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A great amount of new S‐wave data has been combined to image the mantle structure down to lower mantle depth near the southeastern margin of Eurasia and understand the tectonics in South China since the Mesozoic. Our results reveal a large‐scale structure beneath the South China Sea, with a prominent, broad low‐velocity feature of at least 1500‐km wide in and below the mantle transition zone (MTZ) and a pronounced low‐velocity feature of nearly 500‐km wide in the lowermost mantle. Together these features may represent the head‐and‐tail of an upwelling mantle plume that has interacted with and deformed by the subducting plates in the region. The Andaman–Sumatra plate is seen subducting steeply without stagnation in the MTZ over the large‐scale low‐velocity structure, suggesting that the upwelling mantle may have exerted significant influence on the overlying plate tectonics. Our results suggest a long‐term extensional regime near the southeastern margin of Eurasia, which may help to understand the formation of the large‐scale intra‐plate magmatism and mineralization with accumulation of huge amount of rare metal elements in South China during the Mesozoic, and the continental breakup, the southeastward extrusion of Indochina, and the opening of the South China Sea during the Cenozoic. [ABSTRACT FROM AUTHOR]

The Middle and Lower Reaches of the Yangtze River metallogenic belt (MLYMB) is one of the most important Fe‐Cu polymetallic belts in China. However, the mechanism and deep geodynamical process for the formation of this belt are still controversial. Here, we obtain the crustal and the uppermost mantle structures using ambient noise data from a dense seismic profile. A low velocity zone is revealed beneath the Moho of MLYMB, interpreted as the source of the deep mineralization materials. In addition, a low velocity layer (LVL) and a high velocity layer (HVL) are observed in the crust of the southern segment of the profile. The LVL is interpreted as a tectonic detachment layer between the upper and the lower crust, and the HVL is interpreted as the aggregation zone for mineralizing melts or crystallized magma chambers. Based on the observed velocity features, we propose a three‐stage model for the formation of ore deposits in MLYMB. Our model suggests that an upwelling of asthenosphere triggered by the delamination of a previously thickened lithosphere leads to the partial melting of upper mantle rocks, which eventually ponders under the Moho. The magma then infiltrates through the ductile lower crust and reaches a depth of ∼7–13 km, forming a minerals‐enriched magma chamber. Minerals‐rich hot fluids originating from the magma chamber continue to move upward along the pre‐existent faults and the minerals finally precipitate in dense veinlets when reaching shallow depths, forming the ore deposits in and around the MLYMB. Plain Language Summary: The formation of large‐scale mineral deposits is closely related to the lithosphere structure. The Middle and Lower Reaches of the Yangtze River metallogenic belt (MLYMB) is an ideal place to study the mineral system, as it is one of the most important Fe‐Cu polymetallic metallogenic belts in Eastern China and contains more than 200 ore deposits. Yet the mechanism and deep geodynamical process for the formation of this belt are still controversial. In this study, we construct a high‐resolution seismic model of the crust and the uppermost mantle using ambient noise data from a dense seismic profile. Our result reveals velocity features closely related to the metallogenic process in this region. Based on the observed velocity features, we propose a three‐stage model for the formation of the ore deposits in MLYMB, which is of great importance for the development of "mineral system" approaches to the exploration of minerals worldwide. Key Points: We obtain a fine Vs structure of the crust and uppermost mantle beneath the MLYMBWe observe velocity features closely related to the metallogenic process of MLYMBWe propose a three‐stage metallogenic process for the origin of the MLYMB [ABSTRACT FROM AUTHOR]

We apply seismic tomography to 590,213 P‐wave arrival‐time data of 23,486 local earthquakes and 300,051 relative travel‐time residuals of 27,492 teleseismic events to study the 3‐D velocity structure of the crust and upper mantle beneath the entire Philippine Sea Plate (PSP) and its adjacent areas. Our results reveal significant high‐velocity anomalies beneath the Philippine Trench, the Japan‐Izu‐Bonin‐Mariana Trench, and the Nankai Trough, which reflect the subducted Philippine Sea slab, the Pacific slab, and the Shikoku Basin, respectively. On the basis of the tomographic images, we construct morphological models of these slabs. The slab morphologies become complex from the east to west. Taking into account previous results of geochemistry, paleomagnetism and numerical simulations, we deem that the complicated morphologies of the subducted slabs are related to the slab age, subduction rate, collision between different plates, clockwise rotation of the PSP, and retreat rate of trenches. Plain Language Summary: The Philippine Sea Plate (PSP) is almost entirely surrounded by subduction zones. We use P‐wave tomography to study the 3‐D velocity structure of the crust and upper mantle beneath the entire PSP for a better understanding of the slab geometry and subduction dynamics. Our tomographic results reveal obvious high‐velocity (high‐V) anomalies beneath the trenches around the PSP, which reflect the subducting Philippine Sea slab, the Pacific slab, and the Shikoku Basin. We construct morphological models of these slabs according to their high‐V anomalies. These slab exhibit quite different morphologies. Taking into account previous geochemical, paleomagnetic and numerical simulation results, we think that the complex slab morphologies are related to the slab age, subduction rate, collision between different plates, clockwise rotation of the PSP, and retreat rate of oceanic trenches. Key Points: P‐wave tomography is applied to investigate 3‐D velocity structure down to 800 km depth beneath the entire Philippine Sea PlateThe subducting Pacific and Philippine Sea slabs exhibit quite different morphologiesThe morphological differences are caused by the slab age, subduction history and interactions between slab and surrounding mantle [ABSTRACT FROM AUTHOR]

Teleseismic primary (P) to secondary (S) converted waves recorded on the INDEPTH III seismic array have been used to detect lithospheric-scale deformation structures of the central Tibetan Plateau from the central Lhasa terrane to the central Qiangtang terrane. A south-dipping crustal converter is seen from the upper crust near the 500-km-long metamorphic core complex exposures in the Qiangtang terrane to the lower crust near the Bangong-Nujiang suture. At deeper depths, a southeast-dipping mantle converter is seen extending from ~50 km north of the Bangong-Nujiang suture at the depth of the Moho, to a depth of ~180 km, ~100 km south of the Bangong-Nujiang suture. We found the observations to be most consistent with a model of lithospheric deformation involving (1) southward subduction of the Tibetan lithospheric mantle along the Bangong-Nujiang suture and (2) thickening of the central Tibetan crust through a thick-skinned, crustal accretionary thrust-wedge structure in response to the India's collision with Asia. Keywords: receiver function, lithospheric structure, continental collision, Tibetan Plateau.

Massive lithospheric thinning occurred in eastern China and large‐scale magmatism in South China occurred in the Mesozoic. Some geodynamic models have been proposed to explain their mechanisms, but are not consistent with each other. We apply anisotropic tomography to 32,728 P‐wave travel time data of 479 teleseismic events recorded at 225 stations to study the 3‐D anisotropic Vp structure of the upper mantle beneath central‐east China. P‐wave radial anisotropy is investigated for the first time in the study region. Our results show that an obvious low‐velocity zone exists in the asthenosphere under the eastern part of our study region, which represents upwelling thermal flow from the Cathaysia block to the North China block (NCB) according to the results of azimuthal and radial anisotropies. A distinct high‐velocity zone with weak radial anisotropy exists under the middle Yangtze block, which is explained as the stable cratonic root. Two other weak high‐velocity zones appear near or within the mantle transition zone under the middle‐lower Yangtze River and the eastern NCB, which might be detached lithosphere or the stagnant Pacific slab. Combining with previous geological and geochemical results, we consider that both the NCB and the South China block have undergone a common geodynamic process in the Mesozoic due to their similar age trending of igneous rocks, which could be explained by a flat‐slab subduction model and a ridge subduction model. These two models are associated with the paleo‐Pacific plate subduction that might have played a key role in the evolution of eastern China. Key Points: Anisotropic tomography is applied to study the 3D anisotropic velocity structure under central‐east ChinaMantle flow with low P‐wave velocity upwells and moves from the Cathaysia block to the North China blockThe paleo‐Pacific plate subduction might have prompted the thermal material migration [ABSTRACT FROM AUTHOR]

The article discusses an approximate calculation research of the gravity forward modeling method in geophysical exploration based on multiquadric (MQ) radial basis function. Topics covered include the difference of the gravity forward modeling method with the traditional gravity modelling, the design of the workflow of the gravity model forward modeling based on MQ radial basis function, and a comparison of the interpolation results with radial basis function and accumulative point method.

The article discusses a study which examined the lithospheric structure in the South China (SC) block from receiver function and its implications for the source of mineral system. Topics covered include the tectonic mechanism for the Mesozoic large-scale magmatism and mineralization in SC, the results of Common Conversion Point (CCP) stacking and results which suggest that the different deposit combinations in the different metallogenic belts may be associated with different tectonic processes.

A broadband seismic deployment in 1998-1999 in southwestern Tarim provided data for imaging the crust and upper mantle across the contact between the Tarim block and the Tibetan Plateau. A profile composed of migrated teleseismic receiver functions clearly shows lateral structural changes. The crust under the Tarim basin is relatively simple. The Moho discontinuity is mapped at a depth of 42 km near the northern end of the array and dips gently toward the south to ~50 km under the Kunlun foreland. The Tarim basin appears to be rigid, with little shortening. Farther to the south, the imaging reveals a complex of reflectors in the lower crust and the upper mantle. There are both north- and south-dipping upper mantle structures under the Kunlun foreland and Kunlun Shan region. We found the observations to be more consistent with a model of lithospheric collision in which the crust and the upper mantle on both sides interpenetrate and deform. Keywords: receiver function image, lithospheric collision, Tarim, Tibet.

Closely-spaced receiver-function profiles in the east-central India–Tibet collision zone reveal drastic west–east changes of the crustal and upper mantle structure. West of ∼91.5°E, we show the Indian crust-mantle boundary (Moho) extending subhorizontally from ∼50 km depth below sea level under the High Himalaya to ∼90 km under the central Lhasa terrane. Further north, this boundary transitions to become the top of the Indian lithospheric mantle and, becoming faint but still observable, it can be tracked continuously to ∼135 km depth near ∼31.5°N. The top of the Indian lithospheric mantle is clearly beneath the Tibetan Moho that is also a conspicuous boundary, undulatory at 60–75 km depth from the central Lhasa terrane to the north end of our profile at ∼34°N. This geometry is consistent with underthrusting of Indian lower crust and underplating of the Indian plate directly beneath southern Tibet. In contrast, east of ∼91.5°E, the Indian Moho is only seen under the southernmost margin of the Tibetan plateau, and eludes imaging from ∼50 km south of the Yarlung-Zangbo suture to the north. The Indian lower crust thins greatly and in places lacks a clear Moho. This is in contrast to our observation west of ∼91.5°E, that the Indian lower crust thickens northwards. A clear depression of the top of the Indian lower crust is also observed along west–east oriented profiles, centered above the region where the Indian Moho is not imaged. Our observations suggest that roll-back of the Indian lithospheric mantle has occurred east of ∼91.5°E, likely due to delamination associated with density instabilities in eclogitized Indian lower crust, with the center of foundering beneath the southern Lhasa terrane slightly east of 91.5°E. [ABSTRACT FROM AUTHOR]

A 300 km long seismic reflection profile was acquired across the Middle and Lower Reaches of the Yangtze River (MLY) metallogenic belt and its adjacent areas. The objective of the survey was to establish the deep architecture and geodynamic framework of the region. Results based on the interpretation of the deep seismic data include (1) Tan-Lu fault appears as a subvertical thrust fault or transpression fault with its deep portion dipping toward the southeast; (2) the Zhangbaling uplift is squeezed out along this fault; (3) complex upper crustal deformation structures beneath the Chuquan depression include both kink bands, thrusts, imbrication and fold structures reflecting contraction deformation, and detachment fault and normal-fault structures reflecting extensional deformation; (4) the “crocodile” reflection structure emerging beneath the Tan-Lu fault and Ningwu–Lishui volcanic basin, which represents the decoupled deformation process of the upper and lower crust associated with intra-continental subduction; (5) further to the southeast, the upper crust deformation shows a large-scale “wave-form” pattern, making crustal scale syncline and anticline; (6) the entire section of the reflection Moho is clearly discernible at depth of 30.0–34.5 km, and the Moho beneath the Middle and Lower Reaches of Yangtze River metallogenic belt is shallowest, while the Moho beneath the North China block is deeper than that beneath the Yangtze block. The Moho offsets could be seen beneath the Ningwu volcanic basin. The seismic reflection data suggest that lithosphere delamination and asthenosphere upwelling that may result from the Mesozoic intra-continental orogenesis is responsible for the formation of large scale magmatism and mineralization in the MLY metallogenic belt. [ABSTRACT FROM AUTHOR]

Abstract: To understand the formation and the tectonic process of the Mesozoic middle–lower Yangtze metallogenic belt (YMB), the SinoProbe program deployed a quasi-linear passive source seismic array across the belt. We performed receiver function profiling and measurement of shear-wave splitting parameters with the collected data. Our results show that the Moho depth varies significantly along the profile and that a “mantle uplift” exists right beneath the YMB. We also found that the lower crust of the YMB is different from that of its adjacent areas in structure on the receiver function profile. It possesses seismic anisotropy with direction roughly parallel to the belt. Our SKS/SKKS shear-wave splitting results also show similar belt-parallel azimuthal anisotropy right beneath the YMB. We interpret the seismic anisotropy in the lower crust of the YMB as the result of mineral crystal alignment caused by melting and belt-parallel flow in the Mesozoic ore-forming process. Besides, we observed a nearly south-dipping converter extending from shallow to lower crust beneath the Hefei Basin, which most possibly resulted from the Mesozoic crustal extension. We interpret the “mantle uplift” and the crustal extensional structures to be consequences of asthenospheric upwelling during the Mesozoic ore-forming process. Our results suggest that the lower crust of the YMB was most likely one part of the multi-level metallogenic magma system in the Mesozoic magmatism and mineralization processes, and the formation of the metallogenic belt to be a result much similar to the MASH (Melting, Assimilation, Storage and Homogenization; cf. Hildreth and Moorbath, 1988; Richards, 2003) process. First, the asthenospheric upwelling resulted in a crustal extensional environment; then the melts from the upwelling asthenosphere intruded into the lower crust of the YMB, and assimilation occurred when they mixed with in situ lower crustal materials, which led to the formation of adakitic-like magma; the adakitic-like magma rose up along extensional structures, and reacted with country rocks to form mineral deposits. [Copyright &y& Elsevier]

Abstract: During 2006 to 2007, a small array of broadband seismic stations was deployed across the eastern Qaidam–Kunlun border. Receiver functions derived from this data set show a coherent P-to-S converted phase from the Moho at ~65km to ~58km below sea level (b.s.l.) from south to north beneath the Kunlun mountains. The Moho is observed at ~45km b.s.l. beneath the Qaidam basin. A sharp offset of ~15km in the Moho depth is observed just beneath the Qaidam–Kunlun border. The close correlation between the surface topography and the sharp Moho offset substantiates the view that the Kunlun crust is weaker than that of the Qaidam basin and thickens vertically in response to compression between India (through the Tibetan plateau) and the Qaidam basin. Furthermore, a strong steeply north-dipping converted phase can be seen from ~5 to 15km b.s.l. north of the North Kunlun Fault, which is likely a major south-directed thrust fault partially responsible for the thickening of the Kunlun crust. [Copyright &y& Elsevier]

Abstract: Five intersecting reflection seismic profiles were shot over the Lu–Zong volcanic basin, one of the seven ore districts in the middle and lower Yangtze River Metallogenic Belt in east China. The seismic data reveal diversified reflective patterns in the upper crust, which are interpreted as horsts and grabens in general. The middle crust presents both thrust related structures and boudinage and pinch-and-well structure on different profiles, suggesting a strong structural heterogeneity, which developed due to a change from compressional to extensional movement. Below the central part of a volcanic basin, the lower crust shows an obvious reflective anisotropy both at the crust–mantle and the brittle–ductile transition in the crust. This feature may be explained by magma system emplaced along a NE-trending fault or weak zone at different depths. The Tan-Lu fault zone is present as a northwest-dipping fault extending to the middle crust. The lower crust beneath the Tan-Lu fault and peripheries is possibly of Dabie affinities. The Lu–Zong volcanic basin is clearly defined as an asymmetric graben with master faults on both the east and north flanks. A contrasting reflection character suggests a division of the basin into northern and southern parts separated by a concealed fault. The relatively thin volcanic sequences, inferred to be 800–1000m in thickness, cover Triassic and Paleozoic sequences at depth, that provide an exploration target in the northern part for deep porphyry and skarn deposits. The dominant deformation reflects NW–SE-oriented compression and extension formed during the Yanshanian orogenic episode. The contraction deformation is characterized by thrust faults with imbrication of crustal slices, whereas the extension deformation is featured by normal faults, regional detachments and basins. Underplating of mantle-derived magma and a multi-layer magma intrusion model are proposed to explain both seismic features and the NE-striking Lu–Zong volcanism and igneous intrusions in the region. [Copyright &y& Elsevier]

In this study, we conduct ambient noise tomography and teleseismic two-plane-wave tomography to probe the crustal and uppermost mantle structures in the Middle–Lower Yangtze River region. The data used include 14 months (from July 2012 to August 2013) of continuous vertical component ambient noise data and 219 teleseismic earthquakes recorded at 138 broadband seismic stations from Chinese provincial networks and 19 temporary seismic stations deployed by China University of Geosciences (Beijing). First, we apply ambient noise tomography to the collected ambient noise data to generate Rayleigh wave group and phase velocity maps at 5–42 s periods and two-plane-wave tomography method to earthquake data to generate intermediate-to-long period phase velocity maps at 20–143 s periods. We then combine the short-to-intermediate period velocity maps from ambient noise and the intermediate-to-long period phase velocity maps from earthquake data to generate broadband phase velocity maps at periods from 5 to 143 s. By inverting these 5–143 s Rayleigh wave velocity maps, we construct a 3-D shear wave velocity model from the surface to ∼250 km depth in the Middle–Lower Yangtze River region. The 3-D model shows that in the upper crust, the basin regions, including the JiangHan, HeHuai, SuBei, HeFei and NanYang basins, are all featured with low velocities, and the mountain regions with high velocities. In the uppermost mantle, a low-velocity zone at ∼100–200 km depth is observed beneath the Middle–Lower Yangtze River Metallogenic Belt. Moreover, our tomographic results show that the NingWu and NingZhen ore districts are clearly characterized by the strongest low velocity anomaly in the uppermost mantle at ∼70–200 km depth. The depth extent of the low-velocity zone becomes shallower and the amplitude of low velocity anomaly becomes larger from the southwest JiuRui ore district to northeast NingWu ore districts. The change pattern of the low-velocity zone in the depth extent and the amplitude is consistent with the fact that peak ages of magmatic events along the Middle–Lower Yangtze River Metallogenic Belt progressively become younger and younger from 148 Ma in the southwest to 125 Ma in the northeast. The observed low-velocity zone may represent the cooling hot upper mantle which was partially molten in the past resulting from partial melting of the paleo-Pacific plate or of an enriched mantle source induced by the westward subduction of the paleo-Pacific plate. The upwelling of the mantle-derived magmas may result in the formation of these granitic rocks and coeval ores deposits along the Middle–Lower Yangtze River Metallogenic Belt. [ABSTRACT FROM AUTHOR]

A mineralization zone exists in the Middle and Lower Yangtze River (MLYR) region. Previous studies have shown that this zone might be caused by the rich ejection of magma in the Mesozoic. We have applied the teleseismic tomography method to determine a 3-D P-wave velocity structure of the mantle down to 500km depth beneath this region by using 14,740 P-wave arrival times collected from 519 teleseismic events recorded by 46 portable and 47 static seismic stations located in this region. The relative residual times used for the tomography are calculated by the modified multi-channel cross-correlation method which increases not only the efficiency but also the data precisions up to 0.01s. The grid space is set as 1°×1° horizontally and 50–100km vertically. Our tomographic results show that the lithosphere with high velocity anomalies is separated into two parts: one locates above the depth of 100km and the other at the depths between 250km and 400km, and the asthenosphere with low velocity anomalies locates between these two parts of lithosphere, which indicates that the lithosphere delaminated together with the asthenosphere upwelling. The detachment of lithosphere might relate to the subduction of the western Pacific slab. Therefore, our study provides clear evidence to geoscientists for understanding the deep dynamic process beneath this region and a three-stage geodynamic process is developed based on the new evidence. [ABSTRACT FROM AUTHOR]