) as those of slow deformation experiments (D=2.0–2.3) for grain sizes larger than 1μm. These values are independent of the total displacement above a shear strain of about γ=20. The D-values are also independent of the displacement rates in the range of ∼1μm/s to ∼1.3m/s and do not vary in the normal stress range between 0.5MPa and 500MPa. With increasing displacement, grain shapes evolve towards more rounded and less serrated grains. While the grain size distribution remains constant, the progressive grain shape evolution suggests that grain comminution takes place by attrition at clast boundaries. Attrition produces a range of very small grain sizes by crushing with a D<-value=1. The results of the study demonstrate that most cataclastic and gouge fault zones may have resulted from seismic deformation but the distinction of seismic and aseismic deformation cannot be made on the basis of grain size distribution. [Copyright &y& Elsevier]

Abstract: The factors controlling the development of different types of fault rock assemblages and, more specifically, the formation of friction melts are still not fully understood. In this study we compared two exhumed strike–slip faults in the Adamello batholith (Southern Alps): the Gole Larghe and the Passo Cercen fault zones, active at 9–11km depth and temperatures of 250–300°C. Each fault zone consists of hundreds of sub-parallel strands exploiting pre-existing joints. The Gole Larghe fault strikes N105±5° and is dextral; the fault rocks are cataclasites and widespread, centimetre-thick pseudotachylytes. The Passo Cercen fault strikes on average N130° and is formed by multiple fault horizons: fault segments striking N105°–N130° are mainly dextral, whereas faults striking N135°–N140° are mainly sinistral. Microstructural, mineralogical and geochemical investigations show that the fault rocks are cataclasites associated with thick epidote+K-feldspar+quartz veins and rare, millimetre-thick pseudotachylytes. Field evidence suggests that in both fault zones, the direction of the maximum horizontal stress σ 1 was N135°. The Gole Larghe fault strikes at about 30° to σ 1 and is favourably oriented for reactivation. By contrast, the Passo Cercen fault strikes at low angles to σ 1 and is unfavourably oriented for reactivation, therefore requiring the development of high pore pressures, as suggested by the occurrence of extensive epidote veining and hydraulic breccias. It is proposed that frictional melting in the Passo Cercen fault zone was inhibited by the development of high pore pressures and low effective normal stresses. [Copyright &y& Elsevier]

The Globe-Progress gold deposit at Reefton is hosted in a curvilinear mineralised zone that cuts Paleozoic Greenland Group basement metagreywackes. Two discrete phases of mineralisation have resulted in the formation of five different ore types along the shear. An initial phase of mineralisation formed hydrothermal quartz veins and associated Au, As, and S enrichment, with low-grade mineralised host rock. These quartz veins and mineralised host rocks form the outer regions of the mineralised zone. A second hydrothermal phase introduced Sb, Au, As, and S during brittle shear deformation focused on the pre-existing mineralised rocks. This deformation and mineralisation resulted in the formation of metre-scale cataclasite ore and quartz breccia from mineralised host rock and hydrothermal quartz veins, respectively. Cataclasite was derived from argillite layers in the host rock, from which Na, Fe, and Mg have been leached during mineralisation; Al, Ti, and Cr have been conserved; and there has been minor enrichment in Sr, Pb, Zn, and Cu. No quartz was added to the cataclasite or quartz breccia during mineralisation, but some quartz recrystallisation occurred locally, and quartz clasts were physically incorporated into the cataclasite during deformation. The presence of euhedral sulfides in the cataclasite (40% of total sulfides), late-stage undeformed stibnite veins infilling breccia (1-5 cm³ scale), and undeformed free gold in quartz breccia, imply that the second phase of mineralisation persisted both during and after cataclasis and brecciation. Antimony deposition is greatest in the central cataclasite, up to 6 wt%, and locally in the quartz breccia where stibnite veins are present. Concentrations of Sb decrease with distance from the shear zone. The second, Sb-rich phase of mineralisation in the Globe-Progress deposit resembles similar Sb-rich overprints in the correlative Victorian goldfield of Australia. [ABSTRACT FROM AUTHOR]

Abstract: In the North Range of the ca. 1.85Ga Sudbury impact structure, massive bodies of Sudbury breccia cut across the Archean Levack gneiss complex and Early Proterozoic Matachewan diabase dykes. The complex underlies the Sudbury Igneous Complex (SIC), which represents an impact melt sheet that lined the floor of the impact crater. The breccia occurs as 1–100m wide irregular bodies that contain rounded clasts of diabase and tonalitic and dioritic Levack gneiss within a fine-grained to aphanitic, black to dark grey matrix. Mineral chemical analyses and Rietveld analyses based on X-ray diffraction patterns show that the breccia matrix contains microclasts of magnesiohornblende, oligoclase, and quartz, surrounded by metamorphic andesine laths, actinolite, Kfeldspar, albite, and chlorite, which crystallized during cooling of the SIC. On binary oxide-SiO2 diagrams, breccia values plot on a compositional mixing line between those of the more felsic tonalitic gneiss and the more mafic dioritic gneiss and diabase. The breccia has concentrations in rare earth elements (REEs) intermediate between those of the dioritic and tonalitic gneisses and a REE pattern with a negative slope that is less pronounced than those of the gneisses. This is due to the addition of a minor diabase component that has a slightly negative REE slope, suggesting that the breccia is a mix of comminuted tonalitic gneiss, dioritic gneiss, and minor diabase. Comminution and cataclasis of these source rocks occurred along pre-existing anisotropies and fractures that formed and were reactivated during the growth and collapse of the transient crater. The comminuted materials mixed together as large bodies of breccia that were injected in dilational sites that opened during the upward expansion and collapse of the crater. [Copyright &y& Elsevier]