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A 3-D P-wave velocity structure down to 750 km beneath the eastern South China Block is obtained by using a large number of high-quality teleseismic data. Based on our results and those of previous studies, we suggest that late Mesozoic magmatism and lithospheric thinning in the eastern South China Block could be attributed to the subduction of the Paleo-Pacific Plate and its eastward rollback. [Display omitted] • A 3-D P-wave velocity model beneath the eastern South China Block is obtained. • The velocity structures beneath the eastern South China Block are very complicated. • The Paleo-Pacific Plate has had a profound impact on the eastern South China Block. The eastern South China Block (ESCB) is characterized by intense magmatism in the late Mesozoic. To further investigate the mechanism of late Mesozoic magmatism, we apply the tomographic method to construct a P-wave velocity model down to 750 km by using 40,989 P-wave arrival times collected from 687 teleseismic events recorded by 191 stations. Our model shows that (1) a high-Vp anomaly is observed beneath the lower Yangtze Block (YZB) and northern Cathaysia Block (CAB) in the crust and uppermost mantle, which could represent the present lithosphere; (2) two high-Vp anomalies are observed in the upper mantle beneath the YZB, which could be the detached lithosphere and the relict of the subducted SCB; (3) the break-off of the subducted Eurasian Plate has penetrated the 410 km discontinuity beneath central and northern Taiwan Island; (4) the stagnant Paleo-Pacific Plate in the MTZ is mainly beneath the lower YZB; (5) the low-Vp anomaly in the upper mantle that is immediately above the stagnant Paleo-Pacific Plate may represent the thermal asthenosphere caused by plate dehydration; and (6) the low-Vp anomaly beneath the southern CAB extends from the crust downward to the MTZ, which may represent an 'upward channel' for thermal materials. Based on our results and those of previous studies, we suggest that late Mesozoic magmatism in the ESCB could be highly associated with the subduction of the Paleo-Pacific Plate and its eastward rollback. We also suggest that thermal/chemical erosion may be responsible for lithospheric thinning in the ESCB. [ABSTRACT FROM AUTHOR]

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 South China block (SCB) is located at the southeastern margin of the Eurasian plate, where intense Mesozoic magmatism and metallogenic belts occurred. The mechanism of mineralization is still unclear and debated. To clarify this issue, we determine a robust 3-D model of P-wave tomography of the upper mantle beneath the SCB by using 77,969 high-quality travel-time data of 934 teleseismic events recorded at 315 permanent and 72 portable stations in the SCB. Our results show that high-velocity (high-V) zones exist in the upper mantle under the Yangtze block and in the mantle transition zone under the eastern segment of the Jiangnan orogen. The former reflects thicker cratonic lithosphere, whereas the latter may reflect the deeply subducted paleo-Pacific plate. Low-velocity (low-V) anomalies are revealed in the upper mantle beneath the Cathaysia block, which are located above the high-V anomaly in the mantle transition zone. These low-V anomalies may reflect hot upwelling flows in the upper mantle, which might be related to the large-scale magmatic activities in the late Mesozoic. Our results suggest that the low-V hot mantle materials beneath the Cathaysia block have risen to the shallow lithosphere along magmatic channels such as fault zones, which eroded the nearby cratonic root of the Yangtze block and the overlying lithosphere and destroyed the lithosphere beneath the eastern SCB. The hot upwelling materials mineralized in the shallow part and so formed many metallogenic belts in the SCB. • The 3-D upper-mantle structure under the South China block (SCB) is studied using teleseismic tomography. • The Yangtze and Cathaysia blocks exhibit higher and lower P-wave velocities, respectively. • Hot mantle upwelling under the Cathaysia block caused lithospheric thinning and rich metallogenic belts in the eastern SCB. [ABSTRACT FROM AUTHOR]

We studied the crustal structure and tectonics in the north Tibetan Plateau from the Songpan-Ganzi terrane to the Qaidam Basin using teleseismic receiver-function imaging, across a major lithospheric boundary, the Kunlun-Qaidam boundary, where previous studies suggest a ~15–20-km change in crustal thickness from thicker crust in the Kunlun Mountains to thinner crust in the Qaidam Basin. We report P receiver functions for 70 stations, largely the International Deep Profiling of Tibet and the Himalaya (INDEPTH), phase IV, experiment. Our most dense station coverage is located along the roughly north-south INDEPTH-IV active-source seismic profile at approximately 95° E longitude. Azimuthal and geographical changes in the receiver functions reveal significant changes in crustal structure and V p /V s from across the study area. Receiver functions show strong converters that we interpret as the Moho at ~70 km depth beneath the Qiangtang, Songpan-Ganzi terranes and Kunlun Mountains and at ~50 km depth beneath the central Qaidam Basin. This large change in crustal thickness occurs >50 km north of the North Kunlun strike-slip fault, on which the 2001 M8.1 Kunlun earthquake occurred. Receiver functions for some of the stations north of the thickness change at the Kunlun-Qaidam boundary also show a deeper ~70-km bright converter in addition to the 50-km converter. The two converters appear to overlap by up to ~30 km in some locations along the south Qaidam Basin. We combine previous results with these new results to discuss implications for mechanisms for crustal thickening in the north Tibetan Plateau including crustal flow and crustal injection. At depths imaged here, shallower than ~100 km, we see no evidence of southward subduction of Eurasian lithosphere. • Seismic data reveals lithospheric structure and composition in North Tibet. • The crustal thickness changes from 70 to 50 km beneath the Kunlun-Qaidam boundary. • North Tibet may have thickened as a result of crustal flow or injection. [ABSTRACT FROM AUTHOR]

Geophysical methods identify lithospheric structures and potential fluid conduits. Tectonicblock boundaries acted as fluid conduits for ore development. The Late Mesozoic Fe–Cu (Au) mineral system of LYMB was formed by multi-level sources, processes, and conduits communicating each other within an exceptional lithospheric architecture. [Display omitted] • An extensive ore system occurred in the Lower Yangtze Metallogenic Belt. • Geophysical methods identify lithospheric structures and potential fluid conduits. • Tectonic block boundaries acted as fluid conduits for ore development. Diverse seismic (active and passive) and magnetotelluric (MT) surveys have been conducted in the past decade over the Lower Yangtze Metallogenic Belt (LYMB) and adjacent areas, in eastern China. We present an integrated interpretation of these data describing the lithospheric architecture of an extensive Fe–Cu system in the LYMB. A combination of anomalous geophysical features has been observed in the sub-continental lithospheric mantle (SCLM) and asthenospheric mantle, which include: anomalously thin lithosphere (thickness ~70 km), low S- and P-wave seismic velocity in the upper mantle (70–150 km), and a dipping high-conductivity body extending from the lower crust to the asthenosphere (~150 km). We interpret these features to be the result of lithospheric delamination and asthenospheric upwelling during Late Mesozoic orogenesis. Melts and metal-rich (e.g., Cu, and Au) fluids produced by the asthenosphere would have metasomatized the lithospheric conduits (faults) and the lower part of the SCLM. Therefore, we suggest that these areas acted as the primary source regions for the Fe–Cu (Au) mineral system in the LYMB. Seismic reflection profiles across different parts of the LYMB reveal various large-scale structures, including crustal wedges, Moho stacks, mega-thrusts, and even lower crust underthrusting at block boundaries; these features are consistent with collisional orogeny. The spatial coincidence of major block boundaries with the distribution of deposits is evidence that deep-penetrating boundary faults acted as conduits for migrating magmas/fluids from lower crust to the upper crust. Conductive zones in the crust beneath the LYMB are interpreted as the result of alteration by fluids within the conduits. We conclude that the Late Mesozoic Fe–Cu (Au) mineral system of LYMB was formed by during an intra-continental orogeny with multi-level sources, processes, and conduits communicating each other within an exceptional lithospheric architecture. [ABSTRACT FROM AUTHOR]