Search Results (66)

As a bridge connecting processes in the Earth’s interior and the superficial lithosphere, distribution characteristics of global stress fields could benefit the verification of geodynamical models and reflect spatial variations of lithospheric strength. Numerical simulation of the global stress field could provide the temporal evolution process of the stress fields, and reveal the dynamic process of accumulation and release of the in situ stress fields as well as the quantitative relationship between force sources and the stress fields, which could compensate for the sparsity and insufficient representativeness of in situ stress observation data. To advance the investigation on the global stress fields, we review the state-of-the-art progress of numerical simulation tools for global stress fields and their applications, and show the existing problems as well as future trends. Full article

How continental lithosphere stretches and ruptures is a fundamental question in Earth sciences; however, effective constraints on the physical conditions deep within the crust where deformation is concentrated remain elusive. This study offers new insights into this process through a detailed dissection of the Tan-Lu Fault Zone, one of the most extensive fault systems in East Asia. A critical controlling factor for crustal rheological properties is deformation temperature, a challenge we address by employing a thermometer based on the fractal dimension (D-value) of dynamically recrystallized quartz grain boundaries. Analyzing 62 mylonite samples from the Feidong segment, we reveal that left-lateral strike-slip shearing along this fault zone occurred under high temperatures (~450–700 °C). This conclusion is not only derived quantitatively from a quartz D-value thermometer but is also visually corroborated by classic high-temperature microstructures (e.g., extensive grain boundary migration), corresponding to conditions from the upper greenschist to amphibolite facies. Existing geochronological data constrain this high-temperature shearing event to the Early Cretaceous. Such elevated temperature conditions, combined with field and microstructural evidence indicating extension, provide quantitative confirmation that the fault zone operated within a transtensional tectonic regime during that period. Our findings offer a rigorously thermally constrained dynamic model for the deformation behavior of large continental faults during large-scale lithospheric thinning and craton destruction, providing a valuable framework for interpreting crustal rheology and continental dynamics. Full article

Earthquakes are the result of complex interactions between tectonic plates, the mantle, and the lithosphere. Complex geodynamic conditions contribute to the occurrence of seismic phenomena. Tectonic plates can collide, move apart, or slide past each other. Mantle convection by internal heat drives plate motions that deform the lithosphere. Rocks deform elastically as stress accumulates and pore fluid pressure changes. Rupture occurs when stress exceeds frictional resistance. The connection between variations in gravity and the magnitude of earthquakes remains unclear. This work aims to examine aspects of this correlation. Three sets of earthquakes, one with events from all over the world, one from broader Greece, and one from the Hellenic Trench in Greece, aiming to cover all cases of geodynamics, from very different to very similar, were employed. Time series of gravity measurements at earthquake epicenters were extracted from GRACE satellite data. Time derivatives of the gravity field, as well as magnitude-dependent variations—reflecting changes relative to earthquake strength—were computed. Multiple linear regression (MLR), partial least squares (PLS) regression, and neural networks (NN) were used to model the relationship between gravity or its derivatives and earthquake magnitude. A correlation between the earthquake magnitude and magnitude derivatives was found. By using the global and Greek datasets, the best accuracy was obtained with MLR, reporting a mean squared error (MSE) of 0.069 with an R² of 0.979, and MSE was 0.011 with R² score of 0.997, respectively. By using the Hellenic Trench set, PLS regression derived the best correlation results, reporting an MSE of 0.004 and an R² of 0.977. Experimental results suggest that gravity, and therefore crustal density, is related to the magnitude of the impending earthquake, but not to its timing. Full article

Subduction of the South Tianshan Ocean caused widespread Devonian magmatism, lithospheric deformation, and thinning along the south margin of the Central Tianshan Belt. However, the details of this subduction process remain elusive. This study presents comprehensive data on Devonian granitoids from the Kumishi area, including whole-rock geochemical data, Sr-Nb-Pb isotopic compositions, zircon U-Pb ages, and zircon Hf isotopic data. Dioritic porphyrites, medium–fine-grained monzogranites, and coarse–medium-grained monzogranites were emplaced at 397 ± 2 Ma, 397 ± 3 Ma, and 395 ± 3 Ma, respectively. The dioritic porphyrites have relatively high Sr contents, low heavy rare earth element (HREE) and Y contents, and high Sr/Y ratios, which are characteristics of adakites. High Al and Na₂O contents suggest that the rocks formed through partial melting of subducted oceanic crust. The monzogranites display I-type and subduction-related arc affinities, sourced from a mixed magma of crustal materials and mantle wedge components. The granodiorites were emplaced at 373 ± 3 Ma, and also exhibit pronounced I-type and subduction-related arc affinities. Combined with previous data, our results demonstrate that the studied area of Devonian magmatism records the entire spatiotemporal evolution of subduction of the South Tianshan Ocean slab, from initial shallowing of the subduction angle to flat-slab subduction, followed by final slab rollback. Full article

The East China Sea Shelf Basin (ECSSB) and its adjacent areas, as key regions of the ocean–continent transition zone, have been affected by multiple complex plate collisions, subduction, and back-arc tension since the Mesozoic Era. The structural deformation provides a large amount of geological information on the ocean–continent transition zone. There are significant spatiotemporal differences in the structural deformation within the basin. However, the research remains insufficient and understanding is inconsistent, especially regarding the systematic study of the differences and dynamic mechanisms of north–south structural deformation, which is relatively lacking. This study is based on two-dimensional multi-channel deep reflection seismic profiles spanning the southern and northern basin. Through an integrated re-analysis of gravity, magnetic, and OBS data, the deformation characteristics and processes of the Meso-Cenozoic structures in the basin are analyzed. The differences in structural deformation between the southern and northern basin are summarized, and the controlling effects of deep crust–mantle activity and the influencing factors of shallow structural deformation are explored. Based on deep reflection seismic profiles, the structural deformation characteristics of the Yushan–Kume fault are revealed for the first time, and it is proposed that NW faults, represented by the Yushan–Kume fault, have important tuning effects on the north–south structural differential deformation in the ECSSB. The thermal subsidence of the lithosphere is the direct cause of the development of the Mesozoic ECSSB, while the subduction of the Paleo-Pacific plate is one of the important factors contributing to it. The combined effect of the two has led to significant differences between the northern and southern Mesozoic basin. During the Cenozoic Era, the alternating subduction and changes in the direction of subduction of the Pacific Plate led to spatiotemporal differences in structural deformation within the ECSSB. The development of NW faults was a key factor in the differences in structural deformation between the northern and southern basin. The study of structural deformation differences in the ECSSB not only deepens our understanding of the tectonic evolution in the East Asian continental margin region, but also has important significance for the exploration and evaluation of deep hydrocarbon resources in the ECSSB. Full article

Gold mineralisation at Ity (Ivory Coast) is spatially associated with skarns formed at contacts between carbonate-rich Birimian volcano-sedimentary rocks and felsic intrusions, whereas at Dahapleu, a nearby skarn-free prospect, gold occurs in structurally controlled shear zones. Gold occurs as native gold in pyrite or as a Bi–Te–Au–Ag telluride assemblage. Fluid inclusion data indicate that Ity formed through a hybrid model: a mesothermal orogenic gold system dominated by CO₂–CH₄ fluids at >350 °C, superimposed on earlier skarn mineralisation characterised by saline fluids. At Dahapleu, no skarn fluids were identified, but volatile-rich inclusions with more variable signatures (CO₂, CO₂–CH₄, CO₂–N₂) indicate metamorphic fluids circulating in convective, fault-related systems and recording distinct fluid–rock interactions. The Ity–Dahapleu mineralising system thus displays fluid inclusion characteristics typical of mesothermal orogenic gold systems, likely at higher temperatures than most West African Birimian deposits. Overall, the Ity system reflects a long-lived thermal anomaly driving fluid circulation and metal deposition, with successive favourable events: rapid exhumation of hot lithospheric crust, granite intrusion, and skarn formation, followed by shear deformation and hydrothermal activity. Full article

In this study, we analyzed the lithospheric seismic background of the Tianshan and adjacent areas by combining various geophysical methods (effective elastic thickness, time-varying gravity, apparent density, and InSAR), and explored the genesis mechanism of the Wushi Ms7.1 earthquake as an example, which led to the following conclusions: (1) The effective elastic thickness (Te) of the Tianshan lithosphere is low (13–28 km) and weak, while the Tarim and Junggar basins have Te > 30 km with high intensity, and the loads are all mainly from the surface (F < 0.5). Earthquakes occur mostly in areas with low values of Te. (2) Medium and strong earthquakes are prone to occur in regions with alternating positive and negative changes in the gravity field during the stage of large-scale reverse adjustment. It is expected that the risk of a moderate-to-strong earthquake occurring again in the vicinity of the survey area between 2025 and 2026 is relatively high. (3) Before the Wushi earthquake, the positive and negative boundaries of the apparent density of the crust at 12 km shifted to be approximately parallel to the seismic fault, and the earthquake was triggered after undergoing a “solidification” process. (4) The Wushi earthquake is a leptokurtic strike-slip backwash type of earthquake; coseismic deformation shows that subsidence occurs in the high-visual-density zone, and vice versa for uplift. The results of this study reveal the lithosphere-conceiving environment of the Tianshan and adjacent areas and provide a basis for regional earthquake monitoring, early warning, and post-disaster disposal. Full article

The South China block (SCB) is characterized by complex tectonics, large-scale lithospheric deformation, and extensive mineralization in its southeastern region. However, the geodynamic processes and mechanisms driving mineralization remain controversial, partly due to the lack of information on its fine crustal structure. The resolution of crustal seismic tomography is relatively low due to the uneven distribution of local earthquakes in South China. In this study, we conduct a joint inversion of Bouguer gravity and seismic travel-time data to investigate the detailed 3-D P-wave velocity (Vp) structure of the crust beneath the SCB. Our results show the following: (1) strong lateral heterogeneities exist in the crust, which reflect the surface geology and tectonics well; (2) the Vp patterns at different depths beneath the Yangtze block are almost consistent, but those beneath the Cathaysia block vary significantly, which might be related to the lithosphere thinning in the Mesozoic; (3) decoupling between the upper crust and the lower crust occurs at ~20 km depth beneath the eastern SCB; (4) the Vp patterns vary beneath different metallogenic belts; and (5) distinct low-Vp anomalies exist in the lower crust beneath mineral deposits. These results suggest that the deep mineralization is closely associated with the lithospheric thinning and upwelling thermal flow in the Mesozoic beneath the eastern SCB. Our Vp tomographic result also strongly supports the viewpoint that the mineralization mechanism varies for different metallogenic belts. Full article

Continental rifting is the process by which land masses separate and create new ocean basins. The emplacement of large igneous provinces (LIPs) is thought to have played a key role in (super) continental rifting; however, this relationship remains controversial due to the lack of a clearly established mechanism linking LIP emplacement to continental fragmentation. Here, we show that plume flow links LIP magmatism to continental rifting quantitatively. Our findings are further supported by the sedimentary record, as well as by the mineralogy and petrology of the rocks. This study analyzes the early Cretaceous separation of West Gondwana into South America and Africa. Prior to rifting, Jurassic hiatuses in the stratigraphic record of continental sediments from both continents indicate plume ascent and the resulting dynamic topography. Cretaceous mafic dyke swarms and sill intrusions are products of major magmatic events that coincided with continental rifting, leading to the formation of large igneous provinces in South America and Africa, including the Central Atlantic Magmatic Province, Equatorial Magmatic Province, Paraná–Etendeka, and Karoo. It has been suggested that dyke intrusions may weaken the lithosphere by reducing its mechanical strength, creating structural weaknesses that localize extensional deformation and facilitate rift initiation. The sedimentary analysis and petrological evidence from flood basalt magmas indicate that plumes may have migrated from the depths toward the surface during the Jurassic and erupted during the Cretaceous. It is thought that the resulting fast plume flow, induced by one or more mantle plumes, generated a dynamic force that, in combination with lithospheric weakening from dyke intrusion, eventually rifted the lithosphere of West Gondwana. Full article

The internal growth patterns and surface micromorphology of diamonds provide a record of their multi-stage evolution, from initial formation within the mantle to their eventual ascent to the Earth’s surface via deeply derived kimberlite magmas. In this study, gemological microscopic examination, Diamond View^TM, Raman spectroscopy, and electron probe analysis were employed to analyze the surface features, internal patterns, and inclusions of the Tancheng alluvial diamonds in Shandong Province, China. The results show that surface features of octahedra with triangular and sharp edges, thick steps with irregular contours or rounded edges, and thin triangular or serrated layers are developed on diamonds during deep-mantle storage, as well as during the growth process of diamonds, when they are not subjected to intense dissolution. The rounding of octahedral and cubic diamond edges and their transformation into tetrahedral (THH) shapes are attributed to resorption in kimberlitic magma. These characteristics indicate that the Tancheng diamonds were commonly resorbed by carbonate–silicate melts during mantle storage. Abnormal birefringence phenomena, including irregular extinction patterns, petaloid and radial extinction patterns, and banded birefringence, were formed during the diamond growth stage. In contrast, fine grid extinction patterns and composite superimposed extinction patterns are related to later plastic deformation. The studied diamonds mainly contain P-type inclusions of olivine and graphite, with a minority of E-type inclusions, including coesite and omphacite. The pressure of entrapment of olivine inclusions within the Tancheng diamonds ranges from 4.3 to 5.9 GPa, which is consistent with that of coesite inclusions, which yield pressure ranging from 5.2 to 5.5 GPa, and a temperature range of 1083–1264 °C. Overall, the evidence suggests that Tancheng diamonds probably originated from hybrid mantle sources metasomatized by the subduction of ancient oceanic lithosphere. Full article

In this article, we consider the roles of transcrustal magma- and fluid-conducting faults (TCMFCFs) in the formation of mineral deposits, showing the importance of deep sources of heat and hydrothermal solutions in the genesis and history of deposit formation. As a result of the impact on the lithosphere of mantle plumes rising along TCMFCFs, intense block deformations and tectonic movements are generated; rift systems, and volcanic–plutonic belts spatially combined with them, are formed; and intrusive bodies are introduced. These processes cause epithermal ore formation as a consequence of the impact of mantle plumes rising along TCMFCF to the lithosphere. At hydrocarbon fields, they play extremely important roles in conductive and convective heat, as well as in mass transfer to the area of hydrocarbon generation, determining the relationship between the processes of lithogenesis and tectogenesis, and activating the generation of hydrocarbons from oil and gas source rock. Detection of TCMFCFs was carried out using MMSS (the method of microseismic sounding) and MTSM (the magnetotelluric sounding method), in combination with other geological and geophysical data. Practical examples are provided for mineral deposits where subvertical transcrustal columns of increased permeability, traced to considerable depths, have been found; the nature of these unique structures is related to faults of pre-Paleozoic emplacement, which determined the fragmentation of the sub-crystalline structure of the Earth and later, while developing, inherited the conditions of volumetric fluid dynamics, where the residual forms of functioning of fluid-conducting thermohydrocolumns are granitoid batholiths and other magmatic bodies. Experimental modeling of deep processes allowed us to identify the quantum character of crystal structure interactions of minerals with “inert” gases under elevated thermobaric conditions. The roles of helium, nitrogen, and hydrogen in changing the physical properties of rocks, in accordance with their intrastructural diffusion, has been clarified; as a result of low-energy impact, stress fields are formed in the solid rock skeleton, the structures and textures of rocks are rearranged, and general porosity develops. As the pressure increases, energetic interactions intensify, leading to deformations, phase transitions, and the formation of chemical bonds under the conditions of an unstable geological environment, instability which grows with increasing gas saturation, pressure, and temperature. The processes of heat and mass transfer through TCMFCFs to the Earth’s surface occur in stages, accompanied by a release of energy that can manifest as explosions on the surface, in coal and ore mines, and during earthquakes and volcanic eruptions. Full article

The strength of the lithosphere plays an important role in understanding the deformation process of the Earth. In northern South America, the convergence of three tectonic plates has resulted in a zone of active deformation. The effective elastic thickness (T_e) is a parameter that serves as a proxy for the lithospheric strength. This study determined the spatial variations of T_e across northern South America through a joint inversion of admittance and coherence using Bouguer gravity anomaly and topography data. The inversion reveals that T_e ranges from 15 to 60 km, with high T_e (>50 km) corresponding to stable cratons, whereas low T_e (<20 km) is displayed in areas close to continental margins. The Colombian Andes exhibit an intermediate T_e value, ranging from 20 to 40 km. The subsurface-to-surface ratio (F) indicates dominant surface loading in the region. Furthermore, a correlation was observed between T_e and other proxies for lithospheric structure, such as seismic velocity. Full article

Archean craton comprises ancient and stable continental lithosphere, lacking significant seismic activity, magmatic activity, and tectonic deformation. Typically, its lithospheric mantle exhibits high electrical resistivity. However, within the Archean Tanzanian cratonic mantle, a high conductivity layer has been discovered, with an electrical conductivity of approximately 0.1 S/m. We conducted the electrical conductivity experiments on olivine aggregates containing sodium carbonate at the pressure of 3 GPa and the temperature ranging from 600 to 1200 °C. It was found that a very small amount of alkali-carbonate melt can significantly increase the electrical conductivity of dunite. The mass fraction of alkali-carbonate melt is less than 2.0 wt% in the highly conductive layer of the Tanzanian cratonic mantle. The permeability barriers made the melts preserve within the depth range of 80 to 120 km. Therefore, the presence of alkali-rich carbonate melts may be the best mechanism to explain the high conductivity anomaly in the lithospheric mantle of the Tanzanian craton. In contrast, the carbonate melts with high mobility migrated directly to shallow depths along fractures in the mobile belt/rift zone, leaving a dry and resistive residual mantle. Full article

The granitoids of the Kalba–Narym batholith and the Irtysh shear zone (ISZ) are among the main geological features of the late Paleozoic Altai accretion–collision system (AACS) in Eastern Kazakhstan. Traditionally, it is believed that late Paleozoic strike-slip faults played a pivotal role at all stages of the development of the AACS, they were supposed to control deformation, magmatism, and ore deposits. This work is devoted to solving the problem of the tectonic evolution of the AACS based on the reconstruction of the thermal history of granitoids of the Kalba–Narym batholith in connection with the Chechek metamorphic dome structure, which is one of the highly metamorphosed blocks mapped within the ISZ. The new geological and geochronological data presented in this work allowed us to establish the sequence of formation of the Kalba–Narym granitoid batholith and link it with the evolution of the Irtysh shear zone (ISZ). It was revealed that in the late Carboniferous–early Permian (312–289 Ma), during the NE–SW compression, the Irtysh shear zone formed as a gently dipping thrust system into which gabbro of the Surov massif intruded. The combined manifestation of magmatic and tectonic processes caused the formation of tectonic mélange with cataclastic gabbro and metamorphic rocks of the Chechek metamorphic dome structure (312–289 Ma). Compression caused the formation of a cover-thrust structure. The thickening of the crust under the probable thermal action of the Tarim plume led to the formation of the early Permian Kalba–Narym batholith (297–284 Ma) within the Kalba–Narym terrane. Denudation of the orogen occurred before the Early Triassic (280–229 Ma). In this way the sequence of formation of the Kalba–Narym batholith and the ISZ is consistent with the concepts of the stages of plume-lithosphere interaction within the AACS under the influence of the late Carboniferous–early Permian Tarim igneous province, but in the cover-thrust tectonic setting. Full article

During the Mesozoic, NE Asia experienced intense tectonic and magmatic activity, including the closure of the Mongol–Okhotsk Ocean (MOO), the subduction and demise of the Mudanjiang Oceanic Plate (MOP), and the continuous westward subduction of the Paleo-Pacific Plate (PPP). The evolution of the MOP remains highly contentious, particularly regarding its final closure timing and subduction polarity, and warrants further investigation. The Heilongjiang Complex (HLC), primarily distributed within the Mudanjiang Suture Zone (MSZ), which separates the Jiamusi and Songnen blocks, preserves key geological records of the Mudanjiang Oceanic subduction and closure. By employing detailed structural analysis, zircon U-Pb dating, and tomographic imaging, we reconstruct the tectonic history of the HLC and propose its five stages of deformation since the Mesozoic. The first stage, which occurs from the Late Triassic to the Early Jurassic, is characterized by SE-dipping schistosity within the HLC. Integrating the identification of the east-dipping remnants of the oceanic lithosphere west of the MSZ by tomographic imaging suggests an eastward subduction of the MOP underneath the Jiamusi Block during the Early Mesozoic. The second stage, spanning the Early Jurassic to the Late Jurassic, is characterized by E–W-striking tight folds associated with the MOO’s SSE-ward subduction and PPP’s NNW-ward subduction. The third stage of deformation, occurring from the Late Jurassic to Early Cretaceous, features S–N-striking box folds, indicative of the final amalgamation of the Jiamusi, Songnen, and Nadanhada terranes. The fourth stage, taking place in the late Early Cretaceous, is marked by near E–W-striking thrust faults that are associated with the closure of the eastern segment of the MOO. Finally, the fifth stage, which follows the Early Cretaceous, involves nearly NE-striking thrust faults related to NW-ward subduction of the PPP. Full article