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The Triassic was a crucial period in the tectonic evolution of the South China Block. Research on tectonic deformation during this period provides information on intracontinental orogenic mechanisms in South China. In this study, alongside thermochronological analyses, we examine the macroscopic and microscopic structural features of the Rongxian ductile shear zone, located south of the Darongshan granite in the southeastern part of Guangxi Province, on the southern margin of South China. Sinistral shear is indicated by the characteristics of rotated σ‐type feldspar porphyroclasts, stretching lineations defined by elongated quartz grains and the orientations of quartz c‐axes. LA‐ICP‐MS U‐Pb dating of zircons from two samples of granitic mylonite and one of granite yielded ages of ca. 256 Ma. Furthermore, two samples of granitic mylonite yield muscovite 40Ar/39Ar plateau ages of 249–246 Ma. These results indicate that the Rongxian ductile shear zone resulted from Early Triassic deformation of the late Permian Darongshan granite. This deformation was likely related to the closure of the eastern Paleo‐Tethys Ocean and the subsequent collision of the South China and Indochina blocks, during the early stage of the Indosinian orogeny. [ABSTRACT FROM AUTHOR]

The ductile shear deformation of Precambrian basement rocks in Wuyishan provides a crucial perspective on intraplate orogeny in the South China Block (SCB). This study focuses on the Longquan‐Badu ductile shear zone in southeastern Zhejiang, employing field observations, thin section analysis, quartz electron backscatter diffraction (EBSD), zircon U–Pb dating and 40Ar/39Ar geochronology. Two distinct phases of deformation, referred to as D1 and D2, have been identified. D1 is primarily characterized by a WNW–ESE striking foliation within a NE‐plunging lineation, indicating top‐to‐SSW shearing. The paragneiss within the Badu complex that experienced D1 deformation has been dated to 247–239 Ma through zircon U–Pb analysis, corresponding to the prevalent high‐pressure metamorphic age in the region. This correlation suggests that the D1 deformation event coincided with crustal thickening during the Early Triassic. D2 deformation exhibits folds, foliation, S‐C fabrics and mylonitic microstructures and is mainly characterized by striking NNE–SSW with steeply dip, demonstrating a dominant dextral strike–slip component. Quartz c‐axis orientations in mylonitic rocks indicate deformation temperatures between 350°C and 550°C with asymmetric girdle patterns suggesting simultaneous basal and prism slip. The plateau ages of muscovite from mylonitic rocks obtained through 40Ar/39Ar dating are approximately ~228 Ma implying that the D2 deformation occurred under retrograde amphibolite to greenschist facies metamorphic conditions during Middle Triassic. Collectively these data along with regional geological evidence signify two distinct intracontinental orogenic processes occurring in eastern SCB. Considering Early Mesozoic tectonothermal events in Cathaysia Block, it can be inferred that intraplate orogeny in Wuyishan resulted from plate‐margin collisions between SCB and peripheral plates following scissors closure of Palaeo‐Tethys from east to west. [ABSTRACT FROM AUTHOR]

The evolution of metamorphic core complexes is closely related to gold formation. Due to the thick cover and orebodies’ lying depth, exploration regularities, and metallogenic prediction have faced challenges. Therefore, new data were obtained through controlled-source audio magnetotelluric (MT) and broadband MT methods to predict the ore-bearing properties at depth and decipher the spatial coupling relationship, respectively. The results of broadband MT surveys allow us to identify the thick cover (apparent resistivity of 3,000 Ω m), the strongly deformed metamorphic rock (apparent resistivity of 18,000 Ω m), and two low-angle detachment faults (apparent resistivity from 5,000 to 8,000 Ω m). The fault-dip value on the left side is roughly 30°, while on the other side, the values significantly change from 30° to 75°, although they are in the same structure. Moreover, the controllable source audio MT method provides more detailed examinations of the right side fault. The proved ore-bearing gold orebodies were all located in the transition zone where the inclination angle changes from steep to gentle or gentle to steep. The discovery of this mineralization pattern allows us to evaluate the mining prospecting potential and predict the deep-seated metallogenic location. Based on the geotectonic environment and the geophysical profiles, we conclude that the coeval exhumation of the metamorphic core complex with non-symmetrical northwest-southeast shear senses may have resulted from a decratonization event during the retreat of the Paleo-Pacific Plate.

[Display omitted] • Exhumation structures of the TNCO exhibit the presence of many sheath fold. • The TNCO has a prolonged collisional history ranging from 1.97 Ga to 1.84 Ga. • Collisional orogenesis can occur over durations exceeding 100 Mya. Significant understanding of the Trans-North China Orogen (TNCO) has been achieved through previous studies. However, the lack of structural analyses, especially for its southern part, has restricted our understanding of the structural evolution of the TNCO. In this contribution, we present new structural and geochronological data from the Taihua Complex of the Xiaoqinling region to reconstruct the collision-induced deformation history and provide constraints on the structural evolution of the TNCO. Paleoproterozoic collision-induced structures in the Xiaoqinling region are characterized by the development of penetrative, ductile deformation fabrics, localized ductile shear zones, and syn -shearing folds, notably sheath folds. The evolution of the folds and syn -tectonic migmatites records the occurrence of non-coaxial progressive shear deformation within ductile shear zones. Vorticity analysis confirms simple-shear-dominated general-shear deformation within the shear zones, with an increase in a pure shear component during the later stages. The integrated results, encompassing the geometry, kinematics, finite strain, and geochronology of these shear zones and folds, reveal the presence of the regional-scale, collision-induced sheath folds that were associated with low-angle thrust shear zones with WNW-directed kinematics. Deformation temperatures of 500–650 °C indicate that the ductile shear zones and simultaneous sheath folds formed during the exhumation process of the TNCO. New zircon U–Pb ages constrain the timing of the metamorphism and ductile deformation to between 1951 and 1840 Ma. Integration of this and previous dating results reveals a history of prolonged collision for the TNCO, lasting from as early as ∼ 1.97 Ga and continuing until as late as ∼ 1.84 Ga, with the earlier period of 1.97–1.88 Ga representing the continental subduction stage and the later period of 1.88–1.84 Ga corresponding to the subsequent exhumation stage. The protracted orogenic evolution for the TNCO supports the notion that large-scale collisional orogenesis can occur over such long durations (over 100 Mya). These structural and geochronological data support the orogenic model of SE-directed subduction polarity. [ABSTRACT FROM AUTHOR]

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The newly discovered Yongshan gold deposit in Leping City, Jiangxi Province is located in the southeastern Shanmen-Yongshan Au polymetallic metallogenic prospect area, belonging to the northern part of eastern Qinzhou-Hangzhou Metallogenic Belt. According to field geological survey and indoor comprehensive research, the ore-controlling characteristics of Yongshan gold deposit in Leping City were studied with the discussion of the relationship between the NE-NEE-trending ductile shear zone across the mine from west to east and gold mineralization. This paper summarized ore-forming factors and analyzed its ore-searching prospects based on the characteristics of soil geochemical anomalies. The results show that the Yongshan gold deposit occurs in the Neoproterozoic shallow metamorphic rock strata with obvious ductile deformation, the NE-trending ductile shear zone is the main ore-controlling and ore-guiding structure, and the upper member of Fengshuling Formation is the ore-bearing wall rock. The Yongshan gold deposit is determined as ductile shear tectonic-altered rock type and its NE-trending ductile shear zone has a good ore-searching prospects. The discovery of this gold occurrence provides a new thought to the gold searching in the northern part of eastern Qinhang Metallogenic Belt, expanding the prospecting space in this area. [ABSTRACT FROM AUTHOR]

Copyright of World Nuclear Geoscience is the property of World Nuclear Geoscience Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Shanwei Special Cooperation Zone (SSCZ) in Shenzhen is the main distribution area of the Lianhuashan Fault Zone. Two large ductile shear zones pass through the SSCZ. The ductile shear zone of the SSCZ is henceforth referred to as "the zone". Severe plastic progressive deformation, stretching, and compression occurred in the late Jurassic-Neogene period in the zone, because of which the structure and properties of the rock mass underwent significant changes. There are three levels of structural planes in the zone: brittle faults, schistosity planes, and joints in the rock mass. The ductile shearing action changes the rock mass structure, leading to poor integrity. According to existing data, the compressive strength of the rock in the zone is equivalent to 0.31-0.86 of the original rock, indicating that the strength of the rock is obviously attenuated by ductile shear action. Using ground investigation and remote sensing, we found 1,614 topsoil slips in the zone. The density of topsoil slips in the hillside area (16.2 topsoil slips per km2) was much higher than that outside the zone (1.3 topsoil slips per km2), indicating that the slopes in the zone are more prone to shallow damage. To study the geological risk zonation of geological hazards in the SSCZ, it is necessary to determine the characteristics and distribution rules of topsoil slips in the zone, analyze its causal mechanism, and predict its development trend.ⅰ) Ground surveys and remote sensing showed that monocase topsoil slip is small in the zone and sliding mainly occurs along the bedrock surface. Sliding masses are mainly solid and completely weathered rock. ⅱ) The frequency of geological disasters under the action of certain factors in the study area is divided by the frequency of geological disasters in the area. The natural logarithm of the divisor is taken as the information value to evaluate the relationship between geological disasters and various factors. The results show that the density of topsoil slips is positively correlated with the degree of ductile deformation (strong→medium→weak), distance from brittle fracture (near→far), and topographic slope (high→low). Moreover, the distribution density is strongly related to the geomorphic unit, slope direction, original rock type, and slope type. ⅲ) The above analyses are combined with regional, geological, exploration, meteorological, and other data. Results from this combination show that topsoil slips in the zone are produced under weak background conditions formed by the influence of multi-stage tectonic action dominated by ductile shear forces, the slow rise of the hillside area, and the induction of typhoons and rainstorms. Their development and changes are characterized by migration, self-healing, and expansion. ⅳ) Most of the current topsoil slips occurred during Super Typhoon Mujigae in 2015, after which the region experienced several rainfall events with intensities higher than those of Typhoon Mujigae, yet the number of topsoil slips did not increase significantly. This shows that after a general shallow sliding event, the sensitivity of the slope to shallow damage decreased, and generation took a long time before entering the next outbreak period.

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The Shanwei Special Cooperation Zone (SSCZ) in Shenzhen is the main distribution area of the Lianhuashan Fault Zone. Two large ductile shear zones pass through the SSCZ. The ductile shear zone of the SSCZ is henceforth referred to as "the zone". Severe plastic progressive deformation, stretching, and compression occurred in the late Jurassic-Neogene period in the zone, because of which the structure and properties of the rock mass underwent significant changes. There are three levels of structural planes in the zone: brittle faults, schistosity planes, and joints in the rock mass. The ductile shearing action changes the rock mass structure, leading to poor integrity. According to existing data, the compressive strength of the rock in the zone is equivalent to 0.31-0.86 of the original rock, indicating that the strength of the rock is obviously attenuated by ductile shear action. Using ground investigation and remote sensing, we found 1,614 topsoil slips in the zone. The density of topsoil slips in the hillside area (16.2 topsoil slips per km2) was much higher than that outside the zone (1.3 topsoil slips per km2), indicating that the slopes in the zone are more prone to shallow damage. To study the geological risk zonation of geological hazards in the SSCZ, it is necessary to determine the characteristics and distribution rules of topsoil slips in the zone, analyze its causal mechanism, and predict its development trend.ⅰ) Ground surveys and remote sensing showed that monocase topsoil slip is small in the zone and sliding mainly occurs along the bedrock surface. Sliding masses are mainly solid and completely weathered rock. ⅱ) The frequency of geological disasters under the action of certain factors in the study area is divided by the frequency of geological disasters in the area. The natural logarithm of the divisor is taken as the information value to evaluate the relationship between geological disasters and various factors. The results show that the density of topsoil slips is positively correlated with the degree of ductile deformation (strong→medium→weak), distance from brittle fracture (near→far), and topographic slope (high→low). Moreover, the distribution density is strongly related to the geomorphic unit, slope direction, original rock type, and slope type. ⅲ) The above analyses are combined with regional, geological, exploration, meteorological, and other data. Results from this combination show that topsoil slips in the zone are produced under weak background conditions formed by the influence of multi-stage tectonic action dominated by ductile shear forces, the slow rise of the hillside area, and the induction of typhoons and rainstorms. Their development and changes are characterized by migration, selfhealing, and expansion. ⅳ) Most of the current topsoil slips occurred during Super Typhoon Mujigae in 2015, after which the region experienced several rainfall events with intensities higher than those of Typhoon Mujigae, yet the number of topsoil slips did not increase significantly. This shows that after a general shallow sliding event, the sensitivity of the slope to shallow damage decreased, and generation took a long time before entering the next outbreak period. [ABSTRACT FROM AUTHOR]

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The Hadamengou deposit is the largest gold deposit in Inner Mongolia. However, given that the sources of ore-forming alkaline magmatic hydrothermal solutions and ore-controlling structures are still controversial, the theories behind the genesis of the deposit have been controversial. In this study, four controlled-source audio magnetotellurics (CSAMT) and spectral induced polarization (SIP) profiles in the mining area were used to obtain the underground resistivity model and the pseudo section map of the apparent frequency dispersivity based on fine inversion. In the resistivity model, there are two high-resistivity blocks with resistivity greater than 3000 Ω m and three low-resistivity channels with resistivity less than 50 Ω m. Combined with the regional geological and drilling data, it is inferred that the high-resistance bodies, R4 and R5, may be alkaline magmatic intrusions related to multiple stages of magmatic hydrothermal activities, ranging from the Precambrian to Yanshanian periods. The highly conductive channels, C3, C5, and C4, may represent the Baotou-Hohhot fault, secondary faults, and ductile shear zone, respectively, which were formed in the Precambrian era and underwent multiple activations during the Hercynian to Yanshanian period. According to the spatial relationship, it is inferred that the ductile shear zone is an important ore-controlling and ore-hosting structure. However, the Baotou–Hohhot fault may be a pre-metallogenic fault rather than an ore-controlling fault. By comparing the resistivity model with the pseudo section of the apparent frequency dispersivity, it was found that all the known gold veins are located in the superimposed area of low resistivity and high-frequency dispersivity. It is speculated that the ductile shear zone outside the alkaline magmatic rock with the superimposed characteristics of low resistivity and high-frequency dispersivity is the favorable area for mineralization. [ABSTRACT FROM AUTHOR]

The occurrence of plate tectonic processes on Earth during the Paleoproterozoic is supported by ca. 2.2–1.8 Ga subduction‐collision orogens associated with the assembly of the Columbia‐Nuna supercontinent. Subsequent supercontinent breakup is evidence by global ca. 1.8–1.6 Ga large igneous provinces. The North China craton is notable for containing Paleoproterozoic orogens along its margins, herein named the Northern Margin orogen, yet the nature and timing of orogenic and extensional processes of these orogens and their role in the supercontinent cycle remain unclear. In this contribution, we present new field observations, U‐Pb zircon and baddeleyite geochronology dates, and major/trace‐element and isotope geochemical analyses from the northern margin of the North China craton that detail its Paleoproterozoic tectonic and magmatic history. Specifically, we record the occurrence of ca. 2.2–2.0 Ga magmatic arc rocks, ca. 1.9–1.88 Ga tectonic mélange and mylonitic shear zones, and folded lower Paleoproterozoic strata. These rocks were affected by ca. 1.9–1.8 Ga granulite‐facies metamorphism and ca. 1.87–1.78 Ga post‐collisional, extension‐related magmatism along the cratonal northern margin. We interpret that the generation and emplacement of these rocks, and the coupled metamorphic and magmatic processes, were related to oceanic subduction and subsequent continent‐continent collision during the Paleoproterozoic. The occurrence of ca. 1.77–1.73 Ga mafic dykes and ca. 1.75 Ga mylonitic shear zones along the northern margin of the North China craton may have been related to a regional mantle plume event. Our results are consistent with modern style plate tectonics, including oceanic subduction‐related plate convergence and continent‐continent collision, operating in the Paleoproterozoic. Plain Language Summary: Earth likely went through an early magma ocean stage, which rapidly solidified and evolved though about 4.5 billion years to the modern plate‐tectonic lithosphere. Whether plate‐tectonics operate in early Earth's history, is one of the hotly debated questions in Earth Sciences. The North China craton of central Asia is a natural laboratory for investigating early Earth tectonic processes including subduction‐collision and large‐scale horizontal crustal motions. Paleoproterozoic subduction and continent‐continent collisional between the North China craton and outboard craton were associated with the assembly of the oldest‐known Columbia‐Nuna supercontinent. The configuration of cratons forming the supercontinent remains debated, which is partially due to an inadequate understanding of the Paleoproterozoic rocks that form the margins of the cratons and their tectonic histories. Our observations and analyses indicate the development of Paleoproterozoic Northern Margin orogen, the collisions are not just narrow belts in time and space, but rather broad, long‐lived orogenic cycles that exist well within the intraplate continental interior. Key Points: Northern margin of the North China craton experienced two periods of orogenesis in the Neoarchean and Paleoproterozoic, respectivelyNorthern Margin orogen of the North China craton terminated by at least ca. 1.78 GaCa. 1.77–1.73 Ga mafic dykes and ca. 1.75 Ga mylonitic shear zone are associated with a regional mantle plume event [ABSTRACT FROM AUTHOR]

The Kanggur ductile shear zone (KDSZ), located in the south margin of the Central Asia Orogenic Belt (CAOB), plays a critical role in the tectonic evolution and mineralization in eastern Tianshan. Although different isotopic chronologies have been reported, the termination of the KDSZ deformation remains controversial. Here, we provide new data obtained by U-Pb dating of zircon and apatite from Huangshandong synkinematic granite (HSG) and Huludong deformed granite (HDG) to constrain the termination of the KDSZ deformation. The U-Pb age of apatite from HSG (249.1 ± 1.8 Ma) is identical to that of zircon (256.5 ± 2.1 Ma) within the error range. In contrast, the U-Pb age of apatite from HDG (248.1 ± 4.0 Ma) is significantly younger than that of zircon (347.3 ± 2.5 Ma). The HDG and HDG have the geochemical characteristics of I-type granites petrogenesis, including high SiO2 (up to 75.47%), high alkaline (K2O + Na2O = 6.39%–8.05%), low FeOT/MgO (2.4–3.4), and peraluminous (A/CNK = 1.01–1.08). Combined with previous Sr-Nd isotope compositions, the positive zircon εHf(t) values and TDM2 ages indicate that the ca. 347 Ma HDG originated from the re-melting of juvenile crust crustal-derived magma in a volcanic arc environment during the northward subduction of the Kanggur oceanic basin, and the ca. 257 Ma HSG originated from the partial melting of thickened juvenile crust in a post-collisional environment. Although trace elements of zircon show typical magmatic characteristics, apatite does not. With the presence of distinct major and trace elements in apatite, the apatite from HSG is characterized by high Mn (>2500 ppm), slight enrichment in the middle rare earth elements (MREEs), and obvious negative Eu anomalies (δEu = 0.09–0.21), indicating that it is related to magmatic apatite. In contrast, the apatite from HDG, with low Mn (<860 ppm), depleted light rare earth elements (LREEs), and variable Eu anomalies (δEu = 0.30–1.34), demonstrated fluid metasomatism with metamorphic overprinting. Combined with the regional geology and published geochronology data, the HSG is interpreted to be derived from the magma experiencing cooling crystallization in the plastic state from 256.5 to 249.1 Ma, while the HDG is considered to have experienced metamorphism and deformation between 347.3 and 248.1 Ma. Owing to the relatively low closure temperature of the U-Pb isotopic system, the apatite U-Pb ages are interpreted as Early Triassic tectono-magmatism events, corresponding to the end of deformation of the KDSZ. This is inferred to be related to the continuous evolution of the Paleo-Asian Ocean in the Late Permian to Early Triassic. [ABSTRACT FROM AUTHOR]

Abstract The occurrence of plate tectonic processes on Earth during the Paleoproterozoic is supported by ca. 2.2–1.8 Ga subduction‐collision orogens associated with the assembly of the Columbia‐Nuna supercontinent. Subsequent supercontinent breakup is evidence by global ca. 1.8–1.6 Ga large igneous provinces. The North China craton is notable for containing Paleoproterozoic orogens along its margins, herein named the Northern Margin orogen, yet the nature and timing of orogenic and extensional processes of these orogens and their role in the supercontinent cycle remain unclear. In this contribution, we present new field observations, U‐Pb zircon and baddeleyite geochronology dates, and major/trace‐element and isotope geochemical analyses from the northern margin of the North China craton that detail its Paleoproterozoic tectonic and magmatic history. Specifically, we record the occurrence of ca. 2.2–2.0 Ga magmatic arc rocks, ca. 1.9–1.88 Ga tectonic mélange and mylonitic shear zones, and folded lower Paleoproterozoic strata. These rocks were affected by ca. 1.9–1.8 Ga granulite‐facies metamorphism and ca. 1.87–1.78 Ga post‐collisional, extension‐related magmatism along the cratonal northern margin. We interpret that the generation and emplacement of these rocks, and the coupled metamorphic and magmatic processes, were related to oceanic subduction and subsequent continent‐continent collision during the Paleoproterozoic. The occurrence of ca. 1.77–1.73 Ga mafic dykes and ca. 1.75 Ga mylonitic shear zones along the northern margin of the North China craton may have been related to a regional mantle plume event. Our results are consistent with modern style plate tectonics, including oceanic subduction‐related plate convergence and continent‐continent collision, operating in the Paleoproterozoic.

In the present study, we unveil the real significance of mylonitic reworking of the polymetamorphic crystalline basement in the Serre Massif of Calabria (Southern Italy). We use a multidisciplinary approach to comprehend the structural, microstructural and petrologic changes that occurred along a, so far, not much considered shear zone affecting the Variscan lower crustal rocks. It was never before studied in detail, although some late Cretaceous ages were reported for these mylonites, suggesting that this shear zone is of prime importance. Our observations reveal now that the formation of the new structural fabric within the shear zone was accompanied by changes in mineral assemblages, in a dominant compressive tectonic regime. During this tectono-metamorphic event, high-P mylonitic mineral assemblages were stabilized, consisting of chloritoid, kyanite, staurolite, garnet and paragonite, whereas plagioclase became unstable. Average peak P–T conditions of 1.26–1.1 GPa and 572–626 °C were obtained using THERMOCALC software. These data question (i) that the Serre Massif represents an undisturbed continuous section of the Variscan crust, as generally suggested in the literature, and (ii) highlight the role of (eo-)Alpine high-P tectonics in the Serre Massif, recorded within mylonite zones, where the Variscan basement was completely rejuvenated. [ABSTRACT FROM AUTHOR]

The Yeba ductile shear zone is located on the southern margin of the middle Gangdese magmatic belt and southeast of Lhasa, China. In this paper, we systematically investigate the structural deformation history in the Yeba Group and provide the kinematics, strain pattern, mean vorticity number and temperature environment of the Yeba ductile shear zone. Three tectonic events are identified in the Yeba Group of the study area. The Yeba shear zone represents the late stage of the northward subduction of the Neo-Tethys Ocean (D1 stage, 94–85 Ma). Since the collision of the Indian and Eurasian plates, principal compressive stress (σ1) in the north–south direction was generated in the Yeba Group and formed composite folds (D2 stage, ~ 50 Ma). The D3-stage structural deformation event of the Yeba Group in the study area is represented by the Woka ductile shear zone (22.38–14.6 Ma). Electron backscattering diffraction and chlorite geothermometry demonstrate that upper greenschist facies (213–295 °C) and lower greenschist facies (400–550 °C) conditions developed in the Yeba shear zone. Finite strain measurements of the Yeba ductile shear zone indicate that almost all deformed rocks exhibit an oblate ellipsoid consistent with near-flattening strain. Kinematic vorticity analysis of the Yeba shear zone yielded values (Wm) of 0.49–0.78, indicating a bulk general shear deformation regime with a combination of 58% pure shear and 42% simple shear. The kinematic vorticity number (58% pure shear), flattening strain pattern, and presence of opposite indicators in the same mylonitic foliation support the occurrence of a transpressive structure. [ABSTRACT FROM AUTHOR]

Deformation and magnetic fabrics across the Salem and Namakkal Granulite Blocks (southern India) have been integrated to understand the poly-phase (D1–D3 ductile and D4 brittle) tectonic reworking in the study area. D1 gneissic fabric (S1) is the dominant regional-scale mesoscopic fabric in the charnockite host. Localized ductile shearing at low temperature and development of shear bands, mylonite and phyllonite zone with respectively transposed-S1, mylonite (SM) and phyllonite (SP) fabric characterize D3 phase. Presence of true shear zone rocks with distinct deformation and magnetic fabrics helps in demarcating a new Belur–Sarkar Nattar Mangalam–Udayapatti shear zone (BNUSZ). Magnetic fabrics are deformation-controlled and result in vorticity variation from simple shear (Wn = 0.85) to general shear (Wn = 0.64) to pure shear (Wn = 0.1) across the BNUSZ. Magnetic fabrics document a progressive transition from early ductile shear zone to late-stage thrust and flip of the σ1 stress axis from WNW–ESE to NNE–SSW. Down-dip magnetic lineation, north-verging WNW–ESE trending asymmetric folding on SP and pole to S1 recognize a forelimb thrust with northward transport. Stress-localization on the forelimb of D3 shear-induced asymmetric fold initiates thrust. Phyllonitization helps in partitioning of D3 strain and concomitant structural complexity in hangingwall, south of the BNUSZ. Research highlights: A new Belur–Sarkar Nattar Mangalam–Udayapatti Shear zone (BNUSZ) is identified in the Salem Granulite Block (SGB). The BNUSZ represents the sole tectonic marker for last D3 ductile shearing in the SGB. Deformation and magnetic fabric development suggest a forelimb thrust origin for the BNUSZ. A fold-first tectonic model best explains the initiation of the BNUSZ thrust. [ABSTRACT FROM AUTHOR]

The Hadamengou deposit is the largest gold deposit in Inner Mongolia. However, given that the sources of ore-forming alkaline magmatic hydrothermal solutions and ore-controlling structures are still controversial, the theories behind the genesis of the deposit have been controversial. In this study, four controlled-source audio magnetotellurics (CSAMT) and spectral induced polarization (SIP) profiles in the mining area were used to obtain the underground resistivity model and the pseudo section map of the apparent frequency dispersivity based on fine inversion. In the resistivity model, there are two high-resistivity blocks with resistivity greater than 3000 Ω m and three low-resistivity channels with resistivity less than 50 Ω m. Combined with the regional geological and drilling data, it is inferred that the high-resistance bodies, R4 and R5, may be alkaline magmatic intrusions related to multiple stages of magmatic hydrothermal activities, ranging from the Precambrian to Yanshanian periods. The highly conductive channels, C3, C5, and C4, may represent the Baotou-Hohhot fault, secondary faults, and ductile shear zone, respectively, which were formed in the Precambrian era and underwent multiple activations during the Hercynian to Yanshanian period. According to the spatial relationship, it is inferred that the ductile shear zone is an important ore-controlling and ore-hosting structure. However, the Baotou–Hohhot fault may be a pre-metallogenic fault rather than an ore-controlling fault. By comparing the resistivity model with the pseudo section of the apparent frequency dispersivity, it was found that all the known gold veins are located in the superimposed area of low resistivity and high-frequency dispersivity. It is speculated that the ductile shear zone outside the alkaline magmatic rock with the superimposed characteristics of low resistivity and high-frequency dispersivity is the favorable area for mineralization.

The Kanggur ductile shear zone (KDSZ), located in the south margin of the Central Asia Orogenic Belt (CAOB), plays a critical role in the tectonic evolution and mineralization in eastern Tianshan. Although different isotopic chronologies have been reported, the termination of the KDSZ deformation remains controversial. Here, we provide new data obtained by U-Pb dating of zircon and apatite from Huangshandong synkinematic granite (HSG) and Huludong deformed granite (HDG) to constrain the termination of the KDSZ deformation. The U-Pb age of apatite from HSG (249.1 ± 1.8 Ma) is identical to that of zircon (256.5 ± 2.1 Ma) within the error range. In contrast, the U-Pb age of apatite from HDG (248.1 ± 4.0 Ma) is significantly younger than that of zircon (347.3 ± 2.5 Ma). The HDG and HDG have the geochemical characteristics of I-type granites petrogenesis, including high SiO2 (up to 75.47%), high alkaline (K2O + Na2O = 6.39%–8.05%), low FeOT/MgO (2.4–3.4), and peraluminous (A/CNK = 1.01–1.08). Combined with previous Sr-Nd isotope compositions, the positive zircon εHf(t) values and TDM2 ages indicate that the ca. 347 Ma HDG originated from the re-melting of juvenile crust crustal-derived magma in a volcanic arc environment during the northward subduction of the Kanggur oceanic basin, and the ca. 257 Ma HSG originated from the partial melting of thickened juvenile crust in a post-collisional environment. Although trace elements of zircon show typical magmatic characteristics, apatite does not. With the presence of distinct major and trace elements in apatite, the apatite from HSG is characterized by high Mn (>2500 ppm), slight enrichment in the middle rare earth elements (MREEs), and obvious negative Eu anomalies (δEu = 0.09–0.21), indicating that it is related to magmatic apatite. In contrast, the apatite from HDG, with low Mn (

Detailed microstructural, microfabric and chemical analyses of felsic granulite within and around a ductile shear zone at the Plešovice quarry in the southern Bohemian Massif revealed deformation-induced, retrograde transformation of kyanite to andalusite. Although andalusite is absent outside the shear zone, its fraction among Al 2 SiO 5 polymorphs significantly increases up to ∼59% inside the shear zone, while the fraction of kyanite significantly decreases from ∼98% outside the shear zone down to ∼22% inside the shear zone. Three examples of andalusite and the relict kyanite pair suggest a common topotaxial relationship such that andalusite (010) is parallel to the precursory kyanite (100), while andalusite [100] and [001] are parallel to the precursory kyanite [010] and [001], respectively, indicating that the growth of andalusite was crystallographically controlled by the precursory kyanite. The felsic granulite in the ductile shear zone at the Plešovice quarry has been repeatedly subjected to brittle shearing accompanied by pseudotachylite formation and plastic shearing with mylonitization, suggesting development of the ductile shear zone at the brittle–plastic transition zone. Mylonitization of the felsic granulite was promoted by deformation-induced K-feldspar replacement by myrmekite at temperatures of 390–440 °C assuming a pressure of 250 MPa. • Deformation-induced, retrograde transformation of kyanite to andalusite revealed. • Andalusite growth was crystallographically controlled by the precursory kyanite. • Transformation occurred at temperatures of 390–440 °C assuming a pressure of 250 MPa. [ABSTRACT FROM AUTHOR]

The Atotsugawa fault is one of the most active faults in Japan, and the strain accumulation at the fault is considered to be caused by an aseismic shear zone in the fluid‐rich lower crust. To identify the shear zone and investigate the origin of the aqueous fluid in the lower crust, we deployed a Network‐MT survey in addition to a conventional wideband‐MT survey around the fault and performed an inversion combining both the MT data sets. In the inversion, by modifying a conventional inversion algorism, we accurately represented kilometer‐scale dipoles of the Network‐MT measurement to provide constraints on the electrical resistivity structure. In the lower crust under the study area, there are localized conductive anomalies below the Atotsugawa fault, the Ushikubi fault, and the Takayama‐Oppara fault zone. Comparing our electrical resistivity structure with the seismic velocity structure, we interpreted that the lower‐crustal conductors are localized ductile shear zones with highly connected fluid. We considered that the localized ductile shear zones are responsible for the strain accumulation along the respective active faults. In addition, in the mantle wedge above the subducting Philippine Sea slab and its downward extension, a highly conductive portion is detected, which may be attributed to the fluid dehydrated from the Philippine Sea slab and/or the Pacific slab. The existence of the large conductive area supports the suggestion of previous seismic and geochemical studies that the fluid of the lower crust around the Atotsugawa fault originated from subducting slabs. Key Points: Combined inversion method of wideband‐MT and Network‐MT data has been developed to accurately represent long‐dipole measurementsLower‐crustal conductors below active faults and a large conductor above a subducting slab are imaged under a high strain rate zoneLower‐crustal conductors are interpreted as localized ductile shear zones, being responsible for the strain accumulation along the faults [ABSTRACT FROM AUTHOR]

The north–north‐east‐trending (NNE) shear zones, which are defined by the Jiekou shear zone and Huangmao shear zone, are located in the eastern Jiangnan Orogen. This article provides kinematics, geochronological data, and dynamics on the Jiekou and Huangmao shear zones and serves as a reference for understanding the tectonic evolution in the South China Block during the Early Palaeozoic orogeny. All shearing signatures show that the Huangmao shear zone is dextral, and the Jiekou shear zone is sinistral. Both shear zones have certain genetic connections. The rocks from the Jiekou and Huangmao shear zones are metamorphosed and deformed into protomylonite and mylonite. Results of the deformation fabrics of feldspar and quartz and quartz c‐axis fabric analysis indicate that the ductile deformation temperatures of the Jiekou shear zone sinistral shearing are ~400–500°C. Dextral shearing with medium–high temperature (450–550°C) is mainly recorded in the Huangmao shear zone. In combination with the previous geochronology, NNE‐trending sinistral and dextral shearing in the eastern Jiangnan Orogen occurred at 465–430 Ma, coeval with the Early Palaeozoic orogeny. Therefore, the geodynamics of the NNE‐trending shear zones is related to a major strain transformation from NW to WNW, which is remotely affected by the intracontinental convergence of Yangtze and Cathaysia blocks during the Early Palaeozoic orogeny. [ABSTRACT FROM AUTHOR]

In the present study, we unveil the real significance of mylonitic reworking of the polymetamorphic crystalline basement in the Serre Massif of Calabria (Southern Italy). We use a multidisciplinary approach to comprehend the structural, microstructural and petrologic changes that occurred along a, so far, not much considered shear zone affecting the Variscan lower crustal rocks. It was never before studied in detail, although some late Cretaceous ages were reported for these mylonites, suggesting that this shear zone is of prime importance. Our observations reveal now that the formation of the new structural fabric within the shear zone was accompanied by changes in mineral assemblages, in a dominant compressive tectonic regime. During this tectono-metamorphic event, high-P mylonitic mineral assemblages were stabilized, consisting of chloritoid, kyanite, staurolite, garnet and paragonite, whereas plagioclase became unstable. Average peak P–T conditions of 1.26–1.1 GPa and 572–626 °C were obtained using THERMOCALC software. These data question (i) that the Serre Massif represents an undisturbed continuous section of the Variscan crust, as generally suggested in the literature, and (ii) highlight the role of (eo-)Alpine high-P tectonics in the Serre Massif, recorded within mylonite zones, where the Variscan basement was completely rejuvenated.

The Woka ductile shear zone is located at the southern margin of the middle section of the Gangdese magmatic belt and southeast of Lhasa. This article is a systematic study of the Woka ductile shear zone and provides kinematics, strain patterns, rheology, temperature environment, and geochronological data of the shear zone, which have great significance for understanding of the uplift and extension process of the southern section of the Gangdese. All shear indicators, such as asymmetrical folds, rotated porphyroclasts, and S–C fabrics, developed in the shear zone indicate the shear sense of top‐to‐the‐northwest with the shear nature of detachment. Mineral deformation thermometer and EBSD quartz fabric analysis indicate that the shear zone has experienced early high‐temperature (550–650°C) deformation and post‐superimposed low temperature (380–420°C) deformation. The differential stress (σ) of the ductile shear zone was 28.08–46.73 MPa. Strain rates (έ) ranged from 10−10 to 10−14 s−1 under a high‐temperature environment (600°C) and 10−12 to 10−16 s−1 under a low‐temperature environment (420°C). Three‐dimensional strain ellipsoid measurements of the Woka ductile shear zone indicate that all deformed samples appear as prolate ellipsoids (LS‐type tectonites), which represent an elongate strain. The average kinematic vorticity of the Woka ductile shear zone is 0.93, implying that the shear zone was dominated by simple shear. The thickness of the ductile shear zone was reduced by 12–28%. Combined with the U–Pb zircon age of the protolith of granitic protomylonite, the 40Ar/39Ar sericite age of granitic mylonite (22.38 ± 0.31 Ma) can represent the shear age. The Woka shear zone studied in this article may have been formed by the Great Counter Thrust (GCT) activity and uplift of the Gangdese batholith during the transforming period of the Lhasa Terrane from extrusion to a lateral extension. [ABSTRACT FROM AUTHOR]

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Massif-type anorthosites are voluminous, plagioclase-dominated batholiths that occur worldwide, but only during the Proterozoic Eon. Granitoids are closely associated with the anorthosites, and they collectively may form an AMCG suite (i.e., anorthosite, mangerite, charnockite, granite). Many fundamental questions regarding the origin of the AMCG complexes remain unresolved, including their tectonic setting and mode of emplacement. Here, we present new data from reconnaissance structural mapping, U–Pb LA-ICP-MS zircon dating, and 40Ar/39Ar amphibole and mica dating from a 500 km2 area straddling the western margin of one of the world's largest (≥ 15,000 km2), but also least studied AMCG suites, the Kunene Complex (KC) in Angola. The oldest recognized (pre-Kunene) deformation event D1 produced a steep WNW–ESE-striking S1 fabric in supracrustal rocks, migmatite and Paleoproterozoic (1800–1780 Ma) granodiorite before ~ 1680 Ma. This was folded by the D2 event, resulting in steep, N–S-striking S2 leucosomes and gneissosity in the rocks surrounding the KC. Concordant magmatic layering and lamination, and high- to low-temperature gneissic foliation in the marginal Kunene anorthosite and coeval megacrystic granite are parallel with S2 fabrics in the Paleoproterozoic country rocks. Mineral stretching lineations L2 in all rock types across intrusive contacts are steep and associated with west-side-up (thrust) shearing. Overlapping U–Pb zircon/baddeleyite ages from the Kunene megacrystic granite and Kunene anorthosite, with 40Ar/39Ar mica ages from the mantling Paleoproterozoic country rocks, attest to progressive contraction, thrusting and exhumation of the Paleoproterozoic country rocks onto the Kunene anorthosite in the interval 1410–1380 Ma. We suggest that thermal softening of the country rocks caused by heat dissipation from the earliest phase (1500–1410 Ma) of ponding of hot anorthositic magma in the deep crust localized D2 deformation at the margin of the KC. Our data point to a tectonic model whereby anorthosite sheets were emplaced at a high angle to the shortening direction and along host-rock S2 anisotropy deep in the crust and cooled during progressive ductile thrusting and exhumation of the country rocks. These results question the current view that Proterozoic AMCG suites are emplaced in extensional environments as large diapiric bodies and favor formation in a continental arc setting. [ABSTRACT FROM AUTHOR]

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The Bayan Nuru ductile shear zone is located in the Yabulai–Bayan Nuru tectonic belt of the middle part of the southern Central Asian Orogenic Belt (CAOB) and east of the Langshan tectonic belt. This article is the first report on the Bayan Nuru ductile shear zone, and provides dynamic, kinematic, and geochronological data of the shear zone. Accurately determining the shear orientation and estimating the shearing age of the Bayan Nuruductile shear zone, has important reference value and significance for understanding the tectonic evolution in Alxa during "Yanshan movement" period. All shearing signatures, including asymmetrical folds, rotated porphyroclasts, "domino" structures, "mica fishes," S–C fabrics, and asymmetric stress shadows, developed in the shear zone, indicate sinistral shear. The temperature environment at the time of formation of the shear zone was determined by the mineral deformation thermometer and EBSD quartz C‐axis fabric analysis. The temperature was 350–550°C. The differential stress (σ) was estimated to be 44.31–97.94 MPa and the strain rate(έ) to be 10−14 s−1(350°C) and 10−10s−1(550 °C). The average kinematic vorticity of the Bayan Nuru NNE‐trending ductile shear zone is 0.93, indicating that the shear zone was dominated by simple shear. The thickness of the ductile shear zone was reduced by 7%–22%. Combined with the age of granitic mylonite (289.53 ± 0.74 Ma) and the NNE‐trending spread feature, the Bayan Nuru ductile shear zone in the western part of the Langshan fault zone may have been formed in the context of continuous compressional intraplate deformation, caused by the subduction of the Paleo‐Pacific Plate at 170–150 Ma. [ABSTRACT FROM AUTHOR]

Abstract We conduct a two-dimensional numerical experiment on the lower crust under an intraplate strike-slip fault based on laboratory-derived power-law rheologies considering the effects of grain size and water. To understand the effects of far-field loading and material properties on the deformation of the lower crust on a geological time scale, we assume steady fault sliding on the fault in the upper crust and ductile flow for the lower crust. To avoid the stress singularity, we introduce a yield threshold in the brittle–ductile transition near the down-dip edge of the fault. Regarding the physical mechanisms for shear strain concentration in the lower crust, we consider frictional and shear heating, grain size, and power-law creep. We evaluate the significance of these mechanisms in the formation of the shear zone under an intraplate strike-slip fault with slow deformation. The results show that in the lower crust, plastic deformation is possible only when the stress or temperature is sufficiently high. At a similar stress level, $$\sim$$ ∼ 100 MPa, dry anorthite begins to undergo plastic deformation at a depth around 28–29 km, which is about 8 km deeper than wet anorthite. As a result of dynamic recrystallization and grain growth, the grain size in the lower crust may vary laterally and as a function of depth. A comparison of the results with constant and non-constant grain sizes reveals that the shear zone in the lower crust is created by power-law creep and is maintained by dynamically recrystallized material in the shear zone because grain growth occurs in a timescale much longer than the recurrence interval of intraplate earthquakes. Owing to the slow slip rate, shear and frictional heating have negligible effects on the deformation of the shear zone. The heat production rate depends weakly on the rock rheology; the maximum temperature increase over 3 Myr is only about several tens of degrees. Graphical Abstract .

• New formula predicts temperature in ductile shear zones formed by thermal softening. • New localization criterion is based on heat transfer across shear zone. • Thermal thickness of shear zone is considerably larger than finite strain thickness. • We numerically model 1D, 2D and 3D shear zones under pure and simple shear. • Thermal softening likely responsible for ductile strain localization in lithosphere. The generation of ductile shear zones is essential for the formation of tectonic plate boundaries, such as subduction or strike-slip zones. However, the primary mechanism of ductile strain localization is still contentious. We study here the spontaneous generation of ductile shear zones by thermal softening using thermo-mechanical numerical simulations for linear and power-law viscous flow in one-dimension (1D), 2D and 3D. All models are velocity-driven. The 1D model exhibits bulk simple shear whereas the 2D and 3D models exhibit bulk pure shear. The initial conditions include a small temperature perturbation in otherwise homogeneous material. We use a series of 1D simulations to determine a new analytical formula which predicts the temperature evolution inside the shear zone. This temperature prediction requires knowledge of only the boundary velocity, flow law and thermal parameters, but no a priori information about the shear zone itself, such as thickness, stress and strain rate. The prediction is valid for 1D, 2D and 3D shear zones in bulk pure and simple shear. The results show that shear heating dominates over conductive cooling if the relative temperature increase is >50 °C. The temperature variation induced by the shear zone is nearly one order of magnitude wider than the corresponding finite strain variation so that no significant temperature variation occurs between shear zone and wall rock. Applying typical flow laws for lithospheric rocks shows that shear zone generation by thermal softening occurs for typical plate tectonic velocities of few cm.yr−1 or strain rates between 10 − 16 and 10 − 14 s−1. Shear stresses larger than 200 MPa can already cause strain localization. The results indicate that thermal softening is a feasible mechanism for spontaneous ductile shear zone generation in the lithosphere and may be one of the primary mechanisms of lithospheric strain localization. [ABSTRACT FROM AUTHOR]

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The Hetai goldfield, located at the northern edge of the Yunkai Massif in South China, is a significant gold deposit hosted within the Hetai ductile shear zone (HSZ). The deformation history of HSZ and its correlation with the gold mineralization are problematic. In this study, we conducted detailed field observations and microstructure analyses together with zircon U–Pb and muscovite 40Ar/39Ar geochronology on mylonitic granites, aiming to study the deformation features and processes of the ductile shear zone (DSZ) along with their further implications to the gold metallogenic mechanisms of the Hetai goldfield (HGF). The HGF and its periphery have undergone three phases of ductile shear event (DS) since the Palaeozoic: The first DS developed from 468 to 413 Ma, with deformation temperatures above 500°C, accompanied by the formation of large‐scale migmatite and magmatism. The second DS developed from 239 to 211 Ma, with deformation temperatures ranging from 400°C to 500°C and resulted in a low‐angle, top‐to‐the‐SE thrusting. The third DS developed from 198 to 162 Ma, with deformation temperatures between 300°C and 400°C and formed steep, dextral strike‐slip shear zones. The DSs in the HGF have close connection with the gold mineralization. The first DS is coeval with the small‐scale gold mineralization or sulfofication and laid the foundation for later large‐scale gold mineralization. The second DS had no obvious gold mineralization, but the DSZ that developed in this period, together with the earlier DSZs, may have provided a migration pathway for the later gold ore‐forming fluid. Occurrence of the third DS was combined with the main gold mineralization, but the large‐scale gold mineralization mainly occurred during 175–157 Ma, that is, the middle and later periods of dextral strike‐slip. Overall, multiphase DS dominated the large‐scale gold mineralization in this area. [ABSTRACT FROM AUTHOR]

In response to orogenic cycles, the ductile shear zone records a complex crustal deformation history. In this study, we conducted a microstructural analysis of two NW–SE trending ductile shear zones (Deokjeok Shear Zone (DSZ) and Soya Shear Zone (SSZ)) in the Late Triassic post-collisional granites along the western Gyeonggi Massif in the Korean Peninsula. The DSZ, overlain by the Late Triassic to the Early Jurassic post-collisional basin fill (Deokjeok Formation), has asymmetric microstructures indicative of a top-down-to-the-northeast shear. Depending on the structural position, the SSZ, which structurally overlies the Deokjeok Formation, exhibits two contrasting styles of deformation. The lower portion of the SSZ preserves evidence of top-up-to-the-southwest shearing after top-down-to-the-northeast shearing; on the other hand, the upper portion only indicates a top-up movement. Given the primary deformation mechanisms of both quartz and feldspar, the deformation temperatures of DSZ and SSZ were estimated at ~300–350 °C and ~350–400 °C, respectively, indicative of the mid-crustal condition. New zircon U-Pb isotopic ages from mylonitic granite in the SSZ and volcanic rocks in the Deokjeok Formation, combined with previously published geochronological data, indicate that the post-collisional granites and volcano-sedimentary sequence were nearly contemporaneous (ca. 223–217 Ma) and juxtaposed because of the Late Triassic orogenic collapse and subsequent new orogenic event. In this study, we highlight the role of the extensional DSZ as a detachment propagated into the middle crust during the Late Triassic orogenic collapse. Our results report a deformational response to a transition from the collisional Songrim Orogeny to the subduction-related Daebo Orogeny in the western Gyeonggi Massif. This, in turn, provides essential insight into cyclic mountain building/collapse in the East Asian continental margin during the Mesozoic time.

High-resolution geological mapping is an important supporting condition for mineral and energy exploration. However, high-resolution geological mapping work still faces many problems. At present, high-resolution geological mapping is still generated by expert interpretation of survey lines, compasses, and field data. The work in the field is constrained by the weather, terrain, and personnel, and the working methods need to be improved. This paper proposes a new method for high-resolution mapping using Unmanned Aerial Vehicle (UAV) and deep learning algorithms. This method uses the UAV to collect high-resolution remote sensing images, cooperates with some groundwork to anchor the lithology, and then completes most of the mapping work on high-resolution remote sensing images. This method transfers a large amount of field work into the room and provides an automatic mapping process based on the Simple Linear Iterative Clustering-Convolutional Neural Network (SLIC-CNN) algorithm. It uses the convolutional neural network (CNN) to identify the image content and confirms the lithologic distribution, the simple linear iterative cluster (SLIC) algorithm can be used to outline the boundary of the rock mass and determine the contact interface of the rock mass, and the mode and expert decision method is used to clarify the results of the fusion and mapping. The mapping method was applied to the Taili waterfront in Xingcheng City, Liaoning Province, China. In this study, the Area Under the Curve (AUC) of the mapping method was 0.937. The Kappa test result was k = 0.8523, and a high-resolution geological map was obtained.

This study presents in-depth geometric and kinematic analyses of a complex transpressional shear zone (Fellos Shear Zone, FSZ) that integrates structural mapping with microstructural and quartz crystallographic texture data. The FSZ strikes NE-SW and formed in the short limb of a map-scale antiform. The foliation pattern within the zone indicates dextral shearing whereas the macroscopic object lineation is dispersed over a half great-circle girdle along the mean mylonitic foliation. Based on this deformation pattern, the FSZ could be interpreted as a dextral, NE-directed triclinic transpressional zone. However, the integration of field-based with microtectonic data reveal a more complicate kinematic history. We show that the elongation trend is dispersed along an entire great-circle girdle when we take into account the trends of incremental elongations, recorded by fabrics with different strain memories. Mapping of incremental shear directions implies that the FSZ initiated as a NE-directed dextral transpressional shear zone, and progressively evolved into a NW-directed dextral zone. The passage from NE-to NW-directed shearing was accompanied by transpression whilst local transtension likely occurred during the last stages of ductile deformation. Deformation in the FSZ ended up, at semi-ductile conditions, with localized NE-directed dextral shearing. Our study demonstrates that the integration of field observations and fabrics/microstructures that have different strain memories is a powerful tool for unravelling the complex kinematics of high-strain zones. [ABSTRACT FROM AUTHOR]

The Central Tianshan Block is one of the major continental constituents of the Central Asian Orogenic Belt (CAOB) and contains vital information for understanding the amalgamation of the Eurasia continent. Its tectonic affinity remains controversial hindering a better reconstruction of the paleogeographic evolution of the Paleo-Asian Ocean and geodynamic processes of the CAOB. In order to put more constraints on the Precambrian basement composition and crustal evolution of the Central Tianshan Block, we conducted field structural investigations and zircon U-Pb dating on the meta-sedimentary and meta-igneous rocks along the Wulasitai – Wulanmoren ductile shear zone (WWSZ), northern Baluntai area (NW China). The WWSZ is geometrically a SE-NW-striking high-strain deformation zone of ∼1–5 km wide. It is lithologically composed of greenschists, paragneiss, amphibolitic metabasalts, migmatitic granites and mylonitic granites. The greenschist to amphibolite facies meta-sandstones and meta-volcanic rocks belong to the Ahebulake Group, in which NE- or SW-dipping steep mylonitic foliations and sub-horizontal lineations are well developed. Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) U-Pb dating of detrital zircons from four representative meta-sedimentary rocks from the Ahebulake Group yielded several major age groups of 3130–2530 Ma, 2450–2150 Ma, 2000–1700 Ma, 1620–1433 Ma, 1170–655 Ma, ∼450 Ma, ∼425 Ma, ∼400 Ma, ∼360 Ma and ∼312 Ma. Three ductilely deformed and metamorphosed granitic samples show four major zircon U-Pb age peaks at ∼430 Ma, ∼400–390 Ma, ∼360 Ma and ∼330 Ma. On the basis of a careful analysis of the texture of the dated zircons and the structural features of their host rocks, and combined with the available isotopic ages and regional geological data, we propose that: (1) meta-sedimentary rocks from the Ahebulake Group were likely deposited later than about 400 Ma instead of in the Silurian, as previously assumed; (2) the distinct Neoproterozoic detrital zircon age population in these meta-sediments probably reflects the widespread occurrence of coeval in-situ basement rocks as source; (3) the Central Tianshan Block may have close tectonic affinities with both the Yili Block and the Tarim Craton during the Proterozoic; and (4) the ductile shearing along the WWSZ is likely later than ∼330 Ma, probably initiated at ∼312–299 Ma. Our new results provide further arguments for the paleogeographic linkage of the microcontinents within the Paleo-Asian Ocean and tectonic reconstruction of the southwestern CAOB. [ABSTRACT FROM AUTHOR]

The largest crystalline unit representing the mid-crust in the Himalayan belt is the Greater Himalayan Sequence (GHS) which stretches all over the 2400 km of length of the belt. The GHS, recognized since the first geological explorations of the Himalayas, has been considered for a long time as a coherent tectonic unit, exhumed by the contemporaneous shearing along the Main Central Thrust and the South Tibetan Detachment System in the time span ~ 25–17 Ma. A multidisciplinary approach, integrating geological mapping, structural analysis, petrology and geochronology allowed to better constrain on its internal architecture characterized by several levels of tectonic-metamorphic discontinuities on the regional scale with a top-to-the-S/SW sense of shear and active since ~ 40 Ma. The GHS is consequently divided in three main tectonic units exhumed progressively from the upper part to the lower one by ductile shear zones, later involving the Lesser Himalayan Sequence. Above the Main Central Thrust a cryptic tectono-metamorphic discontinuity (Higher Himalayan Discontinuity; HHD) has been recognized and mapped in Central-Eastern Himalaya. The mapping of the HHD has been allowed by the use of a multidisciplinary approach involving structural analysis, geochronology and petrology. A new map of Western Nepal is presented. In this framework the popular models of exhumation of the GHS mainly based on the contemporaneous activity of the two bounding shear zones (Main Central Thrust and the South Tibetan Detachment) and considering the GHS as a coherent tectonic unit, should be reconsidered. An in-sequence shearing tectonic model, from the deeper to the upper structural levels, further affected by out-of-sequence-thrusts, is more appropriate to explain the deformation, metamorphism and exhumation of the mid-crust in the Himalayan belt. Geological mapping of the Himalayan belt is very far away to be exhaustively completed. Anyway during the last 20, and particularly during the last few years, it has been notably improved due to a new multidisciplinary approach. [ABSTRACT FROM AUTHOR]

The ductile shear zones in the North Qinling Orogen, such as the Luonan-Luanchuan, Guanpo-Qiaoduan, Zhuyangguan-Xiaguan, and Shangdan shear zones, play an important role in the preclosure and postclosure evolution of the Proto-Tethys Ocean. On the basis of detailed macrostructural/microstructural analysis and quartz C-axis electron backscattered diffraction fabric analysis, the sense and formation environment of the 4 shear zones have been obtained. The Luonan-Luanchuan and Guanpo-Qiaoduan shear zones mainly present as dextral and sinistral shearing under low temperature, respectively. The Zhuyangguan-Xiaguan shear zone mainly presents as dextral shearing under medium temperature. The Shangdan shear zone underwent an early dextral shearing under medium temperature and a late sinistral shearing under low temperature. The Qinling Group and the Taibai region were intensively affected by the late sinistral shearing of the Shangdan shear zone. According to published metamorphic ages, the 4 shear zones should have been formed during the collision between the North China Block and the South China Block. Due to the opening of the Mianlue and the Paleo-Tethys oceans since ~380 Ma, the North China Block and the South China Block departed from northern Gondwanaland and drifted northward along transform faults, which led to the arrangement between the North China Block and the South China Block that transited from an east-west direction to a north-south direction. Since ~320 Ma, the scissors-type closure between the North China Block and the South Qinling Terrane led to the westward extrusion of the North Qinling Orogen, and the dextral shearing of the Luonan-Luanchuan and the Zhuyangguan-Xiaguan shear zones and the sinistral shearing of the Guanpo-Qiaoduan and the Shangdan shear zones. [ABSTRACT FROM AUTHOR]