Major Shear Research Articles

Geological and hydrochemical controls on water chemistry and stable isotopes of hot springs in the Three Parallel Rivers Region, southeast Tibetan Plateau: The genesis of geothermal waters

The Three Parallel Rivers Region (TPRR) is a tectonically active area in the middle segment of the Sanjiang Tethys Orogen, southeast Tibetan Plateau, characterized by many hot springs. This area is up-and-coming for producing geothermal energy, a CO2-free energy source, which will help China in reducing the effects of climate change. We report here the results of 37 geothermal springs that have been sampled to investigate the physical and chemical characteristics of the thermal water and evolution patterns. These springs are drained along three major N-S faults zones (the Lujiang Fault, the Lancangjiang Fault and the Jinshajiang-Red River Fault) to the interior of the Lanping Basin. Five hydrochemical water facies were recognized with Na-HCO3 being the primary type. Fluorine and boron that are produced through water-rock interactions are commonly enriched in these waters, and their concentrations are further controlled by secondary hydrochemical processes during water migration. The water's stable isotopes (δ18O and δD) suggest the meteoric origin of all thermal waters in the TPRR. The estimated reservoir temperatures range between 61 °C and 118 °C with the relatively hot reservoirs (> 100 °C) generally developed in major shear zones. These results indicate variable water circulation depth exceeding 3000 m, implying that the large-scale shearing displacement plays a vital role in heat acquisition. Conductive cooling and possible mixing of the thermal water with near-surface cold water occurred as the thermal water ascended along the fault systems and was ejected along the outlets of the springs. This study adds insights into hydrogeochemical constrains on evolution of water solutes over a large-scale hydrological cycle in the TPRR.

Zircon U-Pb geochronology of the Lan Sang gneisses and its tectonic implications for the Mae Ping shear zone, NW Thailand

The Mae Ping shear zone (MPSZ), a major shear zone trending NW-SE in Thailand, is responsible for the left-lateral displacement of the N-S Triassic-Jurassic granitoid and gneiss belt. This displacement is postulated to have contributed to Cenozoic extrusion tectonics. Within the Lan Sang National Park, the MPSZ exposes several intensely deformed lithologies, collectively known as the Lan Sang gneisses. These gneisses have attracted considerable attention for their potential to substantiate the extrusion model. However, the timing of the emplacement of the orthogneiss protolith is still debated. Moreover, the origin and distribution of the Eocene syn-shearing granodiorite within this shear zone are not well understood. To shed light on the magmatic history of the MPSZ, this study utilized zircon U-Pb geochronology to systematically investigate the Lan Sang gneisses. Our findings demonstrate that these gneisses can be categorized into paragneiss and orthogneiss groups. Paragneiss samples feature zircons displaying rounded detrital cores ranging from 3,078 to 450 Ma, with metamorphic rim overgrowth of ca. 200 Ma (most Th/U <0.01). This indicates that their Paleozoic sedimentary protoliths experienced high-grade metamorphism during the Triassic-Jurassic Indosinian orogeny. On the other hand, zircon from orthogneiss samples shows that their magmatic protoliths were predominantly emplaced either around ∼200 Ma or within 45-32 Ma. The Eocene-Oligocene magmatism likely coincided with the proposed Eocene metamorphism. Since these samples were deformed by left-lateral shearing, the left-lateral motion of the MPSZ probably ended after 32 Ma. Eocene-Oligocene magmatic events have also been identified in granite, mylonite, and gneiss samples from other regions along the Sibumasu terrane, including the Three Pagodas, Klaeng, Ranong, Khlong Marui shear zones, and the Doi Inthanon area. The Eocene-Oligocene magmatism was likely linked with the movement of the shear zones and may be responsible for the regional cooling pattern. The spatial and temporal distribution of the Eocene-Oligocene magmatism within the Sibumasu terrane supports the hypothesis that the inward migration of magmatism in the overriding plate resulted from the shallowing of the Neo-Tethyan slab.

Long‐Lived (180 Myr) Ductile Flow Within the Great Slave Lake Shear Zone

AbstractThe Great Slave Lake shear zone (GSLsz) is a type example for deeply eroded continental transform boundaries located in the Northwest Territories, Canada. Formed during the oblique convergence of the Archean Rae and Slave cratons, the GSLsz has accommodated up to 700 km of dextral shear. Here we present the results of in situ U‐Pb apatite and titanite geochronology from 11 samples that were collected across the strike of the shear zone. Both geochronometers record a near‐continuous history of ductile shear during crustal cooling and exhumation that spans ca. 1920–1740 Ma. By integrating the geochronological data with structural and metamorphic observations across the structure, we propose a tectonic model for the shear zone that consists of three stages. The first stage (ca. 1920–1880 Ma) is characterized by strain accommodation along two coeval fault strands. During the second stage (ca. 1880–1800 Ma), ductile shear ceases along the northernmost fault strand and the locus of strain migrates southwards toward the hinterland of the Rae cratonic margin. In the third stage (ca. 1800–1740 Ma), ductile strain localizes back along the southern of the two original fault strands, after which the present‐day surface level of the shear zone transitions to brittle shear. Our results highlight both the significance of the lateral migration of the zone of active deformation in major crustal shear zones as well as the localization of strain along existing crustal structures.

Comparison of microstructural, texture and mechanical properties of SiC and Zn particle reinforced FSW 6061-T6 aluminium alloy

This work investigates the microstructure, mechanical characteristics, and texture evolution of friction stir welding (FSW) of AA6061-T6 metal matrix composites (MMCs) reinforced with silicon carbide (SiC) and zinc (Zn) particles. The SZ region of the SiC and Zn particle-reinforced aluminium matrix (Al-matrix) composites has ultra-fine grain refinements of 4.79 and 4.18 μm, respectively, compared to base metal (BM) particle sizes of 44.97 μm. Ultra-fine grain refinement in the SZ zone produces dynamic recrystallization with particulate-driven nucleation, Zenner Hollomon, and homogeneous SiC/Zn particle distribution in the Al-matrix. Recrystallization texture components P {011} <112>, cube {001} <101>, rotating cube (H) {001} <110>, and F {111} <112>, along with primary shear texture components (B/B¯, and C), suggested DRX at the joint interface in the SiC-reinforced Al-matrix composite. However, the Zn-reinforced Al-matrix composite has a high plain strain, recrystallization, and deformation texture components of copper {112} <111>, Brass {011} <211>, cube {001} <101>, Goss {110}, and P 011 <112>, and major shear texture components (B/B¯ and C). SiC and Zn-reinforced Al-matrix composites have 110 ± 4 and 120 ± 5 HV0.2 average microhardness, respectively. Also, SiC and Zn-reinforced Al-matrix composites have 224 and 236 MPa tensile strengths, respectively.

Anisotropic gradients in Iran: Quasi-Love waves illuminate the deep structure and deformation style of the Zagros, Alborz, and Kopet Dagh

We investigate the presence of the quasi-Love wave (qL) at 51 seismic stations of a temporary seismic network across the western Arabia-Eurasia collision zone. We quantify the intensity of the qL observations from the April 12, 2014 Solomon Islands earthquake by calculating the peak-to-peak amplitude ratios of the qL and Love waves, and compare them with predicted qL intensities from previous shear-wave splitting results. We determine the polarity, timing, and period-dependence of the qL observations within the period range of 50–100 s. Our analysis reveals that the qL observations at stations in the Zagros and Alborz mountain belts exhibit opposite characteristics. In contrast to the Alborz stations, the intensity of qL observations at the Zagros stations exhibits relatively negligible dependence on the period, while their receiver-scatterer distances are considerably period-dependent. We approximately locate the anisotropic gradients that generate the qL waves. Our results suggest that a lithospheric gap is responsible for the shallow and abrupt variation in the belt-parallel trend of fast-axis orientations in the westernmost part of the Zagros. Additionally, the period/depth dependence of the anisotropic gradients along the boundary between the central Zagros and central Iran provides insight into the variation in the downward dip of the Arabian lithosphere. The anisotropic gradient located to the north of the Doruneh fault in eastern Iran indicates its role as a major shear zone and lithospheric boundary. Finally, we observe that the spatial distribution of the anisotropic gradient in northeastern Iran matches the higher strain-rate areas in the Kopet Dagh Mountains, suggesting coupling between the lithospheric mantle and crust in that region.

Andean-type, bivergent crustal shortening in the Rinkian orogen: New constraints on the tectonic evolution of Laurentia–West Greenland in the Paleoproterozoic

Abstract The “Rinkian belt” of West Greenland is a metamorphic terrain of Paleoproterozoic age comprising: (1) the north Rinkian fold-thrust belt (FTB)—a pro- or fore-arc domain, highly deformed and metamorphosed with widespread anatexis; (2) the Prøven Igneous Complex—a magmatic arc characterized by hypersthene granitic rocks (“charnockites”); (3) the south Rinkian FTB—an inverted back-arc basin; and 4) a continental margin or foreland. Recognition of this tectonic architecture demonstrates that the “Rinkian” is a bona fide orogenic belt—the Rinkian orogen— and not simply the imbricated lower plate of the Nagssugtoqidian orogen. Arc plutons of the Prøven Igneous Complex were emplaced into the Karrat Group at ca. 1.90–1.85 Ga, dividing a back-arc basin into pro- and retro-arc domains. In the former—the north Rinkian FTB—WSW-directed thrusting (deformation events D1-D2) and high-grade metamorphism were taking place by ca. 1.875 Ga and were continuous through ca. 1.850 Ga with a peak temperature at ca. 1.830 Ma accompanied by anatexis in the Karrat Group and lower units of the Prøven Igneous Complex. In the retro-arc domain—the south Rinkian FTB—thrusting to the E (D1) began at ca. 1.870 Ma followed by thrusting to the W (D2) at ca. 1.830–1.820 Ga with displacement focused into a major high-temperature ductile shear zone which carried the Prøven Igneous Complex in the hanging wall of an Andean-type, crustal-scale, “pop-up” structure. High-temperature deformation continued during D3 when the pro-arc, arc, and retro-arc domains were shortened by bivergent detachment folding and thrusting at ca. 1.820–1.810 Ga.

Substantially enhanced homogeneous plastic flow in hierarchically nanodomained amorphous alloys

To alleviate the mechanical instability of major shear bands in metallic glasses at room temperature, topologically heterogeneous structures were introduced to encourage the multiplication of mild shear bands. Different from the former attention on topological structures, here we present a compositional design approach to build nanoscale chemical heterogeneity to enhance homogeneous plastic flow upon both compression and tension. The idea is realized in a Ti-Zr-Nb-Si-XX/Mg-Zn-Ca-YY hierarchically nanodomained amorphous alloy, where XX and YY denote other elements. The alloy shows ~2% elastic strain and undergoes highly homogeneous plastic flow of ~40% strain (with strain hardening) in compression, surpassing those of mono- and hetero-structured metallic glasses. Furthermore, dynamic atomic intermixing occurs between the nanodomains during plastic flow, preventing possible interface failure. Our design of chemically distinct nanodomains and the dynamic atomic intermixing at the interface opens up an avenue for the development of amorphous materials with ultrahigh strength and large plasticity.

Review of the thermo-tectonic evolution of the Central Zone of the Limpopo Complex with implications for conflicting published geodynamic models

Abstract This paper addresses the credibility of published data utilised to underpin conflicting models recently proposed for the geodynamic evolution of the Limpopo Complex (LC), Southern Africa, in the Neoarchaean and Palaeoproterozoic. We are mainly focused on the tectonic and metamorphic processes that affected the Central Zone (CZ) of the LC, but also consider the significance of the timing of the thermo-tectonic interaction of the Southern Marginal Zone (SMZ) of the LC with the granite-greenstone terrane of the Kaapvaal Craton (KVC) at the position of the steep north-dipping Hout River Shear Zone (HRSZ). HRSZ-linked tectonism at the contact with the KVC is expressed as a narrow “hot-iron zone” directly dated at 2.72 to 2.69 Ga and developed in the footwall of the north-dipping HRSZ. HRSZ-linked tectonic activity intermittently continued up to 2.65 to 2.62 Ga with no structural-metamorphic or geochronological evidence that the SMZ and the rest of the KVC were affected by regional thermo-tectonic (orogenic) activity after ca. 2.68 Ga. The complementary evolution of the CZ at 2.72 to 2.62 Ga prior to emplacement at 2.612 Ga of the Bulai granitic pluton is expressed by two thermo-tectonic events, at 2.72 to 2.66 Ga and 2.65 to 2.62 Ga, respectively. The early 2.72 to 2.66 Ga event was associated with near-vertical exhumation of the CZ from a rising crustal-scale granulite diapir, accompanied by emplacement of steeply-dipping isoclinal folded and granoblastic-textured CZ granulites at the mid-crustal level (20 km depth). A moderately (~45°) northeast-directed shear deformational event, accompanied by extensive granitic diapirism, controlled the final emplacement of the CZ in the Neoarchaean at 2.65 to 2.62 Ga prior to intrusion of the 2.612 Ga Bulai pluton. This second tectono-thermal event is expressed by major sheared structural features that include mega-closed folds, mega-north-south trending folds, and the 29 km-wide southwest-northeast-trending and moderately southeast-dipping and northeast-verging Tshipise Straightening Zone (TSZ) that bounds the CZ in the south. The CZ was finally exhumed and emplaced at the upper crustal level 600 Myr later (at ca. 2.02 Ga) during a regional high-temperature Palaeoproterozoic thermal event associated with major near-vertical strike-slip shear zones that overprint Neoarchaean oblique slip shear zones that bound the CZ. Thermo-tectonic activity in the CZ that is associated with this mainly thermal event is recognised as discrete steeply-dipping narrow fabric-parallel shear zones dated at ca. 2.02 Ga that overprint older structures. A gravity-driven crustal-scale diapiric model is utilised to explain the evolution of the SMZ and CZ of the LC at 2.72 to 2.62 Ga during the Limpopo Orogeny. Data presented and discussed contradict alternative published models that propose a continent-continent collisional orogeny at 2.65 to 2.62 Ga involving the SMZ and KVC, followed 600 Myr later at 2.02 Ga by a transpressional orogeny associated with near-horizontal thrust tectonics.

Fluid migration along deep‐crustal shear zone: A case study of the Rhenosterkoppies Greenstone Belt in the northern Kaapvaal Craton, South Africa

The north‐dipping Hout River Shear Zone (HRSZ), which marks the boundary between the high‐grade Limpopo Complex in its hanging wall and the low‐grade granite‐greenstone terrane of the Kaapvaal Craton in South Africa in its footwall, is a deep‐crustal shear zone that controlled emplacement of hot Limpopo Complex granulites over and against low‐grade granite‐greenstones during exhumation at ~2.72–2.62 Ga. This major shear zone controlled migration of large volumes of hydrous fluids released during devolatilization of underthrusted greenstones that infiltrated into hot overlying granulites, establishing a retrograde anthophyllite‐in isograd and associated zone of retrograde rehydrated granulite that bounds the Limpopo Complex in the south. Here, we report new petrological data based on mineral equilibrium modelling of amphibolites from the Rhenosterkoppies Greenstone Belt (RGB) located in the immediate footwall of the HRSZ and discuss evidence that these rocks also interacted with high‐temperature fluids that infiltrated along the HRSZ. This study provides an important perspective of the interaction of hot granulites with underthrusted relatively cold greenschist‐facies rocks along the steeply north‐dipping section of the HRSZ, and shows that evidence for such interaction is restricted to a relatively narrow zone in the footwall of the HRSZ termed a hot‐iron‐zone. The peak mineral assemblage of a garnet‐free amphibolite from the RGB (magnesio‐hornblende + plagioclase + quartz + clinopyroxene + titanite + ilmenite) yielded the peak P–T condition of 7–8 kbar and 640–680°C with H2O content of 3.5–3.8 mol%. Clinopyroxene is replaced by actinolite + quartz and epidote + quartz symplectites by a post‐peak hydration event at &lt;5 kbar and &lt;590°C caused by elevated H2O content in the rock (&gt;4.0 mol%), possibly related to fluid infiltration along the HRSZ. Mineral equilibria in a garnet‐bearing amphibolite records a prograde path from 5 to 7 kbar and 540–630°C to the peak conditions at 7.6–8.7 kbar and 620–650°C. A clockwise P–T path suggesting rapid compression and decompression has been inferred for the amphibolites from the RGB, possibly because of pressure increase related to overthrusting of the high‐grade terrane (Southern Marginal Zone of the Limpopo Complex) onto the low‐grade granite‐greenstone terrane, followed by rapid exhumation. The quantity of H2O associated with the amphibolite‐facies metamorphism in the RGB was elevated from the peak stage (M(H2O) = 3.5–3.8 mol%) to the retrograde stage (M(H2O) = 4.0–4.5 mol%) of metamorphism in the RGB, possibly suggesting fluid infiltration not only from internal sources but also from external sources. The results of this study indicate that a H2O‐bearing fluid, which infiltrated along the HRSZ, affected both the footwall and the hanging wall sections of the shear zone, although the effect on the footwall section was limited.

One billion years of tectonism at the Paleoproterozoic interface of North and South Australia

The Mount Woods Domain, in the northeastern Gawler Craton, occupies a tectonically important location in Proterozoic Australia, yet there is very little published U–Pb geochronology data from this region to underpin tectonic models. New LA-ICP-MS U–Pb monazite and detrital zircon geochronology reveal Archean to Paleoproterozoic basement in the central Mount Woods Domain, comprising metasedimentary rocks and garnet-bearing granite with protolith ages of c. 2550–2400 Ma and metasedimentary rocks deposited after c. 1855 Ma. The southern Mount Woods Domain contains younger metasedimentary sequences deposited after 1750 Ma. Metamorphic monazite and zircon geochronology combined with phase equilibria modelling show the rocks of the central Mount Woods Domain were metamorphosed to granulite facies between 1700 and 1670 Ma, reaching pressure and temperature conditions of 4.8–5.3 kbar and 800–840 °C. Monazite geochronology from samples located along major shear zones and in the westernmost Mount Woods Domain record amphibolite facies metamorphism and reworking at 1570–1550 Ma, with a further phase of shear zone activity along the northern margin of the Mount Woods Domain at c. 1480 Ma. Laser ablation inductively coupled plasma triple quadrupole mass spectrometry (LA-ICP-QQQ-MS) Rb–Sr biotite ages from across the Mount Woods Domain range between 1480 and 1390 Ma. The protracted geological history in the Mount Woods Domain from c. 2500–1400 Ma provides a piercing point linking different regions of Proterozoic Australia and western Laurentia during the tenure of the Nuna supercontinent.

Structural analysis and design for a warehouse using STAAD PRO

Aim of this study is to brief about the pre-engineered buildings systems proposed for Warehouse Building. The need for steel building increased lot recently, due to its ease, faster construction and weight by strength ratio than concrete structures. There are so many software to analyse and design the elements but lot of students suffer from insufficient knowledge on calculating loads, load combinations and design parameters. Thus took an initiative to detail the design process with a warehouse study and created a report on its loads acting on the structures like vertical and lateral loads, load combinations with design aids provided in code which includes both ASCE standard and IS standards to design. The results obtained from analysis are within the limits also the designed elements are optimized by trial and error method which includes displacement, axial force, compression, bending along major and minor axis and shear check. Steel member sizes are fixed based on the utilization factor and quantity for steel members arrived. The required bolted or welded connections are designed based on the nodal reactions at structural element intersections. STAAD Pro Software used to construct, analyse and design the model of steel members. Moments are high compared to axial loads many elements are designed as tapered section to reduce the quantity of steel and maximize the efficiency with low cost. The overall steel poundage required is 27 kg/sqm to design the structure. The requirement of purlin weight reduced from 400 kN to 132 kN when replaced Channel section with Z-purlin. In overall, the advantages of Z purlins make them a popular choice for construction projects, particularly for industrial and commercial buildings. The results obtained are recorded for the study.

A review of the geophysical knowledge of the Borborema Province, NE-Brazil, and tectonic implications

This review summarizes the results of nearly 50 years of application of geophysical data to study tectonic problems in Borborema Province (BP), Northeastern Brazil. Much information has been obtained from the interpretation of magnetic, gamma-ray spectrometry, gravity, seismological, magnetotelluric, deep seismic and heat flow data. The resulting picture is that, in comparison with other Brazilian geological domains, BP has a thin crust, a lithosphere with small effective elastic thickness, the presence of predominantly positive free-air gravity anomalies, besides the most expressive geoid anomaly, in addition to relatively high heat flow and intraplate seismicity. These facts reinforce the hypothesis that the BP lithosphere suffered a strong impact in Gondwana fragmentation. Predominantly positive free-air gravity anomalies reveal that part of the province has not yet reached isostatic equilibrium. Gravity data established the boundaries of the BP crustal block with neighboring blocks; in particular, the crustal boundary with the São Francisco Craton is located in the innermost regions of the marginal fold belt, tens of kilometers at the north of the conventional limit. Magnetic data allowed to infer the continuity of basement structures beneath sedimentary basins, in particular that BP continues to the Transbrasiliano Lineament, underneath the sedimentary of the Parnaíba Basin. In addition, enhanced magnetic maps made it possible assessing the amount of deformation associated with the major shear zones and identified a continental-scale Cretaceous dike system crossing the BP. Gamma-ray spectrometry data allowed extensive geological mapping of metasedimentary sequences, granitic intrusions and basement complexes. Seismological data allowed to recognize that major shear zones in BP have lithospheric significance. Deep seismic data evidenced a well-defined contrast between the upper and lower crust in BP (Conrad discontinuity). Magnetotelluric data revealed several deep geoelectrical anomalies in BP, some of them interpreted as relics of subduction zones. Intraplate seismicity studies allowed inferring that the current stress state in the BP upper crust is predominantly transcurrent. The list of open problems in BP is also expressive. Notable examples are: a) it has not yet been possible to define which type of orogeny (accretionary or intracontinental?) was dominant in the Neoproterozoic; b) the cause of the expressive geoid anomaly is unknown; c) the tectonic significance of the Transbrasiliano Lineament (collisional suture? Just an intracontinental shear zone?) is also unknown. Regarding economic applications, the use of geophysical data to prospect new ore deposits is still relatively poor. We hope that this review can contribute to increase the familiarity and acceptance of geophysical results by the geological community.

Re-examination of shear design provisions for high-strength longitudinally reinforced concrete beams

The lack of information regarding the shear behaviour of high-strength longitudinally reinforced concrete beams without shear reinforcement (HRCBW) impedes design engineers from using the full yield strength of the material. In this work, current shear design provisions for HRCBW were re-examined based on the probability density function (PDF), confidence interval and confidence level. Based on the principal shear mechanism of beam and arch actions, a probabilistic shear capacity model for HRCBW was developed based on Bayesian theory and the Markov chain Monte Carlo method, taking into account both aleatory and epistemic uncertainties. Statistical characteristics (e.g. mean, standard deviation, distribution type) of the shear capacity of HRCBW were determined by the Kolmogorov–Smirnov test and statistical analysis. The accuracy and applicability of three major shear design provisions for HRCBW (ACI 318-19, BS EN 1992-1-1:2004 and fib Model Code 2010) were re-examined based on the PDF, confidence interval and confidence level.

Remote sensing and geochemical investigations of sulfide-bearing metavolcanic and gabbroic rocks (Egypt): Constraints on host-rock petrogenesis and sulfide genesis

Field geology, geochemical analyses and multi-sensor remotely sensed data of Landsat-8, ASTER and Sentinel-2 were used to detect various types of hydrothermal alteration and sulfide-gold mineralization in Neoproterozoic metavolcanic and gabbroic rocks from Darhib and El-Beida areas in the South Eastern Desert (SED) of Egypt. We also used RADAR data of Sentinel-1 using PCI Geomatica software to decipher the structural lineaments that control this mineralization. Different styles of disseminated to massive sulfide deposits include: 1) undeformed magmatic disseminated ores in Darhib gabbros, metavolcanic rocks and metabasic dykes; 2) deformed (remobilized) massive ores mostly of a magmatic-hydrothermal origin in Darhib tremolite talc rocks along E-W shear zones; 3) hydrothermal sulfide ores along El-Beida NW–SE shear zones. Cu-Zn massive ores represent the main sulfides in the Darhib silicified tremolite-talc rocks and meta-andesites, and occur as bands, veins and patches along Darhib E-W shear zones. Discontinuous occurrences of sulfide ores-bearing tremolite-talc rocks indicate that major shear zones act as structural controls on mineralization. Sulfide ores consist chiefly of chalcopyrite, sphalerite, pyrite and galena as well as minor covellite and bornite. These ores are highly concentrated along E-W striking Darhib shear zones and resulted from granite-derived hydrothermal fluids that form/and or accumulate sulfide minerals from the sulfide-bearing metavolcanic rocks around shear zones. Two stages of hydrothermal alterations are recorded in the Darhib talc mine including pre- (talcification, amphibolitization and carbonatization) and syn- (silicification and chloritization) sulfide ore alterations. Disseminated sulfide mineralization hosted in Darhib gabbros, metavolcanic rocks and metabasic dykes is of a magmatic origin, similar to Cu-Ni sulfide deposits hosted in gabbroic varieties in worldwide mafic–ultramafic intrusions. On the other hand, El-Beida gold-sulfide-bearing quartz and quartz carbonate veins are hosted in ferruginated and silicified metavolcanics/ metavolcaniclastic rocks along NW–SE shear zones (Najd Fault System trend). These are spatially associated with regional convergent structures (high-angle convergent wrench structures), suggesting orogenic gold type mineralization. The E-W with minor WNW-ESE shear zones in Darhib and NW-SE trending shear zones in El- Beida structurally controlled sulfides and gold mineralization in the SED of Egypt. El-Beida sulfide mineralization occurs as disseminated ores that consist mainly of pyrite, chalcopyrite, covelite and chalcocite with occasional occurrence of gold. The spatial occurrence of native gold in ferrigenous alteration zones indicates the role of iron in gold precipitation through buffering of gold-bearing complexes. Mineralogical and geochemical data of Darhib and El-Beida sulfide-bearing rocks indicate that they crystallized from depleted mantle sources in a back-arc basin setting, starting with the generation of arc-like volcanic rocks in a nascent BAB stage followed by the emplacement of plutonic equivalent of MORB/OIB-like rocks such as gabbroic intrusions in a mature BAB.

Mapping geological configuration using geophysics data: an investigative approach in targeting iron ore, gold mineralization and other commodities, a case study of Toko-Nlokeng area (Nyong Greenstone Belt, SW Cameroon)

ABSTRACT Regional geophysical data are important for detecting the presence of mineral deposits under cover. This study used geophysical data coupled with field geology of the Toko-Nlokeng area, Cameroon, to locate and map structures and lithologies as part of an exploration campaign for mineral deposits. The airborne geophysical survey in the Toko-Nlokeng area located in the Nyong complex revealed a predominantly EW striking highly folded series result of polyphase deformation of iron formations and host rocks divided into domains based on magnetic and radiometric character. The geophysical data indicate that major faults and shear zones strike NE-SW, with N–S striking units on the western margin and mainly E–W striking units in the rest of the area. These data suggest a major N–S thrust fault similar to the Borborema Province (NE Brazil) terrane marked by accretionary processes during the assembly of Western Gondwana. Several significant NE–SW striking shear zones are present. The data revealed many moderate to highly magnetic bodies that are interpreted as magnetite-bearing iron formation, mafic–ultramafic intrusions and flows, skarns, carbonatites and kimberlites. The magnetic and radiometric trends reveal the internal regional rock fabric and strike, and iron ore targets with magnetic anomaly up to 27,000 nT related to iron formations and other significant targets for gold, potassium (alteration) and uranium. The Toko-Nlokeng iron deposit is comprised of magnetite-bearing quartzite beds and is concordant with the surrounding host rocks and stands as one of a broad group of magnetite-dominated iron formations that occur throughout West and Central Africa. A new geological map was produced from mapped lithologies and microstructure characteristics of the iron formations, interpretations of the aeromagnetic data and structural features. The study results have important implications for regional exploration programs.

On the crustal framework of the central Alto Pajeú Terrane (Borborema Province, NE Brazil): Geophysical and structural data constrain late Neoproterozoic transpression in Western Gondwana

The structural framework of the Alto Pajeú Terrane, Borborema Province (NE Brazil) records a complex tectonic evolution related to the Neoproterozoic amalgamation of Western Gondwana. Combined, multiscale geophysical and litho-structural datasets for the Central Borborema Province constrain the regional crustal architecture. Magnetic and radiometric lineaments mostly follow NE-SW and E-W trends that correlate to strike-slip shear zones and associated subvertical mylonitic foliations. Regional, outcrop-scale and microstructural kinematic indicators consistently assign sinistral and dextral motion sense for NE-SW and E-W shear zones, respectively. Four sectors with contrasting litho-geophysical and structural patterns are juxtaposed across major shear zones: the Alto Pajeú, Alto Moxotó and Piancó-Alto Brígida terranes, plus a small portion of the Northern Borborema Province. Expressive magnetic lineaments highlight the boundary between the Alto Pajeú and Alto Moxotó terranes, represented by a pair of sinistral strike-slip shear zones. At outcrop scale, relic thrust surfaces (top-to-NW vergence) with associated flat-lying foliation and down-dip mineral stretching lineations affecting Tonian orthogneisses and metapelites disclose a contractional episode of uncertain age. Transposition of the shallowly-dipping foliation in highly sheared domains imply it is older than the shear-related deformation. The shear zone system and associated structures record the transpressional regime that characterizes the late stages of the Brasiliano/Pan-African Orogeny in the region (ca. 575–565 Ma). Microstructures of a mylonitic orthogneiss from the Juru-Belém shear zone reveal greenschist to amphibolite facies deformational conditions, with increasing importance of subgrain rotation mechanisms at higher strain rates and/or temperature. Microstructural similarities between this rock and tectonites along the southern Patos lineament suggest that bordering and internal regions of the Alto Pajeú terrane were subject to similar thermodynamic conditions during the late Brasiliano transpression.

Improving the shear behavior of RC dapped-end beams using precast strain-hardening cementitious composite (P-SHCC) plates

Dapped-end beams (DEBs) are frequently used in precast concrete structures in order to facilitate the construction procedures. However, premature failure is most likely to happen at their re-entrant corner owing to the immense shearing stresses in this region. To mitigate such a problem, a new strengthening system making use of Strain-Hardening Cementitious Composites (SHCC) material was utilized in this paper. For this purpose, an experimental study on ten DEBs specimens, including one defected un-strengthened specimen (BC), was prepared and tested under a monotonic 4-point loading protocol to assess the efficiency of the adopted strengthening system. The traditional reinforcement at the re-entrant corner was substituted by precast SHCC (P-SHCC) plates to upgrade the shear strength and serviceability of the tested DEBs. The P-SHCC plates were pre-cured for about 4 weeks before being used to mitigate any volumetric change issues related to SHCC. A slight amount of reinforcement was provided inside the P-SHCC plates to enhance their cracking behavior and avoid strain localization. The studied parameters were the scheme of P-SHCC plates at the re-entrant corner (continuous or intermittent/discontinuous), the orientation of P-SHCC plates (vertical or 45°-inclined), as well as their position with regard to the beam's cross-section (external or internal). The thickness of each external P-SHCC plate was kept constant at 20 mm so as to be easily incorporated into the concrete cover, whereas the internal P-SHCC plates had varied thicknesses (40, 55, or 70 mm). The test results revealed that providing DEBs with P-SHCC plates could significantly improve both shear capacity and the developed ductility. The gain in the ultimate load reached up to 91 % relative to the un-strengthened specimen (BC). Furthermore, a great reduction in the developed major shear crack width for all strengthened DEBs was attained. At the service load level, all strengthened DEBs showed a decreased crack width, with an average value of about 77 % compared to the specimen BC. Finally, two equations considering the contribution of P-SHCC plates were proposed to predict both the shear strength and the average crack width of the strengthened DEBs. The proposed equations showed good agreement with the experimental results.

Failure Behavior of CFRP-Strengthened Reinforced Concrete Beam–Column Joints under Reversed-Cyclic Lateral Loading: Mechanical and Acoustic Emission Observations

This paper investigates the failure behavior of reinforced concrete beam - column joints (BCJs) strengthened with different schemes of carbon fiber reinforced polymer (CFRP) and the factors causing fracture. In the study, five reinforced concrete BCJ specimens having 1/1 geometric scale were tested under reversed-cyclic lateral loading. While one of them was used as a reference, the others were strengthened with CFRP. Damage development of the specimens was simultaneously monitored by the acoustic emission (AE) technique. Both the structural and AE data were combined to reveal the effects of CFRP strengthening schemes on the fracture pattern ana damage progress. Quantities, scales, levels, and locations of the damage show that the scale of the damage decreased with all strengthening procedures and that the strength and other mechanical properties improved. In addition, extending the strengthening material to the columns and beams contributed more to the structural behavior in terms of strength, energy dissipation capacity and rigidity as well as crack development. Although strengthening by wrapping only the beam and column extensions of the joint can give the desired performance in terms of load bearing capacity, it is not recommended owing to an increased risk of major shear cracks.

In-situ physical and elastic properties of Archaean basement granitoids in the Koyna seismogenic zone, western India from 3 km downhole geophysical well logs: Implications for water percolation at depth

The Koyna region in western India is characterized by recurrent artificial water reservoir triggered seismicity since the impoundment of the Shivaji Sagar lake in 1962. Physical and mechanical properties of the crystalline basement rock beneath the Koyna seismogenic zone are determined from the downhole geophysical logs in a 3 km research borehole. The borehole, KFD1, is located in the proximity of the Donichawadi fissure zone (DFZ), the surface manifestation of the fault associated with the 1967 M 6.3 Koyna earthquake. KFD1 penetrated 1247 m thick Deccan traps and continued 1767 m into the underlying granite-gneiss basement. Geophysical logs provide a rare opportunity to characterize the basement granitoids, which host the recurrent seismicity. Several major zones of anomalous physical and mechanical properties were delineated below a depth of 2 km from the analysis of downhole geophysical logs. High Poisson's ratio and high neutron porosity across anomalous zones imply the presence of water saturated rock. The analyses of Nuclear Magnetic Resonance log reveals the presences of clay bound and free fluid across these zones. Sharp decrease in dynamic Young's modulus with increasing Poisson's ratio imply the presence of fractures saturated with water. These hydraulically conductive fractures are potential locations for fault reactivation. Additionally, strike of major and minor fractures associated with the anomalous zones are compared with the strike of Donichawadi fault. High angle between strike of the major shear fractures in the anomalous zone and strike of the Donichawadi fault imply that borehole KFD1 may have either intersected subsidiaries of the main fault at multiple depths or a new hidden fault system.

Combined Nd isotope systematics and geophysical data constrain the crustal evolution of the disrupted Alto Moxotó Terrane, Borborema Province, Brazil

The accretionary record of Precambrian orogens is often masked by systematic magmatic, metamorphic and/or structural overprints. The Neoproterozoic Borborema Province presents direct linkage to several orogenic belts along western Gondwana, but its crustal evolution is contentious resulting in a range of geological models. In the region, exotic terranes that might have been docked via thrust- and strike slip structures preserve pre-Gondwana events that provide glimpses for the evolution of orogenic systems more generally. A total of 201 SmNd analysis of the Archean-Paleoproterozoic Alto Moxotó Terrane, central Borborema Province reveals source ages in granitic, mafic and metasedimentary rocks that are mostly Paleoarchean to early Paleoproterozoic, which contrast with the adjacent terranes. The successive juvenile inputs and crustal reworking from Neoarchean (ca. 2.6 Ga) to mid-Paleoproterozoic (ca. 2.1 Ga) diverge with the early to late Neoproterozoic dominant crust of the neighboring blocks. 3D geophysical modelling highlights the unique signature of the Alto Moxotó Terrane compared to these blocks, including: i) K-poor and Th-rich crust and ii) higher gravity gradients when compared with the bordering lithospheric record, both in gamma-spectrometric and gravimetric maps. Moreover, prominent magnetic anomalies in all magnetometric maps coincide with the major shear zones, including previously proposed terrane boundaries, suggesting that they might represent cryptic or unmapped suture zones. The isotopic and geophysical data are consistent with derivation of the Alto Moxotó Terrane from older crustal blocks such as the São Francisco and Congo cratons and provide a model to the understanding of the accretionary evolution of western Gondwana.