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The Kumkol basin is located in the northern Tibetan Plateau and is a closed plateau basin with an average altitude of >4000 m and an area of nearly 20000 km2. Its boundaries are limited by the Altyn Tagh fault, East Kunlun orogen and Qimantag orogen. Studying the deep structure of the Kumkol basin reveals 2 significant implications: (1) the basin has developed a large thickness of >7000 m Cenozoic continental sediments, recording the uplift history of the northern Tibetan Plateau, and (2) preliminary work indicates that the basin is likely to have oil and gas prospects. However, owing to the adverse natural conditions of the area and the strong tectonic activity in the Cenozoic, the latter of which was not conducive to hydrocarbon preservation, only regional geological mapping and petroleum exploration route surveys have been carried out, and there is no consensus on strata, structure and tectonic evolution. From 2021 to 2022, a deep seismic reflection profile implemented by the Second Tibetan Plateau Scientific Expedition and Research (STEP) project was the first high-resolution geophysical survey across the Kumkol basin. This study uses seismic reflection migration profiles, first-arrival wave tomographic imaging and previous research results to analyze the deep structure of the basin. The final merged model contains many features of tectonic and resource significance: (1) The Kumkol basin is ∼90 km wide from north to south, with a basement depth of >9000 m. The main component is the Cenozoic continental deposits, which are divided into two major parts: the southern composite basin and the northern faulted basin. Owing to the later compression, the southern composite basin experienced significant deformation, but most parts still preserved their original sedimentary formations. (2) The structural deformation characteristics of the basin reveal a two-stage tectonic evolution process of the northern Tibetan Plateau in the Cenozoic: from the Oligocene to the Pliocene, the main mechanism was vertical differential uplift and subsidence, and after the Pliocene, it transformed to north-south compression and shortened deformation. (3) The strata, formation time, and source-reservoir-cap conditions of the Kumkol basin are similar to those of the Qaidam basin. If a breakthrough can be achieved, it is expected to expand the production capacity of the oil field in the Qaidam basin with a low-cost investment. Thus, further exploration is recommended. [ABSTRACT FROM AUTHOR]

[Display omitted] • The upper crustal structures of "Double Domes" in the eastern Tethys Himalaya are obviously different. • There are significant differences in the velocity structure of the metal deposits around the Cuonadong dome. • The upper crust of the " Double Domes " has obvious thermal structure characteristics. The Tethys Himalayan belt in the southern Qinghai–Tibet Plateau has been intruded by a large amount of leucogranite due to collisional orogeny. In addition, strong tectonic movements since the Cenozoic era have led to the formation of a series of dome structures accompanied by various types of mineralization. The Cuonadong Dome and Yalaxiangbo Dome, forming the "double dome" structure in the eastern part of the Tethys Himalayan Belt, are affected by different geological processes, resulting in differences in their deep structures and affecting the formation of polymetallic minerals. At present, geophysical research on the fine structure of the crust of the "double dome" structure is limited, making it difficult to fully understand the formation of different deep structures in the Tethys Himalayan dome belt. This hinders the progress of research on the genesis of dome structures and large-scale mineralization mechanisms in continental collisional environments. In this study, the ambient noise tomographic method was used to obtain the S-wave velocity structure of the upper crust of the Cuonadong Dome and the Yalaxiangbo Dome, and the following results were found: 1. there is a significant difference in the velocity structures of the two domes, with the core velocity structure of the Yalaxiangbo Dome showing an overall high velocity, extending downward for more than 9 km, while the core of the Cuonadong Dome exhibits low-velocity characteristics, with some high-velocity bodies occurring locally, which may be related to the later intrusion of leucogranite and extensional activity of the Cuona Rift. 2. There are significant differences in the S-wave velocities between the lead–zinc deposits and rare metal deposits in the study area; the lead–zinc deposits occur in basins and graben margins and have large variations in the S-wave velocity, which may be related to the involvement of basin brine in mineralization; below the tungsten–tin–beryllium deposits, the S-wave velocity exhibits high-velocity protrusions, with mineralization occurring at the front ends of the protrusions, which may be caused by crystallization differentiation of leucogranite. 3. The study area has abundant geothermal resources and obvious geothermal structural features. The low-velocity basin in the upper part of the upper crust is a heat storage layer, the low-velocity channel in the middle is a heat-conducting layer, and the lower part is a low-velocity heat source area that continuously supplies heat, forming a special geothermal structural model for the Cuonadong Dome and Yalaxiangbo Dome. [ABSTRACT FROM AUTHOR]

As interference waves in deep reflection data processing, surface waves are often suppressed as noise, but surface waves carry considerable underground media information, including structural information and the physical properties of rocks. Reasonable extraction and use of surface wave signals are of great significance when studying shallow characteristics. Deep reflection data are collected using large offsets, trail spacing, and explosive sources. The surface wave energy tends to be stronger, and the high-frequency surface wave signal is abundant. After extraction and inversion, the shallow shear wave velocity structure can be obtained. Near the Cuonadong dome in the southern Tibetan detachment system (STDS), a large number of leucogranites are developed in the core, containing important rare metal minerals and high metallogenic potential. However, studies regarding the shallow structure in this region are rare. In this paper, we use deep reflection data from a profile through the Cuonadong dome to obtain the S-wave velocity structure of the study area by extracting the surface wave fundamental-mode dispersion curve and inversion. Combined with regional geological and magnetotelluric data, we supposed that the thickness of the Cuonadong dome sediment layer (< 1.4 km/s) varies greatly from east to west, the thickness of the sediment layer is the deepest near the Cuona fault and Jisong fault (more than 1 km), and the core of the dome is the thinnest. Under the Cuonadong dome, there are obvious high-velocity anomalies (> 2.2 km/s), and the horizontal S-wave velocity changes greatly, which is mainly related to the destruction of magmatic activity since the Miocene. These understandings of the structure and velocity field of the Cuonadong dome can provide a powerful geophysical basis for establishing the dome structure model and searching for hidden ore bodies. [ABSTRACT FROM AUTHOR]

The Central Yunnan block (CYB) plays a key role in accommodating the crustal tectonic deformation of the southeastern Tibet, but its exact mechanism is poorly understood. Here we obtained a fine S-wave velocity structure of the upper crust across the Xiaojiang fault system in CYB, using the ambient noise tomography with a linear dense short-period array. The result shows a strong S-wave velocity variation along the profile, which is consistent with geomorphology and hypocenters occurred in this area. The velocity variations along the profile correspond well to the major faults seen on the surface and are consistent with the transition from surface erosion, to ductile basement and to rigid basement in the greater depth. Combining the upper crustal structure from our image with the location of hypocenters, we propose that most faults of Xiaojiang fault system cut through the upper crust steeply and control the tectonic deformation of the upper crust in the CYB. • Ambient noise tomography shows a fine S-wave velocity structure of the upper crust across Xiaojiang fault system. • The velocity variations along the profile correspond well to the major faults seen on the surface and are consistent with geomorphology and hypocenters occurred in this area. • Most faults of Xiaojiang fault system cut through the upper crust steeply and control the tectonic deformation of the upper crust in the Central Yunnan Block. [ABSTRACT FROM AUTHOR]

The North Himalayan gneiss domes (NHGD), as one of the extensional structures widely distributed across the southern Tibetan Plateau, are an important window for studying post-collisional diastrophism and magmation as well as polymetallic mineralization. However, the deep mechanism for the formation of NHGD remains controversial. The magneto-telluric (MT) method was adopted to study the deep structure of the Cuonadong dome in the Northern Himalayas. The characteristics of the dome were explored by using the MT sounding curves and phase tensors. Three-dimensional (3D) MT inversion was performed to determine the electrical resistivity structure beneath the Cuonadong dome. The preferred 3D electrical resistivity model shows that an obvious low-resistivity anomaly develops beneath the Cuonadong dome which is overlaid by a high-resistivity body and surrounded by an apparent subcircular zone of low-resistivity anomalies. The integrated conductivity (longitudinal conductance) from depths of 1–20 km indicates that the average longitudinal conductance at the core of the Cuonadong dome is about 10,000 S. The high-conductivity anomaly at the core is found to be analogous to that of lava, mainly resulting from the crustal partial melting, and the estimated melt content is 11.0–17.3%. The high conductance surrounding the dome reaches 20,000 S on average, which is mainly attributed to saline fluids. MT results in this study support that the Cuonadong dome experienced magmatic diapirism. Taken together with previous geological and geochemical studies, we suggest that under the east-west (E-W) extensional tectonic setting in southern Tibet, deep crustal partial melting constantly accumulated beneath the dome, and therefore the magmatic diapirism resulted in the formation of the Cuonadong dome. In addition, the MT results also indicate that the development of the Cuonadong dome provides abundant mineralizing fluids and the space for migration of metallogenic fluids for (rare-metal) polymetallic mineralization. [ABSTRACT FROM AUTHOR]

The North Himalayan gneiss domes (NHGD), as one of the extensional structures widely distributed across the southern Tibetan Plateau, are an important window for studying post-collisional diastrophism and magmation as well as polymetallic mineralization. However, the deep mechanism for the formation of NHGD remains controversial. The magneto-telluric (MT) method was adopted to study the deep structure of the Cuonadong dome in the Northern Himalayas. The characteristics of the dome were explored by using the MT sounding curves and phase tensors. Three-dimensional (3D) MT inversion was performed to determine the electrical resistivity structure beneath the Cuonadong dome. The preferred 3D electrical resistivity model shows that an obvious low-resistivity anomaly develops beneath the Cuonadong dome which is overlaid by a high-resistivity body and surrounded by an apparent subcircular zone of low-resistivity anomalies. The integrated conductivity (longitudinal conductance) from depths of 1–20 km indicates that the average longitudinal conductance at the core of the Cuonadong dome is about 10,000 S. The high-conductivity anomaly at the core is found to be analogous to that of lava, mainly resulting from the crustal partial melting, and the estimated melt content is 11.0–17.3%. The high conductance surrounding the dome reaches 20,000 S on average, which is mainly attributed to saline fluids. MT results in this study support that the Cuonadong dome experienced magmatic diapirism. Taken together with previous geological and geochemical studies, we suggest that under the east-west (E-W) extensional tectonic setting in southern Tibet, deep crustal partial melting constantly accumulated beneath the dome, and therefore the magmatic diapirism resulted in the formation of the Cuonadong dome. In addition, the MT results also indicate that the development of the Cuonadong dome provides abundant mineralizing fluids and the space for migration of metallogenic fluids for (rare-metal) polymetallic mineralization. [ABSTRACT FROM AUTHOR]

Abstract: The Qiangtang Basin, located in central Tibet, is a thick and widely developed Jurassic marine sedimentary stratum, and it is the largest marine basin on the Chinese mainland without a breakthrough in oil or gas exploration. Various forms of crustal movement related to the convergence between the Eurasian and Indian plates in the Cenozoic have played significant roles in the formation and preservation of the oil and gas resources of the Qiangtang Basin. To determine the shallow crustal structure of the Qiangtang Basin and forecast its prospects for oil and gas extraction, we reprocessed the seismic reflection data (0–6s TWT) from 11 reflection sections acquired at different times by different groups and connected them to form a 350-km shallow seismic reflection profile across the Qiangtang Basin. This profile provides reliable data on the north to south changes of the basement and the upper crustal structures of the Qiangtang Basin. We speculated that the reflective events at 3–4s TWT in the Qiangtang Basin represent the Paleozoic basement, which runs shallow beneath the central anticline. The location of the Proterozoic basement was determined from the discontinuous reflection events at approximately 4.5s TWT. The data indicate that the basements of the Qiangtang Basin are deeper in the south and shallower in the north. The shallow crustal deformations (approximately 0–3s TWT) are quite different between the north and south Qiangtang Basin. In the north Qiangtang Basin, there are strong fold deformations alternating between uplifts and depressions, while the deformations are relatively flat in the south Qiangtang Basin. Continuous arc reflections, interpreted as Paleozoic strata, were found beneath the central anticline of the Qiangtang block. A half graben on the north side of the central anticline represents a possible location for oil and gas resources. [Copyright &y& Elsevier]

Imaging the detailed structure of sedimentary basins is crucial for natural resource exploration and essential for better analysis and correction of sediment responses when studying deeper interior earth structures using seismic data. In the Tarim Basin, previous studies on the sedimentary structures are mostly obtained by active-source seismic surveys, which can provide high-resolution underground interface information but are highly costly or environmentally unfriendly. In this paper, ambient noise tomography, an efficient and economical method based on background vibration, is employed to construct the sedimentary velocity structure at the southeast margin of the Tarim Basin. Based on ambient noise data collected from a linear dense short-period seismic array, we extract Love wave signals from T–T component cross-correlation functions (CCFs) and measure Love wave dispersion curves at a period band of ∼0.3–11.5 s. Then, we utilize a one-step direct surface wave tomography method to image a fine 2-D sedimentary shear wave velocity structure with a depth reaching 10 km. Our results reveal a clear layered sedimentary structure, the palaeo Tadong uplift and the thrust Cherchen fault. Our study provides reference sedimentary velocity models for the southeastern Tarim Basin, focusing on depths shallower than 10 km. This model is intended to serve as crucial input for studies requiring detailed shallow sedimentary velocity data. Moreover, our research demonstrates that the application of the ambient noise tomography method with dense arrays has great potential for enhancing resource exploration efforts in sedimentary basins. [ABSTRACT FROM AUTHOR]

The high topography of the Tibetan Plateau was generated by the Cenozoic India‐Eurasia collision. A high‐resolution shear wave velocity model can provide improved understanding of the Tibetan structure and crustal deformation with complicated tectonic evolution. Based on continuous seismic observations at approximately 400 stations, we collected over 10,000 Rayleigh wave phase velocity dispersion curves extracted from ambient noise cross‐correlation functions. A direct surface wave inversion method was applied to obtain an S wave velocity model of the Tibetan crust. A heterogeneous structure including several prominent low‐velocity zones (LVZs) and relatively narrow low‐velocity bands connecting the LVZs is revealed. Our model shows significant crustal low‐velocity structures with lateral variations along the Himalayan front. In the eastern segment of the Lhasa terrane, the LVZ is spatially correlated with Miocene porphyry Cu deposits, which are probably related to strong tearing of the Indian lithosphere, while preexisting weak zones contribute to the LVZs in the western segment. Meanwhile, the LVZ along the Bangong‐Nujiang suture could be considered as a channel for eastward extrusion of ductile material, that is, crustal flow on geological timescales. This "flow" in the middle‐lower crust probably contributed to the formation of the V‐shaped conjugate strike‐slip fault system in central Tibet. The development of conjugate strike‐slip faults, however, ceased near 90°E, since the eastward "flow" was blocked by an intracrustal high‐velocity block in Amdo. This preexisting rigid zone (containing the Amdo microcontinent) hence influences the pattern of material transport inside the Tibetan crust and the deformation of the plateau. Key Points: Three‐dimensional architecture of crustal low‐velocity zones of the Tibetan Plateau is obtained by dense array ambient noise tomographyLow‐velocity zones along southern Tibet and the Miocene porphyry Cu deposit formation are related to Indian lithosphere tearingEastward crustal flow blocked by a rigid block in Amdo contributed to the formation of conjugate strike‐slip faults in central Tibet [ABSTRACT FROM AUTHOR]

The left‐lateral Altyn Tagh Fault (ATF) system is the northern boundary of the Tibetan Plateau resulted from the India–Eurasia continental collision. How intracontinental deformation across the central ATF responds to the distal collision remains elusive, primarily due to unclear crustal structure. We obtained detailed crustal structure across the central ATF using receiver functions recorded by ∼NW–SE oriented linear dense array. The images reveal the Tarim lower crust is underthrusting beneath the Tibetan Plateau and reaches to a maximum depth of ∼75 km and undergoing partial eclogitization. The two south‐dipping interfaces imaged beneath the Altyn Tagh Range (ATR) represent the thrusting Northern Altyn Fault and its branch fault. Oblique convergent forces extruded upper crustal materials along the thrust faults, creating the pop‐up structure of ATR, supported by low Vp/Vs ratios. Our balanced cross‐section for the Moho suggests intracontinental deformation in the ATR has accelerated since the late Miocene. Plain Language Summary: The Altyn Tagh Fault (ATF), serving as the northern boundary of the Tibetan Plateau, demarcates the Tarim Basin from the Qaidam Basin. Understanding how intracontinental deformation across the boundary region would better inform the uplift and expansion of the plateau. This study reveals the fine crustal structure by analyzing seismic data from a ∼NW–SE oriented linear dense array across the central ATF. Combined with fault slip rates, we propose that the Tarim lower crust is underthrusting beneath the Tibetan Plateau, leading to the extrusion of upper crustal materials and the rapid uplift of the Altyn Tagh Range since the late Miocene, which provides insight into the lateral growth of the plateau. Key Points: Detailed crustal structure beneath the central Altyn Tagh Fault was imaged by receiver functions of a dense 2‐D seismic arrayThe Tarim lower crust is underthrusting to ∼75 km depth beneath the Tibetan PlateauThe Altyn Tagh range was uplifted rapidly since late Miocene through the thickening of the upper crust [ABSTRACT FROM AUTHOR]

The Xiaojiang Fault Zone (XJF) is an important boundary fault on the southeast border of the Tibetan Plateau, with a complex subterranean structure and strong tectonic activity. In the present study, 252 seismograph stations were deployed in the northern section of the XJF to collect ambient noise data in a span of 35 days. The minimum resolution attained was 2 km × 2 km to develop a high-precision underground velocity structure model. The velocity model helped in revealing that the low-velocity distribution originated below the XJF. It was also found that the fault, which is the primary channel for magma to rise, might be the cause of the upper crustal deformation of the XJF. The Dongchuan mining area is located to the west of the XJF, which has a low-velocity structure. However, the high-velocity structure appeared on both sides of the ore body. It is speculated that the ore was formed by magma intrusion. The intrusion serves as a heat source for the mining area and promotes deposit formation. [Display omitted] • A short-period dense array based ambient noise tomography for Xiaojiang fault. • High and low velocity 3D structure under Xiaojiang fault. • Deep ore metallogenesis constraints beneath the Dongchuan ore field. [ABSTRACT FROM AUTHOR]

Internal structure imaging of the Earth, along with determining basin structure, can aid in evaluating potential seismic hazards. However, the high operating cost limits the current geophysical exploration methods; moreover, it is difficult to apply these techniques over a large area, which limits our understanding of the Quaternary structure and the development of earthquake prevention science. A combination of dense array observation technology and ambient noise surface wave tomography is being rapidly developed as a high-resolution urban detection method. Here, we report the ambient noise imaging results of a high-density array experiment. In the ambient noise surface wave tomography method (e.g., surface wave tomography; Eikonal tomography), the signal is assumed to be a single mode. However, several multimode signals were detected in this dataset. With the use of traditional methods to measure the dispersion, mode confusion occurs and the extracted dispersion curve jumps. To solve this problem, by combining the advantages of phase-matched filtering and dispersion compensation, we realized the automatic pickup of fundamental group velocity using reference phase velocity. From this, a Rayleigh wave group velocity map was obtained. The regional average phase velocity information was included in the inversion steps to reduce the uncertainty in the inversion of shear wave velocity. Finally, an S-wave velocity structure model was obtained within a depth of 500 m. The velocity structure was roughly layered and grew with depth. In the depth range of 240–320 m, obvious decreases in the S-wave velocity were observed. Compared with geothermal drilling data, this was speculated to be the reflection of a water-rich (confined water) sand layer. This study provides a technical approach for and a processing example of a high-density array, and its velocity model can be used as a reference for urban subsurface structure, underground space utilization, and earthquake disaster prevention and control. [ABSTRACT FROM AUTHOR]

Deep reflection seismic data are usually accompanied by large-offset data, and the accurate and rapid identification of the first arrivals of seismic records plays an important role in eliminating the effects of topography and other factors that increase with the increasing offsets. In this paper, we propose a method based on convolutional neural networks (CNNs) that can accurately identify the first arrivals of large-offset seismic data. A time window for linear dynamic correction was established to convert the raw seismic data into rectangular images so as to reduce the amount of invalid sample data and improve the training efficiency. In order to enhance the prediction effect of the far-offset first arrivals, we propose the strategy of adjusting the weight of the far-offset data to increase the weight of the far-offset data in the training dataset and, thus, to improve the first arrival accuracy. The manually picked first arrivals are used as labels and the input to the CNNs for training, and the full-offset first arrivals are the output. The travel time tomography velocity is modeled and compared based on the first arrivals obtained through manual picking, industrial software automatic picking, and CNN prediction. The results show that the application of CNNs to large-offset seismic datasets can help researchers to obtain the first arrivals at different offsets, while the inclusion of far-offset weights can effectively improve the modeling depth of the tomography inversion, and the accuracy of the results is high. [ABSTRACT FROM AUTHOR]

Urban structure imaging using noise-based techniques has rapidly developed in recent years. Given the complexity of the cross-correlation function in high-frequency signals, here, the beamforming (BF) method was used to analyze one data set taken from a dense array in the Jizhong Depression and obtain multi-mode dispersion curves. Multi-mode surface waves improved inversion stability, reduced non-uniqueness, and yielded a one-dimensional shear wave (S-wave) velocity model. Interpolation yielded a high-resolution three-dimensional (3D) S-wave velocity model for the study area. The model shows that velocity gradually changed in the horizontal direction and greatly increased in the vertical direction, which is largely consistent with changes in the sedimentary environment related to the continuous subsidence of the Jizhong Depression since the Quaternary. A low-velocity anomaly at a depth of ~300–400 m was revealed and determined to be caused by either a deep-buried ancient river course or low-lying area. This study demonstrates the potential of the BF method for processing dense array data sets of urban exploration. The high-resolution 3D S-wave velocity model provides a new reference for studying the Quaternary structure of the Jizhong Depression, as well as groundwater resources, urban infrastructure, and underground spaces. [ABSTRACT FROM AUTHOR]

The Chuan‐Dian Block (CDB) is located in the southeastern margin of the Tibetan Plateau, with a complex geological structure and active regional faults. The present tectonic condition with strong crustal deformation is closely related to the ongoing collision of the India and Eurasia plates since 65 Ma. The study of the crustal structure of this area is key to revealing the evolution and deep geodynamics of the lateral collision zone of the Tibetan Plateau. Deep seismic sounding is the most efficient method with which to unravel the velocity structure of the whole crust. Since the 1980s, 19 deep seismic sounding profiles have been captured within the CDB area. In this study, we systematically integrate the research results of the 19 profiles in this area, then image the 3D crustal velocity, by sampling with a 5 km spacing and 2D/3D Kriging interpolation. The results show the following. (1) The Moho depth in the study area deepens from 30 km in the south to 66 km in the north, whereas there is no apparent variation from west to east. The Pn wave velocity is higher in stable tectonic units, such as 7.95 km/s in the Lanping‐Simao block and 7.94 km/s in the western margin of the Yangtze block, than in active or mobile tectonic units, such as 7.81 km/s in the Baoshan block, 7.72 km/s in the Tengchong block and 7.82 km/s in the Zhongdian block. (2) The crustal nature of the Tengchong block, the northern Lanping‐Simao block and the Zhongdian block reflects a type of orogenic belt, having relatively strong tectonic activities, whereas the crustal nature of the central Lanping‐Simao block and the western margin of the Yangtze block represents a type of platform. The different features of the upper‐middle crust velocity, Moho depth and Pn wave velocity to both sides of the Red River fault zone and the Xianshuihe fault zone, reflect that they are clearly ultra‐crustal. (3) Based on the distribution of the low velocity zones in the crust, the crustal material of the Tibetan Plateau is flowing in a NW–SE direction to the north of 26°N and to the west of 101°E, then diverting to flowing eastwards to the east of 101°E. [ABSTRACT FROM AUTHOR]

Deep reflection seismic data contain abundant surface wave information for which the velocity structure in the near-surface shallow underground can be obtained using multichannel analysis of surface waves (MASW). This paper uses the MASW method to process deep reflection data in the Yuanmou area in Yunnan province, China. The MASW method uses the phase velocity spectral transformation of Rayleigh waves to obtain its dispersion curve. The initial model for different lithology classifications is established to invert the underground velocity structure. This study obtains a two-dimensional shear wave velocity structure profile to investigate the shear wave velocity structure. Generally, the study results have shown that the shear wave velocity structure obtained by the MASW method corresponds well with the surface conditions and accurately reflects faults' changes, folds, and lithology. Moreover, the formation sand content calculation shows a large difference in Dongshan sag's formation sand content. The sand contents of Cretaceous and Middle Jurassic strata are over 30% similar, and the sandstone content of underlying Early Jurassic strata is mostly 30% lower. The stratum buried depth of Early Jurassic strata is between 0– 800 m. The dip angle of LZJF at this location is 90°. The west side of the LZJF is based on Proterozoic uplift, and the Quaternary sedimentary thickness exceeds 300 m above the uplift stratum. Whereas on the east side of the LZJF, the stratum of the Dongshan sag section is mainly a synclinal structure. • Multichannel analysis of surface waves method is applicable to surface wave data in deep reflection profile. • The interlayer velocity difference method can be used to distinguish strata by shear wave velocity. • Shallow velocity structure can distinguish shallow geological structure with high resolution. [ABSTRACT FROM AUTHOR]

It is well known that the Tibetan plateau exposes a series of terranes that were drifted northward and accreted progressively onto the south margin of Eurasia resulting from ocean closure. However, the processes associated with the ocean closure remains poorly unconstrained. One such issue is whether the demise of the Bangong-Nujiang ocean between the Lhasa and Qiangtang terranes were caused by northward subduction only or both northward and southward subduction. To address this issue, we analyze high-resolution seismic reflection data along a 275-km north-south traverse across the Bangong-Nujiang suture zone. Our work shows that the Moho of the Lhasa terrane lies at 22.5 s (two-way travel time) and the Moho of the Qiangtang terrane lies at 20 s. In the Lhasa terrane, the reflection profile reveals an X-shaped structure that segmented south-dipping reflectors are truncated by continuous north-dipping reflectors. Based on the existing geological and geophysical observations and the cross-cutting relationships among seismic reflectors, we propose that the fossil relics of south-dipping reflectors with relatively weak amplitude in Lhasa terrane were created by the Mesozoic southward subduction of the Bangong-Nujiang ocean, and the north-dipping reflectors were triggered by the younger Cenozoic deformation during the India-Asia collision. In the Qiangtang terrane, our seismic reflection profile displays an antiformal structure with a set of north-dipping reflections in the lower crust, which we interpret as triggered by the northward subduction of the Bangong-Nujiang ocean. The structures as revealed by our seismic observations as a whole indicate that the closure of the Bangong-Nujiang ocean was created by bidirectional oceanic subduction. • Moho geometry is observed on a 275-km, deep seismic profile across the Bangong-Nujiang suture. • X-shaped crustal reflections are observed in Lhasa terrane. • An antiformal structure features the lower crust of Qiangtang terrane. • The crustal architecture indicates the bidirectional subduction of the Bangong-Nujiang Ocean. [ABSTRACT FROM AUTHOR]

Abstract: From October 2009 to May 2010, through the support of the SinoProbe project a series of deep seismic reflection profiles were conducted. In order to image deep crustal structure of central Tibet, these profiles extend from the northern Lhasa terrane to the Qiangtang terrane by crossing the Bangong–Nujiang suture (BNS). The Moho depth varies from 75.1km beneath the northmost Lhasa terrane to 68.9km beneath southmost Qiangtang terrane. There is a 6.2km sharp Moho offset across the BNS. Within 25km to the north of the BNS, the Moho rises smoothly to 62.6km. Distinct Moho reflector lies at 62.6–67.3km beneath the Qiangtang terrane. The boundary of the middle and upper crusts and that between the middle and lower crusts interpreted from INDEPTH velocity model correspond to the strong reflection horizons at about18.8km and 31.3km depth beneath south Qiangtang terrane, respectively. A north-dipping series of reflection packages in the mid- to lower crust may mark subduction of the Lhasa terrane beneath the Qiantang terrane. The central portion of the reflection profile exhibits an antiformal structure at 14.1km in the upper crust, which corresponds with the blueschist-bearing metamorphic belt. [Copyright &y& Elsevier]

• Integrated broadband and dense-nodal seismic-array investigation in northern Tibet. • Revealing significant Moho offsets indicative of deep thrust shear zones. • Imaging stark contrasts across the Haiyuan Fault indicative of strain partitioning. • Northern Tibetan plateau margin was constructed by a lithospheric-scale thrust-wedge. • Our results favor an overall oblique continental subduction model. The Tibetan plateau is one of the best field laboratories to investigate mechanisms of continental-lithosphere deformation, which contrasts sharply with the typical rigid-plate behavior of the oceanic lithosphere. Several end-member processes have been proposed for the plateau formation involving vertically coherent pure-shear shortening, decoupled upper- and lower-crustal shortening, oblique continental subduction, and crustal channelized flow. In order to test the above models, we conducted an integrated broadband and dense-nodal seismic-array investigation along two traverses across the northern Tibetan plateau margin in the Qilian Shan and its foreland region. The integrated observation provides the first coherent structural image of the lithosphere in general and shallow crust correlative to surface geology in particular in northern Tibet with an updated resolution. Our seismic imaging shows that the surface-exposed south-dipping Qilian Shan frontal thrust zone is closely associated with a low-velocity zone with concentrated seismicity in the upper crust, and along an inclined convertor can be extended downward into the middle-lower crust near a >10-km Moho offset beneath the Haiyuan Fault zone. This dipping feature and an inferred lithospheric detachment zone with oriented anisotropic fabrics constitute a lithospheric-scale thrust zone that bounds crustal-scale thick-skinned thrusts above, coupled with the development of distributed thrust shear zones that cut across the lowermost crust and uppermost mantle. We interpret the bounding lithospheric-scale thrust zone as the basal thrust of a thrust-wedge system across the northern Tibetan plateau margin. A minimum ∼26% bulk shortening strain is accommodated in the thrust-wedge system, which is compatible with the surface-geology constraints. Together with magnetotelluric data, our seismic imaging reveals stark contrasts in the crustal structure and rheology across the left-slip Haiyuan Fault. The involvement of strain partitioning across this regional structure in the thrust wedge supports the earlier proposed transpressional continental underthrusting of North China beneath the Tibetan plateau. [ABSTRACT FROM AUTHOR]

The Xainza‐Dinggye rift, an approximately north‐south trending Cenozoic fault zone across the Lhasa Terrane, is an ideal location to investigate extensional mechanisms in the upper crust and lithospheric deformation caused by the subducting Indian Plate beneath the central‐southern Tibetan Plateau. The 3‐D electrical resistivity structure was obtained by modeling magnetotelluric data from an array across the rift zone. Using the temperature distribution throughout the crust combined with the pressure and water content, we compute the pure melt conductivity. This enables estimation of the partial melt fraction of large‐area conductive zones imaged throughout the crust, and thus allows their rheology and strength to be evaluated. The heterogeneous distribution of high melt fraction areas in the crust has implications for the local continuous migration of fluids in the east‐west direction. The electrical structure also reveals a dipping resistive zone beneath the Tethys‐Himalaya terrane that represents the subducted Indian Plate. Significantly, its depth is observed to vary substantially from east (deeper) to west (shallower), which may indicate tearing of the plate. We suggest that the cause of extension and the formation of the crustal rift zone is related to tearing of the plate directly below this location, and the subsequent partial melting of the mid‐lower crust. Furthermore, the ascent of deep hydrothermal fluids, and heating of the shallow subsurface, likely led to the formation of the congruent Xainza‐Dinggye Thermal Belt. Additionally, the emplacement of numerous adjacent magmatic‐hydrothermal ore deposits is also likely related to partial melting and hydrothermal fluid migration in the crust. Plain Language Summary: The Xainza‐Dinggye rift is a north‐south trending fault in the central‐southern Tibetan Plateau. The 3‐D electrical structure is imaged using the magnetotelluric method, which uses natural electromagnetic signals to measure the subsurface electrical resistivity structure and is particularly sensitive to the presence of fluids and partial melts. The resulting model shows resistive regions beneath the Tethys‐Himalaya terrane that represent the subducted Indian plate. Several conductors in the mid‐lower crust may be related to partial melting. With the constraints of the temperature, pressure and water content, estimates of pure melt conductivity were obtained. This analysis is used to evaluate the strength characteristic of the mid‐lower crust. The results show that the formation and scale of the rift‐zone is likely caused by subduction features of the Indian plate (e.g., tearing of the plate) and the deformation characteristic of the mid‐lower crust (e.g., partial melting). Additionally, the rise of hot materials and fluids may have heated the circulating system of underground water and led to the formation of the Xainza‐Dinggye thermal belt and the formation of widespread hot springs. This work provides critical constraints for southward extrusion along the Main Himalaya Thrust and for possible conditions of east‐west fluid migration. Key Points: 3‐D electrical resistivity model used to constrain crustal melt fraction using experimentally derived estimates of pure melt resistivityHeterogeneous distribution of melt zones has implications for the possible east‐west migration of fluid along the Indian Plate below TibetTearing of the plate (East part steeper) and melting of the mid‐lower crust caused congruent rifting, thermal springs, and ore districts [ABSTRACT FROM AUTHOR]

The ongoing India‐Asia collision has led to the formation of the northern Himalayan gneiss domes belt in southern Tibet. The domes are the result of the ongoing convergence and were formed by geological processes that may include crustal thickening, metamorphism, partial melting, and exhumation of middle crustal rocks to the surface. A combination of compressional, extensional, and diapiric processes has been invoked to explain the formation and evolution of these domes. Differentiating among these competing hypotheses requires well‐defined geophysical images of the internal structure of the domes. The Mabja dome is the largest dome within the northern Himalayan gneiss domes belt. A 70‐km long deep seismic reflection profile across Mabja dome was acquired in 2016. The seismic data could provide new information about the structural elements beneath the domes to the depth of 25 Km. We address the structure of the Mabja dome by conducting an integrated analysis of shallow crustal velocity structure and a normal‐incidence seismic reflection image of deeper crust. Our work suggests that the Mabja dome is underlain by shear zones at depths of 10–15 km and two high‐velocity bodies at depths of 3 km possibly representing the eclogitic‐facies rocks or mafic intrusions. We propose that the dome formation may have been controlled by collision‐induced north‐south shortening expressed by thrust stacking of middle crustal rocks, which led to the doming of the upper‐crustal rocks. The proposed mechanism inferred for Mabja dome can be applied to interpret the widespread domes throughout the southern Tibet and other related structures in orogenic mountain belts. Key Points: Two high‐velocity bodies, with an average velocity as high as 6.6 and 7.2 km/s, are constrained at a depth of 3 km from the surfaceA series of sub‐horizontal reflections are observed at depths of 11–20 km which are interpreted to represent a thrust systemThe thrust stacking in the middle crust is the main mechanism that controls the formation of the Mabja dome formation [ABSTRACT FROM AUTHOR]

Various models have been proposed to explain formational mechanisms for the Himalayan orogeny but uncertainties remain concerning uplift processes and deeper crustal structure of the orogen. Imaging of the orogen's deep structure can help resolve these uncertainties. This paper describes one migrated deep seismic reflection profile across the eastern Yarlung-zangbo suture (YZS) at 92° E, which provides a high resolution image of crustal structure that reveals (1) Yarlhashampo dome is divided into upper, middle and lower tectonic units by two detachments from rim, mantle to the core of dome, (2) one blind north-dipping reverse fault that offsets the South Tibet detachment (STD) developed along the northern flank of the Yarlhashampo dome, (3) a shift of the Main Himalayan thrust (MHT) dip angle from 18° into relatively gentle dips (6°) in the central part of the profile (18–20 s, t.w.t). Meantime, further inferring that (4) North-south compression event happened after ca.10 Ma in North Himalayas, (5) multi-stage duplexing as the primary mechanism for crustal thickening in the eastern YZS based on interpreted structures. • Presenting one new seismic reflection line crossing Yarlung-Zangbo suture at 92°E • Revealing duplexing structures of Greater Himalayas in east Himalayas • Found one shift of the Main Himalayan thrust (MHT) into relatively gentle dips northward beneath Tethyan Himalayas • Revealing subsurface structures of Yarlhashampo dome [ABSTRACT FROM AUTHOR]

Abstract The Yarlung Zangbo Suture (YZS) is the collisional front between the Indian and Eurasian plates. The deep structure beneath the YZS has long been a focus of research. Its particular tectonic location and formation time provide a natural laboratory for the study of ongoing continental collisional processes. Lateral variations in the Moho discontinuity provide evidence of basic processes governing plate tectonic evolution. The depth and geometry of the Moho provides first-order information for restoration of complex geodynamic systems. This paper presents a studying result of the Moho, both adjacent to and beneath the YZS, obtained using five large dynamite shots along two profiles. These five large shots were combined to construct two single-fold profiles (YZS-A and YZS-B) and obtain high-resolution images of the Moho beneath the YZS. Both profiles show that continental crust thickness beneath the YZS is twice the global average of continental crust, and the depth of the Moho along profile YZS-B is deeper than YZS-A. YZS-A (81°E) indicates a relatively flat Moho without offset related to continent-continent convergence beneath the collision zone. Conversely, a Moho structure with offset and overlapping reflections was imaged beneath profile YZS-B (88°E). Significant lateral variations in the geometry of the Moho discontinuity along the YZS may indicate that the Indian lithosphere is thrusting beneath Tibet at a different angle from west to east. Highlights • We investigate the Moho discontinuity beneath the Yarlung Zangbo Suture (YZS). • Continental crust thickness beneath the YZS is twice the global average. • Depth of the Moho varies across two profiles taken. • The Indian lithosphere may be thrusting beneath Tibet at different angles. [ABSTRACT FROM AUTHOR]

Abstract The Tibetan Plateau's enigmatic collapse, which was indicated based on extensional faulting in the interior of the plateau and large eastward-directed strike-slip faults, has inspired intensive geologic inquiry and debate. Interaction of the subducting Indian plate with the overlying Asian lithosphere is one factor that may be affecting the plateau. A more detailed image of the subducting Indian plate can help constrain its role, but regional high-resolution seismic data have not been widely available at a relevant scale. Here we present an integrated interpretation based on two types of seismic datasets: (1) two N-S oriented deep seismic-reflection profiles that cross the Yarlung-Zangbo suture, and (2) two E -W receiver function profiles that cross the Xainza-Dingjye and Nyima-Tingri rifts, respectively. These images reveal different crustal-scale structures in the dominant collision zone between the western and central regions, as well as distinctly offset Moho discontinuities across the N-S trending rift grabens in southern Tibet. These crustal variations, combined with previous tomographic studies in Tibet, outline an easterly tilt of the subducting Indian slab, along which crust-mantle decoupling occurred. Together with the spatio-temporal distribution of synchronous potassium-rich volcanics exposed within the grabens in southern Tibet, this offset Moho structure beneath the grabens lends support to the hypothesis that eastward steepening of the subducting Indian slab was accompanied by slab tearing beneath each north-south striking rift. This overall crustal geometric variation suggests a stepwise flattening of the torn Indian slab from west to the east, a process that brought easterly migration of gravitational instability to the overriding Tibetan crust that drove collapse of the Tibetan Plateau once gravitational instability reached a critical level to the east. [ABSTRACT FROM AUTHOR]

The Lhasa terrane in southern Tibetan plateau is a huge tectono-magmatic belt and an important metallogenic belt. Its formation evolution process and mineralization are affected by the subduction of oceanic plate and subsequent continental collision. However, the evolution of Lhasa terrane has been a subject of much debate for a long time. The Lithospheric structure records the deep processes of the subduction of oceanic plate and continental collision. The magnetotelluric (MT) method can probe the sub-surface electrical conductivity, newly dense broadband and long period magnetotelluric data were collected along a south-north trending profile that across the Lhasa terrane at 88°–89°E. Dimensionality analyses demonstrated that the MT data can be interpreted using two-dimensional approaches, and the regional strike direction was determined as N110°E.Based on data analysis results, a two-dimensional (2-D) resistivity model of crust and upper mantle was derived from inversion of the transverse electric mode, transverse magnetic mode and vertical magnetic field data. Inversion model shows a large north-dipping resistor that extended from the upper crust to upper mantle beneath the Himalaya and the south of Lhasa Terrane, which may represent the subducting Indian continental lithosphere. The 31°N may be an important boundary in the Lhasa Terrane, the south performs a prominent high-conductivity anomaly from the lower crust to upper mantle which indicates the existence of asthenosphere upwelling, while the north performs a higher resistivity and may have a reworking ancient basement. The formation of the ore deposits in the study area may be related to the upwelling of the mantle material triggered by slab tearing and/or breaking off of the Indian lithosphere, and the mantle material input also contributed the total thickness of the present-day Tibetan crust. The results provide helpful constrains to understand the mechanism of the continent-continent collision and the regional exploratory prospect of the deep resources. [ABSTRACT FROM AUTHOR]

A new multichannel seismic reflection profile collected across the Sichuan Basin in southern China by SINOPROBE images prominent reflectors that originate within the lower crust and penetrate well into the underlying mantle. The geometry of these mantle reflectors is very similar to those observed on other deep reflection profiles that have been interpreted as relicts of ancient subduction. Considering the geological history of the basement beneath and surrounding Sichuan Basin and ages of granites encountered in nearby wells, we propose that these newly revealed reflectors are the remnants of Neo-Proterozoic subduction that occurred along the NW margin of the Yangtze Craton. This interpretation is consistent with geochemical studies from a gneissic complex at the west margin of the Sichuan Basin. Moreover, preservation of these reflectors supports the idea that the Sichuan lithosphere served as a consolidated tectonic buttress against which the Tibetan Plateau has impinged to produce the Longmenshan orogenic belt. [ABSTRACT FROM AUTHOR]

The Great Xing’an Range is characterized by a complex crustal history involving the successive development of several Paleozoic to Mesozoic tectonic domains. A set of new different geophysical data, including deep seismic reflection profile, seismic refraction/wide-angle reflection profile, and magnetotelluric survey, were conducted recently to establish the lithosphere structure and geodynamic framework of the Great Xing’an Range and adjacent basins. Results based on the interpretation of the integrated geophysical data include the discovery of the “crocodile” style assembly fabric of the Songnen and Xing’an blocks; the intrusion of the Great Xing’an Range continental crust into the Songnen block while the mantle lithosphere of the Songnen block beneath the Xing’an block. The Great Xing’an Range experienced the delamination and the underplating, which is very common in the eastern part of Central Asian Orogenic Belt. The building of the Great Xing’an Range could divide into two phases: (a) the crustal shortening and overlapping resulted from the compression between the Songnen and Xing’an blocks in late Devonian to early Carboniferous; (b) the vertical building by the upwelling and underplating of the magmas in Mesozoic and Cenozoic. [ABSTRACT FROM AUTHOR]

Statics are big challenges for the processing of deep reflection seismic data. In this paper several different statics solutions have been implemented in the processing of deep reflection seismic data in South China and their corresponding results have been compared in order to find proper statics solutions. Either statics solutions based on tomographic principle or combining the low-frequency components of field statics with the high-frequency ones of refraction statics can provide reasonable statics solutions for deep reflection seismic data in South China with very rugged surface topography, and the two statics solutions can correct the statics anomalies of both long spatial wavelengths and short ones. The surface-consistent residual static corrections can serve as the good compensations to the several kinds of the first statics solutions. Proper statics solutions can improve both qualities and resolutions of seismic sections, especially for the reflections of Moho in the upmost mantle. [ABSTRACT FROM AUTHOR]

Abstract: The 2008 Wenchuan earthquake and aftershocks occurred along the northeast-trending Longmenshan fault zone in the eastern margin of the Tibetan plateau. The Tibetan plateau has the strongest negative Bouguer gravity anomaly zone in China and is surrounded by the great gravity horizontal gradient belt. The horizontal gradient belt of the observed gravity anomaly in the Longmenshan area is a part of this giant gravity gradient belt. The Longmenshan fault zone is located to the east of this belt. The horizontal gradient belt of the residual gravity anomaly, obtained by removing large effects of sedimentary basin and variations in the crustal thickness, well matches the Longmenshan fault zone. But this belt is located to the east of the horizontal gradient belt of the observed gravity anomalies. The deviation of the two horizontal gradient belts increases from the southwest to the northeast with a maximum of about 40–50km. A significant difference in density exists in the lower crust and the uppermost mantle between the Songpan-Ganzê block and the Sichuan basin block. The Songpan-Ganzê block is less dense than the Sichuan basin block in the lower crust as well as in the uppermost mantle. The boundary between the two blocks is located to the west of the Wenchuan-Maoxian, Yinxiu-Beichuan, and Anxian-Guanxian faults approximately. The fault plane crosses the lower crust and uppermost mantle. The rigid Sichuan basin block acts as a resistant for the pushing from the Songpan-Ganzê block. Far-field effects of the collision between the Indian and Eurasian plates, might lead to thrust of some brittle layers in the upper crust along the detachment, in the middle crust of the Songpan-Ganzê block. When movement on a large and deep crustal mega-thrust occurs, earthquakes strike the Longmen Shan margin of the Tibetan Plateau. In the Guanxian-Beichuan segment in the southern Longmenshan fault zone, push from the Songpan-Ganzê block is perpendicular to the density boundary, which corresponds to the location of the horizontal gradient belt of the residual gravity. But in the Guanxian-Beichuan segment in the northern Longmenshan fault zone, the push is oblique to the location of this gradient belt. Such a relationship could lead to nearly equal amounts of thrust and right-lateral slip along the Beichuan-Qingchuan segment, and in contrast to nearly pure thrust along the Guanxian-Beichuan segment. An unusually large negative magnetic anomaly occurs around Qingchuan-Wenchuan-Guanxian. The computed magnetic model shows that some crystalline complexes with reversal magnetization might exist in the crust, which might be related to extrusion of the metamorphic basement rocks in the lower to middle crust. [Copyright &y& Elsevier]

As one of the most prominent deformation features on Tibetan plateau, a series of N-S systematic rifts and V-shaped conjugate strike-slip faults are well developed in central-southern Tibet. However the mechanism for the formation of the rifts and conjugate strike-slip faults is still controversial. An east-west trending magnetotelluric (MT) array has been operated across the Gyaring Co Fault (GCF) at the northern end of the Xainza-Dingjye Rift (XDR) in Lhasa block. Three-dimensional (3-D) inversions are employed to image lithospheric resistivity structure. Combined with the previous north-south MT 3-D inversion result, electrical resistivity models reveal obvious conductive layer in the mid-to-lower crust beneath the XDR and apparent resistivity change in the vicinity of the GCF. The calculated depth-integrated conductivity shows that the weak mid-to-lower crust (~30 km- ~ 60 km) characterized by high conductance (≥ ~10,000 S) and melt fraction of ~5–13%, is mainly distributed between the Indus-Yarlung suture (IYS) and the GCF, whereas the relatively rigid crust characterized by low conductance (≤ ~2000 S) and melt fraction of ~2–4% appears to the northeast of the GCF. The weak mid-to-lower crust in southern Tibet and the abrupt difference in the resistivity characteristics of the mid-to-lower crust in the vicinity of the GCF, suggest the formation of the rifts in Lhasa block is closely associated with the weak mid-to-lower crust. Taken together with the upper mantle seismic features, the weak mid-to-lower crust is believed to be attributed to the underplated Indian plate. An alternative geodynamic model is presented to respond to the eastward extrusion during the ongoing N-S convergence between the Indian and Eurasian plates, that the rigid crust in central Tibet is sandwiched by the weak mid-to-lower crust in southern and northern Tibet, and the rifts form above the weak mid-to-lower crust, whereas the conjugate strike-slip faults develop on the rigid crust in central Tibet. [Display omitted] • 3-D inversion resistivity models are obtained from the orthogonal MT arrays in Lhasa terrane. • Apparent resistivity variation in the mid-to-lower crust is revealed beneath the vicinity of the strike-slip faulting. • The rifts form above the weak crust, whereas the conjugate strike-slip faults develop on the rigid crust in central Tibet. [ABSTRACT FROM AUTHOR]

The deep reflection seismic method is an effective technique for detecting the fine structures of the lithosphere and solving deep geological problems. At present, the methods for obtaining the underground velocity from land deep reflection seismic profile mainly rely on the travel-time information based velocity analysis and tomography, which theoretically limit the resolution of the imaging results. To achieve the goal of using deep reflection seismic profile for crustal-scale high-precision velocity imaging, we must finally overcome the problem of full waveform inversion (FWI) using full wavefield data. In this paper, we successfully conduct FWI using the early-arrival wavefields (mainly primary and multiple refraction wavefields) in the deep reflection seismic profile, which can be seen as the first important step towards the goal of crustal-scale high-precision velocity imaging. We propose a robust refraction waves FWI workflow with global normalized cross-correlation, multiple refraction matching, reverse time source estimation and wavenumber domain gradient filtering as its core algorithm. The application of the proposed FWI method to the refraction waves of the deep reflection seismic profiles in the central part of Lhasa Terrane shows that the refraction FWI images have a higher resolution to underground structures both in horizontal and vertical directions than the first-arrival tomography images. The lateral velocity change can be well-matched with the typical geological characteristics of the work area. The FWI result can better describe the lateral boundaries of the strata in different eras. At a depth of less than 3 km from the surface, the refraction FWI can correct the interface morphology of the tomography results and recover some small-scale velocity structures and high-velocity anomalies. • We conduct full waveform inversion using the early arrivals in the land deep reflection seismic profile. • Both primary and multiple refraction waves are inverted in this research. • Some common problems faced by land active source full waveform inversion are mitigated. • The strata of different ages are described clearly by the proposed full waveform inversion result. • High-velocity anomalies and small-scale structures can be imaged. [ABSTRACT FROM AUTHOR]

• A long deep seismic reflection image captured a non-modified syn -Rodinian orogen resting beneath the Sichuan basin, western China. • Contemporaneous continental recycling that assembled the Rodinia Supercontinent is clearly recorded. • Continental recycling in the Neoproterozoic Era still experiences more extensive crustal extraction than the counterparts of modern Earth. Owing to most tectonic events in Precambrian have been modified by intensive post-Precambrian overprinting, the question how exactly crustal recycling operated on earlier Earth remains an open one. Here, we report a SE-striking, 175 km-long deep seismic reflection profile that traverses the Sichuan basin, China. The image shows a well-preserved syn -Rodinian orogen resting beneath flat lying sedimentary cover of the basin. Relative to the counterparts of modern Earth, this orogen shows a structurally complex Moho geometry composed of multiple layers of basaltic sills, exhibiting extensive crustal extraction. The outlined crustal architecture further depicts that growth of the upper plate arose dominantly through tectonothermal processes, while coeval ductile underthrusting and overthrusting drove contemporaneous crustal shortening of the lower plate. Together with accretionary stacking above, these processes coevally generated a crustal thickness to ~ 30 km. This well-preserved syn -Rodinian orogen provides direct evidence for understanding contemporaneous continental recycling that assembled the Rodinia supercontinent. Near-vertical, deep seismic reflection profiling is an effective technique for mapping complicated subsurface structures. In this study, the obtained high-resolution deep seismic reflection image captured a non-modified syn -Rodinian orogenic belt resting beneath flay lying sedimentary cover of the Sichuan basin, western Yangtze block, China. Structural interpretation and associated tectonic implications tell us: (1) the Yangtze block was actually a tectonic collage of microcontinents accreted during Neoproterozoic Rodinian assembly, (2) contemporaneous crustal recycling is featured with extensive crustal extraction, and (3) crustal growth was dominantly driven by tectonothermal events in the upper plate of the convergent zone and crustal shortening in a way of coeval underthrusting and overthrusting in the lower plate, a scenario that has shown no big difference with the counterparts of modern Earth. This well-preserved Neoproterozoic orogenic belt provides direct evidence for helping understand the continental recycling that assembled the Rodinia Supercontinent. [ABSTRACT FROM AUTHOR]

The Gangdese metallogenic belt in the Tibetan Plateau hosts many large ore deposits, of which the Xiongcun and Niangre ore concentration districts are two typical examples. Due to the insufficient geophysical evidence about the deep metallogenic dynamics across these two districts, the electrical structure was obtained by modeling magnetotelluric data to study the relationship of the crustal structure and metallogenic dynamics. Although the mineralization occurred in the past, the continuous magmatic activities after the mineralization could reactivate the previous migration channels to remain some traces, which can be revealed by some geophysical methods. The resistors at depths of less than 20 km may represent the multiple overlapping volcanic rocks related to a serious of magmatic events in the Lhasa-Gangdese terrane. Some conductors that revealed at different depths may be related to the partial melt, aqueous fluids and/or formation of metallic minerals, and were also further indicated as the possible magma chambers. Connecting the conductors at different depths may be further indicated as some ancient migration channels which were probably related to the shear zones and faults. As the ore deposits in both districts belonged to the magmatic-hydrothermal type, the upwelling magma played a crucial role in the metallogenic dynamics. These possible magma chambers at different depths and channels may be also related to the evolution and emplacement of the deep-seated magma, and contributed to the mineralization of both districts. This study can also offer a reference of significance for the deposits in the eastern Gangdese metallogenic belt. Unlabelled Image • Some conductors indicated possible magma chambers during magmatism and mineralization. • Conductive channels indicated possible ancient migration channels related to faults. • A possible relationship between the electrical structure and metallogenic dynamics. [ABSTRACT FROM AUTHOR]

Since the Mesozoic, the Lhasa-Gangdese block has undergone several stages of tectonism-magmatism caused by the closure of the New-Tethys Ocean and the collision between the Indian and Eurasian plates, which led to the lithospheric shortening and crustal uplift. Through the careful processing and analysis of the magnetotelluric data on the eastern margin of the Lhasa-Gangdese block near 92°E, a reliable 3D electrical model was obtained to examine the relationship between the lithospheric electrical structure and geodynamics. Some conductive and resistive layers were obtained, which may be formed in some tectonic processes. The thermal model of the lithospheric uppermost mantle (75–100 km) were calculated using the Arrhenius equation and the Hashin-Shtrikman (HS) boundary condition. Combined with the terrestrial heat flow point and curie isothermal in the study area, the temperature distribution at the 30–100 km depths was calculated. The melt fractions of the mid-lower crust calculated by the classical Archie's law, pressure calculated by density and temperature at different depths can be obtained in a meantime. The resistor beneath the Tethys-Himalaya terrane represented the subduction of the Indian plate with a deep angle. The subduction of the Indian crust may not exceed the Indus-Yarlung Zangbo suture, while the Indian lithospheric mantle may not reach the Luobadui-Milashan fault. Additionally, our electrical and thermal structure indicated that the Indian lithospheric mantle probably detached from the Indian crust. Our study further discussed the underplating of the mantle-derived materials and the southern extrusion along the Main Himalaya Trust, and offered a subsidiary evidence for the possible "south-eastward crustal flow" in a local area. Finally, the relationship between the electrical structure and the deep metallogenic mechanism was briefly established. • The thermal model and pressure model were calculated and established. • The patterns of the subducted Indian lithosphere were discussed. • Three possible types of material migration were discussed. [ABSTRACT FROM AUTHOR]

Although the Lhasa terrane of southern Tibet is an integral part of the Tibetan plateau, how the area has achieved its current high altitude of ~5000 m remains poorly understood. This is largely due to the fact that little is known about deep (>15 km) crustal structures and the depth and geometry of the Moho below the terrane. In this study, we address this question by acquiring and analyzing high-resolution seismic reflection data gathered from four high-energy dynamite shots along a 137-km north-south traverse spanning the southern Lhasa terrane. Our new seismic data reveal the presence of north-dipping reflectors in the crust, a seismically weak-reflection layer at the lowermost crust, and a sub-horizontal and locally discontinuous Moho at depth of 69–72 km with a crustal velocity of 6.30 km/s. The discordant relationship between the crustal dipping reflectors, the subhorizontal lower crustal layer, and the flat Moho suggests that the ~12-km basal section of the Lhasa terrane crust is a decoupling zone accommodating different styles of lithospheric-scale deformation. Because the north-dipping reflectors can be projected and/or connected with the reflectors in the Cenozoic Himalayan thrust system and the southernmost Lhasa terrane, we propose that the dipping crustal reflectors are parts of a south-directed crustal-scale thrust duplex created by the Cenozoic India-Asia collision. The relatively discontinuous and horizontal geometry at the base of the crust indicates that the Moho was reconstituted through ductile deformation in the lowermost crust caused by abnormally high temperature. Unlabelled Image • Moho geometry is observed on a 137-km, deep seismic profile in the Lhasa terrane. • North-dipping intra-crustal reflections are observed. • The Moho depth remains constant at ~69–72 km beneath the Pumqu-Xianza rift. • The flat Moho geometry contrasts with the north-dipping intra-crustal reflections. • A comprehensive model is proposed to document this varied tectonic response. [ABSTRACT FROM AUTHOR]

• The causes of the error of the electrical and geographic locations of the IYS. • The division of the Lhasa terrane according to the electrical structure. • The double-sided subduction of the Bangong-Nujiang Tethyan Ocean (BNT) Ocean. • The smooth subduction of the Longmu Tso-Shuanghu Tethyan Ocean (LST). The Himalaya-Tibetan Plateau that is situated in the southwest China is an ideal natural field laboratory for continental dynamics. In this study, through the careful processing and analyzing of the magnetotellurics data, the reliable 2-D electrical model was obtained to examine the relationship between the lithospheric electrical structure and dynamics in the central Himalaya-Tibetan Plateau. Six conductors mainly result from the partial melting and aqueous fluids, and three resistors are related to different tectonic evolution in the model. Combined with other observations, we summarize that the upwelling hot material (partial melting), aqueous fluids, subduction erosion and crushed zone contribute to the error between the electrical location and the geographic location of the Indus-Yarlung Zangbo suture. The subducted Indian plate is shown by the different angles and different locations of its frontier in different areas. The electrical structure beneath the Lhasa terrane corresponds well with the geological features of an old, locally reworked crust dominantly in the central Lhasa terrane with two young juvenile crustal blocks surrounding the central terrane, and it also shows the relationship among the dynamics, magmatism and mineralization in the Gangdise metallogenic belt. Meanwhile, we indicate that the subducted polarity of the Bangong-Nujiang Tethyan Ocean lithosphere was double-sided, and the smooth subduction of the Longmu Tso-Shuanghu Tethyan Ocean lithosphere may cut through the Moho surface approximately 20 km. Above all, these results can provide helpful constrains to understand the evolution mechanism of the Himalaya-Tibetan Plateau. [ABSTRACT FROM AUTHOR]