Shear Zone Research Articles

Deciphering ore genesis with oxygen and sulfur isotope signatures: A case study from the Singhbhum Shear Zone, Eastern India

The importance of light-stable isotopes and their mass-dependent fractionations in understanding past geological processes is enormous. The present research delivers precise, high-resolution, in-situ oxygen (18/16O) and triple sulfur (32/33/34S) isotope ratios from quartz and sulfide minerals found in the CuAu Kendadih deposit located along the Mesoproterozoic (∼1.6 Ga) Singhbhum Shear Zone (SSZ) in eastern India. Oxygen and sulfur isotope analyses were carried out on quartz and pyrite-chalcopyrite pairs that are in textural equilibrium, using the most advanced Large Geometry-Secondary Ion Mass Spectrometer (LG-SIMS; CAMECA IMS-1300HR3). The results show restricted ranges for δ18Oquartz (+6 to +7.7‰; average: 6.9 ± 0.9‰, n = 50) and δ34Schalcopyrite-pyrite (+11.4 to +11.9‰; average: 11.79 ± 0.2‰, n = 62). This isotopic homogeneity suggests a single, uniform fluid source for the ore-forming metals. The combined oxygen, sulfur isotope ratios, and fluid inclusion data are consistent with a hydrothermal fluid derived from an “I-type” granitic melt. This study incorporates existing fluid inclusion, stable, and radiogenic isotope data from temporally similar deposits within the shear zone, reevaluating their implications in light of the new findings. It proposes that, around 1.6 billion years ago, underplating the Singhbhum Craton by the Dalma Plume resulted in the remelting of the lower crust. This remelting is attributed to the plume's introduction of a significantly elevated thermal perturbation. The process is hypothesized to have led to the generation of second-order granitic melts. Upon emplacement in the lower crust, these granitic melts became the potential source for essential metals, ligands, and hydrothermal fluids, contributing to mineralization within the deep-seated Singhbhum Shear Zone. This research attempts to comprehensively describe the “source-to-sink” ore genesis model by proposing potential magma chamber processes that concentrate metals and ligands at the roof zone, followed by the separation of metal-rich hydrothermal fluids, fluid-rock interaction, and the physicochemical conditions governing the deposition of the extensive polymetallic deposit. This work offers novel insights into the Mesoproterozoic metallogenesis along the Singhbhum Shear Zone, challenging existing paradigms that favored evaporite or seawater brine sources. Furthermore, it sheds light on the Mesoproterozoic sub-crustal processes beneath the Indian Craton in this region.

Importance of grain boundary processes for plasticity in the quartz-dominated crust: Implications for flow laws

When H2O is present along grain boundaries, the deformation processes responsible for plasticity in silicate mineral aggregates can deviate from what may be conventionally expected. Although a necessary component of understanding crustal deformation processes, there is no theoretical framework that incorporates grain boundary processes into polycrystalline quartz rheology. To address this issue, we carried out high-pressure and high-temperature deformation experiments on fine-grained quartz aggregates. Our study illustrates that grain boundary migration (GBM) through dissolution-precipitation (in the presence of an aqueous fluid) and grain boundary sliding (GBS) may act as accommodation mechanisms to prevent hardening from dislocation glide. GBM and GBS can relax incompatibilities resulting from an inadequate number of independent slip systems, plastic anisotropy between neighbouring grains, and non-planar grain boundaries together with grain boundary junctions. As demonstrated earlier in the literature, GBM may act as a recrystallization mechanism counteracting hardening, but also is a potential mechanism that allow H2O to enter in the quartz crystal (hydrolization) at the experimental time-scale. The above serial processes occur over a range of more than two orders of magnitude in grain size (∼3 to 200 μm) and explain a grain-size-insensitive stress exponent (n = 2) and low activation energy (Q = 110 kJ/mol). In the absence of a switch to grain size sensitive deformation mechanisms induced by grain size reduction, our results imply that only a modest weakening (∼5 times the strength of the protolith) is needed (or possible) to localize shear zones in the Earth's crust.

Structural Evolution, Exhumation Rates, and Rheology of the European Crust During Alpine Collision: Constraints From the Rotondo Granite—Gotthard Nappe

AbstractThe rheology of crystalline units controls the large‐scale deformation geometry and dynamics of collisional orogens. Defining a time‐constrained rheological evolution of such units may help unravel the details of collisional dynamics. Here, we integrate field analysis, pseudosection calculations and in situ garnet U–Pb and mica Rb–Sr geochronology to define the structural and rheological evolution of the Rotondo granite (Gotthard nappe, Central Alps). We identify a sequence of four (D1–D4) deformation stages. Pre‐collisional D1 brittle faults developed before Alpine peak metamorphism, which occurred at 34–20 Ma (U–Pb garnet ages) at 590 ± 25°C and 0.9 ± 0.1 GPa. The reactivation of D1 structures controlled the rheological evolution, from D2 reverse mylonitic shearing at amphibolite facies (520 ± 40°C and 0.8 ± 0.1 GPa) at 18–20 Ma (white mica Rb–Sr ages), to strike‐slip, brittle‐ductile shearing at greenschist‐facies D3 (395 ± 25°C and 0.4 ± 0.1 GPa) at 14–15 Ma (white mica and biotite Rb–Sr ages), and then to D4 strike‐slip faulting at shallow conditions. Although highly misoriented for the Alpine collisional stress orientation, D1 brittle structures controlled the localization of D2 ductile mylonites accommodating fast (∼3 mm/yr) exhumation rates due to their weak shear strength (<10 MPa). This structural and rheological evolution is common across External Crystalline Massifs (e.g., Aar, Mont Blanc), suggesting that the European upper crust was extremely weak during Alpine collision, its strength controlled by weak ductile shear zones localized on pre‐collisional deformation structures, that in turn controlled localized exhumation at the scale of the orogen.

What Controls Early Restraining Bend Growth? Structural, Morphometric, and Numerical Modeling Analyses From the Eastern California Shear Zone

AbstractRestraining bends influence topography, strike‐slip evolution, and earthquake rupture dynamics, however the specific factors governing their geometry and development in the crust are not well established. These relationships are challenging to investigate in field examples due to cannibalization and erosion of earlier structures with cumulative strain. To address this knowledge gap, we investigated the structure, morphology, and kinematics of 22 basement‐cored restraining bends on low net‐slip faults (<10 km) within the southern Eastern California shear zone (SECSZ) via mapping, topographic analyses, and 3D numerical modeling. The bends are self‐similar in form with most exhibiting focused relief between high‐angle bounding faults with an arrowhead shape in map view and a “whaleback” longitudinal profile. Slight changes in that form occur with increasing size indicating predictable growth that appears to be primarily controlled by local fault geometries (i.e., bifurcation angle), rather than the influence of fault obliquity relative to far‐field plate motion, due to inefficient slip‐transfer across interconnected irregularly trending closely spaced faults. Modeling results indicate that the self‐similar fault‐bound geometry of SECSZ restraining bends may arise from elevated shear strain at the outer corners of single transpressional fault bends with increasing cumulative slip. This, in turn, promotes growth of a new fault leading to efficient accommodation of local convergent strain via uplift between bounding faults. Finally, our results indicate that the kilometer‐scale restraining bends contribute minimally to regional contraction as they only penetrate the upper third of the seismogenic crust and are therefore also unlikely to impede large earthquake surface ruptures.

Formation and Evolution of the Pacific‐North American (San Andreas) Plate Boundary: Constraints From the Crustal Architecture of Northern California

AbstractThe northward migration of the Mendocino triple junction (MTJ) drives a fundamental plate boundary transformation from convergence to translation; producing a series of strike‐slip faults, that become the San Andreas plate boundary. We find that the 3‐D structure of the Pacific plate lithosphere in the vicinity of the MTJ controls the location of San Andreas plate boundary formation. At the time of initiation of the Pacific‐North America plate boundary (∼30 Ma), the sequential interaction with the western margin of North America of the Pioneer Fracture Zone, soon followed by the Mendocino Fracture Zone, led to the capture of a small segment of partially subducted Farallon lithosphere by the Pacific plate, termed the Pioneer Fragment (PF). Since that time, the PF has translated with the Pacific Plate along the western margin of North America. Recently developed, high‐resolution seismic‐tomographic imagery of northern California indicates that (a) the PF is extant, occupying the western half of the slab window, immediately south of the MTJ; (b) the eastern edge of the PF lies beneath the newly forming Maacama fault system, which develops to become the locus for the primary plate boundary structure after approximately 6–10 Ma; and (c) the location of the translating PF adjacent to the asthenosphere of the slab window generates a shear zone within and below the crust that develops into the plate boundary faults. As a result, the San Andreas plate boundary forms interior to the western margin of North America, rather than at its western edge.

Formation mechanism and structural evolution of recumbent fold nappes: New insights from the bizerte area, northern Tunisia

The structural analysis of the Bizerte area in northern Tunisia, utilizing well data and field observations, reveals a complex arrangement of fold structures characterized by recumbent fold nappes to local sheath-like fold structures, indicative of a deep detachment phenomenon. The genesis and present geometry of these fold structures unravel a multifaceted structural history: (i) In the Tortonian folding phase, a detachment mechanism may have initiated the formation of a horizontal shearing plane at the base of the Paleocene marls. The gradual evolution of syn-shear recumbent fold nappes into sheath folds within sedimentary to pseudo-metamorphic rocks is attributed to a flow perturbation process analogue to “layer-parallel shearing,” dictating the geometric configuration of folds subsequent to a simple shear inducing perturbations in pre-existing layer disturbances. (ii) During the Late Quaternary shortening phase, a NW-trending right lateral shear zone emerged, delineated by the reactivation of pre-existing faults under compression. The reorientation of the anterior fold axes is attributed to the counterclockwise rotation of rigid blocks within the framework of P-type conjugate fractures. (iii) The transition to thin-skinned tectonics, characterized by the uplift of previously buried material, was characterized by a significant increase in shortening during Neogene events, encompassed in the broader regional geodynamic context of continental collision. From the Lower Quaternary onward, the structural model exhibits a combination of layer-parallel and layer-normal shear processes.

Tectonic evolution of high grade metamorphic tectonites of the Meelpaeg structure near Port aux Basques, southwestern Newfoundland during the Silurian Salinic and Early to Middle Devonian Acadian orogenies

The Meelpaeg structure in southwestern Newfoundland comprises allochthonous tectonites formed during the Salinic (D1-2) and Acadian (D3) orogenies. D1-2 occurred between 451 and 417 Ma and culminated in Barrovian metamorphism during terminal collision of the Gander margin with composite Laurentia. Collision was followed by tectonic escape of the deeply buried rocks between 417 and 412 Ma. Rocks of the Victoria arc and Exploits backarc preserved in the Port aux Basques and Grand Bay complexes were emplaced during D1 by the Grandys River shear zone, which is outlined by a narrow band of the ca. 451 Ma Port aux Basques granite, towards the southeast above the Harbour le Cou Group. The contrasting histories displayed across the Grandys River shear zone are typical of the Dog Bay Line further northeast. Salinic structures were overprinted by faults and folds formed during Acadian D3 transpression (≤ 412 Ma), which produced the bi-vergent Meelpaeg structure and emplacement of amphibolite facies tectonites above greenschist facies rocks along its bounding shear zones. F3 folding progressively steepened the faults, which in turn led to progressive localisation of dextral strike-slip in narrow fault zones. The High grade of metamorphism in the Meelpaeg structure is attributed to protracted underthrusting of the Cabot promontory of the Gander margin beneath composite Laurentia. Salinic convergence was sinistral but became dextral during the Early Devonian, diachronous Acadian orogeny. The kinematic switch is proposed as a tool to separate Salinic from Acadian structures in the central part of the northern Appalachians.

Timing and Tectonic Implications of the Development of the Orosirian Qianlishan Ductile Shear Zones in the Khondalite Belt, North China Craton

Orogen-parallel ductile shear zones are conspicuous structures in the Khondalite Belt, but the timing of shearing remains poorly understood. Here, we present field-based structural and zircon U-Pb geochronological studies on the newly discovered Qianlishan ductile shear zones (QDSZ) in the Khondalite Belt. Our results show that the nearly E-W-trending QDSZ are characterized by steeply S(SW)-dipping mylonitic foliations and mainly display a top-to-N(NE) sense of shearing. Two pre-kinematic intrusions yielded zircon crystallization ages of 2055 ± 17 Ma and 1947 ± 9 Ma, providing the maximum age limit for the QDSZ. Additionally, zircon overgrowth rims from three high-temperature mylonites gave metamorphic ages of 1902 ± 8 Ma, 1902 ± 26 Ma and 1884 ± 12 Ma, interpreted to record the timing of development of the QDSZ. Integrated with previous studies, we propose that the Qianlishan Complex suffered three phases of Orosirian deformation (D1–D3), of which the D3 deformation led to the development of the QDSZ. Deformation events D1, D2 and D3 are considered to have occurred at ca. 1.97–1.93 Ga, 1.93–1.90 Ga and 1.90–1.82 Ga, respectively. These events document that the Khondalite Belt underwent a protracted (>100 Myr) orogenic history in response to the collision between the Yinshan and Ordos blocks.

Transtension, brittle-ductile shear zones and hydrothermal ore deposits: Towards quantitative structural and kinematic models

Transtension is a fundamental process for the development of hydrothermal ore deposits, since it allows the required extension and dilatancy for hydrothermal fluid circulation and resulting ore mineralization. Transtension operates at multiple scales and, therefore, is not only relevant for deposits linked with extensional tectonics but also for those related to contraction/transpression. In this context, brittle-ductile shear zones represent a first-order metallotect that control the emplacement of mineralization. The distribution of ore minerals is largely influenced by bulk strain, kinematics and strain fabrics of these mineralized structures. The modified strain triangle is proposed as a simple tool to characterize strain conditions of transtension-related ore deposits associated with brittle-ductile shear zones, providing valuable information for metallogenetic models. In addition, a structural classification of ore deposits is proposed, based on the discussion of key deposit types and case studies. The main advantage of this approach is that it mainly relies on quantitative structural data and, therefore, is extremely useful for exploration. Furthermore, this classification avoids a priori assumptions on the tectonic setting, which can subsequently be inferred based on further regional evidence.

Influence of Rock Slide Geometry on Stability Behavior during Reservoir Impounding

Assessing the stability behavior of deep-seated rock slides in the surroundings of large dam reservoirs requires an understanding of the geometry, the kinematics, the groundwater situation, and the rock mass and shear zone properties. This study focuses on the influence of rock slide geometry on stability evolution during initial reservoir impounding. Therefore, nine different rock slide models, mainly taken from published case studies with a well-explored geometry, were analyzed. Based on the assumption that the rock slides are close to limit equilibrium in a no-reservoir scenario, reservoir impounding causes a reduction in the factor of safety (FoS). The results show a large impact of the water level for rotational slides where the majority of the rock mass is located at the lower part of the slope. This results in a maximum reduction in the FoS of up to 12%. In contrast to this, translational rock slides are less affected by reservoir impounding. The stability analysis shows that the change in FoS is strongly controlled by the kinematics of the rock slide and the geometry near the foot of the slope. Consequently, a comprehensive in situ investigation of the geometry and kinematics is necessary in order to reliably assess the influence of initial reservoir impounding.

Geological fingerprints of deep slow earthquakes: A review of field constraints and directions for future research

Abstract Slow earthquakes, including low-frequency earthquakes, tremor, and geodetically detected slow-slip events, have been widely detected, most commonly at depths of 40–60 km in active subduction zones around the Pacific Ocean Basin. Rocks exhumed from these depths allow us to search for structures that may initiate slow earthquakes. The evidence for high pore-fluid pressures in subduction zones suggests that they may be associated with hydraulic fractures (e.g., veins) and with metamorphic reactions that release or consume water. Loss of continuity and resulting slip at rates exceeding 10−4 m s–1 are required to produce the quasi-seismic signature of low-frequency earthquakes, but the subseismic displacement rates require that the slip rate is slowed by a viscous process, such as low permeability, limiting the rate at which fluid can access a propagating fracture. Displacements during individual low-frequency earthquakes are unlikely to exceed 1 mm, but they need to be more than 0.1 mm and act over an area of ~105 m2 to produce a detectable effective seismic moment. This limits candidate structures to those that have lateral dimensions of ~300 m and move in increments of <1 mm. Possible candidates include arrays of sheeted shear veins showing crack-seal structures; dilational arcs in microfold hinges that form crenulation cleavages; brittle-ductile shear zones in which the viscous component of deformation can limit the displacement rate during slow-slip events; slip surfaces coated with materials, such as chlorite or serpentine, that exhibit a transition from velocity-weakening to velocity-strengthening behavior with increasing slip velocity; and block-in-matrix mélanges.

Optimizing the Utilization of Steel Slag in Cement-Stabilized Base Layers: Insights from Freeze-Thaw and Fatigue Testing.

This paper presents a study on the mechanical properties of cement-stabilized steel-slag-based materials under freeze-thaw cycles for a highway project in Xinjiang. Using 3D scanning technology the specimen model conforming to the real steel slag shape was established. The objectives of the study are as follows: to explore the sensitivity between the macro- and micro-parameters of the specimen and to establish a non-linear regression equation; and to study the changes in mechanical properties of materials under freeze-thaw cycles, fatigue loading, and coupled freeze-thaw cycle-fatigue loading. The results show that there are three stages of compression damage of the specimen, namely, linear elasticity, peak plasticity, and post-peak decline. Maximum contact forces between cracks and particles occur mainly in the shear zone region within the specimen. The compression damage of the specimen is a mixed tensile-shear damage dominated by shear damage. When freeze-thaw cycles or fatigue loads are applied alone, the flexural strength and fatigue life of the specimens show a linear relationship of decline. The decrease in flexural modulus at low stress is divided into the following: a period of rapid decline, a relatively smooth period, and a period of fracture, with a tendency to change towards linear decay with increasing stress. In the case of freeze-thaw-fatigue coupling, the flexural modulus of the specimen decreases drastically by about 50% in the first 2 years, and then enters a period of steady decrease in flexural modulus in the 3rd-5th years.

Brittle initiation of dissolution–precipitation creep in plagioclase-rich rocks: insights from the Bergen arcs, Norway

The initiation of ductile shear zones commonly occurs spatially associated with fluid-rock reactions along brittle precursors. In many cases the relative timing of fracturing, fluid infiltration, reaction, and recrystallisation is unclear, making it difficult to disentangle mechanisms of shear zone initiation from subsequent deformation and recrystallisation. Here we present the study of the transition from a dry plagioclase-diopside-garnet-scapolite host granulite-facies lithology to (1) a low strain amphibolite-facies rock, and (2) a transition from low strain to high strain amphibolite-facies lithologies. Hydration of the granulite-facies precursor at amphibolite-facies conditions produces an assemblage comprised dominantly of plagioclase-amphibole-zoisite-clinozoisite-kyanite-scapolite-quartz. Detailed study of plagioclase chemistry and microstructures across these two transitions using Electron Backscatter Diffraction (EBSD) and Wavelength Dispersive Spectrometry (WDS) allows us to assess the degree of coupling between deformation and fluid-rock reaction across the outcrop. Plagioclase behaves dominantly in a brittle manner at the hydration interface and so the initial weakening of the rock is attributed to grain size reduction caused by fracture damage and fluid infiltration at amphibolite-facies conditions. Extensive fracturing-induced grain size reduction locally increases permeability and allows for continuing plagioclase and secondary mineral growth during shear. Based on plagioclase microstructures, such as, an inherited but dispersed crystallographic preferred orientation (CPO), truncation of chemical zoning, and the dominance of fine (5–150 µm), slightly elongate, polygonal grains we conclude that deformation is dominantly facilitated by dissolution–precipitation creep assisted by grain boundary sliding in the shear zone.

Laser ablation (in situ) Lu-Hf geochronology of epidote group minerals

Epidote group minerals, including allanite, clinozoisite and epidote are common in a range of metamorphic, igneous and hydrothermal systems, and are stable across a wide range of pressure–temperature (P–T) conditions. These minerals can incorporate substantial amounts of rare earth elements (REEs) during their crystallisation, making them potential candidates for Lu–Hf geochronology to provide age constraints on various geological processes. Here we report on a first exploration into the feasibility of in situ Lu–Hf geochronology for epidote group minerals from various geological settings and compare the results with age constraints from other geochronometers. Magmatic allanite samples from pegmatites and monzogranites in the Greenland anorthosite complex, Coompana Province and Qingling Orogen provided dates consistent with magmatic events spanning from c. 2660 to 1171 Ma. In the Qingling pegmatites, a younger phase of hydrothermal allanite was dated at c. 215 Ma, consistent with the timing of regional REE mineralisation. Allanite from the Yambah Shear Zone, Strangways Metamorphic Complex, yielded Lu–Hf age of c. 430 Ma. It predates the garnet and apatite growth at c. 380 Ma, suggesting the Lu–Hf system can be preserved in allanite during prograde amphibolite-facies metamorphism. Additionally, Lu–Hf dates for hydrothermal clinozoisite and epidote are consistent with the timing of hydrothermal alteration and mineralisation in a range of settings, demonstrating the utility of the technique for mineral exploration. Despite the current lack of matrix-matched reference materials, the successful application of laser ablation Lu–Hf geochronology to epidote group minerals offers valuable geochronological insights into various geological processes that can be difficult to access through other geochronometers.

Healing of Undisturbed Slide Zone Soil: Experimental Study on the Huaipa Landslide in Sanmenxia City

The occurrence and development of a landslide is a gradual process of destruction, causing huge losses to people’s lives and property. The shear strength of the shear zone gradually decreases to the residual state during the sliding process but it can recover to a certain extent during a relatively stable period. In a landslide, more than one slide usually occurs; however, after the first slide stops, it can enter a dormant period. The sliding surface can then experience a self-healing strength recovery phenomenon; this self-healing phenomenon has a significant impact on the reactivation of the landslide. Relevant studies have shown that the strength of the sliding surface is slightly greater than the residual strength when a landslide is reactivated; however, the explanations provided by these studies have not been sufficiently systematic. In this study, focusing on the undisturbed slide zone soil of the Huaipa landslide in Sanmenxia City, the “shear–pause–shear–pause–shear” test scheme is adopted. The soil is subjected to 3 h, 6 h, 12 h, 24 h, and 72 h healing shear tests, and combined with the SEM microstructure characteristics of the shear surface, to explore the internal mechanism of self-healing. The results show that the landslide soil exhibits strong self-healing strength recovery characteristics; however, these strength recovery characteristics decrease rapidly after experiencing a very small displacement. The strength recovery was strongly correlated with the vertical stress and healing time. With increasing vertical stress, the strength recovery value of the soil increases. Under low pressure, the strength recovery is small, and under high pressure, the strength recovery is obvious. With increasing healing time, the strength recovery increases; however, the increase in the amplitude diminishes and ultimately approaches zero with increasing healing time. A “healing phenomenon” occurs in the shear surface of slide zone soil after a short period of time. A shear strength value greater than the residual strength can be used to check the landslide design, which can effectively reduce costs.

Kink‐band Kinematic Analysis and its Implications for Late‐stage Deformation in the Internal Parts of the Zagros Collision (Sanandaj‐Sirjan Zone) in West Iran

AbstractIn the internal parts of the Zagros collision zone, several deformation phases have been superimposed. The early deformation phase caused the development of a penetrative foliation. The late‐stage deformation phase was preferentially accommodated within shear zones and caused the generation of shear bands, implying a non‐coaxial component of deformation, the end of this stage deformation was marked by the development of kink‐bands. In the vicinity of Zagros suture zone, the kink angle increased from 40° to 60°, and the kink‐bands was converted to chevron folds. In this region, the external (α) and internal (β) angular ratio is α/β ≠ 1 and kink angle increased, and deformation occurred with 10% to 30% volume loss. Farther from the suture zone in the east, α/β = 1; and total volume was constant or increased by 5% to 10%. Kink‐bands kinematic analysis in the study area revealed this structures were sensitive to deformation conditions and components such that, with decreasing distance to the Zagros suture zone, shearing and rotation increased, a high kinematic vorticity dominated, and volume loss occurred during deformation.

Inferring arsenic anomalies indirectly using airborne hyperspectral imaging – Implication for gold prospecting along the Rise and Shine Shear Zone in New Zealand

Well-exposed mineral deposits are scarce at a global level and presently potential mineral-rich sites are underlying vegetation cover and topsoil, which are suboptimal for direct remote sensing based exploration techniques. This study aims to implement an indirect approach to arsenic (As) distribution mapping using the surface manifestations of the subsurface geology and link it to the known gold mineralisation in the study area. Rise and Shine Shear Zone (RSSZ) in New Zealand is broadly a part of the Otago schist hosting lower to upper green-schist facies rocks manifesting mesothermal gold mineralisation. The area has several surficial geological imprints separating mineralised and non-mineralised zones, but these are dominated by topographic ruggedness, soil moisture and vegetation (mainly grass/tussock) spectra in the hyperspectral data. Initially, a band selection using Recursive Feature Elimination (RFE) was executed. The bands generated were tallied with the field and geological understanding of the area. The resultant 85 bands were then further put through Orthogonal Total Variation Component Analysis (OTVCA) to concise the information in 10 bands. OTVCA output was then classified using Random Forest classifier to map three levels of As concentration (<20 ppm, between 20 and 100 ppm and >100 ppm). The potentially high As concentration zones are likely to be related to the gold mineralisation. The geology of the area correlates with soil exposure which is captured by the classification in some parts, this increases the accuracy but also makes the classification analysis challenging.

Evaluation method for microscale mechanical properties of an epoxy resin

This study offers a detailed quantitative evaluation of microscale properties of polymers utilizing the surface and interfacial cutting analysis system (SAICAS) technique. The investigation focuses on the formation of the primary shear zone (PSZ) during cutting, leading to plastic deformation and subsequent chip curling. This research explores various cutting thicknesses, each demonstrating unique chip formation, and applies a lubricant to mitigate friction noise and stabilize chip formation. An in-depth analysis of force geometries is performed to gain insights into chip formation. The shear strength and shear viscosity are calculated using relevant equations, thus enabling the quantitative characterization of the viscoelastic behavior of polymers. Remarkably, the polymers exhibit shear thinning behavior, where their resistance to shear decreases as the shear rate increases. The shear viscosity–shear rate plot follows the Ostwald-de Waele relationship, indicative of plastic flow behavior. The viscoelastic characteristics were validated by comparing the values calculated based on Atkins's theory with the quantified values. Then, the physical meaning of those values were discussed. This study facilitates the direct measurement of mechanical properties in solidified form of the polymer, offering a more precise representation than traditional test piece measurements. In addition, shear viscosity determination of cross-linked materials without pretreatment is achieved, broadening the scope of material analysis through quantitative comparisons.

Monazite and zircon U–(Th–)Pb dating reveals multiple episodes of HT metamorphism in the Cima Lunga unit (Central Alps): implications for the exhumation of high‐pressure rocks

High- to ultrahigh-pressure (HP–UHP) rocks recording high-temperature (HT) > 700 °C are well exposed in the Central Alps, making it an ideal region to study the timing of metamorphic stages and the mechanisms of deep-seated rocks exhumation. Here, we report an integrated dataset of petrological and U–(Th–)Pb dating of metapelites surrounding ultramafic lenses from the Cima Lunga unit. At the interface with ultramafics preserving (U)HP–HT assemblages (1.5–3.1 GPa, 650–850 °C), metapelites record higher P‒T values (1.3–2.7 GPa, 700–850 °C) and traces of partial melting, whereas the rest of the unit is dominated by amphibolite-facies conditions. U–Th–Pb dating on zircon and monazite from migmatites indicates that partial melting was episodic involving at least two stages at ~38 to 35 Ma and 33–30 Ma, respectively. While the 38–35 Ma stage matches the HP conditions (> 1.5 GPa) and it is recorded around only one lens with scarce volumes of melt, partial melting at 33–30 Ma is witnessed at lower pressure (~1 GPa) and more widely distributed around the lenses, as within the major shear zones. Far from the ultramafics, zircon from the amphibolite-facies metasedimentary rocks record inherited pre-Variscan ages, while monazite ages at ~22 Ma document mineral growth during the Barrovian cooling. Field and petro-chronological evidence highlight that multiple episodes of partial melting locally developed at the rheological interface promoted by the interplay of fluids extracted from the ultramafic lenses associated with shear heating. New evidence suggests that local variation of P‒T equilibria play a significant role during the exhumation history.Graphical

Physical model study on failure mechanism of strip footing on reinforced granular deposit

This study proposes guidelines for predicting the failure mechanism of a shallow strip footing resting on geosynthetic-reinforced granular deposit at different stages of footing settlement. Physical model tests are performed on footings resting on unreinforced and geosynthetic-reinforced soil. The reinforcement parameters varied include the depth between consecutive reinforcements, number of layers and the depth of the reinforced zone. Additionally, contours of deformation and maximum shear strain of soil and mobilised tensile strain in reinforcement with increasing footing settlement are studied. The improvement of bearing capacity ratio and the peak tensile strain in the reinforcement was monitored for three normalised settlement ratios of 5% (low), 10% (medium) and 25% (high). The reinforced soil models were found to depict primarily a punching shear failure limited solely within the reinforced zone at s/B of 5%. This was supplemented with a well-formed triangular wedge in the underlying unreinforced soil at s/B of 10%. In addition to above mechanisms, the radial shear zones were prominent at s/B of 25%. Failure mechanisms have been proposed eventually for each s/B value investigated, including guidelines on the upper and lower bounds of the load dispersion angle in the reinforced soil and wedge angle of the underlying unreinforced soil.