Shear Belt Research Articles

Insights on the Mesoarchean to Neoproterozoic evolution of the western Campo do Meio Shear Belt, SE Brazil, using structural, aerogeophysical and U-Pb zircon data

The Campo do Meio Shear Belt (CMSB) is an approximately 200 × 25 km transcurrent area along the south-southwest margin of the São Francisco Craton. A comprehensive review of geology was performed in the western CMSB, where rocks from the Campos Gerais and Petúnia Complexes are predominant. The Campos Gerais Complex is relatively well positioned in the geotectonic context of the region. It corresponds to an Archean granite-greenstone belt lithological association related to the south-southwest part of the São Francisco Craton. The Petúnia Complex, in contrast, is unraveled in this contribution through the integration of aerogeophysical data from the western Campo do Meio Shear Belt (CMSB) with new fieldwork observations and zircon U–Pb (LA-MC-ICP-MS) dating.The Petúnia Complex has been restricted to two Mesoarchean gneissic units – Petúnia and Ribeirão da Conquista Gneiss, with crystallization ages of 2993 ± 11 Ma and 2870 ± 9 Ma, respectively. Although the ages are broadly coincident with those found in the Campos Gerais Complex, three characteristics suggest an evolutionary independent scenario (pre-S2) during the Archean for the Petúnia and Campos Gerais Complexes: i) the sharp contrast in gamma-ray emissions between these complexes; ii) the absence of komatiite affiliation in the meta-ultramafic rocks from the Petúnia Complex; and, iii) the absence of mafic dykes in the Petúnia Complex. These two complexes also can be distinguished by the frequency of Paleoproterozoic granitoid intrusions. The Petúnia Complex has only one occurrence, the Bom Jesus da Penha Metagranite, with a crystallization age of 2004 ± 11 Ma. On the other hand, several Paleoproterozoic granitoid intrusions (2.0–1.9 Ga) have been found in the Campos Gerais Complex. These Orosirian granitoids are restricted to CMSB and younger than those in the Mineiro Belt. We suggest that these Orosirian granitoids may represent remnants of a collision event that occurred after 2.1 Ga, leading to the integration of the Petúnia and Campo Gerais Complexes into the Columbia paleocontinent. During the Neoproterozoic, the evolution in the CMSBinvolved the cratonic basement and units related to the Southernmost Brasília Orogen. This set configures a tectonic mélange that underwent progressive deformation in a non-coaxial, partitioned transpressional regime.

Machine learning and remote sensing-based lithological mapping of the Duwi Shear-Belt area, Central Eastern Desert, Egypt

Machine learning and remote sensing techniques are widely accepted as valuable, cost-effective tools in lithological discrimination and mineralogical investigations. The current study represents an attempt to use machine learning classification along with several remote sensing techniques being applied to Landsat-8/9 satellite data to discriminate the various outcropping lithological rock units at the Duwi Shear Belt (DSB) area in the Central Eastern Desert of Egypt. Multi-class machine learning classification, multiple conventional remote sensing mapping techniques, spectral separability analysis based on the Jeffries-Matusita (J-M) distance measure, fieldwork, and petrographic investigations were integrated to enhance the lithological discrimination of the exposed rock units at DSB area. The well-recognized machine learning classifier (Support Vector Machine—SVM) was adopted in this study, with training data determined carefully based on enhancing the lithological discrimination attained from various remote sensing techniques of False Color Composites (FCC), Principal Component Analysis (PCA), and Minimum Noise Fraction (MNF), along with the fieldwork data and the previously published geologic maps. High overall accuracy of the SVM classification was obtained, however, inspection of the individual rock unit classes’ accuracies revealed lower accuracy for certain types of rock units which were also found associated with lower separability scores as well. Among the least separable rock units were; metagabbro rocks that showed high spectral similarity with the volcaniclastic metasediments rocks, and the metaultramafics of the ophiolitic mélange showed spectral attitude of high correlation to that of the Hammamat volcanosedimentary rocks. Target-oriented Color Ratio Composites (CRC) technique was implemented to better discriminate these hardly separable rock units. A final integrated geological map was obtained comprising the various discriminated Neoproterozoic basement rock units of the DSB area. The successfully mapped litho-units include; Meatiq Group (amphibolites, gneissic granitoids, and mylonitized granitoids), ophiolitic mélange (metaultramafics, metagabbro-amphibolites, and volcaniclastic metasediments), Dokhan volcanics, Hammamat sediments, and granites. An adequate description of these rock units was also given in light of the conducted intense fieldwork and petrographic investigations.

New Magnetotelluric Data Reveal Deep Fault Boundaries and Contrasting Late Cenozoic Fault Kinematics Between the Qilian Shan Thrust Wedge and Beishan‐Alxa Block, Western China

AbstractThe structural connectivity and kinematic relationship between the Altyn Tagh sinistral strike‐slip fault (ATF) and Qilian Shan fold‐and‐thrust belt along the north Tibetan margin east of 96°E is an important question for tectonicists interested in the evolving active deformation field of Central Asia and associated earthquake hazards of China's Hexi Corridor region. New results from a detailed 130‐km‐long N‐S magnetotelluric (MT) survey from the Qilian Shan to Beishan elucidates the locations and down‐dip orientations of major faults. Importantly, the results indicate that the Heishan‐Jinta’Nanshan fault system roots steeply into the lower crust, is unconnected to the Qilian Shan thrust wedge, and has reactivated the margin of the North China Craton and an older, regional ductile shear belt. The structurally linked ATF‐Heishan‐Jinta’Nanshan system defines a fundamental kinematic boundary in central Asia between the NE directed Qilian Shan thrust belt to the south and the eastwardly extruding Beishan‐Alxa Block to the north.

Fault Striae Analysis and Paleostress Reconstruction of the Northern Tectonic Province (Egyptian Nubian Shield): Insights into the Brittle Deformation History of the Northern East African Orogen

The Egyptian Nubian Shield (ENS), the northwestern continuation of the East African Orogen (EAO), comprises a variety of three lithologically and structurally different tectonic provinces—southern compressional-, central transpressional/wrench-, and northern extensional- provinces. The extensional tectonic province (ETP) extends from Qena‒Safaga shear belt up to the northern tip of the ENS. Several lines of evidence indicate extensional regime in the ETP, such as mantle delamination-induced post-orogenic magmatism and bimodal Dokhan Volcanics, together with the pervasive E‒W dyke swarms and the E‒W (to ENE‒WSW) oriented extensional fractures. The present work is devoted to carry out the fault striae analysis and paleostress reconstruction of the northern tectonic province (ENS) in attempt to add more contribution to the brittle deformation history of the northern EAO. Field measurements collected from six areas (I‒VI) have been processed using Win-Tensor Software. Analysis of fault-slip data revealed four paleostress tensor stages (groups or regimes) that prevailed in the ENS. The stress states and related tectonic regimes are characterized by the stress regime index R' and the horizontal stress axes as follows: 1st stage: transpression (R' = 1.91), E‒W compression (SHmax = N090°‒270° E); 2nd stage: transtension (R' = 1.16), N‒S compression (SHmax = 174°‒354° E); 3rd stage: transpression (R' = 1.81), NE‒SW compression (SHmax = N053°‒233° E); 4th stage: extension (R' = 0.31), E‒W extension (Shmin = N074°‒254° E). The 1st stage can be related to the oblique convergence between E and W Gondwanalands. The 2nd stage was probably concurrent with the N- to NNW-ward migration of the Central Eastern Desert syn-collisional delamination (triggering orogen-parallel extensional collapse) to the North Eastern Desert post-collisional delamination. The 3rd stage was controlled by the generally N‒S shortening which affected the northern and central ENS, post-dating the formation of volcanosedimentary Hammamat Basins. The 4th stage is akin to retreat of the Cadomian arc and the Red Sea rifting.

Petrochronology of low-Al metapelites from Southernmost Brasília Orogen basement: Insights into the role of water-fluxed melting at low T and implications for U[sbnd]Pb zircon geochronology

The Southernmost Brasília Orogen surrounds the southern margins of the São Francisco Craton. It exposes a structural window with a WNW-ESE direction formed by the Archean-Paleoproterozoic basement reworked by the Campo do Meio Shear Belt. Using metamorphic modeling, geothermobarometry, and UPb dating of zircon and monazite, this study established the pressure-temperature-time (P-T-t) evolution of the Colônia metapelite, one of the main units of the Campo do Meio Shear Belt. This revealed a clockwise path with metamorphic peak conditions at 706 ± 16 °C and 9.7 ± 0.7 kbar on a staurolite-kyanite-muscovite-garnet-biotite schist, with cooling at ∼600 °C and ∼ 6 kbar. Forward metamorphic modeling based on the whole-rock composition of this sample supports partial melting in the staurolite stability field, facilitated by water influx. Water-fluxed anatexis promoted dissolution of detrital zircon grains. These processes, occurring during prograde metamorphism, are influenced by temperature, crystal size-distribution, bulk-rock composition, and the permanence of the rock at the thermal peak. Analysis of the zircon overgrowth zones, which were linked to peak metamorphic conditions, produced an age of 605 ± 7 Ma. The monazite age of 580 ± 5 Ma was associated with later syntectonic melt crystallization. The clockwise P-T-t path of the Colônia metapelite is similar to the evolution of Neoproterozoic units from the Southernmost Brasília Orogen. However, the degree of dissolution in detrital zircon grains restricts accurate evaluation of the possible stratigraphic correlations proposed in the literature.

Analysis of the characteristics of the insulation shear belt and the cause of its formation during the failure of the degenerator

This paper studies the characteristics of the insulation shear belt produced by the fracture of the vents of the gunhead desceptor and the reasons for its formation when the shell is fired. The results show that: During the explosion, the rupture of the degenerator belongs to the ligament fracture, and the insulation shear belt produced at the time of the break plays the role of “prefabricated crack”. The smaller the microstructure and grain of alloy steel, the easier it is to promote the production of insulation shear belt.

The atypical Gaoligong orocline: Its geodynamic origin and evolution

Various orocline systems around the India–Eurasia collision zone have long been recognized and studied. Different portions of the India–Eurasia boundaries represent various scales and models of orocline-forming processes, such as the Baluchistan orocline formed by multiple deformation events and the Himalayan orocline formed by a mixture of complex structural mechanisms. The curvature from the eastern Himalayan syntaxis through east Burma to west Yunnan showed a unique convex curvature toward the mantle wedge. This is different from the concave Baluchistan orocline and the Himalayan orocline. The unique geometry of the Gaoligong orocline shows an N-S trend for the northern section and a NE-SW trend for the southern section. This curvature also marks the boundary between the Tengchong and Baoshan blocks along the Santaishan suture in western Yunnan, China. Our structural reconstruction identified five deformation events: 1) D1 is km-scale upright folding, which only affected the Neoproterozoic meta-sedimentary unit, 2) D2 recumbent folding, which only developed in the southern section of the Gaoligong orocline, 3) D3 large-scale gently westward-inclined thrust folding, 4) D4 right-lateral shear belt, and 5) the D5 normal faults. Since the D3 structure is the earliest event that shows penetrative foliation development along the orocline, we consider D1 and D2 as pre-orocline-forming events. The geometry of the Gaoligong orocline is controlled by the distribution of the Ordovician basement between the Tengchong and Baoshan blocks. Both north and south sections experienced the same structural evolution since D3 (a fault-propagation fold system occurred between 40 Ma and 28 Ma), D4 (steep right-lateral shear belt occurred between 28 Ma and 15 Ma), and D5 (normal faults after 15 Ma). The curvature first developed as a shovel-like top-to-the-NE thrust plane (S3) that formed under amphibolite-facies conditions between 40 Ma and 28 Ma. The following deformation events (D4 and D5) show orocline parallel foliation development under lower metamorphic conditions, indicating that the curvature of the Gaoligong orocline is not generated by additional rotation along multiple deformation events. However, due to the lack of orocline parallel foliation development for S3, and the lack of a proper position of the indenter, the Gaoligong orocline cannot be classified as a primary orocline nor a rotational orocline. The curved geometry is an interference pattern of topography relief to the shovel-like thrust plane that developed during D3. Our new reconstructed structural evolution concludes that the Gaoligong orocline is an “atypical” orocline.

Seismic behavior of the assembled walls using uniform precast hollow-core concrete panels restrained by cast-in-place boundary elements in single-story buildings

To achieve efficient construction of single-story buildings and increase economic efficiency while ensuring safety, low-cost, easy-to-assemble, and good seismic performance assembled walls using uniform precast hollow-core concrete panels restrained by cast-in-place boundary elements were designed. Through the low-cyclic loading test of three specimens, the safety and reliability of the connection between the components were verified, the good seismic performance of the structure was proved, and the influence of the number (2, 3, 4) of panels contained in the specimens, that is the shear span ratio (SSR) of the specimens, on their seismic performance was investigated. The study found that all specimens finally show shear-slip damage, and with the decrease of SSR, the ultimate shear-bearing capacity of the specimen increases, the deformation capacity decreases, and the energy dissipation capacity increases. Compared with the specimen of 2 panels, the ultimate shear bearing capacity of 3 panels and 4 panels is increased by 39.2% and 88.9% respectively. The ultimate deformation capacity of 2 panels is similar to that of 3 panels, but that of 4 panels is reduced by 23.3%. In addition, these three specimens are simulated using the finite element analysis software ABAQUS. The stress nephogram of each specimen reflects the presence of vertical shear along the thin wall of the circular hole of the panels under horizontal load, and the vertical shear surface will be linked into the shear belt along the diagonal of the specimen. Combined with experiment and finite element simulation, the calculation method of the ultimate lateral bearing capacity of the structure is established. The ratio of the measured value to the calculated value is greater than 1.0, and the maximum relative error of them is only 6.85%, which proves that the calculation method is safe and reliable. The research results of this paper can provide the necessary basis for the engineering application in single-story buildings.

HT–MP metamorphism in Central Qilian Block, NE Tibet Plateau: Implications on the tectonic evolution of the Qilian Orogen

The metamorphism of the Central Qilian Block in the northeastern Tibetan Plateau records a complete tectonic history of the Qilian Orogen. Here, results of structural measurements, geochronological data, and thermobarometry for metamorphic rocks in the Central Qilian Block were presented, which trace the tectonic evolution of the Qilian Orogen. New U–Pb dating of detrital zircon from one paragneiss shows a main age population between c. 1500 and c. 1250 Ma, with the youngest age of 1085 Ma. This unit was intruded by an orthogneiss which has a U–Pb weighted mean age of 920 ± 18 Ma. Together with c. 1200–1000 Ma ages from inherited zircon cores in amphibolites, these results indicate that the protoliths of the Huangyuan Group were formed during the Mesoproterozoic and Neoproterozoic. Rims of these zircons obtain tightly constrained and concordant ages ranging from c. 459 to c. 427 Ma, with a weighted mean age of c. 450 Ma. Phase equilibrium modelling and conventional thermobarometry jointly indicate high‐temperature/medium‐pressure HT–MP metamorphism along a clockwise pressure–temperature (P–T) path at c. 450 Ma, passing through prograde conditions of 7.8–8.0 kbar and 620–650°C to peak conditions of ~7 kbar and ~780–800°C. Together with documented widespread metamorphism, magmatism, and ductile shear belts, these new results reassert that the Central Qilian Block experienced a three‐stage tectono‐metamorphic evolution during the Early Palaeozoic and the HT–MP metamorphism of Huangyuan Group was developed by a continental collision geodynamic setting with coeval mafic and granitic magmatism.

Deformation time and tectonic significance of the Gudonghe ductile shear belt in the Yanbian area, NE China

Deformation time and tectonic significance of the Gudonghe ductile shear belt in the Yanbian area, NE China

Insights into the Ore Genesis of the Harla Gold Deposit in Eastern Tianshan, NW China: Evidence from Geology, Fluid Inclusions, and H-O-C-S-Pb Isotopes

The Harla gold deposit is located on the eastern segment of the Kanggur-Huangshan ductile shear belt in Eastern Tianshan, on the southern margin of the Central Asian Orogenic Belt. The orebodies show close spatial association with NEE-trending faults and are hosted in volcanic rocks of the Lower Carboniferous Xiaorequanzi Formation. Three mineralization stages were recognized: an early stage characterized by specularite–pyrite–quartz mineralization, an intermediate stage with pyrite–chalcopyrite–gold–quartz genesis, and a late stage defined by sulfide-poor calcite and quartz veins. Three types of fluid inclusions (FIs) were recognized: daughter mineral-bearing triphase FIs (S-type), liquid-dominated biphase FIs (LV-type), and liquid-only monophase FIs (L-type). S- and LV-type FIs entrapped in the early stage show similar homogenization temperatures (Th) at 216–229 °C and 199–222 °C. However, they display contrasting salinities of 32.2–33.4 and 6.7–8.9 wt.% NaCl eqv., respectively. LV-type FIs entrapped in the intermediate stage display Th of 163–191 °C, with salinities of 5.6–7.4 wt.% NaCl eqv. LV-type FIs occur in the late stage display Th of 135–258 °C and salinities of 3.7–5.6 wt.% NaCl eqv. Insights from hydrogen, oxygen, and carbon isotope analyses (δ18OH2O = −10.7 to 3.3‰, δDH2O = −88.1 to −61.4‰, δ13CH2O = −8.9 to −6.2‰), combined with FI characteristics, indicate that the ore-forming fluids were derived from a hybrid source of magmatic and meteoric water, with the latter becoming dominant in the later stage. Sulfide and lead isotopic compositions (δ34Spyrite = 0.2 to 2.5‰, 206Pb/204Pb = 17.709–18.273, 207Pb/204Pb = 15.483–15.569, 208Pb/204Pb = 37.533–37.754) suggest that ore-forming materials were mainly derived from wall rocks (Xiaorequanzi Formation rocks and plagiogranite). By integrating geological background work and fluid inclusion analyses, as well as isotope data, we conclude that the Harla gold deposit is an epithermal-type deposit.

Seismic Response Evaluation of High-Steep Slopes Supported by Anti-Slide Piles with Different Initial Damage Based on Shaking Table Test.

In order to study the instability development process of the slope reinforced by anti-slide piles under earthquake conditions, the dynamic response characteristics of the slope are usually taken as the main characteristics, and the model test and numerical simulation are the main research methods. In this paper, a shaking table model test is designed and completed to investigate the influence of anti-slide piles with different initial damage on the failure mode of high and steep slope under earthquake conditions. The changes in velocity, strain and natural frequency during slope vibration are tested in combination with cloud maps when sinusoidal waves of different accelerations with a peak value of 5 Hz are applied. Thus, the differences of slope failure development process and dynamic response characteristics are obtained. The experimental results show that the anti-slide pile with different initial damage has obvious influence on the slope instability process. Under the condition of good anti-slide pile quality, the failure development of the slope behind the pile is limited to soil sliding on top of the slope, slope sliding and overburden sliding; the front slope foot of pile mainly forms shear belt and local sliding. With the decrease in the initial mass of the anti-slide pile, the slope failure develops into topsoil sliding, slope sliding and deep integral sliding; analogously, the failure of the slope in front of the pile develops into a whole slip along the slip belt. The natural frequency cloud map can directly reflect the damage location of the slope, and the frequency change rate is positively correlated with the cumulative shear strain. It shows that the macro-failure characteristics of the model slope change well when the natural frequency is used as the sensitive index to measure the influence of vibration on the model slope. The threshold value of the natural frequency change rate can distinguish different development stages of the slope; 1% is the threshold value of stage II, and 1.5% is the threshold value of stage III.

Identification of a Quaternary rock avalanche deposit (Central Apennines, Italy): Significance for recognition of fossil catastrophic mass-wasting.

Whereas deposits of extremely‐rapid, ‘catastrophic’ mass wastings >105 m3 in volume (for example, the Marocche di Dro rock avalanche in the Southern Alps and the Flims rockslide in the Western Alps) are easily recognized by their sheer mass and blocky surface, the identification of fossil catastrophic mass wastings partly removed by erosion must be based on deposit characteristics. Herein, a ‘fossil’ (pre‐last glacial) rock avalanche, previously interpreted as either a till or debris flow, is described. The deposit, informally called ‘Rubble Breccia’, is located in the intramontane Campo Imperatore halfgraben that is bounded by a master fault with up to ca 900 m topographic throw. Based on documentation from field to thin section, and by comparative analysis with post‐glacial rock avalanches, tills and debris flows, the Rubble Breccia is reinterpreted as a rock avalanche. The Rubble Breccia consists of an extremely‐poorly sorted, disordered mixture of angular clasts from sand to block size. Many clasts show fitted subclast boundaries in crackle, jigsaw and mosaic fabrics, as diagnostic of catastrophic mass wasting deposits. Intercalated layers of angular to well‐rounded clasts of coarse sand to fine pebble size, and deformed into open to recumbent folds, may represent shear belts folded during terminal avalanche propagation. The clast spectrum of the Rubble Breccia – mainly shallow‐water bioclastic limestones, Saccocoma wackestones and other deep‐water limestones and dolostones – is derived from the front range along the northern margin of the basin. Calcite cement found within the Rubble Breccia was dated with the U/Th disequilibrium method to 124.25 ± 2.76 ka bp, providing an ante‐quam age constraint to the rock avalanche event. Because catastrophic mass wasting is a common erosional process, fossil deposits thereof should be more widespread than have been identified to date, although this may be a consequence of misidentification. The criteria outlined here provide a template to identify fossil catastrophic mass wasting deposits of any age.

A Numerical Simulation of the “1907” Kaiyuan Tornado Weather Process in Liaoning, Northeast China

From 17:00 to 18:00 local standard time (LST) on 3 July 2019, a rare strong tornado occurred in Kaiyuan, Liaoning Province, northeast China. NCEP/NCAR 0.25° × 0.25° reanalysis data and WRF4.0 numerical prediction models were used to carry out the numerical simulation. Double nesting was adopted, and the horizontal grid distance was 9 km by 3 km. Based on the observation data of China meteorological observation stations, surface and upper charts, Doppler radar data, Himawari(HMW)-8 satellite images and numerical simulation results, the mesoscale structure and mechanism of the tornado were studied. The results show that: (1) At the northwest edge of the subtropical high, and the northeast cold vortex located in Northeast China, when the transverse trough moves southward, cold air is supplied continuously. Under the joint influence of the surface northeast cyclone, these are the main synoptic features of the tornado; (2) The northeast cold vortex cloud system was located at the junction of Heilongjiang and Jilin Provinces, and a squall line cloud system is formed. The tornado occurred at the tail of the squall line, and the strongest echo reached 65 dBZ. A mesocyclone, a 20 km northwest–southeast convergence belt, V-shaped gap, echo overhang structure and tornado vortex feature (TVS) were detected by the Doppler radar; (3) Before the tornado occurred, dry and cold air intruded from the northwest of the cold vortex, and a water vapor convergence zone appeared south of the squall line. The water vapor saturation zone with 80% relative humidity in northeast China was concentrated at 700 hPa, and the 20% dry column dropped down to 500 hPa between 115 and 124° E from the west. On the 850 hPa physical fields, there was a −20 × 10−5 s−1 convergence zone, and a 16 × 10−5 s−1 divergence belt appeared south and north of the squall line. A negative vorticity belt and a positive vorticity belt appeared south and north of the squall line, respectively. Kaiyuan is located at the smallest vertical shear, which is the junction place of three large vertical shear belts; (4) After 10:00 LST, the westerly wind 20 (10) m·s−1 dropped to 400 (800) hPa between 126 and 127° E. The northerly gale at 300 hPa north of 45° N moved southward. The rising center of the low level at 17:00 LST at approximately 45° N moved southward, and a sinking center appeared above it; (5) Several pairs of positive and negative vorticity columns formed between the lower troposphere and the place where the tornado occurred. There was convective instability at the lower level. CAPE increased, 0–3 km vertical wind shear increased, and LCL decreased remarkably during the afternoon.

Exhumation of the crustal-scale Gaoligong strike-slip shear belt in SE Asia

The lateral extrusion of blocks is a well-known geological process during continent–continent collision and is always expressed by either brittle strike-slip faults or ductile shear zones. However, the vertical motion along such fault systems remains poorly constrained. The Gaoligong shear zone formed the western boundary of the Indochina block during India–Eurasia collision, resulting in the exhumation of deep crustal rocks, including a large volume of syn-tectonic granites. Combined zircon U–Pb dating and 40 Ar/ 39 Ar thermochronology show that both the unfoliated and foliated granitic intrusions were emplaced during the Early Cretaceous (125–112 Ma), post-magmatic melting occurred from the Early Oligocene ( c. 35 Ma) and subsequent cooling took place during the Mid-Miocene ( c. 13 Ma). The average emplacement depth of Early Cretaceous samples showed that at least 15 km of the hanging wall of the Gaoligong shear zone must have been removed by vertical motion during shearing. Syn-shearing exhumation underlines the role of the initiation of lateral motion of the shear zone by magma-assisted rheological weakening and exhumation at high ambient temperatures within the shear zone. A new model links magmatic channel flow underneath the Tibetan Plateau with magma intrusions and the high geothermal gradients along the shear belts such as the Gaoligong shear zone. Supplementary material: Methods, electron probe microanalysis test results and zircon laser ablation inductively coupled plasma mass spectrometry U–Pb results are available at https://doi.org/10.6084/m9.figshare.c.5598365

Composite Strike-Slip Deformation Belts and Their Control on Oil and Gas Reservoirs: A Case Study of the Northern Part of the Shunbei 5 Strike-Slip Deformation Belt in Tarim Basin, Northwestern China

Strike-slip deformation belts are interesting structures in the crust and are of significance in petroleum exploration. The Shunbei 5 fault belt (SB5), a long strike-slip deformation belt in the Tarim Basin, played an important role in the formation of a recently discovered major oilfield known as the Shunbei oilfield. In this study, models of plan view and vertical profile were established to interpret SB5 with multi-cycled tectonic activities. To this end, its structural framework, tectonic evolution, and associated plate tectonics were investigated using 2D and 3D seismic data. SB5 was formed as a dextral simple shear belt at the end of the Middle Ordovician. In the plan view, R-shears and P-shears with local transpressional and transtensional structures were observed. Along the vertical profiles, various structural styles occurred at various depths and strata in response to various stratigraphy mechanisms. Although these structures show clear boundaries between them, they correspond to the same formation time, indicating that they underwent deformation simultaneously. The second activity of SB5 occurred at the end of the late Ordovician, during which it was a dextral transtensional strike-slip deformation belt consisting of left-stepping en echelon R-shears. The R-shears were transtensional during the progressive deformation. Subsequently, SB5 underwent several strike slips of weak strength. Notably, SB5 cut through a deep Middle Cambrian gypsum salt layer and connected the deep Lower Cambrian source rock with deep Lower and Middle Ordovician carbonates to form the oil and gas reservoirs. The established models are of reference value in the interpretation of other subsurface strike-slip deformation belts.

Non‐material finite element rod model for the lateral run‐off in a two‐pulley belt drive

AbstractA novel mixed Eulerian‐Lagrangian rod finite element formulation based on the theory of unshearable, extensible rods is presented. Geometric imperfections (natural curvature) are introduced to investigate and predict the phenomenon of lateral run‐off in the benchmark problem of a two‐pulley belt drive. The concise description of normal and tangential contact between pulleys and belt contributes to the efficient computation of transient solutions. In resemblance of belt shear theory, it relies on the notion of a thin intermediate layer that connects the belt and the pulleys elastically. Various practically relevant transient solutions are validated against corresponding shell finite element computations available in the literature.

Ediacaran post-collisional K-rich granitic magmatism within the Major Gercino Shear Zone, Southern Brazil: An example of prolonged magmatism and differentiation under active transcurrent tectonism

The post-collisional period of the Brasiliano/Pan-African Orogenic Cycle along the Dom Feliciano Belt in southern Brazil (650–580 Ma) is marked by intense magmatism, comprised of substantial volumes of coeval granitic and mafic rocks emplaced along transcurrent shear zones that constitute the Southern Brazilian Shear Belt. Some representatives of this magmatism are the Estaleiro Granodiorite (EG) and associated fine-grained granites that compose the Estaleiro Granitic Complex (EGC), together with minor volumes of mafic material as enclaves and tabular bodies. The EGC is a syntectonic rock association that registers the main transcurrent phase of the Major Gercino Shear Zone (MGSZ). The Estaleiro Granodiorite and fine-grained granites share the same MGSZ dextral transcurrent kinematics and evolution from magmatic to solid-state conditions under deformational temperatures consistent with upper-greenschist to mid-amphibolite facies. New zircon UPb LA-MC-ICP-MS crystallisation ages, 612 ± 3.5 and 611 ± 5.3 Ma, for the Estaleiro Granodiorite undeformed and deformed portions constrain the timing of transcurrent tectonic activity of the Major Gercino Shear Zone. Geochemical features as SiO2 contents above 63%, the alkaline and potassic predominant character [K2O > (Na2O – 2)], enrichment in Na2O + K2O (6.9–9.2 wt%), high K2O/Na2O ratios (0.8–1.4), high Al2O3 (14.1–16.4 wt%), low TiO2 (0.1–0.8 wt%) and high Fe2O3/FeO (~1.11), Ba (488–1701 ppm),Sr (260–1006 ppm), strong enrichment in LILE relative to HFSE, REE with moderate fractionation [(La/Yb)N = 10.6–51.1] and absence of strong Eu negative anomalies [(Eu/Eu*)N = 0.54–1.23] of the Estaleiro Granitic Complex granitoids are compatible with rocks of shoshonitic affinity. New 87Sr/86Sri ratios and ƐNdt values obtained for fine-grained granites point to increasing crustal contamination along the differentiation of the complex. Whole-rock chemical and SrNd isotope data point to mantle sources modified by previous, subduction-related metasomatism. The primary magmas have evolved through AFC processes, more prominent in the most differentiated and/or deformed rocks. We suggest that the transcurrent tectonism of the Major Gercino Shear Zone played an important role in the activation of mantle sources capable of originating shoshonitic magmas and facilitated their interaction with crustal melts to generate the Estaleiro Granitic Complex granitoids.

Shear-Related Gold Ores in the Wadi Hodein Shear Belt, South Eastern Desert of Egypt: Analysis of Remote Sensing, Field and Structural Data

Space-borne multispectral and radar data were used to comprehensively map geological contacts, lithologies and structural elements controlling gold-bearing quartz veins in the Wadi Hodein area in Egypt. In this study, enhancement algorithms, band combinations, band math (BM), Principal Component Analysis (PCA), decorrelation stretch and mineralogical indices were applied to Landsat-8 OLI, ASTER and ALOS PALSAR following a pre-designed flow chart. Together with the field observations, the results of the image processing techniques were exported to the GIS environment and subsequently fused to generate a potentiality map. The Wadi Hodein shear belt is a ductile shear corridor developed in response to non-coaxial convergence and northward escape tectonics that accompanied the final stages of terrane accretion and cratonization (~680–600 Ma) in the northern part of the Arabian–Nubian Shield. The evolution of this shear belt encompassed a protracted ~E–W shortening and recurrent sinistral transpression as manifested by east-dipping thrusts and high-angle reverse shear zones. Gold-mineralized shear zones cut heterogeneously deformed ophiolites and metavolcaniclastic rocks and attenuate in and around granodioritic intrusions. The gold mineralization event was evidently epigenetic in the metamorphic rocks and was likely attributed to rejuvenated tectonism and circulation of hot fluids during transpressional deformation. The superposition of the NW–SE folds by NNW-trending, kilometer scale tight and reclined folds shaped the overall framework of the Wadi Hodein belt. Shallow NNW- or SSE-plunging mineral and stretching lineations on steeply dipping shear planes depict a considerable simple shear component. The results of image processing complying with field observations and structural analysis suggest that the coincidence of shear zones, hydrothermal alteration and crosscutting dikes in the study area could be considered as a model criterion in exploration for new gold targets.

Remote sensing and structural studies of the Central Asir Shear Zone, Western Arabian Shield: Implications for the late Neoproterozoic E-W Gondwana assembly

The Central Asir Shear Zone (CASZ) is a N- to NNE-oriented inhomogeneous strain zone parallel to the Nabitah shear belt in southern Saudi Arabia. It is ~200 km long and 20 km wide, and traverses the Asir terrane. The deformed terrains in the vicinity of the CASZ have experienced a prolonged history involving three successive phases of deformation: arc-collision, dextral transpression and sinistral strike-slip faulting. Remote-sensing data analysis and field investigation provide insights into the geological and structural features along the CASZ. Image transformation and enhancement reveal faults and folds, and discriminate between granitoids, metavolcanics, gabbros and younger (Ablah Group) sediments. The obtained evidence points to polyphase deformation of the area, characterized by narrow zones of high strain, folding and shearing enclosing slices of less deformed rocks. Lineament analysis shows predominantly NNE, NNW, N and NE trends of folds and shear zones, and NW, NE and E fracture trends. The CASZ has a >100 m.y. long deformation history, including a change from dextral to sinistral shearing. Both shearing senses are found on the older N-S and younger NW-SE fault systems. N-S oriented shearing was accompanied by intrusion of granitoids and localized hydrothermal alteration along N to NNE trending shear zones. Strain analysis shows low strain in the Ablah basin sediments, consistent with Ablah deposition after the tectonic climax in the region.