Gravity Lineaments Research Articles

Crustal silica content of East China: A seismological perspective and its significance

East China has experienced multiple periods of tectonic movements, which have contributed to the composition and rheological properties of its present crust. Estimating the composition of the crust is crucial for understanding the tectonic processes. Based on the teleseismic receiver functions with data from the National Seismic Network of China, we applied the H-κ-c method to obtain the crustal bulk VP/VS ratio and to constrain the SiO2 content in the crust. We estimated the SiO2 content to range from 50.89 wt% to 73.51 wt%, with an average value of 65.87 wt%, indicating a predominant felsic composition of the East China's crust. Our study suggests that the North-South Gravity Lineament (NSGL) is an approximate delimitator of the felsic and mafic crust in East China, hinting at a widespread deficiency of mafic lower crust in the east of the NSGL. The mafic crust is extensively distributed in the Taihang orogenic region (TSR) and WuLingshan gravity gradient belts (WLG), particularly in the Datong volcanic area, which manifests the mantle materials intraplating. The scatteredly distributed mafic crust at the east of the NSGL is mainly concentrated in the southeast coast of China and in the intersection region of the Tanlu Fault (TLF) and Sulu region. In Sulu region, the TLF may primarily provide a channel for the thermal intrusion from the underlying mantle lithosphere, which has increased the mafic content. The Pacific/Philippine Sea plate subduction has triggered a significant amount of crust-mantle material exchange below southeast China that resulted in a high degree of mafic crustal composition.

Influences of the Stagnant Pacific Slab Beyond Its Westernmost Edge: Insights From the Cenozoic Alkaline Basalts in the Dariganga Volcanic Field, SE Mongolia

AbstractIt remains uncertain whether a stagnant slab in the mantle transition zone can affect the asthenospheric mantle beyond its leading edge. To address this question, we investigated Cenozoic alkaline basalts from the Dariganga volcanic field (DVF) in southeastern Mongolia. The DVF is located west of North–South Gravity Lineament (NSGL) in Eastern China, which is spatially coincident with the seismically detected stagnant Pacific slab front. Basalts from the DVF consist of nephelinite, basanite and alkali olivine basalt. These rocks have relatively high Nb/U (average = 58) and Nb/La (>1) ratios and radiogenic Nd–Hf isotopic compositions. They also have high Ca/Al (0.60–1.13), Zn/FeT (13.5–16.5), and FeO/MnO (77–112) ratios as well as low δ26Mg (−0.42‰ to −0.26‰) values, reflecting an asthenospheric mantle source modified by carbonated eclogite‐derived melts. Pb–Nd–Hf isotope characteristics indicate that the carbonated eclogite‐derived melts likely originated from the stagnant Pacific slab. Although Cenozoic basalts from both the east of the NSGL (ENSGL) and DVF domains exhibit light δ26Mg values, basalts from the ENSGL nevertheless have lower δ26Mg values than those in the DVF domain. This suggests a gradual westward decline in the amount of carbonated melts/fluids derived from the stagnant Pacific slab. This variation trend, combined with a more fertile and oxidized asthenospheric mantle toward the ENSGL, indicates that the stagnant slab has affected the mantle and created a compositional aureole beyond its leading edge, which substantially contributed to the formation of the alkaline basalts in the DVF.

Disparate Far‐Field Responses of Deep Pacific‐Plate Subduction Beneath Northeastern Asia: Implication for the North–South Segmented Crustal Modification of the Great Khingan Range

AbstractThe far limit of a plate subduction process and its related far‐field dynamic process are fundamental topics for plate tectonics. The Great Khingan Range (GKAR) in the western flank of NE China is currently under the far‐field influence of the Pacific plate subduction. Benefiting from the newly deployed seismic arrays in the northern GKAR, we take full advantage of seismic data from both temporary and permanent networks and employ an improved scheme of the H‐κ stacking method by introducing surface wave dispersion to obtain the integrated maps of Moho depth and crustal bulk Vp/Vs ratio in this region. Our results show that the Moho depth has a giant step near the North–South Gravity Lineament (NSGL). Meanwhile, the distribution of bulk Vp/Vs ratio presents a north–south difference roughly by 50°N, where the south subregion consists of a collage of high and low Vp/Vs ratio; by contrast, the north subregion is characterized by unified high values. The east‐west structural discrepancies across the NSGL from the Earth's surface to the mantle transition zone indicate the difference in the strength of modifications between the near and far‐fields from the Pacific plate subduction. The complicated distribution of the Vp/Vs ratio in the south subregion supports that secondary small‐scale upwellings underneath the Cenozoic volcanic groups dominate the tectonic reworking in this area. The lack of Cenozoic volcanism and a more straightforward distribution of the Vp/Vs ratio in the north subregion might allude to a tectonically inactive part of NE China.

Shear wave splitting and mantle dynamics of the southern Great Xing'an orogenic belt

We deployed a linear seismic array consisting of 50 broadband stations in the southern part of the Great Xing'an orogenic belt to investigate seismic anisotropy in the Songliao Basin, the orogenic belt and the Erlian Basin by making SKS wave splitting measurements. Different features of anisotropy are revealed on the two sides of the north-south gravity lineament. The anisotropy on the east side of the gravity lineament primarily results from mantle flows in the big mantle wedge above the flat Pacific slab in the mantle transition zone, and the SKS fast polarization direction is generally NW-SE, being consistent with the subduction direction of the western Pacific plate. On the west side of the gravity lineament, the SKS splitting is attributed to freezing anisotropy in the stable lithosphere under the Erlian Basin. The SKS splitting delay times show some changes with azimuths of the teleseismic events, but the fast polarization directions are generally the same, indicating that the anisotropies below these seismic stations have the same origin in the continental lithosphere and active flows in the big mantle wedge.

Anisotropic Rayleigh wave tomography revealed lithospheric modification and tectonic deformation mechanisms in Hubei Province, central China

The collision of the North China and Yangtze blocks, along with multiple orogenic movements, has caused complex tectonic deformation of the lithosphere in Hubei Province. In order to reveal the stress distribution features and tectonic deformation mechanisms of the regional lithosphere, we inverted an azimuthal anisotropic structural model of the Hubei lithosphere from anisotropic Rayleigh wave tomography with data obtained from 48 broadband seismometers deployed in and around the province. Our model revealed strong lateral variations of azimuthal anisotropy in the crust and upper mantle, providing new seismological evidence for the lithospheric modification of the Yangtze block and the layered deformation of the lithosphere east of the North-South Gravity Lineament. We speculate that the primary dynamic factor causing lithospheric modification in the Yangtze block is related to the rifting events associated with the super-mantle plume, triggered by the deep subduction of the Pacific and Philippine plates. Meanwhile, the rifting event is also the main cause of the lithospheric structural layered deformation east of the North-South Gravity Lineament. The inverted anisotropic model, together with the results of previous geodetic and seismologic studies, revealed the causes and tectonic deformation mechanisms of anisotropy generation in the crust and upper mantle in Hubei Province. Crustal deformation in the Hubei region may be related to the eastward expansion of materials from the Tibetan Plateau and the ultra-high pressure metamorphic zone formed by the subduction and collision of the Yangtze and North China blocks, while upper mantle deformation is associated with subduction and collision of Yangtze and North China blocks, preserved fossil anisotropy from previous orogenic movements, and rifting events tied to the super-mantle plume induced by the deep subduction of the Pacific and Philippine plates. Moreover, we analyzed the regional crust-mantle coupling mechanism and concluded that the crust-mantle in the Dabie orogenic belt is coupled, whereas it is decoupled in other regions.

High-resolution lithospheric structure of continental China from joint inversion of surface wave and gravity data

The lithospheric structure of continental China has been previously determined by seismic travel time tomography, surface wave tomography, and joint inversion of body wave and surface wave data. However, due to the inherent limitations of seismic data, the lithospheric structure of continental China is still not well resolved in the shallow part and in some regions where the station coverage is relatively sparse. In this study, we aim at improving the lithospheric structure by joint inversion of seismic surface wave data and satellite gravity data to take advantage of the uniform distribution and complementary strength of the gravity data. The empirical relationship between velocity and density is used as a bridge for joint inversion of surface wave and gravity data. The joint inversion shear-wave velocity Vs (density) model, named as USTClitho1.0g, can fit both surface wave and gravity data well. This high-resolution Vs model can better fit the active airgun source seismic arrival times and better delineate some features in continental China, such as the velocity contrast across the north–south gravity lineament (NSGL), the lithosphere thinning in eastern China, the crustal footprint of the Hainan mantle plume, the likely magma chamber beneath volcanos in northeast China, the middle-lower crust low velocity layer beneath the Tibetan plateau, and the tearing of subducted Indian mantle lithosphere. Our joint inversion Vs model can provide a reference model for geosciences in continental China and surrounding areas.

CONTRIBUTION OF AEROGRAVITY DATA INTERPRETATION TO THE STUDY OF THE DEEP STRUCTURE OF AGADEM PETROLEUM BLOCK (NIGER)

The main information provided by gravity maps is the geographical distribution of density heterogeneities in the subsurface. It is an important tool widely used for the mapping of geological structures, especially in the oil industry. Thus, this study based on the interpretation of aerogravity data has for objective, the qualitative description of the characteristics of the gravity anomalies of the study area, interpretation and mapping of the gravity lineaments as well as their depths, knowing that the lineaments constitute potential structural traps favorable to the accumulation of the hydrocarbons. Methods such as horizontal derivative, upward continuation and Euler deconvolution are used to give a geological signifiance to the different anomalies and to highlight deep structures. Thus, the analysis of the residual anomaly map revealed elongated negative and positive anomaly zones, oriented globally NW-SE, considered respectively as horst and graben zones. Gravity lineaments, considered as normal faults, are mapped using the horizontal gradient method. Finally, the depths of the density contrasts are estimated by the Euler deconvolution calculation using the value “1” as structural index. The depths thus determined are highly variable. The shallowest depths vary between 3000 m and 6000 m, while the deepest depths reach 18000 m.

Mapping of the Structural Lineaments and Sedimentary Basement Relief Using Gravity Data to Guide Mineral Exploration in the Denizli Basin

The Aegean Graben System is a complex tectonic structure in Western Anatolia and the Denizli Graben is a member of this system that hosts many geothermal springs, ore deposits, and travertine areas. In this study, the gravity data were analyzed to determine the subsurface geological structures and the depth model of the basin. The Bouguer gravity anomaly has a NW–SE pattern that is consistent with the general trend of the Denizli Basin. The pre-Neogene basement depths range from 0.1 km to 2.3 km. The Denizli Basin is composed of the Çürüksu Basin and the Laodikia sub-basin. The basins have undulated structures with many depressions; the deepest depression region is in the northern part of the Çürüksu Basin, which is close to the Pamukkale Fault Zone. In addition, the new gravity lineament map was obtained by using new-generation edge detection techniques: the tilt angle of the horizontal gradient amplitude (TAHG), and fast sigmoid-edge detection (FSED) of gravity data. The new proposed lineament map shows that the Denizli Basin has complex structures consisting of NW–SE, E–W, and NE–SE trending lineaments, and the major NW–SE trending faults and NE–SW trending lineaments control the main structural configuration. The uplifts and depressions in the basin deposit and the intersection area of lineaments are promising prospective areas for mineral deposits and have energy resource potential.

Influence of subducted carbonate on the composition of basalts in the Paleo-Asian Ocean domain

The fate of subducted carbonate of the Paleo-Asian Ocean and its control on the compositional variability of Cenozoic basalts to the west of the Daxing'anling–Taihang Gravity Lineament remain uncertain. Here we report major- and trace-element contents and Zn–Sr–Nd isotopic data for Cenozoic basalts from eastern Mongolia. The studied basalt samples from eastern Mongolia are classified as nephelinite, basanite, alkaline basalt, and tholeiite. They have different Zn–Sr–Nd isotopic compositions (δ66Zn = 0.38‰ ± 0.02‰ to 0.50‰ ± 0.04‰, 87Sr/86Sr = 0.704239–0.705175, εNd = 4.72–5.67) but display trace-element signatures of sedimentary marine carbonate, reflecting mantle heterogeneity and marine carbonate imprint. Compared with the high-Si tholeiites, which were erupted over thinner lithosphere, the nephelinites–basanites–alkaline basalts erupted over thicker lithosphere have higher δ66Zn values, La/Yb, Sm/Yb, and Nb/Y ratios, and Nb contents, indicating that these low-Si basalts were the product of lower-degree melting of carbonated mantle under higher pressure. By combining our data with available data for Cenozoic basalts from central Inner Mongolia, we suggest that the compositions of the nephelinite–basanite–alkaline-basalt–tholeiite suite show systematic spatial variation with respect to the northward subduction zone of the Paleo-Asian Ocean. The tholeiites, which have lower δ66Zn values, SiO2 contents, and Sm/Yb ratios, are dominant near the subduction zone, whereas the basanites and alkaline basalts, which have higher δ66Zn values, Sm/Yb ratios, and SiO2 contents, are dominant in the region far from the subduction zone. On the basis of a mixing model for Sr–Nd–Zn isotopic compositions, we suggest that the mantle source of the basanites and alkaline basalts incorporated a higher proportion of marine carbonate, whereas the tholeiite mantle source incorporated a higher proportion of siliceous sediments. We deduce that with increasing depth of slab subduction, more sedimentary carbonates and lesser siliceous sediments were released from the subducted slab.

Cenozoic mantle plume activity in East Asia: Constraints from geochemistry of olivine, spinel, and melt inclusions

It is generally believed that the Cenozoic basalts distributed across eastern China, east of the Daxinganlin-Taihangshan gravity lineament (DTGL), are related to the big mantle wedge (BMW) beneath East Asia. Basalts that are widely distributed across central and eastern Mongolia form a contemporaneous ‘diffuse’ igneous province with similar major element, trace element and Sr-Nd-Hf-Pb isotopic characteristics to those in eastern China. However, they are located to the west of the DTGL, far from the influence of the BMW system. To explain the consistency of geochemistry and eruption ages of Cenozoic basalts on both sides of the DTGL, we have analyzed the compositions of Cenozoic basalts, olivines, spinels, and olivine-hosted melt inclusions from central-eastern Mongolia. We report olivine crystallization temperatures (Tc, up to 1404 and 1343 °C in central and eastern Mongolia, respectively) and mantle potential temperatures (Tp: 1456–1519 °C in eastern Mongolia) that are much higher than those in the MORB source (Tc 1230–1300 °C and Tp ∼ 1350 °C), indicating that there are thermal anomalies in the mantle sources feeding the central-eastern Mongolia volcanism. The Pb isotope ratios of basalts and olivine-hosted melt inclusions on both sides of the gravity zone show a linear array between EM1 and FOZO mantle components, which can be explained by the mixing of ancient recycled ocean crust (EM1-like) with lower mantle peridotite (FOZO-like) in different proportions. Combined with reported high Tp, 3He/4He, and a low-velocity anomaly extending to the lower mantle in the source of the Cenozoic basalts in East Asia, we propose a branched plume model that could explain the similarity of geochemistry and eruption ages for Cenozoic basalts on both sides of the DTGL.

Coupling between Cenozoic extensional exhumation in North China and the subduction of the Pacific Plate

Both the timing and mechanism for the formation of the topographic stepping in East Asia along the North-South Gravity Lineament (NSGL) are critical to understand the coupled influence of tectonics, climate, and surface processes on landscape evolution. The Yanshan Mountains lie in the central portion of the NSGL and offer a chance to reveal the link between surficial tectonic deformation and the underlying subduction to understand the continental dynamics and paleoclimate of NSGL. In this study, we report 22 new apatite (UTh)/He (AHe) data from the Yanshan Mountains. Age-elevation profiles indicate a period of rapid exhumation initiated at ∼27–26 Ma, while the AHe ages generally increase with the distance from the fault coincides with northwestward tilting of the fault footwall. Combining a series of shallow extensional events in East Asia with deep process of the Pacific plate subduction, we suggest that the widely-distributed late Oligocene rapid exhumation represents a phase of Cenozoic re-destruction of the North China Craton (NCC). The Cenozoic re-destruction of the NCC and topographic stepping along the NSGL may be related to the retreat, dehydration, and decarbonization of the underlying stagnant Pacific slab.

Undulating electrical lithosphere–asthenosphere boundary beneath Northeast China; as revealed by long–period magnetotelluric data

The geometry of continental lithosphere–asthenosphere boundary (LAB) significantly affects the movements of tectonic plates and flow of the upper mantle. However, the properties and geometry of this boundary beneath tectonically active regions in Phanerozoic continents are mysterious and elusive. Ninety–three long–period magnetotelluric (LMT) observations across Northeast China (NEC) provide a unique opportunity to image the shape of the LAB. Probabilistic resistivity–depth model inversion was employed to obtain the one–dimensional resistivity structure beneath each LMT site. The depth of the electrical LAB is constrained by the most probable interface at which the resistivity changes rapidly from high to low. The inversion results show that the electrical LAB is undulating beneath NEC. The North–South Gravity Lineament marks the transition from deep to shallow LAB. The thickest lithosphere occurs beneath the Great Xing'an Range (GXAR), where the LAB is ∼200 km deep. The electrical lithosphere is relatively thin in the east, with the thinnest lithosphere (∼50 km) being found beneath the Changbai Mountain volcano. We speculate that melt depletion, together with possible mantle downwelling are the likely causes for the formation of the thick GXAR lithosphere. The unresolved lithosphere beneath the northern Songliao Basin could be ascribed to the strong attenuation of electromagnetic waves in highly conductive sedimentary layers or the weak difference in the resistivity of the lithosphere and asthenosphere. The lithosphere steps that can form the edge-driven convection in the asthenosphere may play key roles in forming the widely-spread intraplate magmatism in NEC.

Characteristics of lineaments using gravity data in the Eastern Cameroon: Structural, hydrogeological and natural risks implications

The East region of the Cameroon is situated in the Adamaoua Yadé Domain, which is composed of CCSZ (Central Cameroon Shear Zone) and Sanaga fault that induced many tectonic movements affecting the studied area. The faults caused by these movements are not yet described. The aim of this work is to improve the knowledge of the tectonic structures in the study area (especially faults) through the exploitation of Bouguer anomaly in view of proposing a structural map that will be useful in the prevention of natural catastrophes related to faults and for hydrogeological prospection. In order to characterize these structures, two methods have been used: the multi-scale analysis of the maxima of the horizontal gradient and the Euler's deconvolution methods. The superposition of Euler's solutions to the maxima of the horizontal gradient extended upwards at several altitudes allowed to highlight the gravity lineaments that are either faults or linear contacts and to draw a structural map of the study area. From the map obtained, thirty eight lineaments have been identified, from which twenty seven linear contacts and eleven faults, which have the depth situated between 5 and 10 km, 15 and 20 km, 15 and 25 km, and 20 and 25 km. The analysis revealed that the deepest faults can constitute a natural risk in the study area. These deep faults require a monitoring within the framework of civil protection. The structural map, combined with the water system and boreholes helped to identify potential productive boreholes. The structural map obtained increases the geologic knowledge of the area and constitutes a useful document in natural risk prevention and the siting of boreholes.

Electrical resistivity structure across the Late Cenozoic Abaga-Dalinor volcanic field, eastern China, from 3-D magnetotelluric imaging and its tectonic implications

The Abaga-Dalinor volcanic field (ADVF) in Inner Mongolia, China, located to the west of the North-South Gravity Lineament (NSGL), is the largest and less known area of Late Cenozoic intraplate volcanism in Northeast China. Knowledge of the subsurface structure beneath the ADVF will improve our understanding of its evolution process and formation mechanisms. New broadband magnetotelluric (MT) data were collected along a profile of about 300 km that crosses the major basaltic areas exposed at the surface in the ADVF and a series of east-north-east (ENE) trending faults. The electrical resistivity structure of the crust and uppermost mantle across the ADVF was generated by 3-D inversion of full impedance tensor and tipper data. This model reveals a thick high-resistivity layer (>1000 Ωm) in the upper crust that may represent the Precambrian basement and Late Paleozoic-Mesozoic granitic plutons. In contrast, high conductivity anomalies dominate the middle-lower crust. The northward-dipping high-conductivity feature at depths of 20–40 km below sea level under the Chagan Obo fault is suggested to be the involvement of the Early Paleozoic subducted oceanic crust. A remarkably high-conductivity zone (1–20 Ωm) exists in the middle-lower crust beneath the Abaga and Dalinor volcanic areas. It is explained to be a saline fluid zone of ∼0.45%–0.48% that exsolved from the partial melts as magma ascent rapidly. The impermeable upper crust traps these fluids in the middle-lower crust. A moderately high-conductivity anomaly in the uppermost mantle below near the Solonker Suture Zone (SSZ) is attributed to a minimum partial melt of ∼3–4% associated with the localized asthenospheric upwelling, which feeds the Abaga and Dalinor volcanos as a common magma source. Integrating our resistivity model with previous geophysical and geochemical studies, we suggest that intraplate volcanism in the ADVF is mainly controlled by the pre-existing tectonic weak zones. The lithosphere within the SSZ is susceptible to thermal perturbation from the upwelling mantle, providing the preconditions for melt generation. A set of ENE trending faults and an inferred NW-SE trending fault jointly dominated the vertical transport of magma and lateral extension along the faults, which may have influenced the spatial distribution of basalts and volcanic cones at the surface in the ADVF. In addition, we tend to suggest that Late Cenozoic intraplate volcanism in the ADVF could be the result of decompressing melting within the localized small-scale asthenospheric upwelling induced by the edge-driven convection near the NSGL, which is indirectly related to the westward subduction and retreat of the (Paleo-)Pacific plate during the Late Mesozoic to Cenozoic.

Continental Reworking in the Eastern South China Block and Its Adjacent Areas Revealed by F‐J Multimodal Ambient Noise Tomography

AbstractThe eastern South China Block (SCB) has experienced complex and drastic reworking processes since the early Neoproterozoic, the mechanisms of which remain unclear. To better understand the continental reworking mechanisms in the eastern SCB, we imaged the shear‐wave velocity structure of the crust and upper mantle in the eastern SCB and its adjacent areas with the F‐J multimodal ambient noise tomography method. The seismic ambient noise data were acquired by 652 seismic stations in this area. The shear‐wave velocity model presents widespread mid‐crustal low‐velocity zones (MCLVZs) and upper mantle low‐velocity zones (UMLVZs), the distribution of which shows a good correlation with regional tectonics. The MCLVZs formed due to compositional and structural layering during the late Neoproterozoic to the early Phanerozoic. The disrupted MCLVZs near the Qinling‐Dabie orogen can be linked to metamorphism caused by a continental collision between the SCB and the North China Craton during the Triassic Indosinian event. The thin crustal and lithospheric thicknesses east of the North‐South Gravity Lineament may be the result of asthenospheric upwelling due to the subduction of the Pacific plate since the late Mesozoic. In the areas near the Shaoxing‐Jiangshan‐Pingxiang fault zone and the Tanlu fault zone, upheaval UMLVZs indicate that these ancient fault zones were reactivated by the subduction of the Pacific plate, providing channels for asthenospheric upwelling. Well‐preserved MCLVZs north of the Qinling‐Dabie orogen can be used to assess compressions and extensions induced by the subduction of the Pacific plate.

Carapaces of the Dnieper-Donets Basin as a New Exploration Target for significant hydrocarbon deposits

New geological structures — displaced blocks of salt overburden — were identified in the axial part of the Dnieper-Donets basin (DDB) beside one of the largest salt domes due to modern high-precision gravity and magnetic surveys and their joint 3D inversion with seismic and well log data.
 Superposition of gravity lineaments and wells penetrating Middle and Lower Carboniferous below Permian and Upper Carboniferous sediments in proximity to salt allowed proposing halokinetic model of displaced salt overburden, assuming Upper Carboniferoussalt reactivation.
 As an analogy todescribed halokinetic deformationswe consider rafts and carapaces of the US Gulf of Mexicobasin.
 Density of Carboniferous rocks within the displaced blocks evidence a high probability of hydrocarbon saturation. Possible traps include uplifted parts of the displaced blocks, abutting Upper Carboniferous reservoirs, and underlying Carboniferous sequence. Play elements (reservoir type and quality, seals, hydrocarbon generation) are analyzed using analogues from the Dnieper-Donets basin and the Gulf of Mexico basin.
 Hydrocarbon reserves of the displacedblocks within the study area are estimated to exceed Q50 (Р50)=150 million cubic meters of oil equivalent.

Thermal and rheological structure of lithosphere beneath Northeast China

We investigate 3-D thermal and rheological structures of the lithosphere beneath Northeast China using detailed P- and S-wave velocity models following mineral physics as well as geothermal methods. Small-scale temperature changes and thermal lithosphere thickness variations between different tectonic blocks are revealed. Our results show that strong lateral heterogeneities exist in the lithospheric thermal structure and rheological structure on both sides of the North-South Gravity Lineament (NSGL). The Changbai volcanic area and the central part of the Songliao Basin in the eastern side of the NSGL exhibit higher temperatures, thinner thermal lithosphere and lower rheological strength, which are closely associated with the western Pacific plate subduction under the Eurasian continent, resulting in upwelling of wet and hot asthenospheric material above the stagnant Pacific slab in the mantle transition zone. The thermo-chemical erosion of the upwelling asthenospheric material may induce delamination of partial lithosphere under the Songliao Basin. In addition, the western and southern edges of the Songliao Basin are characterized by lower temperature, thicker thermal lithosphere and higher rheological strength, which may indicate a relatively stable lithosphere. The Halaha and Abaga volcanic areas in the western side of the NSGL exhibit higher temperature, thinner thermal lithosphere and lower rheological strength, which could be caused by small-scale upwelling of hot asthenospheric material associated with delamination of partial lithosphere beneath the Songliao Basin.

Two-dimensional electrical resistivity structure of the crust and upper mantle across the North-South Gravity Lineament in NE China

The North-South Gravity Lineament (NSGL) is a large anomalous gravity zone that traverses several tectonic units with different properties in northeastern China. Its deep structural features and formation mechanism have long been a topical area of deep geophysical research. This study presents a magnetotelluric profile that extends from the Dongwuqi to Tongliao in Inner Mongolia and passes through geological structures such as the NSGL. Dimensional analysis of the profile data reveals good overall 2D features. 2D nonlinear conjugate gradient inversion of the profile data produced a model of the deep electrical structure. Horizontally, the electrical structure along the profile displays different characteristics in different blocks. The NSGL serves as a boundary for the change in the depth of the Moho discontinuity. Specifically, the Moho discontinuity is deep on the west side of the NSGL and shallow on its east side. Overall, the thickness of the lithosphere varies nonsignificantly, except in the western part of the profile, where the presence of a large low-resistivity anomaly in the shallow layer obscures the boundary of the lithosphere. The large high-resistivity anomaly in the center of the profile may be an indication that the partial delamination of the lithosphere caused by the convection of mantle materials and the upwelling of high-density mantle materials under the action of the westward subduction of the Pacific plate were the major causes of large positive gravity anomalies on the east side of the NSGL. The west side of the NSGL was predominantly controlled by the closure of the Mongol-Okhotsk Ocean, resulting in an increase in the thickness of the crust, which led to the formation of large negative gravity anomalies. These two factors collectively led to the formation of the NSGL.

Lithospheric Structure in Central-East China from Joint Inversion of Surface-Wave Dispersion and CCP-Derived Receiver Function: Implications for Regional Tectonics

Abstract To investigate the lithospheric deformation beneath central-east China, we constructed a 3D crustal and uppermost-mantle velocity model of this region by joint inversion of Rayleigh-wave phase velocities and common conversion point-derived receiver functions. The velocity images at the east and west sides of Xuefeng Mountain presented quite different features and a sharp change in lithospheric thickness beneath this mountain, suggesting that this mountain may be the southwestern segment of the boundary between the Yangtze craton (YZC) and the Cathaysia block (CAB). We observed extensive lithospheric thinning in the eastern South China block (SCB), including the CAB and lower YZC. Considering that the eastern SCB is within the influence of the circum-Pacific system and features intensive Mesozoic magmatic activity, we deduced that subduction of the Pacific plate was the main controlling factor of lithospheric thinning. The westward extension of lithospheric thinning in the SCB terminates in the area east of the north–south gravity lineament. We observed a large-scale, low-velocity zone in the uppermost mantle of the southern Trans-North China orogen that penetrates northwestward into the southeastern corner of the Ordos block. The low-velocity zone intrudes into the bottom of the crust and results in crustal thinning in the region. We proposed that both the southern Trans-North China craton and the southeastern Ordos block are suffering ongoing lithospheric mantle modification.

Distinct Lithospheric Structure in the Xing'an‐Mongolian Orogenic Belt

AbstractDetailed knowledge of the lithospheric structure is essential for a better understanding of the tectonic evolution of the Xing'an‐Mongolian Orogenic Belt (XMOB). We constrained the lithospheric structure across the XMOB by receiver function imaging and shear wave splitting analysis from a dense seismic array. The lithosphere‐asthenosphere boundary (LAB) is coherently imaged in different tectonic blocks. The mid‐lithospheric discontinuity is also identified at ∼75–100 km depth over the deeper LAB (∼110–130 km) beneath the western side of the North‐South Gravity Lineament (NSGL), roughly at the same depth as the LAB beneath the eastern side of the NSGL. The distinct variations in both the lithospheric structure and fast shear‐wave polarization direction across the NSGL are likely caused by different tectonic processes in the two sides, indicating that the NSGL might represent the western boundary influenced by the subduction of the (Paleo‐)Pacific Plate. Lithosphere thinning in the XMOB is evidenced to have been limited mainly to the east of the NSGL.