Deformation In Shear Zone Research Articles

Semibrittle seismic deformation in high-temperature mantle mylonite shear zone along the Romanche transform fault.

Oceanic transform faults, a key element of plate tectonics, represent the first-order discontinuities along mid-ocean ridges, host large earthquakes, and induce extreme thermal gradients in lithosphere. However, the thermal structure along transform faults and its effects on earthquake generation are poorly understood. Here we report the presence of a 10- to 15-kilometer-thick in-depth band of microseismicity in 10 to 34 kilometer depth range associated with a high-temperature (700° to 900°C) mantle below the brittle lithosphere along the Romanche mega transform fault in the equatorial Atlantic Ocean. The occurrence of the shallow 2016 moment magnitude 7.1 supershear rupture earthquake and these deep microearthquakes indicate that although large earthquakes occur in the upper brittle lithosphere, a substantial amount of deformation is accommodated in the semibrittle mylonitic mantle that resides at depths below the 600°C isotherm. We also observe a rapid westward deepening of this band of seismicity indicating a strong lateral heterogeneity.

Investigation of annealing treatment on the interfacial and mechanical properties of Al5052/Cu multilayered composites subjected to ARB process

This research aims to discuss the effect of annealing time and temperature on the interfacial and mechanical properties in Al5052/Cu multilayer composites processed by accumulative roll bonding (ARB). According to the results of XRD and EDS, four intermetallic layers with the chemical composition of Cu9Al4-Cu4Al3-CuAl-Al2Cu were observed at the interface of processed composite with three ARB passes after annealing at 400 °C for 90 min. The results of tensile properties in each specific ARB pass showed that at lower annealing temperatures and times, the recrystallization or recovery was dominant in mechanical properties, and the strength decreased, while at higher annealing temperature and time strength increased due to the thickening of intermetallic compounds. The maximum value of tensile strength (345 MPa) was obtained in the third pass at 400 °C for 90 min. Results of OM analysis on fracture surface by optic microscope of the composites annealed at 350 °C for 60 min demonstrated that from zero to the second pass the fracture path in the macroscopic state was perpendicular to the direction of stress. However, in the third and fourth passes, the macroscopic path of fracture is observed with an angle of 35–45° to the direction of tension, which is due to the formation of shear deformation zones. Also, SEM analysis of the third pass sample annealed at 400 °C for 60 min indicated that the fracture surface of the aluminum layer was ductile type but the copper layer was a knife-edge without dimples and holes.

An Analysis of Loess Tunnel Failure and Its Mechanism

A series of changes of mechanical properties such as fracture development, relaxation, collapse deformation, and strength decreasing of the surrounding rock of loess tunnels occur due to shearing and immersing, and loess tunnels will be prone to engineering failures, including large deformation, fissure, ground collapse, landslide, and lining cracking, seriously threatening the construction and operation safety of tunnels. These problems are especially prominent for long-span loess tunnels. Based on the understanding of features in the construction and operation of the loess tunnel project and proceeding from the perspective of structural evolution of loess, distribution of the shear deformation zone, instability of the excavation face, and adverse effects of geological conditions, the predisposing factors of damage of the surrounding rock and the supporting structure of large-span loess tunnels, common types of failures, and their formation mechanisms are analyzed in this paper. According to the relationship between the evolution of the loess structure and the law of strength change, an improved Mohr–Coulomb elastic-plastic, tension-compression-shear, constitutive model, considering the loess structural property, is established and applied in numerical calculation. The formation mechanism of different failures in the course of loess tunnel construction is revealed by numerical analysis, in which the structural property of loess, loess strata, geological conditions, and excavating and supporting actions are simulated by the numerical method. A reference is provided for the prevention and remediation of engineering failures of a loess tunnel.

Ar-Ar chronology of the brittle deformation age for the ore-controlling shear zones in the Jiaodong Peninsula and it's constrains on gold mineralization

胶东地区是典型的剪切带型金矿集中区，精确厘定该地区控矿剪切带的活动时代，可为探讨剪切带与金矿成因关系提供关键的时限约束，并且对矿床成矿模式的建立具有至关重要的意义。大量矿床地质证据显示胶东地区控矿剪切带中脆性变形活动对金矿体的形成具有直接影响，但其脆性变形时代尚不十分清楚。据此，本文在详细研究金矿体赋存特征的基础上，系统选取胶东焦家、玲珑、邓格庄、乳山这四个金矿区控矿剪切带断层泥中白云母进行⁴⁰Ar-³⁹Ar年代学研究。定年结果显示，胶东地区焦家剪切带、招平剪切带以及牟乳剪切带的脆性变形时代分别为110.3±1.5Ma、122.8±1.7Ma、119.6±1.2Ma~115.8±1.4Ma。其中焦家剪切带的脆性变形时代明显晚于招平和牟乳剪切带，可能代表了焦家蚀变岩型矿化形成后易遭受后期的构造叠加。综合胶东各金矿区控矿剪切带变形时代、岩体侵位时代、成矿时代及剪切带活动特征和矿体产出特征，本文认为在多期岩体侵位以及控矿剪切带递进变形过程中，剪切带韧性变形区中由高压流体作用产生的同期脆性破裂可形成脉型矿化，如乳山金矿；而在脆-韧性和脆性变形区中发生的大规模脆性变形可导致脉型和蚀变岩型矿化的形成，如玲珑、邓格庄和焦家金矿。但随着剪切带的递进变形和隆升剥蚀，后期多期次的脆性构造变形叠加，可导致多种矿化类型出现在同一构造部位，如焦家金矿中石英脉型和蚀变岩型矿化。;Jiaodong Peninsula is a typical concentration area for shear zone type gold deposits. Accurate determination of the deformation age of ore-controlling shear zones in this area can provide a key time limit for exploring the relationship between shear zones and the genesis of gold deposits, and is of vital significance to the establishment of metallogenic mechanism. A large number of geological evidences show that the formation of gold orebodies is directly controlled by brittle deformation activities of ore-controlling shear zones in Jiaodong Peninsula, but this deformation age is still unclear. Based on detailed study of the occurrence characteristics of orebodies, we systematically selected muscovite samples from fault gouge in Jiaojia, Linglong, Denggezhuang and Rushan gold mining areas for the Ar-Ar chronology study. ⁴⁰Ar/³⁹Ar dating results show that the brittle deformation ages of Jiaojia, Zhaoping and Muru shear zones in Jiaodong Peninsula are 110.3±1.5Ma, 122.8±1.7Ma and 119.6±1.2Ma~115.8±1.4Ma, respectively. Among them, the brittle deformation age of Jiaojia shear zone is obviously later than those of Zhaopin and Muru shear zones, which may represent that the altered rock type mineralization in Jiaojia deposit is susceptible to structural superposition in the later period. Comprehensively comparing shear zone deformation ages, pluton emplacement ages, metallogenic ages, shear zone activities and orebody occurrence characteristics in Jiaodong gold deposits, it is suggested that: (1) The contemporaneous brittle fractures caused by high-pressure fluids in ductile deformation region of shear zones can lead to the formation of vein type mineralization, e.g. Rushan gold deposits; (2) Large-scale brittle deformation in brittle-ductile and brittle region can lead to the formation of vein type and altered rock type mineralization, e.g. Linglong, Denggezhuang and Jiaojia gold deposits. Both stages take place during the process of multi-stage emplacement and progressive deformation of ore-controlling shear zones. However, with the progressive deformation and uplift denudation of shear zones, the superposition of brittle deformation in the late stage may lead to the occurrence of multiple mineralization types in the same structural site, e.g. quartz vein type and altered rock type mineralization in Jiaojia gold deposit.

Deformation mechanisms, mineral chemistry and zircon U-Pb geochronological constraints in the south Patos shear zone: implications for the crustal evolution of the Borborema Province, NE Brazil

The southern boundary of the Patos Shear Zone (PSZ) is characterized by mylonites resulting from the deformation of Paleoproterozoic basement gneisses, Neoproterozoic metavolcanic and metasedimentary rocks, granitic and granodioritic intrusions. Among the latter, the Santa Terezinha and Catingueira plutons show stretched shapes in agreement with the the shear zone’s regional trend. Recrystallized quartz grains in these plutons accommodate deformation by dislocation creep. The host banded gneisses show similar deformation structures to the plutons. Quartz crystallographic fabrics mainly record the activity of basal and prism slip planes with local contribution of rhomb planes, whilst feldspar clasts show evidence of intracrystalline deformation in the larger porphyroclasts. These characteristics suggest that shearing occurred at lower-amphibolite facies conditions. U-Pb zircon data for the Santa Terezinha pluton yields an age of 625 ± 7 Ma, which, coupled with the pluton elongated shape and microstructure, suggests that its emplacement was pre-kinematic in relation to the Patos shear zone. Post-emplacement elongation of the granite body occurred along the strike-slip trend. Such structural and geochronological constraints highlight the close association between magma emplacement and shear zone deformation during distinct stages of the Brasiliano-Pan-African orogeny in the Borborema Province.

Sheath fold development around deformable inclusions: Integration of field-analysis (Cima Lunga unit, Central Alps) and 3D numerical models

We investigated complex tectonic structures within a km-scale shear zone (Cima Lunga unit), which is traditionally interpreted as generated by multiple, distinct deformation phases, despite showing unique schistosity and lineation. Based on structural analyses we discovered sheath folds developed in relatively weak gneissic/schistose rocks, enveloping inclusions of stronger ultramafics. The internal layering of inclusions experienced superimposed folding, boudinage and folding, attesting to layer-parallel shortening followed by stretching and further again shortening. Using 3D numerical modelling, we explored the structure evolution within and around deformable viscous inclusions under far-field simple shear. The numerical results showed that the internal deformation of ellipsoidal inclusions and the fold development around the inclusions are both dependent on the viscosity ratio, shear strain and the inclusion aspect ratio. The Cima Lunga structural patterns were reproduced for finite strains exceeding 7.5 and viscosity ratio between 2.8 and 9. Inclusions are characterized by persistent rotation of the internal layering, resulting in super-simple shear regime, with kinematic vorticity number >1. An important corollary is that ultramafics and host rocks experienced coupled deformation since the prograde metamorphic evolution. Finally, we emphasise that progressive deformation in shear zones may offer sufficient explanation for complex structural patterns, without invoking unjustified polyphase deformation.

Study of small-scale structures and their significance in unravelling the accretionary character of Singhbhum shear zone, Jharkhand, India

Localized strain within tabular ductile shear zones is developed from micro- to meso- to even large scales to form complex structures. They grow in width and length through linkage of segments with progressive accumulation of strain and displacement, and finally produce shear zone networks characterized by anastomosing patterns. Singhbhum shear zone (SSZ) represents a large composite zone characterized by a collage of different dismembered lithotectonic segments, with heterogeneous structural features, within a matrix typical of a shear zone. Structural features indicate that the material properties of protoliths have a great role in controlling the mechanics of deformation. Meso- and micro-scale structural studies of the east-central part of the SSZ reveal ‘tectonic complex like’ (? deeper level equivalent of melange type complex) assemblage of dismembered lithoteconic units. Shear-induced foliations, S, C and C′, were developed while the main mylonitic foliation is represented by C-plane. Apart from that, shear lenses are exceptionally well developed in both meso- and micro-scale in most of the units, particularly in schistose rocks. They were formed from different processes during progressive simple shear, which includes (1) anastomosing C-planes, (2) intersection between C- and C′-planes, (3) disruption of stretched out longer limbs of asymmetric folds, and (4) cleavage duplex. Fabrics recorded in rocks indicate that there was a progressive change in the development of predominantly flattening fabric (coaxial pure shear) in the northern part (outside the SSZ), to simple-shear non-coaxial type deformation producing shear fabric, dominating over the flattening fabric, in the southern part (within the SSZ) that is in close proximity with the Singhbhum Craton. Although an overall plane strain simple shear model is apparent, occasional presence of extensional features along two directions of the mylonitic foliation, demonstrative of three-dimensional deformation (simple shear and flattening: X > Y > 1 > Z), may indicate the stretching nature of the SSZ. From the orientation of oblique grain shape fabric [ISAmax (θ < 45°)], there is slight deviation from simple shear, i.e., a sub-simple nature of plane strain shear could be inferred. However, in conformity with simple shear model the ubiquitously developed stretching lineation shows consistency in orientation being parallel to the movement direction. There is no evidence of transpression. Shear sense indicators invariably indicate up-dip ductile thrust movement with vergence top-to-the south. Microstructural deformational characteristics indicate that peak temperature attained during the deformation in shear zone was ~600 °C. Prolonged period of metasomatism, induced by fluid influx, played an important role in strain softening during the development of SSZ.

Deformation Characteristics of the Shear Zone and Movement of Block Stones in Soil–Rock Mixtures Based on Large-Sized Shear Test

Soil–rock mixtures (SRM) have the characteristics of distinct heterogeneity and an obvious structural effect, which make their physical and mechanical properties very complex. This study aimed to investigate the deformation properties and failure mode of the shear zone as well as the movement of block stones in SRM experimentally, not only considering SRM shear strength. The particle composition and proportion of specimens were based on field samples from an SRM slope along national highway 318 in Xigaze, Tibet. Shear zone deformation tests were carried out using an SRM-1000 large-sized geotechnical apparatus controlled by a motor servo, considering the effects of different stone contents by mass (0, 30%, 50%, 70%), vertical pressures (50, 100, 200, 300, and 400 kPa), and block stone sizes (9.5–19.0, 19.0–31.5, and 31.5–53.0 mm). The characteristics of the shear zone deformation and block stone interactions were monitored by placing aluminum wires and dry ash in holes in the specimens. The results showed that the stone content 30% and 70% were two critical thresholds to determine the deformation characteristics of SRM. Under the conditions of high stone content and large particle size, the stones throughout the shear surface tended to extrude and roll during the shear process. The block stones around the shear surface were mainly affected by dilatancy and exhibited extrusion, particle breakage, and redistribution. The deformation pattern could be considered as be analogous to push-type shear deformation from the back to front or composite shear deformation from the front and back to the middle of the slope. It is of great importance to study the shear characteristics and deformation evolution of SRM to understand the progressive shear process of the sliding zone and the failure mode of landslides.

Establishment of macro-micro constitutive model and deformation mechanism of semi-solid Al6061

The compression stress-strain curves of semi-solid metals have evident segmentation characteristics composed of three sections: stress increasing section, stress decreasing section, and stress steady section. At the same time, the semi-solid holding time is introduced into the constitutive model as a new independent variable. Therefore, it is unsatisfactory to use the traditional metal constitutive model to fit semi-solid metals. In this paper, a new form of the constitutive model is proposed. The modified Hansel-Spittel formula is used to fit the characteristic stress points, and these are then used as divides to fit the entire stress-strain curve using the function segment method. The fitting error for the first two stages of the stress-strain curves is found to be 7.01%. At the same time, the microstructure morphologies of different liquid fraction samples at different deformation stages are compared. It was proposed that the three-segment characteristics of the semi-solid stress-strain curve correspond to the process of incubation, growth, and connection of voids in the shear-deformation zone. However, this mechanism of action weakens with the increment of the liquid fraction. For semi-solid metals with liquid fraction more than 25%, it is more appropriate to describe the deformation behavior using non-Newtonian liquid flow model.

Shear zone cooling and fabrics of synkinematic plutons evidence timing and rates of orogenic exhumation in the northwest Borborema Province (NE Brazil)

Ediacaran convergence and collision resulting from amalgamation of West Gondwana are documented in the Borborema Province by high-pressure rock units, contractional tectonics and anatexis. Thermochronological (zircon U-Pb and amphibole-biotite Ar-Ar) and structural (Anisotropy of Magnetic Susceptibility) constraints from shear zone-bounding synkinematic plutons in the Ceará Central Domain provide timing and rates of their subsequent post-collisional evolution. Our results show that: (i) U-Pb ages of zircons of 585–571 Ma record magma crystallisation and a protracted history of assembly for the Tauá batholith, synchronous with deformation in the bounding transcurrent shear zone junction; (ii) AMS fabrics document chamber construction processes and the effect of long-lived strongly localized shear zone deformation; and (iii) 40Ar/39Ar plateau ages of amphibole and biotite from the synkinematic plutons at 577–562 and 559–554 Ma, respectively, yield cooling rates of 20–40 °C/Myr characterising differential cooling paths. Integration of various thermochronometers available for the strike-slip shear zones and the internal high-pressure domain reveals a fast isothermal decompression (long-term unroofing rate of 1.9–5.8 mm/yr), which exhumed high-pressure rock units. Subsequently, fast nearly isobaric cooling (20–40 °C/Myr) occurred in the whole terrane until 590 Ma, with temperatures falling below 320 °C. Due to enhanced magmatic activity during the deformation, the shear zones experienced much higher temperatures at that same depth at 584 Ma followed by fast cooling (20–40 °C/Myr) to temperatures below 320 °C at 560 Ma. These final cooling episodes were accompanied by slow unroofing at an estimated rate of 0.3–0.9 mm/yr, sufficient to bring these rocks close to the surface at 540 Ma, when molassic, pull-apart basins were formed.

Investigation of effect of uncut chip thickness to edge radius ratio on nanoscale cutting behavior of single crystal copper: MD simulation approach

Extremely small cutting depths in nanoscale cutting makes it very difficult to measure the thermodynamic properties and understand the underlying mechanism and behavior of workpiece material. Highly precise single-crystal Cu is popularly employed in optical and electronics industries. This study, therefore, implements the molecular dynamics technique to analyze the cutting behavior and surface and subsurface phenomenon in the nanoscale cutting of copper workpieces with a diamond tool. Molecular dynamics simulation is carried out for different ratios of uncut chip thickness ( a) to cutting edge radius ( r) to investigate material removal mechanism, cutting forces, surface and subsurface defects, material removal rate (MRR), and stresses involved during the nanoscale cutting process. Calculation of forces and amount of plowing indicate that a/ r = 0.5 is the critical ratio for which the average values of both increase to maximum. Material deformation mechanism changes from shear slip to shear zone deformation and then to plowing and elastic rubbing as the cutting depth/uncut chip thickness is reduced. The deformation during nano-cutting in terms of dislocation density changes with respect to cutting time. During the cutting process, it is observed that various subsurface defects like point defects, dislocations and dislocation loops, stacking faults, and stair-rod dislocation take place.

Microstructure-based three-dimensional characterization of chip formation and surface generation in the machining of particulate-reinforced metal matrix composites

Particulate-reinforced metal matrix composites (PRMMCs) are difficult to machine due to the inclusion of hard, brittle reinforcing particles. Existing experimental investigations rarely reveal the complex material removal mechanisms (MRMs) involved in the machining of PRMMCs. This paper develops a three-dimensional (3D) microstructure-based model for investigating the MRM and surface integrity of machined PRMMCs. To accurately mimic the actual microstructure of a PRMMC, polyhedrons were randomly distributed inside the matrix to represent irregular SiC particles. Particle fracture and matrix deformation and failure were taken into account. For the model’s capability comparison, a two-dimensional (2D) analysis was also conducted. Relevant cutting experiments showed that the established 3D model accurately predicted the material removal, chip morphology, machined surface finish, and cutting forces. It was found that the matrix-particle-tool interactions led to particle fractures, mainly in the primary shear and secondary deformation zones along the cutting path and beneath the machined surface. Particle fracture and dilodegment greatly influences the quality of a machined surface. It was also found that although a 2D model can reflect certain material removal features, its ability to predict microstructural variation is limited.

Evolution of Chip-Deformation Mechanisms with Increasing Temperature in Laser-Assisted Microcutting of Amorphous Alloy

NiP coating with an amorphous structure is a commonly used mold material for manufacturing resin optical components. However, due to the inhomogeneous deformation characteristics of amorphous alloys, chippings and burrs are easily produced at the edge of microstructures. Laser-assisted microcutting has proven to effectively inhibit the generation of these defects but the evolution of chip-deformation mechanisms with different laser power remains to be explored. In this study, a simulation of the temperature field under nanosecond laser irradiation was conducted and the laser-assisted cutting of NiP was considered, using the same irradiation parameters. Through the analysis of chip morphology under different conditions, it is found that the temperature in the deformation zone mainly affects the morphology of the secondary shear bands but has no effect on the number of nucleation in the primary and secondary shear bands. The proper temperature in the shear deformation zone can improve the deformation ability of the secondary shear band, thus making the shearing process more stable. This research will prove helpful to understand the material deformation mechanisms to guide the selection of laser parameters in the laser assisted cutting of amorphous alloy.

Calibrating friction coefficients in discrete element method simulations with shear-cell experiments

Discrete Element Method (DEM) simulations coupled with shear cell experimental results have been used to investigate the flow behaviour of a dry particle assembly of glass beads in the quasi-static regime. Experimental studies have been undertaken using an FT4 powder shear cell apparatus, in parallel with extensive DEM simulations of both homogeneous simple shear and the FT4 shear cell itself. The findings show that it is not possible to accurately predict the bulk friction coefficient with homogeneous simple shear simulations unless both rolling and sliding friction are considered. There are, however, multiple pairs of sliding and rolling friction coefficients which can reproduce the experimental bulk friction coefficient. Sliding test experiments were conducted to yield the coefficient of sliding friction, and hence minimise the set of potentially correct pairs. Simulations of the full FT4 shear cell with two different calibration pairs, along with a pair without rolling friction, were then undertaken to understand the effect of their selection on realistic wall-bounded shearing conditions. Discrepancies were mainly found in the obtained radial contact number and velocity profiles, with increasing friction coefficients - particularly sliding friction - found to inhibit packing and particle velocity in the shear deformation zone. Comparison between homogeneous simple shear and shear cell simulation results showed a significant effect of the wall on the obtained force network, with almost a complete absence of the weakest structures which were seen supporting the strong structures in the simple shear scenario.

Structural deformation characteristics and shale gas preservation conditions in the Zhaotong National Shale Gas Demonstration Area along the southern margin of the Sichuan Basin

The Zhaotong National Shale Gas Demonstration Area along the southern margin of the Sichuan Basin is located in the complex marine tectonic area of South China, where shale deformation and reformation are intense and the factors controlling sweet spots are complex, so the preservation conditions have an important impact on the enrichment of shale gas. In order to support the selection and evaluation of shale gas sweet spots in this area and improve the success rate of drilling, this paper carried out a geological survey on field outcrops. Then, based on drilling, mud logging and physical property test data, the structural deformation pattern and the regional deformation characteristics of this demonstration area were analyzed, and the development characteristics of formation joints and fractures, the sealing capacity of shale surrounding rock and the distribution characteristics of gas reservoirs were studied. Finally, the preservation conditions of shale gas in the Wufeng Formation of Upper Ordovician and the Longmaxi Formation of Lower Silurian were discussed. And the following research results were obtained. First, in the Zhaotong National Shale Gas Demonstration Area, three structural deformation patterns are developed from south to north, including trough type, equal amplitude type and baffle type, which are distributed in three major deformation zones, respectively, i.e., the shear deformation zone of Central Guizhou Uplift, the compression–torsion deformation zone of northern Yunnan–Guizhou Depression and the compression deformation zone of Southern Sichuan Depression. Second, three types of joints and fractures whose relationships with the direction of strata are high angle, middle–low angle and bedding intersection are developed in the Wufeng–Longmaxi formations and its overlying strata, and their occurrence characteristics are basically consistent with those of the three major deformation zones. Third, the shale of Wufeng–Longmaxi formations is thick in the north and thin in the south and possesses the preservation conditions of source–reservoir integration and self-sealing hydrocarbon accumulation. And combined with the sealing ability of the overburden strata and the roof and floor, its preservation conditions are overall better. Fourth, from the perspective of shale gas component, this area can be divided into three belts, i.e., methane, methane + nitrogen mixture and nitrogen from north to south. And the preservation conditions of shale gas are generally better in the north and worse in the south. In conclusion, the shale in the central–northern part of Zhaotong National Shale Gas Demonstration Area (compression deformation area and its southern margin) is the most favorable area because of its large shale thickness, weak reformation and deformation, bedding development of joints and fractures, good sealing performance and excellent preservation conditions. The compression–torsion deformation zone of northern Yunnan–Guizhou Depression in the central part is moderate in preservation conditions, and it is the relatively favorable area. The shear deformation zone of Central Guizhou Uplift in the southern part has poor preservation conditions, and it is a prospective area.

The Influence of Scale Parameters of Strengthening Phase on Plastic Shear Zone in Heterophase Alloys with Incoherent Nanoparticles

In this paper, the mathematical simulation is used to study and analyze the shear zone or plastic deformation at a meso-level in dispersion-hardened crystalline materials with an aluminum matrix and incoherent nanoparticles. This study also considers both the macro-level or the behavior of the flow stress curves and the micro-level or the formation of linear and point defects. It is found that the size of the shear zone lowers with the growth in the degree of deformation in all the dispersion-hardened materials at issue. The average size of this zone does not depend on scale parameters of the strengthening phase. The formation and accumulation of various dislocation types in the shear zone mostly depend on the particle size.

Geochronologic constraints on deformation and metasomatism along an exhumed mylonitic shear zone using apatite U-Pb, geochemistry, and microtextural analysis

Directly dating and characterizing deformation and metasomatism in fault zones is critical to understanding fault zone processes and lithospheric evolution. Integrated apatite U-Pb geo-thermochronometry, geochemistry, and microtextural analysis has potential to directly date and characterize deformation and fluid-rock interactions in shear zones using a single mineral phase. Integrated apatite U-Pb, microtextural, and trace and rare earth element results from an exhumed mylonitic shear zone, the Main Mylonitic Band in the Northern Pyrenees, constrain timing of deformation and metasomatism along the shear zone as Early Cretaceous, synchronous with ductile deformation and exhumation of middle-lower crustal gneisses in the footwall, and significant mineralization and metasomatism in the brittle hanging wall. Samples from the hanging wall preserve magmatic apatite U-Pb crystallization ages that overlap with zircon and monazite U-Pb ages of ∼300 Ma, granitic geochemical trends, and primary magmatic growth zoning. Footwall samples below the MMB record dynamic recrystallization of apatite associated with mylonitization and exhumation of the gneisses in the Early Cretaceous. Apatite along the MMB record partial recrystallization via dissolution-reprecipitation associated with shearing and circulation of deeply sourced fluids along the shear zone evident by mixed ages (300-100 Ma), geochemical signatures enriched in light rare earth elements, and patchy microtextures. The MMB likely acted as a conduit for deeply sourced fluids that affected the brittle-ductile transition, strain localization, and fluid pathways through the continental crust. This study demonstrates that the integration of apatite U-Pb geo-thermochronology, geochemistry, and microtextural analysis is a powerful approach to dating deformation and metasomatism, characterizing grain scale deformation and (re)crystallization processes, and geochemically characterizing fluid-rock interactions in exhumed middle crustal shear zones.

Deformation of the seismogenic zone in the northeastern part of the Izu Peninsula, Japan, inferred from GNSS observations

Abstract The Izu collision zone, which is characterized by the collision between the Izu-Bonin arc and the Honshu arc, is located in the northernmost part of the Philippine Sea Plate. Particularly in the northeastern margin of the zone, numerous large earthquakes have occurred throughout history. To clarify the convergent tectonics of this zone related to the occurrence of these large earthquakes, in this study we collected and analysed Global Navigation Satellite System (GNSS) observation data from the Izu collision zone. The result verified that a shear deformation zone exists in the northeastern part of the Izu Peninsula, which agrees with the maximum shear directions in the left-lateral slip of the active Kita-Izu Fault Zone in the study area. In the shear deformation zone, the seismic activities both in the eastern part of the Tanzawa Mountains and the northeastern part of the Izu Peninsula may be related to each other because the temporal patterns of the seismic activity in both areas are correlated. Based on the relative motion between the main part of the Izu Peninsula and the subducting forearc of the Philippine Sea Plate, the shear zone can be regarded as a transition zone affected by both plate collision and subduction.

Chip formation and tribological behavior in high-speed milling of IN718 with ceramic tools

Advanced ceramics exhibit excellent mechanical properties at elevated temperatures suggesting them as plausible cutting tool materials for machining of heat-resistant superalloys. However, despite numerous efforts to date, relative brittleness of ceramic tools can result in chipping or catastrophic failure, especially during an intermittent process where excessive thermo-mechanical alteration occurs, like high-speed face milling. Previous studies by the authors revealed that in high-speed milling of inconel with SiAlON tools, after surpassing a certain cutting speed where extreme levels of strain rates and temperatures exist, the IN718 machinability transforms drastically, showing a significant reduction in cutting force, chipping and tool wear. Following this observation, in the current paper, an attempt has been made to further investigate the phenomena acting at the shear deformation zones through analysis of chip formation mechanisms and tool-workpiece tribosystem. Numerous characterization techniques have been used in this research, such as cutting force measurements, chip cross-section studies, SEM/EDS, TEM, and nanoindentation. Results suggest that a reduction in material flow strength occurs at the extreme conditions of the cut, showing similarities to fluid flow in TEM images of the tool face. Increasing the cutting speed generally facilitates chip formation; However, a rise in cutting force by further increasing the speed, and excessive generation of unstable built-up layers practically limits the cutting speed. Additional XPS studies show that variation in cutting speed also changes the frictional response of the tool-workpiece tribosystem by forming lubricious and thermal-barrier tribofilms.

Integrated Extrusion–Shear Forming Process of the Solid-State Recycled AZ80 Magnesium Alloy via Hot Press Sintering

The consolidation recycled AZ80 billets were successfully fabricated through the cold press and hot press sintering of the AZ80 metal chips. The consolidation recycled billets sintered at 350 °C present the comparable compressive properties and inferior tensile properties compared with the initial cast billets. The defects in the consolidation recycled billet were inclined to propagate along the bond interface between the metal chips during tension, which resulted in the inferior tensile properties of the recycled billets. The recycled billets were then subjected to the integrated extrusion–shear (ES) process. The homogeneous finer dynamic recrystallization grains with an average grain size of 6 μm can be obtained in the shear deformation zone and extrusion sizing zone through integrated ES process at 300 °C with an extrusion velocity of 0.6 mm/s. The recycled billets after integrated ES forming process present rival tensile properties compared with the initial cast billets after integrated ES forming with the same extrusion parameters, which can be ascribed to that the integrated ES forming can nearly eliminate the defects through the severe compressive and shear strain. The solid-state recycling process through hot press sintering and subsequent integrated ES process can fabricate the consolidation recycled AZ80 rod, which demonstrates the comparable tensile properties with the cast–extrusion rod.