Ductile Shear Research Articles

Origin of tearing topography surface in hydrogen-charged pearlitic steel

In the present study, the formation mechanism of tearing topography surface (TTS), which is observed after slow strain-rate tensile tests of H-charged pearlitic specimens, was investigated in detail. The TTS always appeared at the subsurface of failed H-charged specimens, where H atoms were concentrated after room-temperature electrochemical H-charging. The TTS consisted of stepped flat surfaces and dimpled surfaces. The flat surface was caused by the coalescence of sharp micro-shear cracks, not micro-voids, of H-enriched cementite (θ) platelets in a pearlite colony, namely brittle transcolonial fracture. The regions surrounding the flat surface were H-depleted due to the migration of H atoms into neighboring micro-shear cracks during tensile deformation. As a result, the H-depleted regions were fractured by the typical coalescence of micro-voids, namely relatively ductile shear cracking, resulting in dimpled surfaces after tensile fracture. These results mean that the TTS region, strictly speaking, the flat surface region, which is generated by transcolonial fracture inside the TTS region, is an initial site of H-induced cracking of pearlitic steel. The ab-initio calculations of the energy value of H desorption from a C vacancy in θ supported the recent report that H atoms are concentrated inside the θ platelets after H charging.

Thermal architecture of the Salmon River suture zone, Idaho, USA: Implications for the structural evolution of a ductile accretionary complex during arc-continent collision

Abstract Documenting the tectono-thermal evolution of the exhumed ductile portions of orogenic systems is critical for interpreting orogen dynamics. Here, we utilize Raman spectroscopy of carbonaceous material thermometry to quantify the thermal architecture of the Salmon River suture zone in west-central Idaho, USA, which records the Cretaceous collision of the Wallowa island arc terrane with North America. We integrate this thermal architecture with published structural interpretations, geochronology, and pressure-temperature-time histories to interpret the evolution of deformation during arc-continent collision in this portion of the North America Cordillera. Mean peak temperatures within four, ~1–3-km-thick, penetratively deformed thrust sheets in the western part of the suture zone decrease moving structurally downward from 652 ± 28 °C (Pollock Mountain thrust sheet), to 577 ± 30 °C (Rapid River thrust sheet), to 426 ± 32 °C (Morrison Ridge thrust sheet), to 358 ± 18 °C (Heavens Gate thrust sheet). These ductile thrust sheets are separated by 100–500-m-thick intervals of inverted temperatures that surround the mapped positions of thrust faults. We interpret the western part of the suture zone as a ductile accretionary complex that records the progressive underplating and top-to-the-west translation of ductile thrust sheets that were derived from the Wallowa terrane during ca. 144–105 Ma collision-related deformation. Accretion of ductile thrust sheets began at ~30–35 km depths and completed at depths of ~10–20 km. Rocks at all structural levels in the suture zone exhibit distributed ductile fabrics, but the inverted thermal gradients that surround the mapped positions of thrust faults suggest that the majority of top-to-the-west displacement was accommodated within 100–500-m-thick, high-strain, thrust-sense ductile shear zones.

Transition in Interfacial Failure Mechanism of Resistance Spot Welds during Tensile–Shear Loading: Role of Fusion Zone Hardness

The failure of resistance spot welds through the fusion zone along the sheet/sheet interface (i.e., interfacial failure) is critical for automotive crashworthiness. This paper investigates the effect of fusion zone hardness on the interfacial failure behavior of resistance spot welds during the tensile–shear test. AISI 1040 medium carbon steel, producing a high level of hardness mismatch during resistance spot welding, was selected as the base metal. By ex situ tempering heat treatment, various levels of fusion zone hardness are achieved in the welds with constant fusion zone size. It is shown that the interfacial failure of the spot welds is a competition between ductile shear failure and rapid crack propagation. It is found that there is a critical fusion zone hardness beyond which the interfacial failure mechanism transitions from ductile shear failure to rapid crack propagation. In welds with high fusion zone hardness, the mechanism of interfacial failure is rapid crack growth, and fusion zone fracture toughness is the governing factor for the interfacial failure load. Conversely, in welds with low FZ hardness, the mechanism of interfacial failure is a ductile shear failure, and fusion zone hardness would be the governing factor for the interfacial failure load.

Vertical tectonics of a Neoarchean gneiss dome in the eastern North China Craton

Archean gneiss domes are a very common structure in old cratons, these are different from the structural patterns in the post‐Archean linear orogenic belts related to subduction and collision. There are two tectonic models in Archean tectonics: horizontal tectonism and vertical tectonism. The formation mechanisms of Archean gneiss domes are still debated. Here we present data from the Anziling gneiss dome, a typical gneiss dome structure from the eastern North China Craton, which was formed dominantly by vertical tectonism during Neoarchean times (2554–2452 Ma). The Anziling gneiss dome is located in the east of Shuangshanzi, East Heibei Province and consists of the Anziling gneiss (a diopside‐monzonitic gneiss) in the center outwards surrounded by the Jiguanshan gneiss (hornblende‐plagioclase gneiss) and the Niuxinshan gneiss (trondhjemitic gneiss), together showing an irregular elliptical shape with a NE‐ward extending tail on the surface. But in the cross‐section, it represents a deflective dome, both north‐western and south‐eastern limbs dip approximately to the west. The dome suffered inhomogeneous ductile shear deformation, much stronger with more displacement in the north‐western half (especially close to the margin) than that in the eastern half. The core area shows only a relatively weak deformation. Therefore, we suggest that the Anziling gneiss dome was formed by the TTG (trondhjemite, tonalite, granodiorite) pluton rising obliquely up towards the east by diapirism in the first stage, followed by sub‐horizontal emplacement towards the north and then to the north‐east associated with clockwise rotation in the second stage. The Anziling gneiss dome and its neighbouring Shuangshanzi shear zone were formed simultaneously, indicating that the Anziling gneiss dome was driven by both gravitational forces and magma diapirism.

Shear behavior of externally prestressed ultra-high-performance concrete (UHPC) T-beams without stirrups

Externally prestressed ultra-high-performance concrete (UHPC) beams without stirrups (EPUBs-WS) that simplify the reinforcement design and construction procedure are becoming a competitive option in bridge engineering. To investigate the shear behavior of EPUBs-WS, five specimens were designed and tested considering several critical parameters, such as the shear span-to-depth ratio (λ), shear stirrups, and longitudinal reinforcement ratio. The EPUBs-WS exhibits diagonal tension failure as the fibers pull out and the specimen shears off into two parts along the critical diagonal crack. However, the beam with λ = 3.67 exhibited flexural failure due to the large λ. The stiffness, shear-cracking strength, and shear strength of EPUBs-WS decrease as λ increases. Stirrups enhance the shear resistance of EPUBs but result in a more brittle shear failure mode. A higher reinforcement ratio augments the dowel action in EPUBs-WS, which contributes to a ductile shear failure mechanism. The web-shear cracking force accounts for 46% to 87% of the shear capacity, implying that the shear-cracking strength is a significant factor in the design of EPUBs-WS. An equation for predicting the shear-cracking strength of prestressed UHPC beams is proposed and validated using a database of experimental results reported in the literature. A parametric analysis is performed using 40 available specimens to investigate the effects of compressive strength, λ, reinforcement ratio, fiber reinforcing index, and prestressing level on the shear strength of prestressed UHPC beams without stirrups. By considering the key parameters, equations for estimating the shear strength are proposed and exhibit good accuracy.

Titanite Petrochronology Records Secular Temperature and Fluid Evolution During Ductile Deformation: An Example From Late Cretaceous Shear Zones in the Eastern Transverse Ranges

AbstractQuantifying the timing and conditions of ductile deformation is essential for quantitative models of lithospheric deformation. Yet, directly constraining these variables and documenting how they change during a single deformation event remain difficult. We present titanite microstructural, zoning, trace‐element, and U‐Pb data from <m‐scale mylonitic shear zones in the Eastern Transverse Ranges, CA (Joshua Tree National Park) that record (a) the timing and conditions of ductile deformation and (b) the evolution of deformation conditions within a single, punctuated ductile deformation event. Titanite grains in sheared plutonic rocks yield a bimodal distribution of dates (∼151 and ∼75 Ma) interpreted as the independently constrained pluton crystallization and shear zone deformation ages, respectively. Synkinematic titanite neocrystallization at ∼75 Ma documents early deformation at ∼640–710°C under hydrous fluid conditions. Recrystallized titanite rims with ∼75 Ma dates indistinguishable from the neocrystallized titanite record Zr‐in‐titanite temperatures of 600–610°C and higher F contents, suggesting that the fluid became a more halogen‐rich brine as deformation progressed and the system cooled. Chemical zoning related to fluid‐driven recrystallization occurs in tandem with lattice misorientations and partially to fully reset U‐Pb dates in bent titanite, implying that reactive fluid flow is the ultimate mechanism by which dates are reset in titanite deformed by dislocation creep. These data document a punctuated (e.g., ∼1–3 Myr) phase of high‐temperature deformation that accompanied local pluton emplacement and demonstrate that titanite petrochronology can capture multiple, discrete reactions associated with crustal weakening and variables that affect the rheological evolution of ductile shear zones.

Structural evolution of the reactivated Møre–Trøndelag Fault Complex, Fosen Peninsula, Norway

The ENE–WSW-trending Møre–Trøndelag Fault Complex (MTFC) in Central Norway is a 10–50 km-wide, steeply dipping reactivated fault zone. Onshore, it transects Devonian sedimentary rocks and a series of east to SE transported metamorphic nappes, which were emplaced during the Scandian (Silurian–Devonian) Orogeny. Offshore, the MTFC defines the southern margin of the Møre Basin and the northern margin of the Viking Graben, meaning that the fault complex played a major role in controlling the architecture of these Mesozoic basins. Onshore, the MTFC has had a prolonged and heterogeneous kinematic history. The complex comprises two major fault strands: the Hitra–Snåsa Fault (HSF) and the Verran Fault (VF). These two faults seem to have broadly initiated as part of a single system of sinistral ductile shear zones during the early Devonian ( c. 410 Ma). Sinistral transtensional reactivation (Permo-Carboniferous; 290 Ma) of the ENE–WSW-trending HSF and VF led to the development of cataclasites and pseudotachylites together with the formation of north–south-trending faults establishing the present-day brittle fault geometry of the MTFC. Later phases of Mesozoic reactivation focused along the Verran Fault Zone (VFZ) and north–south-linking structures were probably related to mid- to late Jurassic to early Cretaceous rifting and late Cretaceous to early Cenozoic opening of the North Atlantic. Supplementary material: Supplementary datasets are available at https://doi.org/10.6084/m9.figshare.c.6390518 Thematic collection: This article is part of the Caledonian Wilson cycle collection available at: https://www.lyellcollection.org/topic/collections/the-caledonian-wilson-cycle

Intraplate records of a transform margin formation: Brittle deformation in the basement of the basins from the northeastern extremity of the Brazilian equatorial margin

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 D1 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 D2 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 D3 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 (D4) 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 D4 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.

Multisensor Satellite Data and Field Studies for Unravelling the Structural Evolution and Gold Metallogeny of the Gerf Ophiolitic Nappe, Eastern Desert, Egypt

The gold mineralization located in the southern Eastern Desert of Egypt mostly occurs in characteristic geologic and structural settings. The gold-bearing quartz veins and the alteration zones are confined to the ductile shear zones between the highly deformed ophiolitic blocks, sheared metavolcanics, and gabbro-diorite rocks. The present study attempts to integrate multisensor remotely sensed data, structural analysis, and field investigation in unraveling the geologic and structural controls of gold mineralization in the Gabal Gerf area. Multispectral optical sensors of Landsat-8 OLI/TIRS (L8) and Sentinel-2B (S2B) were processed to map the lithologic rock units in the study area. Image processing algorithms including false color composite (FCC), band ratio (BR), principal component analysis (PCA), minimum noise fraction (MNF), and Maximum Likelihood Classifier (MLC) were effective in producing a comprehensive geologic map of the area. The mafic index (MI) = (B13-0.9147) × (B10-1.4366) of ASTER (A) thermal bands and a combined band ratio of S2B and ASTER of (S2B3+A9)/(S2B12+A8) were dramatically successful in discriminating the ophiolitic assemblage, that are considered the favorable lithology for the gold mineralization. Three alteration zones of argillic, phyllic and propylitic were spatially recognized using the mineral indices and constrained energy minimization (CEM) approach to ASTER data. The datasets of ALSO PALSAR and Sentinel-1B were subjected to PCA and filtering to extract the lineaments and their spatial densities in the area. Furthermore, the structural analysis revealed that the area has been subjected to three main phases of deformation; (i) NE-SW convergence and sinistral transpression (D2); (ii) ~E-W far field compressional regime (D3), and (iii) extensional tectonics and terrane exhumation (D4). The gold-bearing quartz veins in several occurrences are controlled by D2 and D3 shear zones that cut heterogeneously deformed serpentinites, sheared metavolcanic rocks and gabbro-diorite intrusions. The information extracted from remotely sensed data, structural interpretation and fieldwork were used to produce a gold mineralization potential zones map which was verified by reference and field observations. The present study demonstrates the remote sensing capabilities for the identification of alteration zones and structural controls of the gold mineralization in highly deformed ophiolitic regions.

Dating Strike‐Slip Ductile Shear Through Combined Zircon‐, Titanite‐ and Apatite U–Pb Geochronology Along the Southern Tan‐Lu Fault Zone, East China

AbstractDating the timing of ductile shear deformation is critical to the understanding of complex, multi‐episode kinematics that commonly occur within the study of continental tectonics. The Tan‐Lu fault zone (TLFZ) in East China is a lithospheric discontinuity that records multistage sinistral strike‐slip shearing during Mesozoic time. Herein, based on field mapping, pressure‐temperature estimates via microstructures, quartz lattice preferred orientations, and geothermobarometer analysis, and U–Pb geochronology, we present a detailed examination of a portion of the southern TLFZ known as the Fucha Shan ductile shear zone. Two phases of sinistral ductile shear deformation in the shear zone are identified. The main phase occurred under amphibolite‐facies metamorphic conditions (500°C–650°C, 2.8–5.2 Kbar). U–Pb dating of synkinematic titanite indicate deformation occurred ca. 142–140 Ma. This age information is consistent with U–Pb dating of zircon from crosscutting granitic dikes that provide an upper limit of the shearing of ca. 134 Ma. A later, but less well‐developed phase of sinistral ductile shearing variably overprints older structures within the Fucha Shan shear zone at greenschist‐facies metamorphic conditions. U–Pb dating of apatite grains in rocks that record this later event are interpreted to indicate that shearing occurred ca. 118–108 Ma. These results provide new insight into Early Cretaceous shear deformation history within the southern TLFZ in the context of the late Mesozoic intracontinental deformation in East Asia.

Origin and evolution of the ore-forming fluids of the Bajiazi gold deposit in the Jiapigou gold ore belt, NE China: Constraints from fluid inclusions, H-O-S isotopes, and pyrite trace element concentrations

The Bajiazi gold deposit, located within the southeastern Jiapigou gold ore belt (JGB) along the northeastern corner of the North China Craton (NCC), contains > 6 tons of gold at an average grade of 24 g/t. More than 20 total auriferous quartz veins are hosted in the Neoarchean basement gneiss and amphibolite and are spatially and temporally associated with Mesozoic intermediate-acid dikes. The distribution of the gold orebodies is mainly controlled by NNE-trending brittle–ductile shear zones and faults. Three hydrothermal stages were identified, namely, quartz–pyrite (stage I), quartz–gold–polymetallic sulfide (stage II), and quartz–carbonate (stage III). Three types of fluid inclusions (FIs) were identified: H2O–NaCl (W-type), CO2–H2O (C-type), and pure CO2 (PC-type) FIs. From stage I to stage III, the FI suite changes from W-type and C-type in stage I to all three types in stage II and to only W-type in stage III. The FIs in the quartz of stages I to III mainly homogenized at temperatures (Th) of 283–395 °C, 183–287 °C and 116–186 °C, respectively, with salinities of 3.87 to 13.01 wt% NaCl equiv, 4.65 to 18.55 wt% NaCl equiv, and 3.83 to 9.68 wt% NaCl equiv, respectively. The ore-forming fluids of the Bajiazi gold deposit evolved from a H2O–NaCl–CO2 system in stages I and II to a H2O–NaCl system in stage III. Fluid immiscibility is an important mechanism leading to rapid precipitation of sulfides and gold. H–O–S isotope signatures indicate that the initial ore-forming fluids and materials were originally derived from magmatic sources. Electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) data on pyrite grains show that abundant gold mineralization occurred in the middle hydrothermal stage. The high Co/Ni ratios of pyrite are consistent with a magmatic–hydrothermal origin. The results, combined with previous regional studies, indicate that the Bajiazi gold deposit is a mesothermal magmatic–hydrothermal lode gold deposit.

Strain Localized Deformation Variation of a Small-Scale Ductile Shear Zone

Strain Localized Deformation Variation of a Small-Scale Ductile Shear Zone

Comparing Performance of Braced Circular Grid Panels and Braced Rectangular Thin Panels

Abstract: Now a days many industries have adopted metal shear panels (MSP’S) in steel structures. MSP’S are effective seismic force-resistant components that are widely used in seismic regions to resist lateral forces. Structural mitigation measures can be adopted to reduce structural damage through engineered actions to maintain structural stability and integrity. This study investigates seismic performance of a combined braced circular damped grid panels (BCDP) and comparing its performance with rectangular braced ductile thin shear panels (BDSP). BCDP specimens are made by replacing rectangular panels on BDSP specimens by concentric circular grids. The system consists of a wall panel, X braced system and to develop an efficient damping characteristics damped circular grid panels provided at crossing of X bracing. It is expected that when reverse cyclic load applied, whole load not transferred to the frame or bracing but to the circular grids. The result showed that when load applied, the frame will not fail instead the circular grid starts yielding and a greater number of cycles can be accommodated without failure and effectively increased seismic capabilities of the system. The specimens are designed and modelled under various parametric studies and investigated analytically. The study includes seismic analysis and push over analysis using ANSYS software.

Lithium isotopic and fluid mobile trace element systematics of the Bay of Islands altered forearc upper to lower ophiolitic crust

Bulk rock Li isotope and select fluid mobile element traverses through the crustal section of the Late Cambrian Bay of Islands Ophiolite Complex (BOIC) in the Taconic Humber Arm Allochthon in the Newfoundland Appalachians are presented to examine the extent and conditions of alteration at different pseudo-stratigraphic levels in the ancient forearc oceanic crust that was obducted during the Middle Ordovician.N-MORB normalized enrichment factors (EFs) calculated for Li and fluid mobile elements (FMEs) show variable extents of enrichments or depletions from shallow to deep oceanic crustal sections in the BOIC that are consistent with a broad range of alteration-related δ7Li values from −2.97 to +20.69 ‰ (vs. unaltered MORB range of +1.5 to +6.1 ‰ with a mean of +3.4 ± 1.4 ‰). EFs and fluid-rock reaction modeling for Li contents and δ7Li values indicate alteration dominantly controlled enrichments and depletions of Li isotopic and FMEs systematics through all crustal levels of the BOIC ophiolite. Alteration fluids are dominated by modern seawater-like δ7Li composition rather than the recently proposed Cambrian seawater that is based on ancient carbonate shell compositions.BOIC basaltic samples proximal to the York Harbor Mine (YHM), similar to the classic mafic Cu-Zn Cyprus-type volcanic massive sulfide (VMS) deposits, show light δ7Li values of −2.97 to +1.59 ‰, but highly enriched Li contents (14.0–40.7 μg/g). Modeling results indicate that these YHM basalts were altered by metal-rich magmatic fluids, in part, derived from deeper plagiogranite intrusions near the base of the sheeted dikes that are possibly admixed with seawater-derived hydrothermal fluids below the VMS deposit. Magmatic volatile exsolution may be associated with the crystallization of directly underlying subvolcanic silicic intrusions, resulting in over-pressuring and fracturing of the carapace that may assist in localizing the high temperature (400–200 °C) upflow zones of the seafloor hydrothermal system.The BOIC layered gabbroic rocks also show evidence of variable extent of alteration as reflected by both Li content (EF both >1 and < 1) and δ7Li composition (+0.79 to +9.47 ‰), likely indicating high-temperature amphibolite (800–600 °C within the ductile deformation field) to lower temperature greenschist facies paragenesis, with down-temperature complex retrograde petrogenetic lineages. Mylonites and ductile shear zones commonly show heavier δ7Li values between +5.47 and + 18.83 ‰. We suggest that mylonite zones and coarser-grained high-strain zones allowed near-axis fluid penetration at high to lower temperatures that extended to the basal gabbroic sections in the crust during ongoing igneous activity. Shear zones were associated with rheologic weakening and initial permeable pathways for hydrothermal fluids. Shallow on-axis and deep off-axis hydrothermal circulation likely occurred at a relatively fast-spreading rate, which may account for the significant shallow to deep crustal heat extraction as predicted by the multiple sill model of lithospheric cooling.

The Gondwanide deformation along the southwestern border of the Río de la Plata Craton: Geochemical and geochronological constraints on ductile shear zones from the Ventania System basement, Argentina

This work deals with the study of Gondwanide ductile shear zones developed in Neoproterozoic–middle Cambrian basement rocks of the Ventania System and possibly related to the reactivation of the Sierra de la Ventana Shear Zone. This reactivation was caused by the northeastward migration of the Gondwanide deformation from the North Patagonian Massif. The crustal shortening related to the Gondwanide Orogeny gave rise to thrusting of the Ventania System basement over Paleoproterozoic rocks of the Río de la Plata Craton. This work focuses on the study of muscovite ± quartz phyllonites of the Ventania System basement and quartz ± muscovite veins crosscutting basement and Paleozoic cover rocks of the system. Structural and magnetic surveys were performed in order to characterize the Gondwanide structures of the basement, while petrographic, X-ray diffraction, geochemical, and geochronological studies were carried out in order to investigate the nature, P-T conditions, element mobility, and age of these shear zone-related rocks. In the Sauce Chico Inlier, mylonitized basement rocks crop out along the western edge of the system, near the basement–Paleozoic cover interface, where the main structures are top-to-NNE reverse ductile shear zones with related phyllonites. Ductile shearing under greenschist-grade conditions (125–340 MPa and 300–400 °C) promoted major and trace element mobility. Phyllonites are the result of extreme hydrolysis of feldspars from the acidic igneous rocks of the basement, producing muscovite and releasing aqueous SiO2 later redeposited as quartz veins. These phyllonites developed in connection with reactivated contacts between basement units and also the basement–Paleozoic cover interface. New Rb–Sr quartz-muscovite and Ar/Ar muscovite ages for phyllonites and a quartz vein indicate a protracted tectono-metamorphic history mainly restricted to the Cisuralian (ca. 287 Ma), comprising regional folding and metamorphism, shear zone activity, vein-type mineralization, and syntectonic deposition of the Tunas Formation. Subsequent reactivations during the Lopingian (ca. 256 Ma) and probably in Late Triassic times (ca. 227 Ma) resulted from localized shearing along mylonitic belts.

Intracontinental deformation around the fixed tip of the continental-scale, strike-slip Tan–Lu fault zone in eastern China

It remains unclear whether large-scale polyphase displacement along strike-slip faults is associated with tip propagation, and how the tip-damage zones of these faults respond to intracontinental block movements. Damage structures around the southern tip of the 2400 km long Tan–Lu fault zone (TLFZ) in eastern China provide an ideal opportunity to investigate deformation mechanisms at the tip of an intracontinental strike-slip fault. Structural and geochronological data from the southern Zhangbaling uplift within the TLFZ show that following the Triassic initiation of the fault, two phases of sinistral faulting occurred: an earlier phase at the beginning of the Early Cretaceous and later phase between the Early and Late Cretaceous. The early sinistral structures are expressed by ductile shear zones in the southern Zhangbaling uplift, whereas the younger sinistral structures are expressed as shear zones in the north and brittle faults in the south. Zircon U–Pb dating results for felsic gneiss of the TLFZ suggest that c. 200 km of cumulative displacement occurred during the Cretaceous and was restricted to wall rocks on the western side of the fault. The southern tip of the TLFZ remained fixed during the displacement, and the dilational quadrant associated with the fault is interpreted to have been stationary. The current c. 400 km of sinistral offset of the Dabie and Sulu orogens represents the original offset caused by the Triassic collision of the North China Craton and South China Block. The two phases of sinistral motion were induced by two phases of compression along the c. 460 km long contractional quadrant, which was dominated by thrusting along pre-existing faults as well as fault-related folding and uplift. Damage structures at the southern tip of the TLFZ show that large-scale polyphase strike-slip motion may be associated with a fixed fault tip, hundreds of kilometres of displacement can be restricted to one side of a major fault, and displacement can be accommodated by thrusting along pre-existing faults in the contractional quadrants. Supplementary material : LA-ICP-MS zircon U–Pb data for the felsic gneiss sample FD30 are available at https://doi.org/10.6084/m9.figshare.c.6368850

Mid-crustal reactivation processes linked to frictional melting and deep void development during seismogenic slip: examples from the Lewisian Complex, NW Scotland

Exhumed examples of ancient fault voids formed during seismic slip at depths &gt;10 km are well preserved in the Assynt Terrane of the Lewisian Complex, NW Scotland. They are interpreted to have formed during regional Mesoproterozoic ( c. 1.55 Ga; ‘Assyntian’) strike-slip faulting. Deformation is characterized by sinistral reactivation of pre-existing NW–SE-trending features including intrusive contacts of ( c. 2.4 Ga) mafic dykes and Paleoproterozoic ductile shear zone fabrics ( c. 1.75 Ga). Reactivation occurred at palaeodepths of 10–15 km, where frictional–viscous deformation synchronous with co-seismic frictional melting led to cycles of millimetre- to decimetre-scale cavity dilation and collapse. Although individual melt-generating slip surfaces may have become rapidly welded, faulting was able to repeatedly localize along adjacent pre-existing planar anisotropies favourably oriented for slip, leading to the creation of a mesh of foliation-parallel melt generation surfaces linked by foliation-perpendicular dilational voids. The latter features are filled by chaotic clast-supported wall rock collapse breccias, localized injected frictional melts and hydrothermal mineralization. The fills act as natural props, holding cavities open and preserving them as long-term, pipe-like fluid flow conduits. These exhumed features are likely to be typical of multi-rupture seismogenic fault systems formed by direct reactivation of pre-existing basement structures.

Experimental Study on Seismic Behavior of Lightweight Concrete-Filled Cold-Formed Steel Shear Walls Strengthened Using Horizontal Reinforcement

ABSTRACT To improve the seismic behavior and thermal property of traditional cold-formed steel (CFS) walls for satisfying the requirements multistory structures, a new type of fiber-reinforced lightweight concrete (FLC)-filled CFS shear wall strengthened using horizontal reinforcement is proposed in this study. Four full-scale specimens were tested under reversed cyclic loading to investigate the seismic behavior, including failure mode, hysteresis curve, shear capacity, deformability, stiffness degradation, and energy-dissipating capacity. Test results indicated that the restrictive effect of FLC on the studs and its diagonal-bracing effect improved the wall’s hysteretic behavior, making the wall exhibit the ductile shear failure. Increasing the wall thickness increased the shear strength, lateral stiffness, and energy-dissipating capacity, whereas installing the coupling-section interior studs enhanced the ductility. Finally, a simplified strut-and-tie model was proposed to evaluate the shear capability of FLC-filled walls, and the calculated values exhibited good agreement with the test results, but the further verification is required.

High temperature ductile deformation, lithological and geochemical differentiation along the Shagou shear zone, Qinling Orogen, China

Lithological and geochemical differentiation in ductile shear zone is essential to understanding element mobility during ductile deformation in the mid-lower crust. The Shagou ductile shear zone characterized with intensive compositional layering is investigated to understand element behaviors during high temperature ductile deformation. Geochemistry and zircon U–Pb chronology suggest the protoliths were magmatic rocks crystallized at ca. 735-723 Ma, overprinted by ductile deformation at ca. 198–184 Ma. Microstructure, quartz fabric, and thermometer coupled with barometer constrain the deformation to occur at 4.50–6.12 kbar and 633–713 °C. Field observations, geochemical and zircon U–Pb geochronological data suggest that the amphibolitic and gneissic mylonites were generated from geochemical differentiation during high-temperature ductile shearing. The geochemical contents of progressively deformed mylonites show systematic increasing or decreasing with enhancing mylonitization. Silica displays remarkably decreasing with enhancing mylonitization, whereas Mg, Fe, Mn, Ti and P tend to migrate to higher strain, more acid environment. REEs, LILEs, HFSEs, Zn and V display negative correlations with increasing mylonitization, suggesting that nearly all the trace elements migrate to lower strain in the amphibolitic mylonites. However, HREEs, HFSEs, Cr, Ni, Zn and V exhibit positive correlations with increasing mylonitization in the gneissic mylonites. It implies that these elements tend to migrate to higher strain, more acid environment during ductile deformation.

A new design proposal for composite beams with powder actuated shear connectors

This paper introduces a proposal for the SP 266.1325800 code update, which is applied as a national building code for composite structure design in Russian and some CIS countries. The proposal is based on deep codes analyze and comparison and previous authors’ publications. The research is dedicated to nailed shear connectors’ behavior in composite beams with profiled sheeting. The proposal provides a less conservative approach for composite beams with ductile shear connectors and takes into account additional conditions, such as decking geometry and the structure’s performance under fire. The proposed methodology defines the main geometric characteristics of the composite cross-section before determining the shear connector type. If ductile connectors are chosen, it is recommended to use partial design methods for shear connection definition due to the economic benefits of the proposal. The proposal is verified on powder-actuated shear connectors and should be double-checked with other working examples and connector types. The results show that the structure designed according to the new proposal is 13% less utilized with a smaller quantity of shear connectors (22% less) under the same load. It provides benefits from the structure costs and labor time.